diff --git a/apps/desktop/src/store/todos.test.ts b/apps/desktop/src/store/todos.test.ts
index 98ec0dd5fd..8980e4a82c 100644
--- a/apps/desktop/src/store/todos.test.ts
+++ b/apps/desktop/src/store/todos.test.ts
@@ -134,4 +134,22 @@ describe('revisioned snapshots', () => {
     restoreSessionTodosFromSnapshot('s1', snapshot, true)
     expect($todosBySession.get().s1?.[0]?.id).toBe('active')
   })
+
+  it('applies an unversioned update after a revisioned snapshot (tool.start merge)', () => {
+    setSessionTodos('s1', [todo('a', 'pending'), todo('b', 'pending')], 5)
+    setSessionTodos('s1', [todo('a', 'completed'), todo('b', 'pending')])
+
+    expect($todosBySession.get().s1?.[0]?.status).toBe('completed')
+    expect($todoRevisionsBySession.get().s1).toBe(5)
+  })
+
+  it('does not stamp a watermark from an unused empty snapshot', () => {
+    restoreSessionTodosFromSnapshot('s1', { revision: 0, todos: [] }, true)
+
+    expect($todosBySession.get().s1).toBeUndefined()
+    expect($todoRevisionsBySession.get().s1).toBeUndefined()
+
+    setSessionTodos('s1', [todo('a', 'in_progress')])
+    expect($todosBySession.get().s1?.[0]?.id).toBe('a')
+  })
 })
diff --git a/apps/desktop/src/store/todos.ts b/apps/desktop/src/store/todos.ts
index 5d7906364a..1454bd28d1 100644
--- a/apps/desktop/src/store/todos.ts
+++ b/apps/desktop/src/store/todos.ts
@@ -74,8 +74,10 @@ function acceptRevision(sid: string, revision?: null | number): boolean {
   const revisions = $todoRevisionsBySession.get()
   const current = revisions[sid]
 
+  // tool.start has no revision. Apply the merge locally and leave the
+  // watermark alone so a later todo.updated / tool.complete can still win.
   if (revision == null) {
-    return current == null
+    return true
   }
 
   if (current != null && revision < current) {
@@ -156,6 +158,14 @@ export function restoreSessionTodosFromSnapshot(sid: string, snapshot: unknown,
   }
 
   const revision = parseTodoRevision(snapshot)
+
+  // An unused store serializes as {todos: [], revision: 0}. That is not a
+  // real snapshot. Applying it would stamp watermark 0 and leave an empty
+  // list in the map.
+  if (todos.length === 0 && (revision == null || revision === 0)) {
+    return
+  }
+
   const visible = running ? todos : todosForHydration(todos)
 
   if (visible !== null) {
diff --git a/tests/tui_gateway/test_todo_state_events.py b/tests/tui_gateway/test_todo_state_events.py
index 425f6a8ad7..8ac433c95c 100644
--- a/tests/tui_gateway/test_todo_state_events.py
+++ b/tests/tui_gateway/test_todo_state_events.py
@@ -78,3 +78,23 @@ def test_live_snapshot_prefers_the_highest_revision():
     payload = server._attach_todo_state({}, session)
 
     assert payload["todo_state"]["revision"] == 5
+
+
+def test_unused_store_is_not_attached():
+    class Store:
+        @staticmethod
+        def snapshot():
+            return {"todos": [], "revision": 0}
+
+    class Agent:
+        _todo_store = Store()
+
+    payload = server._attach_todo_state({}, {"agent": Agent()})
+
+    assert "todo_state" not in payload
+
+
+def test_empty_list_at_nonzero_revision_is_a_real_clear():
+    state = server._normalize_todo_state({"todos": [], "revision": 2})
+
+    assert state == {"todos": [], "revision": 2}
diff --git a/tui_gateway/server.py b/tui_gateway/server.py
index 0536cb056b..576d6db45f 100644
--- a/tui_gateway/server.py
+++ b/tui_gateway/server.py
@@ -7645,7 +7645,13 @@ def _normalize_todo_state(value: object) -> dict | None:
         revision = max(0, int(value.get("revision") or 0))
     except (TypeError, ValueError):
         return None
-    return {"todos": list(value["todos"]), "revision": revision}
+    todos = list(value["todos"])
+    # Unused TodoStore snapshot() is {todos: [], revision: 0}. Attaching
+    # that on resume stamps a client watermark and blocks unversioned
+    # tool.start merges. An empty list at revision >= 1 is a real clear.
+    if not todos and revision == 0:
+        return None
+    return {"todos": todos, "revision": revision}
 
 
 def _session_todo_state(session: dict) -> dict | None: