Fix silently swallowed / unpropagated errors in bind, polling disconnect, and websocket writes

[devin-ai-integration]

Description

Review of error handling in the core module surfaced a few places where failures were silently swallowed or not propagated. This tightens those up without changing intended behavior.

Type of Change

• Bug fix (non-breaking change which fixes an issue)

Changes Made

• SocketIOServer — bind failure cause was dropped. On a failed bind the code logged a generic "Failed to start server on port {}" but discarded future.cause(), so the real reason (port in use, permission denied, …) was invisible. Now logs future.cause().
• SocketIOServer — swallowed port-resolution exception. The catch (Exception ignore) {} around resolving the actual bound port (used with port=0) is now catch (Exception e) with a debug log so the failure isn't completely invisible.
• PollingTransport — NPE on disconnect for unknown session. The disconnect branch called client.onChannelDisconnect() without a null check, unlike onGet/onPost/onOptions. A disconnect request for an already-removed session threw an NPE up the pipeline. Now mirrors the sibling handlers: logs and returns an error response when the client is missing.
• EncoderHandler.readVersion — swallowed IOException. An unreadable MANIFEST.MF was skipped with an empty catch; now logged at debug (still non-fatal so other manifests are still scanned).

Testing

• All existing tests pass
• Tests pass locally with mvn test (ran EncoderHandlerTest (21), AuthorizeHandlerTest (11), InPacketHandlerTest, PacketListenerTest)
• mvn checkstyle:check → 0 violations
• mvn -pl netty-socketio-core -am compile succeeds

Additional Notes

• An earlier revision also aggregated the main WebSocket frame writes into ChannelFutureList so send-promise failures would propagate; reverted per review feedback.
• Pub/sub event stores (NATS/Redis/Kafka) intentionally swallow-and-warn on publish/listener errors for resilience and were left unchanged.

Link to Devin session: https://app.devin.ai/sessions/99a4ba93decd4b47be31cb129923fe6e
Requested by: @sanjomo

[devin-ai-integration]

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[sanjomo]

@devin-ai just adding in ChannelFutureList is no use

[devin-ai-integration]

@sanjomo agreed — reverted the ChannelFutureList change in handleWebsocket (8f0ea9e). The remaining fixes (bind-failure cause logging, port-resolution debug log, polling disconnect null-check, readVersion IOException log) are unchanged.

If you'd still like WebSocket write failures surfaced on the send promise, I'd rather do it properly (e.g. a PromiseCombiner over the frame writes) than bolt onto ChannelFutureList — happy to add that in a follow-up if you want it.

[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.