fix: Fix leaky Frigate subscriptions/unsubscriptions (#2513)

src/camera-manager/camera.ts

@@ -58,6 +58,7 @@ export class Camera {
   protected _capabilities?: Capabilities;
   protected _eventCallback?: CameraEventCallback;
   protected _destroyCallbacks: DestroyCallback[] = [];
+  protected _destroyed = false;
   protected _entity: Entity | null = null;
 
   constructor(
@@ -91,7 +92,7 @@ export class Camera {
       await this._getTriggerEntities(options);
       this._config.triggers.entities = uniq(this._config.triggers.entities);
 
-      // Subscribe to state based triggers.
+      // Subscribe to state based triggers (sync; no race with destroy).
       options.stateWatcher.subscribe(
         this._stateChangeHandler,
         this._config.triggers.entities,
@@ -101,14 +102,34 @@ export class Camera {
       // Subscribe to event based triggers.
       for (const event of this._config.triggers.events) {
         const request = this._buildEventSubscriptionRequest(event);
-        await options.eventWatcher.subscribe(options.hass, request);
-        this._onDestroy(() => options.eventWatcher.unsubscribe(request));
+        await this._setupSubscription(
+          () => options.eventWatcher.subscribe(options.hass, request),
+          () => options.eventWatcher.unsubscribe(request),
+        );
       }
     }
 
     return this;
   }
 
+  /**
+   * Wire up an async subscription with its teardown. Registers the unsubscribe
+   * callback synchronously before awaiting subscribe, so a destroy during the
+   * await reliably triggers cleanup; short-circuits if destroy has already
+   * run, so the cleanup callback can't fire (and enqueue an unsubscribe)
+   * before the subscribe runs.
+   */
+  protected async _setupSubscription(
+    subscribe: () => Promise<void>,
+    unsubscribe: () => void | Promise<void>,
+  ): Promise<void> {
+    if (this._destroyed) {
+      return;
+    }
+    this._onDestroy(unsubscribe);
+    await subscribe();
+  }
+
   private _buildEventSubscriptionRequest(event: TriggerEvent): EventSubscriptionRequest {
     const filter = event.event_data;
     return {
@@ -246,7 +267,10 @@ export class Camera {
   }
 
   public async destroy(): Promise<void> {
-    await Promise.all(this._destroyCallbacks.map((callback) => callback()));
+    this._destroyed = true;
+    const callbacks = this._destroyCallbacks;
+    this._destroyCallbacks = [];
+    await Promise.all(callbacks.map((callback) => callback()));
   }
 
   public getConfig(): CameraConfig {

src/camera-manager/frigate/camera.ts

@@ -473,8 +473,10 @@ export class FrigateCamera extends Camera {
         event.after.camera === config.frigate.camera_name,
     };
 
-    await frigateEventWatcher.subscribe(hass, request);
-    this._onDestroy(() => frigateEventWatcher.unsubscribe(request));
+    await this._setupSubscription(
+      () => frigateEventWatcher.subscribe(hass, request),
+      () => frigateEventWatcher.unsubscribe(request),
+    );
   }
 
   private _frigateEventHandler = (ev: FrigateEventChange): void => {
@@ -548,8 +550,10 @@ export class FrigateCamera extends Camera {
         review.after.camera === config.frigate.camera_name,
     };
 
-    await frigateReviewWatcher.subscribe(hass, request);
-    this._onDestroy(() => frigateReviewWatcher.unsubscribe(request));
+    await this._setupSubscription(
+      () => frigateReviewWatcher.subscribe(hass, request),
+      () => frigateReviewWatcher.unsubscribe(request),
+    );
   }
 
   private _frigateReviewHandler = (review: FrigateReviewChange): void => {

src/camera-manager/frigate/watcher.ts

@@ -1,5 +1,6 @@
 import { z } from 'zod';
-import { HomeAssistant, SubscriptionUnsubscribe } from '../../ha/types';
+import { HomeAssistant } from '../../ha/types';
+import { KeyedSubscriptionManager } from '../../utils/keyed-subscription-manager';
 import {
   FrigateEventChange,
   FrigateReviewChange,
@@ -17,53 +18,39 @@ export interface FrigateWatcherRequest<T> {
 // Generic subscription interface
 export interface FrigateWatcherSubscriptionInterface<T> {
   subscribe(hass: HomeAssistant, request: FrigateWatcherRequest<T>): Promise<void>;
-  unsubscribe(request: FrigateWatcherRequest<T>): void;
+  unsubscribe(request: FrigateWatcherRequest<T>): Promise<void>;
 }
 
 /**
- * Base class for Frigate WebSocket watchers.
- * Handles subscription management and message routing to callbacks.
+ * Base class for Frigate WebSocket watchers. Counted per `instanceID`: the
+ * first subscriber for an instance opens the WS subscription, the last to
+ * unsubscribe tears it down. Each message is parsed, schema-validated, and
+ * fanned out to every registered request whose `instanceID` matches and whose
+ * `matcher` accepts the payload.
  */
 abstract class FrigateWatcher<T> implements FrigateWatcherSubscriptionInterface<T> {
   protected abstract _type: string;
   protected abstract _schema: z.ZodType<T>;
 
-  protected _requests: FrigateWatcherRequest<T>[] = [];
-  protected _unsubscribeCallback: Record<string, SubscriptionUnsubscribe> = {};
+  private _subscriptions = new KeyedSubscriptionManager<
+    string,
+    FrigateWatcherRequest<T>
+  >((request) => request.instanceID);
 
   public async subscribe(
     hass: HomeAssistant,
     request: FrigateWatcherRequest<T>,
   ): Promise<void> {
-    const shouldSubscribe = !this._hasSubscribers(request.instanceID);
-    this._requests.push(request);
-    if (shouldSubscribe) {
-      this._unsubscribeCallback[request.instanceID] =
-        await hass.connection.subscribeMessage<string>(
-          (data) => this._receiveHandler(request.instanceID, data),
-          { type: this._type, instance_id: request.instanceID },
-        );
-    }
+    await this._subscriptions.subscribe(request, () =>
+      hass.connection.subscribeMessage<string>(
+        (data) => this._receiveHandler(request.instanceID, data),
+        { type: this._type, instance_id: request.instanceID },
+      ),
+    );
   }
 
   public async unsubscribe(request: FrigateWatcherRequest<T>): Promise<void> {
-    this._requests = this._requests.filter(
-      (existingRequest) => existingRequest !== request,
-    );
-
-    if (!this._hasSubscribers(request.instanceID)) {
-      const callback = this._unsubscribeCallback[request.instanceID];
-      delete this._unsubscribeCallback[request.instanceID];
-
-      // Callback may be undefined if unsubscribe is called while subscribe is
-      // still awaiting the Home Assistant connection.
-      await callback?.();
-    }
-  }
-
-  protected _hasSubscribers(instanceID: string): boolean {
-    return !!this._requests.filter((request) => request.instanceID === instanceID)
-      .length;
+    await this._subscriptions.unsubscribe(request);
   }
 
   protected _receiveHandler(instanceID: string, data: string): void {
@@ -82,11 +69,8 @@ abstract class FrigateWatcher<T> implements FrigateWatcherSubscriptionInterface<
       return;
     }
 
-    for (const request of this._requests) {
-      if (
-        request.instanceID === instanceID &&
-        (!request.matcher || request.matcher(parseResult.data))
-      ) {
+    for (const request of this._subscriptions.getRequestsForKey(instanceID)) {
+      if (!request.matcher || request.matcher(parseResult.data)) {
         request.callback(parseResult.data);
       }
     }

src/camera-manager/manager.ts

@@ -256,7 +256,7 @@ export class CameraManager {
     );
 
     const destroyCameras = async () => {
-      cameras.forEach((camera) => camera.destroy());
+      await allPromises(cameras, (camera) => camera.destroy());
     };
     const cameraIDs: Set<string> = new Set();
 

src/card-controller/call/ringtone.ts

@@ -12,9 +12,10 @@ import { WestminsterTone } from './tones/westminster';
 // card placed twice), all of which may independently react to the same trigger
 // state change -- with no lock, every instance would start its own AudioContext
 // and the audio would layer. First-to-start wins; subsequent `start()` calls
-// from other holders are no-ops until the active one releases via `stop()`. The
-// lock auto-recovers from a holder that forgot to release (e.g. a controller
-// GC'd without disconnect cleanup) via the `isPlaying()` sweep below.
+// from other holders are no-ops until the active one releases via `stop()`.
+// The `isPlaying()` sweep below is defensive against a future code path that
+// clears `_tone` without removing from the lock -- today every such path keeps
+// them in sync, but the sweep prevents a regression from wedging the lock.
 const sharedLock = new Set<Ringtone>();
 
 export class Ringtone {

src/card-controller/hass/event-watcher.ts

@@ -1,5 +1,6 @@
 import { HassEvent } from 'home-assistant-js-websocket';
-import { HomeAssistant, SubscriptionUnsubscribe } from '../../ha/types';
+import { HomeAssistant } from '../../ha/types';
+import { KeyedSubscriptionManager } from '../../utils/keyed-subscription-manager';
 
 export interface EventSubscriptionRequest {
   event_type: string;
@@ -23,50 +24,30 @@ export interface EventWatcherSubscriptionInterface {
  * payload.
  */
 export class EventWatcher implements EventWatcherSubscriptionInterface {
-  private _requests: EventSubscriptionRequest[] = [];
-
-  // Stored as a promise so an unsubscribe that races against an in-flight
-  // subscribe can await completion before tearing down -- otherwise the unsub
-  // func is unavailable and the subscription would leak (via hass.connection's
-  // internal subscription map).
-  private _unsubscribers = new Map<string, Promise<SubscriptionUnsubscribe>>();
+  private _subscriptions = new KeyedSubscriptionManager<
+    string,
+    EventSubscriptionRequest
+  >((request) => request.event_type);
 
   public async subscribe(
     hass: HomeAssistant,
     request: EventSubscriptionRequest,
   ): Promise<void> {
-    const isFirst = !this._hasSubscribers(request.event_type);
-    this._requests.push(request);
-    if (isFirst) {
-      const pendingSubscription = hass.connection.subscribeEvents<HassEvent>(
+    await this._subscriptions.subscribe(request, () =>
+      hass.connection.subscribeEvents<HassEvent>(
         (event) => this._receiveEvent(event),
         request.event_type,
-      );
-      this._unsubscribers.set(request.event_type, pendingSubscription);
-      await pendingSubscription;
-    }
+      ),
+    );
   }
 
   public async unsubscribe(request: EventSubscriptionRequest): Promise<void> {
-    this._requests = this._requests.filter((r) => r !== request);
-    if (!this._hasSubscribers(request.event_type)) {
-      const pendingSubscription = this._unsubscribers.get(request.event_type);
-      this._unsubscribers.delete(request.event_type);
-      const unsubscribeCallback = await pendingSubscription;
-      await unsubscribeCallback?.();
-    }
-  }
-
-  private _hasSubscribers(eventType: string): boolean {
-    return this._requests.some((r) => r.event_type === eventType);
+    await this._subscriptions.unsubscribe(request);
   }
 
   private _receiveEvent(event: HassEvent): void {
-    for (const request of this._requests) {
-      if (
-        request.event_type === event.event_type &&
-        (!request.matcher || request.matcher(event.data))
-      ) {
+    for (const request of this._subscriptions.getRequestsForKey(event.event_type)) {
+      if (!request.matcher || request.matcher(event.data)) {
         request.callback(event.data);
       }
     }

src/ha/types.ts

@@ -243,8 +243,6 @@ export interface HassStateDifference {
   newState: HassEntity;
 }
 
-export type SubscriptionUnsubscribe = () => Promise<void>;
-
 // *************************************************************************
 //                     Home Assistant API types.
 // *************************************************************************

src/utils/keyed-subscription-manager.ts

@@ -0,0 +1,65 @@
+import PQueue from 'p-queue';
+
+type UnsubscribeFn = () => Promise<void>;
+type SubscribeFn = () => Promise<UnsubscribeFn>;
+
+/**
+ * Manages subscriptions keyed by `K`: the first subscriber for a key invokes
+ * `subscribeFn` to establish the underlying connection, subsequent subscribers
+ * for the same key piggyback on it, and the last to unsubscribe tears it down.
+ *
+ * Operations for a given key run through a single-concurrency queue, so
+ * subscribe and unsubscribe cannot interleave for the same key -- no race
+ * windows by construction. This aims to a leak-proof reusable subscription
+ * manager.
+ */
+export class KeyedSubscriptionManager<K, R> {
+  private _requests: R[] = [];
+  private _unsubscribers = new Map<K, UnsubscribeFn>();
+  private _queues = new Map<K, PQueue>();
+  private _getKeyFn: (request: R) => K;
+
+  constructor(getKeyFn: (request: R) => K) {
+    this._getKeyFn = getKeyFn;
+  }
+
+  public async subscribe(request: R, subscribeFn: SubscribeFn): Promise<void> {
+    const key = this._getKeyFn(request);
+    await this._queueFor(key).add(async () => {
+      this._requests.push(request);
+      if (!this._unsubscribers.has(key)) {
+        const unsubscribe = await subscribeFn();
+        this._unsubscribers.set(key, unsubscribe);
+      }
+    });
+  }
+
+  public async unsubscribe(request: R): Promise<void> {
+    const key = this._getKeyFn(request);
+    await this._queueFor(key).add(async () => {
+      this._requests = this._requests.filter((r) => r !== request);
+      if (!this._hasSubscribers(key)) {
+        const unsubscribe = this._unsubscribers.get(key);
+        this._unsubscribers.delete(key);
+        await unsubscribe?.();
+      }
+    });
+  }
+
+  public getRequestsForKey(key: K): readonly R[] {
+    return this._requests.filter((r) => this._getKeyFn(r) === key);
+  }
+
+  private _queueFor(key: K): PQueue {
+    let queue = this._queues.get(key);
+    if (!queue) {
+      queue = new PQueue({ concurrency: 1 });
+      this._queues.set(key, queue);
+    }
+    return queue;
+  }
+
+  private _hasSubscribers(key: K): boolean {
+    return this._requests.some((r) => this._getKeyFn(r) === key);
+  }
+}

tests/camera-manager/frigate/camera.test.ts

@@ -1,5 +1,5 @@
 import { format } from 'date-fns';
-import { beforeEach, describe, expect, it, vi } from 'vitest';
+import { assert, beforeEach, describe, expect, it, vi } from 'vitest';
 import { mock } from 'vitest-mock-extended';
 import { CameraManagerEngine } from '../../../src/camera-manager/engine';
 import { FrigateCamera } from '../../../src/camera-manager/frigate/camera';
@@ -27,6 +27,7 @@ import { ViewMediaType } from '../../../src/view/item';
 import { EntityRegistryManagerMock } from '../../ha/registry/entity/mock';
 import {
   createCameraConfig,
+  createCapabilities,
   createHASS,
   createRegistryEntity,
   createStateEntity,
@@ -965,6 +966,61 @@ describe('FrigateCamera', () => {
       expect(eventWatcher.unsubscribe).toBeCalled();
     });
 
+    it('should unsubscribe on destroy while event subscription is pending', async () => {
+      const camera = new FrigateCamera(
+        createCameraConfig({
+          frigate: { client_id: 'CLIENT_ID', camera_name: 'front_door' },
+          triggers: {
+            media_events: ['events'],
+            reviews: { severities: ['high'] },
+          },
+        }),
+        mock<CameraManagerEngine>(),
+      );
+      const hass = createHASS();
+      let resolveSubscribe: () => void = () => {};
+      const eventWatcher = mock<FrigateEventWatcher>();
+      const reviewWatcher = mock<FrigateReviewWatcher>();
+      vi.mocked(eventWatcher.subscribe).mockReturnValue(
+        new Promise<void>((resolve) => {
+          resolveSubscribe = resolve;
+        }),
+      );
+
+      const initializePromise = camera.initialize({
+        hass: hass,
+        entityRegistryManager: mock<EntityRegistryManager>(),
+        stateWatcher: mock<StateWatcherSubscriptionInterface>(),
+        eventWatcher: mock<EventWatcherSubscriptionInterface>(),
+        frigateEventWatcher: eventWatcher,
+        frigateReviewWatcher: reviewWatcher,
+
+        // Pre-built so `_buildCapabilities` (which calls the un-mocked
+        // `liveProviderSupports2WayAudio`) is skipped and init reaches the
+        // pending Frigate event subscribe.
+        capabilityOptions: { capabilities: createCapabilities({ trigger: true }) },
+      });
+      await vi.waitFor(() => expect(eventWatcher.subscribe).toBeCalled());
+
+      await camera.destroy();
+
+      // Destroy iterated `_destroyCallbacks` and called the unsubscribe that
+      // was registered before the (still pending) event subscribe.
+      const subscribeCall = vi.mocked(eventWatcher.subscribe).mock.calls[0];
+      assert(subscribeCall);
+      expect(eventWatcher.unsubscribe).toBeCalledWith(subscribeCall[1]);
+
+      resolveSubscribe();
+      await initializePromise;
+
+      // The subsequent `_subscribeToReviews` short-circuited on `_destroyed`,
+      // so the review watcher was never subscribed (and so never needs an
+      // unsubscribe -- which would otherwise be ordered before the subscribe
+      // in the per-key PQueue and leak the resulting subscription).
+      expect(reviewWatcher.subscribe).not.toBeCalled();
+      expect(reviewWatcher.unsubscribe).not.toBeCalled();
+    });
+
     describe('should call handler correctly', () => {
       describe('should handle event type correctly', () => {
         it.each([

tests/camera-manager/frigate/watcher.test.ts

@@ -138,12 +138,19 @@ describe('FrigateEventWatcher', () => {
     const subscribePromise = stateWatcher.subscribe(hass, request);
 
     // Unsubscribe while subscription is still pending.
-    await stateWatcher.unsubscribe(request);
+    const unsubscribePromise = stateWatcher.unsubscribe(request);
 
-    // Complete the subscription.
+    // Complete the subscription: both subscribe and unsubscribe await the same
+    // pending promise, and unsubscribe then invokes the resolved unsub.
+    const unsubscribeCallback = vi.fn();
     assert(resolveSubscription);
-    resolveSubscription(vi.fn());
+    resolveSubscription(unsubscribeCallback);
     await subscribePromise;
+    await unsubscribePromise;
+
+    expect(unsubscribeCallback).toBeCalledTimes(1);
+    callHASubscribeMessageCallback(hass, JSON.stringify(createEventChange()));
+    expect(request.callback).not.toBeCalled();
   });
 
   describe('should call handler', () => {

tests/camera-manager/manager.test.ts

@@ -27,6 +27,7 @@ import {
   QueryType,
 } from '../../src/camera-manager/types.js';
 import { CardController } from '../../src/card-controller/controller.js';
+import { StateWatcherSubscriptionInterface } from '../../src/card-controller/hass/state-watcher.js';
 import { sortItems } from '../../src/card-controller/view/sort.js';
 import { CameraConfig } from '../../src/config/schema/cameras.js';
 import { advancedCameraCardConfigSchema } from '../../src/config/schema/types.js';
@@ -274,6 +275,7 @@ describe('CameraManager', () => {
       config?: CameraConfig;
       engineType?: Engine | null;
       capabilties?: Capabilities;
+      stateWatcher?: StateWatcherSubscriptionInterface;
     }[] = [{}],
     factory?: CameraManagerEngineFactory,
   ): CameraManager => {
@@ -300,6 +302,7 @@ describe('CameraManager', () => {
               cameraConfig,
               mockEngine,
               camera.capabilties ?? createCapabilities(),
+              camera.stateWatcher,
             ),
         );
       }
@@ -399,6 +402,48 @@ describe('CameraManager', () => {
       );
     });
 
+    it('should await camera destruction before throwing on duplicate id', async () => {
+      const api = createCardAPI();
+      vi.mocked(api.getHASSManager().getHASS).mockReturnValue(createHASS());
+
+      const cameraConfig = createCameraConfig({
+        id: 'DUPLICATE',
+        engine: 'generic',
+      });
+
+      // Camera.destroy() awaits its _destroyCallbacks, one of which is the
+      // trigger-path unsubscribe. By returning a deferred Promise from each
+      // camera's stateWatcher.unsubscribe, we make destroy completion
+      // externally observable without spying on any Camera method.
+      const order: string[] = [];
+      const buildStateWatcher = (): StateWatcherSubscriptionInterface => {
+        const watcher = mock<StateWatcherSubscriptionInterface>();
+        vi.mocked(watcher.unsubscribe).mockImplementation(
+          () =>
+            new Promise<void>((resolve) =>
+              setTimeout(() => {
+                order.push('destroy-done');
+                resolve();
+              }, 0),
+            ),
+        );
+        return watcher;
+      };
+
+      const cameraEntry = {
+        config: cameraConfig,
+        capabilties: createCapabilities({ trigger: true }),
+      };
+      const manager = createCameraManager(api, mock<CameraManagerEngine>(), [
+        { ...cameraEntry, stateWatcher: buildStateWatcher() },
+        { ...cameraEntry, stateWatcher: buildStateWatcher() },
+      ]);
+
+      await manager.initializeCamerasFromConfig().catch(() => order.push('throw'));
+
+      expect(order).toEqual(['destroy-done', 'destroy-done', 'throw']);
+    });
+
     it('should reject missing engine', async () => {
       const api = createCardAPI();
       vi.mocked(api.getHASSManager().getHASS).mockReturnValue(createHASS());

tests/test-utils.ts

@@ -120,11 +120,12 @@ export const createInitializedCamera = async (
   config: CameraConfig,
   engine: CameraManagerEngine,
   capabilities?: Capabilities,
+  stateWatcher?: StateWatcherSubscriptionInterface,
 ): Promise<Camera> => {
   const camera = new Camera(config, engine);
   await camera.initialize({
     hass: createHASS(),
-    stateWatcher: mock<StateWatcherSubscriptionInterface>(),
+    stateWatcher: stateWatcher ?? mock<StateWatcherSubscriptionInterface>(),
     eventWatcher: mock<EventWatcherSubscriptionInterface>(),
     ...(capabilities ? { capabilityOptions: { capabilities } } : {}),
   });

tests/utils/keyed-subscription-manager.test.ts

@@ -0,0 +1,102 @@
+import { describe, expect, it, vi } from 'vitest';
+import { KeyedSubscriptionManager } from '../../src/utils/keyed-subscription-manager';
+
+interface TestRequest {
+  key: string;
+  callback: () => void;
+}
+
+const create = (): KeyedSubscriptionManager<string, TestRequest> =>
+  new KeyedSubscriptionManager<string, TestRequest>((r) => r.key);
+
+describe('KeyedSubscriptionManager', () => {
+  it('should open the subscription once per key regardless of subscriber count', async () => {
+    const manager = create();
+    const subscribeFn = vi.fn().mockResolvedValue(vi.fn());
+
+    await manager.subscribe({ key: 'a', callback: vi.fn() }, subscribeFn);
+    await manager.subscribe({ key: 'a', callback: vi.fn() }, subscribeFn);
+
+    expect(subscribeFn).toBeCalledTimes(1);
+  });
+
+  it('should open a separate subscription for each distinct key', async () => {
+    const manager = create();
+    const subscribeFn = vi.fn().mockResolvedValue(vi.fn());
+
+    await manager.subscribe({ key: 'a', callback: vi.fn() }, subscribeFn);
+    await manager.subscribe({ key: 'b', callback: vi.fn() }, subscribeFn);
+
+    expect(subscribeFn).toBeCalledTimes(2);
+  });
+
+  it('should tear down the subscription only when the last subscriber for a key unsubscribes', async () => {
+    const manager = create();
+    const unsub = vi.fn();
+    const subscribeFn = vi.fn().mockResolvedValue(unsub);
+
+    const req1 = { key: 'a', callback: vi.fn() };
+    const req2 = { key: 'a', callback: vi.fn() };
+    await manager.subscribe(req1, subscribeFn);
+    await manager.subscribe(req2, subscribeFn);
+
+    await manager.unsubscribe(req1);
+    expect(unsub).not.toBeCalled();
+
+    await manager.unsubscribe(req2);
+    expect(unsub).toBeCalledTimes(1);
+  });
+
+  it('should await a pending subscribe before tearing down when unsubscribed mid-flight', async () => {
+    const manager = create();
+    const unsub = vi.fn();
+
+    let resolveOpen: ((cb: () => Promise<void>) => void) | undefined;
+    const openPromise = new Promise<() => Promise<void>>((resolve) => {
+      resolveOpen = resolve;
+    });
+    const subscribeFn = vi.fn().mockReturnValue(openPromise);
+
+    const req = { key: 'a', callback: vi.fn() };
+    const subscribePromise = manager.subscribe(req, subscribeFn);
+    const unsubscribePromise = manager.unsubscribe(req);
+
+    resolveOpen?.(unsub);
+    await subscribePromise;
+    await unsubscribePromise;
+
+    expect(unsub).toBeCalledTimes(1);
+  });
+
+  it('should expose the requests matching a given key', async () => {
+    const manager = create();
+    const subscribeFn = vi.fn().mockResolvedValue(vi.fn());
+
+    const reqA1 = { key: 'a', callback: vi.fn() };
+    const reqA2 = { key: 'a', callback: vi.fn() };
+    const reqB = { key: 'b', callback: vi.fn() };
+    await manager.subscribe(reqA1, subscribeFn);
+    await manager.subscribe(reqA2, subscribeFn);
+    await manager.subscribe(reqB, subscribeFn);
+
+    expect(manager.getRequestsForKey('a')).toEqual([reqA1, reqA2]);
+    expect(manager.getRequestsForKey('b')).toEqual([reqB]);
+
+    await manager.unsubscribe(reqA1);
+    expect(manager.getRequestsForKey('a')).toEqual([reqA2]);
+  });
+
+  it('should treat unsubscribe of an unknown request as a no-op', async () => {
+    const manager = create();
+    const unsub = vi.fn();
+    const subscribeFn = vi.fn().mockResolvedValue(unsub);
+
+    const subscribed = { key: 'a', callback: vi.fn() };
+    await manager.subscribe(subscribed, subscribeFn);
+
+    await manager.unsubscribe({ key: 'a', callback: vi.fn() });
+
+    expect(unsub).not.toBeCalled();
+    expect(manager.getRequestsForKey('a')).toEqual([subscribed]);
+  });
+});