server, dispatcher: improve node liveness self fence

[asddongmen]

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[gemini-code-assist]

Code Review

This pull request introduces a local fencing mechanism to ensure that downstream writes are stopped immediately when a capture loses its etcd session or lease. This is achieved by adding a session watchdog in the server and implementing a LocalFence method across the DispatcherOrchestrator and DispatcherManager to bypass graceful draining in failure scenarios. The review feedback identifies potential nil pointer dereferences in the DispatcherManager's shutdown logic, specifically regarding the redoSink when redo logging is enabled.

[gemini-code-assist]

Potential nil pointer dereference. If redoEnabled is true but the redoSink failed to initialize or is not yet set (e.g., during a failed startup sequence), calling e.redoSink.SinkType() will cause a panic. Given that e.sink is explicitly checked for nil below, e.redoSink should also be guarded.

Suggested change

	if e.IsRedoEnabled() {
	closeAllDispatchers(e.changefeedID, e.redoDispatcherMap, e.redoSink.SinkType())
	if e.IsRedoEnabled() && e.redoSink != nil {
	closeAllDispatchers(e.changefeedID, e.redoDispatcherMap, e.redoSink.SinkType())

[gemini-code-assist]

Potential nil pointer dereference. Similar to the pattern used for e.sink, e.redoSink should be checked for nil before calling Close() to ensure that cleanup of partially initialized managers does not result in a panic.

Suggested change

	if e.IsRedoEnabled() {
	e.redoSink.Close()
	if e.IsRedoEnabled() && e.redoSink != nil {
	e.redoSink.Close()
	}

[asddongmen]

/test all

[ti-chi-bot]

@asddongmen: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-cdc-mysql-integration-light	2620b94	link	true	/test pull-cdc-mysql-integration-light
pull-cdc-pulsar-integration-light	2620b94	link	false	/test pull-cdc-pulsar-integration-light
pull-cdc-storage-integration-light	2620b94	link	true	/test pull-cdc-storage-integration-light
pull-cdc-pulsar-integration-heavy	2620b94	link	false	/test pull-cdc-pulsar-integration-heavy
pull-cdc-kafka-integration-light	2620b94	link	true	/test pull-cdc-kafka-integration-light

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