diff --git a/packages/web/src/stores/pendingMessageStore.test.ts b/packages/web/src/stores/pendingMessageStore.test.ts
new file mode 100644
index 00000000..9f146400
--- /dev/null
+++ b/packages/web/src/stores/pendingMessageStore.test.ts
@@ -0,0 +1,110 @@
+import { describe, it, expect, beforeEach, vi } from 'vitest';
+import 'fake-indexeddb/auto';
+
+// Break the import chain before transferStore pulls voiceStore → AudioManager →
+// @sapphi-red/web-noise-suppressor (jsdom can't provide AudioWorkletNode).
+vi.mock('./authStore', () => ({
+  useAuthStore: {
+    getState: () => ({ token: 'test-token', user: { id: 'u-9', username: 'tester' } }),
+  },
+}));
+
+import { usePendingMessageStore, type PendingBubble } from './pendingMessageStore';
+import { useTransferStore, type Transfer } from './transferStore';
+
+function bubble(over: Partial<PendingBubble> = {}): PendingBubble {
+  return {
+    clientId: over.clientId ?? 'c-1',
+    channelId: 'ch-1',
+    content: '',
+    replyToId: null,
+    transferIds: ['t-1'],
+    createdAtLocal: 1000,
+    state: 'sending',
+    tusExpiresAt: Date.now() + 60_000,
+    retryCount: 0,
+    ...over,
+  };
+}
+
+function makeTransfer(over: Partial<Transfer> & Pick<Transfer, 'id'>): Transfer {
+  return {
+    type: 'upload',
+    state: 'queued',
+    file: { name: 'a', size: 1, mimetype: 'image/png' },
+    progress: { loaded: 0, total: 1 },
+    tray: true,
+    ...over,
+  };
+}
+
+describe('pendingMessageStore', () => {
+  beforeEach(() => {
+    usePendingMessageStore.setState({ bubbles: new Map() });
+    useTransferStore.setState({ transfers: new Map() });
+    if (typeof localStorage !== 'undefined') localStorage.clear();
+  });
+
+  it('appends a bubble in sending state', () => {
+    usePendingMessageStore.getState().append(bubble());
+    expect(usePendingMessageStore.getState().listForChannel('ch-1').length).toBe(1);
+  });
+
+  it('matchAndRemove dedups by content + sortedAttachmentIds, oldest first', () => {
+    useTransferStore.setState({
+      transfers: new Map<string, Transfer>([
+        ['t-A', makeTransfer({ id: 't-A', state: 'completed', attachmentId: 'att-1', progress: { loaded: 1, total: 1 } })],
+        ['t-B', makeTransfer({ id: 't-B', state: 'completed', attachmentId: 'att-2', progress: { loaded: 1, total: 1 } })],
+      ]),
+    });
+    usePendingMessageStore.getState().append(bubble({ clientId: 'b1', createdAtLocal: 1000, content: 'x', transferIds: ['t-A', 't-B'] }));
+    usePendingMessageStore.getState().append(bubble({ clientId: 'b2', createdAtLocal: 2000, content: 'x', transferIds: ['t-A', 't-B'] }));
+    const removed = usePendingMessageStore.getState().matchAndRemove('ch-1', 'x', ['att-2', 'att-1']);
+    expect(removed?.clientId).toBe('b1');
+    expect(usePendingMessageStore.getState().listForChannel('ch-1').map((b) => b.clientId)).toEqual(['b2']);
+  });
+
+  it('discardExpired drops bubbles past tusExpiresAt', () => {
+    usePendingMessageStore.getState().append(bubble({ clientId: 'old', tusExpiresAt: 1 }));
+    usePendingMessageStore.getState().append(bubble({ clientId: 'new', tusExpiresAt: Date.now() + 60_000 }));
+    const dropped = usePendingMessageStore.getState().discardExpired(Date.now());
+    expect(dropped.map((b) => b.clientId)).toEqual(['old']);
+    expect(usePendingMessageStore.getState().listForChannel('ch-1').map((b) => b.clientId)).toEqual(['new']);
+  });
+
+  it('listReadyForDeferredSend returns bubbles whose all transfers have attachmentIds', () => {
+    useTransferStore.setState({
+      transfers: new Map<string, Transfer>([
+        ['t-1', makeTransfer({ id: 't-1', state: 'completed', attachmentId: 'att-9', progress: { loaded: 1, total: 1 } })],
+      ]),
+    });
+    usePendingMessageStore.getState().append(bubble({ clientId: 'r1', transferIds: ['t-1'] }));
+    expect(usePendingMessageStore.getState().listReadyForDeferredSend().map((b) => b.clientId)).toEqual(['r1']);
+  });
+
+  it('matchAndRemove returns null when only some referenced transfers have completed', () => {
+    useTransferStore.setState({
+      transfers: new Map([
+        ['t-1', makeTransfer({ id: 't-1', state: 'completed', attachmentId: 'att-1' })],
+        ['t-2', makeTransfer({ id: 't-2', state: 'active' })], // no attachmentId yet
+      ]),
+    });
+    usePendingMessageStore.getState().append(bubble({ clientId: 'b1', transferIds: ['t-1', 't-2'] }));
+    const result = usePendingMessageStore.getState().matchAndRemove('ch-1', '', ['att-1', 'att-2']);
+    expect(result).toBeNull();
+    expect(usePendingMessageStore.getState().listForChannel('ch-1').length).toBe(1); // bubble still there
+  });
+
+  it('markFailed on a missing clientId is a no-op (does not throw)', () => {
+    expect(() => usePendingMessageStore.getState().markFailed('does-not-exist')).not.toThrow();
+  });
+
+  it('discardExpired with no expired bubbles does not mutate state', () => {
+    usePendingMessageStore.getState().append(bubble({ clientId: 'live', tusExpiresAt: Date.now() + 60_000 }));
+    const before = usePendingMessageStore.getState().bubbles;
+    const dropped = usePendingMessageStore.getState().discardExpired(Date.now());
+    const after = usePendingMessageStore.getState().bubbles;
+    expect(dropped).toEqual([]);
+    expect(after).toBe(before); // same Map reference
+  });
+});
diff --git a/packages/web/src/stores/pendingMessageStore.ts b/packages/web/src/stores/pendingMessageStore.ts
new file mode 100644
index 00000000..01858758
--- /dev/null
+++ b/packages/web/src/stores/pendingMessageStore.ts
@@ -0,0 +1,211 @@
+import { create } from 'zustand';
+import { persist, type PersistStorage, type StorageValue } from 'zustand/middleware';
+import { useTransferStore } from './transferStore';
+
+export type PendingBubbleState = 'sending' | 'failed';
+
+export interface PendingBubble {
+  clientId: string;
+  channelId: string;
+  content: string;
+  replyToId: string | null;
+  transferIds: string[];
+  createdAtLocal: number;
+  state: PendingBubbleState;
+  tusExpiresAt: number;
+  retryCount: number;
+}
+
+interface PendingMessageStoreState {
+  bubbles: Map<string, PendingBubble[]>; // channelId → bubbles
+}
+
+interface PendingMessageStoreActions {
+  append: (b: PendingBubble) => void;
+  removeByClientId: (channelId: string, clientId: string) => void;
+  markFailed: (clientId: string) => void;
+  markSending: (clientId: string) => void;
+  bumpRetry: (clientId: string) => void;
+  listForChannel: (channelId: string) => PendingBubble[];
+  matchAndRemove: (
+    channelId: string,
+    content: string,
+    sortedAttachmentIds: string[],
+  ) => PendingBubble | null;
+  discardExpired: (now: number) => PendingBubble[];
+  listReadyForDeferredSend: () => PendingBubble[];
+}
+
+type PendingMessageStore = PendingMessageStoreState & PendingMessageStoreActions;
+
+function findBubble(
+  map: Map<string, PendingBubble[]>,
+  clientId: string,
+): { ch: string; bubble: PendingBubble } | null {
+  for (const [ch, list] of map) {
+    const b = list.find((x) => x.clientId === clientId);
+    if (b) return { ch, bubble: b };
+  }
+  return null;
+}
+
+function setBubble(
+  map: Map<string, PendingBubble[]>,
+  clientId: string,
+  mut: (b: PendingBubble) => PendingBubble,
+): Map<string, PendingBubble[]> {
+  const found = findBubble(map, clientId);
+  if (!found) return map;
+  const next = new Map(map);
+  const list = next.get(found.ch) ?? [];
+  next.set(
+    found.ch,
+    list.map((b) => (b.clientId === clientId ? mut(b) : b)),
+  );
+  return next;
+}
+
+// Custom storage that serializes Map<string, PendingBubble[]> as an array of entries.
+// Mirrors composerStore's mapAwareStorage; only the `bubbles` slice is persisted.
+const mapAwareStorage: PersistStorage<Pick<PendingMessageStoreState, 'bubbles'>> = {
+  getItem: (name) => {
+    const raw = typeof localStorage !== 'undefined' ? localStorage.getItem(name) : null;
+    if (!raw) return null;
+    try {
+      const parsed = JSON.parse(raw) as {
+        state: { bubbles: [string, PendingBubble[]][] };
+        version?: number;
+      };
+      const stateOut: Pick<PendingMessageStoreState, 'bubbles'> = {
+        bubbles: new Map<string, PendingBubble[]>(parsed.state.bubbles ?? []),
+      };
+      return { state: stateOut, version: parsed.version } as StorageValue<
+        Pick<PendingMessageStoreState, 'bubbles'>
+      >;
+    } catch {
+      return null;
+    }
+  },
+  setItem: (name, value) => {
+    if (typeof localStorage === 'undefined') return;
+    const entries = Array.from(value.state.bubbles.entries());
+    const payload = JSON.stringify({ state: { bubbles: entries }, version: value.version });
+    try {
+      localStorage.setItem(name, payload);
+    } catch (err) {
+      console.warn(`[pendingMessageStore] persist failed:`, err);
+    }
+  },
+  removeItem: (name) => {
+    if (typeof localStorage !== 'undefined') localStorage.removeItem(name);
+  },
+};
+
+export const usePendingMessageStore = create<PendingMessageStore>()(
+  persist(
+    (set, get) => ({
+      bubbles: new Map<string, PendingBubble[]>(),
+
+      append: (b) =>
+        set((s) => {
+          const next = new Map(s.bubbles);
+          next.set(b.channelId, [...(next.get(b.channelId) ?? []), b]);
+          return { bubbles: next };
+        }),
+
+      removeByClientId: (channelId, clientId) =>
+        set((s) => {
+          const list = s.bubbles.get(channelId);
+          if (!list) return s;
+          const next = new Map(s.bubbles);
+          next.set(
+            channelId,
+            list.filter((b) => b.clientId !== clientId),
+          );
+          return { bubbles: next };
+        }),
+
+      markFailed: (clientId) =>
+        set((s) => ({
+          bubbles: setBubble(s.bubbles, clientId, (b) => ({ ...b, state: 'failed' })),
+        })),
+
+      markSending: (clientId) =>
+        set((s) => ({
+          bubbles: setBubble(s.bubbles, clientId, (b) => ({ ...b, state: 'sending' })),
+        })),
+
+      bumpRetry: (clientId) =>
+        set((s) => ({
+          bubbles: setBubble(s.bubbles, clientId, (b) => ({ ...b, retryCount: b.retryCount + 1 })),
+        })),
+
+      listForChannel: (channelId) => get().bubbles.get(channelId) ?? [],
+
+      matchAndRemove: (channelId, content, sortedAttachmentIds) => {
+        const list = get().bubbles.get(channelId);
+        if (!list) return null;
+        const transfers = useTransferStore.getState().transfers;
+        const target = [...sortedAttachmentIds].sort();
+        const matches = list
+          .filter((b) => b.content === content)
+          .filter((b) => {
+            const ids = b.transferIds
+              .map((tid) => transfers.get(tid)?.attachmentId)
+              .filter((id): id is string => typeof id === 'string' && id.length > 0);
+            const sorted = [...ids].sort();
+            return sorted.length === target.length && sorted.every((v, i) => v === target[i]);
+          })
+          .sort((a, b) => a.createdAtLocal - b.createdAtLocal);
+        if (matches.length === 0) return null;
+        const winner = matches[0]!;
+        get().removeByClientId(channelId, winner.clientId);
+        return winner;
+      },
+
+      discardExpired: (now) => {
+        const map = get().bubbles;
+        const dropped: PendingBubble[] = [];
+        let mutated = false;
+        const next = new Map<string, PendingBubble[]>();
+        for (const [ch, list] of map) {
+          const surviving: PendingBubble[] = [];
+          for (const b of list) {
+            if (b.tusExpiresAt < now) {
+              dropped.push(b);
+              mutated = true;
+            } else {
+              surviving.push(b);
+            }
+          }
+          if (surviving.length > 0) next.set(ch, surviving);
+          else if (list.length > 0) mutated = true; // dropping a non-empty channel entry counts as mutation
+        }
+        if (mutated) set({ bubbles: next });
+        return dropped;
+      },
+
+      listReadyForDeferredSend: () => {
+        const transfers = useTransferStore.getState().transfers;
+        const ready: PendingBubble[] = [];
+        for (const list of get().bubbles.values()) {
+          for (const b of list) {
+            if (b.state !== 'sending') continue;
+            const allDone = b.transferIds.every((tid) => {
+              const t = transfers.get(tid);
+              return t?.state === 'completed' && !!t.attachmentId;
+            });
+            if (allDone) ready.push(b);
+          }
+        }
+        return ready;
+      },
+    }),
+    {
+      name: 'pendingMessageStore@v1',
+      version: 1,
+      storage: mapAwareStorage,
+      partialize: (s) => ({ bubbles: s.bubbles }),
+    },
+  ),
+);