refactor(mobile): collapse the broker replay guard into one window

Two classes and two Sets tracked the same thing: a page-minted id the broker
has already honoured. Request and subscription ids share one window now. It
stays a module rather than a broker field because the broker sits at its
max-lines ceiling.

Claude-Session: https://claude.ai/code/session_01JNnE9qzUZMMnqpZWCqM3nb

mobile/src/mobile-web/mobile-web-broker-replay-guard.ts

@@ -1,35 +0,0 @@
-import {
-  MOBILE_WEB_BRIDGE_MAX_PENDING_REQUESTS,
-  MOBILE_WEB_BRIDGE_MAX_SUBSCRIPTIONS
-} from '../../../src/shared/mobile-web/bridge-contract'
-import { MobileWebMessageReplayWindow } from './mobile-web-message-replay-window'
-
-export class MobileWebBrokerReplayGuard {
-  private readonly requests = new MobileWebMessageReplayWindow(
-    MOBILE_WEB_BRIDGE_MAX_PENDING_REQUESTS * 4
-  )
-  private readonly subscriptions = new MobileWebMessageReplayWindow(
-    MOBILE_WEB_BRIDGE_MAX_SUBSCRIPTIONS * 4
-  )
-
-  acceptRequest(id: string, active: boolean): boolean {
-    if (active || this.requests.has(id)) {
-      return false
-    }
-    this.requests.remember(id)
-    return true
-  }
-
-  acceptSubscription(id: string): boolean {
-    if (this.subscriptions.has(id)) {
-      return false
-    }
-    this.subscriptions.remember(id)
-    return true
-  }
-
-  clear(): void {
-    this.requests.clear()
-    this.subscriptions.clear()
-  }
-}

mobile/src/mobile-web/mobile-web-broker-replay-window.test.ts

@@ -0,0 +1,34 @@
+import { describe, expect, it } from 'vitest'
+import { MobileWebBrokerReplayWindow } from './mobile-web-broker-replay-window'
+
+describe('mobile web broker replay window', () => {
+  it('honours an id once and shares one window across request and subscription ids', () => {
+    const replay = new MobileWebBrokerReplayWindow()
+
+    expect(replay.accept('request-1')).toBe(true)
+    expect(replay.accept('request-1')).toBe(false)
+    expect(replay.accept('subscription-1')).toBe(true)
+    expect(replay.accept('subscription-1')).toBe(false)
+  })
+
+  it('evicts the oldest id rather than exhausting a long-lived session', () => {
+    const replay = new MobileWebBrokerReplayWindow()
+    const ids = Array.from({ length: 5_000 }, (_, index) => `id-${index}`)
+
+    for (const id of ids) {
+      expect(replay.accept(id)).toBe(true)
+    }
+
+    expect(replay.accept(ids[0]!)).toBe(true)
+    expect(replay.accept(ids.at(-1)!)).toBe(false)
+  })
+
+  it('clears all authority on disposal', () => {
+    const replay = new MobileWebBrokerReplayWindow()
+
+    replay.accept('request-1')
+    replay.clear()
+
+    expect(replay.accept('request-1')).toBe(true)
+  })
+})

mobile/src/mobile-web/mobile-web-broker-replay-window.ts

@@ -0,0 +1,31 @@
+import {
+  MOBILE_WEB_BRIDGE_MAX_PENDING_REQUESTS,
+  MOBILE_WEB_BRIDGE_MAX_SUBSCRIPTIONS
+} from '../../../src/shared/mobile-web/bridge-contract'
+
+// One window covers request and subscription ids alike: both are page-minted and honoured once.
+const REPLAY_WINDOW =
+  (MOBILE_WEB_BRIDGE_MAX_PENDING_REQUESTS + MOBILE_WEB_BRIDGE_MAX_SUBSCRIPTIONS) * 4
+
+export class MobileWebBrokerReplayWindow {
+  private readonly ids = new Set<string>()
+
+  /** An id evicted from the window while still in flight is caught by the broker's pending map. */
+  accept(id: string): boolean {
+    if (this.ids.has(id)) {
+      return false
+    }
+    this.ids.add(id)
+    if (this.ids.size > REPLAY_WINDOW) {
+      const oldest = this.ids.values().next().value
+      if (oldest !== undefined) {
+        this.ids.delete(oldest)
+      }
+    }
+    return true
+  }
+
+  clear(): void {
+    this.ids.clear()
+  }
+}

mobile/src/mobile-web/mobile-web-capability-broker.ts

@@ -20,7 +20,7 @@ import { executeMobileWebCapabilityRequest } from './mobile-web-capability-execu
 import { MobileWebCapabilityAuthorities } from './mobile-web-capability-authorities'
 import type { MobileWebCapabilityBrokerOptions } from './mobile-web-capability-broker-options'
 import { MobileWebBrokerMessageSender } from './mobile-web-broker-message-sender'
-import { MobileWebBrokerReplayGuard } from './mobile-web-broker-replay-guard'
+import { MobileWebBrokerReplayWindow } from './mobile-web-broker-replay-window'
 import { rememberMobileWebBrokerRoute } from './mobile-web-broker-route-memory'
 import { resolveMobileWebHostNavigationRoute } from './mobile-web-host-navigation-route'
 import {
@@ -40,7 +40,7 @@ type PendingRequest = { operationKey: string; subscriptionId?: string; cancelled
 
 export class MobileWebCapabilityBroker {
   private readonly pending = new Map<string, PendingRequest>()
-  private readonly replay = new MobileWebBrokerReplayGuard()
+  private readonly replay = new MobileWebBrokerReplayWindow()
   private readonly subscriptions: MobileWebCapabilitySubscriptions
   private readonly terminalStreams: MobileWebTerminalStreams
   private readonly speechAuthority: MobileWebSpeechAuthority
@@ -146,7 +146,7 @@ export class MobileWebCapabilityBroker {
     )
   }
   private async handleRequest(request: PageRequest): Promise<void> {
-    if (!this.replay.acceptRequest(request.requestId, this.pending.has(request.requestId))) {
+    if (this.pending.has(request.requestId) || !this.replay.accept(request.requestId)) {
       await this.messages.error(request.requestId, 'invalid_request', false)
       return
     }
@@ -158,10 +158,7 @@ export class MobileWebCapabilityBroker {
       await this.messages.error(request.requestId, 'unsupported_capability', false)
       return
     }
-    if (
-      request.mode === 'subscription' &&
-      !this.replay.acceptSubscription(request.subscriptionId)
-    ) {
+    if (request.mode === 'subscription' && !this.replay.accept(request.subscriptionId)) {
       await this.messages.error(request.requestId, 'invalid_request', false)
       return
     }

mobile/src/mobile-web/mobile-web-message-replay-window.test.ts

@@ -1,33 +0,0 @@
-import { describe, expect, it } from 'vitest'
-import { MobileWebMessageReplayWindow } from './mobile-web-message-replay-window'
-
-describe('mobile web message replay window', () => {
-  it('rejects recent IDs without permanently exhausting a long-lived session', () => {
-    const replay = new MobileWebMessageReplayWindow(3)
-
-    replay.remember('a')
-    replay.remember('b')
-    replay.remember('c')
-    expect(replay.has('a')).toBe(true)
-
-    replay.remember('d')
-    expect(replay.has('a')).toBe(false)
-    expect(replay.has('b')).toBe(true)
-    expect(replay.has('d')).toBe(true)
-  })
-
-  it('refreshes an existing ID and clears all authority on disposal', () => {
-    const replay = new MobileWebMessageReplayWindow(2)
-
-    replay.remember('a')
-    replay.remember('b')
-    replay.remember('a')
-    replay.remember('c')
-    expect(replay.has('a')).toBe(true)
-    expect(replay.has('b')).toBe(false)
-
-    replay.clear()
-    expect(replay.has('a')).toBe(false)
-    expect(replay.has('c')).toBe(false)
-  })
-})

mobile/src/mobile-web/mobile-web-message-replay-window.ts

@@ -1,31 +0,0 @@
-export class MobileWebMessageReplayWindow {
-  private readonly ids = new Set<string>()
-
-  constructor(private readonly limit: number) {
-    if (!Number.isInteger(limit) || limit < 1) {
-      throw new Error('mobile_web_replay_window_invalid')
-    }
-  }
-
-  has(id: string): boolean {
-    return this.ids.has(id)
-  }
-
-  remember(id: string): void {
-    if (this.ids.delete(id)) {
-      this.ids.add(id)
-      return
-    }
-    this.ids.add(id)
-    if (this.ids.size > this.limit) {
-      const oldest = this.ids.values().next().value
-      if (oldest !== undefined) {
-        this.ids.delete(oldest)
-      }
-    }
-  }
-
-  clear(): void {
-    this.ids.clear()
-  }
-}