diff --git a/src/app/api/auth/me/coach-prefs/__tests__/route.test.ts b/src/app/api/auth/me/coach-prefs/__tests__/route.test.ts
new file mode 100644
index 000000000..0eec03dd1
--- /dev/null
+++ b/src/app/api/auth/me/coach-prefs/__tests__/route.test.ts
@@ -0,0 +1,157 @@
+/**
+ * v1.32.22 (M4) — `PUT /api/auth/me/coach-prefs` optimistic concurrency.
+ *
+ * A full-replace endpoint hydrated from a stale GET (two tabs / two devices)
+ * clobbers silently; the base token 409s that. The guarded write covers BOTH
+ * `coachPrefsJson` AND the mirrored `insightsExcludeMetrics` column in one
+ * conditional update, so a 409 leaves both untouched together. A tokenless PUT
+ * keeps the prior unconditional write.
+ */
+import { beforeEach, describe, expect, it, vi } from "vitest";
+
+vi.mock("@/lib/db", () => ({
+  prisma: {
+    user: {
+      findUnique: vi.fn(),
+      update: vi.fn(),
+      updateMany: vi.fn(),
+    },
+  },
+}));
+
+vi.mock("@/lib/auth/session", () => ({ getSession: vi.fn() }));
+
+vi.mock("@/lib/logging/transports", () => ({ emitIfSampled: vi.fn() }));
+
+vi.mock("@/lib/db-compat", () => ({
+  ensureDbCompatibility: vi.fn().mockResolvedValue(undefined),
+}));
+
+vi.mock("@/lib/logging/context", async (importOriginal) => {
+  const actual = await importOriginal<typeof import("@/lib/logging/context")>();
+  return { ...actual, annotate: vi.fn() };
+});
+
+vi.mock("next/headers", () => ({
+  headers: vi.fn(async () => ({ get: () => null })),
+  cookies: vi.fn(async () => ({
+    get: () => undefined,
+    set: () => {},
+    delete: () => {},
+  })),
+}));
+
+import { GET, PUT } from "../route";
+import { prisma } from "@/lib/db";
+import { getSession } from "@/lib/auth/session";
+
+const SESSION_OK = {
+  session: { id: "sess-1", expiresAt: new Date(Date.now() + 3_600_000) },
+  user: { id: "user-1", username: "testuser", role: "USER" as const },
+};
+
+function mkPut(body: unknown): Request {
+  return new Request("http://localhost/api/auth/me/coach-prefs", {
+    method: "PUT",
+    body: JSON.stringify(body),
+    headers: { "Content-Type": "application/json" },
+  });
+}
+
+beforeEach(() => {
+  vi.clearAllMocks();
+  vi.mocked(getSession).mockResolvedValue(SESSION_OK as never);
+});
+
+describe("GET /api/auth/me/coach-prefs", () => {
+  it("returns the prefs plus the optimistic-concurrency token", async () => {
+    vi.mocked(prisma.user.findUnique).mockResolvedValue({
+      coachPrefsJson: null,
+      updatedAt: new Date("2026-07-24T10:00:00.000Z"),
+    } as never);
+
+    const res = await (GET as () => Promise<Response>)();
+    expect(res.status).toBe(200);
+    const env = (await res.json()) as {
+      data: { tone: string; updatedAt?: string };
+    };
+    expect(env.data.tone).toBe("warm");
+    expect(env.data.updatedAt).toBe("2026-07-24T10:00:00.000Z");
+  });
+});
+
+describe("PUT /api/auth/me/coach-prefs — optimistic concurrency", () => {
+  it("guards both columns in one conditional write and echoes the token", async () => {
+    vi.mocked(prisma.user.findUnique).mockResolvedValue({
+      updatedAt: new Date("2026-07-24T10:05:00.000Z"),
+    } as never);
+    vi.mocked(prisma.user.updateMany).mockResolvedValue({ count: 1 } as never);
+
+    const res = await (PUT as (r: Request) => Promise<Response>)(
+      mkPut({
+        excludeMetrics: ["weight"],
+        baseUpdatedAt: "2026-07-24T10:00:00.000Z",
+      }),
+    );
+    expect(res.status).toBe(200);
+    expect(prisma.user.updateMany).toHaveBeenCalledTimes(1);
+    const call = vi.mocked(prisma.user.updateMany).mock.calls[0]?.[0] as {
+      where: { id: string; updatedAt: Date };
+      data: { coachPrefsJson: unknown; insightsExcludeMetrics: string[] };
+    };
+    expect((call.where.updatedAt as Date).toISOString()).toBe(
+      "2026-07-24T10:00:00.000Z",
+    );
+    // Both mirror columns ride the SAME guarded update.
+    expect(call.data.coachPrefsJson).toBeTruthy();
+    expect(call.data.insightsExcludeMetrics).toEqual(["weight"]);
+    expect(prisma.user.update).not.toHaveBeenCalled();
+    const env = (await res.json()) as { data: { updatedAt: string } };
+    expect(env.data.updatedAt).toBe("2026-07-24T10:05:00.000Z");
+  });
+
+  it("interleaved writers: a stale token 409s and leaves BOTH columns untouched", async () => {
+    vi.mocked(prisma.user.updateMany).mockResolvedValue({ count: 0 } as never);
+
+    const res = await (PUT as (r: Request) => Promise<Response>)(
+      mkPut({
+        excludeMetrics: ["weight"],
+        baseUpdatedAt: "2026-07-24T08:00:00.000Z",
+      }),
+    );
+    expect(res.status).toBe(409);
+    const env = (await res.json()) as { meta?: { errorCode?: string } };
+    expect(env.meta?.errorCode).toBe("coach_prefs_conflict");
+    // Nothing written — the single guarded update matched no row.
+    expect(prisma.user.updateMany).toHaveBeenCalledTimes(1);
+    expect(prisma.user.update).not.toHaveBeenCalled();
+  });
+
+  it("keeps the unconditional write when the token is omitted (compat)", async () => {
+    vi.mocked(prisma.user.update).mockResolvedValue({
+      updatedAt: new Date("2026-07-24T11:00:00.000Z"),
+    } as never);
+
+    const res = await (PUT as (r: Request) => Promise<Response>)(
+      mkPut({ excludeMetrics: ["weight"] }),
+    );
+    expect(res.status).toBe(200);
+    expect(prisma.user.update).toHaveBeenCalledTimes(1);
+    const call = vi.mocked(prisma.user.update).mock.calls[0]?.[0] as {
+      data: { coachPrefsJson: unknown; insightsExcludeMetrics: string[] };
+    };
+    expect(call.data.insightsExcludeMetrics).toEqual(["weight"]);
+    expect(prisma.user.updateMany).not.toHaveBeenCalled();
+  });
+
+  it("422s a malformed base token without touching the row", async () => {
+    const res = await (PUT as (r: Request) => Promise<Response>)(
+      mkPut({ excludeMetrics: ["weight"], baseUpdatedAt: "not-a-date" }),
+    );
+    expect(res.status).toBe(422);
+    const env = (await res.json()) as { meta?: { errorCode?: string } };
+    expect(env.meta?.errorCode).toBe("invalid_base_updated_at");
+    expect(prisma.user.update).not.toHaveBeenCalled();
+    expect(prisma.user.updateMany).not.toHaveBeenCalled();
+  });
+});
diff --git a/src/app/api/auth/me/modules/__tests__/route.test.ts b/src/app/api/auth/me/modules/__tests__/route.test.ts
index d64f33bc5..3bc33635d 100644
--- a/src/app/api/auth/me/modules/__tests__/route.test.ts
+++ b/src/app/api/auth/me/modules/__tests__/route.test.ts
@@ -12,6 +12,7 @@ vi.mock("@/lib/db", () => ({
     user: {
       findUnique: vi.fn(),
       update: vi.fn(),
+      updateMany: vi.fn(),
     },
     cycleProfile: {
       findUnique: vi.fn(),
@@ -198,6 +199,7 @@ describe("PATCH /api/auth/me/modules", () => {
 
     expect(prisma.user.update).toHaveBeenCalledWith({
       where: { id: "user-1" },
+      select: { updatedAt: true },
       data: { modulePreferencesJson: { mood: false } },
     });
     expect(auditLog).toHaveBeenCalledWith(
@@ -220,6 +222,7 @@ describe("PATCH /api/auth/me/modules", () => {
 
     expect(prisma.user.update).toHaveBeenCalledWith({
       where: { id: "user-1" },
+      select: { updatedAt: true },
       data: { modulePreferencesJson: { glucose: false, sleep: false } },
     });
   });
@@ -234,6 +237,7 @@ describe("PATCH /api/auth/me/modules", () => {
 
     expect(prisma.user.update).toHaveBeenCalledWith({
       where: { id: "user-1" },
+      select: { updatedAt: true },
       data: { modulePreferencesJson: { glucose: true } },
     });
   });
@@ -310,7 +314,100 @@ describe("PATCH /api/auth/me/modules", () => {
 
     expect(prisma.user.update).toHaveBeenCalledWith({
       where: { id: "user-1" },
+      select: { updatedAt: true },
       data: { modulePreferencesJson: { sleep: false, labs: false } },
     });
   });
 });
+
+/**
+ * v1.32.22 (M3) — optimistic concurrency. The base token is stripped BEFORE
+ * the `.strict()` schema parse, so it never trips strict validation; a stale
+ * token 409s and writes nothing; a tokenless PATCH keeps the unconditional
+ * write.
+ */
+describe("PATCH /api/auth/me/modules — optimistic concurrency", () => {
+  it("guards on the base token and skips the unconditional write", async () => {
+    vi.mocked(getSession).mockResolvedValue(SESSION_OK as never);
+    primeUser({ modulePreferencesJson: null });
+    vi.mocked(prisma.user.updateMany).mockResolvedValue({ count: 1 } as never);
+
+    const res = await (PATCH as (r: Request) => Promise<Response>)(
+      mkPatch({ mood: false, baseUpdatedAt: "2026-07-24T10:00:00.000Z" }),
+    );
+    expect(res.status).toBe(200);
+    expect(prisma.user.updateMany).toHaveBeenCalledTimes(1);
+    const whereArg = vi.mocked(prisma.user.updateMany).mock.calls[0]?.[0]
+      ?.where as { id: string; updatedAt: Date };
+    expect(whereArg.id).toBe("user-1");
+    expect((whereArg.updatedAt as Date).toISOString()).toBe(
+      "2026-07-24T10:00:00.000Z",
+    );
+    expect(prisma.user.update).not.toHaveBeenCalled();
+  });
+
+  it("interleaved writers: the stale-base second writer gets 409 and clobbers nothing", async () => {
+    vi.mocked(getSession).mockResolvedValue(SESSION_OK as never);
+    primeUser({ modulePreferencesJson: null });
+    vi.mocked(prisma.user.updateMany).mockResolvedValue({ count: 0 } as never);
+
+    const res = await (PATCH as (r: Request) => Promise<Response>)(
+      mkPatch({ mood: false, baseUpdatedAt: "2026-07-24T08:00:00.000Z" }),
+    );
+    expect(res.status).toBe(409);
+    const env = (await res.json()) as { meta?: { errorCode?: string } };
+    expect(env.meta?.errorCode).toBe("modules_conflict");
+    expect(prisma.user.updateMany).toHaveBeenCalledTimes(1);
+    expect(prisma.user.update).not.toHaveBeenCalled();
+  });
+
+  it("keeps the unconditional write when the token is omitted (compat)", async () => {
+    vi.mocked(getSession).mockResolvedValue(SESSION_OK as never);
+    primeUser({ modulePreferencesJson: null });
+
+    const res = await (PATCH as (r: Request) => Promise<Response>)(
+      mkPatch({ mood: false }),
+    );
+    expect(res.status).toBe(200);
+    expect(prisma.user.update).toHaveBeenCalledTimes(1);
+    expect(prisma.user.updateMany).not.toHaveBeenCalled();
+  });
+
+  it("strips the token pre-parse: a token ALONE does not trip the strict schema", async () => {
+    vi.mocked(getSession).mockResolvedValue(SESSION_OK as never);
+    primeUser({ modulePreferencesJson: null });
+    vi.mocked(prisma.user.updateMany).mockResolvedValue({ count: 1 } as never);
+
+    const res = await (PATCH as (r: Request) => Promise<Response>)(
+      mkPatch({ mood: false, baseUpdatedAt: "2026-07-24T10:00:00.000Z" }),
+    );
+    // 200, not 422 — `baseUpdatedAt` was removed before the strict parse.
+    expect(res.status).toBe(200);
+  });
+
+  it("still 422s an unknown key even alongside a valid token (strict stays strict)", async () => {
+    vi.mocked(getSession).mockResolvedValue(SESSION_OK as never);
+    primeUser({ modulePreferencesJson: null });
+
+    const res = await (PATCH as (r: Request) => Promise<Response>)(
+      mkPatch({ notAModule: false, baseUpdatedAt: "2026-07-24T10:00:00.000Z" }),
+    );
+    expect(res.status).toBe(422);
+    expect(prisma.user.update).not.toHaveBeenCalled();
+    expect(prisma.user.updateMany).not.toHaveBeenCalled();
+  });
+
+  it("422s a malformed base token without touching the row", async () => {
+    vi.mocked(getSession).mockResolvedValue(SESSION_OK as never);
+    primeUser({ modulePreferencesJson: null });
+
+    const res = await (PATCH as (r: Request) => Promise<Response>)(
+      mkPatch({ mood: false, baseUpdatedAt: "not-a-date" }),
+    );
+    expect(res.status).toBe(422);
+    const env = (await res.json()) as { meta?: { errorCode?: string } };
+    expect(env.meta?.errorCode).toBe("invalid_base_updated_at");
+    expect(prisma.user.update).not.toHaveBeenCalled();
+    expect(prisma.user.updateMany).not.toHaveBeenCalled();
+  });
+});
diff --git a/src/app/api/auth/me/notification-prefs/__tests__/route.test.ts b/src/app/api/auth/me/notification-prefs/__tests__/route.test.ts
index c67287ba2..088cecd53 100644
--- a/src/app/api/auth/me/notification-prefs/__tests__/route.test.ts
+++ b/src/app/api/auth/me/notification-prefs/__tests__/route.test.ts
@@ -5,6 +5,7 @@ vi.mock("@/lib/db", () => ({
     user: {
       findUnique: vi.fn(),
       update: vi.fn(),
+      updateMany: vi.fn(),
     },
   },
   toJson: <T>(v: T) => v,
@@ -234,10 +235,13 @@ describe("PATCH /api/auth/me/notification-prefs", () => {
       measurementReminder: {
         clientManaged: false,
       },
+      // v1.32.22 (M1) — the write echoes the fresh optimistic-concurrency token.
+      updatedAt: expect.any(String),
     });
 
     expect(prisma.user.update).toHaveBeenCalledWith({
       where: { id: "user-1" },
+      select: { updatedAt: true },
       data: {
         notificationPrefs: {
           medication: {
@@ -365,6 +369,7 @@ describe("PATCH /api/auth/me/notification-prefs", () => {
 
     expect(prisma.user.update).toHaveBeenCalledWith({
       where: { id: "user-1" },
+      select: { updatedAt: true },
       data: {
         notificationPrefs: {
           medication: {
@@ -427,10 +432,13 @@ describe("PATCH /api/auth/me/notification-prefs", () => {
       measurementReminder: {
         clientManaged: false,
       },
+      // v1.32.22 (M1) — the write echoes the fresh optimistic-concurrency token.
+      updatedAt: expect.any(String),
     });
 
     expect(prisma.user.update).toHaveBeenCalledWith({
       where: { id: "user-1" },
+      select: { updatedAt: true },
       data: {
         notificationPrefs: {
           medication: {
@@ -476,6 +484,7 @@ describe("PATCH /api/auth/me/notification-prefs", () => {
 
     expect(prisma.user.update).toHaveBeenCalledWith({
       where: { id: "user-1" },
+      select: { updatedAt: true },
       data: {
         notificationPrefs: {
           medication: {
@@ -531,6 +540,7 @@ describe("PATCH /api/auth/me/notification-prefs", () => {
 
     expect(prisma.user.update).toHaveBeenCalledWith({
       where: { id: "user-1" },
+      select: { updatedAt: true },
       data: {
         notificationPrefs: expect.objectContaining({
           medication: {
@@ -588,3 +598,113 @@ describe("PATCH /api/auth/me/notification-prefs", () => {
     expect(prisma.user.update).not.toHaveBeenCalled();
   });
 });
+
+/**
+ * v1.32.22 (M1) — optimistic concurrency (issue #581 family). A PATCH carrying
+ * the `baseUpdatedAt` it was based on writes CONDITIONALLY on the stored row
+ * still carrying that token. The headline case: a concurrent web PATCH of a
+ * DIFFERENT category can no longer silently revert the iOS `clientManaged`
+ * flag (the double-reminder class). A tokenless PATCH keeps the prior
+ * unconditional write — the iOS-compat arm.
+ */
+describe("PATCH /api/auth/me/notification-prefs — optimistic concurrency", () => {
+  function mkTokenedPatch(body: unknown, baseUpdatedAt?: string): Request {
+    return mkPatch(
+      baseUpdatedAt !== undefined
+        ? { ...(body as object), baseUpdatedAt }
+        : body,
+    );
+  }
+
+  it("guards on the base token and echoes the advanced token", async () => {
+    vi.mocked(getSession).mockResolvedValue(SESSION_OK as never);
+    vi.mocked(prisma.user.findUnique)
+      // merge read
+      .mockResolvedValueOnce({ notificationPrefs: null } as never)
+      // post-write fresh-token read
+      .mockResolvedValueOnce({
+        updatedAt: new Date("2026-07-24T10:05:00.000Z"),
+      } as never);
+    vi.mocked(prisma.user.updateMany).mockResolvedValue({ count: 1 } as never);
+
+    const res = await (PATCH as (r: Request) => Promise<Response>)(
+      mkTokenedPatch(
+        { medication: { clientManaged: true } },
+        "2026-07-24T10:00:00.000Z",
+      ),
+    );
+    expect(res.status).toBe(200);
+
+    // Conditional write, no unconditional fallback.
+    expect(prisma.user.updateMany).toHaveBeenCalledTimes(1);
+    const whereArg = vi.mocked(prisma.user.updateMany).mock.calls[0]?.[0]
+      ?.where as { id: string; updatedAt: Date };
+    expect(whereArg.id).toBe("user-1");
+    expect((whereArg.updatedAt as Date).toISOString()).toBe(
+      "2026-07-24T10:00:00.000Z",
+    );
+    expect(prisma.user.update).not.toHaveBeenCalled();
+
+    const env = (await res.json()) as { data: { updatedAt: string } };
+    expect(env.data.updatedAt).toBe("2026-07-24T10:05:00.000Z");
+  });
+
+  it("regression: a stale-token web write does NOT revert the iOS clientManaged flag", async () => {
+    // iOS set medication.clientManaged = true (row now carries it). A web card
+    // PATCH based on a pre-iOS read of a DIFFERENT category arrives with a stale
+    // token: it must 409 and write NOTHING, so clientManaged survives.
+    vi.mocked(getSession).mockResolvedValue(SESSION_OK as never);
+    vi.mocked(prisma.user.findUnique).mockResolvedValue({
+      notificationPrefs: { medication: { clientManaged: true } },
+    } as never);
+    vi.mocked(prisma.user.updateMany).mockResolvedValue({ count: 0 } as never);
+
+    const res = await (PATCH as (r: Request) => Promise<Response>)(
+      mkTokenedPatch({ mood: { reminderHour: 9 } }, "2026-07-24T08:00:00.000Z"),
+    );
+    expect(res.status).toBe(409);
+    const env = (await res.json()) as {
+      data: null;
+      meta?: { errorCode?: string };
+    };
+    expect(env.data).toBeNull();
+    expect(env.meta?.errorCode).toBe("notification_prefs_conflict");
+
+    // The guarded write matched no row; nothing was written, so the persisted
+    // clientManaged flag is untouched.
+    expect(prisma.user.updateMany).toHaveBeenCalledTimes(1);
+    expect(prisma.user.update).not.toHaveBeenCalled();
+  });
+
+  it("compat: the SAME second write TOKENLESS still lands (old clients keep last-write-wins)", async () => {
+    // Deliberate: a tokenless client keeps the pre-guard race. This pins that
+    // the clobber for old clients is a documented choice, not an accident.
+    vi.mocked(getSession).mockResolvedValue(SESSION_OK as never);
+    vi.mocked(prisma.user.findUnique).mockResolvedValue({
+      notificationPrefs: { medication: { clientManaged: true } },
+    } as never);
+    vi.mocked(prisma.user.update).mockResolvedValue({
+      updatedAt: new Date("2026-07-24T11:00:00.000Z"),
+    } as never);
+
+    const res = await (PATCH as (r: Request) => Promise<Response>)(
+      mkPatch({ mood: { reminderHour: 9 } }),
+    );
+    expect(res.status).toBe(200);
+    expect(prisma.user.update).toHaveBeenCalledTimes(1);
+    expect(prisma.user.updateMany).not.toHaveBeenCalled();
+  });
+
+  it("422s a malformed base token without touching the row", async () => {
+    vi.mocked(getSession).mockResolvedValue(SESSION_OK as never);
+
+    const res = await (PATCH as (r: Request) => Promise<Response>)(
+      mkTokenedPatch({ medication: { clientManaged: true } }, "not-a-date"),
+    );
+    expect(res.status).toBe(422);
+    const env = (await res.json()) as { meta?: { errorCode?: string } };
+    expect(env.meta?.errorCode).toBe("invalid_base_updated_at");
+    expect(prisma.user.updateMany).not.toHaveBeenCalled();
+    expect(prisma.user.update).not.toHaveBeenCalled();
+  });
+});
diff --git a/src/app/api/medications/[id]/inventory/[itemId]/__tests__/route.test.ts b/src/app/api/medications/[id]/inventory/[itemId]/__tests__/route.test.ts
index ff22da059..ad3f124ce 100644
--- a/src/app/api/medications/[id]/inventory/[itemId]/__tests__/route.test.ts
+++ b/src/app/api/medications/[id]/inventory/[itemId]/__tests__/route.test.ts
@@ -9,16 +9,23 @@
 import { describe, it, expect, vi, beforeEach } from "vitest";
 import { NextRequest } from "next/server";
 
-vi.mock("@/lib/db", () => ({
-  prisma: {
+vi.mock("@/lib/db", () => {
+  // v1.32.22 (M5) — the PATCH / DELETE now run inside `prisma.$transaction`
+  // that takes the per-medication advisory lock. The mock transaction runs the
+  // callback with the base client as the tx, so the existing model mocks apply
+  // inside the transaction and `$queryRaw` (the advisory lock) is observable.
+  const prisma: Record<string, unknown> = {
     medication: { findUnique: vi.fn() },
     medicationInventoryItem: {
       findUnique: vi.fn(),
       update: vi.fn(),
       delete: vi.fn(),
     },
-  },
-}));
+    $queryRaw: vi.fn(),
+    $transaction: vi.fn((fn: (tx: unknown) => unknown) => fn(prisma)),
+  };
+  return { prisma };
+});
 
 vi.mock("@/lib/auth/session", () => ({ getSession: vi.fn() }));
 vi.mock("@/lib/auth/audit", () => ({
@@ -52,11 +59,16 @@ vi.mock("next/headers", () => ({
   })),
 }));
 
-import { PATCH } from "../route";
+import { PATCH, DELETE } from "../route";
 import { prisma } from "@/lib/db";
 import { getSession } from "@/lib/auth/session";
 import { checkRateLimit } from "@/lib/rate-limit";
 
+const prismaTx = prisma as unknown as {
+  $queryRaw: ReturnType<typeof vi.fn>;
+  $transaction: ReturnType<typeof vi.fn>;
+};
+
 const SESSION_OK = {
   session: { id: "sess-1", expiresAt: new Date(Date.now() + 3_600_000) },
   user: { id: "user-1", username: "tester", role: "USER" as const },
@@ -76,6 +88,11 @@ const ROUTE_CTX = {
 
 beforeEach(() => {
   vi.resetAllMocks();
+  // `resetAllMocks` clears the transaction implementation — re-establish it so
+  // the callback still runs with the base client as the tx.
+  prismaTx.$transaction.mockImplementation((fn: (tx: unknown) => unknown) =>
+    fn(prisma),
+  );
   vi.mocked(getSession).mockResolvedValue(SESSION_OK as never);
   vi.mocked(checkRateLimit).mockResolvedValue({ allowed: true } as never);
   vi.mocked(prisma.medicationInventoryItem.findUnique).mockResolvedValue({
@@ -244,3 +261,95 @@ describe("PATCH /api/medications/[id]/inventory/[itemId] — carton labelling",
     expect("doseStrength" in arg.data).toBe(false);
   });
 });
+
+/**
+ * v1.32.22 (M5) — the stock-correction PATCH and the DELETE route their
+ * read-compose-write through the SAME per-medication advisory lock that
+ * `consumeForIntake` takes, so an absolute stock write can no longer clobber a
+ * concurrent dose decrement. These pin the routing: the write runs inside a
+ * transaction that takes the advisory lock BEFORE it reads + writes.
+ */
+describe("PATCH / DELETE inventory — advisory-lock serialisation (M5)", () => {
+  beforeEach(() => {
+    vi.mocked(prisma.medicationInventoryItem.findUnique).mockResolvedValue({
+      id: "i1",
+      medicationId: "m1",
+      userId: "user-1",
+      firstUseAt: null,
+      state: "IN_USE",
+      unitsTotal: 4,
+      unitsRemaining: 3,
+      printedExpiry: null,
+      notes: null,
+    } as never);
+    vi.mocked(prisma.medicationInventoryItem.update).mockImplementation(
+      (async (args: { data: Record<string, unknown> }) => ({
+        id: "i1",
+        ...args.data,
+      })) as never,
+    );
+    vi.mocked(prisma.medicationInventoryItem.delete).mockResolvedValue({
+      id: "i1",
+    } as never);
+  });
+
+  it("takes the medication advisory lock inside a transaction before the write", async () => {
+    const res = await PATCH(patchReq({ unitsRemaining: 1 }), ROUTE_CTX);
+    expect(res.status).toBe(200);
+
+    // One transaction, one advisory-lock query.
+    expect(prismaTx.$transaction).toHaveBeenCalledTimes(1);
+    expect(prismaTx.$queryRaw).toHaveBeenCalledTimes(1);
+
+    // The lock SQL is the canonical `pg_advisory_xact_lock` — proves the route
+    // shares the intake hook's key rather than re-deriving one.
+    const sql = prismaTx.$queryRaw.mock.calls[0]?.[0] as {
+      strings?: string[];
+    };
+    expect((sql.strings ?? []).join("")).toContain("pg_advisory_xact_lock");
+
+    // Lock is acquired BEFORE the row update (serialises against a concurrent
+    // consume decrement).
+    const lockOrder = prismaTx.$queryRaw.mock.invocationCallOrder[0];
+    const updateOrder = vi.mocked(prisma.medicationInventoryItem.update).mock
+      .invocationCallOrder[0];
+    expect(lockOrder).toBeLessThan(updateOrder);
+  });
+
+  it("re-reads the row INSIDE the locked transaction", async () => {
+    await PATCH(patchReq({ unitsRemaining: 1 }), ROUTE_CTX);
+    // The ownership re-read runs after the lock is taken.
+    const lockOrder = prismaTx.$queryRaw.mock.invocationCallOrder[0];
+    const readOrder = vi.mocked(prisma.medicationInventoryItem.findUnique).mock
+      .invocationCallOrder[0];
+    expect(lockOrder).toBeLessThan(readOrder);
+  });
+
+  it("DELETE takes the same lock before deleting", async () => {
+    const res = await DELETE(patchReq({}), ROUTE_CTX);
+    expect(res.status).toBe(200);
+    expect(prismaTx.$queryRaw).toHaveBeenCalledTimes(1);
+    const lockOrder = prismaTx.$queryRaw.mock.invocationCallOrder[0];
+    const deleteOrder = vi.mocked(prisma.medicationInventoryItem.delete).mock
+      .invocationCallOrder[0];
+    expect(lockOrder).toBeLessThan(deleteOrder);
+  });
+
+  it("still 404s an item owned by another user (checked inside the lock)", async () => {
+    vi.mocked(prisma.medicationInventoryItem.findUnique).mockResolvedValue({
+      id: "i1",
+      medicationId: "m1",
+      userId: "someone-else",
+      state: "IN_USE",
+      unitsTotal: 4,
+      unitsRemaining: 3,
+      printedExpiry: null,
+      firstUseAt: null,
+      notes: null,
+    } as never);
+
+    const res = await PATCH(patchReq({ unitsRemaining: 1 }), ROUTE_CTX);
+    expect(res.status).toBe(404);
+    expect(prisma.medicationInventoryItem.update).not.toHaveBeenCalled();
+  });
+});
diff --git a/src/app/api/medications/[id]/inventory/__tests__/route.test.ts b/src/app/api/medications/[id]/inventory/__tests__/route.test.ts
index ecbe8bfa3..bb4926240 100644
--- a/src/app/api/medications/[id]/inventory/__tests__/route.test.ts
+++ b/src/app/api/medications/[id]/inventory/__tests__/route.test.ts
@@ -1,8 +1,12 @@
 import { describe, it, expect, vi, beforeEach } from "vitest";
 import { NextRequest } from "next/server";
 
-vi.mock("@/lib/db", () => ({
-  prisma: {
+vi.mock("@/lib/db", () => {
+  // v1.32.22 (M5) — the [itemId] PATCH / DELETE now run inside a transaction
+  // that takes the per-medication advisory lock. The mock transaction runs the
+  // callback with the base client as tx, and `$queryRaw` stands in for the
+  // advisory-lock query.
+  const prisma: Record<string, unknown> = {
     medication: { findUnique: vi.fn() },
     medicationInventoryItem: {
       findMany: vi.fn(),
@@ -11,8 +15,11 @@ vi.mock("@/lib/db", () => ({
       update: vi.fn(),
       delete: vi.fn(),
     },
-  },
-}));
+    $queryRaw: vi.fn(),
+    $transaction: vi.fn((fn: (tx: unknown) => unknown) => fn(prisma)),
+  };
+  return { prisma };
+});
 
 vi.mock("@/lib/auth/session", () => ({ getSession: vi.fn() }));
 
@@ -72,6 +79,12 @@ function jsonReq(url: string, body: unknown, method = "POST"): NextRequest {
 
 beforeEach(() => {
   vi.resetAllMocks();
+  // `resetAllMocks` clears the transaction implementation — re-establish it.
+  (
+    prisma as unknown as { $transaction: ReturnType<typeof vi.fn> }
+  ).$transaction.mockImplementation((fn: (tx: unknown) => unknown) =>
+    fn(prisma),
+  );
   vi.mocked(checkRateLimit).mockResolvedValue({
     allowed: true,
     remaining: 29,
diff --git a/src/app/api/mood/tags/__tests__/layout.test.ts b/src/app/api/mood/tags/__tests__/layout.test.ts
index e99571dde..03dab52c0 100644
--- a/src/app/api/mood/tags/__tests__/layout.test.ts
+++ b/src/app/api/mood/tags/__tests__/layout.test.ts
@@ -7,7 +7,7 @@ import { beforeEach, describe, expect, it, vi } from "vitest";
 import { NextRequest } from "next/server";
 
 const db = vi.hoisted(() => ({
-  user: { findUnique: vi.fn(), update: vi.fn() },
+  user: { findUnique: vi.fn(), update: vi.fn(), updateMany: vi.fn() },
   moodTagCategory: { findMany: vi.fn() },
 }));
 
@@ -103,6 +103,8 @@ describe("PUT /api/mood/tags/layout", () => {
     expect(res.status).toBe(200);
     expect(db.user.update).toHaveBeenCalledWith({
       where: { id: "user-1" },
+      // v1.32.22 (M2) — tokenless write echoes the fresh `updatedAt` token.
+      select: { updatedAt: true },
       data: {
         moodTagLayoutJson: {
           groupOrder: ["custom", "feelings"],
diff --git a/src/app/api/mood/tags/layout/__tests__/route.test.ts b/src/app/api/mood/tags/layout/__tests__/route.test.ts
new file mode 100644
index 000000000..2417e5b4d
--- /dev/null
+++ b/src/app/api/mood/tags/layout/__tests__/route.test.ts
@@ -0,0 +1,173 @@
+/**
+ * v1.32.22 (M2) — `PUT /api/mood/tags/layout` optimistic concurrency.
+ *
+ * The two manage cards write DIFFERENT fields of the same blob (group order
+ * vs placements) from the same page; a stale merge would resurrect the other
+ * card's overwritten field. The base token 409s that instead. A tokenless PUT
+ * keeps the prior unconditional write.
+ */
+import { beforeEach, describe, expect, it, vi } from "vitest";
+import { NextRequest } from "next/server";
+
+vi.mock("@/lib/db", () => ({
+  prisma: {
+    user: {
+      findUnique: vi.fn(),
+      update: vi.fn(),
+      updateMany: vi.fn(),
+    },
+    moodTagCategory: {
+      findMany: vi.fn(),
+    },
+  },
+  toJson: <T>(v: T) => v,
+}));
+
+vi.mock("@/lib/auth/session", () => ({ getSession: vi.fn() }));
+
+vi.mock("@/lib/logging/transports", () => ({ emitIfSampled: vi.fn() }));
+
+vi.mock("@/lib/db-compat", () => ({
+  ensureDbCompatibility: vi.fn().mockResolvedValue(undefined),
+}));
+
+vi.mock("@/lib/logging/context", async (importOriginal) => {
+  const actual = await importOriginal<typeof import("@/lib/logging/context")>();
+  return { ...actual, annotate: vi.fn() };
+});
+
+vi.mock("next/headers", () => ({
+  headers: vi.fn(async () => ({ get: () => null })),
+  cookies: vi.fn(async () => ({
+    get: () => undefined,
+    set: () => {},
+    delete: () => {},
+  })),
+}));
+
+import { GET, PUT } from "../route";
+import { prisma } from "@/lib/db";
+import { getSession } from "@/lib/auth/session";
+
+const SESSION_OK = {
+  session: { id: "sess-1", expiresAt: new Date(Date.now() + 3_600_000) },
+  user: { id: "user-1", username: "testuser", role: "USER" as const },
+};
+
+function mkPut(body: unknown): NextRequest {
+  return new NextRequest("http://localhost/api/mood/tags/layout", {
+    method: "PUT",
+    headers: { "content-type": "application/json" },
+    body: JSON.stringify(body),
+  });
+}
+
+beforeEach(() => {
+  vi.clearAllMocks();
+  vi.mocked(getSession).mockResolvedValue(SESSION_OK as never);
+  vi.mocked(prisma.moodTagCategory.findMany).mockResolvedValue([] as never);
+});
+
+describe("GET /api/mood/tags/layout", () => {
+  it("returns the layout plus the optimistic-concurrency token", async () => {
+    vi.mocked(prisma.user.findUnique).mockResolvedValue({
+      moodTagLayoutJson: { groupOrder: ["a", "b"], placements: {} },
+      updatedAt: new Date("2026-07-24T10:00:00.000Z"),
+    } as never);
+
+    const res = await (GET as () => Promise<Response>)();
+    expect(res.status).toBe(200);
+    const env = (await res.json()) as {
+      data: { groupOrder: string[]; updatedAt?: string };
+    };
+    expect(env.data.updatedAt).toBe("2026-07-24T10:00:00.000Z");
+  });
+
+  it("omits updatedAt for a fresh user (null row)", async () => {
+    vi.mocked(prisma.user.findUnique).mockResolvedValue({
+      moodTagLayoutJson: null,
+    } as never);
+
+    const res = await (GET as () => Promise<Response>)();
+    const env = (await res.json()) as {
+      data: { updatedAt?: string };
+    };
+    expect(env.data.updatedAt).toBeUndefined();
+  });
+});
+
+describe("PUT /api/mood/tags/layout — optimistic concurrency", () => {
+  it("guards on the base token and echoes the advanced token", async () => {
+    vi.mocked(prisma.user.findUnique)
+      // merge read
+      .mockResolvedValueOnce({ moodTagLayoutJson: null } as never)
+      // post-write fresh token
+      .mockResolvedValueOnce({
+        updatedAt: new Date("2026-07-24T10:05:00.000Z"),
+      } as never);
+    vi.mocked(prisma.user.updateMany).mockResolvedValue({ count: 1 } as never);
+
+    const res = await (PUT as (r: NextRequest) => Promise<Response>)(
+      mkPut({
+        groupOrder: ["a", "b"],
+        baseUpdatedAt: "2026-07-24T10:00:00.000Z",
+      }),
+    );
+    expect(res.status).toBe(200);
+    expect(prisma.user.updateMany).toHaveBeenCalledTimes(1);
+    const whereArg = vi.mocked(prisma.user.updateMany).mock.calls[0]?.[0]
+      ?.where as { id: string; updatedAt: Date };
+    expect((whereArg.updatedAt as Date).toISOString()).toBe(
+      "2026-07-24T10:00:00.000Z",
+    );
+    expect(prisma.user.update).not.toHaveBeenCalled();
+    const env = (await res.json()) as { data: { updatedAt: string } };
+    expect(env.data.updatedAt).toBe("2026-07-24T10:05:00.000Z");
+  });
+
+  it("interleaved writers: the stale-base second writer gets 409 and clobbers nothing", async () => {
+    vi.mocked(prisma.user.findUnique).mockResolvedValue({
+      moodTagLayoutJson: { groupOrder: ["a"], placements: {} },
+    } as never);
+    vi.mocked(prisma.user.updateMany).mockResolvedValue({ count: 0 } as never);
+
+    const res = await (PUT as (r: NextRequest) => Promise<Response>)(
+      mkPut({
+        placements: { a: ["t1"] },
+        baseUpdatedAt: "2026-07-24T08:00:00.000Z",
+      }),
+    );
+    expect(res.status).toBe(409);
+    const env = (await res.json()) as { meta?: { errorCode?: string } };
+    expect(env.meta?.errorCode).toBe("mood_tag_layout_conflict");
+    expect(prisma.user.updateMany).toHaveBeenCalledTimes(1);
+    expect(prisma.user.update).not.toHaveBeenCalled();
+  });
+
+  it("keeps the unconditional write when the token is omitted (compat)", async () => {
+    vi.mocked(prisma.user.findUnique).mockResolvedValue({
+      moodTagLayoutJson: null,
+    } as never);
+    vi.mocked(prisma.user.update).mockResolvedValue({
+      updatedAt: new Date("2026-07-24T11:00:00.000Z"),
+    } as never);
+
+    const res = await (PUT as (r: NextRequest) => Promise<Response>)(
+      mkPut({ groupOrder: ["a", "b"] }),
+    );
+    expect(res.status).toBe(200);
+    expect(prisma.user.update).toHaveBeenCalledTimes(1);
+    expect(prisma.user.updateMany).not.toHaveBeenCalled();
+  });
+
+  it("422s a malformed base token without touching the row", async () => {
+    const res = await (PUT as (r: NextRequest) => Promise<Response>)(
+      mkPut({ groupOrder: ["a"], baseUpdatedAt: "not-a-date" }),
+    );
+    expect(res.status).toBe(422);
+    const env = (await res.json()) as { meta?: { errorCode?: string } };
+    expect(env.meta?.errorCode).toBe("invalid_base_updated_at");
+    expect(prisma.user.update).not.toHaveBeenCalled();
+    expect(prisma.user.updateMany).not.toHaveBeenCalled();
+  });
+});
diff --git a/src/components/settings/__tests__/modules-section.test.tsx b/src/components/settings/__tests__/modules-section.test.tsx
index f1b7a97ab..88c93e4d1 100644
--- a/src/components/settings/__tests__/modules-section.test.tsx
+++ b/src/components/settings/__tests__/modules-section.test.tsx
@@ -38,7 +38,14 @@ const mutateSpy = vi.fn();
 const invalidateSpy = vi.fn();
 
 vi.mock("@tanstack/react-query", () => ({
-  useQueryClient: () => ({ invalidateQueries: invalidateSpy }),
+  useQueryClient: () => ({
+    invalidateQueries: invalidateSpy,
+    // v1.32.22 (M3) — the writer reads/seeds the optimistic-concurrency token
+    // via the query cache; no token seeded → tokenless (unconditional) write.
+    getQueryData: () => undefined,
+    setQueryData: vi.fn(),
+    removeQueries: vi.fn(),
+  }),
   useMutation: (config: MutationConfig) => {
     lastMutation = config;
     return { mutate: mutateSpy, isPending: false };
diff --git a/src/lib/insights/__tests__/comprehensive-briefing-grounding-disposal.test.ts b/src/lib/insights/__tests__/comprehensive-briefing-grounding-disposal.test.ts
index 5159ef7e3..1ad03b0e3 100644
--- a/src/lib/insights/__tests__/comprehensive-briefing-grounding-disposal.test.ts
+++ b/src/lib/insights/__tests__/comprehensive-briefing-grounding-disposal.test.ts
@@ -29,6 +29,13 @@ vi.mock("@/lib/db", () => ({
     user: {
       findUnique: (...a: unknown[]) => findUnique(...a),
       update: (...a: unknown[]) => userUpdate(...a),
+      // v1.32.22 (M6) — the cache commit is now a privacy-mode-guarded
+      // updateMany; record it on the same spy but return a matched count so the
+      // guard proceeds (mode unchanged in these tests).
+      updateMany: (...a: unknown[]) => {
+        userUpdate(...a);
+        return Promise.resolve({ count: 1 });
+      },
     },
     auditLog: { deleteMany: vi.fn() },
   },
diff --git a/src/lib/insights/__tests__/comprehensive-briefing-reroll.test.ts b/src/lib/insights/__tests__/comprehensive-briefing-reroll.test.ts
index 17fce6442..9b8e680b7 100644
--- a/src/lib/insights/__tests__/comprehensive-briefing-reroll.test.ts
+++ b/src/lib/insights/__tests__/comprehensive-briefing-reroll.test.ts
@@ -29,6 +29,13 @@ vi.mock("@/lib/db", () => ({
     user: {
       findUnique: (...a: unknown[]) => findUnique(...a),
       update: (...a: unknown[]) => userUpdate(...a),
+      // v1.32.22 (M6) — the cache commit is now a privacy-mode-guarded
+      // updateMany; record it on the same spy but return a matched count so the
+      // guard proceeds (mode unchanged in these tests).
+      updateMany: (...a: unknown[]) => {
+        userUpdate(...a);
+        return Promise.resolve({ count: 1 });
+      },
     },
     auditLog: { deleteMany: vi.fn() },
   },
diff --git a/src/lib/insights/__tests__/comprehensive-budget-refusal.test.ts b/src/lib/insights/__tests__/comprehensive-budget-refusal.test.ts
index 205fca7b1..7b439de55 100644
--- a/src/lib/insights/__tests__/comprehensive-budget-refusal.test.ts
+++ b/src/lib/insights/__tests__/comprehensive-budget-refusal.test.ts
@@ -46,6 +46,13 @@ vi.mock("@/lib/db", () => ({
     user: {
       findUnique: (...a: unknown[]) => findUnique(...a),
       update: (...a: unknown[]) => userUpdate(...a),
+      // v1.32.22 (M6) — the cache commit is now a privacy-mode-guarded
+      // updateMany; record it on the same spy but return a matched count so the
+      // guard proceeds (mode unchanged in these tests).
+      updateMany: (...a: unknown[]) => {
+        userUpdate(...a);
+        return Promise.resolve({ count: 1 });
+      },
     },
     auditLog: { deleteMany: vi.fn() },
   },
diff --git a/src/lib/insights/__tests__/comprehensive-generate-force.test.ts b/src/lib/insights/__tests__/comprehensive-generate-force.test.ts
index b952be436..049a1863c 100644
--- a/src/lib/insights/__tests__/comprehensive-generate-force.test.ts
+++ b/src/lib/insights/__tests__/comprehensive-generate-force.test.ts
@@ -36,6 +36,13 @@ vi.mock("@/lib/db", () => ({
     user: {
       findUnique: (...a: unknown[]) => findUnique(...a),
       update: (...a: unknown[]) => userUpdate(...a),
+      // v1.32.22 (M6) — the cache commit is now a privacy-mode-guarded
+      // updateMany; record it on the same spy but return a matched count so the
+      // guard proceeds (mode unchanged in these tests).
+      updateMany: (...a: unknown[]) => {
+        userUpdate(...a);
+        return Promise.resolve({ count: 1 });
+      },
     },
     auditLog: {
       deleteMany: (...a: unknown[]) => auditDeleteMany(...a),
diff --git a/src/lib/insights/__tests__/comprehensive-json-retry.test.ts b/src/lib/insights/__tests__/comprehensive-json-retry.test.ts
index cf1fb723b..7f4a3a8f2 100644
--- a/src/lib/insights/__tests__/comprehensive-json-retry.test.ts
+++ b/src/lib/insights/__tests__/comprehensive-json-retry.test.ts
@@ -27,6 +27,13 @@ vi.mock("@/lib/db", () => ({
     user: {
       findUnique: (...a: unknown[]) => findUnique(...a),
       update: (...a: unknown[]) => userUpdate(...a),
+      // v1.32.22 (M6) — the cache commit is now a privacy-mode-guarded
+      // updateMany; record it on the same spy but return a matched count so the
+      // guard proceeds (mode unchanged in these tests).
+      updateMany: (...a: unknown[]) => {
+        userUpdate(...a);
+        return Promise.resolve({ count: 1 });
+      },
     },
     auditLog: { deleteMany: vi.fn() },
   },
diff --git a/src/lib/insights/__tests__/comprehensive-privacy-flip.test.ts b/src/lib/insights/__tests__/comprehensive-privacy-flip.test.ts
new file mode 100644
index 000000000..fe7be5219
--- /dev/null
+++ b/src/lib/insights/__tests__/comprehensive-privacy-flip.test.ts
@@ -0,0 +1,221 @@
+/**
+ * v1.32.22 (M6) — a privacy-mode flip that lands WHILE a comprehensive
+ * generation is in flight must not be overwritten by that generation.
+ *
+ * The generation reads `insightsPrivacyMode` at snapshot time and builds its
+ * payload under that scope. `PUT /api/insights/settings` flips the mode and
+ * nulls the cache. If the in-flight generation then committed unconditionally
+ * it would stamp an old-scope briefing over the null the flip wrote. Every
+ * cache commit is now guarded on the mode still being what the generation
+ * read: a mismatch (simulated here by the guarded `updateMany` matching zero
+ * rows) returns `{ status: "skipped", reason: "privacy-mode-changed" }` and
+ * writes nothing.
+ */
+import { describe, it, expect, vi, beforeEach } from "vitest";
+
+const findUnique = vi.fn();
+const userUpdate = vi.fn();
+const userUpdateMany = vi.fn();
+const resolveProviderChain = vi.fn();
+const resolveProvider = vi.fn();
+const runRawCompletionWithFallback = vi.fn();
+const extractFeatures = vi.fn();
+const invalidateUserInsights = vi.fn();
+const annotate = vi.fn();
+
+vi.mock("@/lib/db", () => ({
+  prisma: {
+    $queryRaw: vi.fn(async () => [{ total_tokens: 0 }]),
+    $executeRaw: vi.fn(async () => 0),
+    user: {
+      findUnique: (...a: unknown[]) => findUnique(...a),
+      update: (...a: unknown[]) => userUpdate(...a),
+      // Controllable per test: `{ count: 0 }` emulates a privacy flip having
+      // advanced the guarded column since the generation read it.
+      updateMany: (...a: unknown[]) => userUpdateMany(...a),
+    },
+    auditLog: { deleteMany: vi.fn() },
+  },
+}));
+vi.mock("@/lib/ai/provider", () => ({
+  resolveProviderChain: (...a: unknown[]) => resolveProviderChain(...a),
+  resolveProvider: (...a: unknown[]) => resolveProvider(...a),
+}));
+vi.mock("@/lib/ai/provider-runner", () => ({
+  AllProvidersFailedError: class extends Error {},
+  runRawCompletionWithFallback: (...a: unknown[]) =>
+    runRawCompletionWithFallback(...a),
+}));
+vi.mock("@/lib/insights/features", () => ({
+  FeaturesPayloadTooLargeError: class extends Error {
+    sizeBytes = 0;
+  },
+  extractFeatures: (...a: unknown[]) => extractFeatures(...a),
+  BRIEFING_FEATURE_WINDOW_DAYS: 400,
+}));
+vi.mock("@/lib/insights/illness-cycle-briefing", () => ({
+  buildBriefingIllnessCycleContext: vi.fn().mockResolvedValue(null),
+  buildBriefingIllnessCyclePrompt: vi.fn().mockReturnValue(""),
+}));
+vi.mock("@/lib/insights/glp1-plateau", () => ({
+  detectGlp1Plateau: vi.fn(async () => null),
+  buildGlp1PlateauPrompt: vi.fn(() => ""),
+}));
+vi.mock("@/lib/ai/coach/about-me", () => ({
+  getSelfContextTextForUser: vi.fn(async () => null),
+  buildAboutMeInsightBlock: vi.fn(() => ""),
+}));
+vi.mock("@/lib/cache/invalidate", () => ({
+  invalidateUserInsights: (...a: unknown[]) => invalidateUserInsights(...a),
+}));
+vi.mock("@/lib/logging/context", async (importOriginal) => {
+  const actual = await importOriginal<typeof import("@/lib/logging/context")>();
+  return { ...actual, annotate: (...a: unknown[]) => annotate(...a) };
+});
+
+import { generateComprehensiveInsight } from "../comprehensive-generate";
+import { hashInsightSnapshot } from "../snapshot-hash";
+import { compactSections } from "@/lib/ai/prompts/compact-sections";
+
+const FEATURES = { weight: { count: 12, latest: 81.4, mean30: 82.1 } };
+const FEATURES_HASH = hashInsightSnapshot({
+  features: compactSections(FEATURES as unknown as Record<string, unknown>),
+  aboutMe: null,
+  comparisonBaseline: "none",
+  generationLocale: "de",
+});
+
+const todayKey = new Date().toISOString().slice(0, 10);
+
+const CACHED_WITH_BRIEFING = JSON.stringify({
+  summary: "stable summary",
+  dailyBriefing: {
+    paragraph: "Yesterday's phrasing.",
+    keyFindings: [{ headline: "BP steady", tone: "good" }],
+  },
+});
+
+function annotatedPrivacyChange(): boolean {
+  return annotate.mock.calls.some(
+    (c) =>
+      (c[0] as { action?: { name?: string } })?.action?.name ===
+      "insights.generate.privacy_mode_changed",
+  );
+}
+
+beforeEach(() => {
+  vi.clearAllMocks();
+  resolveProviderChain.mockResolvedValue([
+    { providerType: "openai", instance: {} },
+  ]);
+  resolveProvider.mockResolvedValue({ type: "none" });
+  extractFeatures.mockResolvedValue(FEATURES);
+  userUpdate.mockResolvedValue({});
+});
+
+describe("generateComprehensiveInsight — privacy-mode flip guard (M6)", () => {
+  it("main commit: refuses to write when the mode flipped, returns privacy-mode-changed", async () => {
+    findUnique.mockResolvedValue({
+      insightsPrivacyMode: "aggregated",
+      insightsCachedAt: new Date(Date.now() - 26 * 60 * 60 * 1000),
+      insightsCachedText: JSON.stringify({ dailyBriefing: { p: "old" } }),
+      insightsExcludeMetrics: [],
+      insightsSnapshotHash: "0".repeat(64), // changed → full generation
+    });
+    runRawCompletionWithFallback.mockResolvedValue({
+      result: {
+        content: JSON.stringify({ dailyBriefing: { p: "new" } }),
+        tokensUsed: 10,
+        providerType: "openai",
+        model: "m",
+      },
+      workingProvider: { providerType: "openai" },
+      fallbackHops: [],
+    });
+    // The flip landed: the guarded commit matches zero rows.
+    userUpdateMany.mockResolvedValue({ count: 0 });
+
+    const outcome = await generateComprehensiveInsight("u1", { locale: "de" });
+
+    expect(outcome).toEqual({
+      status: "skipped",
+      reason: "privacy-mode-changed",
+    });
+    // The generation reached the commit (provider was called) …
+    expect(runRawCompletionWithFallback).toHaveBeenCalledTimes(1);
+    // … the commit was the guarded update, keyed on the mode read …
+    expect(userUpdateMany).toHaveBeenCalledTimes(1);
+    const where = userUpdateMany.mock.calls[0][0].where as {
+      insightsPrivacyMode: string;
+    };
+    expect(where.insightsPrivacyMode).toBe("aggregated");
+    // … and it did NOT fall back to an unconditional write.
+    expect(userUpdate).not.toHaveBeenCalled();
+    expect(invalidateUserInsights).not.toHaveBeenCalled();
+    expect(annotatedPrivacyChange()).toBe(true);
+  });
+
+  it("main commit: control — with the mode unchanged the same generation commits", async () => {
+    findUnique.mockResolvedValue({
+      insightsPrivacyMode: "aggregated",
+      insightsCachedAt: new Date(Date.now() - 26 * 60 * 60 * 1000),
+      insightsCachedText: JSON.stringify({ dailyBriefing: { p: "old" } }),
+      insightsExcludeMetrics: [],
+      insightsSnapshotHash: "0".repeat(64),
+    });
+    runRawCompletionWithFallback.mockResolvedValue({
+      result: {
+        content: JSON.stringify({ dailyBriefing: { p: "new" } }),
+        tokensUsed: 10,
+        providerType: "openai",
+        model: "m",
+      },
+      workingProvider: { providerType: "openai" },
+      fallbackHops: [],
+    });
+    userUpdateMany.mockResolvedValue({ count: 1 });
+
+    const outcome = await generateComprehensiveInsight("u1", { locale: "de" });
+
+    expect(outcome).toEqual({ status: "generated", providerType: "openai" });
+    expect(userUpdateMany).toHaveBeenCalledTimes(1);
+    expect(invalidateUserInsights).toHaveBeenCalledWith("u1");
+    expect(annotatedPrivacyChange()).toBe(false);
+  });
+
+  it("reroll arm: a flip refuses the paragraph re-roll write too", async () => {
+    findUnique.mockResolvedValue({
+      insightsPrivacyMode: "aggregated",
+      insightsCachedAt: new Date(Date.now() - 26 * 60 * 60 * 1000),
+      insightsCachedText: CACHED_WITH_BRIEFING,
+      insightsExcludeMetrics: [],
+      insightsSnapshotHash: FEATURES_HASH, // unchanged → reroll path
+      insightsBriefingRerollDate: null,
+    });
+    runRawCompletionWithFallback.mockResolvedValue({
+      result: {
+        content: JSON.stringify({
+          dailyBriefing: { paragraph: "Today's fresh phrasing." },
+        }),
+        tokensUsed: 50,
+        providerType: "openai",
+        model: "m",
+      },
+      workingProvider: { providerType: "openai" },
+      fallbackHops: [],
+    });
+    userUpdateMany.mockResolvedValue({ count: 0 });
+
+    const outcome = await generateComprehensiveInsight("u1", { locale: "de" });
+
+    expect(outcome).toEqual({
+      status: "skipped",
+      reason: "privacy-mode-changed",
+    });
+    expect(userUpdateMany).toHaveBeenCalledTimes(1);
+    expect(invalidateUserInsights).not.toHaveBeenCalled();
+    expect(annotatedPrivacyChange()).toBe(true);
+    // Not marked as a used-today reroll, since nothing committed.
+    expect(todayKey).toBe(new Date().toISOString().slice(0, 10));
+  });
+});
diff --git a/src/lib/insights/__tests__/comprehensive-timeout-honored.test.ts b/src/lib/insights/__tests__/comprehensive-timeout-honored.test.ts
index e9c65af4a..2c8692e50 100644
--- a/src/lib/insights/__tests__/comprehensive-timeout-honored.test.ts
+++ b/src/lib/insights/__tests__/comprehensive-timeout-honored.test.ts
@@ -31,6 +31,13 @@ vi.mock("@/lib/db", () => ({
     user: {
       findUnique: (...a: unknown[]) => findUnique(...a),
       update: (...a: unknown[]) => userUpdate(...a),
+      // v1.32.22 (M6) — the cache commit is now a privacy-mode-guarded
+      // updateMany; record it on the same spy but return a matched count so the
+      // guard proceeds (mode unchanged in these tests).
+      updateMany: (...a: unknown[]) => {
+        userUpdate(...a);
+        return Promise.resolve({ count: 1 });
+      },
     },
     auditLog: { deleteMany: vi.fn(), create: vi.fn() },
   },
diff --git a/src/lib/insights/__tests__/comprehensive-warm-timeout.test.ts b/src/lib/insights/__tests__/comprehensive-warm-timeout.test.ts
index c7b385097..138aff034 100644
--- a/src/lib/insights/__tests__/comprehensive-warm-timeout.test.ts
+++ b/src/lib/insights/__tests__/comprehensive-warm-timeout.test.ts
@@ -33,6 +33,13 @@ vi.mock("@/lib/db", () => ({
     user: {
       findUnique: (...a: unknown[]) => findUnique(...a),
       update: (...a: unknown[]) => userUpdate(...a),
+      // v1.32.22 (M6) — the cache commit is now a privacy-mode-guarded
+      // updateMany; record it on the same spy but return a matched count so the
+      // guard proceeds (mode unchanged in these tests).
+      updateMany: (...a: unknown[]) => {
+        userUpdate(...a);
+        return Promise.resolve({ count: 1 });
+      },
     },
     auditLog: { deleteMany: vi.fn() },
   },