observe: drop fallback hrefs on late notify; skip empty subpolls

on_notification discards from fallback_hrefs so a late first push
(after the 80% quorum snapshot) self-corrects instead of staying on
the 3s GET cadence. Empty subpoll slots skip the session lock.

custom_components/localthings/coordinator.py

@@ -998,6 +998,8 @@ class LocalThingsCoordinator(DataUpdateCoordinator[dict[str, Any]]):
         for i in range(1, 10):  # slots 1..9  (T+3 s … T+27 s)
             await asyncio.sleep(step)
             hrefs = list(hot) + (list(warm) if i % 2 == 0 else [])
+            if not hrefs:
+                continue
             async with self._session_lock:
                 try:
                     await self.hass.async_add_executor_job(self._poll_hrefs_blocking, hrefs)

custom_components/localthings/observe.py

@@ -95,13 +95,14 @@ class ObserveManager:
         self._notified: set[str] = set()
         self._last_notify_ts: float | None = None
         # Wakes try_enter_observe_mode's grace wait early once enough hrefs
-        # have notified. Guards only `_notified` mutations + the `wait_for`.
+        # have notified. Guards `_notified` mutations, the `wait_for`, and
+        # fallback_hrefs discards from on_notification.
         self._notify_cond = threading.Condition()
         # Idle while polling, except after downgrade_to_poll (every href
         # that was subscribed). While in observe mode this is the set of
-        # hrefs that were subscribed but never notified during the grace
-        # period (issue #92) -- they stay on the hot/warm sub-poll cadence
-        # instead of waiting for the 30s /device/0 sweep.
+        # subscribed hrefs that have not yet notified (issue #92) -- they
+        # stay on the hot/warm sub-poll cadence. on_notification discards
+        # an href once it pushes, so a late first notify self-corrects.
         self.fallback_hrefs: set[str] = set()
         self._on_applied: Callable[[str, dict, str], None] | None = None
         self._refresh_task: ObserveRefreshTask | None = None
@@ -210,6 +211,10 @@ class ObserveManager:
             return
         with self._notify_cond:
             self._notified.add(href)
+            # Snapshot in enter_observe_mode is at the 80% quorum, not the
+            # full grace period -- a late first push (blockwise refetch)
+            # must drop the href so we don't keep GET-polling a live one.
+            self.fallback_hrefs.discard(href)
             self._last_notify_ts = time.monotonic()
             self._notify_cond.notify_all()
         self.log.debug("observe notify: %s", href)
@@ -280,6 +285,8 @@ class ObserveManager:
         # Issue #92: subscribed-but-silent hrefs are counted as covered by
         # push if we drop this, but they never emit a notify. Keep them on
         # the poll cadence via fallback_hrefs (otherwise idle in observe).
+        # This is the 80% quorum snapshot; a later notify discards the
+        # href in on_notification.
         self.fallback_hrefs = set(subscribed) - notified
         self._set_mode(MODE_OBSERVE)
         self.start_refresh_task(session)

tests/localthings/test_coordinator.py

@@ -1106,6 +1106,38 @@ async def test_observe_mode_skips_subpolls_when_nothing_is_silent(
     mock_sleep.assert_not_called()
 
 
+async def test_observe_mode_skips_empty_subpoll_slots(
+    hass: HomeAssistant, mock_entry, mock_coordinator_observe_session
+) -> None:
+    """Once hot is empty, odd slots would otherwise take the session lock
+    and dispatch a no-op executor job. Skip those."""
+    await hass.config_entries.async_setup(mock_entry.entry_id)
+    await hass.async_block_till_done()
+    coordinator: LocalThingsCoordinator = hass.data[DOMAIN][mock_entry.entry_id]
+    coordinator._observe.mode = MODE_OBSERVE
+    coordinator._hot_hrefs = []
+    coordinator._warm_hrefs = ["/warm/vs/0"]
+    coordinator._observe.fallback_hrefs = {"/warm/vs/0"}
+
+    polled: list[list[str]] = []
+
+    def _capture(hrefs):
+        polled.append(list(hrefs))
+
+    with (
+        patch.object(coordinator, "_poll_hrefs_blocking", side_effect=_capture),
+        patch(
+            "custom_components.localthings.coordinator.asyncio.sleep",
+            new_callable=AsyncMock,
+        ),
+    ):
+        await coordinator._run_subpolls()
+
+    assert polled
+    for batch in polled:
+        assert batch == ["/warm/vs/0"]
+
+
 async def test_write_marks_href_pending_before_post(
     hass: HomeAssistant, mock_entry, mock_coordinator_observe_session
 ) -> None:

tests/localthings/test_observe.py

@@ -236,6 +236,24 @@ def test_enter_observe_mode_keeps_silent_hrefs_on_fallback():
         mgr.close()
 
 
+def test_on_notification_drops_href_from_fallback():
+    """A late first notify (after the 80% snapshot) self-corrects
+    fallback_hrefs so a slow-but-pushing href is not polled for the rest
+    of the session -- multi-block resources being the reliable victim."""
+    mgr = _manager()
+    session = _FakeSession()
+    subscribed = {"/a/vs/0", "/b/vs/0", "/c/vs/0"}
+    mgr.on_notification("/a/vs/0", cbor2.dumps({"x": 1}))
+    mgr.on_notification("/b/vs/0", cbor2.dumps({"x": 1}))
+    try:
+        mgr.enter_observe_mode(session, subscribed)
+        assert mgr.fallback_hrefs == {"/c/vs/0"}
+        mgr.on_notification("/c/vs/0", cbor2.dumps({"x": 1}))
+        assert mgr.fallback_hrefs == set()
+    finally:
+        mgr.close()
+
+
 def test_try_enter_observe_mode_meets_success_fraction_with_partial_notifies():
     mgr = _manager()
     session = _FakeSession()