fix: never swallow task exceptions - diagnose WHY the bot died

The restart-loop with only 'Starting discord bot' in the logs was caused by
gather(return_exceptions=True) eating the client.start() exception: a failed
login looked like a clean exit and docker just restarted the container.

bot.py:
- _run_bot: catch discord.LoginFailure / PrivilegedIntentsRequired with
  CRITICAL messages telling exactly what to fix (token entry / Developer
  Portal intents), full traceback for anything else, then re-raise
- main() returns an exit code; every task exception is re-logged as the
  LAST line in docker logs ('Task died: ...'); process exits 1 on failure
- log the token source (env vs netrc) and its length at startup to catch
  truncated/wrong-field netrc entries
- _run_comm_subroutine: comm crash is logged loudly but no longer relies on
  gather to surface it (bot keeps running - Discord side is independent)

communication_subroutine.py (crash found by the new stub tests):
- comm_subroutine used 'logger' before its local assignment
  (UnboundLocalError killed the whole comm layer at every startup)
- re-comment the flask_debug thread: it binds the same host:port as
  waitress, so running both dies with 'address in use'

Verified via stub-injected client: LoginFailure -> CRITICAL + exit 1,
PrivilegedIntentsRequired -> CRITICAL + exit 1, unknown exception -> full
traceback + exit 1, clean shutdown -> exit 0; comm layer no longer crashes.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

bot.py

@@ -216,19 +216,62 @@ async def on_ready():
 
 
 async def _run_comm_subroutine(stop_event: threading.Event) -> None:
-    """Run the blocking comm subroutine in a worker thread."""
+    """Run the blocking comm subroutine in a worker thread.
-    await asyncio.to_thread(comm_subroutine, stop_event)
+
+    A crash here takes down the internal HTTP endpoints only - the Discord
+    side keeps running, so log loudly and swallow.
+    """
+    try:
+        await asyncio.to_thread(comm_subroutine, stop_event)
+    except Exception:  # pylint: disable=broad-exception-caught
+        logger.exception(
+            "Comm layer crashed - internal HTTP endpoints are down "
+            "(musician/librarian callbacks will not arrive); bot continues"
+        )
 
 
 async def _run_bot(token: str, shutdown_event: asyncio.Event) -> None:
-    """Start the Discord client and flag shutdown when it returns."""
+    """Start the Discord client; log WHY it died before flagging shutdown.
+
+    Exceptions were previously swallowed by ``gather(return_exceptions=True)``
+    which made a failed login look like a clean exit (silent crash-loop in
+    docker). Now every death is diagnosed on the console first.
+    """
     try:
         await client.start(token, log_handler=None)
+    except discord.LoginFailure:
+        logger.critical(
+            "FATAL: Discord REJECTED the token (Improper token). Fix the "
+            "'discord' entry in the netrc mounted at CONJURER_NETRC_FILE or "
+            "the DISCORD_TOKEN env var. If the token leaked/reset, generate a "
+            "new one in the Discord Developer Portal -> Bot -> Reset Token."
+        )
+        raise
+    except discord.PrivilegedIntentsRequired:
+        logger.critical(
+            "FATAL: this bot application does not have the Privileged Gateway "
+            "Intents enabled. Open Discord Developer Portal -> your app -> "
+            "Bot -> enable 'Presence', 'Server Members' and 'Message Content' "
+            "Intents, then restart."
+        )
+        raise
+    except Exception:  # pylint: disable=broad-exception-caught
+        logger.exception("FATAL: Discord client crashed at startup/runtime")
+        raise
     finally:
         shutdown_event.set()
 
 
-async def main() -> None:
+async def main() -> int:
+    """Run both halves; return a process exit code (0 = clean shutdown)."""
+    if TOKEN:
+        token_source = (
+            "env DISCORD_TOKEN" if os.getenv("DISCORD_TOKEN") else "netrc file"
+        )
+        logger.info(
+            "Discord token: loaded from %s (length %d)", token_source, len(TOKEN)
+        )
+
     logger.info("Starting discord bot")
     shutdown_event = asyncio.Event()
     comm_stop_event = threading.Event()
@@ -236,6 +279,7 @@ async def main() -> None:
     comm_task = asyncio.create_task(_run_comm_subroutine(comm_stop_event))
     bot_task = asyncio.create_task(_run_bot(TOKEN, shutdown_event))
 
+    exit_code = 0
     try:
         await shutdown_event.wait()
     except (KeyboardInterrupt, asyncio.CancelledError):
@@ -246,7 +290,16 @@ async def main() -> None:
         comm_stop_event.set()
         if not client.is_closed():
             await client.close()
-        await asyncio.gather(bot_task, comm_task, return_exceptions=True)
+        results = await asyncio.gather(bot_task, comm_task, return_exceptions=True)
+        for result in results:
+            if isinstance(result, BaseException) and not isinstance(
+                result, asyncio.CancelledError
+            ):
+                # Already logged with full traceback inside the task; repeat
+                # the one-liner so it is the LAST thing in `docker logs`.
+                logger.critical("Task died: %r", result)
+                exit_code = 1
+    return exit_code
 
 
 # *================================== Run
@@ -264,4 +317,4 @@ if __name__ == "__main__":
         )
         logger.critical(MSG)
         sys.exit(MSG)
-    asyncio.run(main())
+    sys.exit(asyncio.run(main()))

communication_subroutine.py

@@ -234,11 +234,14 @@ def comm_subroutine(stop_event: Optional[threading.Event] = None):
     :param stop_event: optional :class:`threading.Event` shared with the caller
     to coordinate a cooperative shutdown.
     """
-    logger.setLevel(logging.DEBUG)
     logger = logging.getLogger("discord")
+    logger.setLevel(logging.DEBUG)
     logger.info("Started comms")
     threads = []
-    threads.append(threading.Thread(target=flask_debug))
+    # NOTE: flask_debug is the dev server bound to the SAME host:port as
+    # waitress - running both kills the comm layer with 'address in use'.
+    # Enable it only INSTEAD of waitress_run, never alongside.
+    # threads.append(threading.Thread(target=flask_debug))
     threads.append(threading.Thread(target=waitress_run, daemon=True))
     threads.append(
         threading.Thread(