test(gateway): change-watcher behavior contracts; align status-snapshot test with 60s cadence

Real temp-HERMES_HOME tests for _broadcast_watched_changes: silent seed,
cron/sessions signature moves, the 2s sessions floor's trailing edge, the
pet signature staying 'off' without a renderable pet, meta payload on
pet.changed, and a broken probe never killing the pass. Part of #73618.

apps/desktop/src/app/shell/hooks/use-status-snapshot.test.ts

@@ -158,7 +158,7 @@ describe('useStatusSnapshot', () => {
     })
 
     await act(async () => {
-      await vi.advanceTimersByTimeAsync(14_999)
+      await vi.advanceTimersByTimeAsync(59_999)
     })
     expect(requestGatewayMock).toHaveBeenCalledTimes(2)
 

tests/tui_gateway/test_change_watcher.py

@@ -0,0 +1,135 @@
+"""The generalized change watcher (#73618): cheap on-disk signatures →
+``pet.changed`` / ``cron.changed`` / ``sessions.changed`` global broadcasts.
+
+Behavior contracts, exercised against a real temp HERMES_HOME (no mocks on the
+filesystem path): first sighting seeds silently, a moved signature broadcasts
+once, the sessions floor coalesces a write burst but keeps its trailing edge,
+and the pet signature only moves for a *renderable* pet.
+"""
+
+import time
+
+import pytest
+
+from tui_gateway import server
+
+
+@pytest.fixture()
+def watcher_home(tmp_path, monkeypatch):
+    (tmp_path / "config.yaml").write_text("display: {}\n")
+    (tmp_path / "cron").mkdir()
+
+    monkeypatch.setattr(server, "_hermes_home", str(tmp_path))
+    monkeypatch.setattr(server, "_cfg_cache", None)
+    monkeypatch.setattr(server, "_change_sigs", {})
+    monkeypatch.setattr(server, "_change_checked_at", {})
+    monkeypatch.setattr(server, "_change_broadcast_at", {})
+
+    events = []
+    monkeypatch.setattr(
+        server, "_broadcast_global_event", lambda ev, payload=None: events.append((ev, payload))
+    )
+    return tmp_path, events
+
+
+def test_first_sighting_seeds_without_broadcasting(watcher_home):
+    home, events = watcher_home
+    (home / "cron" / "jobs.json").write_text("[]")
+    (home / "state.db").write_text("x")
+
+    server._broadcast_watched_changes(now=0.0)
+
+    assert events == []
+
+
+def test_cron_jobs_file_move_broadcasts_cron_changed(watcher_home):
+    home, events = watcher_home
+    server._broadcast_watched_changes(now=0.0)
+
+    (home / "cron" / "jobs.json").write_text("[]")
+    server._broadcast_watched_changes(now=10.0)
+
+    assert ("cron.changed", {}) in events
+
+
+def test_state_db_move_broadcasts_sessions_changed(watcher_home):
+    home, events = watcher_home
+    server._broadcast_watched_changes(now=0.0)
+
+    (home / "state.db").write_text("x")
+    server._broadcast_watched_changes(now=10.0)
+
+    assert ("sessions.changed", {}) in events
+
+
+def test_sessions_floor_coalesces_burst_but_keeps_trailing_edge(watcher_home):
+    home, events = watcher_home
+    server._broadcast_watched_changes(now=0.0)
+
+    (home / "state.db").write_text("x")
+    server._broadcast_watched_changes(now=10.0)
+    events.clear()
+
+    # A second write lands inside the 2s floor: no broadcast yet…
+    time.sleep(0.02)
+    (home / "state.db").write_text("xy")
+    server._broadcast_watched_changes(now=11.0)
+    assert events == []
+
+    # …but the change is not lost — it fires once the window opens.
+    server._broadcast_watched_changes(now=13.0)
+    assert ("sessions.changed", {}) in events
+
+
+def test_pet_sig_stays_off_without_a_renderable_pet(watcher_home):
+    home, events = watcher_home
+    server._broadcast_watched_changes(now=0.0)
+
+    # Config flips enabled but no pet exists on disk → signature stays ("off",).
+    (home / "config.yaml").write_text("display:\n  pet:\n    enabled: true\n    slug: boba\n")
+    server._cfg_cache = None
+    server._broadcast_watched_changes(now=10.0)
+
+    assert not [e for e in events if e[0] == "pet.changed"]
+
+
+def test_renderable_pet_broadcasts_meta_payload(watcher_home, monkeypatch):
+    home, events = watcher_home
+    (home / "config.yaml").write_text("display:\n  pet:\n    enabled: true\n    slug: boba\n")
+    server._cfg_cache = None
+    server._broadcast_watched_changes(now=0.0)
+
+    sheet = home / "sheet.png"
+    sheet.write_text("png")
+
+    class FakePet:
+        slug = "boba"
+        display_name = "Boba"
+        exists = True
+        spritesheet = sheet
+
+    monkeypatch.setattr(server, "_pet_active_selection", lambda: (True, FakePet(), 0.33))
+    server._broadcast_watched_changes(now=10.0)
+
+    pet_events = [e for e in events if e[0] == "pet.changed"]
+    assert pet_events
+    payload = pet_events[0][1]
+    assert payload["enabled"] is True
+    assert payload["slug"] == "boba"
+    assert payload["spritesheetRevision"]
+
+
+def test_broken_probe_never_kills_the_pass(watcher_home, monkeypatch):
+    home, events = watcher_home
+    server._broadcast_watched_changes(now=0.0)
+
+    monkeypatch.setitem(
+        server._CHANGE_WATCHES,
+        "cron.changed",
+        (1.0, lambda: (_ for _ in ()).throw(RuntimeError("boom")), lambda: {}),
+    )
+    (home / "state.db").write_text("x")
+    server._broadcast_watched_changes(now=10.0)
+
+    # The broken cron probe is skipped; sessions still broadcasts.
+    assert ("sessions.changed", {}) in events