diff --git a/docs/api/openapi.yaml b/docs/api/openapi.yaml
index 5559a9937..0e21cb822 100644
--- a/docs/api/openapi.yaml
+++ b/docs/api/openapi.yaml
@@ -1873,9 +1873,15 @@ paths:
       description: "Web only. Checks the link and the username, sets a sealed `hl_claim` cookie (10 minutes, `httpOnly`) and
         answers where to continue: `/api/auth/oidc/login?intent=claim`. The OIDC callback binds the identity provider's
         subject to the profile and signs the new owner in; a subject already bound to an account, or a verified email
-        another account holds, is refused there. Works on a single-sign-on-only instance. 404 `profile_claim.invalid`
-        (no usable link) or `profile_claim.sso_unavailable` (no identity provider configured); 409 `profile_claim.taken`
-        (username) or `auth.already_authenticated`; rate-limited per source address like the password claim."
+        another account holds, is refused there. Works on a single-sign-on-only instance. When the callback refuses, the
+        browser lands on `/auth/claim?error=<reason>` with reason `claim_expired` (the link was used, withdrawn,
+        replaced or expired in the meantime, or the cookie is missing, expired or belongs to another start),
+        `claim_sso_subject_bound`, `claim_email_taken`, `claim_username_taken` (taken during the round trip),
+        `claim_signed_in`, or one of the sign-in reasons (`oidc_denied`, `oidc_state`, `oidc_failed`,
+        `oidc_rate_limited`, `oidc_disabled`); on success it lands on `/onboarding/handover`, where the new owner
+        decides each guardian's access. The cookie is cleared either way. 404 `profile_claim.invalid` (no usable link)
+        or `profile_claim.sso_unavailable` (no identity provider configured); 409 `profile_claim.taken` (username) or
+        `auth.already_authenticated`; rate-limited per source address like the password claim."
       requestBody:
         required: true
         content:
@@ -1904,15 +1910,6 @@ paths:
                 $ref: "#/components/schemas/ErrorEnvelope"
         "422": *a4
         "429": *a5
-        "501": &a44
-          description: "Not implemented on this server yet: the contract is published, the effect is not. `meta.errorCode` =
-            `not_implemented`, `meta.operation` names the operation. Authentication, module gates and request validation
-            already answer as documented. A client reaches this only by ignoring the server feature flag that guards the
-            operation."
-          content:
-            application/json:
-              schema:
-                $ref: "#/components/schemas/ErrorEnvelope"
   /api/auth/claim/preview:
     post:
       security: []
@@ -1921,7 +1918,8 @@ paths:
       summary: Preview a managed-profile handover link
       description: "What a handover link would hand over: the profile's display name, the link's expiry, and each guardian's
         proposal. Anonymous; the token travels in the body. An unknown, expired, used or withdrawn token, and a link
-        whose creator lost access, all answer the same 404. Rate-limited per source address."
+        whose creator lost access, all answer the same 404. Rate-limited per source address. Since v1.43 answered on a
+        single-sign-on-only instance too, with `methods` naming the ways in."
       requestBody:
         required: true
         content:
@@ -1936,12 +1934,6 @@ paths:
               schema:
                 $ref: "#/components/schemas/ProfileClaimPreviewEnvelope"
         "401": *a1
-        "403":
-          description: "The instance allows single sign-on only (`meta.errorCode: profile_claim.oidc_only_unsupported`)."
-          content:
-            application/json:
-              schema:
-                $ref: "#/components/schemas/ErrorEnvelope"
         "404":
           description: "No usable link behind this token (`meta.errorCode: profile_claim.invalid`). Every failure class answers
             identically."
@@ -3738,6 +3730,19 @@ paths:
             type: string
           description: "Browser leg only: where to land after login. Sanitised to an in-app path; ignored entirely on the native
             leg."
+        - in: query
+          name: intent
+          schema:
+            description: "v1.43 — `claim` continues a managed-profile claim started at POST /api/auth/claim/sso; the link and
+              username ride the sealed `hl_claim` cookie that call set, never this URL. Without a valid cookie for a
+              still-usable link the start redirects to `/auth/claim?error=claim_expired`. Browser leg only: with
+              `client=native` it fails with `oidc_invalid_request`. `next` is ignored."
+            type: string
+            const: claim
+          description: "v1.43 — `claim` continues a managed-profile claim started at POST /api/auth/claim/sso; the link and
+            username ride the sealed `hl_claim` cookie that call set, never this URL. Without a valid cookie for a
+            still-usable link the start redirects to `/auth/claim?error=claim_expired`. Browser leg only: with
+            `client=native` it fails with `oidc_invalid_request`. `next` is ignored."
         - in: query
           name: client_proto
           schema:
@@ -3762,7 +3767,8 @@ paths:
           description: "Browser leg only: `location.host` of that page, read together with `client_proto`."
       responses:
         "302":
-          description: Always a redirect. To the provider on success. On failure to `/auth/login?error=<reason>` (browser) or
+          description: Always a redirect. To the provider on success. On failure to `/auth/login?error=<reason>` (browser;
+            `/auth/claim?error=<reason>` with `intent=claim`, where `claim_expired` is one more reason) or
             `healthlog://oidc-callback?error=<reason>` (native), where reason is one of `oidc_disabled`,
             `oidc_rate_limited`, `oidc_invalid_request`, `oidc_failed`, and on the browser leg `insecure_transport` (see
             `client_proto`). The provider then returns to the callback (not listed here, because the identity provider
@@ -18893,7 +18899,7 @@ paths:
               schema:
                 $ref: "#/components/schemas/NutrientCatalogEnvelope"
         "401": *a1
-        "403": &a45
+        "403": &a44
           description: >-
             The opt-in `nutrients` module is off for this account (errorCode `module.disabled`). Stop syncing and do not
             retry; offer the enable-in-settings hint. Only run the HealthKit read-authorization flow while the module is
@@ -18915,7 +18921,15 @@ paths:
                 $ref: "#/components/schemas/ErrorEnvelope"
         "422": *a4
         "429": *a5
-        "501": *a44
+        "501": &a69
+          description: "Not implemented on this server yet: the contract is published, the effect is not. `meta.errorCode` =
+            `not_implemented`, `meta.operation` names the operation. Authentication, module gates and request validation
+            already answer as documented. A client reaches this only by ignoring the server feature flag that guards the
+            operation."
+          content:
+            application/json:
+              schema:
+                $ref: "#/components/schemas/ErrorEnvelope"
   /api/nutrients/batch:
     post:
       tags:
@@ -19041,7 +19055,7 @@ paths:
               schema:
                 $ref: "#/components/schemas/NutrientOverviewEnvelope"
         "401": *a1
-        "403": *a45
+        "403": *a44
         "422": *a4
         "429": *a5
   /api/nutrients/daily:
@@ -19077,7 +19091,7 @@ paths:
               schema:
                 $ref: "#/components/schemas/NutrientDailySeriesEnvelope"
         "401": *a1
-        "403": *a45
+        "403": *a44
         "422": *a4
         "429": *a5
   /api/nutrients/water:
@@ -19106,7 +19120,7 @@ paths:
               schema:
                 $ref: "#/components/schemas/NutrientWaterWriteEnvelope"
         "401": *a1
-        "403": *a45
+        "403": *a44
         "409": *a7
         "422": *a4
         "429": *a5
@@ -19608,26 +19622,26 @@ paths:
             application/json:
               schema:
                 $ref: "#/components/schemas/WithingsCredentialsUpdateEnvelope"
-        "400": &a46
+        "400": &a45
           description: Body is not parseable JSON.
           content:
             application/json:
               schema:
                 $ref: "#/components/schemas/ErrorEnvelope"
         "401": *a1
-        "413": &a47
+        "413": &a46
           description: Body exceeds 64 KiB.
           content:
             application/json:
               schema:
                 $ref: "#/components/schemas/ErrorEnvelope"
-        "415": &a48
+        "415": &a47
           description: Content-Type is not `application/json`.
           content:
             application/json:
               schema:
                 $ref: "#/components/schemas/ErrorEnvelope"
-        "422": &a49
+        "422": &a48
           description: "`clientId` and `clientSecret` are both required and each must be 1–200 characters. The envelope carries a
             single fixed message, not per-field issues."
           content:
@@ -19813,11 +19827,11 @@ paths:
             application/json:
               schema:
                 $ref: "#/components/schemas/FitbitCredentialsUpdateEnvelope"
-        "400": *a46
+        "400": *a45
         "401": *a1
-        "413": *a47
-        "415": *a48
-        "422": *a49
+        "413": *a46
+        "415": *a47
+        "422": *a48
         "429": *a5
     delete:
       tags:
@@ -19960,11 +19974,11 @@ paths:
             application/json:
               schema:
                 $ref: "#/components/schemas/GoogleHealthCredentialsUpdateEnvelope"
-        "400": *a46
+        "400": *a45
         "401": *a1
-        "413": *a47
-        "415": *a48
-        "422": *a49
+        "413": *a46
+        "415": *a47
+        "422": *a48
         "429": *a5
     delete:
       tags:
@@ -20125,11 +20139,11 @@ paths:
             application/json:
               schema:
                 $ref: "#/components/schemas/OuraCredentialsUpdateEnvelope"
-        "400": *a46
+        "400": *a45
         "401": *a1
-        "413": *a47
-        "415": *a48
-        "422": *a49
+        "413": *a46
+        "415": *a47
+        "422": *a48
         "429": *a5
     delete:
       tags:
@@ -20205,21 +20219,21 @@ paths:
               schema:
                 $ref: "#/components/schemas/OuraTestEnvelope"
         "401": *a1
-        "422": &a50
+        "422": &a49
           description: No usable connection for this provider — nothing stored, or the stored grant could no longer be resolved
             into an access token. `meta.errorCode` = `not_configured`.
           content:
             application/json:
               schema:
                 $ref: "#/components/schemas/ErrorEnvelope"
-        "429": &a51
+        "429": &a50
           description: More than 5 requests in 60 s from this user. `meta.errorCode` = `rate_limited_self` — this is the local
             limiter, distinct from a `rate_limited` 502 which is the provider's.
           content:
             application/json:
               schema:
                 $ref: "#/components/schemas/ErrorEnvelope"
-        "502": &a52
+        "502": &a51
           description: "The probe did not complete. `meta.errorCode` names the class: `credentials_rejected` (the provider
             answered 401/403 — the stored grant is gone), `rate_limited` (the PROVIDER answered 429, which is not this
             endpoint's own limiter), `upstream_error` (5xx), `timeout` (no answer within 5 s), `connection_failed`
@@ -20264,11 +20278,11 @@ paths:
             application/json:
               schema:
                 $ref: "#/components/schemas/PolarCredentialsUpdateEnvelope"
-        "400": *a46
+        "400": *a45
         "401": *a1
-        "413": *a47
-        "415": *a48
-        "422": *a49
+        "413": *a46
+        "415": *a47
+        "422": *a48
         "429": *a5
     delete:
       tags:
@@ -20344,9 +20358,9 @@ paths:
               schema:
                 $ref: "#/components/schemas/PolarTestEnvelope"
         "401": *a1
-        "422": *a50
-        "429": *a51
-        "502": *a52
+        "422": *a49
+        "429": *a50
+        "502": *a51
   /api/strava/credentials:
     get:
       tags:
@@ -20382,11 +20396,11 @@ paths:
             application/json:
               schema:
                 $ref: "#/components/schemas/StravaCredentialsUpdateEnvelope"
-        "400": *a46
+        "400": *a45
         "401": *a1
-        "413": *a47
-        "415": *a48
-        "422": *a49
+        "413": *a46
+        "415": *a47
+        "422": *a48
         "429": *a5
     delete:
       tags:
@@ -20464,9 +20478,9 @@ paths:
               schema:
                 $ref: "#/components/schemas/StravaTestEnvelope"
         "401": *a1
-        "422": *a50
-        "429": *a51
-        "502": *a52
+        "422": *a49
+        "429": *a50
+        "502": *a51
   /api/integrations/status:
     get:
       tags:
@@ -20502,7 +20516,7 @@ paths:
                 $ref: "#/components/schemas/FitbitResumeEnvelope"
         "401": *a1
         "422": *a4
-        "429": *a51
+        "429": *a50
   /api/integrations/fitbit/test:
     post:
       tags:
@@ -20520,9 +20534,9 @@ paths:
               schema:
                 $ref: "#/components/schemas/FitbitIntegrationTestEnvelope"
         "401": *a1
-        "422": *a50
-        "429": *a51
-        "502": *a52
+        "422": *a49
+        "429": *a50
+        "502": *a51
   /api/integrations/google-health/resume:
     post:
       tags:
@@ -20539,7 +20553,7 @@ paths:
                 $ref: "#/components/schemas/GoogleHealthResumeEnvelope"
         "401": *a1
         "422": *a4
-        "429": *a51
+        "429": *a50
   /api/integrations/google-health/test:
     post:
       tags:
@@ -20572,9 +20586,9 @@ paths:
             application/json:
               schema:
                 $ref: "#/components/schemas/ErrorEnvelope"
-        "422": *a50
-        "429": *a51
-        "502": *a52
+        "422": *a49
+        "429": *a50
+        "502": *a51
   /api/integrations/whoop/resume:
     post:
       tags:
@@ -20591,7 +20605,7 @@ paths:
                 $ref: "#/components/schemas/WhoopResumeEnvelope"
         "401": *a1
         "422": *a4
-        "429": *a51
+        "429": *a50
   /api/integrations/whoop/test:
     post:
       tags:
@@ -20608,9 +20622,9 @@ paths:
               schema:
                 $ref: "#/components/schemas/WhoopIntegrationTestEnvelope"
         "401": *a1
-        "422": *a50
-        "429": *a51
-        "502": *a52
+        "422": *a49
+        "429": *a50
+        "502": *a51
   /api/integrations/withings/resume:
     post:
       tags:
@@ -20628,7 +20642,7 @@ paths:
                 $ref: "#/components/schemas/WithingsResumeEnvelope"
         "401": *a1
         "422": *a4
-        "429": *a51
+        "429": *a50
   /api/integrations/withings/test:
     post:
       tags:
@@ -20646,8 +20660,8 @@ paths:
               schema:
                 $ref: "#/components/schemas/WithingsIntegrationTestEnvelope"
         "401": *a1
-        "422": *a50
-        "429": *a51
+        "422": *a49
+        "429": *a50
         "502":
           description: "The probe did not complete. The shared codes apply (`credentials_rejected`, `rate_limited`,
             `upstream_error`, `timeout`, `connection_failed`) and this path adds one of its own:
@@ -20903,7 +20917,9 @@ paths:
                 $ref: "#/components/schemas/ManagedProfileHandoverEnvelope"
         "401": *a1
         "403":
-          description: "The instance allows single sign-on only (`meta.errorCode: profile_claim.oidc_only_unsupported`)."
+          description: "Neither a password nor single sign-on could redeem a link on this instance (`meta.errorCode:
+            profile_claim.oidc_only_unsupported`). Since v1.43 a single-sign-on-only instance hands over through the
+            identity provider, so a working configuration never answers this."
           content:
             application/json:
               schema:
@@ -21049,7 +21065,7 @@ paths:
               schema:
                 $ref: "#/components/schemas/RecordActivityEnvelope"
         "401": *a1
-        "403": &a53
+        "403": &a52
           description: Refused. `meta.errorCode` is `sharing.not_permitted` when the request was made while acting on another
             account (grant management is never delegable), or `sharing.access.denied` when the caller may not act as the
             account they named. The latter is byte-identical for an account that does not exist and one that granted
@@ -21074,7 +21090,7 @@ paths:
               schema:
                 $ref: "#/components/schemas/AccountGrantListEnvelope"
         "401": *a1
-        "403": *a53
+        "403": *a52
         "422": *a4
         "429": *a5
     post:
@@ -21176,7 +21192,7 @@ paths:
               schema:
                 $ref: "#/components/schemas/AcceptedAccountGrantEnvelope"
         "401": *a1
-        "403": *a53
+        "403": *a52
         "404":
           description: No such invitation for this account.
           content:
@@ -21220,7 +21236,7 @@ paths:
               schema:
                 $ref: "#/components/schemas/RevokedAccountGrantEnvelope"
         "401": *a1
-        "403": *a53
+        "403": *a52
         "404":
           description: No such grant on this account's record.
           content:
@@ -21261,7 +21277,7 @@ paths:
               schema:
                 $ref: "#/components/schemas/RenouncedAccountGrantEnvelope"
         "401": *a1
-        "403": *a53
+        "403": *a52
         "404":
           description: No such grant held by this account.
           content:
@@ -21643,7 +21659,7 @@ paths:
               schema:
                 $ref: "#/components/schemas/ErrorEnvelope"
         "401": *a1
-        "403": *a53
+        "403": *a52
         "409":
           description: "The record this browser session is on is not the record the request asserted. `meta.errorCode` is
             `sharing.session.changed`. It is not a refusal of access — the caller may well be entitled to both records —
@@ -22023,7 +22039,7 @@ paths:
               schema:
                 $ref: "#/components/schemas/McpConnectionListEnvelope"
         "401": *a1
-        "403": &a54
+        "403": &a53
           description: The operator has disabled the API instance-wide. Every route in this module refuses while that setting is
             off, for a cookie session as well as for a Bearer token; it is not a per-user permission and retrying will
             not help.
@@ -22056,7 +22072,7 @@ paths:
               schema:
                 $ref: "#/components/schemas/McpConnectionRevokeEnvelope"
         "401": *a1
-        "403": *a54
+        "403": *a53
         "404":
           description: No live connection with this id for this caller — also the answer for an already-revoked one, so a repeat
             revoke is 404 rather than an idempotent 200.
@@ -22083,7 +22099,7 @@ paths:
               schema:
                 $ref: "#/components/schemas/McpConnectorTokenListEnvelope"
         "401": *a1
-        "403": *a54
+        "403": *a53
         "422": *a4
         "429": *a5
     post:
@@ -22116,7 +22132,7 @@ paths:
               schema:
                 $ref: "#/components/schemas/ErrorEnvelope"
         "401": *a1
-        "403": *a54
+        "403": *a53
         "413":
           description: Body exceeds 16 KiB.
           content:
@@ -22159,7 +22175,7 @@ paths:
               schema:
                 $ref: "#/components/schemas/McpConnectorTokenRevokeEnvelope"
         "401": *a1
-        "403": *a54
+        "403": *a53
         "404":
           description: No `health:read` token with this id for this caller. An already-revoked token is still found, so a repeat
             revoke answers 200.
@@ -22218,7 +22234,7 @@ paths:
       description: Returns the named family's resolved settings for the record the session is acting on. Cookie session or
         Bearer, while acting on a managed record the caller guards.
       parameters:
-        - &a55
+        - &a54
           name: family
           in: path
           required: true
@@ -22262,7 +22278,7 @@ paths:
         ride the audit row. Body capped at 64 KiB. Cookie session or Bearer, while acting on a managed record the caller
         guards.
       parameters:
-        - *a55
+        - *a54
       requestBody:
         required: true
         content:
@@ -22835,13 +22851,13 @@ paths:
             application/json:
               schema:
                 $ref: "#/components/schemas/AdminBackupDocument"
-        "403": &a56
+        "403": &a55
           description: Caller is not an admin. `requireAdmin()` is cookie-only, so a Bearer token lands here whatever its scope.
           content:
             application/json:
               schema:
                 $ref: "#/components/schemas/ErrorEnvelope"
-        "404": &a57
+        "404": &a56
           description: No stored copy with this id.
           content:
             application/json:
@@ -22915,8 +22931,8 @@ paths:
             application/json:
               schema:
                 $ref: "#/components/schemas/ErrorEnvelope"
-        "403": *a56
-        "404": *a57
+        "403": *a55
+        "404": *a56
         "409":
           description: A restore of the same account is already queued or running (`meta.errorCode` = `backup.restore.active`,
             `meta.jobId` names it), the stored copy was replaced by a newer one while it was being checked
@@ -22960,7 +22976,7 @@ paths:
             application/json:
               schema:
                 $ref: "#/components/schemas/AdminBackupRestoreJobListResponse"
-        "403": *a56
+        "403": *a55
   /api/admin/backups/restores/{jobId}:
     get:
       tags:
@@ -22983,7 +22999,7 @@ paths:
             application/json:
               schema:
                 $ref: "#/components/schemas/AdminBackupRestoreJobResponse"
-        "403": *a56
+        "403": *a55
         "404":
           description: No restore job with this id.
           content:
@@ -23002,7 +23018,7 @@ paths:
         request leaves the server. Needs neither the Documents module nor the list: with the list unset, `available` is
         false and any connection still stored is listed (with `originAllowed: false`) so it can be removed. Cookie
         session only; not delegable."
-      security: &a58
+      security: &a57
         - cookieAuth: []
       responses:
         "200":
@@ -23012,7 +23028,7 @@ paths:
               schema:
                 $ref: "#/components/schemas/DocumentSourcesStatusEnvelope"
         "401": *a1
-        "403": &a59
+        "403": &a58
           description: "Refused before any request to the source: `documents.sources.browserOnly` for a Bearer caller,
             `sharing.not_permitted` while acting on another person's record (a delegate or guardian never uses the
             owner's archive), or `module.disabled` when the Documents module is off."
@@ -23035,9 +23051,9 @@ paths:
         `documents.sources.tokenRequired`), so a stored token is never sent to an address it was not saved for. A Papra
         organization id is letters, digits, `_` and `-`. The token is stored encrypted (AES-256-GCM) and never returned.
         Ten saves and tests a minute per person. Cookie session only; not delegable."
-      security: *a58
+      security: *a57
       parameters:
-        - &a60
+        - &a59
           name: system
           in: path
           required: true
@@ -23076,8 +23092,8 @@ paths:
               schema:
                 $ref: "#/components/schemas/DocumentSourceConnectionEnvelope"
         "401": *a1
-        "403": *a59
-        "404": &a61
+        "403": *a58
+        "404": &a60
           description: "`documents.sources.unavailable`: the operator has not listed any origin in `DOCUMENT_SOURCE_ORIGINS`, so
             the picker is off. `documents.sources.notConnected`: no connection is saved for this system.
             `documents.sources.notFound`: the source has no such document, or (Papra) no such organization, including
@@ -23096,7 +23112,7 @@ paths:
               schema:
                 $ref: "#/components/schemas/ErrorEnvelope"
         "429": *a5
-        "502": &a62
+        "502": &a61
           description: "The source could not answer usefully, with the reason in `meta.errorCode` and, when the source answered at
             all, its HTTP status in `meta.upstreamStatus` (its body is never passed on): `documents.sources.unreachable`
             (no connection, timeout, or a destination refused at dial time), `documents.sources.redirected` (the source
@@ -23115,9 +23131,9 @@ paths:
       description: Deletes the caller's connection for this system, and its token with it. Works even after the operator
         removed the origin from the list, and with the Documents module switched off. `disconnected` is false when there
         was nothing to delete. Cookie session only; not delegable.
-      security: *a58
+      security: *a57
       parameters:
-        - *a60
+        - *a59
       responses:
         "200":
           description: Removed, or there was nothing to remove.
@@ -23126,7 +23142,7 @@ paths:
               schema:
                 $ref: "#/components/schemas/DocumentSourceDisconnectEnvelope"
         "401": *a1
-        "403": *a59
+        "403": *a58
         "422": *a4
         "429": *a5
   /api/documents/sources/{system}/test:
@@ -23137,9 +23153,9 @@ paths:
       description: One request to the source with the stored token. Answers `ok` with the round-trip time and stamps
         `lastVerifiedAt`, or the reason in `meta.errorCode`. Shares the save's allowance of ten a minute. Cookie session
         only; not delegable.
-      security: *a58
+      security: *a57
       parameters:
-        - *a60
+        - *a59
       responses:
         "200":
           description: The source answered.
@@ -23148,9 +23164,9 @@ paths:
               schema:
                 $ref: "#/components/schemas/DocumentSourceTestEnvelope"
         "401": *a1
-        "403": *a59
-        "404": *a61
-        "422": &a63
+        "403": *a58
+        "404": *a60
+        "422": &a62
           description: "`documents.sources.originNotAllowed`: the base address's origin is not on the operator's list (checked on
             every request, so a connection saved earlier is cut off once its origin is removed), or another validation
             failure."
@@ -23159,7 +23175,7 @@ paths:
               schema:
                 $ref: "#/components/schemas/ErrorEnvelope"
         "429": *a5
-        "502": *a62
+        "502": *a61
   /api/documents/sources/{system}/tags:
     get:
       tags:
@@ -23167,9 +23183,9 @@ paths:
       summary: Tags of a connected archive
       description: The source's tags for the picker's filter, the first 250 by name, in the source's own ids. Shares the
         search allowance of sixty a minute. Cookie session only; not delegable.
-      security: *a58
+      security: *a57
       parameters:
-        - *a60
+        - *a59
       responses:
         "200":
           description: The tags.
@@ -23178,11 +23194,11 @@ paths:
               schema:
                 $ref: "#/components/schemas/DocumentSourceTagsEnvelope"
         "401": *a1
-        "403": *a59
-        "404": *a61
-        "422": *a63
+        "403": *a58
+        "404": *a60
+        "422": *a62
         "429": *a5
-        "502": *a62
+        "502": *a61
   /api/documents/sources/{system}/search:
     get:
       tags:
@@ -23196,9 +23212,9 @@ paths:
         under that source key: `new`, `imported` with the vault document's `documentId`, or `deleted` (deleted in
         HealthLog; importing it again stores nothing). Nothing is stored. Sixty searches a minute, shared with the tag
         read. Cookie session only; not delegable."
-      security: *a58
+      security: *a57
       parameters:
-        - *a60
+        - *a59
         - name: q
           in: query
           required: false
@@ -23239,11 +23255,11 @@ paths:
               schema:
                 $ref: "#/components/schemas/DocumentSourceSearchEnvelope"
         "401": *a1
-        "403": *a59
-        "404": *a61
-        "422": *a63
+        "403": *a58
+        "404": *a60
+        "422": *a62
         "429": *a5
-        "502": *a62
+        "502": *a61
   /api/documents/sources/{system}/import:
     post:
       tags:
@@ -23262,9 +23278,9 @@ paths:
         fetched), including a duplicate. `kind` sets the document type (default OTHER). Automatic AI reading follows the
         person's own setting. Counts against the person's upload allowance (60 an hour) and storage quota. 201 for a new
         document, 200 otherwise. Cookie session only; not delegable."
-      security: *a58
+      security: *a57
       parameters:
-        - *a60
+        - *a59
       requestBody:
         required: true
         content:
@@ -23322,7 +23338,7 @@ paths:
               schema:
                 $ref: "#/components/schemas/DocumentSourceImportEnvelope"
         "401": *a1
-        "403": *a59
+        "403": *a58
         "404":
           description: "`documents.sources.unavailable`: the operator has not listed any origin in `DOCUMENT_SOURCE_ORIGINS`, so
             the picker is off. `documents.sources.notConnected`: no connection is saved for this system.
@@ -23353,7 +23369,7 @@ paths:
             application/json:
               schema:
                 $ref: "#/components/schemas/ErrorEnvelope"
-        "422": *a63
+        "422": *a62
         "429":
           description: "`documents.inbound.rateLimited` (the person's hourly upload allowance, with the rate-limit headers) or
             `documents.inbound.uploadBusy` (too many uploads in progress; `Retry-After: 1`)."
@@ -23361,7 +23377,7 @@ paths:
             application/json:
               schema:
                 $ref: "#/components/schemas/ErrorEnvelope"
-        "502": *a62
+        "502": *a61
   /api/symptoms/definitions:
     get:
       tags:
@@ -23385,7 +23401,7 @@ paths:
               schema:
                 $ref: "#/components/schemas/ListSymptomDefinitionsEnvelope"
         "401": *a1
-        "403": &a64
+        "403": &a63
           description: >-
             `illness.disabled`: the record has the illness module switched off (or the operator turned it off
             server-wide); symptoms ride that module.
@@ -23428,7 +23444,7 @@ paths:
               schema:
                 $ref: "#/components/schemas/CreateSymptomDefinitionEnvelope"
         "401": *a1
-        "403": *a64
+        "403": *a63
         "409": *a7
         "422": *a4
         "429": *a5
@@ -23458,8 +23474,8 @@ paths:
               schema:
                 $ref: "#/components/schemas/UpdateSymptomDefinitionEnvelope"
         "401": *a1
-        "403": *a64
-        "404": &a65
+        "403": *a63
+        "404": &a64
           description: "`symptoms.definition.notFound`: no definition with this id on the record."
           content:
             application/json:
@@ -23493,8 +23509,8 @@ paths:
               schema:
                 $ref: "#/components/schemas/DeleteSymptomDefinitionEnvelope"
         "401": *a1
-        "403": *a64
-        "404": *a65
+        "403": *a63
+        "404": *a64
         "422": *a4
         "429": *a5
   /api/symptoms/events:
@@ -23543,7 +23559,7 @@ paths:
               schema:
                 $ref: "#/components/schemas/ListSymptomEventsEnvelope"
         "401": *a1
-        "403": *a64
+        "403": *a63
         "422": *a4
         "429": *a5
     post:
@@ -23569,8 +23585,8 @@ paths:
               schema:
                 $ref: "#/components/schemas/CreateSymptomEventEnvelope"
         "401": *a1
-        "403": *a64
-        "404": *a65
+        "403": *a63
+        "404": *a64
         "409": *a7
         "422": *a4
         "429": *a5
@@ -23600,8 +23616,8 @@ paths:
               schema:
                 $ref: "#/components/schemas/UpdateSymptomEventEnvelope"
         "401": *a1
-        "403": *a64
-        "404": &a66
+        "403": *a63
+        "404": &a65
           description: "`symptoms.event.notFound`: no occurrence with this id on the record."
           content:
             application/json:
@@ -23628,8 +23644,8 @@ paths:
               schema:
                 $ref: "#/components/schemas/DeleteSymptomEventEnvelope"
         "401": *a1
-        "403": *a64
-        "404": *a66
+        "403": *a63
+        "404": *a65
         "422": *a4
         "429": *a5
   /api/day/index:
@@ -23779,7 +23795,7 @@ paths:
               schema:
                 $ref: "#/components/schemas/TimelineEnvelope"
         "401": *a1
-        "403": &a67
+        "403": &a66
           description: >-
             `module.disabled` with `meta.module = timeline`: the record has the timeline switched off (it is opt-in), or
             the operator turned it off server-wide.
@@ -23816,7 +23832,7 @@ paths:
               schema:
                 $ref: "#/components/schemas/TimelineReadinessEnvelope"
         "401": *a1
-        "403": *a67
+        "403": *a66
         "422": *a4
         "429": *a5
   /api/life-events:
@@ -23834,7 +23850,7 @@ paths:
               schema:
                 $ref: "#/components/schemas/LifeEventListEnvelope"
         "401": *a1
-        "403": &a68
+        "403": &a67
           description: >-
             Owner-only in v1.42: no share reaches life events, not a `profile` share, a whole-record share or MANAGE,
             and not a guardian acting for a managed profile.
@@ -23874,7 +23890,7 @@ paths:
               schema:
                 $ref: "#/components/schemas/CreateLifeEventEnvelope"
         "401": *a1
-        "403": *a68
+        "403": *a67
         "409": *a7
         "422": *a4
         "429": *a12
@@ -23905,8 +23921,8 @@ paths:
               schema:
                 $ref: "#/components/schemas/UpdateLifeEventEnvelope"
         "401": *a1
-        "403": *a68
-        "404": &a69
+        "403": *a67
+        "404": &a68
           description: No such life event on this account.
           content:
             application/json:
@@ -23933,8 +23949,8 @@ paths:
               schema:
                 $ref: "#/components/schemas/DeleteLifeEventEnvelope"
         "401": *a1
-        "403": *a68
-        "404": *a69
+        "403": *a67
+        "404": *a68
         "422": *a4
         "429": *a5
   /api/search:
@@ -24053,7 +24069,7 @@ paths:
         "409": *a7
         "422": *a4
         "429": *a5
-        "501": *a44
+        "501": *a69
   /api/medications/{id}/ingredients/extract:
     post:
       tags:
@@ -24094,7 +24110,7 @@ paths:
                 $ref: "#/components/schemas/ErrorEnvelope"
         "422": *a4
         "429": *a5
-        "501": *a44
+        "501": *a69
         "503":
           description: "`aiRuns.workerUnavailable`: the run could not be handed to the background worker. Nothing was read and
             nothing was charged; try again."
@@ -24119,7 +24135,7 @@ paths:
         "403": *a11
         "422": *a4
         "429": *a5
-        "501": *a44
+        "501": *a69
   /api/anamnesis/life-circumstances/ai-sections:
     patch:
       tags:
@@ -24149,7 +24165,7 @@ paths:
                 $ref: "#/components/schemas/ErrorEnvelope"
         "422": *a4
         "429": *a5
-        "501": *a44
+        "501": *a69
   /api/anamnesis/life-circumstances/confirm:
     post:
       tags:
@@ -24173,7 +24189,7 @@ paths:
         "401": *a1
         "422": *a4
         "429": *a5
-        "501": *a44
+        "501": *a69
   /api/anamnesis/audit-c:
     post:
       tags:
@@ -24206,7 +24222,7 @@ paths:
         "409": *a7
         "422": *a4
         "429": *a5
-        "501": *a44
+        "501": *a69
   /api/anamnesis/audit-c/{id}:
     delete:
       tags:
@@ -24235,7 +24251,7 @@ paths:
                 $ref: "#/components/schemas/ErrorEnvelope"
         "422": *a4
         "429": *a5
-        "501": *a44
+        "501": *a69
   /api/dawarich/connect:
     post:
       tags:
@@ -24261,7 +24277,7 @@ paths:
         "403": *a19
         "422": *a4
         "429": *a5
-        "501": *a44
+        "501": *a69
   /api/dawarich/status:
     get:
       tags:
@@ -24278,7 +24294,7 @@ paths:
         "403": *a19
         "422": *a4
         "429": *a5
-        "501": *a44
+        "501": *a69
   /api/dawarich/places:
     get:
       tags:
@@ -24309,7 +24325,7 @@ paths:
                 $ref: "#/components/schemas/ErrorEnvelope"
         "422": *a4
         "429": *a5
-        "501": *a44
+        "501": *a69
         "502":
           description: "`dawarich.unreachable`."
           content:
@@ -24339,7 +24355,7 @@ paths:
         "403": *a19
         "422": *a4
         "429": *a5
-        "501": *a44
+        "501": *a69
   /api/dawarich/test:
     post:
       tags:
@@ -24358,7 +24374,7 @@ paths:
         "403": *a19
         "422": *a4
         "429": *a5
-        "501": *a44
+        "501": *a69
   /api/dawarich/sync:
     post:
       tags:
@@ -24393,7 +24409,7 @@ paths:
                 $ref: "#/components/schemas/ErrorEnvelope"
         "422": *a4
         "429": *a5
-        "501": *a44
+        "501": *a69
   /api/dawarich/disconnect:
     post:
       tags:
@@ -24422,7 +24438,7 @@ paths:
         "403": *a19
         "422": *a4
         "429": *a5
-        "501": *a44
+        "501": *a69
   /api/environment/travel/suggestions:
     get:
       tags:
@@ -24439,7 +24455,7 @@ paths:
         "403": *a19
         "422": *a4
         "429": *a5
-        "501": *a44
+        "501": *a69
   /api/environment/travel/suggestions/{id}/dismiss:
     post:
       tags:
@@ -24469,7 +24485,7 @@ paths:
                 $ref: "#/components/schemas/ErrorEnvelope"
         "422": *a4
         "429": *a5
-        "501": *a44
+        "501": *a69
   /api/medications/{id}/links:
     post:
       tags:
@@ -24506,7 +24522,7 @@ paths:
                 $ref: "#/components/schemas/ErrorEnvelope"
         "422": *a4
         "429": *a5
-        "501": *a44
+        "501": *a69
     delete:
       tags:
         - Links
@@ -24542,7 +24558,7 @@ paths:
                 $ref: "#/components/schemas/ErrorEnvelope"
         "422": *a4
         "429": *a5
-        "501": *a44
+        "501": *a69
   /api/labs/{id}/links:
     post:
       tags:
@@ -24579,7 +24595,7 @@ paths:
                 $ref: "#/components/schemas/ErrorEnvelope"
         "422": *a4
         "429": *a5
-        "501": *a44
+        "501": *a69
     delete:
       tags:
         - Links
@@ -24615,7 +24631,7 @@ paths:
                 $ref: "#/components/schemas/ErrorEnvelope"
         "422": *a4
         "429": *a5
-        "501": *a44
+        "501": *a69
   /api/bugreport:
     post:
       security: []
@@ -35632,17 +35648,17 @@ components:
                 personal_records.invalid_query; practitioner — practitioner.invalid; profile —
                 profile.update.emailInUse, profile.update.emailRateLimited, profile.update.emailSecondFactorRequired,
                 profile.update.invalidBody, profile.update.nothingSaved; profile_claim — profile_claim.invalid,
-                profile_claim.oidc_only_unsupported, profile_claim.taken; record_write — record_write.rate_limited;
-                report-selection — report-selection.body.invalid_json, report-selection.body.invalid_shape,
-                report-selection.leaves.unknown; route — route.retired; search — search.invalid; share-link —
-                share-link.document.decryptFailed, share-link.document.notFound, share-link.document.rateLimited,
-                share-link.documents.invalid, share-link.report.notFound, share-link.report.rateLimited,
-                share-link.selection.forbidden_leaf, share-link.selection.unknown_leaf; sharing —
-                sharing.accept.expired, sharing.accept.not_found, sharing.accept.not_pending, sharing.accept.revoked,
-                sharing.access.denied, sharing.invite.duplicate, sharing.invite.invalid, sharing.invite.invalid_scope,
-                sharing.invite.manage_browser_only, sharing.invite.refused, sharing.invite.self, sharing.not_permitted,
-                sharing.renounce.already_ended, sharing.renounce.not_found, sharing.revoke.already_ended,
-                sharing.revoke.not_found, sharing.session.changed, sharing.switch.invalid,
+                profile_claim.oidc_only_unsupported, profile_claim.sso_unavailable, profile_claim.taken; record_write —
+                record_write.rate_limited; report-selection — report-selection.body.invalid_json,
+                report-selection.body.invalid_shape, report-selection.leaves.unknown; route — route.retired; search —
+                search.invalid; share-link — share-link.document.decryptFailed, share-link.document.notFound,
+                share-link.document.rateLimited, share-link.documents.invalid, share-link.report.notFound,
+                share-link.report.rateLimited, share-link.selection.forbidden_leaf, share-link.selection.unknown_leaf;
+                sharing — sharing.accept.expired, sharing.accept.not_found, sharing.accept.not_pending,
+                sharing.accept.revoked, sharing.access.denied, sharing.invite.duplicate, sharing.invite.invalid,
+                sharing.invite.invalid_scope, sharing.invite.manage_browser_only, sharing.invite.refused,
+                sharing.invite.self, sharing.not_permitted, sharing.renounce.already_ended, sharing.renounce.not_found,
+                sharing.revoke.already_ended, sharing.revoke.not_found, sharing.session.changed, sharing.switch.invalid,
                 sharing.switch.wrong_transport; source-priority — source-priority.body.invalid_json,
                 source-priority.body.invalid_shape; symptoms — symptoms.definition.limitReached,
                 symptoms.definition.notFound, symptoms.episode.notOpen, symptoms.event.notFound, symptoms.invalid;
diff --git a/docs/self-hosting/account-sharing.md b/docs/self-hosting/account-sharing.md
index 05e2a9b14..62df60982 100644
--- a/docs/self-hosting/account-sharing.md
+++ b/docs/self-hosting/account-sharing.md
@@ -231,11 +231,58 @@ as something to log in as.
   person it was sent to, so the admin notification diagnostic can answer
   "who was this for" and "whose record was it about" separately.
 
-There is no emancipation flow: no route, no control and no copy suggests
-a managed profile can be turned into an ordinary account. The data model
-leaves room for it (the credentials are nullable and the managed marker
-can be cleared) and clearing that marker stops the notification fan-out,
-but nothing in v1.37.0 exercises any of that.
+### Handing a record over to its person
+
+Since v1.42 a guardian can hand a managed profile over to the person it
+describes, so the record becomes their own account with its whole history.
+Nothing is copied or moved; the profile's row gets credentials, loses the
+managed marker, and stops fanning reminders out to its guardians.
+
+- A guardian with a fresh second factor creates a one-time link (valid for
+  one, seven or fourteen days, shown once) and proposes, for each guardian,
+  no access, view only or manage. Only a keyed hash of the link is stored,
+  at most one link per profile is open, and any guardian can withdraw it
+  without a second factor.
+- The person opens the link, sees the record's name, the expiry and who
+  keeps which access, and chooses how they sign in. The claim runs as one
+  transaction: the link is consumed, the proposals are applied, open
+  invitations the record offered are withdrawn, and the disclaimer,
+  onboarding and AI consent are reset so the person gives them themselves.
+  After the first sign-in they confirm or change each guardian's access.
+- How the person signs in depends on the instance:
+
+  | Instance                          | Ways in                    |
+  | --------------------------------- | -------------------------- |
+  | No SSO configured                 | Password                   |
+  | SSO configured, `OIDC_ONLY` unset | Password or single sign-on |
+  | `OIDC_ONLY="true"`                | Single sign-on only        |
+
+  The guardian's panel and the claim page both show which ways are open.
+
+- **Through single sign-on** (v1.43) the person picks a username and
+  continues to the identity provider. When they come back, the provider's
+  `(issuer, sub)` pair is bound to the record in the same transaction, the
+  address is taken from the provider only when it asserts
+  `email_verified: true` (otherwise the account has no address), and no
+  password is set. Refused, with the record left exactly as it was:
+  a provider identity that already signs in to an account on this instance
+  (one identity, one account; the refusal is audited on that account as
+  `auth.oidc.claim_conflict`), a verified address another account holds,
+  a username taken in the meantime, a link that was used, withdrawn,
+  replaced or expired while the person was at the provider, and a browser
+  that is signed in to another account.
+- The link never appears in a URL the server builds: the claim page sends it
+  in request bodies only, and the single-sign-on leg carries a sealed,
+  ten-minute, HttpOnly cookie that names the link by its id. The `/claim/`
+  path and `hlp_` tokens are scrubbed from logs.
+- The iOS app does not claim. The person claims in a browser and then signs
+  in to the app as usual (with SSO, through the app's own SSO sign-in).
+
+Audit rows: `managed_profile.handover.created` and `.revoked` on the record,
+`managed_profile.claim_sso.started` when a single-sign-on claim starts,
+`managed_profile.claimed` and `auth.claim` (with `method: "password"` or
+`"sso"`) when it lands, and `managed_profile.handed_over` on each guardian's
+own account.
 
 ## Seeing what happened
 
diff --git a/docs/self-hosting/sso.md b/docs/self-hosting/sso.md
index aedefa419..c537083e1 100644
--- a/docs/self-hosting/sso.md
+++ b/docs/self-hosting/sso.md
@@ -112,6 +112,12 @@ Client registration essentials only — the IdP's own docs cover the rest.
   MFA in the IdP's policy engine — that is the point of delegating
   authentication. HealthLog-side 2FA remains available on top for the
   step-up gates above.
+- **Claiming a managed profile binds a fresh identity only.** When a
+  person claims a managed profile through SSO, their `(issuer, sub)` is
+  bound to that record, and only if no account on the instance already
+  holds it, and the provider's address is used only when it is verified
+  and not already taken. A claim can therefore never attach somebody's
+  existing sign-in to a second record or take over an existing account.
 - **Linking is once.** There is no unlink/relink flow in this cut; the
   pin is deliberately sticky. Moving an account to a new IdP identity is
   an operator decision (a manual `users.oidc_issuer` / `users.oidc_sub`
@@ -134,6 +140,10 @@ Consequences to accept before turning it on:
 - **Self-disabling on half-config.** The flag only takes effect while
   the three provider vars are fully set, so a typo in the provider group
   can never lock every user out.
+- **Managed profiles are still handed over** (v1.43). The person claims the
+  record through the identity provider instead of setting a password; the
+  password claim is refused. See
+  [Handing a record over to its person](account-sharing.md#handing-a-record-over-to-its-person).
 
 ### Break-glass (IdP down or misconfigured)
 
diff --git a/messages/de.json b/messages/de.json
index 22defd4fa..f7c26583e 100644
--- a/messages/de.json
+++ b/messages/de.json
@@ -528,7 +528,7 @@
       "loading": "Dein Link wird geprüft…",
       "invalid": "Dieser Link funktioniert nicht mehr",
       "invalidHint": "Er ist unbekannt, abgelaufen, zurückgezogen oder schon benutzt. Bitte die Person, die ihn dir gegeben hat, um einen neuen.",
-      "oidcOnly": "Dieser Server erlaubt nur Single Sign-on, deshalb lässt sich ein Profil hier noch nicht übernehmen.",
+      "oidcOnly": "Dieser Server erlaubt nur Single Sign-on. Fahre stattdessen mit deinem Identitätsanbieter fort.",
       "signedInTitle": "Melde dich zuerst ab",
       "signedInBody": "Du bist als {username} angemeldet. Dieser Link richtet eine Anmeldung für jemand anderen ein, melde dich also ab, bevor du ihn benutzt.",
       "signOut": "Abmelden und weiter",
@@ -545,7 +545,19 @@
       "errorTaken": "Dieser Benutzername oder diese E-Mail-Adresse ist schon vergeben.",
       "errorRateLimit": "Zu viele Versuche. Warte ein paar Minuten und versuche es erneut.",
       "errorFailed": "Das hat nicht geklappt. Versuche es gleich noch einmal.",
-      "errorOffline": "Das hat den Server nicht erreicht. Prüfe deine Verbindung und versuche es erneut."
+      "errorOffline": "Das hat den Server nicht erreicht. Prüfe deine Verbindung und versuche es erneut.",
+      "ssoContinue": "Weiter mit {provider}",
+      "ssoStarting": "Weiterleitung…",
+      "ssoHint": "Ab dann meldest du dich hier mit deinem Konto bei {provider} an.",
+      "ssoDivider": "oder",
+      "ssoFallbackName": "Single Sign-on",
+      "errorTitle": "Die Übernahme hat nicht geklappt",
+      "errorSubjectBound": "Diese Anmeldung gehört schon zu einem anderen Konto auf diesem Server. Öffne den Link noch einmal und nimm ein anderes Konto bei deinem Identitätsanbieter.",
+      "errorEmailTaken": "Dein Identitätsanbieter hat eine E-Mail-Adresse geliefert, die hier schon ein anderes Konto nutzt. Öffne den Link noch einmal und nimm ein anderes Konto, oder frag die Person, die den Server betreibt.",
+      "errorUsernameTaken": "Jemand hat diesen Benutzernamen inzwischen vergeben. Öffne den Link noch einmal und wähle einen anderen.",
+      "errorSignedIn": "Bei der Rückkehr warst du angemeldet. Melde dich ab und öffne den Link noch einmal.",
+      "errorSso": "Die Anmeldung bei deinem Identitätsanbieter hat nicht funktioniert. Öffne den Link noch einmal, um es erneut zu versuchen.",
+      "signInInstead": "Bei diesem Konto anmelden"
     },
     "inviteInvalid": {
       "title": "Einladung ungültig",
@@ -11989,9 +12001,11 @@
         "revokeFailed": "Der Link ließ sich nicht zurückziehen. Versuche es erneut.",
         "errorFailed": "Der Übergabelink ließ sich nicht erstellen.",
         "errorRosterChanged": "Inzwischen hat sich geändert, wer die Akte betreut. Schließe das hier und öffne es erneut.",
-        "oidcOnly": "Ein Profil zu übergeben ist nicht möglich, solange dieser Server nur Single Sign-on erlaubt.",
+        "oidcOnly": "Ein Profil zu übergeben ist auf diesem Server nicht möglich.",
         "loadError": "Der Stand der Übergabe ließ sich nicht laden.",
-        "entryHint": "Wenn {name} die Akte selbst führen möchte."
+        "entryHint": "Wenn {name} die Akte selbst führen möchte.",
+        "methodSso": "{name} meldet sich beim Einlösen des Links über Single Sign-on an.",
+        "methodBoth": "{name} kann ein Passwort festlegen oder sich über Single Sign-on anmelden."
       }
     },
     "toast": {
diff --git a/messages/en.json b/messages/en.json
index 874ee9856..4d2ef1aa2 100644
--- a/messages/en.json
+++ b/messages/en.json
@@ -528,7 +528,7 @@
       "loading": "Checking your link…",
       "invalid": "This link no longer works",
       "invalidHint": "It is unknown, expired, withdrawn or already used. Ask the person who sent it for a new one.",
-      "oidcOnly": "This server only allows single sign-on, so a profile cannot be taken over here yet.",
+      "oidcOnly": "This server only allows single sign-on. Continue with your identity provider instead.",
       "signedInTitle": "Sign out first",
       "signedInBody": "You are signed in as {username}. This link sets up a sign-in for someone else, so sign out before you use it.",
       "signOut": "Sign out and continue",
@@ -545,7 +545,19 @@
       "errorTaken": "That username or email address is already in use.",
       "errorRateLimit": "Too many attempts. Wait a few minutes and try again.",
       "errorFailed": "That did not work. Try again in a moment.",
-      "errorOffline": "That did not reach the server. Check your connection and try again."
+      "errorOffline": "That did not reach the server. Check your connection and try again.",
+      "ssoContinue": "Continue with {provider}",
+      "ssoStarting": "Redirecting…",
+      "ssoHint": "From then on you sign in here with your {provider} account.",
+      "ssoDivider": "or",
+      "ssoFallbackName": "single sign-on",
+      "errorTitle": "The handover did not go through",
+      "errorSubjectBound": "This sign-in already belongs to another account on this server. Open the link again and use a different account at your identity provider.",
+      "errorEmailTaken": "Your identity provider gave an email address that another account here already uses. Open the link again and use a different account, or ask the server's administrator.",
+      "errorUsernameTaken": "Someone took that username in the meantime. Open the link again and choose another one.",
+      "errorSignedIn": "You were signed in when you came back. Sign out, then open the link again.",
+      "errorSso": "Signing in with your identity provider did not work. Open the link again to try once more.",
+      "signInInstead": "Sign in to that account"
     },
     "inviteInvalid": {
       "title": "Invitation invalid",
@@ -11989,9 +12001,11 @@
         "revokeFailed": "The link could not be withdrawn. Try again.",
         "errorFailed": "The handover link could not be created.",
         "errorRosterChanged": "The list of guardians changed in the meantime. Close this and open it again.",
-        "oidcOnly": "Handing over a profile is not available while this server allows single sign-on only.",
+        "oidcOnly": "Handing over a profile is not available on this server.",
         "loadError": "The handover status could not be loaded.",
-        "entryHint": "When {name} is ready to look after this record themselves."
+        "entryHint": "When {name} is ready to look after this record themselves.",
+        "methodSso": "{name} signs in through single sign-on when they use the link.",
+        "methodBoth": "{name} can set a password or sign in through single sign-on."
       }
     },
     "toast": {
diff --git a/messages/es.json b/messages/es.json
index e27e98043..932799bd1 100644
--- a/messages/es.json
+++ b/messages/es.json
@@ -528,7 +528,7 @@
       "loading": "Comprobando tu enlace…",
       "invalid": "Este enlace ya no funciona",
       "invalidHint": "Es desconocido, ha caducado, se ha retirado o ya se ha usado. Pide uno nuevo a quien te lo envió.",
-      "oidcOnly": "Este servidor solo permite el inicio de sesión único, así que aquí todavía no se puede asumir un perfil.",
+      "oidcOnly": "Este servidor solo permite el inicio de sesión único. Continúa con tu proveedor de identidad.",
       "signedInTitle": "Cierra la sesión primero",
       "signedInBody": "Has iniciado sesión como {username}. Este enlace crea un acceso para otra persona, así que cierra la sesión antes de usarlo.",
       "signOut": "Cerrar sesión y continuar",
@@ -545,7 +545,19 @@
       "errorTaken": "Ese nombre de usuario o correo electrónico ya está en uso.",
       "errorRateLimit": "Demasiados intentos. Espera unos minutos y vuelve a intentarlo.",
       "errorFailed": "No ha funcionado. Vuelve a intentarlo en un momento.",
-      "errorOffline": "No se llegó al servidor. Comprueba tu conexión y vuelve a intentarlo."
+      "errorOffline": "No se llegó al servidor. Comprueba tu conexión y vuelve a intentarlo.",
+      "ssoContinue": "Continuar con {provider}",
+      "ssoStarting": "Redirigiendo…",
+      "ssoHint": "A partir de entonces inicias sesión aquí con tu cuenta de {provider}.",
+      "ssoDivider": "o",
+      "ssoFallbackName": "inicio de sesión único",
+      "errorTitle": "La entrega no se ha completado",
+      "errorSubjectBound": "Este inicio de sesión ya pertenece a otra cuenta de este servidor. Vuelve a abrir el enlace y usa otra cuenta en tu proveedor de identidad.",
+      "errorEmailTaken": "Tu proveedor de identidad ha enviado una dirección de correo que ya usa otra cuenta aquí. Vuelve a abrir el enlace y usa otra cuenta, o pregunta a quien administra el servidor.",
+      "errorUsernameTaken": "Alguien ha cogido ese nombre de usuario mientras tanto. Vuelve a abrir el enlace y elige otro.",
+      "errorSignedIn": "Tenías una sesión iniciada al volver. Cierra la sesión y vuelve a abrir el enlace.",
+      "errorSso": "No se ha podido iniciar sesión con tu proveedor de identidad. Vuelve a abrir el enlace para intentarlo otra vez.",
+      "signInInstead": "Iniciar sesión en esa cuenta"
     },
     "inviteInvalid": {
       "title": "Invitación no válida",
@@ -11989,9 +12001,11 @@
         "revokeFailed": "No se pudo retirar el enlace. Vuelve a intentarlo.",
         "errorFailed": "No se pudo crear el enlace de entrega.",
         "errorRosterChanged": "Mientras tanto ha cambiado quién se ocupa del historial. Cierra esto y vuelve a abrirlo.",
-        "oidcOnly": "No se puede entregar un perfil mientras este servidor solo permita el inicio de sesión único.",
+        "oidcOnly": "En este servidor no se puede entregar un perfil.",
         "loadError": "No se pudo cargar el estado de la entrega.",
-        "entryHint": "Cuando {name} quiera llevar este historial por su cuenta."
+        "entryHint": "Cuando {name} quiera llevar este historial por su cuenta.",
+        "methodSso": "{name} inicia sesión con el inicio de sesión único cuando usa el enlace.",
+        "methodBoth": "{name} puede elegir una contraseña o iniciar sesión con el inicio de sesión único."
       }
     },
     "toast": {
diff --git a/messages/fr.json b/messages/fr.json
index 2743484ab..9638f8572 100644
--- a/messages/fr.json
+++ b/messages/fr.json
@@ -528,7 +528,7 @@
       "loading": "Vérification de votre lien…",
       "invalid": "Ce lien ne fonctionne plus",
       "invalidHint": "Il est inconnu, expiré, retiré ou déjà utilisé. Demandez-en un nouveau à la personne qui vous l'a envoyé.",
-      "oidcOnly": "Ce serveur n'autorise que l'authentification unique, un profil ne peut donc pas encore être repris ici.",
+      "oidcOnly": "Ce serveur n'autorise que l'authentification unique. Continuez plutôt avec votre fournisseur d'identité.",
       "signedInTitle": "Déconnectez-vous d'abord",
       "signedInBody": "Vous êtes connecté en tant que {username}. Ce lien crée une connexion pour quelqu'un d'autre, déconnectez-vous donc avant de l'utiliser.",
       "signOut": "Se déconnecter et continuer",
@@ -545,7 +545,19 @@
       "errorTaken": "Ce nom d'utilisateur ou cette adresse e-mail est déjà utilisé.",
       "errorRateLimit": "Trop de tentatives. Attendez quelques minutes puis réessayez.",
       "errorFailed": "Cela n'a pas fonctionné. Réessayez dans un instant.",
-      "errorOffline": "Le serveur n'a pas été atteint. Vérifiez votre connexion et réessayez."
+      "errorOffline": "Le serveur n'a pas été atteint. Vérifiez votre connexion et réessayez.",
+      "ssoContinue": "Continuer avec {provider}",
+      "ssoStarting": "Redirection…",
+      "ssoHint": "Ensuite, vous vous connectez ici avec votre compte {provider}.",
+      "ssoDivider": "ou",
+      "ssoFallbackName": "l'authentification unique",
+      "errorTitle": "La transmission n'a pas abouti",
+      "errorSubjectBound": "Cette connexion appartient déjà à un autre compte sur ce serveur. Rouvrez le lien et utilisez un autre compte chez votre fournisseur d'identité.",
+      "errorEmailTaken": "Votre fournisseur d'identité a transmis une adresse e-mail déjà utilisée par un autre compte ici. Rouvrez le lien et utilisez un autre compte, ou contactez la personne qui administre le serveur.",
+      "errorUsernameTaken": "Quelqu'un a pris ce nom d'utilisateur entre-temps. Rouvrez le lien et choisissez-en un autre.",
+      "errorSignedIn": "Vous étiez connecté à votre retour. Déconnectez-vous, puis rouvrez le lien.",
+      "errorSso": "La connexion avec votre fournisseur d'identité n'a pas fonctionné. Rouvrez le lien pour réessayer.",
+      "signInInstead": "Se connecter à ce compte"
     },
     "inviteInvalid": {
       "title": "Invitation invalide",
@@ -11989,9 +12001,11 @@
         "revokeFailed": "Le lien n'a pas pu être retiré. Réessayez.",
         "errorFailed": "Le lien de transmission n'a pas pu être créé.",
         "errorRosterChanged": "Entre-temps, les personnes qui s'occupent du dossier ont changé. Fermez ceci et rouvrez-le.",
-        "oidcOnly": "Transmettre un profil n'est pas possible tant que ce serveur n'autorise que l'authentification unique.",
+        "oidcOnly": "Transmettre un profil n'est pas possible sur ce serveur.",
         "loadError": "L'état de la transmission n'a pas pu être chargé.",
-        "entryHint": "Quand {name} souhaite tenir ce dossier de façon autonome."
+        "entryHint": "Quand {name} souhaite tenir ce dossier de façon autonome.",
+        "methodSso": "{name} se connecte par authentification unique en utilisant le lien.",
+        "methodBoth": "{name} peut définir un mot de passe ou se connecter par authentification unique."
       }
     },
     "toast": {
diff --git a/messages/it.json b/messages/it.json
index 80f4e0504..2d68f0d6a 100644
--- a/messages/it.json
+++ b/messages/it.json
@@ -528,7 +528,7 @@
       "loading": "Controllo del link…",
       "invalid": "Questo link non funziona più",
       "invalidHint": "È sconosciuto, scaduto, ritirato o già usato. Chiedine uno nuovo a chi te l'ha inviato.",
-      "oidcOnly": "Questo server consente solo il single sign-on, quindi qui non è ancora possibile prendere in carico un profilo.",
+      "oidcOnly": "Questo server consente solo il single sign-on. Continua invece con il tuo provider di identità.",
       "signedInTitle": "Prima esci",
       "signedInBody": "Hai effettuato l'accesso come {username}. Questo link crea un accesso per un'altra persona, quindi esci prima di usarlo.",
       "signOut": "Esci e continua",
@@ -545,7 +545,19 @@
       "errorTaken": "Questo nome utente o indirizzo email è già in uso.",
       "errorRateLimit": "Troppi tentativi. Attendi qualche minuto e riprova.",
       "errorFailed": "Non ha funzionato. Riprova tra un momento.",
-      "errorOffline": "Il server non è stato raggiunto. Controlla la connessione e riprova."
+      "errorOffline": "Il server non è stato raggiunto. Controlla la connessione e riprova.",
+      "ssoContinue": "Continua con {provider}",
+      "ssoStarting": "Reindirizzamento…",
+      "ssoHint": "Da quel momento accedi qui con il tuo account {provider}.",
+      "ssoDivider": "oppure",
+      "ssoFallbackName": "single sign-on (SSO)",
+      "errorTitle": "La consegna non è andata a buon fine",
+      "errorSubjectBound": "Questo accesso appartiene già a un altro account su questo server. Riapri il link e usa un altro account presso il tuo provider di identità.",
+      "errorEmailTaken": "Il tuo provider di identità ha fornito un indirizzo email che qui usa già un altro account. Riapri il link e usa un altro account, oppure chiedi a chi amministra il server.",
+      "errorUsernameTaken": "Nel frattempo qualcuno ha preso quel nome utente. Riapri il link e scegline un altro.",
+      "errorSignedIn": "Al ritorno avevi già effettuato l'accesso. Esci, poi riapri il link.",
+      "errorSso": "L'accesso con il tuo provider di identità non è riuscito. Riapri il link per riprovare.",
+      "signInInstead": "Accedi a quell'account"
     },
     "inviteInvalid": {
       "title": "Invito non valido",
@@ -11989,9 +12001,11 @@
         "revokeFailed": "Impossibile ritirare il link. Riprova.",
         "errorFailed": "Impossibile creare il link di consegna.",
         "errorRosterChanged": "Nel frattempo è cambiato chi si occupa della cartella. Chiudi e riapri.",
-        "oidcOnly": "Non è possibile consegnare un profilo finché questo server consente solo il single sign-on.",
+        "oidcOnly": "Su questo server non è possibile consegnare un profilo.",
         "loadError": "Impossibile caricare lo stato della consegna.",
-        "entryHint": "Quando {name} vuole tenere questa cartella in autonomia."
+        "entryHint": "Quando {name} vuole tenere questa cartella in autonomia.",
+        "methodSso": "{name} accede con il single sign-on quando usa il link.",
+        "methodBoth": "{name} può impostare una password oppure accedere con il single sign-on."
       }
     },
     "toast": {
diff --git a/messages/ko.json b/messages/ko.json
index 29f8be638..c60235d85 100644
--- a/messages/ko.json
+++ b/messages/ko.json
@@ -528,7 +528,7 @@
       "loading": "링크를 확인하는 중…",
       "invalid": "이 링크는 더 이상 작동하지 않습니다",
       "invalidHint": "알 수 없거나, 만료되었거나, 철회되었거나, 이미 사용된 링크입니다. 보낸 사람에게 새 링크를 요청하세요.",
-      "oidcOnly": "이 서버는 통합 로그인(SSO)만 허용하므로 아직 여기서 프로필을 넘겨받을 수 없습니다.",
+      "oidcOnly": "이 서버는 통합 로그인(SSO)만 허용합니다. 대신 ID 공급자로 계속하세요.",
       "signedInTitle": "먼저 로그아웃하세요",
       "signedInBody": "{username} 계정으로 로그인되어 있습니다. 이 링크는 다른 사람의 로그인을 만드는 링크이므로 사용하기 전에 로그아웃하세요.",
       "signOut": "로그아웃하고 계속",
@@ -545,7 +545,19 @@
       "errorTaken": "이미 사용 중인 사용자 이름 또는 이메일 주소입니다.",
       "errorRateLimit": "시도 횟수가 너무 많습니다. 몇 분 후 다시 시도하세요.",
       "errorFailed": "처리하지 못했습니다. 잠시 후 다시 시도하세요.",
-      "errorOffline": "서버에 연결하지 못했습니다. 연결을 확인하고 다시 시도하세요."
+      "errorOffline": "서버에 연결하지 못했습니다. 연결을 확인하고 다시 시도하세요.",
+      "ssoContinue": "{provider}(으)로 계속",
+      "ssoStarting": "이동하는 중…",
+      "ssoHint": "이후에는 {provider} 계정으로 여기에 로그인합니다.",
+      "ssoDivider": "또는",
+      "ssoFallbackName": "통합 로그인(SSO)",
+      "errorTitle": "넘겨받기를 완료하지 못했습니다",
+      "errorSubjectBound": "이 로그인은 이미 이 서버의 다른 계정에 연결되어 있습니다. 링크를 다시 열고 ID 공급자에서 다른 계정을 사용하세요.",
+      "errorEmailTaken": "ID 공급자가 보낸 이메일 주소를 이 서버의 다른 계정이 이미 사용하고 있습니다. 링크를 다시 열고 다른 계정을 사용하거나 서버 관리자에게 문의하세요.",
+      "errorUsernameTaken": "그 사이에 다른 사람이 이 사용자 이름을 사용했습니다. 링크를 다시 열고 다른 이름을 선택하세요.",
+      "errorSignedIn": "돌아왔을 때 이미 로그인되어 있었습니다. 로그아웃한 다음 링크를 다시 여세요.",
+      "errorSso": "ID 공급자로 로그인하지 못했습니다. 링크를 다시 열어 한 번 더 시도하세요.",
+      "signInInstead": "그 계정으로 로그인"
     },
     "inviteInvalid": {
       "title": "유효하지 않은 초대예요",
@@ -11989,9 +12001,11 @@
         "revokeFailed": "링크를 철회하지 못했습니다. 다시 시도하세요.",
         "errorFailed": "넘겨주기 링크를 만들지 못했습니다.",
         "errorRosterChanged": "그 사이 기록을 돌보는 사람이 바뀌었습니다. 닫았다가 다시 여세요.",
-        "oidcOnly": "이 서버가 통합 로그인(SSO)만 허용하는 동안에는 프로필을 넘겨줄 수 없습니다.",
+        "oidcOnly": "이 서버에서는 프로필을 넘겨줄 수 없습니다.",
         "loadError": "넘겨주기 상태를 불러오지 못했습니다.",
-        "entryHint": "{name} 님이 이 기록을 직접 관리할 준비가 되었을 때."
+        "entryHint": "{name} 님이 이 기록을 직접 관리할 준비가 되었을 때.",
+        "methodSso": "{name}님은 링크를 사용할 때 통합 로그인(SSO)으로 로그인합니다.",
+        "methodBoth": "{name}님은 비밀번호를 정하거나 통합 로그인(SSO)으로 로그인할 수 있습니다."
       }
     },
     "toast": {
diff --git a/messages/pl.json b/messages/pl.json
index 8b9d69342..0df1eadae 100644
--- a/messages/pl.json
+++ b/messages/pl.json
@@ -528,7 +528,7 @@
       "loading": "Sprawdzanie linku…",
       "invalid": "Ten link już nie działa",
       "invalidHint": "Jest nieznany, wygasł, został wycofany albo już użyty. Poproś osobę, która go wysłała, o nowy.",
-      "oidcOnly": "Ten serwer pozwala tylko na logowanie jednokrotne (SSO), więc profilu nie można tu jeszcze przejąć.",
+      "oidcOnly": "Ten serwer pozwala tylko na logowanie jednokrotne (SSO). Kontynuuj u swojego dostawcy tożsamości.",
       "signedInTitle": "Najpierw się wyloguj",
       "signedInBody": "Masz zalogowaną sesję jako {username}. Ten link tworzy logowanie dla kogoś innego, więc wyloguj się, zanim go użyjesz.",
       "signOut": "Wyloguj i kontynuuj",
@@ -545,7 +545,19 @@
       "errorTaken": "Ta nazwa użytkownika lub adres e-mail jest już zajęty.",
       "errorRateLimit": "Zbyt wiele prób. Odczekaj kilka minut i spróbuj ponownie.",
       "errorFailed": "Nie udało się. Spróbuj ponownie za chwilę.",
-      "errorOffline": "Nie udało się połączyć z serwerem. Sprawdź połączenie i spróbuj ponownie."
+      "errorOffline": "Nie udało się połączyć z serwerem. Sprawdź połączenie i spróbuj ponownie.",
+      "ssoContinue": "Kontynuuj przez {provider}",
+      "ssoStarting": "Przekierowywanie…",
+      "ssoHint": "Od tej pory logujesz się tutaj swoim kontem {provider}.",
+      "ssoDivider": "lub",
+      "ssoFallbackName": "logowanie jednokrotne (SSO)",
+      "errorTitle": "Przejęcie się nie udało",
+      "errorSubjectBound": "To logowanie należy już do innego konta na tym serwerze. Otwórz link ponownie i użyj innego konta u swojego dostawcy tożsamości.",
+      "errorEmailTaken": "Twój dostawca tożsamości przekazał adres e-mail, którego używa już inne konto na tym serwerze. Otwórz link ponownie i użyj innego konta albo zapytaj osobę, która administruje serwerem.",
+      "errorUsernameTaken": "W międzyczasie ktoś zajął tę nazwę użytkownika. Otwórz link ponownie i wybierz inną.",
+      "errorSignedIn": "Po powrocie byłeś zalogowany. Wyloguj się i otwórz link ponownie.",
+      "errorSso": "Logowanie u dostawcy tożsamości się nie powiodło. Otwórz link ponownie, aby spróbować jeszcze raz.",
+      "signInInstead": "Zaloguj się na to konto"
     },
     "inviteInvalid": {
       "title": "Nieprawidłowe zaproszenie",
@@ -11989,9 +12001,11 @@
         "revokeFailed": "Nie udało się wycofać linku. Spróbuj ponownie.",
         "errorFailed": "Nie udało się utworzyć linku przekazania.",
         "errorRosterChanged": "W międzyczasie zmieniło się, kto opiekuje się kartą. Zamknij to i otwórz ponownie.",
-        "oidcOnly": "Przekazanie profilu nie jest możliwe, dopóki ten serwer pozwala tylko na logowanie jednokrotne (SSO).",
+        "oidcOnly": "Przekazanie profilu nie jest możliwe na tym serwerze.",
         "loadError": "Nie udało się wczytać stanu przekazania.",
-        "entryHint": "Gdy {name} chce samodzielnie prowadzić tę kartę."
+        "entryHint": "Gdy {name} chce samodzielnie prowadzić tę kartę.",
+        "methodSso": "{name} loguje się przez logowanie jednokrotne (SSO), gdy użyje linku.",
+        "methodBoth": "{name} może ustawić hasło albo zalogować się przez logowanie jednokrotne (SSO)."
       }
     },
     "toast": {
diff --git a/src/__tests__/contract-stub-inventory.test.ts b/src/__tests__/contract-stub-inventory.test.ts
index 5d73a18ab..56aea5d1d 100644
--- a/src/__tests__/contract-stub-inventory.test.ts
+++ b/src/__tests__/contract-stub-inventory.test.ts
@@ -37,7 +37,6 @@ const CONTRACT_STUBS: Readonly<Record<string, readonly string[]>> = {
     "anamnesis.life_circumstances.confirm",
   ],
   "anamnesis/life-circumstances/route.ts": ["anamnesis.life_circumstances.get"],
-  "auth/claim/sso/route.ts": ["profile_claim.sso.start"],
   "dawarich/connect/route.ts": ["dawarich.connect"],
   "dawarich/disconnect/route.ts": ["dawarich.disconnect"],
   "dawarich/places/route.ts": ["dawarich.places.get"],
@@ -61,7 +60,7 @@ const CONTRACT_STUBS: Readonly<Record<string, readonly string[]>> = {
 };
 
 /** The size of the register when it was written; see the header. */
-const REGISTER_SIZE = 21;
+const REGISTER_SIZE = 20;
 
 function routeFiles(): string[] {
   return walkSourceFiles(API_ROOT, { floor: 400, extensions: [".ts"] })
diff --git a/src/__tests__/session-surface-guard.test.ts b/src/__tests__/session-surface-guard.test.ts
index d27126a2b..6fdcd8534 100644
--- a/src/__tests__/session-surface-guard.test.ts
+++ b/src/__tests__/session-surface-guard.test.ts
@@ -100,9 +100,11 @@ describe("S1 — the direct session-resolution set is frozen", () => {
     "app/api/auth/claim/sso/route.ts":
       "refuses to start a single-sign-on claim over a live session",
     // Anonymous IdP callback. Probes for an already-valid session so a
-    // replayed callback redirects instead of minting a second identity.
+    // replayed callback redirects instead of minting a second identity, and
+    // (v1.43, #959) so a single-sign-on claim is refused over a live session,
+    // as the claim routes refuse it.
     "app/api/auth/oidc/callback/route.ts":
-      "duplicate-callback probe on an otherwise anonymous route",
+      "duplicate-callback probe and the claim's live-session refusal on an otherwise anonymous route",
     // Public liveness probe. The session read only decides whether the body
     // carries operational detail; the status code is computed without it.
     "app/api/health/route.ts": "admin-only detail on a public probe",
@@ -370,6 +372,48 @@ describe("S2 — the URL-token authentication set is frozen", () => {
   });
 });
 
+describe("S4 — the single-sign-on claim cookie set is frozen", () => {
+  /**
+   * v1.43 (#959). A third way to act without a session: the sealed `hl_claim`
+   * cookie carries a managed-profile claim from `POST /api/auth/claim/sso`
+   * through the OIDC round trip, and the callback turns it — together with
+   * the provider's subject — into somebody's account. It is neither a session
+   * nor a URL credential, so neither leg above sees it.
+   *
+   * The handover token itself still only travels in the claim routes' bodies
+   * and the claim page's query string (S2); the cookie names the link by id.
+   * What this freezes is who may mint the cookie and who may act on it.
+   */
+  const CLAIM_COOKIE_ALLOWLIST: Record<string, string> = {
+    "app/api/auth/claim/sso/route.ts":
+      "mints the cookie, only after checking the token and the username",
+    "app/api/auth/oidc/login/route.ts":
+      "requires the cookie for intent=claim and binds it into the OIDC state",
+    "app/api/auth/oidc/callback/route.ts":
+      "binds the provider's subject to the profile the cookie names",
+  };
+
+  const CLAIM_COOKIE_USE =
+    /\b(readClaimCookie|setClaimCookie|claimMatchesBinding|clearClaimCookie)\s*\(|\bCLAIM_COOKIE\b|["']hl_claim["']/;
+
+  it("no file under src/app touches the claim cookie unlisted", () => {
+    const users = appFilesMatching(CLAIM_COOKIE_USE);
+    expect(users.length).toBeGreaterThan(0);
+    expect(users).toEqual(Object.keys(CLAIM_COOKIE_ALLOWLIST).sort());
+  });
+
+  it("only the single-sign-on start mints it", () => {
+    const minters = appFilesMatching(/\bsetClaimCookie\s*\(/);
+    expect(minters).toEqual(["app/api/auth/claim/sso/route.ts"]);
+  });
+
+  it("every allowlist entry carries a reason", () => {
+    for (const [rel, reason] of Object.entries(CLAIM_COOKIE_ALLOWLIST)) {
+      expect(reason.trim().length, `${rel} has no reason`).toBeGreaterThan(0);
+    }
+  });
+});
+
 describe("S3 — the two families stay distinct", () => {
   /**
    * A file that both resolves a session AND authenticates by a URL token is
diff --git a/src/app/api/auth/claim/__tests__/route.test.ts b/src/app/api/auth/claim/__tests__/route.test.ts
index b5b9722b1..49d2fc9c4 100644
--- a/src/app/api/auth/claim/__tests__/route.test.ts
+++ b/src/app/api/auth/claim/__tests__/route.test.ts
@@ -5,7 +5,11 @@
  * (`tests/integration/managed-profile-handover.test.ts`); here the order of
  * the refusals is pinned, because each one is a security property:
  *
- *   - single sign-on only refuses before anything else;
+ *   - single sign-on only refuses the PASSWORD claim before anything else,
+ *     while the preview answers there and names `sso` as the way in (v1.43);
+ *   - the single-sign-on start needs a configured provider, refuses a live
+ *     session before the rate limit, checks the link before the username,
+ *     and seals the link's id (never the token) into `hl_claim`;
  *   - a live session is refused BEFORE the rate limit (a state, not an
  *     attempt), and before any token is read;
  *   - the rate limit runs before the body is parsed;
@@ -24,7 +28,18 @@ vi.mock("@/lib/auth/session", () => ({
   createSession: vi.fn(),
   getSession: vi.fn(),
 }));
-vi.mock("@/lib/auth/oidc", () => ({ isOidcOnly: vi.fn() }));
+vi.mock("@/lib/auth/oidc", () => ({
+  isOidcOnly: vi.fn(),
+  isOidcConfigured: vi.fn(),
+  getOidcConfig: vi.fn(),
+}));
+vi.mock("@/lib/crypto", () => ({
+  encrypt: vi.fn((s: string) => `sealed(${s})`),
+  decrypt: vi.fn(),
+}));
+vi.mock("@/lib/auth/secure-cookie", () => ({
+  shouldEmitSecureCookie: () => true,
+}));
 vi.mock("@/lib/rate-limit", () => ({
   checkRateLimit: vi.fn(),
   checkAuthSurfaceRateLimit: vi.fn(),
@@ -49,6 +64,7 @@ vi.mock("@/lib/managed-profiles/handover", async () => {
   return {
     HandoverError: actual.HandoverError,
     previewHandover: vi.fn(),
+    usableHandoverForToken: vi.fn(),
     claimManagedProfile: vi.fn(),
   };
 });
@@ -67,9 +83,11 @@ vi.mock("next/headers", () => ({
 
 import { POST as claim } from "../route";
 import { POST as preview } from "../preview/route";
+import { POST as claimSso } from "../sso/route";
 import { prisma } from "@/lib/db";
 import { createSession, getSession } from "@/lib/auth/session";
-import { isOidcOnly } from "@/lib/auth/oidc";
+import { getOidcConfig, isOidcConfigured, isOidcOnly } from "@/lib/auth/oidc";
+import { auditLog } from "@/lib/auth/audit";
 import { checkAuthSurfaceRateLimit } from "@/lib/rate-limit";
 import { checkPasswordStrength, hashPassword } from "@/lib/auth/password";
 import { checkPasswordBreachIfEnabled } from "@/lib/password-breach-check";
@@ -77,6 +95,7 @@ import {
   claimManagedProfile,
   HandoverError,
   previewHandover,
+  usableHandoverForToken,
 } from "@/lib/managed-profiles/handover";
 import { notifyGuardiansOfHandover } from "@/lib/managed-profiles/handover-notify";
 
@@ -105,6 +124,12 @@ const PREVIEW = {
 beforeEach(() => {
   vi.resetAllMocks();
   vi.mocked(isOidcOnly).mockReturnValue(false);
+  vi.mocked(isOidcConfigured).mockReturnValue(false);
+  vi.mocked(getOidcConfig).mockReturnValue(null);
+  vi.mocked(usableHandoverForToken).mockResolvedValue({
+    handoverId: "h1",
+    profileId: "p1",
+  });
   vi.mocked(getSession).mockResolvedValue(null as never);
   vi.mocked(checkAuthSurfaceRateLimit).mockResolvedValue({
     allowed: true,
@@ -131,19 +156,62 @@ async function errorCode(res: Response): Promise<unknown> {
   return body.meta?.errorCode;
 }
 
+const OIDC_CONFIG = {
+  issuerUrl: "https://idp.example.test",
+  clientId: "c",
+  clientSecret: "s",
+  scopes: "openid email",
+  buttonLabel: "Example ID",
+};
+
+function singleSignOnOnly(): void {
+  vi.mocked(isOidcOnly).mockReturnValue(true);
+  vi.mocked(isOidcConfigured).mockReturnValue(true);
+  vi.mocked(getOidcConfig).mockReturnValue(OIDC_CONFIG);
+}
+
+describe("on a single-sign-on-only instance", () => {
+  it("refuses the password claim before anything else", async () => {
+    singleSignOnOnly();
+    vi.mocked(getSession).mockResolvedValue({ user: { id: "u1" } } as never);
+    const res = await claim(post("/api/auth/claim", BODY));
+    expect(res.status).toBe(403);
+    expect(await errorCode(res)).toBe("profile_claim.oidc_only_unsupported");
+    expect(previewHandover).not.toHaveBeenCalled();
+  });
+
+  it("answers the preview and names single sign-on as the only way in", async () => {
+    singleSignOnOnly();
+    const res = await preview(
+      post("/api/auth/claim/preview", { token: TOKEN }),
+    );
+    expect(res.status).toBe(200);
+    const body = (await res.json()) as { data: Record<string, unknown> };
+    expect(body.data.methods).toEqual(["sso"]);
+    expect(body.data.ssoProviderName).toBe("Example ID");
+  });
+});
+
 describe.each([
   ["claim", claim, "/api/auth/claim", BODY],
   ["preview", preview, "/api/auth/claim/preview", { token: TOKEN }],
+  ["sso", claimSso, "/api/auth/claim/sso", { token: TOKEN, username: "alex" }],
 ] as const)(
   "POST %s — refusals that read no token",
-  (_n, route, path, body) => {
-    it("refuses on a single-sign-on-only instance before anything else", async () => {
-      vi.mocked(isOidcOnly).mockReturnValue(true);
-      vi.mocked(getSession).mockResolvedValue({ user: { id: "u1" } } as never);
-      const res = await route(post(path, body));
-      expect(res.status).toBe(403);
-      expect(await errorCode(res)).toBe("profile_claim.oidc_only_unsupported");
-      expect(previewHandover).not.toHaveBeenCalled();
+  (name, route, path, body) => {
+    beforeEach(() => {
+      if (name === "sso") {
+        vi.mocked(isOidcConfigured).mockReturnValue(true);
+        vi.mocked(getOidcConfig).mockReturnValue(OIDC_CONFIG);
+      }
+      if (name === "sso") {
+        vi.mocked(usableHandoverForToken).mockImplementation(async () => {
+          // Routes the sso start through the same "link" spy the other two
+          // use, so one set of assertions covers all three.
+          const found = await previewHandover(TOKEN);
+          return found ? { handoverId: "h1", profileId: "p1" } : null;
+        });
+      }
     });
 
     it("refuses over a live session before spending the rate limit", async () => {
@@ -234,7 +302,7 @@ describe("POST /api/auth/claim", () => {
     expect(res.status).toBe(201);
     expect(claimManagedProfile).toHaveBeenCalledWith(
       expect.objectContaining({
-        rawToken: TOKEN,
+        link: { rawToken: TOKEN },
         username: "alex",
         email: "alex@example.test",
         passwordHash: "argon2-hash",
@@ -260,7 +328,101 @@ describe("POST /api/auth/claim/preview", () => {
       "displayName",
       "expiresAt",
       "guardians",
+      "methods",
+      "ssoProviderName",
     ]);
+    expect(body.data.methods).toEqual(["password"]);
+    expect(body.data.ssoProviderName).toBeNull();
     expect(body.data.expiresAt).toBe("2030-01-01T00:00:00.000Z");
   });
 });
+
+describe("POST /api/auth/claim/sso", () => {
+  const SSO_BODY = { token: TOKEN, username: "alex" };
+
+  beforeEach(() => {
+    vi.mocked(isOidcConfigured).mockReturnValue(true);
+    vi.mocked(getOidcConfig).mockReturnValue(OIDC_CONFIG);
+  });
+
+  it("answers 404 sso_unavailable without an identity provider, before anything else", async () => {
+    vi.mocked(isOidcConfigured).mockReturnValue(false);
+    vi.mocked(getSession).mockResolvedValue({ user: { id: "u1" } } as never);
+    const res = await claimSso(post("/api/auth/claim/sso", SSO_BODY));
+    expect(res.status).toBe(404);
+    expect(await errorCode(res)).toBe("profile_claim.sso_unavailable");
+    expect(checkAuthSurfaceRateLimit).not.toHaveBeenCalled();
+    expect(usableHandoverForToken).not.toHaveBeenCalled();
+  });
+
+  it("works on a single-sign-on-only instance", async () => {
+    singleSignOnOnly();
+    const res = await claimSso(post("/api/auth/claim/sso", SSO_BODY));
+    expect(res.status).toBe(200);
+  });
+
+  it("draws on the password claim's bucket", async () => {
+    await claimSso(post("/api/auth/claim/sso", SSO_BODY));
+    expect(checkAuthSurfaceRateLimit).toHaveBeenCalledWith(
+      expect.anything(),
+      "auth:claim",
+      5,
+      15 * 60 * 1000,
+    );
+  });
+
+  it("checks the link before the username probe", async () => {
+    vi.mocked(usableHandoverForToken).mockResolvedValue(null);
+    vi.mocked(prisma.user.findUnique).mockResolvedValue({ id: "x" } as never);
+    const res = await claimSso(post("/api/auth/claim/sso", SSO_BODY));
+    expect(res.status).toBe(404);
+    expect(await errorCode(res)).toBe("profile_claim.invalid");
+    expect(prisma.user.findUnique).not.toHaveBeenCalled();
+    expect(res.headers.get("set-cookie")).toBeNull();
+  });
+
+  it("answers 409 taken for a username in use, and sets no cookie", async () => {
+    vi.mocked(prisma.user.findUnique).mockResolvedValue({ id: "x" } as never);
+    const res = await claimSso(post("/api/auth/claim/sso", SSO_BODY));
+    expect(res.status).toBe(409);
+    expect(await errorCode(res)).toBe("profile_claim.taken");
+    expect(res.headers.get("set-cookie")).toBeNull();
+  });
+
+  it("refuses an unknown field and a managed- username (strict body)", async () => {
+    for (const body of [
+      { ...SSO_BODY, email: "x@example.test" },
+      { ...SSO_BODY, username: "managed-alex" },
+    ]) {
+      const res = await claimSso(post("/api/auth/claim/sso", body));
+      expect(res.status).toBe(422);
+    }
+    expect(usableHandoverForToken).not.toHaveBeenCalled();
+  });
+
+  it("seals the link's id and the username, never the token, into hl_claim", async () => {
+    const res = await claimSso(post("/api/auth/claim/sso", SSO_BODY));
+    expect(res.status).toBe(200);
+    expect((await res.json()).data).toEqual({
+      redirectTo: "/api/auth/oidc/login?intent=claim",
+    });
+    const cookie = res.headers.get("set-cookie") ?? "";
+    expect(cookie).toMatch(/^hl_claim=/);
+    expect(cookie).toMatch(/Path=\/api\/auth\/oidc/);
+    expect(cookie).toMatch(/HttpOnly/i);
+    expect(cookie).toMatch(/Secure/i);
+    expect(cookie).toMatch(/SameSite=lax/i);
+    expect(cookie).toMatch(/Max-Age=600/);
+    const sealed = decodeURIComponent(cookie.split(";")[0]!.slice(9));
+    const payload = JSON.parse(sealed.replace(/^sealed\(/, "").slice(0, -1));
+    expect(payload.h).toBe("h1");
+    expect(payload.u).toBe("alex");
+    expect(typeof payload.b).toBe("string");
+    expect(cookie).not.toContain(TOKEN);
+    expect(JSON.stringify(vi.mocked(auditLog).mock.calls)).not.toContain(TOKEN);
+    expect(auditLog).toHaveBeenCalledWith(
+      "managed_profile.claim_sso.started",
+      expect.objectContaining({ userId: "p1", details: { handoverId: "h1" } }),
+    );
+  });
+});
diff --git a/src/app/api/auth/claim/preview/route.ts b/src/app/api/auth/claim/preview/route.ts
index 865f7fdfb..b5cb0b924 100644
--- a/src/app/api/auth/claim/preview/route.ts
+++ b/src/app/api/auth/claim/preview/route.ts
@@ -4,6 +4,8 @@
  * access (v1.42, #959). No health data.
  *
  * Anonymous by design: the person opening the link has no credentials yet.
+ * Answered on a single-sign-on-only server too (v1.43): `methods` then names
+ * only `sso`, and the page offers the identity provider.
  * The one-time `hlp_` token travels in the BODY, never in this request's URL,
  * so it never reaches an access log or a wide event's `http.path`. Every
  * unusable link — malformed, unknown, expired, used, withdrawn, a profile no
@@ -15,7 +17,12 @@ import { apiHandler } from "@/lib/api-handler";
 import { apiSuccess, returnAllZodIssues, safeJson } from "@/lib/api-response";
 import { getSession } from "@/lib/auth/session";
 import { annotate } from "@/lib/logging/context";
-import { claimGate, claimInvalid } from "@/lib/managed-profiles/claim-gate";
+import {
+  claimGate,
+  claimInvalid,
+  handoverMethods,
+  ssoProviderName,
+} from "@/lib/managed-profiles/claim-gate";
 import { previewHandover } from "@/lib/managed-profiles/handover";
 import { claimPreviewSchema } from "@/lib/validations/managed-profile-handover";
 
@@ -46,5 +53,9 @@ export const POST = apiHandler(async (request: NextRequest) => {
     displayName: preview.displayName,
     expiresAt: preview.expiresAt.toISOString(),
     guardians: preview.guardians,
+    // v1.43 (#959) — which ways in this server offers, so the page shows the
+    // password form, the provider button, or both.
+    methods: handoverMethods(),
+    ssoProviderName: ssoProviderName(),
   });
 });
diff --git a/src/app/api/auth/claim/route.ts b/src/app/api/auth/claim/route.ts
index 82bba356d..9ca4e09c2 100644
--- a/src/app/api/auth/claim/route.ts
+++ b/src/app/api/auth/claim/route.ts
@@ -104,7 +104,7 @@ export const POST = apiHandler(async (request: NextRequest) => {
   let claimed;
   try {
     claimed = await claimManagedProfile({
-      rawToken: token,
+      link: { rawToken: token },
       username,
       email,
       passwordHash,
diff --git a/src/app/api/auth/claim/sso/route.ts b/src/app/api/auth/claim/sso/route.ts
index 01b591758..21fd4938b 100644
--- a/src/app/api/auth/claim/sso/route.ts
+++ b/src/app/api/auth/claim/sso/route.ts
@@ -1,29 +1,47 @@
 /**
  * `POST /api/auth/claim/sso` — start claiming a managed profile through
- * single sign-on (#959).
+ * single sign-on (v1.43, #959).
  *
- * Anonymous, like the password claim beside it. `{ token, username }`: the
- * link is checked and the username reserved for the round trip, a sealed
- * `hl_claim` cookie (10 minutes, `httpOnly`, `Secure` through
- * `shouldEmitSecureCookie()`) carries `{ handoverId, username, exp }`, and the
- * answer names where to go: `{ redirectTo: "/api/auth/oidc/login?intent=claim" }`.
- * The OIDC callback binds the identity provider's subject to the profile. The
- * token never rides a URL. Works on a single-sign-on-only server; 404
- * `profile_claim.sso_unavailable` when no identity provider is configured.
+ * Anonymous, like the password claim beside it, and ordered like it:
+ *
+ *   1. refusals that read no token (`claimGate`: no identity provider, a live
+ *      session, the per-address bucket the password claim also draws on);
+ *   2. the body, strictly parsed, and the link checked;
+ *   3. the username probe, so the person learns a name is taken here rather
+ *      than after the round trip to the provider.
+ *
+ * Nothing about the account changes here. The answer is a sealed `hl_claim`
+ * cookie (`claim-cookie.ts`) naming the link by its id and carrying the
+ * chosen username, and `{ redirectTo }` for the browser to navigate to. The
+ * OIDC callback binds the provider's subject to the profile, under the lock,
+ * with every check repeated. The token never rides a URL and never reaches the
+ * cookie.
  */
 import { NextRequest } from "next/server";
 
 import { apiHandler } from "@/lib/api-handler";
-import { returnAllZodIssues, safeJson } from "@/lib/api-response";
+import {
+  apiError,
+  apiSuccess,
+  returnAllZodIssues,
+  safeJson,
+} from "@/lib/api-response";
+import { auditLog } from "@/lib/auth/audit";
 import { getSession } from "@/lib/auth/session";
-import { notImplemented } from "@/lib/http/not-implemented";
-import { claimGate } from "@/lib/managed-profiles/claim-gate";
+import { prisma } from "@/lib/db";
+import { annotate } from "@/lib/logging/context";
+import {
+  CLAIM_SSO_REDIRECT,
+  setClaimCookie,
+} from "@/lib/managed-profiles/claim-cookie";
+import { claimGate, claimInvalid } from "@/lib/managed-profiles/claim-gate";
+import { usableHandoverForToken } from "@/lib/managed-profiles/handover";
 import { claimSsoSchema } from "@/lib/validations/claim-sso";
 
 export const POST = apiHandler(async (request: NextRequest) => {
   // Refuses a signed-in caller and rate-limits the address, as the password
   // claim does.
-  const gate = await claimGate(request, "claim", (await getSession()) !== null);
+  const gate = await claimGate(request, "sso", (await getSession()) !== null);
   if (gate.refusal) return gate.refusal;
 
   const { data: body, error: jsonError } = await safeJson(request, {
@@ -32,6 +50,43 @@ export const POST = apiHandler(async (request: NextRequest) => {
   if (jsonError) return jsonError;
   const parsed = claimSsoSchema.safeParse(body);
   if (!parsed.success) return returnAllZodIssues(parsed.error, 422);
+  const { token, username } = parsed.data;
 
-  return notImplemented("profile_claim.sso.start");
+  // The link first, so the username probe below is no oracle for anybody
+  // without a live link (the password claim's argument).
+  const link = await usableHandoverForToken(token);
+  if (!link) {
+    annotate({
+      action: { name: "profile_claim.sso.start" },
+      meta: { found: false },
+    });
+    return claimInvalid();
+  }
+
+  const existing = await prisma.user.findUnique({
+    where: { username },
+    select: { id: true },
+  });
+  if (existing) {
+    return apiError("Username already taken", 409, {
+      errorCode: "profile_claim.taken",
+    });
+  }
+
+  const response = apiSuccess({ redirectTo: CLAIM_SSO_REDIRECT });
+  setClaimCookie(response, { handoverId: link.handoverId, username });
+
+  // Filed under the record, with no actor: nobody is signed in yet. No token,
+  // no username — the username is not the person's until the claim lands.
+  await auditLog("managed_profile.claim_sso.started", {
+    userId: link.profileId,
+    actorUserId: null,
+    ipAddress: gate.ip,
+    details: { handoverId: link.handoverId },
+  });
+  annotate({
+    action: { name: "profile_claim.sso.start" },
+    meta: { found: true },
+  });
+  return response;
 });
diff --git a/src/app/api/auth/oidc/callback/route.ts b/src/app/api/auth/oidc/callback/route.ts
index 0c090f4a0..af57ea28a 100644
--- a/src/app/api/auth/oidc/callback/route.ts
+++ b/src/app/api/auth/oidc/callback/route.ts
@@ -38,6 +38,18 @@ import {
   mintNativeHandoff,
 } from "@/lib/auth/oidc-native-handoff";
 import { setPendingLinkCookie } from "@/lib/auth/oidc-pending-link";
+import {
+  CLAIM_COOKIE,
+  CLAIM_ERROR_PATH,
+  claimMatchesBinding,
+  clearClaimCookie,
+  readClaimCookie,
+} from "@/lib/managed-profiles/claim-cookie";
+import {
+  completeSsoClaim,
+  SSO_CLAIM_LANDING,
+} from "@/lib/managed-profiles/claim-sso";
+import { isHandoverUsable } from "@/lib/managed-profiles/handover";
 
 const LOGIN_ERROR_URL = "/auth/login";
 
@@ -102,6 +114,14 @@ interface StoredOidcState {
   native?: boolean;
   /** The app's S256 PKCE challenge, bound at login; verified at the exchange. */
   appCodeChallenge?: string;
+  /**
+   * v1.43 (#959) — set only when the login carried `intent=claim` and a valid
+   * `hl_claim` cookie. The callback then claims the managed profile the
+   * cookie names instead of signing in, and only when the cookie still
+   * carries this exact binding. Web only: never together with `native`.
+   */
+  intent?: "claim";
+  claimBinding?: string;
 }
 
 function isStoredOidcState(value: unknown): value is StoredOidcState {
@@ -122,6 +142,13 @@ function isStoredOidcState(value: unknown): value is StoredOidcState {
     if (v.native !== true) return false;
     if (typeof v.appCodeChallenge !== "string") return false;
   }
+  if (v.intent !== undefined) {
+    if (v.intent !== "claim") return false;
+    if (typeof v.claimBinding !== "string" || v.claimBinding.length === 0) {
+      return false;
+    }
+    if (v.native !== undefined) return false;
+  }
   return true;
 }
 
@@ -153,12 +180,27 @@ export const GET = apiHandler(async (req: NextRequest) => {
     }
   }
   const isNative = stored?.native === true;
+  const isClaim = stored?.intent === "claim";
 
   // Native-aware error redirect: the custom scheme for a decrypted native flow,
   // the web login page otherwise. Deletes the single-use state cookie either
   // way. An error redirect carries no code, ticket, or session, so routing it
   // to the scheme leaks nothing (spec §1).
+  // v1.43 (#959) — a refused claim returns to the claim page, never the
+  // sign-in page, and takes the claim cookie with it: the person starts again
+  // from the link, which is still theirs to use if the refusal left it open.
+  // Browser-only, like `errorRedirect`: a claim is never native.
+  const claimRedirect = (reason: string): NextResponse => {
+    const response = NextResponse.redirect(
+      oidcAppUrl(`${CLAIM_ERROR_PATH}?error=${reason}`),
+    );
+    deleteStateCookie(response);
+    clearClaimCookie(response);
+    return response;
+  };
+
   const failRedirect = (reason: string): NextResponse => {
+    if (isClaim) return claimRedirect(reason);
     if (isNative) {
       const response = NextResponse.redirect(
         buildNativeCallbackUrl({ error: reason }),
@@ -198,7 +240,9 @@ export const GET = apiHandler(async (req: NextRequest) => {
   // Broken round-trip / missing-or-unreadable state blob / CSRF mismatch all
   // resolve to the web `oidc_state` fallback: the flow is fundamentally broken
   // and there is nothing safe to hand the app (spec §1 web-fallback).
-  if (!code || !state) return errorRedirect("oidc_state");
+  if (!code || !state) {
+    return isClaim ? claimRedirect("oidc_state") : errorRedirect("oidc_state");
+  }
 
   if (!stored) {
     // Defence-in-depth idempotency for a duplicated callback. The single-use
@@ -240,7 +284,34 @@ export const GET = apiHandler(async (req: NextRequest) => {
     !timingSafeEqual(Buffer.from(state), Buffer.from(stored.state))
   ) {
     annotate({ meta: { reason: "csrf" } });
-    return errorRedirect("oidc_state");
+    return isClaim ? claimRedirect("oidc_state") : errorRedirect("oidc_state");
+  }
+
+  // v1.43 (#959) — a claim is never finished over a live session (the claim
+  // routes' rule: a Guardian finishing their own link would otherwise be
+  // signed out of their account and into the person's), and is admitted only
+  // with its own sealed cookie, still bound to this sign-in, for a link that
+  // is still usable. All of it before the code is redeemed, so a refused claim
+  // spends nothing at the provider.
+  const pendingClaim = isClaim
+    ? readClaimCookie(req.cookies.get(CLAIM_COOKIE)?.value)
+    : null;
+  if (isClaim) {
+    const liveSession = await validateSessionFromCookieValue(
+      req.cookies.get(SESSION_COOKIE_NAME)?.value,
+    );
+    if (liveSession) {
+      annotate({ meta: { reason: "claim_signed_in" } });
+      return failRedirect("claim_signed_in");
+    }
+    if (
+      !pendingClaim ||
+      !claimMatchesBinding(pendingClaim, stored.claimBinding as string) ||
+      !(await isHandoverUsable(pendingClaim.handoverId))
+    ) {
+      annotate({ meta: { reason: "claim_expired" } });
+      return failRedirect("claim_expired");
+    }
   }
 
   try {
@@ -274,6 +345,28 @@ export const GET = apiHandler(async (req: NextRequest) => {
       emailVerified = userinfo.emailVerified;
     }
 
+    // v1.43 (#959) — the claim. The provider has authenticated somebody; bind
+    // that subject to the profile the cookie names, or refuse. Never falls
+    // through to the sign-in below: a refused claim signs nobody in, and
+    // provisions and links nothing.
+    if (pendingClaim) {
+      const outcome = await completeSsoClaim({
+        handoverId: pendingClaim.handoverId,
+        username: pendingClaim.username,
+        issuer: metadata.issuer,
+        sub: identity.sub,
+        email,
+        emailVerified,
+        ipAddress: ip,
+        userAgent: req.headers.get("user-agent"),
+      });
+      if (!outcome.ok) return failRedirect(outcome.reason);
+      const response = NextResponse.redirect(oidcAppUrl(SSO_CLAIM_LANDING));
+      deleteStateCookie(response);
+      clearClaimCookie(response);
+      return response;
+    }
+
     // (1) Durable identity match — the (issuer, sub) pair stamped on a
     // previous login, link, or provision. Email is deliberately NOT
     // consulted here: after the stamp it is a display field, so an
diff --git a/src/app/api/auth/oidc/login/__tests__/route.test.ts b/src/app/api/auth/oidc/login/__tests__/route.test.ts
index 38c13a58f..1d9fc1584 100644
--- a/src/app/api/auth/oidc/login/__tests__/route.test.ts
+++ b/src/app/api/auth/oidc/login/__tests__/route.test.ts
@@ -214,3 +214,50 @@ describe("GET /api/auth/oidc/login", () => {
     });
   });
 });
+
+describe("GET /api/auth/oidc/login?intent=claim (v1.43, #959)", () => {
+  beforeEach(() => {
+    vi.mocked(getOidcConfig).mockReturnValue({
+      issuerUrl: "https://idp.example.com",
+      clientId: "client-1",
+      clientSecret: "secret-1",
+      scopes: "openid email profile",
+      buttonLabel: "SSO",
+    });
+  });
+
+  it("refuses a claim on the native leg with oidc_invalid_request", async () => {
+    const res = await GET(
+      makeRequest(
+        `/api/auth/oidc/login?intent=claim&client=native&code_challenge=${"a".repeat(43)}`,
+      ),
+    );
+    expect(res.headers.get("location")).toMatch(
+      /^healthlog:\/\/oidc-callback\?error=oidc_invalid_request$/,
+    );
+    expect(discoverOidcMetadata).not.toHaveBeenCalled();
+    expect(res.cookies.get("oidc_auth_state")).toBeUndefined();
+  });
+
+  it("sends a claim without its cookie back to the claim page, before the provider", async () => {
+    const res = await GET(makeRequest("/api/auth/oidc/login?intent=claim"));
+    expect(res.headers.get("location")).toBe(
+      "https://healthlog.example.com/auth/claim?error=claim_expired",
+    );
+    expect(discoverOidcMetadata).not.toHaveBeenCalled();
+    expect(res.cookies.get("oidc_auth_state")).toBeUndefined();
+  });
+
+  it("routes the claim's other failures to the claim page too", async () => {
+    vi.mocked(checkAuthSurfaceRateLimit).mockResolvedValue({
+      allowed: false,
+      remaining: 0,
+      reset: 0,
+      ip: "1.2.3.4",
+    } as never);
+    const res = await GET(makeRequest("/api/auth/oidc/login?intent=claim"));
+    expect(res.headers.get("location")).toBe(
+      "https://healthlog.example.com/auth/claim?error=oidc_rate_limited",
+    );
+  });
+});
diff --git a/src/app/api/auth/oidc/login/route.ts b/src/app/api/auth/oidc/login/route.ts
index 9e55d9c0a..dd0dc1cc8 100644
--- a/src/app/api/auth/oidc/login/route.ts
+++ b/src/app/api/auth/oidc/login/route.ts
@@ -21,6 +21,12 @@ import {
   OIDC_STATE_COOKIE_PATH,
   OIDC_STATE_TTL_MS,
 } from "@/lib/auth/oidc-cookie";
+import {
+  CLAIM_COOKIE,
+  CLAIM_ERROR_PATH,
+  readClaimCookie,
+} from "@/lib/managed-profiles/claim-cookie";
+import { isHandoverUsable } from "@/lib/managed-profiles/handover";
 
 /**
  * Redirects the browser to the configured OIDC provider's authorization
@@ -40,16 +46,34 @@ export const GET = apiHandler(async (req: NextRequest) => {
   // nothing — an error redirect carries no code, ticket, or session (spec §1).
   const isNative = req.nextUrl.searchParams.get("client") === "native";
   const appCodeChallenge = req.nextUrl.searchParams.get("code_challenge");
+  // v1.43 (#959) — `intent=claim`: the sign-in claims a managed profile. The
+  // link and the username ride the sealed `hl_claim` cookie set by
+  // `POST /api/auth/claim/sso`, never this URL; the intent only says to look
+  // for it. Web only.
+  const isClaim = req.nextUrl.searchParams.get("intent") === "claim";
 
   // Native-aware error redirect: the scheme for a native start, the web login
-  // page otherwise. Machine-readable `error=<reason>` in both.
+  // page otherwise, and the claim page for a claim. Machine-readable
+  // `error=<reason>` in all three.
   const loginError = (reason: string): NextResponse => {
     if (isNative) {
       return NextResponse.redirect(buildNativeCallbackUrl({ error: reason }));
     }
+    if (isClaim) {
+      return NextResponse.redirect(
+        oidcAppUrl(`${CLAIM_ERROR_PATH}?error=${reason}`),
+      );
+    }
     return NextResponse.redirect(oidcAppUrl(`/auth/login?error=${reason}`));
   };
 
+  // The app never claims a profile: the claim runs in a browser, and the new
+  // owner signs in to the app afterwards through the ordinary native leg.
+  if (isClaim && isNative) {
+    annotate({ meta: { reason: "claim_on_native" } });
+    return loginError("oidc_invalid_request");
+  }
+
   const config = getOidcConfig();
   if (!config) {
     return loginError("oidc_disabled");
@@ -90,6 +114,19 @@ export const GET = apiHandler(async (req: NextRequest) => {
     return loginError("oidc_invalid_request");
   }
 
+  // A claim needs its sealed cookie and a link that is still usable. Checked
+  // here, after the rate limit, so a dead link is told before the round trip
+  // to the provider; the callback checks both again.
+  let claimBinding: string | null = null;
+  if (isClaim) {
+    const claim = readClaimCookie(req.cookies.get(CLAIM_COOKIE)?.value);
+    if (!claim || !(await isHandoverUsable(claim.handoverId))) {
+      annotate({ meta: { reason: "claim_expired" } });
+      return loginError("claim_expired");
+    }
+    claimBinding = claim.binding;
+  }
+
   let metadata;
   try {
     metadata = await discoverOidcMetadata(config);
@@ -104,10 +141,12 @@ export const GET = apiHandler(async (req: NextRequest) => {
   const codeChallenge = s256Challenge(codeVerifier);
 
   // `next` is a post-login WEB path, meaningless to the app — pin it to "/" on
-  // the native branch (one less input to sanitize).
-  const safeNext = isNative
-    ? "/"
-    : sanitizeOidcNextPath(req.nextUrl.searchParams.get("next"), req.url);
+  // the native branch (one less input to sanitize). A claim lands on a fixed
+  // page the callback names, so its `next` is pinned too.
+  const safeNext =
+    isNative || isClaim
+      ? "/"
+      : sanitizeOidcNextPath(req.nextUrl.searchParams.get("next"), req.url);
 
   const redirectUri = getOidcRedirectUri();
   const authorizationUrl = buildAuthorizationUrl({
@@ -133,6 +172,12 @@ export const GET = apiHandler(async (req: NextRequest) => {
       ...(isNative
         ? { native: true as const, appCodeChallenge: appCodeChallenge! }
         : {}),
+      // The claim's binding, inside the same tamper-authenticated blob: the
+      // callback admits the claim only when the cookie it carries back holds
+      // this exact value.
+      ...(claimBinding !== null
+        ? { intent: "claim" as const, claimBinding }
+        : {}),
     }),
   );
   response.cookies.set(OIDC_STATE_COOKIE, cookiePayload, {
diff --git a/src/app/api/managed-profiles/[id]/handover/route.ts b/src/app/api/managed-profiles/[id]/handover/route.ts
index 3c702f200..1177988b2 100644
--- a/src/app/api/managed-profiles/[id]/handover/route.ts
+++ b/src/app/api/managed-profiles/[id]/handover/route.ts
@@ -30,8 +30,8 @@ import {
   safeJson,
 } from "@/lib/api-response";
 import { buildHandoverUrl } from "@/lib/auth/handover-token";
-import { isOidcOnly } from "@/lib/auth/oidc";
 import { annotate } from "@/lib/logging/context";
+import { handoverMethods } from "@/lib/managed-profiles/claim-gate";
 import {
   createHandover,
   HandoverError,
@@ -49,16 +49,15 @@ const notFound = () =>
   });
 
 /**
- * v1.42 refuses the handover on a single-sign-on-only instance: the claim
- * sets a password, and such an instance admits none. The SSO arm of the claim
- * is a separate piece of work.
+ * A link nobody could redeem is not minted. Since v1.43 the person can claim
+ * through the identity provider, so a single-sign-on-only server hands over
+ * too; this answers only when neither a password nor single sign-on is
+ * possible, which a working configuration never produces.
  */
-const oidcOnlyRefusal = () =>
-  apiError(
-    "Handing over a profile is not available while this server allows single sign-on only",
-    403,
-    { errorCode: "profile_claim.oidc_only_unsupported" },
-  );
+const noMethodRefusal = () =>
+  apiError("Handing over a profile is not available on this server", 403, {
+    errorCode: "profile_claim.oidc_only_unsupported",
+  });
 
 /** Same ceiling as creating, editing and inviting: ten an hour per caller. */
 const CREATE_LIMIT = 10;
@@ -79,8 +78,10 @@ export const GET = apiHandler(
       action: { name: "managed_profile.handover.read" },
       meta: { profile_id: id, open: status.open !== null },
     });
+    const methods = handoverMethods();
     return apiSuccess({
-      available: !isOidcOnly(),
+      available: methods.length > 0,
+      methods,
       open: status.open
         ? {
             id: status.open.id,
@@ -107,7 +108,7 @@ export const POST = apiHandler(
     if (!rateLimit.allowed) {
       return apiError("Too many handover links, try again later", 429);
     }
-    if (isOidcOnly()) return oidcOnlyRefusal();
+    if (handoverMethods().length === 0) return noMethodRefusal();
     const { id } = await params;
 
     const { data: body, error: jsonError } = await safeJson(request, {
diff --git a/src/app/auth/claim/page.tsx b/src/app/auth/claim/page.tsx
index 217302b9c..2a37b693f 100644
--- a/src/app/auth/claim/page.tsx
+++ b/src/app/auth/claim/page.tsx
@@ -6,7 +6,9 @@ import { ClaimProfile } from "@/components/auth/claim-profile";
 
 /**
  * v1.42 (#959) — `/auth/claim?token=hlp_…`, where the link a Guardian handed
- * over (`/claim/<token>`) lands after the edge redirect.
+ * over (`/claim/<token>`) lands after the edge redirect. Since v1.43 also
+ * `/auth/claim?error=<reason>`, where a refused single-sign-on claim returns;
+ * the reason is a fixed word, never a credential.
  *
  * A URL-credential surface by shape (`session-surface-guard.test.ts`, S2): the
  * page reads the one-time token off the query string and passes it to the
@@ -16,5 +18,10 @@ import { ClaimProfile } from "@/components/auth/claim-profile";
  */
 export default function ClaimProfilePage() {
   const searchParams = useSearchParams();
-  return <ClaimProfile token={searchParams.get("token")} />;
+  return (
+    <ClaimProfile
+      token={searchParams.get("token")}
+      error={searchParams.get("error")}
+    />
+  );
 }
diff --git a/src/components/auth/__tests__/claim-profile-invalid.test.tsx b/src/components/auth/__tests__/claim-profile-invalid.test.tsx
index b240065c0..5e0881043 100644
--- a/src/components/auth/__tests__/claim-profile-invalid.test.tsx
+++ b/src/components/auth/__tests__/claim-profile-invalid.test.tsx
@@ -19,6 +19,7 @@ vi.mock("@/hooks/use-auth", () => ({
 vi.mock("@/lib/queries/use-profile-claim", () => ({
   useProfileClaimPreview: () => ({ data: undefined, error: null }),
   useClaimProfile: () => ({ mutate: () => {}, isPending: false }),
+  useClaimProfileSso: () => ({ mutate: () => {}, isPending: false }),
 }));
 
 import { ClaimProfile } from "../claim-profile";
diff --git a/src/components/auth/__tests__/claim-profile-sso.test.tsx b/src/components/auth/__tests__/claim-profile-sso.test.tsx
new file mode 100644
index 000000000..75d1c8d99
--- /dev/null
+++ b/src/components/auth/__tests__/claim-profile-sso.test.tsx
@@ -0,0 +1,105 @@
+import { describe, it, expect, vi } from "vitest";
+import { renderToStaticMarkup } from "react-dom/server";
+import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
+
+import { I18nProvider } from "@/lib/i18n/context";
+import type { ProfileClaimPreview } from "@/lib/queries/use-profile-claim";
+
+/**
+ * v1.43 (#959) — the claim page offers the ways in the server names: the
+ * password form, the identity provider, or both. A refused single-sign-on
+ * claim comes back with `?error=` and no link, and says what happened.
+ */
+
+let previewData: ProfileClaimPreview | undefined;
+
+vi.mock("next/navigation", () => ({
+  useRouter: () => ({ replace: () => {}, refresh: () => {}, push: () => {} }),
+}));
+vi.mock("@/hooks/use-auth", () => ({
+  useAuth: () => ({ user: null }),
+  clearCachesForSessionEnd: () => {},
+}));
+vi.mock("@/lib/queries/use-profile-claim", () => ({
+  useProfileClaimPreview: () => ({ data: previewData, error: null }),
+  useClaimProfile: () => ({ mutate: () => {}, isPending: false }),
+  useClaimProfileSso: () => ({ mutate: () => {}, isPending: false }),
+}));
+
+import { ClaimProfile, claimSsoErrorKey } from "../claim-profile";
+
+const BASE: ProfileClaimPreview = {
+  displayName: "Robin",
+  expiresAt: "2030-01-01T00:00:00.000Z",
+  guardians: [],
+};
+
+function render(props: { token: string | null; error?: string | null }) {
+  return renderToStaticMarkup(
+    <QueryClientProvider client={new QueryClient()}>
+      <I18nProvider initialLocale="en">
+        <ClaimProfile {...props} />
+      </I18nProvider>
+    </QueryClientProvider>,
+  );
+}
+
+describe("ClaimProfile — ways in", () => {
+  it("offers only the provider on a single-sign-on-only server", () => {
+    previewData = { ...BASE, methods: ["sso"], ssoProviderName: "Example ID" };
+    const html = render({ token: "hlp_x" });
+    expect(html).toContain('data-slot="claim-sso-continue"');
+    expect(html).toContain("Continue with Example ID");
+    expect(html).not.toContain('id="claim-password"');
+    expect(html).not.toContain('id="claim-email"');
+    expect(html).not.toContain('data-slot="claim-submit"');
+    expect(html).toContain('id="claim-username"');
+  });
+
+  it("offers both when both are allowed", () => {
+    previewData = {
+      ...BASE,
+      methods: ["password", "sso"],
+      ssoProviderName: "Example ID",
+    };
+    const html = render({ token: "hlp_x" });
+    expect(html).toContain('data-slot="claim-sso-continue"');
+    expect(html).toContain('id="claim-password"');
+    expect(html).toContain('data-slot="claim-submit"');
+  });
+
+  it("offers only the password when an older server names no methods", () => {
+    previewData = { ...BASE };
+    const html = render({ token: "hlp_x" });
+    expect(html).not.toContain('data-slot="claim-sso-continue"');
+    expect(html).toContain('id="claim-password"');
+  });
+});
+
+describe("ClaimProfile — a refused single-sign-on claim", () => {
+  it("says what happened and offers a way on", () => {
+    previewData = undefined;
+    const html = render({ token: null, error: "claim_sso_subject_bound" });
+    expect(html).toContain('data-testid="claim-sso-error"');
+    expect(html).toContain("already belongs to another account");
+    expect(html).toContain('href="/auth/login"');
+  });
+
+  it("maps every reason the callback sends, and reads an unknown one as a failure", () => {
+    expect(claimSsoErrorKey("claim_expired")).toBe("auth.claim.invalidHint");
+    expect(claimSsoErrorKey("claim_sso_subject_bound")).toBe(
+      "auth.claim.errorSubjectBound",
+    );
+    expect(claimSsoErrorKey("claim_email_taken")).toBe(
+      "auth.claim.errorEmailTaken",
+    );
+    expect(claimSsoErrorKey("claim_username_taken")).toBe(
+      "auth.claim.errorUsernameTaken",
+    );
+    expect(claimSsoErrorKey("claim_signed_in")).toBe(
+      "auth.claim.errorSignedIn",
+    );
+    expect(claimSsoErrorKey("oidc_failed")).toBe("auth.claim.errorSso");
+    expect(claimSsoErrorKey("<script>")).toBe("auth.claim.errorSso");
+  });
+});
diff --git a/src/components/auth/claim-profile.tsx b/src/components/auth/claim-profile.tsx
index 1b9713839..8231d112c 100644
--- a/src/components/auth/claim-profile.tsx
+++ b/src/components/auth/claim-profile.tsx
@@ -4,9 +4,10 @@ import { useId, useState } from "react";
 import Link from "next/link";
 import { useRouter } from "next/navigation";
 import { useQueryClient } from "@tanstack/react-query";
-import { KeyRound, Loader2, LogOut } from "lucide-react";
+import { KeyRound, Loader2, LogIn, LogOut } from "lucide-react";
 
 import { accessLabel } from "@/components/settings/access/managed-profile-handover";
+import { useClientTransport } from "@/components/auth/insecure-transport-banner";
 import { Button } from "@/components/ui/button";
 import { Input } from "@/components/ui/input";
 import { Label } from "@/components/ui/label";
@@ -15,8 +16,10 @@ import { PasswordStrength } from "@/components/ui/password-strength";
 import { clearCachesForSessionEnd, useAuth } from "@/hooks/use-auth";
 import { ApiError, apiFetchRaw } from "@/lib/api/api-fetch";
 import { useFormatters, useTranslations } from "@/lib/i18n/context";
+import { loadDocument } from "@/lib/navigation/load-document";
 import {
   useClaimProfile,
+  useClaimProfileSso,
   useProfileClaimPreview,
 } from "@/lib/queries/use-profile-claim";
 import { queryKeys } from "@/lib/query-keys";
@@ -33,8 +36,22 @@ import { queryKeys } from "@/lib/query-keys";
  * record's name, who keeps which access for now, and until when the link
  * holds. No health data. The decision about each Guardian comes right after
  * the first sign-in, on the screen the claim lands on.
+ *
+ * v1.43 — the ways in follow the preview's `methods`: the password form, a
+ * "Continue with <provider>" button that claims through single sign-on, or
+ * both. The single-sign-on leg leaves the page for the identity provider and
+ * comes back to `/onboarding/handover`, or to this page with `?error=` when
+ * the callback refused; the link is not in that URL, so the error card asks
+ * the person to open the link again.
  */
-export function ClaimProfile({ token }: { token: string | null }) {
+export function ClaimProfile({
+  token,
+  error = null,
+}: {
+  token: string | null;
+  /** The single-sign-on callback's refusal, from `?error=`. */
+  error?: string | null;
+}) {
   const router = useRouter();
   const queryClient = useQueryClient();
   const { t } = useTranslations();
@@ -44,6 +61,8 @@ export function ClaimProfile({ token }: { token: string | null }) {
   const { user } = useAuth();
   const preview = useProfileClaimPreview(token, !user);
   const claim = useClaimProfile();
+  const claimSso = useClaimProfileSso();
+  const clientTransport = useClientTransport();
 
   const [username, setUsername] = useState("");
   const [email, setEmail] = useState("");
@@ -73,6 +92,25 @@ export function ClaimProfile({ token }: { token: string | null }) {
     }
   }
 
+  function continueWithSso() {
+    if (!token || claimSso.isPending || usernameReserved) return;
+    claimSso.mutate(
+      { token, username },
+      {
+        onSuccess: ({ redirectTo }) => {
+          // Only the path and query of the server's answer, so a response
+          // could never send the browser off this origin.
+          const next = new URL(redirectTo, window.location.origin);
+          if (clientTransport) {
+            next.searchParams.set("client_proto", clientTransport.protocol);
+            next.searchParams.set("client_host", clientTransport.host);
+          }
+          loadDocument(`${next.pathname}${next.search}`);
+        },
+      },
+    );
+  }
+
   function submit(event: React.FormEvent) {
     event.preventDefault();
     if (!token || claim.isPending || usernameReserved) return;
@@ -118,6 +156,35 @@ export function ClaimProfile({ token }: { token: string | null }) {
     );
   }
 
+  if (!token && error) {
+    const bound = error === "claim_sso_subject_bound";
+    return (
+      <ClaimCard testId="claim-sso-error">
+        <Header
+          title={
+            error === "claim_expired"
+              ? t("auth.claim.invalid")
+              : t("auth.claim.errorTitle")
+          }
+          description={t(claimSsoErrorKey(error))}
+        />
+        {/* The way on: the sign-in page (for a sign-in that already belongs
+            to an account, that account's). The link itself is not here. */}
+        <Button
+          asChild
+          variant="outline"
+          size="lg"
+          className="mt-8 min-h-11 w-full"
+          data-slot="claim-to-login"
+        >
+          <Link href="/auth/login">
+            {bound ? t("auth.claim.signInInstead") : t("auth.login")}
+          </Link>
+        </Button>
+      </ClaimCard>
+    );
+  }
+
   if (!token || previewStatus === 404 || previewStatus === 422) {
     return (
       <ClaimCard testId="claim-invalid">
@@ -192,12 +259,18 @@ export function ClaimProfile({ token }: { token: string | null }) {
   }
 
   const data = preview.data;
-  const errorKey = claim.isError ? claimErrorKey(claim.error) : null;
+  // An older server sends no `methods`: it only ever offered the password.
+  const methods = data.methods ?? ["password"];
+  const offersPassword = methods.includes("password");
+  const offersSso = methods.includes("sso");
+  const providerName = data.ssoProviderName ?? t("auth.claim.ssoFallbackName");
+  const failed = claimSso.isError ? claimSso : claim;
+  const errorKey = failed.isError ? claimErrorKey(failed.error) : null;
   const errorText =
-    claim.error instanceof ApiError &&
-    claim.error.status === 422 &&
-    claim.error.message
-      ? claim.error.message
+    failed.error instanceof ApiError &&
+    failed.error.status === 422 &&
+    failed.error.message
+      ? failed.error.message
       : errorKey
         ? t(errorKey)
         : null;
@@ -241,7 +314,19 @@ export function ClaimProfile({ token }: { token: string | null }) {
         </p>
       </section>
 
-      <form onSubmit={submit} className="mt-6 space-y-4" data-slot="claim-form">
+      <form
+        onSubmit={
+          offersPassword
+            ? submit
+            : (event) => {
+                // Enter in the username field on an SSO-only server.
+                event.preventDefault();
+                continueWithSso();
+              }
+        }
+        className="mt-6 space-y-4"
+        data-slot="claim-form"
+      >
         <div className="space-y-2">
           <Label htmlFor="claim-username">{t("auth.username")}</Label>
           <Input
@@ -270,36 +355,43 @@ export function ClaimProfile({ token }: { token: string | null }) {
               : t("auth.claim.usernameHint")}
           </p>
         </div>
-        <div className="space-y-2">
-          <Label htmlFor="claim-email">{t("auth.email")}</Label>
-          <Input
-            id="claim-email"
-            type="email"
-            value={email}
-            onChange={(e) => setEmail(e.target.value)}
-            required
-            autoComplete="email"
-            autoCapitalize="none"
-            spellCheck={false}
-            aria-describedby={`${errorId}-email`}
-          />
-          <p id={`${errorId}-email`} className="text-muted-foreground text-xs">
-            {t("auth.claim.emailHint")}
-          </p>
-        </div>
-        <div className="space-y-2">
-          <Label htmlFor="claim-password">{t("auth.password")}</Label>
-          <Input
-            id="claim-password"
-            type="password"
-            value={password}
-            onChange={(e) => setPassword(e.target.value)}
-            required
-            autoComplete="new-password"
-            placeholder={t("auth.passwordMinLength")}
-          />
-          <PasswordStrength password={password} />
-        </div>
+        {offersPassword && (
+          <>
+            <div className="space-y-2">
+              <Label htmlFor="claim-email">{t("auth.email")}</Label>
+              <Input
+                id="claim-email"
+                type="email"
+                value={email}
+                onChange={(e) => setEmail(e.target.value)}
+                required
+                autoComplete="email"
+                autoCapitalize="none"
+                spellCheck={false}
+                aria-describedby={`${errorId}-email`}
+              />
+              <p
+                id={`${errorId}-email`}
+                className="text-muted-foreground text-xs"
+              >
+                {t("auth.claim.emailHint")}
+              </p>
+            </div>
+            <div className="space-y-2">
+              <Label htmlFor="claim-password">{t("auth.password")}</Label>
+              <Input
+                id="claim-password"
+                type="password"
+                value={password}
+                onChange={(e) => setPassword(e.target.value)}
+                required
+                autoComplete="new-password"
+                placeholder={t("auth.passwordMinLength")}
+              />
+              <PasswordStrength password={password} />
+            </div>
+          </>
+        )}
 
         <p className="text-sm">{t("auth.claim.consentNote")}</p>
         <p className="text-muted-foreground text-xs">
@@ -320,22 +412,63 @@ export function ClaimProfile({ token }: { token: string | null }) {
           </div>
         )}
 
-        <Button
-          type="submit"
-          size="lg"
-          className="min-h-11 w-full"
-          disabled={claim.isPending || usernameReserved}
-          data-slot="claim-submit"
-        >
-          {claim.isPending ? (
-            <Loader2 className="size-4 animate-spin motion-reduce:animate-none" />
-          ) : (
-            <KeyRound className="size-4" />
-          )}
-          {claim.isPending
-            ? t("auth.claim.submitting")
-            : t("auth.claim.submit")}
-        </Button>
+        {offersPassword && (
+          <Button
+            type="submit"
+            size="lg"
+            className="min-h-11 w-full"
+            disabled={claim.isPending || usernameReserved}
+            data-slot="claim-submit"
+          >
+            {claim.isPending ? (
+              <Loader2 className="size-4 animate-spin motion-reduce:animate-none" />
+            ) : (
+              <KeyRound className="size-4" />
+            )}
+            {claim.isPending
+              ? t("auth.claim.submitting")
+              : t("auth.claim.submit")}
+          </Button>
+        )}
+
+        {offersPassword && offersSso && (
+          <div
+            className="text-muted-foreground flex items-center gap-3 text-xs"
+            aria-hidden="true"
+          >
+            <span className="bg-border h-px flex-1" />
+            {t("auth.claim.ssoDivider")}
+            <span className="bg-border h-px flex-1" />
+          </div>
+        )}
+
+        {offersSso && (
+          <div className="space-y-2" data-slot="claim-sso">
+            <Button
+              type="button"
+              size="lg"
+              variant={offersPassword ? "outline" : "default"}
+              className="min-h-11 w-full"
+              disabled={
+                claimSso.isPending || usernameReserved || username.length < 3
+              }
+              onClick={continueWithSso}
+              data-slot="claim-sso-continue"
+            >
+              {claimSso.isPending ? (
+                <Loader2 className="size-4 animate-spin motion-reduce:animate-none" />
+              ) : (
+                <LogIn className="size-4" />
+              )}
+              {claimSso.isPending
+                ? t("auth.claim.ssoStarting")
+                : t("auth.claim.ssoContinue", { provider: providerName })}
+            </Button>
+            <p className="text-muted-foreground text-xs">
+              {t("auth.claim.ssoHint", { provider: providerName })}
+            </p>
+          </div>
+        )}
       </form>
     </ClaimCard>
   );
@@ -378,6 +511,28 @@ function Header({
   );
 }
 
+/**
+ * v1.43 — the message for the single-sign-on callback's refusal, from the
+ * claim page's `?error=`. Exported and pure so it can be pinned. A reason this
+ * build does not know reads as the generic failure.
+ */
+export function claimSsoErrorKey(reason: string): string {
+  switch (reason) {
+    case "claim_expired":
+      return "auth.claim.invalidHint";
+    case "claim_sso_subject_bound":
+      return "auth.claim.errorSubjectBound";
+    case "claim_email_taken":
+      return "auth.claim.errorEmailTaken";
+    case "claim_username_taken":
+      return "auth.claim.errorUsernameTaken";
+    case "claim_signed_in":
+      return "auth.claim.errorSignedIn";
+    default:
+      return "auth.claim.errorSso";
+  }
+}
+
 /** The message for a refused claim. Exported and pure so it can be pinned. */
 export function claimErrorKey(err: unknown): string {
   if (!(err instanceof ApiError)) return "auth.claim.errorOffline";
diff --git a/src/components/settings/access/managed-profile-handover.tsx b/src/components/settings/access/managed-profile-handover.tsx
index c5a79fcce..e3c3e45b3 100644
--- a/src/components/settings/access/managed-profile-handover.tsx
+++ b/src/components/settings/access/managed-profile-handover.tsx
@@ -110,6 +110,18 @@ export function ManagedProfileHandover({
           name: profileName,
         })}
       </p>
+      {/* v1.43 — how the person will get in, when it is not only a password
+          they set themselves (the description already implies that one). */}
+      {status.data.available && status.data.methods?.includes("sso") ? (
+        <p className="text-sm" data-slot="managed-profile-handover-methods">
+          {t(
+            status.data.methods.includes("password")
+              ? "recordSharing.managed.handover.methodBoth"
+              : "recordSharing.managed.handover.methodSso",
+            { name: profileName },
+          )}
+        </p>
+      ) : null}
 
       {!status.data.available ? (
         <>
diff --git a/src/lib/logging/__tests__/redact.test.ts b/src/lib/logging/__tests__/redact.test.ts
index 911136e31..1f9a9db98 100644
--- a/src/lib/logging/__tests__/redact.test.ts
+++ b/src/lib/logging/__tests__/redact.test.ts
@@ -1,3 +1,4 @@
+import { redactSensitiveFields } from "@/lib/observability/redact-payload";
 import { describe, expect, it } from "vitest";
 import { redactSecrets, redactOptional, PATH_SECRET_PATHS } from "../redact";
 
@@ -249,6 +250,25 @@ describe("redactSecrets", () => {
         "/api/auth/claim/preview",
       );
       expect(redactSecrets("/api/auth/claim")).toBe("/api/auth/claim");
+      // v1.43 (#959) — the single-sign-on start and its landing carry no
+      // credential in the URL, and stay readable.
+      expect(redactSecrets("/api/auth/claim/sso")).toBe("/api/auth/claim/sso");
+      expect(redactSecrets("/api/auth/oidc/login?intent=claim")).toBe(
+        "/api/auth/oidc/login?intent=claim",
+      );
+      expect(redactSecrets("/auth/claim?error=claim_expired")).toBe(
+        "/auth/claim?error=claim_expired",
+      );
+    });
+
+    it("redacts the handover token in a single-sign-on claim body", () => {
+      const token = `hlp_${"ef".repeat(32)}`;
+      const excerpt = JSON.stringify(
+        redactSensitiveFields({ token, username: "robin" }),
+      );
+      expect(excerpt).not.toContain(token);
+      expect(excerpt).toContain("robin");
+      expect(redactSecrets(JSON.stringify({ token }))).not.toContain(token);
     });
 
     it("registers the clinician share-view prefix in PATH_SECRET_PATHS", () => {
diff --git a/src/lib/managed-profiles/claim-cookie.ts b/src/lib/managed-profiles/claim-cookie.ts
new file mode 100644
index 000000000..f99e05b55
--- /dev/null
+++ b/src/lib/managed-profiles/claim-cookie.ts
@@ -0,0 +1,111 @@
+/**
+ * v1.43 (#959) — the sealed cookie that carries a single-sign-on claim through
+ * the round trip to the identity provider.
+ *
+ * `POST /api/auth/claim/sso` checks the handover token and the chosen username
+ * and seals `{ handoverId, username, binding, exp }` into `hl_claim`. The
+ * token itself never leaves that request: the cookie names the link by its
+ * id, and it can only have been minted by a request that held the token.
+ *
+ *   - AES-256-GCM with the at-rest key (`encrypt`), so it can be neither read
+ *     nor forged, and it carries its own expiry on top of `Max-Age`.
+ *   - `HttpOnly`, `SameSite=Lax` (the browser returns from the provider on a
+ *     cross-site top-level GET and must carry it), `Secure` through
+ *     `shouldEmitSecureCookie()`.
+ *   - Scoped to `/api/auth/oidc`, the only two routes that read it.
+ *   - `binding` is a fresh random value per start. The login copies it into
+ *     the encrypted OIDC state, and the callback admits the claim only when
+ *     the cookie and the state carry the same one, so a claim cookie from a
+ *     different start (another tab, an older attempt) cannot be paired with
+ *     this sign-in.
+ */
+import { randomBytes, timingSafeEqual } from "node:crypto";
+import type { NextResponse } from "next/server";
+
+import { decrypt, encrypt } from "@/lib/crypto";
+import { shouldEmitSecureCookie } from "@/lib/auth/secure-cookie";
+
+export const CLAIM_COOKIE = "hl_claim";
+export const CLAIM_COOKIE_PATH = "/api/auth/oidc";
+export const CLAIM_COOKIE_TTL_MS = 10 * 60 * 1000;
+
+/**
+ * Where `POST /api/auth/claim/sso` sends the browser next. A fixed path:
+ * nothing caller-supplied ever reaches a redirect on this flow.
+ */
+export const CLAIM_SSO_REDIRECT = "/api/auth/oidc/login?intent=claim";
+
+/** Where every refusal on the single-sign-on claim lands, with `?error=`. */
+export const CLAIM_ERROR_PATH = "/auth/claim";
+
+export interface PendingSsoClaim {
+  handoverId: string;
+  username: string;
+  binding: string;
+}
+
+/** Attach a freshly sealed claim to a response. Returns what was sealed. */
+export function setClaimCookie(
+  response: NextResponse,
+  claim: { handoverId: string; username: string },
+  now: number = Date.now(),
+): PendingSsoClaim {
+  const binding = randomBytes(32).toString("base64url");
+  const sealed = encrypt(
+    JSON.stringify({
+      h: claim.handoverId,
+      u: claim.username,
+      b: binding,
+      e: now + CLAIM_COOKIE_TTL_MS,
+    }),
+  );
+  response.cookies.set(CLAIM_COOKIE, sealed, {
+    httpOnly: true,
+    secure: shouldEmitSecureCookie(),
+    sameSite: "lax",
+    maxAge: Math.floor(CLAIM_COOKIE_TTL_MS / 1000),
+    path: CLAIM_COOKIE_PATH,
+  });
+  return { ...claim, binding };
+}
+
+/** The claim a cookie value carries, or null when absent, forged or expired. */
+export function readClaimCookie(
+  raw: string | undefined,
+  now: number = Date.now(),
+): PendingSsoClaim | null {
+  if (!raw) return null;
+  try {
+    const parsed = JSON.parse(decrypt(raw)) as Record<string, unknown>;
+    if (
+      typeof parsed.h !== "string" ||
+      parsed.h.length === 0 ||
+      typeof parsed.u !== "string" ||
+      parsed.u.length === 0 ||
+      typeof parsed.b !== "string" ||
+      parsed.b.length === 0 ||
+      typeof parsed.e !== "number" ||
+      parsed.e <= now
+    ) {
+      return null;
+    }
+    return { handoverId: parsed.h, username: parsed.u, binding: parsed.b };
+  } catch {
+    return null;
+  }
+}
+
+/** Whether a claim belongs to the sign-in whose state carries `binding`. */
+export function claimMatchesBinding(
+  claim: PendingSsoClaim,
+  binding: string,
+): boolean {
+  const a = Buffer.from(claim.binding);
+  const b = Buffer.from(binding);
+  return a.length === b.length && timingSafeEqual(a, b);
+}
+
+/** Expire the claim cookie on a response; the path must repeat the set's. */
+export function clearClaimCookie(response: NextResponse): void {
+  response.cookies.delete({ name: CLAIM_COOKIE, path: CLAIM_COOKIE_PATH });
+}
diff --git a/src/lib/managed-profiles/claim-gate.ts b/src/lib/managed-profiles/claim-gate.ts
index 3c1a4ec47..2173fd6e0 100644
--- a/src/lib/managed-profiles/claim-gate.ts
+++ b/src/lib/managed-profiles/claim-gate.ts
@@ -1,11 +1,14 @@
 /**
- * v1.42 (#959) — the refusals both anonymous claim routes give before they
- * look at a token, in one place so the preview and the claim cannot disagree.
+ * v1.42 (#959) — the refusals the anonymous claim routes give before they look
+ * at a token, in one place so the preview and the claims cannot disagree.
  *
  * Order matters and is the register route's order:
  *
- *   1. A single-sign-on-only instance admits no password, and the claim sets
- *      one, so the handover is refused outright in v1.42.
+ *   1. What this server cannot do at all. The password claim sets a password,
+ *      so a single-sign-on-only instance refuses it outright; the
+ *      single-sign-on claim (v1.43) needs an identity provider, and answers
+ *      404 `profile_claim.sso_unavailable` without one. The preview is
+ *      refused by neither: it is what tells the page which way is open.
  *   2. A signed-in caller is refused with 409. Claiming creates a session for
  *      the new owner, and a Guardian testing their own link would otherwise be
  *      signed out of their account and into the person's. Refused before the
@@ -13,12 +16,14 @@
  *      would lock out the person the link is for, who may share the address.
  *   3. The per-address rate limit, the anonymous auth-surface pattern: a
  *      misconfigured proxy trust chain collapses every caller into one tight
- *      bucket rather than one free-for-all.
+ *      bucket rather than one free-for-all. Both claims share one bucket, so
+ *      switching between them buys no extra attempts.
  */
 import { NextResponse } from "next/server";
 
 import { apiError } from "@/lib/api-response";
-import { isOidcOnly } from "@/lib/auth/oidc";
+import { getOidcConfig, isOidcConfigured, isOidcOnly } from "@/lib/auth/oidc";
+import type { HandoverMethod } from "@/lib/validations/claim-sso";
 import { annotate } from "@/lib/logging/context";
 import { checkAuthSurfaceRateLimit, rateLimitHeaders } from "@/lib/rate-limit";
 
@@ -29,9 +34,28 @@ export function claimInvalid() {
   });
 }
 
+/**
+ * v1.43 (#959) — how a handover link can be redeemed on this server: with a
+ * password unless the server allows single sign-on only, and through the
+ * identity provider whenever one is configured. Never empty in practice
+ * (`OIDC_ONLY` only takes effect with a configured provider), but the Guardian
+ * side refuses on an empty list rather than assuming it.
+ */
+export function handoverMethods(): HandoverMethod[] {
+  const methods: HandoverMethod[] = [];
+  if (!isOidcOnly()) methods.push("password");
+  if (isOidcConfigured()) methods.push("sso");
+  return methods;
+}
+
+/** The provider's name for the "Continue with …" button, or null. */
+export function ssoProviderName(): string | null {
+  return getOidcConfig()?.buttonLabel ?? null;
+}
+
 export async function claimGate(
   request: Request,
-  surface: "preview" | "claim",
+  surface: "preview" | "claim" | "sso",
   /**
    * Whether the request carries a live session. Resolved by the ROUTE with
    * `getSession()` and handed in, rather than resolved here: a session read
@@ -41,15 +65,24 @@ export async function claimGate(
    */
   signedIn: boolean,
 ): Promise<{ refusal: Response } | { refusal: null; ip: string | null }> {
-  if (isOidcOnly()) {
+  if (surface === "claim" && isOidcOnly()) {
     return {
       refusal: apiError(
-        "Taking over a profile is not available while this server allows single sign-on only",
+        "This server allows single sign-on only; take the profile over through the identity provider",
         403,
         { errorCode: "profile_claim.oidc_only_unsupported" },
       ),
     };
   }
+  if (surface === "sso" && !isOidcConfigured()) {
+    return {
+      refusal: apiError(
+        "Single sign-on is not configured on this server",
+        404,
+        { errorCode: "profile_claim.sso_unavailable" },
+      ),
+    };
+  }
 
   if (signedIn) {
     annotate({
diff --git a/src/lib/managed-profiles/claim-sso.ts b/src/lib/managed-profiles/claim-sso.ts
new file mode 100644
index 000000000..6fbf8c843
--- /dev/null
+++ b/src/lib/managed-profiles/claim-sso.ts
@@ -0,0 +1,178 @@
+/**
+ * v1.43 (#959) — the callback's half of claiming a managed profile through
+ * single sign-on: the identity provider has authenticated somebody, the
+ * sealed claim cookie names the link and the chosen username, and this binds
+ * the one to the other.
+ *
+ * The refusals, in order, each one before anything about any account changes:
+ *
+ *   1. `claim_expired` — the link is no longer usable (used, withdrawn,
+ *      replaced, expired, its creator gone, the profile no longer managed).
+ *   2. `claim_sso_subject_bound` — the provider's `(issuer, sub)` already
+ *      signs in to an account here. One subject, one account: binding it a
+ *      second time would make the sign-in ambiguous, and re-pointing it would
+ *      hand the existing account's sign-in to the claimed profile.
+ *   3. `claim_email_taken` — the provider vouches (`email_verified: true`) for
+ *      an address another account holds. An unverified address is not used at
+ *      all: the account is created without one rather than with a claim
+ *      nobody checked.
+ *   4. `claim_username_taken` — the username chosen at the start was taken in
+ *      the ten minutes since.
+ *
+ * Then `claimManagedProfile` — the password claim's own transaction, under
+ * the managed-profile lock, with every link check repeated — sets the
+ * username, the address, no password and the subject; applies each Guardian's
+ * proposed access; resets disclaimer, onboarding and AI consent. A race lost
+ * at the unique indexes is re-read and answered as the refusal it turned out
+ * to be. The session is minted only after that commit.
+ */
+import { auditLog } from "@/lib/auth/audit";
+import { recordSignInDevice } from "@/lib/auth/login-alert";
+import { createSession } from "@/lib/auth/session";
+import { prisma } from "@/lib/db";
+import { annotate } from "@/lib/logging/context";
+import {
+  claimManagedProfile,
+  HandoverError,
+  isHandoverUsable,
+} from "@/lib/managed-profiles/handover";
+import { notifyGuardiansOfHandover } from "@/lib/managed-profiles/handover-notify";
+
+export type SsoClaimRefusal =
+  | "claim_expired"
+  | "claim_sso_subject_bound"
+  | "claim_email_taken"
+  | "claim_username_taken";
+
+export type SsoClaimOutcome =
+  { ok: true; profileId: string } | { ok: false; reason: SsoClaimRefusal };
+
+/** Where the new owner lands: the decision about each former Guardian. */
+export const SSO_CLAIM_LANDING = "/onboarding/handover";
+
+interface SsoClaimInput {
+  handoverId: string;
+  username: string;
+  issuer: string;
+  sub: string;
+  email: string | null;
+  emailVerified: boolean | undefined;
+  ipAddress: string;
+  userAgent: string | null;
+}
+
+/** Which of the three unique values is held by an account already. */
+async function collision(input: {
+  issuer: string;
+  sub: string;
+  email: string | null;
+  username: string;
+}): Promise<SsoClaimRefusal | null> {
+  const bound = await prisma.user.findFirst({
+    where: { oidcIssuer: input.issuer, oidcSub: input.sub },
+    select: { id: true },
+  });
+  if (bound) {
+    // Under the account that holds the subject, so its owner's history shows
+    // that somebody tried to bind their sign-in to a second record.
+    await auditLog("auth.oidc.claim_conflict", {
+      userId: bound.id,
+      actorUserId: null,
+    });
+    return "claim_sso_subject_bound";
+  }
+  if (input.email) {
+    const byEmail = await prisma.user.findFirst({
+      where: { email: { equals: input.email, mode: "insensitive" } },
+      select: { id: true },
+    });
+    if (byEmail) return "claim_email_taken";
+  }
+  const byName = await prisma.user.findUnique({
+    where: { username: input.username },
+    select: { id: true },
+  });
+  return byName ? "claim_username_taken" : null;
+}
+
+export async function completeSsoClaim(
+  input: SsoClaimInput,
+): Promise<SsoClaimOutcome> {
+  const refuse = (reason: SsoClaimRefusal): SsoClaimOutcome => {
+    annotate({
+      action: { name: "profile_claim.sso.refused" },
+      meta: { reason },
+    });
+    return { ok: false, reason };
+  };
+
+  if (!(await isHandoverUsable(input.handoverId))) {
+    return refuse("claim_expired");
+  }
+
+  const email =
+    input.email && input.emailVerified === true
+      ? input.email.toLowerCase()
+      : null;
+  const identity = {
+    issuer: input.issuer,
+    sub: input.sub,
+    email,
+    username: input.username,
+  };
+
+  const early = await collision(identity);
+  if (early) return refuse(early);
+
+  let claimed;
+  try {
+    claimed = await claimManagedProfile({
+      link: { handoverId: input.handoverId },
+      username: input.username,
+      email,
+      passwordHash: null,
+      oidc: { issuer: input.issuer, sub: input.sub },
+      ipAddress: input.ipAddress,
+    });
+  } catch (error) {
+    if (error instanceof HandoverError) {
+      if (error.code === "taken") {
+        // Lost a race at a unique index: say which one.
+        return refuse((await collision(identity)) ?? "claim_username_taken");
+      }
+      return refuse("claim_expired");
+    }
+    throw error;
+  }
+
+  // The new owner starts with onboarding owed, as after the password claim.
+  // The fifth argument stays null: single sign-on is a delegated factor and
+  // must never satisfy a step-up (the OIDC login's rule).
+  await createSession(
+    claimed.profileId,
+    true,
+    input.ipAddress,
+    input.userAgent,
+    null,
+  );
+  void recordSignInDevice({
+    userId: claimed.profileId,
+    ip: input.ipAddress,
+    userAgent: input.userAgent,
+    alertOnNew: false,
+  });
+  await auditLog("auth.claim", {
+    userId: claimed.profileId,
+    actorUserId: null,
+    ipAddress: input.ipAddress,
+    details: { method: "sso" },
+  });
+
+  notifyGuardiansOfHandover("claimed", claimed.displayName, claimed.guardians);
+
+  annotate({
+    action: { name: "profile_claim.complete" },
+    meta: { guardians: claimed.guardians.length, method: "sso" },
+  });
+  return { ok: true, profileId: claimed.profileId };
+}
diff --git a/src/lib/managed-profiles/handover.ts b/src/lib/managed-profiles/handover.ts
index 431bd30d8..b09ce6596 100644
--- a/src/lib/managed-profiles/handover.ts
+++ b/src/lib/managed-profiles/handover.ts
@@ -444,17 +444,19 @@ export interface HandoverPreview {
 }
 
 /**
- * What a link would hand over, or null for every kind of unusable link.
- *
- * Deliberately minimal: the profile's name, the expiry, and who keeps which
- * access. No health data, no date of birth, no usernames and no grant ids —
- * the person holding the link has not proved anything yet beyond holding it.
+ * The open link behind a stored row, or null when it can no longer be
+ * claimed: used, withdrawn, expired, a state this code cannot read, a profile
+ * no longer managed, or a creator who lost access. The one definition of
+ * "usable" the preview, the single-sign-on start and the callback share.
  */
-export async function previewHandover(
-  rawToken: string,
-  now: Date = new Date(),
-): Promise<HandoverPreview | null> {
-  const row = await findHandoverByToken(prisma, rawToken);
+async function usableHandover(
+  row: Awaited<ReturnType<typeof findHandoverByToken>>,
+  now: Date,
+): Promise<{
+  row: NonNullable<Awaited<ReturnType<typeof findHandoverByToken>>>;
+  state: HandoverState;
+  displayName: string | null;
+} | null> {
   if (!row || !isOpen(row, now)) return null;
   const state = parseHandoverState(row.proposalsJson);
   if (!state) return null;
@@ -467,6 +469,26 @@ export async function previewHandover(
   if (!(await isActiveGuardian(prisma, row.profileId, row.createdById, now))) {
     return null;
   }
+  return { row, state, displayName: profile.displayName };
+}
+
+/**
+ * What a link would hand over, or null for every kind of unusable link.
+ *
+ * Deliberately minimal: the profile's name, the expiry, and who keeps which
+ * access. No health data, no date of birth, no usernames and no grant ids —
+ * the person holding the link has not proved anything yet beyond holding it.
+ */
+export async function previewHandover(
+  rawToken: string,
+  now: Date = new Date(),
+): Promise<HandoverPreview | null> {
+  const usable = await usableHandover(
+    await findHandoverByToken(prisma, rawToken),
+    now,
+  );
+  if (!usable) return null;
+  const { row, state } = usable;
 
   const guardians = await prisma.accountGrant.findMany({
     where: { grantorId: row.profileId, ...activeGuardianWhere(now) },
@@ -477,7 +499,7 @@ export async function previewHandover(
     orderBy: { createdAt: "asc" },
   });
   return {
-    displayName: profile.displayName,
+    displayName: usable.displayName,
     expiresAt: row.expiresAt,
     guardians: guardians.map((g) => ({
       displayName: g.grantee.displayName?.trim() || null,
@@ -486,6 +508,39 @@ export async function previewHandover(
   };
 }
 
+/**
+ * v1.43 (#959) — the usable link behind a raw token, or null. The
+ * single-sign-on start seals its id, never the token, into the claim cookie.
+ */
+export async function usableHandoverForToken(
+  rawToken: string,
+  now: Date = new Date(),
+): Promise<{ handoverId: string; profileId: string } | null> {
+  const usable = await usableHandover(
+    await findHandoverByToken(prisma, rawToken),
+    now,
+  );
+  return usable
+    ? { handoverId: usable.row.id, profileId: usable.row.profileId }
+    : null;
+}
+
+/**
+ * v1.43 (#959) — whether the link with this id can still be claimed. The
+ * single-sign-on legs re-ask on every step, so a link withdrawn or replaced
+ * while the person is at the identity provider is refused before any account
+ * changes. The claim re-checks under the lock; this decides nothing alone.
+ */
+export async function isHandoverUsable(
+  handoverId: string,
+  now: Date = new Date(),
+): Promise<boolean> {
+  const row = await prisma.managedProfileHandover.findUnique({
+    where: { id: handoverId },
+  });
+  return (await usableHandover(row, now)) !== null;
+}
+
 export interface ClaimedProfile {
   profileId: string;
   username: string;
@@ -502,15 +557,33 @@ export interface ClaimedProfile {
  * strength: none of that work belongs inside the lock.
  */
 export async function claimManagedProfile(input: {
-  rawToken: string;
+  /**
+   * The link: the raw token from the password form, or (v1.43) the id the
+   * single-sign-on start sealed into the claim cookie after checking the
+   * token itself.
+   */
+  link: { rawToken: string } | { handoverId: string };
   username: string;
-  email: string;
-  passwordHash: string;
+  /** Null on a single-sign-on claim whose provider vouched for no address. */
+  email: string | null;
+  /** Null on a single-sign-on claim: the account signs in at the provider. */
+  passwordHash: string | null;
+  /**
+   * v1.43 (#959) — the identity provider's subject, bound to the profile in
+   * the same transaction. The `(issuer, sub)` unique index refuses a subject
+   * that another account holds, as `taken`.
+   */
+  oidc?: { issuer: string; sub: string };
   ipAddress?: string | null;
   now?: Date;
 }): Promise<ClaimedProfile> {
   const now = input.now ?? new Date();
-  const found = await findHandoverByToken(prisma, input.rawToken);
+  const found =
+    "rawToken" in input.link
+      ? await findHandoverByToken(prisma, input.link.rawToken)
+      : await prisma.managedProfileHandover.findUnique({
+          where: { id: input.link.handoverId },
+        });
   if (!found) throw new HandoverError("invalid");
 
   try {
@@ -551,6 +624,9 @@ export async function claimManagedProfile(input: {
             username: input.username,
             email: input.email,
             passwordHash: input.passwordHash,
+            ...(input.oidc
+              ? { oidcIssuer: input.oidc.issuer, oidcSub: input.oidc.sub }
+              : {}),
             disclaimerAcknowledgedAt: null,
             disclaimerAcknowledgedVersion: null,
             onboardingCompletedAt: null,
@@ -636,6 +712,7 @@ export async function claimManagedProfile(input: {
             })),
             withdrawnInvitations,
             consentsWithdrawn: consent.revoked.length,
+            method: input.oidc ? "sso" : "password",
           },
           client: tx,
         });
diff --git a/src/lib/openapi/error-codes.ts b/src/lib/openapi/error-codes.ts
index fe46b8534..6330171da 100644
--- a/src/lib/openapi/error-codes.ts
+++ b/src/lib/openapi/error-codes.ts
@@ -355,6 +355,7 @@ export const ERROR_CODE_CATALOGUE: Readonly<Record<string, readonly string[]>> =
     profile_claim: [
       "profile_claim.invalid",
       "profile_claim.oidc_only_unsupported",
+      "profile_claim.sso_unavailable",
       "profile_claim.taken",
     ],
     record_write: ["record_write.rate_limited"],
diff --git a/src/lib/openapi/routes/account-sharing.ts b/src/lib/openapi/routes/account-sharing.ts
index 8f0d1ff35..eeea2cb37 100644
--- a/src/lib/openapi/routes/account-sharing.ts
+++ b/src/lib/openapi/routes/account-sharing.ts
@@ -736,7 +736,7 @@ export const accountSharingPaths: NonNullable<ZodOpenApiObject["paths"]> = {
         },
         "403": {
           description:
-            "The instance allows single sign-on only (`meta.errorCode: profile_claim.oidc_only_unsupported`).",
+            "Neither a password nor single sign-on could redeem a link on this instance (`meta.errorCode: profile_claim.oidc_only_unsupported`). Since v1.43 a single-sign-on-only instance hands over through the identity provider, so a working configuration never answers this.",
           content: { "application/json": { schema: errorEnvelope } },
         },
         "404": {
diff --git a/src/lib/openapi/routes/auth.ts b/src/lib/openapi/routes/auth.ts
index 4103ae971..2556bb59d 100644
--- a/src/lib/openapi/routes/auth.ts
+++ b/src/lib/openapi/routes/auth.ts
@@ -43,7 +43,6 @@ import {
 } from "@/lib/validations/step-up";
 import {
   dataEnvelope,
-  notImplementedResponse,
   profileEmailRateLimitResponse,
   stdResponses,
   errorEnvelope,
@@ -768,7 +767,7 @@ export const authPaths: NonNullable<ZodOpenApiObject["paths"]> = {
       tags: ["Auth"],
       summary: "Claim a managed profile through single sign-on (v1.43)",
       description:
-        "Web only. Checks the link and the username, sets a sealed `hl_claim` cookie (10 minutes, `httpOnly`) and answers where to continue: `/api/auth/oidc/login?intent=claim`. The OIDC callback binds the identity provider's subject to the profile and signs the new owner in; a subject already bound to an account, or a verified email another account holds, is refused there. Works on a single-sign-on-only instance. 404 `profile_claim.invalid` (no usable link) or `profile_claim.sso_unavailable` (no identity provider configured); 409 `profile_claim.taken` (username) or `auth.already_authenticated`; rate-limited per source address like the password claim.",
+        "Web only. Checks the link and the username, sets a sealed `hl_claim` cookie (10 minutes, `httpOnly`) and answers where to continue: `/api/auth/oidc/login?intent=claim`. The OIDC callback binds the identity provider's subject to the profile and signs the new owner in; a subject already bound to an account, or a verified email another account holds, is refused there. Works on a single-sign-on-only instance. When the callback refuses, the browser lands on `/auth/claim?error=<reason>` with reason `claim_expired` (the link was used, withdrawn, replaced or expired in the meantime, or the cookie is missing, expired or belongs to another start), `claim_sso_subject_bound`, `claim_email_taken`, `claim_username_taken` (taken during the round trip), `claim_signed_in`, or one of the sign-in reasons (`oidc_denied`, `oidc_state`, `oidc_failed`, `oidc_rate_limited`, `oidc_disabled`); on success it lands on `/onboarding/handover`, where the new owner decides each guardian's access. The cookie is cleared either way. 404 `profile_claim.invalid` (no usable link) or `profile_claim.sso_unavailable` (no identity provider configured); 409 `profile_claim.taken` (username) or `auth.already_authenticated`; rate-limited per source address like the password claim.",
       requestBody: {
         required: true,
         content: { "application/json": { schema: claimSsoRequest } },
@@ -795,7 +794,6 @@ export const authPaths: NonNullable<ZodOpenApiObject["paths"]> = {
           content: { "application/json": { schema: errorEnvelope } },
         },
         ...stdResponses,
-        ...notImplementedResponse,
       },
     },
   },
@@ -807,7 +805,7 @@ export const authPaths: NonNullable<ZodOpenApiObject["paths"]> = {
       tags: ["Auth"],
       summary: "Preview a managed-profile handover link",
       description:
-        "What a handover link would hand over: the profile's display name, the link's expiry, and each guardian's proposal. Anonymous; the token travels in the body. An unknown, expired, used or withdrawn token, and a link whose creator lost access, all answer the same 404. Rate-limited per source address.",
+        "What a handover link would hand over: the profile's display name, the link's expiry, and each guardian's proposal. Anonymous; the token travels in the body. An unknown, expired, used or withdrawn token, and a link whose creator lost access, all answer the same 404. Rate-limited per source address. Since v1.43 answered on a single-sign-on-only instance too, with `methods` naming the ways in.",
       requestBody: {
         required: true,
         content: { "application/json": { schema: claimPreviewRequest } },
@@ -821,11 +819,6 @@ export const authPaths: NonNullable<ZodOpenApiObject["paths"]> = {
             },
           },
         },
-        "403": {
-          description:
-            "The instance allows single sign-on only (`meta.errorCode: profile_claim.oidc_only_unsupported`).",
-          content: { "application/json": { schema: errorEnvelope } },
-        },
         "404": {
           description:
             "No usable link behind this token (`meta.errorCode: profile_claim.invalid`). Every failure class answers identically.",
@@ -2338,6 +2331,12 @@ export const authPaths: NonNullable<ZodOpenApiObject["paths"]> = {
             .describe(
               "Browser leg only: where to land after login. Sanitised to an in-app path; ignored entirely on the native leg.",
             ),
+          intent: z
+            .literal("claim")
+            .optional()
+            .describe(
+              "v1.43 — `claim` continues a managed-profile claim started at POST /api/auth/claim/sso; the link and username ride the sealed `hl_claim` cookie that call set, never this URL. Without a valid cookie for a still-usable link the start redirects to `/auth/claim?error=claim_expired`. Browser leg only: with `client=native` it fails with `oidc_invalid_request`. `next` is ignored.",
+            ),
           client_proto: z
             .enum(["http", "https"])
             .optional()
@@ -2356,7 +2355,7 @@ export const authPaths: NonNullable<ZodOpenApiObject["paths"]> = {
       responses: {
         "302": {
           description:
-            "Always a redirect. To the provider on success. On failure to `/auth/login?error=<reason>` (browser) or `healthlog://oidc-callback?error=<reason>` (native), where reason is one of `oidc_disabled`, `oidc_rate_limited`, `oidc_invalid_request`, `oidc_failed`, and on the browser leg `insecure_transport` (see `client_proto`). The provider then returns to the callback (not listed here, because the identity provider drives it rather than a client), which ends the native leg at `healthlog://oidc-callback` with `code=<hlh_…>`, with `mfa_ticket=<ticket>&methods=<list>`, or with `error=<reason>`, where reason is one of `oidc_disabled`, `oidc_rate_limited`, `oidc_denied`, `oidc_no_email`, `oidc_email_unverified`, `oidc_identity_conflict`, `oidc_link_required`, `oidc_registration_disabled`, `oidc_failed`. `oidc_link_required` means the provider's e-mail matches an existing local account that is not linked yet; the owner links it by signing in once with that account's own password or passkey in a browser. The reasons are this exact snake_case vocabulary on both legs; a client maps a value it does not know to a generic sign-in failure.",
+            "Always a redirect. To the provider on success. On failure to `/auth/login?error=<reason>` (browser; `/auth/claim?error=<reason>` with `intent=claim`, where `claim_expired` is one more reason) or `healthlog://oidc-callback?error=<reason>` (native), where reason is one of `oidc_disabled`, `oidc_rate_limited`, `oidc_invalid_request`, `oidc_failed`, and on the browser leg `insecure_transport` (see `client_proto`). The provider then returns to the callback (not listed here, because the identity provider drives it rather than a client), which ends the native leg at `healthlog://oidc-callback` with `code=<hlh_…>`, with `mfa_ticket=<ticket>&methods=<list>`, or with `error=<reason>`, where reason is one of `oidc_disabled`, `oidc_rate_limited`, `oidc_denied`, `oidc_no_email`, `oidc_email_unverified`, `oidc_identity_conflict`, `oidc_link_required`, `oidc_registration_disabled`, `oidc_failed`. `oidc_link_required` means the provider's e-mail matches an existing local account that is not linked yet; the owner links it by signing in once with that account's own password or passkey in a browser. The reasons are this exact snake_case vocabulary on both legs; a client maps a value it does not know to a generic sign-in failure.",
         },
       },
     },
diff --git a/src/lib/queries/use-managed-profiles.ts b/src/lib/queries/use-managed-profiles.ts
index 429517734..582900718 100644
--- a/src/lib/queries/use-managed-profiles.ts
+++ b/src/lib/queries/use-managed-profiles.ts
@@ -20,6 +20,7 @@
  * invalidation path (`grantDependentKeys`).
  */
 
+import type { HandoverMethod } from "@/lib/validations/claim-sso";
 import {
   useMutation,
   useQuery,
@@ -346,8 +347,13 @@ export function useRemoveManagedProfileGuardian() {
 
 /** What `GET /api/managed-profiles/{id}/handover` answers. */
 export interface ManagedProfileHandoverStatus {
-  /** False on a single-sign-on-only instance, where no link can be made. */
+  /** False only when no way to redeem a link exists on this instance. */
   available: boolean;
+  /**
+   * v1.43 — how the person can redeem the link here. Absent from an older
+   * server, which only offered the password.
+   */
+  methods?: HandoverMethod[];
   open: {
     id: string;
     createdAt: string;
diff --git a/src/lib/queries/use-profile-claim.ts b/src/lib/queries/use-profile-claim.ts
index 9c4b23910..160a3ff69 100644
--- a/src/lib/queries/use-profile-claim.ts
+++ b/src/lib/queries/use-profile-claim.ts
@@ -12,6 +12,7 @@ import { useMutation, useQuery } from "@tanstack/react-query";
 
 import { apiPost } from "@/lib/api/api-fetch";
 import type { HandoverAccess } from "@/lib/managed-profiles/handover-access";
+import type { HandoverMethod } from "@/lib/validations/claim-sso";
 import { queryKeys } from "@/lib/query-keys";
 
 export interface ProfileClaimPreview {
@@ -21,6 +22,13 @@ export interface ProfileClaimPreview {
     displayName: string | null;
     proposal: HandoverAccess;
   }[];
+  /**
+   * v1.43 — the ways in this server offers. Absent from an older server,
+   * which only ever offered the password.
+   */
+  methods?: HandoverMethod[];
+  /** v1.43 — the provider's name for the button, or null. */
+  ssoProviderName?: string | null;
 }
 
 export function useProfileClaimPreview(token: string | null, enabled: boolean) {
@@ -64,3 +72,31 @@ export function useClaimProfile() {
       ),
   });
 }
+
+/** Exactly the body `POST /api/auth/claim/sso` accepts (strict). */
+export interface ProfileClaimSsoInput {
+  token: string;
+  username: string;
+}
+
+export function claimSsoBody(
+  input: ProfileClaimSsoInput,
+): ProfileClaimSsoInput {
+  return { token: input.token, username: input.username };
+}
+
+/**
+ * v1.43 (#959) — start claiming through the identity provider. The answer
+ * sets the sealed claim cookie and names where the browser goes next; the
+ * caller navigates there as a full page load.
+ */
+export function useClaimProfileSso() {
+  return useMutation({
+    mutationKey: queryKeys.profileClaimSso(),
+    mutationFn: (input: ProfileClaimSsoInput) =>
+      apiPost<{ redirectTo: string }>(
+        "/api/auth/claim/sso",
+        claimSsoBody(input),
+      ),
+  });
+}
diff --git a/src/lib/query-keys/sharing.ts b/src/lib/query-keys/sharing.ts
index 48755f2d4..38a071974 100644
--- a/src/lib/query-keys/sharing.ts
+++ b/src/lib/query-keys/sharing.ts
@@ -99,4 +99,6 @@ export const sharingKeys = {
     ["managed-profiles", "handover", "revoke"] as const,
   handoverDecide: () => ["account", "handover-decision", "decide"] as const,
   profileClaim: () => ["profile-claim", "submit"] as const,
+  /** v1.43 (#959) — starting the claim through single sign-on. */
+  profileClaimSso: () => ["profile-claim", "sso"] as const,
 };
diff --git a/src/lib/validations/claim-sso.ts b/src/lib/validations/claim-sso.ts
index e53466a1b..5e14ac63b 100644
--- a/src/lib/validations/claim-sso.ts
+++ b/src/lib/validations/claim-sso.ts
@@ -15,3 +15,4 @@ export type ClaimSsoInput = z.infer<typeof claimSsoSchema>;
 
 /** How a handover link can be redeemed on this server. */
 export const HANDOVER_METHODS = ["password", "sso"] as const;
+export type HandoverMethod = (typeof HANDOVER_METHODS)[number];
diff --git a/tests/integration/managed-profile-handover-sso.test.ts b/tests/integration/managed-profile-handover-sso.test.ts
new file mode 100644
index 000000000..842e9e8c7
--- /dev/null
+++ b/tests/integration/managed-profile-handover-sso.test.ts
@@ -0,0 +1,906 @@
+/**
+ * v1.43 (#959) — handing a managed profile over on a server that signs in
+ * through an identity provider, end to end: the real start route, the real
+ * OIDC login and callback, a real Postgres, and a mock identity provider that
+ * speaks the wire (discovery, JWKS, a token endpoint that checks PKCE, and
+ * ES256-signed ID tokens), so state, nonce, PKCE and the signature are the
+ * production code's own checks rather than stubs.
+ *
+ * Every refusal is asserted twice: where the browser lands, and that nothing
+ * about any account changed (the profile is still managed, the subject is not
+ * bound, nobody got a session, the link is still as it was).
+ */
+import { createServer, type Server } from "node:http";
+import { createHash } from "node:crypto";
+import type { AddressInfo } from "node:net";
+
+import { exportJWK, generateKeyPair, SignJWT, type CryptoKey } from "jose";
+import { NextRequest } from "next/server";
+import {
+  afterAll,
+  afterEach,
+  beforeAll,
+  beforeEach,
+  describe,
+  expect,
+  it,
+  vi,
+} from "vitest";
+
+import { cookieJar, headerJar } from "./mock-next-headers";
+import { getPrismaClient, truncateAllTables } from "./setup";
+import { createManagedProfile } from "@/lib/managed-profiles/create";
+import { acceptGrant, inviteGrant } from "@/lib/sharing/grants";
+import { readPendingHandoverDecision } from "@/lib/managed-profiles/handover";
+import { _resetOidcCacheForTests } from "@/lib/auth/oidc";
+import { handoverCreateBody } from "@/lib/queries/use-managed-profiles";
+import { claimBody, claimSsoBody } from "@/lib/queries/use-profile-claim";
+import type { HandoverAccess } from "@/lib/managed-profiles/handover-access";
+
+vi.mock("next/headers", async () => {
+  const { cookieJar, headerJar } = await import("./mock-next-headers");
+  return {
+    headers: vi.fn(async () => ({
+      get: (name: string) => headerJar.get(name.toLowerCase()) ?? null,
+    })),
+    cookies: vi.fn(async () => ({
+      get: (name: string) => {
+        const value = cookieJar.get(name);
+        return value ? { name, value } : undefined;
+      },
+      set: (name: string, value: string) => cookieJar.set(name, value),
+      delete: (name: string) => cookieJar.delete(name),
+    })),
+  };
+});
+
+vi.mock("@/lib/db-compat", () => ({
+  ensureDbCompatibility: vi.fn().mockResolvedValue(undefined),
+}));
+
+vi.mock("@/lib/password-breach-check", () => ({
+  checkPasswordBreachIfEnabled: vi.fn().mockResolvedValue(null),
+}));
+
+const sent: { userId: string; messageKey: string }[] = [];
+vi.mock("@/lib/notifications/dispatch-localised", () => ({
+  dispatchLocalisedNotification: vi.fn(
+    async (opts: { userId: string; messageKey: string }) => {
+      sent.push({ userId: opts.userId, messageKey: opts.messageKey });
+    },
+  ),
+}));
+
+const APP = "http://localhost:3000";
+const CLIENT_ID = "healthlog-test";
+const CLIENT_SECRET = "client-secret-for-the-mock-idp";
+
+// ── The mock identity provider ──────────────────────────────────────────────
+
+interface Grant {
+  sub: string;
+  email?: string;
+  emailVerified?: boolean;
+  nonce: string;
+  codeChallenge: string;
+  /** The provider would redeem the code more than once (a replay test). */
+  reusable?: boolean;
+  /** Sign the ID token with this nonce instead of the requested one. */
+  nonceOverride?: string;
+}
+
+let idp: Server;
+let ISSUER = "";
+let privateKey: CryptoKey;
+let publicJwk: Record<string, unknown>;
+const grants = new Map<string, Grant>();
+const redeemed: string[] = [];
+
+function s256(verifier: string): string {
+  return createHash("sha256").update(verifier).digest("base64url");
+}
+
+async function readBody(req: import("node:http").IncomingMessage) {
+  let body = "";
+  for await (const chunk of req) body += chunk;
+  return new URLSearchParams(body);
+}
+
+beforeAll(async () => {
+  const pair = await generateKeyPair("ES256");
+  privateKey = pair.privateKey;
+  publicJwk = { ...(await exportJWK(pair.publicKey)), kid: "k1", alg: "ES256" };
+
+  idp = createServer(async (req, res) => {
+    const json = (status: number, body: unknown) => {
+      res.writeHead(status, { "content-type": "application/json" });
+      res.end(JSON.stringify(body));
+    };
+    const path = new URL(req.url ?? "/", ISSUER).pathname;
+    if (path === "/.well-known/openid-configuration") {
+      return json(200, {
+        issuer: ISSUER,
+        authorization_endpoint: `${ISSUER}/authorize`,
+        token_endpoint: `${ISSUER}/token`,
+        jwks_uri: `${ISSUER}/jwks`,
+      });
+    }
+    if (path === "/jwks") return json(200, { keys: [publicJwk] });
+    if (path === "/token" && req.method === "POST") {
+      const form = await readBody(req);
+      const code = form.get("code") ?? "";
+      const grant = grants.get(code);
+      if (
+        !grant ||
+        form.get("client_id") !== CLIENT_ID ||
+        form.get("client_secret") !== CLIENT_SECRET ||
+        form.get("redirect_uri") !== `${APP}/api/auth/oidc/callback` ||
+        // PKCE, as a provider enforces it.
+        s256(form.get("code_verifier") ?? "") !== grant.codeChallenge
+      ) {
+        return json(400, { error: "invalid_grant" });
+      }
+      if (!grant.reusable) grants.delete(code);
+      redeemed.push(code);
+      const idToken = await new SignJWT({
+        nonce: grant.nonceOverride ?? grant.nonce,
+        ...(grant.email !== undefined ? { email: grant.email } : {}),
+        ...(grant.emailVerified !== undefined
+          ? { email_verified: grant.emailVerified }
+          : {}),
+      })
+        .setProtectedHeader({ alg: "ES256", kid: "k1" })
+        .setIssuer(ISSUER)
+        .setAudience(CLIENT_ID)
+        .setSubject(grant.sub)
+        .setIssuedAt()
+        .setExpirationTime("5m")
+        .sign(privateKey);
+      return json(200, { id_token: idToken, token_type: "Bearer" });
+    }
+    json(404, { error: "not_found" });
+  });
+  await new Promise<void>((resolve) => idp.listen(0, "127.0.0.1", resolve));
+  ISSUER = `http://127.0.0.1:${(idp.address() as AddressInfo).port}`;
+});
+
+afterAll(async () => {
+  await new Promise<void>((resolve) => idp.close(() => resolve()));
+});
+
+// ── The household ───────────────────────────────────────────────────────────
+
+let sequence = 0;
+
+async function person(label: string) {
+  const suffix = sequence++;
+  const prisma = getPrismaClient();
+  const user = await prisma.user.create({
+    data: {
+      username: `${label}-${suffix}`,
+      email: `${label}-${suffix}@example.test`,
+      totpConfirmedAt: new Date(),
+    },
+  });
+  const session = await prisma.session.create({
+    data: {
+      userId: user.id,
+      expiresAt: new Date(Date.now() + 60 * 60 * 1000),
+      mfaVerifiedAt: new Date(),
+    },
+  });
+  return { id: user.id, username: user.username, sessionId: session.id };
+}
+
+/** A profile with two Guardians: its creator and one more. */
+async function household() {
+  const creator = await person("creator");
+  const second = await person("second");
+  const { profile, creatorGrant } = await createManagedProfile({
+    creatorId: creator.id,
+    displayName: "Robin",
+    dateOfBirth: null,
+    locale: "en",
+    timezone: "UTC",
+  });
+  const invitation = await inviteGrant({
+    grantorId: profile.id,
+    granteeId: second.id,
+    access: "MANAGE",
+    scope: null,
+  });
+  const secondGrant = await acceptGrant({
+    grantId: invitation.id,
+    granteeId: second.id,
+  });
+  return { creator, second, profile, creatorGrant, secondGrant };
+}
+
+const json = (body: unknown) => ({
+  method: "POST",
+  headers: { "content-type": "application/json" },
+  body: JSON.stringify(body),
+});
+
+/** Mint a link as the creator (the Guardian side), then sign out. */
+async function mintToken(
+  creator: { sessionId: string },
+  profileId: string,
+  proposals: { grantId: string; proposal: HandoverAccess }[] = [],
+): Promise<string> {
+  cookieJar.set("healthlog_session", creator.sessionId);
+  const { POST } =
+    await import("@/app/api/managed-profiles/[id]/handover/route");
+  const response = await POST(
+    new NextRequest(
+      `${APP}/api/managed-profiles/${profileId}/handover`,
+      json(handoverCreateBody({ profileId, expiresInDays: 7, proposals })),
+    ),
+    { params: Promise.resolve({ id: profileId }) },
+  );
+  expect(response.status).toBe(201);
+  cookieJar.clear();
+  return (await response.json()).data.token as string;
+}
+
+async function handoverStatus(creator: { sessionId: string }, id: string) {
+  cookieJar.set("healthlog_session", creator.sessionId);
+  const { GET } =
+    await import("@/app/api/managed-profiles/[id]/handover/route");
+  const response = await GET(
+    new NextRequest(`${APP}/api/managed-profiles/${id}/handover`),
+    { params: Promise.resolve({ id }) },
+  );
+  cookieJar.clear();
+  return response;
+}
+
+async function preview(token: string) {
+  const { POST } = await import("@/app/api/auth/claim/preview/route");
+  return POST(
+    new NextRequest(`${APP}/api/auth/claim/preview`, json({ token })),
+  );
+}
+
+async function passwordClaim(token: string) {
+  const suffix = sequence++;
+  const { POST } = await import("@/app/api/auth/claim/route");
+  return POST(
+    new NextRequest(
+      `${APP}/api/auth/claim`,
+      json(
+        claimBody({
+          token,
+          username: `robinpw${suffix}`,
+          email: `robin-pw-${suffix}@example.test`,
+          password: "correct horse battery staple 1959",
+        }),
+      ),
+    ),
+  );
+}
+
+async function startSso(token: string, username: string) {
+  const { POST } = await import("@/app/api/auth/claim/sso/route");
+  return POST(
+    new NextRequest(
+      `${APP}/api/auth/claim/sso`,
+      json(claimSsoBody({ token, username })),
+    ),
+  );
+}
+
+function cookieHeader(cookies: Record<string, string | undefined>): string {
+  return Object.entries(cookies)
+    .filter((entry): entry is [string, string] => Boolean(entry[1]))
+    .map(([k, v]) => `${k}=${v}`)
+    .join("; ");
+}
+
+/** The value a response sets for a cookie, or undefined. */
+function setCookie(response: Response, name: string): string | undefined {
+  const cookie = (response as NextResponseLike).cookies?.get(name);
+  return cookie?.value || undefined;
+}
+type NextResponseLike = Response & {
+  cookies?: { get(name: string): { value: string } | undefined };
+};
+
+async function login(claimCookie: string | undefined, query = "intent=claim") {
+  const { GET } = await import("@/app/api/auth/oidc/login/route");
+  return GET(
+    new NextRequest(`${APP}/api/auth/oidc/login?${query}`, {
+      headers: { cookie: cookieHeader({ hl_claim: claimCookie }) },
+    }),
+  );
+}
+
+interface Identity {
+  sub: string;
+  email?: string;
+  emailVerified?: boolean;
+  reusable?: boolean;
+  nonceOverride?: string;
+}
+
+/** Where the provider sends the browser back, and with which cookies. */
+interface Callback {
+  url: string;
+  stateCookie: string;
+  claimCookie: string | undefined;
+}
+
+/** The provider authenticates `identity` for an authorize redirect. */
+function authorize(loginResponse: Response, identity: Identity, code: string) {
+  const location = new URL(loginResponse.headers.get("location") ?? "");
+  expect(location.origin + location.pathname).toBe(`${ISSUER}/authorize`);
+  expect(location.searchParams.get("code_challenge_method")).toBe("S256");
+  grants.set(code, {
+    ...identity,
+    nonce: location.searchParams.get("nonce") ?? "",
+    codeChallenge: location.searchParams.get("code_challenge") ?? "",
+  });
+  return location.searchParams.get("state") ?? "";
+}
+
+async function callback(
+  cb: Callback,
+  extra: Record<string, string | undefined> = {},
+) {
+  const { GET } = await import("@/app/api/auth/oidc/callback/route");
+  return GET(
+    new NextRequest(cb.url, {
+      headers: {
+        cookie: cookieHeader({
+          oidc_auth_state: cb.stateCookie,
+          hl_claim: cb.claimCookie,
+          ...extra,
+        }),
+      },
+    }),
+  );
+}
+
+/** Start, log in and come back from the provider; the callback not yet run. */
+async function throughProvider(
+  token: string,
+  identity: Identity,
+  username = `robin${sequence++}`,
+): Promise<Callback> {
+  const started = await startSso(token, username);
+  expect(started.status).toBe(200);
+  expect((await started.json()).data.redirectTo).toBe(
+    "/api/auth/oidc/login?intent=claim",
+  );
+  const claimCookie = setCookie(started, "hl_claim");
+  expect(claimCookie).toBeDefined();
+  const loginResponse = await login(claimCookie);
+  const stateCookie = setCookie(loginResponse, "oidc_auth_state");
+  expect(stateCookie).toBeDefined();
+  const code = `code-${sequence++}`;
+  const state = authorize(loginResponse, identity, code);
+  return {
+    url: `${APP}/api/auth/oidc/callback?code=${code}&state=${encodeURIComponent(state)}`,
+    stateCookie: stateCookie!,
+    claimCookie,
+  };
+}
+
+function landedOn(response: Response): string {
+  expect([302, 303, 307]).toContain(response.status);
+  const location = new URL(response.headers.get("location") ?? "");
+  expect(location.origin).toBe(APP);
+  return location.pathname + location.search;
+}
+
+async function profileRow(id: string) {
+  return getPrismaClient().user.findUniqueOrThrow({
+    where: { id },
+    select: {
+      username: true,
+      email: true,
+      passwordHash: true,
+      oidcIssuer: true,
+      oidcSub: true,
+      managedProfileAt: true,
+      onboardingCompletedAt: true,
+    },
+  });
+}
+
+/** The account did not change at all, and nobody signed in to it. */
+async function expectUntouched(profileId: string) {
+  const row = await profileRow(profileId);
+  expect(row.managedProfileAt).not.toBeNull();
+  expect(row.oidcSub).toBeNull();
+  expect(row.email).toBeNull();
+  expect(row.username.startsWith("managed-")).toBe(true);
+  expect(
+    await getPrismaClient().session.count({ where: { userId: profileId } }),
+  ).toBe(0);
+  expect(
+    await getPrismaClient().auditLog.count({
+      where: { userId: profileId, action: "auth.claim" },
+    }),
+  ).toBe(0);
+}
+
+function oidcEnv(only: boolean) {
+  process.env.OIDC_ISSUER_URL = ISSUER;
+  process.env.OIDC_CLIENT_ID = CLIENT_ID;
+  process.env.OIDC_CLIENT_SECRET = CLIENT_SECRET;
+  process.env.OIDC_BUTTON_LABEL = "Example ID";
+  if (only) process.env.OIDC_ONLY = "true";
+  else delete process.env.OIDC_ONLY;
+}
+
+beforeEach(async () => {
+  await truncateAllTables(getPrismaClient());
+  cookieJar.clear();
+  headerJar.clear();
+  grants.clear();
+  redeemed.length = 0;
+  sent.length = 0;
+  _resetOidcCacheForTests();
+  process.env.APP_URL = APP;
+  process.env.NEXT_PUBLIC_APP_URL = APP;
+  oidcEnv(true);
+});
+
+afterEach(() => {
+  for (const key of [
+    "OIDC_ISSUER_URL",
+    "OIDC_CLIENT_ID",
+    "OIDC_CLIENT_SECRET",
+    "OIDC_BUTTON_LABEL",
+    "OIDC_ONLY",
+  ]) {
+    delete process.env[key];
+  }
+});
+
+// ── The tests ───────────────────────────────────────────────────────────────
+
+describe("claiming through single sign-on on an SSO-only server", () => {
+  it("hands the profile over and binds the provider's subject", async () => {
+    const { creator, second, profile, secondGrant } = await household();
+
+    // The Guardian side: available, through single sign-on only.
+    const status = (await (await handoverStatus(creator, profile.id)).json())
+      .data;
+    expect(status.available).toBe(true);
+    expect(status.methods).toEqual(["sso"]);
+
+    const token = await mintToken(creator, profile.id, [
+      { grantId: secondGrant.id, proposal: "read" },
+    ]);
+
+    // The person's side: the preview names the provider, the password claim
+    // stays closed.
+    const shown = (await (await preview(token)).json()).data;
+    expect(shown.methods).toEqual(["sso"]);
+    expect(shown.ssoProviderName).toBe("Example ID");
+    const refused = await passwordClaim(token);
+    expect(refused.status).toBe(403);
+    expect((await refused.json()).meta.errorCode).toBe(
+      "profile_claim.oidc_only_unsupported",
+    );
+
+    const cb = await throughProvider(
+      token,
+      {
+        sub: "subject-robin",
+        email: "Robin@Example.test",
+        emailVerified: true,
+      },
+      "robin",
+    );
+    const response = await callback(cb);
+    expect(landedOn(response)).toBe("/onboarding/handover");
+    // Both single-use cookies go with the answer.
+    expect(response.headers.get("set-cookie")).toMatch(/hl_claim=;/);
+    expect(response.headers.get("set-cookie")).toMatch(/oidc_auth_state=;/);
+    // The provider redeemed the code with the matching PKCE verifier.
+    expect(redeemed).toHaveLength(1);
+
+    const row = await profileRow(profile.id);
+    expect(row).toMatchObject({
+      username: "robin",
+      email: "robin@example.test",
+      passwordHash: null,
+      oidcIssuer: ISSUER,
+      oidcSub: "subject-robin",
+      managedProfileAt: null,
+      onboardingCompletedAt: null,
+    });
+
+    // The link is spent; a session exists for the new owner, and only one.
+    const link =
+      await getPrismaClient().managedProfileHandover.findFirstOrThrow({
+        where: { profileId: profile.id },
+      });
+    expect(link.usedAt).not.toBeNull();
+    expect(
+      await getPrismaClient().session.count({ where: { userId: profile.id } }),
+    ).toBe(1);
+    expect(cookieJar.get("healthlog_session")).toBeDefined();
+
+    // The Guardians' proposals hold and wait for the owner's decision.
+    const decision = await readPendingHandoverDecision(profile.id);
+    expect(
+      decision?.guardians.map((g) => [g.displayName, g.proposal, g.current]),
+    ).toEqual(
+      expect.arrayContaining([
+        [expect.stringContaining("second"), "read", "read"],
+      ]),
+    );
+    const secondNow = await getPrismaClient().accountGrant.findFirst({
+      where: { grantorId: profile.id, granteeId: second.id, revokedAt: null },
+    });
+    expect(secondNow?.access).toBe("READ");
+
+    // Audited as an SSO claim, and the Guardians were told.
+    const audits = await getPrismaClient().auditLog.findMany({
+      where: { userId: profile.id },
+      select: { action: true, details: true },
+    });
+    const actions = audits.map((a) => a.action);
+    expect(actions).toEqual(
+      expect.arrayContaining([
+        "managed_profile.claim_sso.started",
+        "managed_profile.claimed",
+        "auth.claim",
+      ]),
+    );
+    const claimAudit = audits.find((a) => a.action === "auth.claim");
+    expect(JSON.parse(claimAudit!.details!)).toEqual({ method: "sso" });
+    // The token never reached an audit row.
+    expect(JSON.stringify(audits)).not.toContain(token);
+    expect(sent.map((s) => s.userId).sort()).toEqual(
+      [creator.id, second.id].sort(),
+    );
+  });
+
+  it("creates the account without an address the provider did not verify", async () => {
+    const { creator, profile } = await household();
+    const token = await mintToken(creator, profile.id);
+    const cb = await throughProvider(token, {
+      sub: "subject-unverified",
+      email: "robin@example.test",
+      emailVerified: false,
+    });
+    expect(landedOn(await callback(cb))).toBe("/onboarding/handover");
+    const row = await profileRow(profile.id);
+    expect(row.email).toBeNull();
+    expect(row.oidcSub).toBe("subject-unverified");
+  });
+
+  it("ignores a caller-supplied next and lands on the fixed page", async () => {
+    const { creator, profile } = await household();
+    const token = await mintToken(creator, profile.id);
+    const started = await startSso(token, "robin");
+    const claimCookie = setCookie(started, "hl_claim");
+    const loginResponse = await login(
+      claimCookie,
+      "intent=claim&next=https%3A%2F%2Fevil.example%2Fphish",
+    );
+    const state = authorize(loginResponse, { sub: "s-next" }, "code-next");
+    const response = await callback({
+      url: `${APP}/api/auth/oidc/callback?code=code-next&state=${encodeURIComponent(state)}`,
+      stateCookie: setCookie(loginResponse, "oidc_auth_state")!,
+      claimCookie,
+    });
+    expect(response.headers.get("location")).toBe(`${APP}/onboarding/handover`);
+  });
+});
+
+describe("refusals", () => {
+  it("refuses a subject already bound to another account (no double binding)", async () => {
+    const { creator, profile } = await household();
+    const holder = await getPrismaClient().user.create({
+      data: {
+        username: "holder",
+        email: "holder@example.test",
+        oidcIssuer: ISSUER,
+        oidcSub: "subject-taken",
+      },
+    });
+    const token = await mintToken(creator, profile.id);
+    const cb = await throughProvider(token, { sub: "subject-taken" });
+
+    expect(landedOn(await callback(cb))).toBe(
+      "/auth/claim?error=claim_sso_subject_bound",
+    );
+    await expectUntouched(profile.id);
+    // The holder keeps their sign-in and is told somebody tried.
+    expect((await profileRow(holder.id)).oidcSub).toBe("subject-taken");
+    expect(
+      await getPrismaClient().auditLog.count({
+        where: { userId: holder.id, action: "auth.oidc.claim_conflict" },
+      }),
+    ).toBe(1);
+    // The link survives for the right person.
+    expect((await preview(token)).status).toBe(200);
+  });
+
+  it("refuses a second profile for a subject that already claimed one", async () => {
+    const first = await household();
+    const second = await household();
+    const tokenA = await mintToken(first.creator, first.profile.id);
+    const tokenB = await mintToken(second.creator, second.profile.id);
+
+    const a = await throughProvider(tokenA, { sub: "one-person" });
+    expect(landedOn(await callback(a))).toBe("/onboarding/handover");
+    cookieJar.clear();
+
+    const b = await throughProvider(tokenB, { sub: "one-person" });
+    expect(landedOn(await callback(b))).toBe(
+      "/auth/claim?error=claim_sso_subject_bound",
+    );
+    await expectUntouched(second.profile.id);
+  });
+
+  it("refuses a verified address another account holds", async () => {
+    const { creator, profile } = await household();
+    const token = await mintToken(creator, profile.id);
+    const cb = await throughProvider(token, {
+      sub: "subject-email",
+      email: creator.username + "@EXAMPLE.test",
+      emailVerified: true,
+    });
+    expect(landedOn(await callback(cb))).toBe(
+      "/auth/claim?error=claim_email_taken",
+    );
+    await expectUntouched(profile.id);
+  });
+
+  it("refuses a username taken during the round trip", async () => {
+    const { creator, profile } = await household();
+    const token = await mintToken(creator, profile.id);
+    const cb = await throughProvider(token, { sub: "subject-name" }, "robin");
+    await getPrismaClient().user.create({
+      data: { username: "robin", email: "other@example.test" },
+    });
+    expect(landedOn(await callback(cb))).toBe(
+      "/auth/claim?error=claim_username_taken",
+    );
+    await expectUntouched(profile.id);
+  });
+
+  it.each([
+    [
+      "expired",
+      async (profileId: string) => {
+        await getPrismaClient().managedProfileHandover.updateMany({
+          where: { profileId },
+          data: { expiresAt: new Date(Date.now() - 1000) },
+        });
+      },
+    ],
+    [
+      "withdrawn",
+      async (profileId: string) => {
+        await getPrismaClient().managedProfileHandover.updateMany({
+          where: { profileId },
+          data: { revokedAt: new Date() },
+        });
+      },
+    ],
+  ])(
+    "refuses a link %s while the person was at the provider",
+    async (_n, spoil) => {
+      const { creator, profile } = await household();
+      const token = await mintToken(creator, profile.id);
+      const cb = await throughProvider(token, { sub: "subject-late" });
+      await spoil(profile.id);
+      expect(landedOn(await callback(cb))).toBe(
+        "/auth/claim?error=claim_expired",
+      );
+      await expectUntouched(profile.id);
+      // Refused before the code was redeemed: nothing spent at the provider.
+      expect(redeemed).toHaveLength(0);
+    },
+  );
+
+  it("refuses a link used by a password claim in the meantime", async () => {
+    oidcEnv(false);
+    const { creator, profile } = await household();
+    const token = await mintToken(creator, profile.id);
+    const cb = await throughProvider(token, { sub: "subject-slow" });
+    expect((await passwordClaim(token)).status).toBe(201);
+    cookieJar.clear();
+    expect(landedOn(await callback(cb))).toBe(
+      "/auth/claim?error=claim_expired",
+    );
+    const row = await profileRow(profile.id);
+    expect(row.oidcSub).toBeNull();
+    expect(row.passwordHash).not.toBeNull();
+  });
+
+  it("stops an expired link at the login, before the provider", async () => {
+    const { creator, profile } = await household();
+    const token = await mintToken(creator, profile.id);
+    const started = await startSso(token, "robin");
+    await getPrismaClient().managedProfileHandover.updateMany({
+      where: { profileId: profile.id },
+      data: { expiresAt: new Date(Date.now() - 1000) },
+    });
+    const response = await login(setCookie(started, "hl_claim"));
+    expect(landedOn(response)).toBe("/auth/claim?error=claim_expired");
+    expect(setCookie(response, "oidc_auth_state")).toBeUndefined();
+  });
+
+  it("answers the start with 404 for a used or unknown link", async () => {
+    const { creator, profile } = await household();
+    const token = await mintToken(creator, profile.id);
+    const cb = await throughProvider(token, { sub: "subject-once" });
+    expect(landedOn(await callback(cb))).toBe("/onboarding/handover");
+    cookieJar.clear();
+    for (const t of [token, `hlp_${"0".repeat(64)}`]) {
+      const response = await startSso(t, "someone");
+      expect(response.status).toBe(404);
+      expect((await response.json()).meta.errorCode).toBe(
+        "profile_claim.invalid",
+      );
+    }
+  });
+});
+
+describe("replay, state, nonce and the claim cookie", () => {
+  it("does nothing on a replayed callback, even if the provider redeemed the code twice", async () => {
+    const { creator, profile } = await household();
+    const token = await mintToken(creator, profile.id);
+    const cb = await throughProvider(token, {
+      sub: "subject-replay",
+      reusable: true,
+    });
+    expect(landedOn(await callback(cb))).toBe("/onboarding/handover");
+    const sessionsAfterFirst = await getPrismaClient().session.count({
+      where: { userId: profile.id },
+    });
+    const sessionCookie = cookieJar.get("healthlog_session");
+    expect(sessionCookie).toMatch(/^hls_/);
+    cookieJar.clear();
+
+    // The same request again, cookies and all, from a browser without the
+    // session (a captured request): the link is spent.
+    expect(landedOn(await callback(cb))).toBe(
+      "/auth/claim?error=claim_expired",
+    );
+    // From the browser that now holds the session: refused as signed in,
+    // before the link is even looked at.
+    expect(
+      landedOn(await callback(cb, { healthlog_session: sessionCookie })),
+    ).toBe("/auth/claim?error=claim_signed_in");
+
+    expect(
+      await getPrismaClient().session.count({ where: { userId: profile.id } }),
+    ).toBe(sessionsAfterFirst);
+    expect(
+      await getPrismaClient().auditLog.count({
+        where: { userId: profile.id, action: "auth.claim" },
+      }),
+    ).toBe(1);
+  });
+
+  it("refuses a callback whose state does not match", async () => {
+    const { creator, profile } = await household();
+    const token = await mintToken(creator, profile.id);
+    const cb = await throughProvider(token, { sub: "subject-state" });
+    const forged = cb.url.replace(/state=[^&]+/, "state=forged-state-value");
+    expect(landedOn(await callback({ ...cb, url: forged }))).toBe(
+      "/auth/claim?error=oidc_state",
+    );
+    await expectUntouched(profile.id);
+    expect(redeemed).toHaveLength(0);
+  });
+
+  it("refuses an ID token minted for another nonce", async () => {
+    const { creator, profile } = await household();
+    const token = await mintToken(creator, profile.id);
+    const cb = await throughProvider(token, {
+      sub: "subject-nonce",
+      nonceOverride: "some-other-sign-in",
+    });
+    expect(landedOn(await callback(cb))).toBe("/auth/claim?error=oidc_failed");
+    await expectUntouched(profile.id);
+  });
+
+  it("refuses a callback that comes back without the claim cookie", async () => {
+    const { creator, profile } = await household();
+    const token = await mintToken(creator, profile.id);
+    const cb = await throughProvider(token, { sub: "subject-nocookie" });
+    expect(landedOn(await callback({ ...cb, claimCookie: undefined }))).toBe(
+      "/auth/claim?error=claim_expired",
+    );
+    await expectUntouched(profile.id);
+    expect(redeemed).toHaveLength(0);
+  });
+
+  it("refuses a claim cookie from a different start", async () => {
+    const { creator, profile } = await household();
+    const token = await mintToken(creator, profile.id);
+    const cb = await throughProvider(token, { sub: "subject-swap" });
+    // A second start in the same browser seals a new binding; the sign-in
+    // that began with the first one cannot finish with it.
+    const other = setCookie(await startSso(token, "robin2"), "hl_claim");
+    expect(landedOn(await callback({ ...cb, claimCookie: other }))).toBe(
+      "/auth/claim?error=claim_expired",
+    );
+    await expectUntouched(profile.id);
+  });
+
+  it("refuses a forged claim cookie", async () => {
+    const { creator, profile } = await household();
+    const token = await mintToken(creator, profile.id);
+    const cb = await throughProvider(token, { sub: "subject-forged" });
+    const link =
+      await getPrismaClient().managedProfileHandover.findFirstOrThrow({
+        where: { profileId: profile.id },
+      });
+    const forged = Buffer.from(
+      JSON.stringify({ h: link.id, u: "x", b: "y", e: Date.now() + 1e6 }),
+    ).toString("base64");
+    expect(landedOn(await callback({ ...cb, claimCookie: forged }))).toBe(
+      "/auth/claim?error=claim_expired",
+    );
+    await expectUntouched(profile.id);
+  });
+
+  it("does not adopt a session id the browser brought along", async () => {
+    const { creator, profile } = await household();
+    const token = await mintToken(creator, profile.id);
+    const cb = await throughProvider(token, { sub: "subject-fixation" });
+    const planted = "planted-session-id-chosen-by-somebody-else";
+    expect(landedOn(await callback(cb, { healthlog_session: planted }))).toBe(
+      "/onboarding/handover",
+    );
+    const sessions = await getPrismaClient().session.findMany({
+      where: { userId: profile.id },
+      select: { id: true },
+    });
+    expect(sessions).toHaveLength(1);
+    expect(sessions[0]!.id).not.toBe(planted);
+    expect(cookieJar.get("healthlog_session")).not.toBe(planted);
+  });
+});
+
+describe("which ways in a server offers", () => {
+  it("offers both with a provider and passwords allowed, and both work", async () => {
+    oidcEnv(false);
+    const { creator, profile } = await household();
+    const status = (await (await handoverStatus(creator, profile.id)).json())
+      .data;
+    expect(status.methods).toEqual(["password", "sso"]);
+    const token = await mintToken(creator, profile.id);
+    expect((await (await preview(token)).json()).data.methods).toEqual([
+      "password",
+      "sso",
+    ]);
+    const cb = await throughProvider(token, { sub: "subject-mixed" });
+    expect(landedOn(await callback(cb))).toBe("/onboarding/handover");
+
+    const other = await household();
+    const token2 = await mintToken(other.creator, other.profile.id);
+    expect((await passwordClaim(token2)).status).toBe(201);
+  });
+
+  it("offers only the password without a provider, and the SSO start says so", async () => {
+    for (const key of ["OIDC_ISSUER_URL", "OIDC_CLIENT_ID", "OIDC_ONLY"]) {
+      delete process.env[key];
+    }
+    const { creator, profile } = await household();
+    const status = (await (await handoverStatus(creator, profile.id)).json())
+      .data;
+    expect(status.methods).toEqual(["password"]);
+    const token = await mintToken(creator, profile.id);
+    const shown = (await (await preview(token)).json()).data;
+    expect(shown.methods).toEqual(["password"]);
+    expect(shown.ssoProviderName).toBeNull();
+    const response = await startSso(token, "robin");
+    expect(response.status).toBe(404);
+    expect((await response.json()).meta.errorCode).toBe(
+      "profile_claim.sso_unavailable",
+    );
+  });
+});
diff --git a/tests/integration/managed-profile-handover.test.ts b/tests/integration/managed-profile-handover.test.ts
index b40171a30..6a6c5a5c7 100644
--- a/tests/integration/managed-profile-handover.test.ts
+++ b/tests/integration/managed-profile-handover.test.ts
@@ -18,7 +18,8 @@
  *   - the races that matter: two claims, a claim against a new link, a claim
  *     against the profile's deletion;
  *   - the anonymous surface: uniform 404, live-session 409, rate limit, and
- *     the refusal on a single-sign-on-only instance;
+ *     the password claim's refusal on a single-sign-on-only instance (the
+ *     single-sign-on claim has its own file);
  *   - the new owner's decision afterwards, including a restored MANAGE and a
  *     row that moved since the claim and is left alone.
  */
@@ -811,7 +812,7 @@ describe("claiming the profile", () => {
     // cookie jar, and the race is between the two transactions, not cookies.
     const [claimed, minted] = await Promise.allSettled([
       claimManagedProfile({
-        rawToken: first,
+        link: { rawToken: first },
         username: "racer",
         email: "racer@example.test",
         passwordHash: "hash",
@@ -862,7 +863,7 @@ describe("claiming the profile", () => {
     }
   });
 
-  it("refuses over a live session and on a single-sign-on-only instance", async () => {
+  it("refuses over a live session, and the password claim on a single-sign-on-only instance", async () => {
     const { creator, profile } = await household();
     signIn(creator);
     const token = await mintToken(profile.id);
@@ -877,7 +878,9 @@ describe("claiming the profile", () => {
     process.env.OIDC_CLIENT_ID = "client";
     process.env.OIDC_CLIENT_SECRET = "secret";
     process.env.OIDC_ONLY = "true";
-    expect((await mint(profile.id)).status).toBe(403);
+    // v1.43 (#959): the handover itself works there, through the identity
+    // provider (tests/integration/managed-profile-handover-sso.test.ts); only
+    // the password claim stays closed.
     const status = await (
       await (
         await import("@/app/api/managed-profiles/[id]/handover/route")
@@ -888,14 +891,17 @@ describe("claiming the profile", () => {
         { params: Promise.resolve({ id: profile.id }) },
       )
     ).json();
-    expect(status.data.available).toBe(false);
+    expect(status.data.available).toBe(true);
+    expect(status.data.methods).toEqual(["sso"]);
     signOut();
-    for (const response of [await preview(token), await claim(token)]) {
-      expect(response.status).toBe(403);
-      expect((await response.json()).meta.errorCode).toBe(
-        "profile_claim.oidc_only_unsupported",
-      );
-    }
+    const shown = await preview(token);
+    expect(shown.status).toBe(200);
+    expect((await shown.json()).data.methods).toEqual(["sso"]);
+    const refused = await claim(token);
+    expect(refused.status).toBe(403);
+    expect((await refused.json()).meta.errorCode).toBe(
+      "profile_claim.oidc_only_unsupported",
+    );
     // The profile is still managed: nothing was taken over.
     const account = await getPrismaClient().user.findUniqueOrThrow({
       where: { id: profile.id },