fix(api): accept an Idempotency-Key on the titration step and the custom symptom

Two more creates the client replays out of its offline outbox ran the
handler again on the replay. A titration step carries no natural key at
all, so a lost success response left the medication with two dose
changes on the same day and the runway estimate reading off the wrong
one. A custom cycle symptom is unique on its label, so the replay did
not duplicate — it answered the 409 that uniqueness raises, reporting a
conflict the client cannot act on for a row it has no record of
creating.

Both wrap in `withIdempotency`, the composition their siblings already
ship, and both operations publish the header and the in-flight 409 so a
client generated against the contract can tell a retry is safe.

The integration file that drives the medication creates twice against
real Postgres gains the titration case: one dose-change row after the
replay, and a replayed 201 carrying `X-Idempotent-Replay: true`.

`POST /api/mcp/tokens` is deliberately not on this list. Its response
carries a freshly minted `hlk_` credential, and the wrapper refuses to
persist a secret-shaped body — publishing the header there would
promise a replay the mechanism will never perform.

src/app/api/cycle/symptoms/custom/route.ts

@@ -26,6 +26,7 @@ import {
 } from "@/lib/api-response";
 import { apiHandler, requireRecordAuth } from "@/lib/api-handler";
 import { annotate } from "@/lib/logging/context";
+import { withIdempotency } from "@/lib/idempotency";
 import { auditLog } from "@/lib/auth/audit";
 import { checkRateLimit } from "@/lib/rate-limit";
 import { requireCycleEnabled } from "@/lib/cycle/gate";
@@ -67,7 +68,18 @@ export const GET = apiHandler(async () => {
   return apiSuccess({ symptoms });
 });
 
-export const POST = apiHandler(async (request: NextRequest) => {
+/**
+ * Wrapped in `withIdempotency`: a custom symptom is minted from the client's
+ * offline outbox under the same `Idempotency-Key`, and a replay after a lost
+ * success response would otherwise answer the 409 the label's unique key
+ * raises rather than the 201 the first attempt produced — a create the client
+ * has no record of, reported as a conflict it cannot act on.
+ */
+export const POST = apiHandler(
+  withIdempotency<[NextRequest]>(postCustomSymptom),
+);
+
+async function postCustomSymptom(request: NextRequest): Promise<Response> {
   // v1.37.0 — MANAGE. The record's own symptom vocabulary, which the day-log
   // writes the level admits need in order to say anything.
   const { user, actor } = await requireRecordAuth("manage", "cycle");
@@ -151,4 +163,4 @@ export const POST = apiHandler(async (request: NextRequest) => {
     },
     201,
   );
-});
+}

src/app/api/medications/[id]/glp1/route.ts

@@ -28,6 +28,7 @@ import {
 import { checkRateLimit, rateLimitHeaders } from "@/lib/rate-limit";
 import { glp1PostBodySchema } from "@/lib/validations/medication";
 import { assertMedicationOwnership } from "@/lib/medications/route-guards";
+import { withIdempotency } from "@/lib/idempotency";
 import {
   estimateDailyDoseCount,
   estimateRunwayDays,
@@ -236,103 +237,71 @@ export const GET = apiHandler(
  * Rate-limit: 30/min/user (same as sibling POST routes).
  * Audit: `medication.glp1.update` for every successful mutation.
  */
+/**
+ * Wrapped in `withIdempotency`: a titration step is replayed out of the
+ * client's offline outbox under the same `Idempotency-Key`, and a replay after
+ * a lost success response would otherwise write a second dose change or a
+ * second supply delta. Neither row carries a natural key, so the wrapper is the
+ * only thing that can collapse the retry.
+ */
 export const POST = apiHandler(
-  async (request: NextRequest, { params }: RouteParams) => {
-    // v1.37.0 — MANAGE. A titration step is record data and the dose is what
-    // the server acts on; administering one is the case the level names.
-    const { user, actor } = await requireRecordAuth("manage", "medications");
-    const { id } = await params;
+  withIdempotency<[NextRequest, RouteParams]>(postGlp1Update),
+);
 
-    const guard = await assertMedicationOwnership(id, user.id);
-    if (guard) return guard;
+async function postGlp1Update(
+  request: NextRequest,
+  { params }: RouteParams,
+): Promise<Response> {
+  // v1.37.0 — MANAGE. A titration step is record data and the dose is what
+  // the server acts on; administering one is the case the level names.
+  const { user, actor } = await requireRecordAuth("manage", "medications");
+  const { id } = await params;
 
-    // Per-caller POST rate-limit — matches the 30/min sibling routes
-    // (inventory, side-effects). Generous for a hand-driven session,
-    // tight enough to cut off the spam case.
-    //
-    // v1.37.0 — C1: keyed on the ACTOR, so a manager burns their own
-    // allowance and cannot collect a fresh one by switching records.
-    const rl = await checkRateLimit(
-      `medication-glp1:post:${actor.id}`,
-      POST_RATE_LIMIT,
-      POST_WINDOW_MS,
-    );
-    if (!rl.allowed) {
-      return apiError("Too many requests", 429, {
-        headers: rateLimitHeaders(rl),
-      });
-    }
+  const guard = await assertMedicationOwnership(id, user.id);
+  if (guard) return guard;
 
-    const { data: body, error: jsonError } = await safeJson(request, {
-      maxBytes: 64 * 1024,
+  // Per-caller POST rate-limit — matches the 30/min sibling routes
+  // (inventory, side-effects). Generous for a hand-driven session,
+  // tight enough to cut off the spam case.
+  //
+  // v1.37.0 — C1: keyed on the ACTOR, so a manager burns their own
+  // allowance and cannot collect a fresh one by switching records.
+  const rl = await checkRateLimit(
+    `medication-glp1:post:${actor.id}`,
+    POST_RATE_LIMIT,
+    POST_WINDOW_MS,
+  );
+  if (!rl.allowed) {
+    return apiError("Too many requests", 429, {
+      headers: rateLimitHeaders(rl),
     });
-    if (jsonError) return jsonError;
+  }
 
-    const parsed = glp1PostBodySchema.safeParse(body);
-    if (!parsed.success) {
-      // v1.4.43 W6 — multi-issue 422.
-      return returnAllZodIssues(parsed.error, 422);
-    }
+  const { data: body, error: jsonError } = await safeJson(request, {
+    maxBytes: 64 * 1024,
+  });
+  if (jsonError) return jsonError;
 
-    const ip = getClientIp(request);
+  const parsed = glp1PostBodySchema.safeParse(body);
+  if (!parsed.success) {
+    // v1.4.43 W6 — multi-issue 422.
+    return returnAllZodIssues(parsed.error, 422);
+  }
 
-    if (parsed.data.doseChange) {
-      const { effectiveFrom, doseValue, doseUnit, note } =
-        parsed.data.doseChange;
-      const created = await prisma.medicationDoseChange.create({
-        data: {
-          medicationId: id,
-          effectiveFrom,
-          doseValue,
-          doseUnit,
-          // Encrypt the titration note at rest; the plaintext column stays null.
-          noteEncrypted: encryptNote(note),
-          note: null,
-        },
-      });
+  const ip = getClientIp(request);
 
-      await auditLog("medication.glp1.update", {
-        userId: user.id,
-        ipAddress: ip,
-        details: {
-          medicationId: id,
-          kind: "doseChange",
-          doseChangeId: created.id,
-          doseValue,
-          doseUnit,
-        },
-      });
-
-      annotate({
-        action: {
-          name: "medication.glp1.doseChange.create",
-          entity_type: "medication_dose_change",
-          entity_id: created.id,
-        },
-        meta: { medication_id: id, doseValue, doseUnit },
-      });
-
-      // A dose change shifts the daily-dose estimate the list payload's
-      // runway derivation uses. Hard-evict the medications + compliance
-      // buckets so the card reflects the new runway on the next read.
-      invalidateUserMedications(user.id, { evict: true });
-
-      return apiSuccess({ doseChange: shapeDoseChangeNote(created) }, 201);
-    }
-
-    // The schema's XOR refinement guarantees `inventory` is present
-    // when `doseChange` is not, so the non-null assertion is safe.
-    //
-    // DEPRECATED branch (v1.16.10): this writes the legacy
-    // MedicationInventoryEvent running-sum ledger. The per-item
-    // endpoints (`POST /api/medications/[id]/inventory`,
-    // `PATCH /api/medications/[id]/inventory/[itemId]`) replaced it;
-    // GET above and the Coach snapshot read the ledger only while the
-    // medication has zero inventory items. New callers must register
-    // containers instead of posting deltas.
-    const { delta, reason } = parsed.data.inventory!;
-    const created = await prisma.medicationInventoryEvent.create({
-      data: { medicationId: id, delta, reason },
+  if (parsed.data.doseChange) {
+    const { effectiveFrom, doseValue, doseUnit, note } = parsed.data.doseChange;
+    const created = await prisma.medicationDoseChange.create({
+      data: {
+        medicationId: id,
+        effectiveFrom,
+        doseValue,
+        doseUnit,
+        // Encrypt the titration note at rest; the plaintext column stays null.
+        noteEncrypted: encryptNote(note),
+        note: null,
+      },
     });
 
     await auditLog("medication.glp1.update", {
@@ -340,27 +309,70 @@ export const POST = apiHandler(
       ipAddress: ip,
       details: {
         medicationId: id,
-        kind: "inventory",
-        inventoryEventId: created.id,
-        delta,
-        reason,
+        kind: "doseChange",
+        doseChangeId: created.id,
+        doseValue,
+        doseUnit,
       },
     });
 
     annotate({
       action: {
-        name: "medication.glp1.inventory.create",
-        entity_type: "medication_inventory_event",
+        name: "medication.glp1.doseChange.create",
+        entity_type: "medication_dose_change",
         entity_id: created.id,
       },
-      meta: { medication_id: id, delta },
+      meta: { medication_id: id, doseValue, doseUnit },
     });
 
-    // A legacy ledger delta changes the stock the list payload reports
-    // for a medication with no per-item containers. Hard-evict so the
-    // card reflects it on the next read.
+    // A dose change shifts the daily-dose estimate the list payload's
+    // runway derivation uses. Hard-evict the medications + compliance
+    // buckets so the card reflects the new runway on the next read.
     invalidateUserMedications(user.id, { evict: true });
 
-    return apiSuccess({ inventory: created }, 201);
-  },
-);
+    return apiSuccess({ doseChange: shapeDoseChangeNote(created) }, 201);
+  }
+
+  // The schema's XOR refinement guarantees `inventory` is present
+  // when `doseChange` is not, so the non-null assertion is safe.
+  //
+  // DEPRECATED branch (v1.16.10): this writes the legacy
+  // MedicationInventoryEvent running-sum ledger. The per-item
+  // endpoints (`POST /api/medications/[id]/inventory`,
+  // `PATCH /api/medications/[id]/inventory/[itemId]`) replaced it;
+  // GET above and the Coach snapshot read the ledger only while the
+  // medication has zero inventory items. New callers must register
+  // containers instead of posting deltas.
+  const { delta, reason } = parsed.data.inventory!;
+  const created = await prisma.medicationInventoryEvent.create({
+    data: { medicationId: id, delta, reason },
+  });
+
+  await auditLog("medication.glp1.update", {
+    userId: user.id,
+    ipAddress: ip,
+    details: {
+      medicationId: id,
+      kind: "inventory",
+      inventoryEventId: created.id,
+      delta,
+      reason,
+    },
+  });
+
+  annotate({
+    action: {
+      name: "medication.glp1.inventory.create",
+      entity_type: "medication_inventory_event",
+      entity_id: created.id,
+    },
+    meta: { medication_id: id, delta },
+  });
+
+  // A legacy ledger delta changes the stock the list payload reports
+  // for a medication with no per-item containers. Hard-evict so the
+  // card reflects it on the next read.
+  invalidateUserMedications(user.id, { evict: true });
+
+  return apiSuccess({ inventory: created }, 201);
+}

src/lib/openapi/routes/cycle.ts

@@ -516,6 +516,7 @@ export const cyclePaths: NonNullable<ZodOpenApiObject["paths"]> = {
       },
     },
     post: {
+      parameters: [idempotencyKeyParameter],
       tags: ["Cycle"],
       summary: "Create a custom cycle symptom (v1.15.1)",
       description:
@@ -527,6 +528,7 @@ export const cyclePaths: NonNullable<ZodOpenApiObject["paths"]> = {
         },
       },
       responses: {
+        ...idempotentWrite(),
         "201": {
           description: "The created custom symptom.",
           content: {

src/lib/openapi/routes/medications/paths.ts

@@ -321,6 +321,7 @@ export const medicationPaths: NonNullable<ZodOpenApiObject["paths"]> = {
       },
     },
     post: {
+      parameters: [idempotencyKeyParameter],
       tags: ["Medications"],
       summary: "Record a titration step or a legacy stock correction",
       description:
@@ -331,6 +332,7 @@ export const medicationPaths: NonNullable<ZodOpenApiObject["paths"]> = {
         content: { "application/json": { schema: glp1PostBodySchema } },
       },
       responses: {
+        ...idempotentWrite(),
         ...recordRefusal(),
         "201": {
           description: