Subscriber resilience and RabbitMQ fixes (#765)

Subscriber resilience: recreate consumer after connection failure

- Move consumer creation from Subscriber.start() into the run() loop,
  matching the pattern used by Consumer. If the connection drops and the
  consumer is closed in the finally block, the loop now recreates it on
  the next iteration instead of spinning forever on a None consumer.

Consumer thread safety:
- Dedicated ThreadPoolExecutor per consumer so all pika operations
  (create, receive, acknowledge, negative_acknowledge) run on the
  same thread — pika BlockingConnection is not thread-safe
- Applies to both Consumer and Subscriber classes

Config handler type audit — fix four mismatched type registrations:
- librarian: was ["librarian"] (non-existent type), now ["flow",
  "active-flow"] (matches config["flow"] that the handler reads)
- cores/service: was ["kg-core"], now ["flow"] (reads
  config["flow"])
- metering/counter: was ["token-costs"], now ["token-cost"]
  (singular)
- agent/mcp_tool: was ["mcp-tool"], now ["mcp"] (reads
  config["mcp"])

Update tests

tests/unit/test_base/test_subscriber_graceful_shutdown.py

@@ -61,23 +61,21 @@ async def test_subscriber_deferred_acknowledgment_success():
         max_size=10,
         backpressure_strategy="block"
     )
-    
-    # Start subscriber to initialize consumer
-    await subscriber.start()
-    
+    subscriber.consumer = mock_consumer
+
     # Create queue for subscription
     queue = await subscriber.subscribe("test-queue")
-    
+
     # Create mock message with matching queue name
     msg = create_mock_message("test-queue", {"data": "test"})
-    
+
     # Process message
     await subscriber._process_message(msg)
-    
+
     # Should acknowledge successful delivery
     mock_consumer.acknowledge.assert_called_once_with(msg)
     mock_consumer.negative_acknowledge.assert_not_called()
-    
+
     # Message should be in queue
     assert not queue.empty()
     received_msg = await queue.get()
@@ -108,9 +106,7 @@ async def test_subscriber_dropped_message_still_acks():
         max_size=1,  # Very small queue
         backpressure_strategy="drop_new"
     )
-
-    # Start subscriber to initialize consumer
-    await subscriber.start()
+    subscriber.consumer = mock_consumer
 
     # Create queue and fill it
     queue = await subscriber.subscribe("test-queue")
@@ -151,9 +147,7 @@ async def test_subscriber_orphaned_message_acks():
         max_size=10,
         backpressure_strategy="block"
     )
-
-    # Start subscriber to initialize consumer
-    await subscriber.start()
+    subscriber.consumer = mock_consumer
 
     # Don't create any queues - message will be orphaned
     # This simulates a response arriving after the waiter has unsubscribed
@@ -189,9 +183,7 @@ async def test_subscriber_backpressure_strategies():
         max_size=2,
         backpressure_strategy="drop_oldest"
     )
-    
-    # Start subscriber to initialize consumer
-    await subscriber.start()
+    subscriber.consumer = mock_consumer
     
     queue = await subscriber.subscribe("test-queue")
     

tests/unit/test_concurrency/test_consumer_concurrency.py

@@ -81,9 +81,8 @@ class TestTaskGroupConcurrency:
 
         # Track how many consume_from_queue calls are made
         call_count = 0
-        original_running = True
 
-        async def mock_consume(backend_consumer):
+        async def mock_consume(backend_consumer, executor=None):
             nonlocal call_count
             call_count += 1
             # Wait a bit to let all tasks start, then signal stop
@@ -107,7 +106,7 @@ class TestTaskGroupConcurrency:
         consumer = _make_consumer(concurrency=1)
         call_count = 0
 
-        async def mock_consume(backend_consumer):
+        async def mock_consume(backend_consumer, executor=None):
             nonlocal call_count
             call_count += 1
             await asyncio.sleep(0.01)
@@ -294,9 +293,8 @@ class TestPollTimeout:
             raise type('Timeout', (Exception,), {})("timeout")
 
         mock_pulsar_consumer.receive = capture_receive
-        consumer.consumer = mock_pulsar_consumer
 
-        await consumer.consume_from_queue()
+        await consumer.consume_from_queue(mock_pulsar_consumer)
 
         assert received_kwargs.get("timeout_millis") == 100