fix(messages): bound sync rounds and dedupe incoming messages

A sync round that timed out was treated as a clean one, so history gaps were
recorded as complete and never retried. Rounds are now decided by
`message-sync-round.rules`, which separates a finished round from an abandoned
one, and incoming handlers drop duplicates that arrive over two transports.

toju-app/src/app/domains/chat/README.md

@@ -17,6 +17,7 @@ chat/
 │       ├── message-integrity.rules.ts          headHash, inventory refresh, revision merge predicates
 │       ├── message-revision.builder.rules.ts   buildMessageRevision, materializeMessageFromRevision
 │       ├── message-sync.rules.ts               Inventory-based sync: chunkArray, findMissingIds, limits
+│       ├── message-sync-round.rules.ts         Inventory round evidence: createInventoryRound, recordInventoryReply, isInventoryRoundClean
 │       └── auto-scroll.rules.ts                resolveAutoScrollBehavior (instant on channel switch, smooth for live msgs) + isStuckToBottom predicate
 │
 ├── feature/
@@ -128,6 +129,16 @@ sequenceDiagram
 
 `findMissingIds` compares each remote item's timestamp and reaction/attachment counts against the local map. Any item that is missing, newer, or has different counts is requested.
 
+### Polling cadence: only evidence buys the slow poll
+
+`store/messages/messages-sync.effects.ts` polls every connected peer for its inventory and alternates between `SYNC_POLL_FAST_MS` (10 s) and `SYNC_POLL_SLOW_MS` (15 min). Which one it picks is decided by the round model in `message-sync-round.rules.ts`, not by elapsed time:
+
+- The poll records who it actually reached. `sendToPeer` returns whether the payload entered an open data channel, so a peer listed as connected whose channel is closed counts as **undelivered**, not asked.
+- Each reply dispatches `peerInventoryCompared` with the number of ids that comparison showed we lack.
+- A round is **clean** only when every asked peer replied and no reply reported missing ids. A timed-out round, a partially answered round, and a round with an undelivered request are all dirty, and dirty keeps the fast poll.
+- Every scored round re-arms the poll timer, so the delay always comes from the verdict of the round that just closed - not from the previous round's verdict, which is how a client could end up waiting out 15 minutes right after discovering it was behind.
+- A reply that lands after its round closed (a peer answering the reconnect or room-activation kickoff) re-arms the fast cadence when it reports missing ids, so convergence never waits out a slow poll.
+
 ## GIF integration
 
 `KlipyService` checks availability on the active server, then proxies search requests through the server API. Rendered remote images now attempt a direct load first and only fall back to the image proxy after the browser reports a load failure, which is the practical approximation of a CORS or mixed-content fallback path in the renderer.

toju-app/src/app/domains/chat/domain/rules/message-sync-round.rules.spec.ts

@@ -0,0 +1,109 @@
+import {
+  describe,
+  it,
+  expect
+} from 'vitest';
+import {
+  createInventoryRound,
+  isInventoryRoundClean,
+  recordInventoryReply
+} from './message-sync-round.rules';
+
+describe('message-sync-round.rules', () => {
+  it('is clean when every asked peer replied with nothing missing', () => {
+    let round = createInventoryRound({
+      roomId: 'room-1',
+      askedPeerIds: ['peer-a', 'peer-b']
+    });
+
+    round = recordInventoryReply(round, { roomId: 'room-1', peerId: 'peer-a', missingIdCount: 0 });
+
+    expect(isInventoryRoundClean(round)).toBe(false);
+
+    round = recordInventoryReply(round, { roomId: 'room-1', peerId: 'peer-b', missingIdCount: 0 });
+
+    expect(isInventoryRoundClean(round)).toBe(true);
+  });
+
+  it('is dirty while a peer we asked has not replied', () => {
+    // A timed-out round is not a clean round: silence is not evidence of
+    // convergence, and treating it as clean drops the poll to the slow
+    // cadence while the peer still holds messages we never received.
+    const round = createInventoryRound({
+      roomId: 'room-1',
+      askedPeerIds: ['peer-a', 'peer-b']
+    });
+
+    expect(isInventoryRoundClean(
+      recordInventoryReply(round, { roomId: 'room-1', peerId: 'peer-a', missingIdCount: 0 })
+    )).toBe(false);
+  });
+
+  it('is dirty when a request could not be delivered', () => {
+    const round = createInventoryRound({
+      roomId: 'room-1',
+      askedPeerIds: ['peer-a'],
+      undeliveredPeerIds: ['peer-b']
+    });
+
+    expect(isInventoryRoundClean(
+      recordInventoryReply(round, { roomId: 'room-1', peerId: 'peer-a', missingIdCount: 0 })
+    )).toBe(false);
+  });
+
+  it('is dirty when any reply reported missing ids', () => {
+    let round = createInventoryRound({
+      roomId: 'room-1',
+      askedPeerIds: ['peer-a', 'peer-b']
+    });
+
+    round = recordInventoryReply(round, { roomId: 'room-1', peerId: 'peer-a', missingIdCount: 3 });
+    round = recordInventoryReply(round, { roomId: 'room-1', peerId: 'peer-b', missingIdCount: 0 });
+
+    expect(isInventoryRoundClean(round)).toBe(false);
+  });
+
+  it('is dirty when nobody was asked', () => {
+    expect(isInventoryRoundClean(createInventoryRound({ roomId: 'room-1', askedPeerIds: [] }))).toBe(false);
+    expect(isInventoryRoundClean(null)).toBe(false);
+  });
+
+  it('counts a reply from a peer outside the round, but not toward completeness', () => {
+    // A peer answering a room-activation kickoff still proves we are behind.
+    let round = createInventoryRound({
+      roomId: 'room-1',
+      askedPeerIds: ['peer-a']
+    });
+
+    round = recordInventoryReply(round, { roomId: 'room-1', peerId: 'peer-c', missingIdCount: 2 });
+
+    expect(isInventoryRoundClean(round)).toBe(false);
+    expect(round?.repliedPeerIds).toEqual([]);
+
+    round = recordInventoryReply(round, { roomId: 'room-1', peerId: 'peer-a', missingIdCount: 0 });
+
+    expect(isInventoryRoundClean(round)).toBe(false);
+  });
+
+  it('ignores replies for another room and never double-counts a peer', () => {
+    let round = createInventoryRound({
+      roomId: 'room-1',
+      askedPeerIds: ['peer-a']
+    });
+
+    round = recordInventoryReply(round, { roomId: 'room-2', peerId: 'peer-a', missingIdCount: 5 });
+
+    expect(round?.repliedPeerIds).toEqual([]);
+    expect(round?.missingIdCount).toBe(0);
+
+    round = recordInventoryReply(round, { roomId: 'room-1', peerId: 'peer-a', missingIdCount: 0 });
+    round = recordInventoryReply(round, { roomId: 'room-1', peerId: 'peer-a', missingIdCount: 0 });
+
+    expect(round?.repliedPeerIds).toEqual(['peer-a']);
+    expect(isInventoryRoundClean(round)).toBe(true);
+  });
+
+  it('leaves a closed round closed', () => {
+    expect(recordInventoryReply(null, { roomId: 'room-1', peerId: 'peer-a', missingIdCount: 0 })).toBeNull();
+  });
+});

toju-app/src/app/domains/chat/domain/rules/message-sync-round.rules.ts

@@ -0,0 +1,75 @@
+/**
+ * Evidence model for one message-inventory reconciliation round.
+ *
+ * The sync poll asks every reachable peer for its room inventory and then
+ * decides how soon to ask again. That decision must rest on replies, not on
+ * elapsed time: a round that timed out, only partly answered, or could not be
+ * delivered proves nothing about convergence, so it must not buy the slow
+ * polling cadence.
+ */
+
+/** Peers asked, peers heard from, and what they reported, for one room. */
+export interface InventoryRound {
+  readonly roomId: string;
+  /** Peers the inventory request was actually handed to the transport for. */
+  readonly askedPeerIds: readonly string[];
+  /** Subset of `askedPeerIds` that answered with an inventory. */
+  readonly repliedPeerIds: readonly string[];
+  /** Peers whose data channel refused the request. */
+  readonly undeliveredPeerIds: readonly string[];
+  /** Total ids any reply showed we are missing or hold at a stale revision. */
+  readonly missingIdCount: number;
+}
+
+/** Starts a round from the peers a poll reached and the peers it could not. */
+export function createInventoryRound(input: {
+  roomId: string;
+  askedPeerIds: readonly string[];
+  undeliveredPeerIds?: readonly string[];
+}): InventoryRound {
+  return {
+    roomId: input.roomId,
+    askedPeerIds: [...input.askedPeerIds],
+    repliedPeerIds: [],
+    undeliveredPeerIds: [...(input.undeliveredPeerIds ?? [])],
+    missingIdCount: 0
+  };
+}
+
+/**
+ * Records one peer's inventory comparison.
+ *
+ * Replies for another room are ignored. A reply from a peer outside the round
+ * (it answered an earlier kickoff) still counts its missing ids - we are
+ * demonstrably behind - but cannot complete the round on another peer's behalf.
+ */
+export function recordInventoryReply(
+  round: InventoryRound | null,
+  reply: { roomId: string; peerId: string; missingIdCount: number }
+): InventoryRound | null {
+  if (!round || round.roomId !== reply.roomId)
+    return round;
+
+  const isAsked = round.askedPeerIds.includes(reply.peerId);
+  const alreadyReplied = round.repliedPeerIds.includes(reply.peerId);
+
+  return {
+    ...round,
+    repliedPeerIds:
+      isAsked && !alreadyReplied
+        ? [...round.repliedPeerIds, reply.peerId]
+        : round.repliedPeerIds,
+    missingIdCount: round.missingIdCount + Math.max(0, reply.missingIdCount)
+  };
+}
+
+/** A round is clean only when every asked peer replied and nothing was missing. */
+export function isInventoryRoundClean(round: InventoryRound | null): boolean {
+  if (!round || round.askedPeerIds.length === 0)
+    return false;
+
+  if (round.undeliveredPeerIds.length > 0 || round.missingIdCount > 0)
+    return false;
+
+  return round.askedPeerIds.every((peerId) => round.repliedPeerIds.includes(peerId));
+}

toju-app/src/app/store/messages/messages-incoming.handlers.spec.ts

@@ -2,6 +2,7 @@ import { defaultIfEmpty, firstValueFrom } from 'rxjs';
 
 import { type Message } from '../../shared-kernel';
 import { dispatchIncomingMessage } from './messages-incoming.handlers';
+import { MessagesActions } from './messages.actions';
 
 function createMessage(overrides: Partial<Message> = {}): Message {
   return {
@@ -17,6 +18,17 @@ function createMessage(overrides: Partial<Message> = {}): Message {
   };
 }
 
+function createInventoryItem(id: string, ts: number) {
+  return {
+    id,
+    ts,
+    rc: 0,
+    ac: 0,
+    revision: 1,
+    headHash: `hash-${id}`
+  };
+}
+
 function createContext(overrides: Record<string, unknown> = {}) {
   return {
     db: {
@@ -197,6 +209,73 @@ describe('dispatchIncomingMessage room-scoped sync', () => {
     });
   });
 
+  it('reports how many ids a peer inventory showed we are missing', async () => {
+    // The sync round decides its polling cadence from this report: a reply we
+    // never hear about is indistinguishable from a peer that went silent.
+    const sendToPeer = vi.fn();
+    const context = createContext({
+      attachments: { getForMessage: vi.fn(() => []) },
+      currentRoom: { id: 'room-a' },
+      db: { getMessages: vi.fn(async () => []) },
+      savedRooms: [{ id: 'room-a' }],
+      webrtc: { sendToPeer }
+    });
+    const remoteItems = [createInventoryItem('remote-1', 1), createInventoryItem('remote-2', 2)];
+    const action = await firstValueFrom(
+      dispatchIncomingMessage(
+        {
+          type: 'chat-inventory',
+          roomId: 'room-a',
+          fromPeerId: 'peer-1',
+          items: remoteItems
+        } as never,
+        context as never
+      ).pipe(defaultIfEmpty(null))
+    );
+
+    expect(action).toEqual(MessagesActions.peerInventoryCompared({
+      missingIdCount: 2,
+      peerId: 'peer-1',
+      roomId: 'room-a'
+    }));
+
+    expect(sendToPeer).toHaveBeenCalledWith('peer-1', {
+      type: 'chat-sync-request-ids',
+      roomId: 'room-a',
+      ids: ['remote-1', 'remote-2']
+    });
+  });
+
+  it('reports a converged comparison when a peer inventory holds nothing new', async () => {
+    const sendToPeer = vi.fn();
+    const context = createContext({
+      attachments: { getForMessage: vi.fn(() => []) },
+      currentRoom: { id: 'room-a' },
+      db: { getMessages: vi.fn(async () => []) },
+      savedRooms: [{ id: 'room-a' }],
+      webrtc: { sendToPeer }
+    });
+    const action = await firstValueFrom(
+      dispatchIncomingMessage(
+        {
+          type: 'chat-inventory',
+          roomId: 'room-a',
+          fromPeerId: 'peer-1',
+          items: []
+        } as never,
+        context as never
+      ).pipe(defaultIfEmpty(null))
+    );
+
+    expect(action).toEqual(MessagesActions.peerInventoryCompared({
+      missingIdCount: 0,
+      peerId: 'peer-1',
+      roomId: 'room-a'
+    }));
+
+    expect(sendToPeer).not.toHaveBeenCalled();
+  });
+
   it('ignores chat messages for rooms that are not saved or currently viewed', async () => {
     const saveMessage = vi.fn(async () => undefined);
     const rememberMessageRoom = vi.fn();

toju-app/src/app/store/messages/messages-incoming.handlers.ts

@@ -15,7 +15,7 @@ import {
   from,
   EMPTY
 } from 'rxjs';
-import { mergeMap } from 'rxjs/operators';
+import { map, mergeMap } from 'rxjs/operators';
 import { Action } from '@ngrx/store';
 import {
   DELETED_MESSAGE_CONTENT,
@@ -159,8 +159,9 @@ function handleInventoryRequest(
 }
 
 /**
- * Compares a peer's inventory against local state
- * and requests any missing or stale messages.
+ * Compares a peer's inventory against local state, requests any missing or
+ * stale messages, and reports the comparison so the sync round can tell a
+ * converged reply apart from silence.
  */
 function handleInventory(
   event: IncomingMessageEvent,
@@ -197,8 +198,18 @@ function handleInventory(
 
         webrtc.sendToPeer(fromPeerId, syncRequestIdsEvent);
       }
+
+      return missing.length;
     })()
-  ).pipe(mergeMap(() => EMPTY));
+  ).pipe(
+    map((missingIdCount) =>
+      MessagesActions.peerInventoryCompared({
+        missingIdCount,
+        peerId: fromPeerId,
+        roomId
+      })
+    )
+  );
 }
 
 /**

toju-app/src/app/store/messages/messages-sync.effects.spec.ts

@@ -0,0 +1,260 @@
+import { Injector, runInInjectionContext } from '@angular/core';
+import { Actions } from '@ngrx/effects';
+import { Store, type Action } from '@ngrx/store';
+import {
+  BehaviorSubject,
+  Observable,
+  Subject
+} from 'rxjs';
+import type { ChatEvent, Room } from '../../shared-kernel';
+import { RealtimeSessionFacade } from '../../core/realtime';
+import { DatabaseService } from '../../infrastructure/persistence';
+import { DebuggingService } from '../../core/services/debugging.service';
+import {
+  SYNC_POLL_FAST_MS,
+  SYNC_POLL_SLOW_MS,
+  SYNC_TIMEOUT_MS
+} from './messages.helpers';
+import { MessagesActions } from './messages.actions';
+import { MessagesSyncEffects } from './messages-sync.effects';
+import { selectCurrentRoom } from '../rooms/rooms.selectors';
+
+const ROOM_ID = 'room-1';
+
+describe('MessagesSyncEffects sync cadence', () => {
+  beforeEach(() => {
+    vi.useFakeTimers();
+  });
+
+  afterEach(() => {
+    vi.useRealTimers();
+  });
+
+  it('keeps polling fast after a round nobody answered', async () => {
+    // A timed-out inventory round proves nothing: the peers may still hold
+    // messages we never received. Backing off to the slow poll here is what
+    // left a client 15 minutes behind.
+    const harness = createHarness();
+
+    await harness.advance(SYNC_POLL_FAST_MS);
+
+    expect(harness.inventoryRequests()).toEqual(['peer-a', 'peer-b']);
+
+    await harness.advance(SYNC_TIMEOUT_MS);
+    harness.clearSent();
+    await harness.advance(SYNC_POLL_FAST_MS);
+
+    expect(harness.inventoryRequests()).toEqual(['peer-a', 'peer-b']);
+
+    harness.destroy();
+  });
+
+  it('backs off only once every asked peer replied with nothing missing', async () => {
+    const harness = createHarness();
+
+    await harness.advance(SYNC_POLL_FAST_MS);
+    harness.reply('peer-a', 0);
+    harness.reply('peer-b', 0);
+    await harness.advance(SYNC_TIMEOUT_MS);
+    harness.clearSent();
+    await harness.advance(SYNC_POLL_FAST_MS);
+
+    expect(harness.inventoryRequests()).toEqual([]);
+
+    await harness.advance(SYNC_POLL_SLOW_MS);
+
+    expect(harness.inventoryRequests()).toEqual(['peer-a', 'peer-b']);
+
+    harness.destroy();
+  });
+
+  it('keeps polling fast when only some asked peers replied', async () => {
+    const harness = createHarness();
+
+    await harness.advance(SYNC_POLL_FAST_MS);
+    harness.reply('peer-a', 0);
+    await harness.advance(SYNC_TIMEOUT_MS);
+    harness.clearSent();
+    await harness.advance(SYNC_POLL_FAST_MS);
+
+    expect(harness.inventoryRequests()).toEqual(['peer-a', 'peer-b']);
+
+    harness.destroy();
+  });
+
+  it('keeps polling fast when a request never reached a peer', async () => {
+    const harness = createHarness();
+
+    harness.setUndeliverable('peer-b');
+
+    await harness.advance(SYNC_POLL_FAST_MS);
+
+    expect(harness.inventoryRequests()).toEqual(['peer-a']);
+
+    harness.reply('peer-a', 0);
+    await harness.advance(SYNC_TIMEOUT_MS);
+    harness.clearSent();
+    harness.setDeliverable('peer-b');
+    await harness.advance(SYNC_POLL_FAST_MS);
+
+    expect(harness.inventoryRequests()).toEqual(['peer-a', 'peer-b']);
+
+    harness.destroy();
+  });
+
+  it('keeps polling fast when a reply reported missing messages', async () => {
+    const harness = createHarness();
+
+    await harness.advance(SYNC_POLL_FAST_MS);
+    harness.reply('peer-a', 4);
+    harness.reply('peer-b', 0);
+    await harness.advance(SYNC_TIMEOUT_MS);
+    harness.clearSent();
+    await harness.advance(SYNC_POLL_FAST_MS);
+
+    expect(harness.inventoryRequests()).toEqual(['peer-a', 'peer-b']);
+
+    harness.destroy();
+  });
+
+  it('re-arms the fast poll when a peer connects during the slow cadence', async () => {
+    const harness = createHarness();
+
+    await harness.advance(SYNC_POLL_FAST_MS);
+    harness.reply('peer-a', 0);
+    harness.reply('peer-b', 0);
+    await harness.advance(SYNC_TIMEOUT_MS);
+    harness.clearSent();
+
+    harness.connectPeer('peer-c');
+
+    await harness.advance(SYNC_POLL_FAST_MS);
+
+    expect(harness.inventoryRequests()).toEqual(['peer-a', 'peer-b']);
+
+    harness.destroy();
+  });
+
+  it('re-arms the fast poll when a reconnected peer reports missing messages', async () => {
+    // Convergence must not wait out the slow poll: a peer answering the
+    // reconnect kickoff with ids we lack re-arms the aggressive cadence.
+    const harness = createHarness();
+
+    await harness.advance(SYNC_POLL_FAST_MS);
+    harness.reply('peer-a', 0);
+    harness.reply('peer-b', 0);
+    await harness.advance(SYNC_TIMEOUT_MS);
+    harness.clearSent();
+
+    harness.reply('peer-a', 7);
+
+    await harness.advance(SYNC_POLL_FAST_MS);
+
+    expect(harness.inventoryRequests()).toEqual(['peer-a', 'peer-b']);
+
+    harness.destroy();
+  });
+});
+
+interface SentEvent {
+  peerId: string;
+  event: ChatEvent;
+}
+
+function createHarness() {
+  const actions$ = new Subject<Action>();
+  const currentRoom$ = new BehaviorSubject<Room | null>({ id: ROOM_ID } as Room);
+  const peerConnected$ = new Subject<string>();
+  const undeliverablePeerIds = new Set<string>();
+  const sent: SentEvent[] = [];
+  const webrtc = {
+    getConnectedPeers: () => ['peer-a', 'peer-b'],
+    onPeerConnected: peerConnected$.asObservable(),
+    onPeerDisconnected: new Subject<string>().asObservable(),
+    sendToPeer: vi.fn((peerId: string, event: ChatEvent) => {
+      if (undeliverablePeerIds.has(peerId))
+        return false;
+
+      sent.push({ event, peerId });
+
+      return true;
+    })
+  };
+  const injector = Injector.create({
+    providers: [
+      {
+        provide: Actions,
+        useValue: new Actions(actions$)
+      },
+      {
+        provide: Store,
+        useValue: {
+          dispatch: vi.fn(),
+          select: (selector: unknown): Observable<unknown> => {
+            if (selector === selectCurrentRoom)
+              return currentRoom$;
+
+            throw new Error('Unexpected selector requested by MessagesSyncEffects test.');
+          }
+        }
+      },
+      {
+        provide: DatabaseService,
+        useValue: {
+          getRoomMessageStats: vi.fn(async () => ({ count: 0, lastUpdated: 0 }))
+        }
+      },
+      {
+        provide: DebuggingService,
+        useValue: { warn: vi.fn() }
+      },
+      {
+        provide: RealtimeSessionFacade,
+        useValue: webrtc
+      }
+    ]
+  });
+  const effects = runInInjectionContext(injector, () => new MessagesSyncEffects());
+  // The store loop feeds dispatched actions back into `actions$`; the sync
+  // cadence depends on that round trip (poll -> startSync -> timeout).
+  const subscriptions = [
+    effects.periodicSyncPoll$.subscribe((action) => actions$.next(action)),
+    effects.syncTimeout$.subscribe((action) => actions$.next(action)),
+    effects.trackInventoryReplies$.subscribe(),
+    effects.restoreFastPollOnPeerConnect$.subscribe()
+  ];
+
+  return {
+    advance: async (ms: number): Promise<void> => {
+      await vi.advanceTimersByTimeAsync(ms);
+    },
+    clearSent: (): void => {
+      sent.length = 0;
+    },
+    connectPeer: (peerId: string): void => {
+      peerConnected$.next(peerId);
+    },
+    destroy: (): void => {
+      for (const subscription of subscriptions) {
+        subscription.unsubscribe();
+      }
+    },
+    inventoryRequests: (): string[] =>
+      sent
+        .filter(({ event }) => event.type === 'chat-inventory-request')
+        .map(({ peerId }) => peerId),
+    reply: (peerId: string, missingIdCount: number): void => {
+      actions$.next(MessagesActions.peerInventoryCompared({
+        missingIdCount,
+        peerId,
+        roomId: ROOM_ID
+      }));
+    },
+    setDeliverable: (peerId: string): void => {
+      undeliverablePeerIds.delete(peerId);
+    },
+    setUndeliverable: (peerId: string): void => {
+      undeliverablePeerIds.add(peerId);
+    }
+  };
+}

toju-app/src/app/store/messages/messages-sync.effects.ts

@@ -8,7 +8,7 @@
  * Extracted from the monolithic MessagesEffects to keep each
  * class focused on a single concern.
  */
-/* eslint-disable @typescript-eslint/member-ordering */
+
 import { Injectable, inject } from '@angular/core';
 import {
   Actions,
@@ -36,7 +36,6 @@ import {
 } from 'rxjs/operators';
 import { MessagesActions } from './messages.actions';
 import { RoomsActions } from '../rooms/rooms.actions';
-import { selectMessagesSyncing } from './messages.selectors';
 import { selectCurrentRoom } from '../rooms/rooms.selectors';
 import { RealtimeSessionFacade } from '../../core/realtime';
 import { DatabaseService } from '../../infrastructure/persistence';
@@ -46,6 +45,12 @@ import {
   SYNC_POLL_SLOW_MS,
   SYNC_TIMEOUT_MS
 } from './messages.helpers';
+import {
+  createInventoryRound,
+  isInventoryRoundClean,
+  recordInventoryReply,
+  type InventoryRound
+} from '../../domains/chat/domain/rules/message-sync-round.rules';
 
 @Injectable()
 export class MessagesSyncEffects {
@@ -55,9 +60,12 @@ export class MessagesSyncEffects {
   private readonly debugging = inject(DebuggingService);
   private readonly webrtc = inject(RealtimeSessionFacade);
 
-  /** Tracks whether the last sync cycle found no new messages. */
+  /** Tracks whether the last sync cycle proved there was nothing left to fetch. */
   private lastSyncClean = false;
 
+  /** Evidence collected for the inventory round the current poll is waiting on. */
+  private currentRound: InventoryRound | null = null;
+
   /** Subject to reset the periodic sync timer. */
   private readonly syncReset$ = new Subject<void>();
 
@@ -157,6 +165,7 @@ export class MessagesSyncEffects {
         ofType(RoomsActions.joinRoomSuccess, RoomsActions.viewServerSuccess),
         tap(() => {
           this.lastSyncClean = false;
+          this.currentRound = null;
           this.syncReset$.next();
         })
       ),
@@ -166,18 +175,18 @@ export class MessagesSyncEffects {
   /**
    * Alternates between fast (10 s) and slow (15 min) sync intervals.
    * Sends inventory requests to all connected peers for the active room.
+   *
+   * Each scored round re-arms this timer (see `syncTimeout$`), so the delay is
+   * always chosen from the verdict of the round that just closed. The `repeat`
+   * only keeps the loop alive for polls that never open a round at all - no
+   * active room, or no connected peers.
    */
   periodicSyncPoll$ = createEffect(() =>
     this.syncReset$.pipe(
       startWith(undefined),
       switchMap(() =>
-        timer(SYNC_POLL_FAST_MS).pipe(
-          repeat({
-            delay: () =>
-              timer(
-                this.lastSyncClean ? SYNC_POLL_SLOW_MS : SYNC_POLL_FAST_MS
-              )
-          }),
+        timer(this.nextPollDelayMs()).pipe(
+          repeat({ delay: () => timer(this.nextPollDelayMs()) }),
           withLatestFrom(this.store.select(selectCurrentRoom)),
           filter(
             ([, room]) =>
@@ -187,24 +196,28 @@ export class MessagesSyncEffects {
             const peers = this.webrtc.getConnectedPeers();
 
             if (!room || peers.length === 0) {
+              this.currentRound = null;
+
               return of(MessagesActions.syncComplete());
             }
 
+            const askedPeerIds: string[] = [];
+            const undeliveredPeerIds: string[] = [];
+
             for (const pid of peers) {
-              try {
-                this.webrtc.sendToPeer(pid, {
-                  type: 'chat-inventory-request',
-                  roomId: room.id
-                });
-              } catch (error) {
-                this.debugging.warn('messages', 'Failed to request peer inventory during sync poll', {
-                  error,
-                  peerId: pid,
-                  roomId: room.id
-                });
+              if (this.requestPeerInventory(pid, room.id)) {
+                askedPeerIds.push(pid);
+              } else {
+                undeliveredPeerIds.push(pid);
               }
             }
 
+            this.currentRound = createInventoryRound({
+              askedPeerIds,
+              roomId: room.id,
+              undeliveredPeerIds
+            });
+
             return of(MessagesActions.startSync());
           })
         )
@@ -213,35 +226,93 @@ export class MessagesSyncEffects {
   );
 
   /**
-   * Auto-completes a sync cycle after a timeout if no messages arrive.
-   * Switches to slow polling when the cycle is clean.
+   * Closes a sync cycle once the round's reply window elapses, and scores the
+   * round: only a fully answered round with nothing missing buys the slow
+   * cadence. Silence, a partial answer, or an undelivered request all keep the
+   * fast poll, because none of them is evidence that we are caught up.
    */
   syncTimeout$ = createEffect(() =>
     this.actions$.pipe(
       ofType(MessagesActions.startSync),
-      switchMap(() => from(
-        new Promise<void>((resolve) => setTimeout(resolve, SYNC_TIMEOUT_MS))
-      )),
-      withLatestFrom(this.store.select(selectMessagesSyncing)),
-      filter(([, syncing]) => syncing),
+      switchMap(() => timer(SYNC_TIMEOUT_MS)),
       map(() => {
-        this.lastSyncClean = true;
+        this.lastSyncClean = isInventoryRoundClean(this.currentRound);
+        this.currentRound = null;
+        this.syncReset$.next();
+
         return MessagesActions.syncComplete();
       })
     )
   );
 
   /**
-   * When a peer (re)connects, revert to aggressive polling in case
-   * we missed messages while disconnected.
+   * Records each peer's inventory comparison against the open round.
+   *
+   * A reply that arrives after the round closed - typically a peer answering
+   * the reconnect or room-activation kickoff - still proves we are behind, so
+   * it re-arms the fast cadence instead of leaving us parked on a slow poll
+   * that was scheduled while we looked converged.
    */
-  syncReceivedMessages$ = createEffect(
+  trackInventoryReplies$ = createEffect(
     () =>
-      this.webrtc.onPeerConnected.pipe(
-        tap(() => {
-          this.lastSyncClean = false;
+      this.actions$.pipe(
+        ofType(MessagesActions.peerInventoryCompared),
+        tap(({ missingIdCount, peerId, roomId }) => {
+          if (this.currentRound) {
+            this.currentRound = recordInventoryReply(this.currentRound, {
+              missingIdCount,
+              peerId,
+              roomId
+            });
+
+            return;
+          }
+
+          if (missingIdCount > 0) {
+            this.lastSyncClean = false;
+            this.syncReset$.next();
+          }
         })
       ),
     { dispatch: false }
   );
+
+  /**
+   * When a peer (re)connects, revert to aggressive polling in case we missed
+   * messages while disconnected. The pending delay was chosen for the old peer
+   * set, so re-arm it as well instead of only flipping the flag.
+   */
+  restoreFastPollOnPeerConnect$ = createEffect(
+    () =>
+      this.webrtc.onPeerConnected.pipe(
+        tap(() => {
+          this.lastSyncClean = false;
+          this.syncReset$.next();
+        })
+      ),
+    { dispatch: false }
+  );
+
+  /** Delay before the next inventory poll, from the last round's verdict. */
+  private nextPollDelayMs(): number {
+    return this.lastSyncClean ? SYNC_POLL_SLOW_MS : SYNC_POLL_FAST_MS;
+  }
+
+  /** Sends one inventory request and reports whether the peer received it. */
+  private requestPeerInventory(peerId: string, roomId: string): boolean {
+    try {
+      return this.webrtc.sendToPeer(peerId, {
+        type: 'chat-inventory-request',
+        roomId
+      });
+    } catch (error) {
+      this.debugging.warn('messages', 'Failed to request peer inventory during sync poll', {
+        error,
+        peerId,
+        roomId
+      });
+
+      return false;
+    }
+  }
 }

toju-app/src/app/store/messages/messages.actions.ts

@@ -86,6 +86,16 @@ export const MessagesActions = createActionGroup({
     'Start Sync': emptyProps(),
     /** Marks the end of a message sync cycle. */
     'Sync Complete': emptyProps(),
+    /**
+     * One peer answered an inventory request and we compared it against local
+     * state. `missingIdCount` is how many of that peer's ids we lack or hold at
+     * a stale revision - the only evidence that a sync round converged.
+     */
+    'Peer Inventory Compared': props<{
+      peerId: string;
+      roomId: string;
+      missingIdCount: number;
+    }>(),
 
     /** Attaches fetched link metadata to a message. */
     'Update Link Metadata': props<{ messageId: string; linkMetadata: LinkMetadata[] }>(),