diff --git a/docs/api/openapi.yaml b/docs/api/openapi.yaml
index 0a6360a77..5e957b8d5 100644
--- a/docs/api/openapi.yaml
+++ b/docs/api/openapi.yaml
@@ -3081,6 +3081,50 @@ paths:
         "401": *a1
         "422": *a3
         "429": *a4
+  /api/auth/me/modules:
+    get:
+      tags:
+        - Auth
+      summary: Read the resolved per-user module enable/disable map
+      description: "Returns the fully-resolved `{ <moduleKey>: boolean }` map for every toggleable module. `cycle` reflects
+        the cycle gate, `coach` reflects the resolved per-user opt-out + operator master flag, and the rest read the
+        per-user disabled-allowlist (`modulePreferencesJson`). Default-on: a fresh account reads every module enabled.
+        iOS/web read this to hide a whole module surface end-to-end."
+      responses:
+        "200":
+          description: Resolved module map.
+          content:
+            application/json:
+              schema:
+                $ref: "#/components/schemas/GetModulesResponse"
+        "401": *a1
+        "422": *a3
+        "429": *a4
+    patch:
+      tags:
+        - Auth
+      summary: Update per-user module enable/disable preferences
+      description: Merges the supplied keys into the persisted disabled-allowlist (`modulePreferencesJson`) field-by-field — a
+        PATCH touching only one module leaves the siblings intact. Refuses to disable a core module (`weight`,
+        `bloodPressure`, `pulse`, `medications`) or any unknown key with a 422. `userId` is never accepted from the
+        body. Always returns the fully-resolved next-state map so clients can hard-set their optimistic update.
+        Rate-limit 60/min per user.
+      requestBody:
+        required: true
+        content:
+          application/json:
+            schema:
+              $ref: "#/components/schemas/ModulePrefsPatchRequest"
+      responses:
+        "200":
+          description: Resolved next-state module map echoed back.
+          content:
+            application/json:
+              schema:
+                $ref: "#/components/schemas/PatchModulesResponse"
+        "401": *a1
+        "422": *a3
+        "429": *a4
   /api/auth/me/source-priority:
     get:
       tags:
@@ -6548,6 +6592,37 @@ components:
       required:
         - disableCoach
       description: Per-account Coach opt-out toggle (v1.4.47 W3). `true` hides the Coach FAB and short-circuits its API gates.
+    ModulePrefsPatchRequest:
+      type: object
+      properties:
+        cycle:
+          type: boolean
+        mood:
+          type: boolean
+        sleep:
+          type: boolean
+        glucose:
+          type: boolean
+        workouts:
+          type: boolean
+        recovery:
+          type: boolean
+        labs:
+          type: boolean
+        achievements:
+          type: boolean
+        coach:
+          type: boolean
+        insights:
+          type: boolean
+        doctorReport:
+          type: boolean
+      additionalProperties: false
+      description: Partial module enable/disable update. Each key is an optional boolean; an omitted key is left untouched,
+        `false` disables the module, `true` (re-)enables it. Only the toggleable "secondary domains" are accepted — a
+        core-domain key (`weight`, `bloodPressure`, `pulse`, `medications`) or any unknown key is a 422, so the
+        measurement engine + medications can never be disabled here. `cycle`/`coach` are accepted for forward-compat but
+        their real enabled-state is owned elsewhere (the cycle gate / `disableCoach` + the operator assistant flag).
     ProfileUpdateRequest:
       type: object
       properties:
@@ -12057,6 +12132,100 @@ components:
         - data
         - error
       additionalProperties: false
+    GetModulesResponse:
+      type: object
+      properties:
+        data:
+          $ref: "#/components/schemas/ModulesResponse"
+        error:
+          type: "null"
+        meta:
+          type: object
+          properties:
+            requestId:
+              type: string
+          additionalProperties: false
+      required:
+        - data
+        - error
+      additionalProperties: false
+    ModulesResponse:
+      type: object
+      properties:
+        modules:
+          $ref: "#/components/schemas/ModuleMap"
+      required:
+        - modules
+      additionalProperties: false
+    ModuleMap:
+      type: object
+      properties:
+        cycle:
+          type: boolean
+          description: Whether the "cycle" module is enabled for this account.
+        mood:
+          type: boolean
+          description: Whether the "mood" module is enabled for this account.
+        sleep:
+          type: boolean
+          description: Whether the "sleep" module is enabled for this account.
+        glucose:
+          type: boolean
+          description: Whether the "glucose" module is enabled for this account.
+        workouts:
+          type: boolean
+          description: Whether the "workouts" module is enabled for this account.
+        recovery:
+          type: boolean
+          description: Whether the "recovery" module is enabled for this account.
+        labs:
+          type: boolean
+          description: Whether the "labs" module is enabled for this account.
+        achievements:
+          type: boolean
+          description: Whether the "achievements" module is enabled for this account.
+        coach:
+          type: boolean
+          description: Whether the "coach" module is enabled for this account.
+        insights:
+          type: boolean
+          description: Whether the "insights" module is enabled for this account.
+        doctorReport:
+          type: boolean
+          description: Whether the "doctorReport" module is enabled for this account.
+      required:
+        - cycle
+        - mood
+        - sleep
+        - glucose
+        - workouts
+        - recovery
+        - labs
+        - achievements
+        - coach
+        - insights
+        - doctorReport
+      additionalProperties: false
+      description: Fully-resolved per-user module enable/disable map. Every toggleable module key is present. `false` means
+        the surface should disappear end-to-end (nav, dashboard, insights, …). `cycle` mirrors `cycleTrackingEnabled`;
+        `coach` mirrors the resolved per-user opt-out + operator master flag.
+    PatchModulesResponse:
+      type: object
+      properties:
+        data:
+          $ref: "#/components/schemas/ModulesResponse"
+        error:
+          type: "null"
+        meta:
+          type: object
+          properties:
+            requestId:
+              type: string
+          additionalProperties: false
+      required:
+        - data
+        - error
+      additionalProperties: false
     GetSourcePriorityResponse:
       type: object
       properties:
diff --git a/prisma/migrations/0167_module_enable_disable/migration.sql b/prisma/migrations/0167_module_enable_disable/migration.sql
new file mode 100644
index 000000000..0a5a69144
--- /dev/null
+++ b/prisma/migrations/0167_module_enable_disable/migration.sql
@@ -0,0 +1,38 @@
+-- v1.18.0 — module enable/disable foundation.
+--
+-- A single nullable JSONB blob on `users` carrying a DISABLED allowlist
+-- for the optional ("secondary") domains (mood, sleep, glucose, workouts,
+-- recovery, labs, achievements, insights, doctor-report, …). The contract
+-- is default-on:
+--
+--   * NULL column            → every module enabled
+--   * empty object `{}`       → every module enabled
+--   * key absent              → that module enabled
+--   * key present & `false`   → that module DISABLED
+--   * key present & `true`    → enabled (redundant-but-allowed)
+--
+-- No backfill — every existing user keeps every module on. The
+-- application resolver (`src/lib/modules/gate.ts`) tolerates a missing
+-- column / null row and reads all-on, so a partial deploy where the
+-- schema lands ahead of (or behind) the app code keeps working.
+--
+-- CORE domains (weight, blood pressure, pulse, medications) are never
+-- written here and the write endpoint refuses to disable them, so the
+-- measurement engine + meds can never be turned off via this column.
+-- `cycle` and `coach` keep their existing source of truth
+-- (`CycleProfile.cycle_tracking_enabled` / `users.disable_coach` +
+-- the operator assistant master flag) — this column does not own them.
+--
+-- No additional index — reads are per-user (`WHERE id = $1`), matching
+-- the convention set by `coach_prefs_json`, `source_priority_json`,
+-- `doctor_report_prefs_json`, and `notification_prefs` on the same table
+-- (no GIN index on any of them).
+--
+-- Idempotent guard (`IF NOT EXISTS`) so reruns are safe on prod.
+--
+-- Reversibility: down migration is
+--   ALTER TABLE "users" DROP COLUMN IF EXISTS "module_preferences_json";
+-- A roll-back loses per-user module opt-outs (every user falls back to
+-- all-on), which is the safe default — no data is destroyed.
+ALTER TABLE "users"
+    ADD COLUMN IF NOT EXISTS "module_preferences_json" JSONB;
diff --git a/prisma/schema.prisma b/prisma/schema.prisma
index dbf1b8bf7..354486506 100644
--- a/prisma/schema.prisma
+++ b/prisma/schema.prisma
@@ -401,6 +401,35 @@ model User {
   // `useAuth()` hook.
   disableCoach Boolean @default(false) @map("disable_coach")
 
+  // v1.18.0 — module enable/disable foundation.
+  //
+  // A DISABLED allowlist for the optional ("secondary") domains. The
+  // contract is default-on: a NULL column, an empty object, or a key
+  // simply absent all mean "module enabled". A key present and set to
+  // `false` means that module is OFF; `true` is redundant-but-allowed.
+  // No backfill — every existing user reads as all-on.
+  //
+  // Shape (string keys ⇒ boolean):
+  //   { "mood": false, "glucose": false, ... }
+  //
+  // The canonical key set + which keys are toggleable lives in
+  // `src/lib/modules/registry.ts`; the resolver + 403 guard live in
+  // `src/lib/modules/gate.ts`. CORE domains (weight, blood pressure,
+  // pulse, medications — the measurement engine + meds) are NEVER
+  // present here and the gate refuses to disable them, so a crafted
+  // `{ "weight": false }` blob cannot turn the core engine off.
+  //
+  // Two modules do NOT resolve from this column to avoid a double
+  // source of truth: `cycle` delegates to `CycleProfile`/`isCycleEnabled`
+  // and `coach` delegates to `User.disableCoach` + the operator-level
+  // assistant master flag. The column may still carry a `cycle`/`coach`
+  // key for forward-compat but the gate ignores it for those two.
+  //
+  // Persisted via `PATCH /api/auth/me/modules` with field-by-field
+  // merge semantics (no mass assignment); surfaced resolved on
+  // `GET /api/auth/me` as a `modules: { <key>: boolean }` map.
+  modulePreferencesJson Json? @map("module_preferences_json")
+
   // v1.5.5 — self-hosted avatar storage.
   //
   // Replaces the Gravatar third-party leak (the old `getGravatarUrl`
diff --git a/src/app/api/auth/me/modules/__tests__/route.test.ts b/src/app/api/auth/me/modules/__tests__/route.test.ts
new file mode 100644
index 000000000..d7d80ce70
--- /dev/null
+++ b/src/app/api/auth/me/modules/__tests__/route.test.ts
@@ -0,0 +1,307 @@
+/**
+ * v1.18.0 — PATCH/GET /api/auth/me/modules.
+ *
+ * Covers the read projection, the field-by-field merge, core-module
+ * refusal (strict schema), the cycle/coach delegation reflected in the
+ * resolved map, and the standard auth / rate-limit / 422 envelope.
+ */
+import { beforeEach, describe, expect, it, vi } from "vitest";
+
+vi.mock("@/lib/db", () => ({
+  prisma: {
+    user: {
+      findUnique: vi.fn(),
+      update: vi.fn(),
+    },
+    cycleProfile: {
+      findUnique: vi.fn(),
+    },
+  },
+}));
+
+vi.mock("@/lib/auth/session", () => ({ getSession: vi.fn() }));
+
+vi.mock("@/lib/auth/audit", () => ({
+  auditLog: vi.fn().mockResolvedValue(undefined),
+}));
+
+vi.mock("@/lib/logging/transports", () => ({ emitIfSampled: vi.fn() }));
+
+vi.mock("@/lib/db-compat", () => ({
+  ensureDbCompatibility: vi.fn().mockResolvedValue(undefined),
+}));
+
+vi.mock("@/lib/rate-limit", () => ({
+  checkRateLimit: vi.fn().mockResolvedValue({
+    allowed: true,
+    remaining: 59,
+    resetAt: Date.now() + 60_000,
+  }),
+  rateLimitHeaders: () => ({}),
+}));
+
+// Operator master flag = on by default; coach delegation keys off it.
+// Partial mock — api-handler imports `AssistantDisabledError` from here.
+vi.mock("@/lib/feature-flags", async (importOriginal) => {
+  const actual = await importOriginal<typeof import("@/lib/feature-flags")>();
+  return {
+    ...actual,
+    getAssistantFlags: vi.fn().mockResolvedValue({ coach: true }),
+  };
+});
+
+vi.mock("next/headers", () => ({
+  headers: vi.fn(async () => ({ get: () => null })),
+  cookies: vi.fn(async () => ({
+    get: () => undefined,
+    set: () => {},
+    delete: () => {},
+  })),
+}));
+
+import { GET, PATCH } from "../route";
+import { prisma } from "@/lib/db";
+import { getSession } from "@/lib/auth/session";
+import { auditLog } from "@/lib/auth/audit";
+import { checkRateLimit } from "@/lib/rate-limit";
+import { getAssistantFlags } from "@/lib/feature-flags";
+
+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 },
+};
+
+type ModuleMap = Record<string, boolean>;
+
+function mkPatch(body: unknown): Request {
+  return new Request("http://localhost/api/auth/me/modules", {
+    method: "PATCH",
+    body: JSON.stringify(body),
+    headers: { "Content-Type": "application/json" },
+  });
+}
+
+/**
+ * Default DB shape: fresh user, no module prefs, no cycle row. The
+ * `findUnique` mock reads from a mutable holder so a PATCH `update`
+ * (which writes `modulePreferencesJson`) is reflected by the post-update
+ * `resolveModuleMap` re-read — mirroring real DB round-trip semantics.
+ */
+function primeUser(over: {
+  gender?: string | null;
+  disableCoach?: boolean;
+  modulePreferencesJson?: unknown;
+  cycleTrackingEnabled?: boolean | null;
+} = {}) {
+  const row: {
+    gender: string | null;
+    disableCoach: boolean;
+    modulePreferencesJson: unknown;
+  } = {
+    gender: over.gender ?? null,
+    disableCoach: over.disableCoach ?? false,
+    modulePreferencesJson: over.modulePreferencesJson ?? null,
+  };
+  vi.mocked(prisma.user.findUnique).mockImplementation(
+    (() => Promise.resolve({ ...row })) as never,
+  );
+  vi.mocked(prisma.user.update).mockImplementation(((args: {
+    data?: { modulePreferencesJson?: unknown };
+  }) => {
+    const data = args.data;
+    if (data && "modulePreferencesJson" in data) {
+      row.modulePreferencesJson = data.modulePreferencesJson;
+    }
+    return Promise.resolve({});
+  }) as never);
+  vi.mocked(prisma.cycleProfile.findUnique).mockResolvedValue(
+    over.cycleTrackingEnabled === undefined
+      ? null
+      : ({ cycleTrackingEnabled: over.cycleTrackingEnabled } as never),
+  );
+}
+
+beforeEach(() => {
+  vi.clearAllMocks();
+  vi.mocked(getAssistantFlags).mockResolvedValue({ coach: true } as never);
+});
+
+describe("GET /api/auth/me/modules", () => {
+  it("rejects an unauthenticated request with 401", async () => {
+    vi.mocked(getSession).mockResolvedValue(null);
+    const res = await (GET as (r: Request) => Promise<Response>)(
+      new Request("http://localhost/api/auth/me/modules"),
+    );
+    expect(res.status).toBe(401);
+  });
+
+  it("returns every toggleable module on for a fresh user", async () => {
+    vi.mocked(getSession).mockResolvedValue(SESSION_OK as never);
+    primeUser();
+    const res = await (GET as (r: Request) => Promise<Response>)(
+      new Request("http://localhost/api/auth/me/modules"),
+    );
+    expect(res.status).toBe(200);
+    const env = (await res.json()) as { data: { modules: ModuleMap } };
+    expect(env.data.modules.mood).toBe(true);
+    expect(env.data.modules.sleep).toBe(true);
+    expect(env.data.modules.insights).toBe(true);
+    // cycle gender-derived (null gender ⇒ off); coach delegated (on).
+    expect(env.data.modules.cycle).toBe(false);
+    expect(env.data.modules.coach).toBe(true);
+  });
+
+  it("reflects a disabled module from the persisted allowlist", async () => {
+    vi.mocked(getSession).mockResolvedValue(SESSION_OK as never);
+    primeUser({ modulePreferencesJson: { glucose: false } });
+    const res = await (GET as (r: Request) => Promise<Response>)(
+      new Request("http://localhost/api/auth/me/modules"),
+    );
+    const env = (await res.json()) as { data: { modules: ModuleMap } };
+    expect(env.data.modules.glucose).toBe(false);
+    expect(env.data.modules.mood).toBe(true);
+  });
+
+  it("reflects coach delegation (operator master flag off)", async () => {
+    vi.mocked(getSession).mockResolvedValue(SESSION_OK as never);
+    vi.mocked(getAssistantFlags).mockResolvedValue({ coach: false } as never);
+    primeUser();
+    const res = await (GET as (r: Request) => Promise<Response>)(
+      new Request("http://localhost/api/auth/me/modules"),
+    );
+    const env = (await res.json()) as { data: { modules: ModuleMap } };
+    expect(env.data.modules.coach).toBe(false);
+  });
+});
+
+describe("PATCH /api/auth/me/modules", () => {
+  it("rejects an unauthenticated request with 401", async () => {
+    vi.mocked(getSession).mockResolvedValue(null);
+    const res = await (PATCH as (r: Request) => Promise<Response>)(
+      mkPatch({ mood: false }),
+    );
+    expect(res.status).toBe(401);
+    expect(prisma.user.update).not.toHaveBeenCalled();
+  });
+
+  it("disables a module and persists the merged allowlist", 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);
+    const env = (await res.json()) as { data: { modules: ModuleMap } };
+    expect(env.data.modules.mood).toBe(false);
+
+    expect(prisma.user.update).toHaveBeenCalledWith({
+      where: { id: "user-1" },
+      data: { modulePreferencesJson: { mood: false } },
+    });
+    expect(auditLog).toHaveBeenCalledWith(
+      "user.modules.update",
+      expect.objectContaining({
+        userId: "user-1",
+        details: expect.objectContaining({ changed: ["mood"] }),
+      }),
+    );
+  });
+
+  it("merges over the existing allowlist field-by-field (siblings intact)", async () => {
+    vi.mocked(getSession).mockResolvedValue(SESSION_OK as never);
+    // user previously disabled glucose; now disabling sleep too.
+    primeUser({ modulePreferencesJson: { glucose: false } });
+
+    await (PATCH as (r: Request) => Promise<Response>)(mkPatch({ sleep: false }));
+
+    expect(prisma.user.update).toHaveBeenCalledWith({
+      where: { id: "user-1" },
+      data: { modulePreferencesJson: { glucose: false, sleep: false } },
+    });
+  });
+
+  it("can re-enable a previously disabled module", async () => {
+    vi.mocked(getSession).mockResolvedValue(SESSION_OK as never);
+    primeUser({ modulePreferencesJson: { glucose: false } });
+
+    await (PATCH as (r: Request) => Promise<Response>)(mkPatch({ glucose: true }));
+
+    expect(prisma.user.update).toHaveBeenCalledWith({
+      where: { id: "user-1" },
+      data: { modulePreferencesJson: { glucose: true } },
+    });
+  });
+
+  it("REFUSES to disable a core module (strict schema 422)", async () => {
+    vi.mocked(getSession).mockResolvedValue(SESSION_OK as never);
+    primeUser();
+
+    for (const core of ["weight", "bloodPressure", "pulse", "medications"]) {
+      const res = await (PATCH as (r: Request) => Promise<Response>)(
+        mkPatch({ [core]: false }),
+      );
+      expect(res.status).toBe(422);
+    }
+    expect(prisma.user.update).not.toHaveBeenCalled();
+  });
+
+  it("rejects an unknown module key with 422", async () => {
+    vi.mocked(getSession).mockResolvedValue(SESSION_OK as never);
+    primeUser();
+    const res = await (PATCH as (r: Request) => Promise<Response>)(
+      mkPatch({ notAModule: false }),
+    );
+    expect(res.status).toBe(422);
+    expect(prisma.user.update).not.toHaveBeenCalled();
+  });
+
+  it("rejects a non-boolean value with 422", async () => {
+    vi.mocked(getSession).mockResolvedValue(SESSION_OK as never);
+    primeUser();
+    const res = await (PATCH as (r: Request) => Promise<Response>)(
+      mkPatch({ mood: "false" }),
+    );
+    expect(res.status).toBe(422);
+    expect(prisma.user.update).not.toHaveBeenCalled();
+  });
+
+  it("rejects malformed JSON with 422", async () => {
+    vi.mocked(getSession).mockResolvedValue(SESSION_OK as never);
+    const req = new Request("http://localhost/api/auth/me/modules", {
+      method: "PATCH",
+      body: "{ not valid json",
+      headers: { "Content-Type": "application/json" },
+    });
+    const res = await (PATCH as (r: Request) => Promise<Response>)(req);
+    expect(res.status).toBe(422);
+    expect(prisma.user.update).not.toHaveBeenCalled();
+  });
+
+  it("returns 429 when the per-user rate-limit fires", async () => {
+    vi.mocked(getSession).mockResolvedValue(SESSION_OK as never);
+    vi.mocked(checkRateLimit).mockResolvedValueOnce({
+      allowed: false,
+      remaining: 0,
+      resetAt: Date.now() + 30_000,
+    });
+    const res = await (PATCH as (r: Request) => Promise<Response>)(
+      mkPatch({ mood: false }),
+    );
+    expect(res.status).toBe(429);
+    expect(prisma.user.update).not.toHaveBeenCalled();
+  });
+
+  it("drops a previously-corrupted stored blob to clean booleans on merge", async () => {
+    vi.mocked(getSession).mockResolvedValue(SESSION_OK as never);
+    // junk in the stored row must not leak into the persisted merge.
+    primeUser({ modulePreferencesJson: { mood: "yes", sleep: false } });
+
+    await (PATCH as (r: Request) => Promise<Response>)(mkPatch({ labs: false }));
+
+    expect(prisma.user.update).toHaveBeenCalledWith({
+      where: { id: "user-1" },
+      data: { modulePreferencesJson: { sleep: false, labs: false } },
+    });
+  });
+});
diff --git a/src/app/api/auth/me/modules/route.ts b/src/app/api/auth/me/modules/route.ts
new file mode 100644
index 000000000..2be6c5b5d
--- /dev/null
+++ b/src/app/api/auth/me/modules/route.ts
@@ -0,0 +1,123 @@
+/**
+ * v1.18.0 — per-user module enable/disable preferences.
+ *
+ *  GET   /api/auth/me/modules  — resolved `{ <moduleKey>: boolean }` map
+ *                                for every toggleable module (cycle/coach
+ *                                reflect their real delegated state).
+ *  PATCH /api/auth/me/modules  — body `{ <moduleKey>?: boolean }`. Merges
+ *                                the supplied keys into the persisted
+ *                                `modulePreferencesJson` DISABLED allowlist
+ *                                (field-by-field, no mass assignment) and
+ *                                returns the freshly-resolved module map.
+ *
+ * The body schema (`modulePrefsPatchSchema`) is `strict()` over the
+ * canonical toggleable key set, so a core-domain key (`weight`,
+ * `bloodPressure`, `pulse`, `medications`) or any unknown key is a 422 —
+ * the core measurement engine + meds can never be disabled here.
+ *
+ * `userId` is always narrowed from `requireAuth()`; the body never
+ * carries it. The semantics are a DISABLED allowlist: a key set to
+ * `false` disables that module; `true` (or absence) leaves it enabled.
+ * cycle/coach keys are accepted for forward-compat but the gate ignores
+ * the blob for them (they delegate to their existing source of truth).
+ */
+import { apiHandler, requireAuth, HttpError } from "@/lib/api-handler";
+import {
+  apiError,
+  apiSuccess,
+  getClientIp,
+  returnAllZodIssues,
+} from "@/lib/api-response";
+import { annotate } from "@/lib/logging/context";
+import { auditLog } from "@/lib/auth/audit";
+import { prisma } from "@/lib/db";
+import { checkRateLimit, rateLimitHeaders } from "@/lib/rate-limit";
+import { resolveModuleMap, normalisePrefs } from "@/lib/modules/gate";
+import { modulePrefsPatchSchema } from "@/lib/validations/modules";
+
+export const dynamic = "force-dynamic";
+
+const PATCH_RATE_LIMIT = 60;
+const PATCH_WINDOW_MS = 60_000;
+
+export const GET = apiHandler(async () => {
+  const { user } = await requireAuth();
+  annotate({ action: { name: "auth.me.modules.get" } });
+
+  const modules = await resolveModuleMap(user.id);
+  return apiSuccess({ modules });
+});
+
+export const PATCH = apiHandler(async (req: Request) => {
+  const { user } = await requireAuth();
+
+  const rl = await checkRateLimit(
+    `modules:patch:${user.id}`,
+    PATCH_RATE_LIMIT,
+    PATCH_WINDOW_MS,
+  );
+  if (!rl.allowed) {
+    const response = apiError("Too many requests", 429);
+    for (const [k, v] of Object.entries(rateLimitHeaders(rl))) {
+      response.headers.set(k, v);
+    }
+    return response;
+  }
+
+  let body: unknown;
+  try {
+    body = await req.json();
+  } catch {
+    throw new HttpError(422, "modules.body.invalid_json");
+  }
+
+  const parsed = modulePrefsPatchSchema.safeParse(body ?? {});
+  if (!parsed.success) {
+    annotate({
+      action: { name: "auth.me.modules.patch.invalid_shape" },
+      meta: { issues: parsed.error.issues.length },
+    });
+    return returnAllZodIssues(parsed.error, 422, {
+      errorCode: "modules.invalid",
+    });
+  }
+
+  // Merge the supplied keys into the persisted DISABLED allowlist,
+  // field-by-field. `normalisePrefs` strips any junk from the stored
+  // row so a previously-corrupted blob can't poison the merge, and the
+  // strict schema guarantees `parsed.data` carries only toggleable keys
+  // (core domains were rejected at the 422 above).
+  const existing = await prisma.user.findUnique({
+    where: { id: user.id },
+    select: { modulePreferencesJson: true },
+  });
+  const merged: Record<string, boolean> = normalisePrefs(
+    existing?.modulePreferencesJson,
+  );
+  const changed: string[] = [];
+  for (const [key, value] of Object.entries(parsed.data)) {
+    if (value === undefined) continue;
+    merged[key] = value;
+    changed.push(key);
+  }
+
+  await prisma.user.update({
+    where: { id: user.id },
+    data: { modulePreferencesJson: merged },
+  });
+
+  const modules = await resolveModuleMap(user.id);
+
+  await auditLog("user.modules.update", {
+    userId: user.id,
+    ipAddress: getClientIp(req),
+    details: { changed },
+  });
+
+  annotate({
+    action: { name: "auth.me.modules.patch" },
+    meta: { changed },
+  });
+
+  return apiSuccess({ modules });
+});
diff --git a/src/app/api/auth/me/route.ts b/src/app/api/auth/me/route.ts
index 6538c5818..6da40db69 100644
--- a/src/app/api/auth/me/route.ts
+++ b/src/app/api/auth/me/route.ts
@@ -6,6 +6,7 @@ import { buildAvatarUrl } from "@/lib/avatar";
 import { decrypt } from "@/lib/crypto";
 import { prisma } from "@/lib/db";
 import { isCycleEnabled } from "@/lib/cycle/gate";
+import { resolveModuleMap } from "@/lib/modules/gate";
 
 export const dynamic = "force-dynamic";
 
@@ -21,12 +22,18 @@ export const GET = apiHandler(async () => {
   // cycle-tracking gate; no row is forced, a NULL toggle derives from
   // gender) is a Postgres round-trip. Running them sequentially added
   // the cookie hop to every /me — and /me sits on every app boot path.
-  const [, cycleProfile] = await Promise.all([
+  const [, cycleProfile, modules] = await Promise.all([
     setOnboardingPendingCookie(user.onboardingCompletedAt == null),
     prisma.cycleProfile.findUnique({
       where: { userId: user.id },
       select: { cycleTrackingEnabled: true },
     }),
+    // v1.18.0 — resolved module enable/disable map for every toggleable
+    // module. cycle/coach reflect their real delegated state (the cycle
+    // gate / disableCoach + operator assistant flag); the rest read the
+    // disabled-allowlist `modulePreferencesJson`. Default-on. Clients
+    // hide a whole module surface end-to-end when its key is `false`.
+    resolveModuleMap(user.id),
   ]);
   const cycleTrackingEnabled = isCycleEnabled(user.gender, cycleProfile);
 
@@ -85,5 +92,12 @@ export const GET = apiHandler(async () => {
     // v1.15.0 — cycle-tracking feature gate, resolved server-side. iOS
     // hides the whole cycle tab when this is false.
     cycleTrackingEnabled,
+    // v1.18.0 — module enable/disable map. `{ <moduleKey>: boolean }`
+    // for every toggleable module; `false` means the module is OFF and
+    // the surface should disappear end-to-end (nav, dashboard, insights,
+    // …). `cycle` mirrors `cycleTrackingEnabled` and `coach` mirrors the
+    // resolved `disableCoach` + operator master flag, so this map is the
+    // single thing a client needs to gate every secondary domain.
+    modules,
   });
 });
diff --git a/src/lib/feature-flags/__tests__/coach-user-disable.test.tsx b/src/lib/feature-flags/__tests__/coach-user-disable.test.tsx
index caedd7d9e..902aa2783 100644
--- a/src/lib/feature-flags/__tests__/coach-user-disable.test.tsx
+++ b/src/lib/feature-flags/__tests__/coach-user-disable.test.tsx
@@ -317,6 +317,12 @@ describe("Coach per-user disableCoach invariant", () => {
     // builder.
     "src/lib/dashboard/snapshot.ts",
     "src/app/api/dashboard/snapshot/route.ts",
+    // v1.18.0 — the module enable/disable gate delegates the `coach`
+    // module to the SAME two-layer source of truth (`user.disableCoach`
+    // AND the operator assistant master flag) rather than owning a
+    // second copy in `modulePreferencesJson`. Covered by the coach-
+    // delegation cases in `src/lib/modules/__tests__/gate.test.ts`.
+    "src/lib/modules/gate.ts",
   ];
 
   /**
diff --git a/src/lib/modules/__tests__/gate.test.ts b/src/lib/modules/__tests__/gate.test.ts
new file mode 100644
index 000000000..14ee98578
--- /dev/null
+++ b/src/lib/modules/__tests__/gate.test.ts
@@ -0,0 +1,189 @@
+/**
+ * v1.18.0 — module enable/disable gate resolver.
+ *
+ * Exercises the PURE resolver (`resolveModuleEnabled`) + the registry
+ * helpers, so the disabled-allowlist + delegation logic is asserted
+ * without a DB. The async `isModuleEnabled` / `requireModuleEnabled`
+ * thin wrappers are covered by the route test.
+ */
+import { describe, it, expect } from "vitest";
+
+import {
+  resolveModuleEnabled,
+  normalisePrefs,
+  MODULE_DISABLED_ERROR_CODE,
+  type ModuleGateInputs,
+} from "../gate";
+import {
+  isCoreDomain,
+  isModuleKey,
+  moduleDelegatesTo,
+  MODULE_KEYS,
+  CORE_DOMAIN_KEYS,
+} from "../registry";
+
+function inputs(over: Partial<ModuleGateInputs> = {}): ModuleGateInputs {
+  return {
+    gender: null,
+    disableCoach: false,
+    modulePreferences: {},
+    cycleTrackingEnabled: null,
+    ...over,
+  };
+}
+
+describe("resolveModuleEnabled — disabled allowlist (default-on)", () => {
+  it("enables a module when no preference is recorded", () => {
+    expect(resolveModuleEnabled("mood", inputs(), true)).toBe(true);
+    expect(resolveModuleEnabled("sleep", inputs(), true)).toBe(true);
+    expect(resolveModuleEnabled("labs", inputs(), true)).toBe(true);
+  });
+
+  it("enables a module when the key is present and true", () => {
+    expect(
+      resolveModuleEnabled("mood", inputs({ modulePreferences: { mood: true } }), true),
+    ).toBe(true);
+  });
+
+  it("disables a module ONLY on an explicit false", () => {
+    expect(
+      resolveModuleEnabled(
+        "glucose",
+        inputs({ modulePreferences: { glucose: false } }),
+        true,
+      ),
+    ).toBe(false);
+  });
+
+  it("isolates per-module: disabling one leaves siblings on", () => {
+    const i = inputs({ modulePreferences: { workouts: false } });
+    expect(resolveModuleEnabled("workouts", i, true)).toBe(false);
+    expect(resolveModuleEnabled("recovery", i, true)).toBe(true);
+    expect(resolveModuleEnabled("labs", i, true)).toBe(true);
+  });
+});
+
+describe("resolveModuleEnabled — cycle delegation", () => {
+  it("ignores the module blob and reads the cycle gate (gender-derived)", () => {
+    // Even a crafted `{ cycle: false }` blob cannot override the real
+    // FEMALE-derived enablement — the gate delegates to isCycleEnabled.
+    const i = inputs({
+      gender: "FEMALE",
+      cycleTrackingEnabled: null,
+      modulePreferences: { cycle: false },
+    });
+    expect(resolveModuleEnabled("cycle", i, true)).toBe(true);
+  });
+
+  it("respects the cycle toggle when set", () => {
+    expect(
+      resolveModuleEnabled(
+        "cycle",
+        inputs({ gender: "MALE", cycleTrackingEnabled: true }),
+        true,
+      ),
+    ).toBe(true);
+    expect(
+      resolveModuleEnabled(
+        "cycle",
+        inputs({ gender: "FEMALE", cycleTrackingEnabled: false }),
+        true,
+      ),
+    ).toBe(false);
+  });
+
+  it("a MALE account with a null toggle is cycle-disabled", () => {
+    expect(
+      resolveModuleEnabled("cycle", inputs({ gender: "MALE" }), true),
+    ).toBe(false);
+  });
+});
+
+describe("resolveModuleEnabled — coach delegation (two-layer)", () => {
+  it("is enabled only when the operator master flag AND !disableCoach", () => {
+    expect(
+      resolveModuleEnabled("coach", inputs({ disableCoach: false }), true),
+    ).toBe(true);
+  });
+
+  it("is disabled when the per-user opt-out is set", () => {
+    expect(
+      resolveModuleEnabled("coach", inputs({ disableCoach: true }), true),
+    ).toBe(false);
+  });
+
+  it("is disabled when the operator master flag is off", () => {
+    expect(
+      resolveModuleEnabled("coach", inputs({ disableCoach: false }), false),
+    ).toBe(false);
+  });
+
+  it("ignores the module blob for coach", () => {
+    // A crafted `{ coach: true }` cannot re-enable against a disabled
+    // operator flag or a user opt-out.
+    const i = inputs({ disableCoach: true, modulePreferences: { coach: true } });
+    expect(resolveModuleEnabled("coach", i, true)).toBe(false);
+  });
+});
+
+describe("insights — narrative layer, not a delegated module", () => {
+  it("resolves from the disabled allowlist like the other secondary domains", () => {
+    expect(resolveModuleEnabled("insights", inputs(), true)).toBe(true);
+    expect(
+      resolveModuleEnabled(
+        "insights",
+        inputs({ modulePreferences: { insights: false } }),
+        true,
+      ),
+    ).toBe(false);
+  });
+
+  it("is not delegated (no double source of truth marker)", () => {
+    expect(moduleDelegatesTo("insights")).toBeUndefined();
+  });
+});
+
+describe("normalisePrefs — fail-open coercion", () => {
+  it("treats null / non-object / array as empty (all-on)", () => {
+    expect(normalisePrefs(null)).toEqual({});
+    expect(normalisePrefs(undefined)).toEqual({});
+    expect(normalisePrefs("nope")).toEqual({});
+    expect(normalisePrefs(["mood"])).toEqual({});
+  });
+
+  it("keeps only boolean values, dropping junk entries", () => {
+    expect(
+      normalisePrefs({ mood: false, sleep: "yes", glucose: 0, labs: true }),
+    ).toEqual({ mood: false, labs: true });
+  });
+});
+
+describe("registry — core domains can never be disabled", () => {
+  it("the four core domains are not toggleable module keys", () => {
+    for (const core of CORE_DOMAIN_KEYS) {
+      expect(isModuleKey(core)).toBe(false);
+      expect(isCoreDomain(core)).toBe(true);
+    }
+  });
+
+  it("a crafted core-domain key is inert (never read as a module)", () => {
+    // `weight: false` in the blob can't matter: weight is not a ModuleKey,
+    // so the gate never consults it. The resolver only ever runs for the
+    // 11 declared toggleable keys.
+    expect(isModuleKey("weight")).toBe(false);
+    expect(isModuleKey("medications")).toBe(false);
+  });
+
+  it("every toggleable key is a known module and not a core domain", () => {
+    for (const key of MODULE_KEYS) {
+      expect(isModuleKey(key)).toBe(true);
+      expect(isCoreDomain(key)).toBe(false);
+    }
+  });
+});
+
+describe("wire contract", () => {
+  it("exports the iOS-classifier errorCode", () => {
+    expect(MODULE_DISABLED_ERROR_CODE).toBe("module.disabled");
+  });
+});
diff --git a/src/lib/modules/gate.ts b/src/lib/modules/gate.ts
new file mode 100644
index 000000000..58658e73b
--- /dev/null
+++ b/src/lib/modules/gate.ts
@@ -0,0 +1,201 @@
+/**
+ * v1.18.0 — module enable/disable gate.
+ *
+ * The ONE enforcement point for the module foundation. Every leak-point
+ * (nav, dashboard tiles, insights sections, coach snapshot, status
+ * routes, reminder jobs, achievements, doctor-report / FHIR, search,
+ * quick-add) resolves its decision through `isModuleEnabled(userId, key)`
+ * and `requireModuleEnabled(userId, key)`. Mirrors the cycle gate
+ * (`src/lib/cycle/gate.ts`) and the assistant feature flags
+ * (`src/lib/feature-flags/index.ts`).
+ *
+ * Source-of-truth discipline (NO double source of truth):
+ *
+ *   - `cycle`  delegates to `isCycleEnabled(gender, CycleProfile)` — the
+ *              existing cycle gate. `modulePreferencesJson.cycle` is
+ *              ignored on purpose.
+ *   - `coach`  delegates to `User.disableCoach` AND the operator-level
+ *              assistant master flag (`getAssistantFlags().coach`). Both
+ *              must agree, matching the two-layer model the client gates
+ *              already enforce.
+ *   - every other module resolves purely from `modulePreferencesJson`
+ *              as a DISABLED allowlist (absent / empty / `true` ⇒ on; an
+ *              explicit `false` ⇒ off). Default-on.
+ *
+ * Fail-closed posture: the resolver only ever DISABLES a module when it
+ * sees an explicit, well-typed `false` (or, for delegated modules, the
+ * delegated source returning disabled). A malformed blob, a missing
+ * column, an unknown key — none of these can silently disable a module
+ * (default-on), and none can enable a delegated one against its real
+ * source. A crafted `{ "weight": false }` blob is inert because `weight`
+ * is a core domain, not a `ModuleKey`.
+ *
+ * Reads are memoised per-request (the assistant-flags pattern) so a
+ * single request that gates several modules hits the row once.
+ */
+import { apiError } from "@/lib/api-response";
+import { prisma } from "@/lib/db";
+import { isCycleEnabled } from "@/lib/cycle/gate";
+import { getAssistantFlags } from "@/lib/feature-flags";
+import { memoizePerRequest } from "@/lib/request-cache";
+import {
+  MODULE_KEYS,
+  moduleDelegatesTo,
+  type ModuleKey,
+} from "./registry";
+
+export { MODULE_KEYS } from "./registry";
+export type { ModuleKey } from "./registry";
+
+/** Wire `errorCode` the iOS retry classifier branches on. */
+export const MODULE_DISABLED_ERROR_CODE = "module.disabled";
+
+/**
+ * The per-user fields the gate needs. Bundled so the resolver does a
+ * single round-trip and the memo caches one row per request.
+ */
+export interface ModuleGateInputs {
+  gender: string | null;
+  disableCoach: boolean;
+  modulePreferences: Record<string, boolean>;
+  /** `CycleProfile.cycleTrackingEnabled`; NULL ⇒ derive from gender. */
+  cycleTrackingEnabled: boolean | null;
+}
+
+/**
+ * Coerce the persisted blob into a plain `Record<string, boolean>`,
+ * keeping only boolean values. A null column, a non-object, or junk
+ * entries all collapse to an empty / partial map — which the
+ * disabled-allowlist semantics read as "all on". Fail-open per key:
+ * only a literal `false` disables.
+ */
+export function normalisePrefs(raw: unknown): Record<string, boolean> {
+  if (raw == null || typeof raw !== "object" || Array.isArray(raw)) {
+    return {};
+  }
+  const out: Record<string, boolean> = {};
+  for (const [k, v] of Object.entries(raw as Record<string, unknown>)) {
+    if (typeof v === "boolean") {
+      out[k] = v;
+    }
+  }
+  return out;
+}
+
+/**
+ * Pure resolver — exposed for unit tests so the disabled-allowlist +
+ * delegation logic can be asserted without a DB. `assistantCoach` is the
+ * resolved operator-level `getAssistantFlags().coach`; pass it in so this
+ * stays synchronous and side-effect-free.
+ */
+export function resolveModuleEnabled(
+  key: ModuleKey,
+  inputs: ModuleGateInputs,
+  assistantCoach: boolean,
+): boolean {
+  const delegate = moduleDelegatesTo(key);
+
+  if (delegate === "cycle") {
+    // Single source of truth: the cycle gate. The module blob is ignored.
+    return isCycleEnabled(inputs.gender, {
+      cycleTrackingEnabled: inputs.cycleTrackingEnabled,
+    });
+  }
+
+  if (delegate === "coach") {
+    // Two-layer model: operator master flag AND per-user opt-out.
+    return assistantCoach && !inputs.disableCoach;
+  }
+
+  // Disabled allowlist: only an explicit `false` turns the module off.
+  return inputs.modulePreferences[key] !== false;
+}
+
+/** Internal: load the gate inputs once per request. */
+function loadInputs(userId: string): Promise<ModuleGateInputs> {
+  return memoizePerRequest(`module-gate-inputs:${userId}`, async () => {
+    const [user, cycleProfile] = await Promise.all([
+      prisma.user.findUnique({
+        where: { id: userId },
+        select: {
+          gender: true,
+          disableCoach: true,
+          modulePreferencesJson: true,
+        },
+      }),
+      prisma.cycleProfile.findUnique({
+        where: { userId },
+        select: { cycleTrackingEnabled: true },
+      }),
+    ]);
+    return {
+      gender: user?.gender ?? null,
+      disableCoach: user?.disableCoach ?? false,
+      modulePreferences: normalisePrefs(user?.modulePreferencesJson),
+      cycleTrackingEnabled: cycleProfile?.cycleTrackingEnabled ?? null,
+    };
+  });
+}
+
+/**
+ * Resolve whether a module is enabled for an account. Default-on:
+ * an unknown / absent / non-`false` state reads as enabled. Delegated
+ * modules (`cycle`, `coach`) resolve through their real source.
+ */
+export async function isModuleEnabled(
+  userId: string,
+  moduleKey: ModuleKey,
+): Promise<boolean> {
+  const inputs = await loadInputs(userId);
+  const delegate = moduleDelegatesTo(moduleKey);
+  // Only pay the assistant-flags read when resolving the coach delegate.
+  const assistantCoach =
+    delegate === "coach" ? (await getAssistantFlags()).coach : false;
+  return resolveModuleEnabled(moduleKey, inputs, assistantCoach);
+}
+
+/**
+ * Resolve the full `{ <key>: boolean }` map for every toggleable module,
+ * suitable for the `GET /api/auth/me` projection. cycle/coach reflect
+ * their real delegated state.
+ */
+export async function resolveModuleMap(
+  userId: string,
+): Promise<Record<ModuleKey, boolean>> {
+  const inputs = await loadInputs(userId);
+  const assistantCoach = (await getAssistantFlags()).coach;
+  const out = {} as Record<ModuleKey, boolean>;
+  for (const key of MODULE_KEYS) {
+    out[key] = resolveModuleEnabled(key, inputs, assistantCoach);
+  }
+  return out;
+}
+
+/**
+ * Route-guard outcome: either a clear pass or a ready 403 envelope to
+ * return verbatim — mirrors `CycleGateResult`.
+ */
+export type ModuleGateResult =
+  | { enabled: true }
+  | { enabled: false; response: Response };
+
+/**
+ * Enforce the gate for a module-scoped route. Returns a 403
+ * `module.disabled` envelope (carrying the module key in `meta`) when the
+ * account has the module turned off — even with a valid Bearer token.
+ */
+export async function requireModuleEnabled(
+  userId: string,
+  moduleKey: ModuleKey,
+): Promise<ModuleGateResult> {
+  if (await isModuleEnabled(userId, moduleKey)) {
+    return { enabled: true };
+  }
+  return {
+    enabled: false,
+    response: apiError(`Module "${moduleKey}" is not enabled`, 403, {
+      errorCode: MODULE_DISABLED_ERROR_CODE,
+      module: moduleKey,
+    }),
+  };
+}
diff --git a/src/lib/modules/registry.ts b/src/lib/modules/registry.ts
new file mode 100644
index 000000000..45f2781c1
--- /dev/null
+++ b/src/lib/modules/registry.ts
@@ -0,0 +1,215 @@
+/**
+ * v1.18.0 — canonical module registry.
+ *
+ * The single source of truth for "what is a module" in HealthLog's
+ * enable/disable foundation. Every leak-point (nav, dashboard tiles,
+ * insights sections, coach snapshot, status routes, reminder jobs,
+ * achievements, doctor-report / FHIR, search, quick-add) reads its gate
+ * decision through `src/lib/modules/gate.ts`, which keys off the entries
+ * declared here.
+ *
+ * Two classes of domain:
+ *
+ *   - CORE (always-on): weight, blood pressure, pulse, medications — the
+ *     measurement engine + meds. These are NOT in `MODULE_KEYS` and have
+ *     NO registry entry. They can never be disabled; the gate has no key
+ *     to flip and the write endpoint refuses them. This is structural,
+ *     not a runtime check future code can soften.
+ *
+ *   - TOGGLEABLE (the "secondary domains"): the maintainer-chosen scope
+ *     below. Each carries a stable key, an i18n label + description key,
+ *     a category for the Settings hub grouping, and an optional
+ *     `delegatesTo` marker for the two modules whose enabled-state is
+ *     owned elsewhere (no double source of truth).
+ *
+ * The persisted shape (`User.modulePreferencesJson`) is a DISABLED
+ * allowlist: absent / empty / `true` ⇒ enabled, an explicit `false` ⇒
+ * disabled. Default-on, no backfill.
+ */
+
+/**
+ * Where a module's enabled-state is resolved when it is NOT owned by
+ * `modulePreferencesJson` directly. Keeps a single source of truth:
+ *
+ *   - "cycle"  → `isCycleEnabled(gender, CycleProfile)` (the existing
+ *                cycle gate; `modulePreferencesJson.cycle` is ignored).
+ *   - "coach"  → `User.disableCoach` AND the operator-level assistant
+ *                master flag (`getAssistantFlags().coach`); again the
+ *                module blob is ignored for this key.
+ *
+ * Every other toggleable module has no `delegatesTo` and resolves purely
+ * from `modulePreferencesJson`.
+ */
+export type ModuleDelegation = "cycle" | "coach";
+
+/** Coarse grouping for the Settings "What you track" hub. */
+export type ModuleCategory =
+  | "tracking" // user-logged domains (mood, cycle, glucose, labs)
+  | "device" // device / passive-sync domains (sleep, workouts, recovery)
+  | "engagement" // gamification (achievements)
+  | "intelligence" // AI-driven surfaces (coach, insights)
+  | "export"; // outbound reporting (doctor report / FHIR)
+
+export interface ModuleDefinition {
+  /** Stable key — the literal used in `modulePreferencesJson` + the API. */
+  key: ModuleKey;
+  /** i18n key for the human-readable module name (messages/*.json). */
+  labelKey: string;
+  /** i18n key for the one-line "what turning this off does" explainer. */
+  descriptionKey: string;
+  /** Settings-hub grouping. */
+  category: ModuleCategory;
+  /**
+   * When set, the module's enabled-state is NOT resolved from
+   * `modulePreferencesJson` — the gate delegates to the named source so
+   * there is exactly one source of truth. See `ModuleDelegation`.
+   */
+  delegatesTo?: ModuleDelegation;
+}
+
+/**
+ * The toggleable modules — the maintainer's "secondary domains" scope.
+ *
+ * Declared as a const tuple so `ModuleKey` is the exact union and the
+ * registry stays exhaustively typed.
+ */
+export const MODULE_KEYS = [
+  "cycle",
+  "mood",
+  "sleep",
+  "glucose",
+  "workouts",
+  "recovery",
+  "labs",
+  "achievements",
+  "coach",
+  "insights",
+  "doctorReport",
+] as const;
+
+export type ModuleKey = (typeof MODULE_KEYS)[number];
+
+/**
+ * CORE domains — the always-on measurement engine + medications. Listed
+ * here for documentation + the write-endpoint denylist; they have NO
+ * `ModuleDefinition` and can never appear as a toggle. A crafted
+ * `{ "weight": false }` blob is inert: `weight` is not a `ModuleKey`, so
+ * the gate never reads it and the PATCH validator rejects it.
+ */
+export const CORE_DOMAIN_KEYS = [
+  "weight",
+  "bloodPressure",
+  "pulse",
+  "medications",
+] as const;
+
+export type CoreDomainKey = (typeof CORE_DOMAIN_KEYS)[number];
+
+const CORE_DOMAIN_SET: ReadonlySet<string> = new Set(CORE_DOMAIN_KEYS);
+
+/** True for the four always-on core domains (never disableable). */
+export function isCoreDomain(key: string): key is CoreDomainKey {
+  return CORE_DOMAIN_SET.has(key);
+}
+
+/**
+ * The registry. Order is the Settings-hub display order (grouped by
+ * category in the UI; this flat order is the canonical iteration order).
+ *
+ * `insights` decision (documented): disabling `insights` hides only the
+ * AI-ANALYSIS surfaces — the Daily Briefing, the per-metric AI status
+ * cards, the correlation narration, the Health-Score explainer. It does
+ * NOT hide the raw weight / BP / pulse charts or any measurement data:
+ * those are core and render from live measurements regardless. `insights`
+ * is the narrative layer, not the data layer. (The operator-level
+ * assistant master flag is a separate, server-wide kill-switch; this
+ * per-user toggle sits below it.)
+ *
+ * `coach` is the per-user opt-out half of the existing two-layer model
+ * (`User.disableCoach` AND the operator master flag). It is surfaced here
+ * so the Modules hub lists it alongside its siblings, but it delegates —
+ * the module blob never owns it.
+ */
+export const MODULE_REGISTRY: Readonly<Record<ModuleKey, ModuleDefinition>> =
+  Object.freeze({
+    cycle: {
+      key: "cycle",
+      labelKey: "modules.cycle.label",
+      descriptionKey: "modules.cycle.description",
+      category: "tracking",
+      delegatesTo: "cycle",
+    },
+    mood: {
+      key: "mood",
+      labelKey: "modules.mood.label",
+      descriptionKey: "modules.mood.description",
+      category: "tracking",
+    },
+    glucose: {
+      key: "glucose",
+      labelKey: "modules.glucose.label",
+      descriptionKey: "modules.glucose.description",
+      category: "tracking",
+    },
+    labs: {
+      key: "labs",
+      labelKey: "modules.labs.label",
+      descriptionKey: "modules.labs.description",
+      category: "tracking",
+    },
+    sleep: {
+      key: "sleep",
+      labelKey: "modules.sleep.label",
+      descriptionKey: "modules.sleep.description",
+      category: "device",
+    },
+    workouts: {
+      key: "workouts",
+      labelKey: "modules.workouts.label",
+      descriptionKey: "modules.workouts.description",
+      category: "device",
+    },
+    recovery: {
+      key: "recovery",
+      labelKey: "modules.recovery.label",
+      descriptionKey: "modules.recovery.description",
+      category: "device",
+    },
+    achievements: {
+      key: "achievements",
+      labelKey: "modules.achievements.label",
+      descriptionKey: "modules.achievements.description",
+      category: "engagement",
+    },
+    coach: {
+      key: "coach",
+      labelKey: "modules.coach.label",
+      descriptionKey: "modules.coach.description",
+      category: "intelligence",
+      delegatesTo: "coach",
+    },
+    insights: {
+      key: "insights",
+      labelKey: "modules.insights.label",
+      descriptionKey: "modules.insights.description",
+      category: "intelligence",
+    },
+    doctorReport: {
+      key: "doctorReport",
+      labelKey: "modules.doctorReport.label",
+      descriptionKey: "modules.doctorReport.description",
+      category: "export",
+    },
+  });
+
+const MODULE_KEY_SET: ReadonlySet<string> = new Set(MODULE_KEYS);
+
+/** True when `key` is a known toggleable module. */
+export function isModuleKey(key: string): key is ModuleKey {
+  return MODULE_KEY_SET.has(key);
+}
+
+/** The two delegated keys, resolved by their existing source of truth. */
+export function moduleDelegatesTo(key: ModuleKey): ModuleDelegation | undefined {
+  return MODULE_REGISTRY[key].delegatesTo;
+}
diff --git a/src/lib/openapi/routes/profile.ts b/src/lib/openapi/routes/profile.ts
index 3a6f4224c..1c200012e 100644
--- a/src/lib/openapi/routes/profile.ts
+++ b/src/lib/openapi/routes/profile.ts
@@ -10,8 +10,45 @@ import type { ZodOpenApiObject } from "zod-openapi";
 import { coachPrefsSchema } from "@/lib/validations/coach-prefs";
 import { notificationPrefsSchema } from "@/lib/validations/notification-prefs";
 import { sourcePrioritySchema } from "@/lib/validations/source-priority";
+import { modulePrefsPatchSchema } from "@/lib/validations/modules";
+import { MODULE_KEYS } from "@/lib/modules/registry";
 import { dataEnvelope, errorEnvelope, stdResponses } from "./shared";
 
+// v1.18.0 — module enable/disable. The PATCH request is the REAL runtime
+// validator (`modulePrefsPatchSchema` — strict over the toggleable key
+// set; a core-domain or unknown key is a 422). The response is the
+// fully-resolved `{ <moduleKey>: boolean }` map for every toggleable
+// module: `cycle` mirrors the cycle gate, `coach` mirrors the resolved
+// `disableCoach` + operator master flag, the rest read the per-user
+// disabled-allowlist. The map is the single thing a client needs to gate
+// every secondary domain end-to-end.
+const modulePrefsPatchRequest = modulePrefsPatchSchema.meta({
+  id: "ModulePrefsPatchRequest",
+  description:
+    'Partial module enable/disable update. Each key is an optional boolean; an omitted key is left untouched, `false` disables the module, `true` (re-)enables it. Only the toggleable "secondary domains" are accepted — a core-domain key (`weight`, `bloodPressure`, `pulse`, `medications`) or any unknown key is a 422, so the measurement engine + medications can never be disabled here. `cycle`/`coach` are accepted for forward-compat but their real enabled-state is owned elsewhere (the cycle gate / `disableCoach` + the operator assistant flag).',
+});
+
+const moduleMapResolved = z
+  .object(
+    Object.fromEntries(
+      MODULE_KEYS.map((k) => [
+        k,
+        z
+          .boolean()
+          .describe(`Whether the "${k}" module is enabled for this account.`),
+      ]),
+    ),
+  )
+  .meta({
+    id: "ModuleMap",
+    description:
+      "Fully-resolved per-user module enable/disable map. Every toggleable module key is present. `false` means the surface should disappear end-to-end (nav, dashboard, insights, …). `cycle` mirrors `cycleTrackingEnabled`; `coach` mirrors the resolved per-user opt-out + operator master flag.",
+  });
+
+const moduleMapEnvelopeInner = z
+  .object({ modules: moduleMapResolved })
+  .meta({ id: "ModulesResponse" });
+
 // v1.4.49 — single schema for the per-user Coach opt-out flag. Previously
 // split into `disableCoachBody` (PATCH request) and `disableCoachData`
 // (response payload), both `z.object({ disableCoach: z.boolean() })`. The
@@ -374,6 +411,54 @@ export const profilePaths: NonNullable<ZodOpenApiObject["paths"]> = {
       },
     },
   },
+  "/api/auth/me/modules": {
+    get: {
+      tags: ["Auth"],
+      summary: "Read the resolved per-user module enable/disable map",
+      description:
+        "Returns the fully-resolved `{ <moduleKey>: boolean }` map for every toggleable module. `cycle` reflects the cycle gate, `coach` reflects the resolved per-user opt-out + operator master flag, and the rest read the per-user disabled-allowlist (`modulePreferencesJson`). Default-on: a fresh account reads every module enabled. iOS/web read this to hide a whole module surface end-to-end.",
+      responses: {
+        "200": {
+          description: "Resolved module map.",
+          content: {
+            "application/json": {
+              schema: dataEnvelope(
+                moduleMapEnvelopeInner,
+                "GetModulesResponse",
+              ),
+            },
+          },
+        },
+        ...stdResponses,
+      },
+    },
+    patch: {
+      tags: ["Auth"],
+      summary: "Update per-user module enable/disable preferences",
+      description:
+        "Merges the supplied keys into the persisted disabled-allowlist (`modulePreferencesJson`) field-by-field — a PATCH touching only one module leaves the siblings intact. Refuses to disable a core module (`weight`, `bloodPressure`, `pulse`, `medications`) or any unknown key with a 422. `userId` is never accepted from the body. Always returns the fully-resolved next-state map so clients can hard-set their optimistic update. Rate-limit 60/min per user.",
+      requestBody: {
+        required: true,
+        content: {
+          "application/json": { schema: modulePrefsPatchRequest },
+        },
+      },
+      responses: {
+        "200": {
+          description: "Resolved next-state module map echoed back.",
+          content: {
+            "application/json": {
+              schema: dataEnvelope(
+                moduleMapEnvelopeInner,
+                "PatchModulesResponse",
+              ),
+            },
+          },
+        },
+        ...stdResponses,
+      },
+    },
+  },
   "/api/auth/me/source-priority": {
     get: {
       tags: ["Auth"],
diff --git a/src/lib/validations/modules.ts b/src/lib/validations/modules.ts
new file mode 100644
index 000000000..44c29ebf6
--- /dev/null
+++ b/src/lib/validations/modules.ts
@@ -0,0 +1,33 @@
+/**
+ * v1.18.0 — module enable/disable request validation.
+ *
+ * The PATCH body is a partial map of TOGGLEABLE module keys → boolean.
+ * Only keys in the canonical registry (`MODULE_KEYS`) are accepted; a
+ * core-domain key (`weight`, `bloodPressure`, `pulse`, `medications`) or
+ * any unknown key is a 422 — so the core measurement engine + meds can
+ * never be disabled through this surface (defence-in-depth on top of the
+ * gate, which has no key to flip for core domains anyway).
+ *
+ * `strict()` rejects unknown keys outright rather than silently dropping
+ * them, so a client gets a clear error instead of a no-op.
+ *
+ * The shared shape is reused by the OpenAPI registry so the wire
+ * contract stays single-source.
+ */
+import { z } from "zod/v4";
+
+import { MODULE_KEYS } from "@/lib/modules/registry";
+
+/** Build `{ <toggleableKey>?: boolean }` from the canonical key list. */
+const moduleShape = Object.fromEntries(
+  MODULE_KEYS.map((k) => [k, z.boolean().optional()]),
+) as Record<(typeof MODULE_KEYS)[number], z.ZodOptional<z.ZodBoolean>>;
+
+/**
+ * Partial module-preferences PATCH body. Every key is an optional
+ * boolean; omitted keys are left untouched server-side. `strict()`
+ * rejects any key not in `MODULE_KEYS` (including core domains).
+ */
+export const modulePrefsPatchSchema = z.object(moduleShape).strict();
+
+export type ModulePrefsPatch = z.infer<typeof modulePrefsPatchSchema>;