Test/caller disconnect callee crash

[markope]

a rundown on what the issue is and how it impacts the callee:

Exception Flow: Caller Disconnect Causes Callee Session Crash

When a caller disconnects during an in-flight RPC, the callee's session can be terminated due to unhandled exception propagation:

The Problem

1. Caller disconnects during an in-flight RPC call
2. Callee completes work and sends YIELD message with the result
3. Dealer receives YIELD but the invocation tracking data is stale (points to disconnected caller)
4. processYield() in dealer.py tries to send result to caller._transport which is None
5. Exception is raised → propagates up to router.process()
6. router.process() re-raises ProtocolError (see router.py#L355-356)
7. Exception bubbles to Autobahn's WampWebSocketProtocol.onMessage()
8. Autobahn catches ProtocolError and calls _bailout() with CLOSE_STATUS_CODE_PROTOCOL_ERROR
9. WebSocket connection is closed → Callee's session is terminated

Code Path

Callee sends YIELD
  → RouterSession.onMessage()
    → router.process()
      → dealer.processYield()
        → Exception (stale invocation / None transport)
      → ProtocolError re-raised
    → Exception propagates (no catch)
  → WampWebSocketProtocol.onMessage() catches ProtocolError
    → _bailout() → _fail_connection()
      → WebSocket closed → Callee session LOST

Impact

Any ProtocolError raised in the dealer causes the entire session's WebSocket connection to be closed, which is catastrophic for the callee who did nothing wrong.

The Fix

Clean up invocation tracking when the caller detaches, so that when the callee later calls processYield():

• The invocation is already gone from _invocations
• processYield() simply logs a debug message and returns None
• No exception is raised
• Callee's session remains intact

The Test

The test creates the scenario sketched above and expects the dealer.py to not raise an error in step 4 (processYield).
Currently without the fix the test does not pass.

[markope]

tests #2133

Failed test visible here

[markope]

all tests pass now see here

[markope]

@oberstet I hope I followed your required procedure here. I motivated the issue more clearly in the initial PR comment above. The comments in the new test case give some additional details about the nature of the test and why the fix is a fix.

[oberstet]

fantastic! this is a showcase example for the workflow!

it's perfect - both for me reviewing, as well as (IMO) for users.

thanks also in particular for the detailed comments on the new test test_caller_detach_cleans_up_invocation_tracking_without_cancel_support()!

ah, and the remaining failed code quality check was completely unrelated to this PR.

merging.

[oberstet]

love it. thanks so much for the fix! and for taking so much care following the workflow.

fwiw, now (together with fixed typo wrt check-typing), workflows are 100% green & happy:

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the release.yml - correctly - posted a new nightly/development github release: https://github.com/crossbario/crossbar/releases/tag/master-202601040913

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[oberstet]

what is still missing here is: release-post-comment.yml - which posts a github discussions post in CI-CD (https://github.com/crossbario/crossbar/discussions/categories/ci-cd) => filed as #2154