diff --git a/CHANGELOG.md b/CHANGELOG.md
index 97946122c..45d96f795 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -18,6 +18,12 @@
 
 ### Fixed
 
+- **Periods from Garmin and Oura open their cycles.** Period days imported
+  from a watch or a ring were stored as days only, so the cycle tracker saw
+  no cycle start, no lengths and no forecast. They now open and fill their
+  cycles like a period logged by hand, a finished Garmin period also marks
+  its last day, and periods imported earlier are repaired once on the next
+  start. A day you logged yourself is never changed. (#1333)
 - **Typing into the smoking history.** "When you stopped" only took text
   that was already a whole YYYY-MM month, so every keystroke was dropped
   and only a paste got in. The start year clamped each keystroke into its
diff --git a/src/lib/cycle/subordinate-period-days.ts b/src/lib/cycle/subordinate-period-days.ts
new file mode 100644
index 000000000..569451520
--- /dev/null
+++ b/src/lib/cycle/subordinate-period-days.ts
@@ -0,0 +1,113 @@
+/**
+ * Period days a wearable reports (Garmin, Oura), written as a SUBORDINATE
+ * source.
+ *
+ * `CycleDayLog` holds one canonical row per `(userId, date)`, and the shared
+ * upsert (`./day-log-write.ts`) partial-merges a re-post over whatever is
+ * stored regardless of source. An hourly poll going through it would demote a
+ * day the person logged themselves (their HEAVY re-tagged LIGHT on the next
+ * tick). So a wearable day is only ever CREATED, when no row exists for that
+ * date at all, and never updated.
+ *
+ * What the shared upsert does beyond the row itself happens here too, through
+ * the same functions: a created day is attributed to the cycle it falls in,
+ * and a first bleeding day opens its cycle (`ensureCycleForBleedingDay`),
+ * which closes the cycle before it and takes its own end from the one after
+ * it. Without that a period imported from a watch was a run of rows the
+ * engine never read: no cycle start, no lengths, no forecast.
+ */
+import { prisma } from "@/lib/db";
+import { getEvent } from "@/lib/logging/context";
+import type { FlowLevel } from "@/generated/prisma/client";
+
+import { ensureCycleForBleedingDay } from "./cycle-boundaries";
+import { findOwningCycleId } from "./cycle-attribution";
+
+/** The wearables that write period days under this rule. */
+export type SubordinateCycleSource = "GARMIN" | "OURA";
+
+/**
+ * The conservative "logged, intensity unknown" level: a detected bleeding day
+ * is at least light, never invented as MEDIUM or HEAVY.
+ */
+export const SUBORDINATE_PERIOD_FLOW: FlowLevel = "LIGHT";
+
+function isUniqueViolation(err: unknown): boolean {
+  return (
+    typeof err === "object" &&
+    err !== null &&
+    "code" in err &&
+    (err as { code?: unknown }).code === "P2002"
+  );
+}
+
+/**
+ * Create the period days no row covers yet, oldest first, each attributed to
+ * its cycle, and open the cycle a first bleeding day starts. Returns how many
+ * rows were created.
+ */
+export async function createSubordinatePeriodDays(
+  userId: string,
+  source: SubordinateCycleSource,
+  days: readonly string[],
+): Promise<number> {
+  if (days.length === 0) return 0;
+  const user = await prisma.user.findUnique({
+    where: { id: userId },
+    select: { timezone: true },
+  });
+  const tz = user?.timezone ?? null;
+  let created = 0;
+  for (const day of [...new Set(days)].sort()) {
+    try {
+      await prisma.cycleDayLog.create({
+        data: {
+          userId,
+          date: day,
+          tz,
+          source,
+          flow: SUBORDINATE_PERIOD_FLOW,
+          cycleId: await findOwningCycleId(userId, day),
+        },
+      });
+    } catch (err) {
+      // A row already exists: the person's own, an import's, or this
+      // source's earlier write. A wearable never overwrites.
+      if (isUniqueViolation(err)) continue;
+      getEvent()?.addWarning(
+        `${source.toLowerCase()}: cycle day-log create failed for ${userId} ${day}: ${err}`,
+      );
+      continue;
+    }
+    created += 1;
+    // After the create, so the opened cycle claims the row just written.
+    await ensureCycleForBleedingDay(userId, day, tz, {
+      flow: SUBORDINATE_PERIOD_FLOW,
+      intermenstrualBleeding: false,
+    });
+  }
+  return created;
+}
+
+/**
+ * Stamp the last day of a finished period on the cycle that opens at
+ * `start`, when that cycle has no period end yet. A person's own end, or one
+ * an earlier pass stamped, stays. Returns whether a stamp was written.
+ */
+export async function stampSubordinatePeriodEnd(
+  userId: string,
+  start: string,
+  lastDay: string,
+): Promise<boolean> {
+  if (lastDay < start) return false;
+  const stamped = await prisma.menstrualCycle.updateMany({
+    where: {
+      userId,
+      startDate: start,
+      deletedAt: null,
+      periodEndDate: null,
+    },
+    data: { periodEndDate: lastDay, syncVersion: { increment: 1 } },
+  });
+  return stamped.count > 0;
+}
diff --git a/src/lib/garmin/__tests__/map.test.ts b/src/lib/garmin/__tests__/map.test.ts
index 6a01d2e10..83050b5ee 100644
--- a/src/lib/garmin/__tests__/map.test.ts
+++ b/src/lib/garmin/__tests__/map.test.ts
@@ -370,13 +370,24 @@ describe("cycle summary", () => {
         "2026-10-13",
         "2026-10-14",
       ],
+      ended: true,
     });
-    expect(
-      periodFromGarminCycleSummary(
-        { startDate: "2026-11-03", periodLength: 5 },
-        "2026-11-04",
-      )?.days,
-    ).toEqual(["2026-11-03", "2026-11-04"]);
+    const ongoing = periodFromGarminCycleSummary(
+      { startDate: "2026-11-03", periodLength: 5 },
+      "2026-11-04",
+    );
+    expect(ongoing?.days).toEqual(["2026-11-03", "2026-11-04"]);
+    expect(ongoing?.ended).toBe(false);
+  });
+
+  it("calls a period ended only once its last day is past", () => {
+    const summary = { startDate: "2026-11-01", periodLength: 4 };
+    expect(periodFromGarminCycleSummary(summary, "2026-11-04")?.ended).toBe(
+      false,
+    );
+    expect(periodFromGarminCycleSummary(summary, "2026-11-05")?.ended).toBe(
+      true,
+    );
   });
 
   it("imports nothing from a predicted cycle or a pregnancy", () => {
diff --git a/src/lib/garmin/cycle-sync.ts b/src/lib/garmin/cycle-sync.ts
index b76c78f21..a826847e0 100644
--- a/src/lib/garmin/cycle-sync.ts
+++ b/src/lib/garmin/cycle-sync.ts
@@ -4,7 +4,10 @@
  * import (`src/lib/oura/cycle-sync.ts`): a day is only ever CREATED when no
  * `CycleDayLog` row exists for it at all (any source), and never updated, so
  * a person's own entry always wins and an hourly poll can never demote it.
- * No `MenstrualCycle` span is created; cycle spans stay an explicit action.
+ * The write goes through `createSubordinatePeriodDays`, which attributes each
+ * created day to its cycle and opens the cycle a first bleeding day starts,
+ * as every other cycle writer does. A finished period also stamps its last
+ * day on that cycle, when the cycle has no period end yet.
  *
  * `GET /periodichealth-service/menstrualcycle/summary/{date}` describes the
  * cycle a date falls in: its start and its period length. A cycle Garmin
@@ -16,15 +19,15 @@
  * Gated behind the cycle module (`isCycleAvailableForUser`), checked before
  * Garmin is asked, so an account with cycle tracking off costs no request.
  */
-import { prisma } from "@/lib/db";
-import { getEvent } from "@/lib/logging/context";
 import { isCycleAvailableForUser } from "@/lib/cycle/gate";
+import {
+  createSubordinatePeriodDays,
+  stampSubordinatePeriodEnd,
+} from "@/lib/cycle/subordinate-period-days";
 
 import { GARMIN_PATHS, shiftGarminDay, type GarminSession } from "./client";
 import type { GarminCycleDate, GarminCycleSummary } from "./wire-types";
 
-const GARMIN_PERIOD_FLOW = "LIGHT" as const;
-
 /** The longest period a single summary may claim before it is not believed. */
 const MAX_PERIOD_DAYS = 14;
 
@@ -53,6 +56,8 @@ export interface GarminCyclePeriod {
   start: string;
   /** The period's days, oldest first, none after `today`. */
   days: string[];
+  /** Every day of the period lies before `today`: its last day is known. */
+  ended: boolean;
 }
 
 /** The logged period a summary describes, or null when there is none. */
@@ -67,57 +72,33 @@ export function periodFromGarminCycleSummary(
   const length = summary.periodLength;
   if (typeof length !== "number" || !Number.isFinite(length)) return null;
   const n = Math.round(length);
-  if (n < 1 || n > MAX_PERIOD_DAYS) return { start, days: [] };
+  if (n < 1 || n > MAX_PERIOD_DAYS) return { start, days: [], ended: false };
   const days: string[] = [];
   for (let i = 0; i < n; i++) {
     const day = shiftGarminDay(start, i);
     if (day > today) break;
     days.push(day);
   }
-  return { start, days };
+  const ended = days.length === n && days[n - 1]! < today;
+  return { start, days, ended };
 }
 
-function isUniqueViolation(err: unknown): boolean {
-  return (
-    typeof err === "object" &&
-    err !== null &&
-    "code" in err &&
-    (err as { code?: unknown }).code === "P2002"
-  );
-}
-
-/** Create the period days no row covers yet. Returns how many were created. */
-export async function writeGarminPeriodDays(
+/**
+ * Write one period: create the days no row covers yet (opening and
+ * attributing its cycle), then stamp the period's end once it is over.
+ * Returns how many days were created.
+ */
+export async function writeGarminPeriod(
   userId: string,
-  days: readonly string[],
+  period: GarminCyclePeriod,
 ): Promise<number> {
-  if (days.length === 0) return 0;
-  const user = await prisma.user.findUnique({
-    where: { id: userId },
-    select: { timezone: true },
-  });
-  const tz = user?.timezone ?? null;
-  let created = 0;
-  for (const day of days) {
-    try {
-      await prisma.cycleDayLog.create({
-        data: {
-          userId,
-          date: day,
-          tz,
-          source: "GARMIN",
-          flow: GARMIN_PERIOD_FLOW,
-        },
-      });
-      created += 1;
-    } catch (err) {
-      // A row already exists: the person's own, an import's, or this
-      // module's earlier write. Garmin never overwrites.
-      if (isUniqueViolation(err)) continue;
-      getEvent()?.addWarning(
-        `garmin: cycle day-log create failed for ${userId} ${day}: ${err}`,
-      );
-    }
+  const created = await createSubordinatePeriodDays(
+    userId,
+    "GARMIN",
+    period.days,
+  );
+  if (period.ended) {
+    await stampSubordinatePeriodEnd(userId, period.start, period.days.at(-1)!);
   }
   return created;
 }
@@ -147,5 +128,5 @@ export async function syncGarminCycle(
   const summary = await readGarminCycleSummary(session, today);
   const period = periodFromGarminCycleSummary(summary, today);
   if (!period) return 0;
-  return writeGarminPeriodDays(userId, period.days);
+  return writeGarminPeriod(userId, period);
 }
diff --git a/src/lib/jobs/__tests__/queue-policy-tables.test.ts b/src/lib/jobs/__tests__/queue-policy-tables.test.ts
index 41c5b2f3d..b3e6004b6 100644
--- a/src/lib/jobs/__tests__/queue-policy-tables.test.ts
+++ b/src/lib/jobs/__tests__/queue-policy-tables.test.ts
@@ -114,12 +114,12 @@ describe("maintenance group queue policies", () => {
 
   // One-shot repairs on a fixed singleton key: a boot during a run must be
   // able to queue the next pass, so only queued duplicates collapse.
-  it.each([["lab-document-date-repair", "short"]])(
-    "%s is %s",
-    (queue, policy) => {
-      expectPolicy("maintenance", queue, policy);
-    },
-  );
+  it.each([
+    ["lab-document-date-repair", "short"],
+    ["wearable-cycle-repair", "short"],
+  ])("%s is %s", (queue, policy) => {
+    expectPolicy("maintenance", queue, policy);
+  });
 
   it("environment-fetch is deliberately left on standard", () => {
     // Its explicit-range backfill sends with no key at all, on purpose, so any
diff --git a/src/lib/jobs/garmin-backfill.ts b/src/lib/jobs/garmin-backfill.ts
index 7409a03d8..c9b37b029 100644
--- a/src/lib/jobs/garmin-backfill.ts
+++ b/src/lib/jobs/garmin-backfill.ts
@@ -44,7 +44,7 @@ import {
 import {
   periodFromGarminCycleSummary,
   readGarminCycleSummary,
-  writeGarminPeriodDays,
+  writeGarminPeriod,
 } from "@/lib/garmin/cycle-sync";
 import { garminUnavailableCode } from "@/lib/garmin/unavailable";
 import {
@@ -212,7 +212,7 @@ async function readStepWindow(
     const period = periodFromGarminCycleSummary(summary, progress.anchor);
     // No logged cycle at or before this day: the walk is over.
     if (!period || period.start > state.before) return null;
-    await writeGarminPeriodDays(userId, period.days);
+    await writeGarminPeriod(userId, period);
     state.before = shiftDateKey(period.start, -1);
     return 0;
   }
diff --git a/src/lib/jobs/queue-runtime.ts b/src/lib/jobs/queue-runtime.ts
index 94b0107d0..3f65887bc 100644
--- a/src/lib/jobs/queue-runtime.ts
+++ b/src/lib/jobs/queue-runtime.ts
@@ -493,6 +493,9 @@ export const QUEUE_RUNTIME: Readonly<Record<string, QueueRuntime>> = {
   "lab-document-date-repair": short(
     "Reads the document lab values still filed at their confirmation moment, a handful per account, and moves each with one update.",
   ),
+  "wearable-cycle-repair": short(
+    "Reads the wearable period days still without a cycle, a few hundred per account at most, and opens or attributes each with a short transaction.",
+  ),
   "measurement-maintenance": {
     runtime: "long",
     expireInSeconds: MEASUREMENT_MAINTENANCE_SEND_OPTIONS.expireInSeconds,
diff --git a/src/lib/jobs/registry/maintenance-discovery.ts b/src/lib/jobs/registry/maintenance-discovery.ts
index 2de44262a..d4dbbe866 100644
--- a/src/lib/jobs/registry/maintenance-discovery.ts
+++ b/src/lib/jobs/registry/maintenance-discovery.ts
@@ -86,6 +86,15 @@ export const MAINTENANCE_DISCOVERY: readonly BootDiscovery[] = [
         await import("@/lib/jobs/lab-document-date-repair")
       ).enqueueBootTimeLabDocumentDateRepair(),
   },
+  // Converges to nothing once the wearable period days have their cycles; a
+  // boot with none costs one query.
+  {
+    name: "wearable-cycle-repair",
+    run: async () =>
+      (
+        await import("@/lib/jobs/wearable-cycle-repair")
+      ).enqueueBootTimeWearableCycleRepair(),
+  },
   // Self-limiting and idempotent; a boot with no backlog costs one query.
   {
     name: "compaction-tombstone-purge",
diff --git a/src/lib/jobs/registry/maintenance-repairs.ts b/src/lib/jobs/registry/maintenance-repairs.ts
index 2d3224e86..d76cf7b14 100644
--- a/src/lib/jobs/registry/maintenance-repairs.ts
+++ b/src/lib/jobs/registry/maintenance-repairs.ts
@@ -5,6 +5,7 @@
  * something to repair.
  */
 import { LAB_DOCUMENT_DATE_REPAIR_QUEUE } from "@/lib/jobs/lab-document-date-repair-queue";
+import { WEARABLE_CYCLE_REPAIR_QUEUE } from "@/lib/jobs/wearable-cycle-repair-queue";
 
 import { defineJob, type JobDefinition } from "./define-job";
 
@@ -22,4 +23,17 @@ export const MAINTENANCE_REPAIR_JOBS: readonly JobDefinition[] = [
       (await import("@/lib/jobs/lab-document-date-repair"))
         .handleLabDocumentDateRepair,
   }),
+  // Wearable period days imported without the cycles they open.
+  defineJob({
+    queue: WEARABLE_CYCLE_REPAIR_QUEUE,
+    policy: {
+      policy: "short",
+      reason:
+        "Fixed singleton key; collapse queued duplicates only, so a boot during a run can queue the next one.",
+    },
+    work: { localConcurrency: 1 },
+    load: async () =>
+      (await import("@/lib/jobs/wearable-cycle-repair"))
+        .handleWearableCycleRepair,
+  }),
 ];
diff --git a/src/lib/jobs/subsystem-surface.ts b/src/lib/jobs/subsystem-surface.ts
index b94351e76..5296c702d 100644
--- a/src/lib/jobs/subsystem-surface.ts
+++ b/src/lib/jobs/subsystem-surface.ts
@@ -124,6 +124,7 @@ const subsystemSurface = {
   "compaction-tombstone-purge": { audience: "system" },
   "measurement-fold-repair": { audience: "system" },
   "lab-document-date-repair": { audience: "system" },
+  "wearable-cycle-repair": { audience: "system" },
   "measurement-maintenance": { audience: "system" },
   "pulse-day-mean": { audience: "system" },
   "medication-intake-import": { audience: "system" },
diff --git a/src/lib/jobs/wearable-cycle-repair-queue.ts b/src/lib/jobs/wearable-cycle-repair-queue.ts
new file mode 100644
index 000000000..d106718aa
--- /dev/null
+++ b/src/lib/jobs/wearable-cycle-repair-queue.ts
@@ -0,0 +1,9 @@
+/**
+ * The queue facts of `wearable-cycle-repair.ts`: its name and its one
+ * singleton key. They live apart from the job so the worker registry and the
+ * boot discovery can read them without loading it.
+ */
+export const WEARABLE_CYCLE_REPAIR_QUEUE = "wearable-cycle-repair";
+
+/** One pass covers every account, so there is only ever one job. */
+export const WEARABLE_CYCLE_REPAIR_SINGLETON_KEY = "wearable-cycle-repair";
diff --git a/src/lib/jobs/wearable-cycle-repair.ts b/src/lib/jobs/wearable-cycle-repair.ts
new file mode 100644
index 000000000..f4ed25108
--- /dev/null
+++ b/src/lib/jobs/wearable-cycle-repair.ts
@@ -0,0 +1,271 @@
+/**
+ * One-shot repair: period days Garmin or Oura imported before their write
+ * learned to open and attribute cycles.
+ *
+ * Both wearables wrote their period days as bare rows, past the seam every
+ * other cycle writer goes through (`ensureCycleForBleedingDay`), so an account
+ * whose periods came from a watch or a ring held day-logs and no cycle: no
+ * start, no lengths, no forecast. The write now goes through
+ * `createSubordinatePeriodDays`; this pass gives the rows written before it
+ * the cycles they should have opened, by the same rule, oldest first per
+ * account.
+ *
+ * A row is a candidate when it is a live GARMIN or OURA bleeding day without
+ * a cycle and the rule can still place it: either a cycle starts on or before
+ * it (the row only needs its attribution), or no cycle does and nothing in the
+ * way stops it opening one (`ensureCycleForBleedingDay` declines a day that
+ * lies too close before a later start without being the same period). A day
+ * the rule declines stays unattributed and drops out of the predicate, so the
+ * pass converges: a second run finds nothing, and a boot with nothing to
+ * repair costs one query.
+ *
+ * Only cycles and the `cycleId` link move. No day-log's own content is
+ * touched, a person's own rows included. A Garmin period whose cycle this pass
+ * opened and that is over (a later cycle has started) has its last day stamped
+ * as the period end, from the run of consecutive Garmin days at its start.
+ */
+import type { Job } from "pg-boss";
+
+import { Prisma, type PrismaClient } from "@/generated/prisma/client";
+import { activeAccountSql } from "@/lib/account-deletion/active-account";
+import { ensureCycleForBleedingDay } from "@/lib/cycle/cycle-boundaries";
+import { addDays } from "@/lib/cycle/day-math";
+import { stampSubordinatePeriodEnd } from "@/lib/cycle/subordinate-period-days";
+import { HARD_CYCLE_MIN, PERIOD_MAX } from "@/lib/cycle/types";
+import { prisma as defaultPrisma } from "@/lib/db";
+import { getGlobalBoss } from "@/lib/jobs/boss-instance";
+import { jobDone, jobFailed, type JobOutcome } from "@/lib/jobs/job-outcome";
+import { workerLog } from "@/lib/jobs/reminder/shared";
+import { annotate } from "@/lib/logging/context";
+import { withBackgroundEvent } from "@/lib/logging/background";
+
+import {
+  WEARABLE_CYCLE_REPAIR_QUEUE,
+  WEARABLE_CYCLE_REPAIR_SINGLETON_KEY,
+} from "./wearable-cycle-repair-queue";
+
+/** The longest run of Garmin days read as one period. */
+const MAX_PERIOD_RUN_DAYS = 14;
+
+interface CandidateRow {
+  id: string;
+  userId: string;
+  date: string;
+}
+
+/**
+ * The SQL half of the rule. `limit` turns it into the boot's existence check.
+ * The second arm mirrors `ensureCycleForBleedingDay`: with no cycle on or
+ * before the day, it opens one unless a later start lies within the hard
+ * minimum cycle length without being the same period.
+ */
+function candidateQuery(limit: number | null): Prisma.Sql {
+  return Prisma.sql`
+    SELECT d."id", d."user_id" AS "userId", d."date"
+    FROM "cycle_day_logs" d
+    WHERE d."source" IN ('GARMIN', 'OURA')
+      AND d."deleted_at" IS NULL
+      AND d."cycle_id" IS NULL
+      AND d."flow" IS NOT NULL
+      AND d."flow" NOT IN ('NONE', 'SPOTTING')
+      AND NOT d."intermenstrual_bleeding"
+      AND (
+        EXISTS (
+          SELECT 1 FROM "menstrual_cycles" c
+          WHERE c."user_id" = d."user_id" AND c."deleted_at" IS NULL
+            AND c."start_date" <= d."date"
+        )
+        OR NOT EXISTS (
+          SELECT 1 FROM "menstrual_cycles" c
+          WHERE c."user_id" = d."user_id" AND c."deleted_at" IS NULL
+            AND c."start_date" >= to_char(d."date"::date + ${PERIOD_MAX}::int, 'YYYY-MM-DD')
+            AND c."start_date" < to_char(d."date"::date + ${HARD_CYCLE_MIN}::int, 'YYYY-MM-DD')
+        )
+      )
+      AND ${activeAccountSql('d."user_id"')}
+    ORDER BY d."user_id", d."date"
+    ${limit === null ? Prisma.empty : Prisma.sql`LIMIT ${limit}`}
+  `;
+}
+
+export interface WearableCycleRepairResult {
+  /** Rows the SQL predicate returned. */
+  scanned: number;
+  /** Cycles a row opened. */
+  opened: number;
+  /** Rows given the cycle they fall in. */
+  attributed: number;
+  /** Garmin period ends stamped on an opened cycle. */
+  periodEnds: number;
+  /** Accounts touched. */
+  accounts: number;
+}
+
+/** The last day of the run of consecutive Garmin days starting at `start`. */
+async function garminRunEnd(
+  prisma: PrismaClient,
+  userId: string,
+  start: string,
+): Promise<string | null> {
+  const rows = await prisma.cycleDayLog.findMany({
+    where: {
+      userId,
+      source: "GARMIN",
+      deletedAt: null,
+      date: { gte: start, lt: addDays(start, MAX_PERIOD_RUN_DAYS) },
+    },
+    orderBy: { date: "asc" },
+    select: { date: true },
+  });
+  let end: string | null = null;
+  for (const row of rows) {
+    if (row.date !== (end === null ? start : addDays(end, 1))) break;
+    end = row.date;
+  }
+  return end;
+}
+
+/** Repair one account's rows, oldest first. */
+async function repairAccount(
+  prisma: PrismaClient,
+  userId: string,
+  rows: readonly CandidateRow[],
+  result: WearableCycleRepairResult,
+): Promise<void> {
+  const user = await prisma.user.findUnique({
+    where: { id: userId },
+    select: { timezone: true },
+  });
+  const tz = user?.timezone ?? null;
+  const openedGarminStarts: string[] = [];
+  for (const row of rows) {
+    // Re-read. A cycle opened for an earlier row claims every day after it
+    // until the next start, this one included, so a claimed row is still
+    // asked whether it starts a cycle of its own.
+    const live = await prisma.cycleDayLog.findFirst({
+      where: { id: row.id, deletedAt: null },
+      select: {
+        source: true,
+        flow: true,
+        intermenstrualBleeding: true,
+        cycleId: true,
+      },
+    });
+    if (!live) continue;
+    const opened = await ensureCycleForBleedingDay(userId, row.date, tz, {
+      flow: live.flow,
+      intermenstrualBleeding: live.intermenstrualBleeding,
+    });
+    if (opened) {
+      result.opened += 1;
+      if (live.source === "GARMIN") openedGarminStarts.push(row.date);
+      continue;
+    }
+    if (live.cycleId !== null) continue;
+    const owning = await prisma.menstrualCycle.findFirst({
+      where: { userId, deletedAt: null, startDate: { lte: row.date } },
+      orderBy: { startDate: "desc" },
+      select: { id: true },
+    });
+    if (!owning) continue;
+    const moved = await prisma.cycleDayLog.updateMany({
+      where: { id: row.id, cycleId: null },
+      data: { cycleId: owning.id, syncVersion: { increment: 1 } },
+    });
+    result.attributed += moved.count;
+  }
+  for (const start of openedGarminStarts) {
+    const cycle = await prisma.menstrualCycle.findFirst({
+      where: { userId, startDate: start, deletedAt: null },
+      select: { endDate: true },
+    });
+    // An open cycle may still be bleeding; the hourly sync stamps its end.
+    if (!cycle?.endDate) continue;
+    const end = await garminRunEnd(prisma, userId, start);
+    if (end && (await stampSubordinatePeriodEnd(userId, start, end))) {
+      result.periodEnds += 1;
+    }
+  }
+}
+
+/** The repair itself, across every account. */
+export async function repairWearableCycleDays(
+  prisma: PrismaClient = defaultPrisma,
+): Promise<WearableCycleRepairResult> {
+  const rows = await prisma.$queryRaw<CandidateRow[]>(candidateQuery(null));
+  const byUser = new Map<string, CandidateRow[]>();
+  for (const row of rows) {
+    const list = byUser.get(row.userId) ?? [];
+    list.push(row);
+    byUser.set(row.userId, list);
+  }
+  const result: WearableCycleRepairResult = {
+    scanned: rows.length,
+    opened: 0,
+    attributed: 0,
+    periodEnds: 0,
+    accounts: byUser.size,
+  };
+  for (const [userId, list] of byUser) {
+    await repairAccount(prisma, userId, list, result);
+  }
+  return result;
+}
+
+/** The queue handler: one run over every account. */
+export async function handleWearableCycleRepair(
+  _jobs: Job<Record<string, never>>[],
+  prisma: PrismaClient = defaultPrisma,
+): Promise<JobOutcome> {
+  return withBackgroundEvent("job.wearable_cycle_repair", async () => {
+    let result: WearableCycleRepairResult;
+    try {
+      result = await repairWearableCycleDays(prisma);
+    } catch (err) {
+      workerLog("error", "[wearable-cycle-repair] failed", err);
+      return jobFailed("wearable cycle repair failed", err);
+    }
+    workerLog(
+      "info",
+      `[wearable-cycle-repair] scanned=${result.scanned} opened=${result.opened} attributed=${result.attributed} periodEnds=${result.periodEnds} accounts=${result.accounts}`,
+    );
+    annotate({
+      action: { name: "cycle.wearableDays.repair" },
+      meta: { ...result },
+    });
+    return jobDone({
+      candidates_scanned: result.scanned,
+      // Cycles opened, rows attributed, period ends stamped, accounts.
+      created: result.opened,
+      linked: result.attributed,
+      updated: result.periodEnds,
+      users: result.accounts,
+    });
+  });
+}
+
+/**
+ * Boot discovery: one existence query, and the one job only when there is
+ * something to repair.
+ */
+export async function enqueueBootTimeWearableCycleRepair(
+  prisma: PrismaClient = defaultPrisma,
+): Promise<{ enqueued: boolean; error: string | null }> {
+  const boss = getGlobalBoss();
+  if (!boss) return { enqueued: false, error: null };
+  try {
+    const any = await prisma.$queryRaw<CandidateRow[]>(candidateQuery(1));
+    if (any.length === 0) return { enqueued: false, error: null };
+    const id = await boss.send(
+      WEARABLE_CYCLE_REPAIR_QUEUE,
+      {},
+      { singletonKey: WEARABLE_CYCLE_REPAIR_SINGLETON_KEY, retryLimit: 2 },
+    );
+    return { enqueued: id !== null, error: null };
+  } catch (err) {
+    return {
+      enqueued: false,
+      error: err instanceof Error ? err.message : String(err),
+    };
+  }
+}
diff --git a/src/lib/oura/__tests__/cycle-sync.test.ts b/src/lib/oura/__tests__/cycle-sync.test.ts
index 4319cbfed..ac926f39e 100644
--- a/src/lib/oura/__tests__/cycle-sync.test.ts
+++ b/src/lib/oura/__tests__/cycle-sync.test.ts
@@ -6,13 +6,21 @@
  */
 import { beforeEach, describe, expect, it, vi } from "vitest";
 
-const { fetchCyclePhasesMock, isCycleAvailableMock, findUserMock, createMock } =
-  vi.hoisted(() => ({
-    fetchCyclePhasesMock: vi.fn(),
-    isCycleAvailableMock: vi.fn(),
-    findUserMock: vi.fn(),
-    createMock: vi.fn(),
-  }));
+const {
+  fetchCyclePhasesMock,
+  isCycleAvailableMock,
+  findUserMock,
+  createMock,
+  ensureCycleMock,
+  owningCycleMock,
+} = vi.hoisted(() => ({
+  fetchCyclePhasesMock: vi.fn(),
+  isCycleAvailableMock: vi.fn(),
+  findUserMock: vi.fn(),
+  createMock: vi.fn(),
+  ensureCycleMock: vi.fn(),
+  owningCycleMock: vi.fn(),
+}));
 
 vi.mock("@/lib/db", () => ({
   prisma: {
@@ -21,6 +29,14 @@ vi.mock("@/lib/db", () => ({
   },
 }));
 
+vi.mock("@/lib/cycle/cycle-boundaries", () => ({
+  ensureCycleForBleedingDay: ensureCycleMock,
+}));
+
+vi.mock("@/lib/cycle/cycle-attribution", () => ({
+  findOwningCycleId: owningCycleMock,
+}));
+
 vi.mock("@/lib/cycle/gate", () => ({
   isCycleAvailableForUser: isCycleAvailableMock,
 }));
@@ -50,6 +66,8 @@ beforeEach(() => {
   isCycleAvailableMock.mockReset().mockResolvedValue(true);
   findUserMock.mockReset().mockResolvedValue({ timezone: "Europe/Berlin" });
   createMock.mockReset().mockResolvedValue({ id: "cdl-1" });
+  ensureCycleMock.mockReset().mockResolvedValue(null);
+  owningCycleMock.mockReset().mockResolvedValue(null);
 });
 
 describe("syncUserOuraCyclePhases", () => {
@@ -93,10 +111,41 @@ describe("syncUserOuraCyclePhases", () => {
         tz: "Europe/Berlin",
         source: "OURA",
         flow: "LIGHT",
+        cycleId: null,
       },
     });
   });
 
+  it("attributes a created day to its cycle and lets a first bleeding day open one", async () => {
+    fetchCyclePhasesMock.mockResolvedValue([
+      { day: "2026-06-05", phase: "menstrual" },
+    ]);
+    owningCycleMock.mockResolvedValue("cycle-before");
+    await syncUserOuraCyclePhases("u1", "tok", WINDOW);
+    expect(createMock).toHaveBeenCalledWith({
+      data: expect.objectContaining({ cycleId: "cycle-before" }),
+    });
+    expect(ensureCycleMock).toHaveBeenCalledWith(
+      "u1",
+      "2026-06-05",
+      "Europe/Berlin",
+      { flow: "LIGHT", intermenstrualBleeding: false },
+    );
+    // The inference runs after the create, so the opened cycle claims it.
+    expect(createMock.mock.invocationCallOrder[0]).toBeLessThan(
+      ensureCycleMock.mock.invocationCallOrder[0]!,
+    );
+  });
+
+  it("infers no cycle from a day it did not create", async () => {
+    fetchCyclePhasesMock.mockResolvedValue([
+      { day: "2026-06-05", phase: "menstrual" },
+    ]);
+    createMock.mockRejectedValue(uniqueViolation());
+    await syncUserOuraCyclePhases("u1", "tok", WINDOW);
+    expect(ensureCycleMock).not.toHaveBeenCalled();
+  });
+
   it("skips a day that already has ANY existing row (manual wins) — unique-violation swallowed silently", async () => {
     fetchCyclePhasesMock.mockResolvedValue([
       { day: "2026-06-05", phase: "menstrual" },
diff --git a/src/lib/oura/cycle-sync.ts b/src/lib/oura/cycle-sync.ts
index 5a8db8876..b2b33052a 100644
--- a/src/lib/oura/cycle-sync.ts
+++ b/src/lib/oura/cycle-sync.ts
@@ -17,45 +17,26 @@
  * So this module never touches the shared upsert helper. It only ever
  * CREATEs a day that has NO existing `CycleDayLog` row at all (any source),
  * and never updates a row it did not itself create. A day already owned by
- * this module (source = OURA) is left alone on re-sync too — the marker is
- * a fixed single-value hint (`flow: LIGHT`), not a corrigible reading, so
- * there is nothing to refresh. The whole path degenerates to a cheap
- * "create if absent, otherwise no-op".
+ * this module (source = OURA) is left alone on re-sync too: the marker is a
+ * fixed single-value hint (`flow: LIGHT`), not a corrigible reading, so there
+ * is nothing to refresh.
+ *
+ * The create goes through `createSubordinatePeriodDays`, which does what the
+ * shared upsert does around the row: the day is attributed to the cycle it
+ * falls in, and a first bleeding day opens its cycle, the same inference the
+ * single capture, the bulk drain, the Apple Health fold and the Health Connect
+ * import run. Oura reports no period length, so no period end is stamped.
  *
  * Gated behind the SAME two-layer cycle-module gate every other cycle
  * writer respects (`isCycleAvailableForUser`) so an operator-disabled
  * instance, or a user who turned cycle tracking off, never accumulates rows
- * from a background Oura poll. No `MenstrualCycle` span is ever created or
- * mutated here — mirrors the Apple Health importer precedent
- * (`src/lib/cycle/import-accumulator.ts`), which attributes day-logs to an
- * EXISTING cycle but never synthesises a new one from flow data either;
- * cycle-span creation stays an explicit user action
- * (`POST /api/cycle/period`).
+ * from a background Oura poll.
  */
-import { prisma } from "@/lib/db";
-import { getEvent } from "@/lib/logging/context";
 import { isCycleAvailableForUser } from "@/lib/cycle/gate";
+import { createSubordinatePeriodDays } from "@/lib/cycle/subordinate-period-days";
 import { fetchDailyCyclePhases } from "./client";
 import { derivePeriodDaysFromCyclePhases } from "./map";
 
-/** The conservative "logged but unspecified intensity" flow level — mirrors
- * the HealthKit `unspecified` → `LIGHT` boundary documented in
- * `healthkit-mapping.ts`: a detected-but-unmeasured bleeding day is at least
- * light flow, never invented as MEDIUM/HEAVY. */
-const OURA_PERIOD_FLOW = "LIGHT" as const;
-
-/** Prisma P2002 (unique constraint) detector, mirrored locally from
- * `day-log-write.ts` rather than imported — a two-line duplicate is cheaper
- * than coupling this module to that helper's internals. */
-function isUniqueViolation(err: unknown): boolean {
-  return (
-    typeof err === "object" &&
-    err !== null &&
-    "code" in err &&
-    (err as { code?: unknown }).code === "P2002"
-  );
-}
-
 /**
  * Sync one user's Oura `daily_cycle_phases` window into `CycleDayLog`.
  * Returns the count of days newly created.
@@ -88,36 +69,5 @@ export async function syncUserOuraCyclePhases(
   const available = await isCycleAvailableForUser(userId);
   if (!available) return 0;
 
-  const user = await prisma.user.findUnique({
-    where: { id: userId },
-    select: { timezone: true },
-  });
-  const tz = user?.timezone ?? null;
-
-  let created = 0;
-  for (const day of periodDays) {
-    try {
-      await prisma.cycleDayLog.create({
-        data: {
-          userId,
-          date: day,
-          tz,
-          source: "OURA",
-          flow: OURA_PERIOD_FLOW,
-        },
-      });
-      created += 1;
-    } catch (err) {
-      if (isUniqueViolation(err)) {
-        // A row already exists for this date — the user's own entry, an
-        // Apple Health import, or this module's own prior write. Never
-        // overwrite: Oura is a subordinate signal here.
-        continue;
-      }
-      getEvent()?.addWarning(
-        `oura: cycle day-log create failed for ${userId} ${day}: ${err}`,
-      );
-    }
-  }
-  return created;
+  return createSubordinatePeriodDays(userId, "OURA", periodDays);
 }
diff --git a/tests/integration/__golden__/queue-registration.json b/tests/integration/__golden__/queue-registration.json
index 0560c4642..5bb1305d3 100644
--- a/tests/integration/__golden__/queue-registration.json
+++ b/tests/integration/__golden__/queue-registration.json
@@ -1,5 +1,5 @@
 {
-  "registeredQueueCount": 129,
+  "registeredQueueCount": 130,
   "registeredQueues": [
     "account-deletion-purge",
     "achievement-unlock-sweep",
@@ -117,6 +117,7 @@
     "supplement-nutrient-recompute",
     "system-job-alert",
     "tls-pin-monitor",
+    "wearable-cycle-repair",
     "whoop-backfill",
     "whoop-cycle-sync",
     "whoop-oauth-state-cleanup",
@@ -1872,6 +1873,21 @@
       "retry_delay_max": null,
       "retry_limit": 2
     },
+    {
+      "dead_letter": null,
+      "deletion_seconds": 604800,
+      "expire_seconds": 900,
+      "heartbeat_seconds": null,
+      "name": "wearable-cycle-repair",
+      "notify": false,
+      "partition": false,
+      "policy": "short",
+      "retention_seconds": 1209600,
+      "retry_backoff": false,
+      "retry_delay": 0,
+      "retry_delay_max": null,
+      "retry_limit": 2
+    },
     {
       "dead_letter": null,
       "deletion_seconds": 604800,
@@ -3801,6 +3817,12 @@
         "pollingIntervalSeconds": 30
       }
     },
+    {
+      "queue": "wearable-cycle-repair",
+      "options": {
+        "localConcurrency": 1
+      }
+    },
     {
       "queue": "whoop-backfill",
       "options": {
diff --git a/tests/integration/garmin-sync.test.ts b/tests/integration/garmin-sync.test.ts
index 0fadd773c..33a572b80 100644
--- a/tests/integration/garmin-sync.test.ts
+++ b/tests/integration/garmin-sync.test.ts
@@ -77,6 +77,8 @@ const fake = vi.hoisted(() => ({
   rateLimitHit: -1,
   /** First day of the one logged cycle, relative to today. */
   cycleStart: "",
+  /** Several logged cycles instead of the one; when set, `cycleStart` is unused. */
+  cycles: [] as Array<{ start: string; periodLength: number }>,
   /**
    * The weigh-in shape: `spec` is Garmin's document (kilograms, no
    * `samplePk`, a string instant), `live` the shape seen on the live
@@ -260,6 +262,18 @@ function answer(path: string, q: URLSearchParams): unknown {
   if (path.startsWith("/periodichealth-service/menstrualcycle/summary/")) {
     if (fake.cycleStatus !== 200) return { status: fake.cycleStatus };
     const day = path.split("/").pop()!;
+    if (fake.cycles.length > 0) {
+      const at = [...fake.cycles]
+        .sort((a, b) => b.start.localeCompare(a.start))
+        .find((c) => c.start <= day);
+      return at
+        ? {
+            startDate: { localDate: at.start },
+            periodLength: at.periodLength,
+            predictedCycle: false,
+          }
+        : {};
+    }
     const cycleStart = fake.cycleStart;
     return day >= cycleStart
       ? { startDate: cycleStart, periodLength: 4, predictedCycle: false }
@@ -362,6 +376,7 @@ beforeEach(async () => {
   fake.today = new Date().toISOString().slice(0, 10);
   fake.historyFrom = addDays(fake.today, -20);
   fake.cycleStart = addDays(fake.today, -15);
+  fake.cycles = [];
   fake.weightShape = "spec";
   fake.extraWeighDays = [];
   fake.cycleStatus = 200;
@@ -596,6 +611,122 @@ describe("Garmin history backfill", () => {
   });
 });
 
+describe("Garmin cycle history", () => {
+  async function backfillToEnd() {
+    const { runGarminBackfillForUser } =
+      await import("@/lib/jobs/garmin-backfill");
+    for (let slice = 0; slice < 20; slice++) {
+      const user = await getPrismaClient().user.findUnique({
+        where: { id: USER_ID },
+        select: { garminBackfillCompletedAt: true },
+      });
+      if (user?.garminBackfillCompletedAt) return;
+      await runGarminBackfillForUser(USER_ID, () => false, slice);
+    }
+    throw new Error("backfill did not finish");
+  }
+
+  async function liveCycles() {
+    return getPrismaClient().menstrualCycle.findMany({
+      where: { userId: USER_ID, deletedAt: null },
+      orderBy: { startDate: "asc" },
+      select: {
+        id: true,
+        startDate: true,
+        endDate: true,
+        lengthDays: true,
+        periodEndDate: true,
+      },
+    });
+  }
+
+  it("opens a cycle per back-filled period, newest first, with lengths and a forecast", async () => {
+    await connectUser();
+    fake.historyFrom = addDays(fake.today, -100);
+    const starts = [-80, -52, -24].map((n) => addDays(fake.today, n));
+    fake.cycles = starts.map((start) => ({ start, periodLength: 5 }));
+    // A day the person logged inside the middle period.
+    const ownDay = addDays(starts[1]!, 2);
+    const prisma = getPrismaClient();
+    await prisma.cycleDayLog.create({
+      data: { userId: USER_ID, date: ownDay, flow: "HEAVY" },
+    });
+
+    await backfillToEnd();
+
+    const cycles = await liveCycles();
+    expect(
+      cycles.map((c) => [
+        c.startDate,
+        c.endDate,
+        c.lengthDays,
+        c.periodEndDate,
+      ]),
+    ).toEqual([
+      [starts[0], addDays(starts[1]!, -1), 28, addDays(starts[0]!, 4)],
+      [starts[1], addDays(starts[2]!, -1), 28, addDays(starts[1]!, 4)],
+      [starts[2], null, null, addDays(starts[2]!, 4)],
+    ]);
+    // Every Garmin day belongs to the period it is part of.
+    const days = await prisma.cycleDayLog.findMany({
+      where: { userId: USER_ID },
+      orderBy: { date: "asc" },
+      select: { date: true, source: true, flow: true, cycleId: true },
+    });
+    expect(days).toHaveLength(15);
+    for (const day of days) {
+      const owner = [...cycles].reverse().find((c) => c.startDate <= day.date);
+      expect(day.cycleId).toBe(owner?.id);
+    }
+    // The person's own day is theirs, as they logged it.
+    expect(days.find((d) => d.date === ownDay)).toMatchObject({
+      source: "MANUAL",
+      flow: "HEAVY",
+    });
+
+    const { getOrCreateCycleProfile } = await import("@/lib/cycle/profile");
+    await getOrCreateCycleProfile(USER_ID);
+    const { refreshPredictionCacheForUser } =
+      await import("@/lib/cycle/prediction-refresh");
+    expect(await refreshPredictionCacheForUser(USER_ID)).toBe("persisted");
+    const forecast = await prisma.cyclePrediction.findUnique({
+      where: { userId: USER_ID },
+    });
+    expect(forecast).not.toBeNull();
+
+    // A second full backfill changes nothing.
+    await prisma.user.update({
+      where: { id: USER_ID },
+      data: {
+        garminBackfillProgress: Prisma.DbNull,
+        garminBackfillCompletedAt: null,
+      },
+    });
+    await backfillToEnd();
+    expect(await liveCycles()).toEqual(cycles);
+    expect(await prisma.cycleDayLog.count({ where: { userId: USER_ID } })).toBe(
+      15,
+    );
+  });
+
+  it("opens the current cycle from the hourly sync and leaves its end open while bleeding", async () => {
+    await connectUser();
+    const start = addDays(fake.today, -1);
+    fake.cycles = [{ start, periodLength: 5 }];
+    const { syncUserGarmin } = await import("@/lib/garmin/sync");
+    await syncUserGarmin(USER_ID, { lookbackDays: 2 });
+    const cycles = await liveCycles();
+    expect(cycles).toHaveLength(1);
+    expect(cycles[0]).toMatchObject({ startDate: start, periodEndDate: null });
+    const days = await getPrismaClient().cycleDayLog.findMany({
+      where: { userId: USER_ID },
+      select: { cycleId: true },
+    });
+    expect(days).toHaveLength(2);
+    expect(days.every((d) => d.cycleId === cycles[0]!.id)).toBe(true);
+  });
+});
+
 describe("Garmin connect and disconnect", () => {
   function post(url: string, body?: unknown) {
     return new NextRequest(`http://localhost${url}`, {
diff --git a/tests/integration/wearable-cycle-repair.test.ts b/tests/integration/wearable-cycle-repair.test.ts
new file mode 100644
index 000000000..b9d95b54a
--- /dev/null
+++ b/tests/integration/wearable-cycle-repair.test.ts
@@ -0,0 +1,200 @@
+/**
+ * The one-shot repair of wearable period days imported without the cycles
+ * they open (real Postgres).
+ *
+ * Garmin and Oura used to write their period days as bare rows, so an
+ * account whose periods came from a watch or a ring held day-logs and no
+ * cycle. The repair opens the cycles those rows start, attributes the rest,
+ * stamps the end of a finished Garmin period, and touches no day-log's own
+ * content. A day the cycle rule declines stays as it is and drops out of the
+ * candidate set, so the boot check converges; a second run changes nothing.
+ */
+import { beforeEach, describe, expect, it, vi } from "vitest";
+
+import { getPrismaClient, truncateAllTables } from "./setup";
+
+const sends = vi.hoisted(() => [] as string[]);
+
+vi.mock("@/lib/jobs/boss-instance", () => ({
+  getGlobalBoss: () => ({
+    send: async (queue: string) => {
+      sends.push(queue);
+      return `job-${sends.length}`;
+    },
+  }),
+}));
+
+import {
+  enqueueBootTimeWearableCycleRepair,
+  repairWearableCycleDays,
+} from "@/lib/jobs/wearable-cycle-repair";
+
+const GARMIN_USER = "user-wearable-repair-garmin";
+const OURA_USER = "user-wearable-repair-oura";
+const BLOCKED_USER = "user-wearable-repair-blocked";
+
+const DAY_MS = 86_400_000;
+const addDays = (day: string, n: number) =>
+  new Date(Date.parse(`${day}T00:00:00Z`) + n * DAY_MS)
+    .toISOString()
+    .slice(0, 10);
+
+const GARMIN_STARTS = ["2026-07-01", "2026-07-29", "2026-08-26"];
+
+async function seedUser(id: string) {
+  await getPrismaClient().user.create({
+    data: {
+      id,
+      username: id,
+      email: `${id}@example.test`,
+      timezone: "UTC",
+      gender: "FEMALE",
+    },
+  });
+}
+
+/** Day-logs as a v1.47.0 import left them: no cycle. */
+async function orphanDays(
+  userId: string,
+  source: "GARMIN" | "OURA",
+  days: string[],
+) {
+  await getPrismaClient().cycleDayLog.createMany({
+    data: days.map((date) => ({
+      userId,
+      date,
+      tz: "UTC",
+      source,
+      flow: "LIGHT" as const,
+    })),
+  });
+}
+
+async function liveCycles(userId: string) {
+  return getPrismaClient().menstrualCycle.findMany({
+    where: { userId, deletedAt: null },
+    orderBy: { startDate: "asc" },
+    select: {
+      id: true,
+      startDate: true,
+      endDate: true,
+      lengthDays: true,
+      periodEndDate: true,
+      syncVersion: true,
+    },
+  });
+}
+
+beforeEach(async () => {
+  const prisma = getPrismaClient();
+  await truncateAllTables(prisma);
+  sends.length = 0;
+  for (const id of [GARMIN_USER, OURA_USER, BLOCKED_USER]) await seedUser(id);
+
+  await orphanDays(
+    GARMIN_USER,
+    "GARMIN",
+    GARMIN_STARTS.flatMap((start) =>
+      [0, 1, 2, 3, 4].map((i) => addDays(start, i)),
+    ).filter((d) => d !== "2026-07-31"),
+  );
+  // The person's own day inside the middle period, logged before any cycle.
+  await prisma.cycleDayLog.create({
+    data: {
+      userId: GARMIN_USER,
+      date: "2026-07-31",
+      flow: "HEAVY",
+      source: "MANUAL",
+    },
+  });
+
+  await orphanDays(OURA_USER, "OURA", ["2026-06-01", "2026-06-29"]);
+
+  // A Garmin day 15 days before a start the person tapped: too close to be a
+  // cycle of its own, too far to be the same period. The rule declines it.
+  await prisma.menstrualCycle.create({
+    data: { userId: BLOCKED_USER, startDate: "2026-09-16", tz: "UTC" },
+  });
+  await orphanDays(BLOCKED_USER, "GARMIN", ["2026-09-01"]);
+});
+
+describe("wearable cycle repair", () => {
+  it("gives orphaned wearable period days their cycles", async () => {
+    expect(await enqueueBootTimeWearableCycleRepair()).toEqual({
+      enqueued: true,
+      error: null,
+    });
+
+    const result = await repairWearableCycleDays();
+    expect(result).toMatchObject({ opened: 5, periodEnds: 2, accounts: 2 });
+
+    const garmin = await liveCycles(GARMIN_USER);
+    expect(
+      garmin.map((c) => [
+        c.startDate,
+        c.endDate,
+        c.lengthDays,
+        c.periodEndDate,
+      ]),
+    ).toEqual([
+      ["2026-07-01", "2026-07-28", 28, "2026-07-05"],
+      // The person's day breaks the Garmin run, so the end is the day before.
+      ["2026-07-29", "2026-08-25", 28, "2026-07-30"],
+      // Still open: the hourly sync stamps its end.
+      ["2026-08-26", null, null, null],
+    ]);
+    const prisma = getPrismaClient();
+    const days = await prisma.cycleDayLog.findMany({
+      where: { userId: GARMIN_USER },
+      orderBy: { date: "asc" },
+    });
+    for (const day of days) {
+      const owner = [...garmin].reverse().find((c) => c.startDate <= day.date);
+      expect(day.cycleId).toBe(owner!.id);
+    }
+    expect(days.find((d) => d.date === "2026-07-31")).toMatchObject({
+      source: "MANUAL",
+      flow: "HEAVY",
+    });
+
+    const oura = await liveCycles(OURA_USER);
+    expect(oura.map((c) => [c.startDate, c.lengthDays])).toEqual([
+      ["2026-06-01", 28],
+      ["2026-06-29", null],
+    ]);
+
+    // The declined day stays as it was and no longer counts as work.
+    const blocked = await prisma.cycleDayLog.findFirst({
+      where: { userId: BLOCKED_USER },
+    });
+    expect(blocked?.cycleId).toBeNull();
+    expect(await liveCycles(BLOCKED_USER)).toHaveLength(1);
+
+    sends.length = 0;
+    expect(await enqueueBootTimeWearableCycleRepair()).toEqual({
+      enqueued: false,
+      error: null,
+    });
+    expect(sends).toEqual([]);
+  });
+
+  it("changes nothing on a second run", async () => {
+    await repairWearableCycleDays();
+    const before = await liveCycles(GARMIN_USER);
+    const daysBefore = await getPrismaClient().cycleDayLog.findMany({
+      where: { userId: GARMIN_USER },
+      orderBy: { date: "asc" },
+      select: { id: true, cycleId: true, syncVersion: true, flow: true },
+    });
+    const again = await repairWearableCycleDays();
+    expect(again).toMatchObject({ scanned: 0, opened: 0, attributed: 0 });
+    expect(await liveCycles(GARMIN_USER)).toEqual(before);
+    expect(
+      await getPrismaClient().cycleDayLog.findMany({
+        where: { userId: GARMIN_USER },
+        orderBy: { date: "asc" },
+        select: { id: true, cycleId: true, syncVersion: true, flow: true },
+      }),
+    ).toEqual(daysBefore);
+  });
+});