feat(transport): per-radio serialized+paced outbound send queue (#93)

* feat(transport): per-radio serialized+paced outbound send queue

Prevents simultaneous LoRa transmissions when N events arrive at once.

## Mechanism

Two `RadioSendQueue` instances (one MT, one MC), each a FIFO asyncio.Queue
with a long-running drain task.  The MT queue drains on the main asyncio
loop; the MC queue drains on MeshCore's dedicated event-loop thread.

- MT sends: `run_in_executor` offloads the blocking `sendText` call;
  queue started in `set_message_callback`, cancelled in `disconnect`.
- MC sends: drain loop runs pure-async MC lib coroutines directly on the
  MC loop (no `_run_coro` deadlock); cross-loop callers bridge via
  `concurrent.futures.Future` + `asyncio.wrap_future`.
- Pacing: `await asyncio.sleep(pacing_seconds)` between items; read live
  from config per iteration; floor clamped to 0.25 s.
- Config knobs: `meshtastic_send_pacing_seconds` (default 2.0) and
  `meshcore_send_pacing_seconds` (default 2.0) on `ConnectionConfig`.

## Send sites rerouted

All callers now `await connector.send_message_async(...)`:
- `notifications/channels.py` — MeshBroadcast/MeshCoreBroadcast/MeshDM/
  MeshCoreDM deliver(), test_connection(), deliver_test()
- `responder.py` — DM replies in send_response()
- `transport/meshcore_transport.py` — periodic_advert_loop, telemetry
  poll loop, send_advert() → send_advert_async(), req_telemetry()
  → req_telemetry_async() (all queue-routed from main loop)
- `dashboard/api/mesh_send_routes.py` — test-send, advert, telemetry poll

## Audit accuracy

`deliver()` now returns the actual bool from the radio send (not
optimistic True), so `mesh_broadcasts_out` reflects the real result.

## Tests

17 new tests in tests/test_send_queue.py covering FIFO ordering, no drops,
pacing gap, pacing floor enforcement, event-loop non-blocking, serialization,
lifecycle, MT fallback, config round-trip.  Existing test stubs updated to
wire `send_message_async = AsyncMock(side_effect=send_message)` so prior
call_count / call_args assertions remain valid without changes.

Full suite: 2135 passed, 17 pre-existing failures (unchanged), 0 new regressions.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* fix(send-queue): resolve MC telemetry self-deadlock + resolve pending futures on teardown/reconnect; composite MC-channel kwarg; audit no-op false

BLOCKER 1 — req_telemetry_async self-deadlock (meshcore_transport.py):
_req_telemetry_async was calling _enqueue_mc_loop_send inside itself;
when _telem_job_outer ran inside the drain it nested another enqueue+await
on the same single-threaded drain — permanent deadlock on first telemetry poll.
Fix: _req_telemetry_async is now fully inline (no _enqueue_mc_loop_send).
_telemetry_poll_loop wraps its call in _enqueue_mc_loop_send for serialization.
req_telemetry_async's outer job calls _req_telemetry_async inline (safe).

BLOCKER 2 — pending futures abandoned on teardown/reconnect:
RadioSendQueue.stop() only cancelled the drain task; queue-sitting items had
their concurrent.futures.Futures left unresolved, causing wrap_future() callers
to hang indefinitely. Fix: stop() drains the remaining queue with get_nowait()
and cancels every pending cfut. _cancel_mc_queue() schedules the same drain-
and-cancel via call_soon_threadsafe. _start_mc_queue() cancels old drain task
and drains old queue cfuts before arming the new queue (reconnect path).
connector.disconnect() now .result(timeout=5) on stop() instead of fire-and-forget.

SHOULD-FIX 3 — composite passes MC channel as wrong kwarg (composite_transport.py):
_broadcast_async no-hint loop was calling send_message_async(channel=child_channel)
for the meshcore child; should be meshcore_channel=child_channel. Silent drop fixed.

NIT 5 — false success on zero-channel MC send (meshcore_transport.py):
send_message_async returned True when meshcore_channel is None (nothing sent).
Now returns False so audit does not record a success for a no-op.

NIT 7 — config comment contradiction (config.py):
meshtastic_send_pacing_seconds comment said "0 disables the floor" while
simultaneously stating "still floored at 0.25". Removed the contradiction.

Regression tests (tests/test_send_queue.py — 3 new, all in TestDeadlockRegression):
- test_telemetry_queue_no_deadlock: drives req_telemetry_async through a real
  _mc_send_queue with fake MC commands; times out on pre-fix code (deadlock).
- test_teardown_resolves_pending_futures: enqueues slow+fast jobs, stops mid-drain,
  asserts every task resolves promptly; hangs on pre-fix code.
- test_reconnect_resolves_old_futures: calls _start_mc_queue twice, asserts old
  cfuts are cancelled; pre-fix leaves them unresolved.

All 17 pre-existing send-queue tests still pass (20 total now).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Matt Johnson <mj@k7zvx.com>
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

work/tests/test_composite_transport.py

@@ -76,12 +76,27 @@ class FakeChild:
         destination: Optional[str] = None,
         channel: int = 0,
         transport: Optional[str] = None,
+        meshcore_channel: Optional[str] = None,
     ) -> bool:
         self.send_calls.append(
             {"text": text, "destination": destination, "channel": channel, "transport": transport}
         )
         return True
 
+    async def send_message_async(
+        self,
+        text: str,
+        destination: Optional[str] = None,
+        channel: int = 0,
+        transport: Optional[str] = None,
+        meshcore_channel: Optional[str] = None,
+    ) -> bool:
+        """Async variant required by composite transport after send-queue refactor."""
+        return self.send_message(
+            text=text, destination=destination, channel=channel,
+            transport=transport, meshcore_channel=meshcore_channel,
+        )
+
     def set_message_callback(self, callback, loop) -> None:
         self._callback = callback
         self._callback_loop = loop