fix(socket_mode): recreate a closed aiohttp session when reconnecting

[Shubham-Padkonde]

Fixes #1922.

The aiohttp SocketModeClient shares one ClientSession for all connections. Once that session was closed, every attempt in connect()'s retry loop failed with RuntimeError: Session is closed and the client retried forever.

• connect() now creates a new session at the start of an attempt when the current one is closed. The loop still stops once the client itself is closed, so close() does not trigger a new session.
• Session recreation uses the running loop and is guarded by not self.closed, including shutdown while closing the old WebSocket. is_connected() retains its existing WebSocket-state check.

The added test closes the session, runs connect() with ws_connect stubbed, and checks that the connection attempt uses a new open session; it fails before this change. The original async Socket Mode tests, ruff and mypy passed before this follow-up.

🤖 Generated with Claude Code

Review follow-up validation

• New shutdown-during-reconnect regression fails before the guard and passes after it. All 8 aiohttp tests pass via scripts/run_tests.sh.
• A real local aiohttp WebSocket check confirms close detection and reconnection with a fresh HTTP session.
• scripts/lint.sh --no-install passes.
• Broader Socket Mode run passes 13 tests before timing out in the unchanged websockets backend after 180 seconds.
• scripts/run_mypy.sh --no-install encounters the existing Windows-only missing signal.SIGHUP error in unchanged RTM code. No full-suite or complete type-check pass is claimed for this follow-up.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.16%. Comparing base (b9f4666) to head (4a754cd).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1966      +/-   ##
==========================================
+ Coverage   84.15%   84.16%   +0.01%     
==========================================
  Files         118      118              
  Lines       13566    13570       +4     
==========================================
+ Hits        11416    11421       +5     
+ Misses       2150     2149       -1     

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[AmyScript]

Thanks for the fix! The recreate is safely guarded. It lives inside while not self.closed, and close() sets self.closed = True before it closes the shared session, so a normal shutdown can't trigger a spurious new session (the loop has already exited). And the not self.aiohttp_client_session.closed check in is_connected() directly addresses the production symptom in the issue which was a watchdog on is_connected() couldn't detect the dead HTTP session while the WS layer still looked connected.

[WilliamBergamin]

Thanks for picking this up 🙏

The approach looks right to me: recreating the session right before ws_connect is the smallest fix that actually ends the loop. Raising or breaking instead wouldn't be enough, because monitor_current_session catches the error and calls connect_to_new_endpoint() again every ping_interval, so the infinite loop would just move there.

A couple of suggestions to trim it down, left inline.

[WilliamBergamin]

I don't think we need to store the loop. connect() always runs inside the running event loop, and aiohttp.ClientSession() binds to the running loop by default. So we can drop this attribute and create the session with no arguments below.

[WilliamBergamin]

Could this be simplified, with one extra guard?

Suggested change

	if self.aiohttp_client_session.closed:
	# All connections share this session. Once it has been closed,
	# every connection attempt fails, so it has to be recreated.
	self.logger.info("The aiohttp client session is closed; creating a new one")
	self.aiohttp_client_session = aiohttp.ClientSession(loop=self._loop)
	if self.aiohttp_client_session.closed and not self.closed:
	self.logger.info("The aiohttp client session is closed; creating a new one")
	self.aiohttp_client_session = aiohttp.ClientSession()

[Shubham-Padkonde]

Addressed all three suggestions in 89b7542: removed the stored loop, create the replacement session with no arguments and the extra shutdown guard, and removed the HTTP-session clause from is_connected(). Added a regression for shutdown while awaiting the old WebSocket close (fails before, passes after). All 8 aiohttp tests and project lint pass. A real local WebSocket check also confirms close detection and successful reconnection. The broader run times out in the unchanged websockets backend, and Windows mypy hits the unchanged RTM signal.SIGHUP error; these limits are recorded in the PR description.

[WilliamBergamin]

I think this clause can go. ws_connect never releases its connection back to the pool, so ClientSession.close() closes the WebSocket's transport too. I tested it against a local server: current_session.closed and is_connected() both flip immediately without this line, and the monitor reconnects on a fresh session.