Auto-rebuild listener on fatal socket errors and refactor listener creation

[CypherPotato]

Motivation

• Improve robustness of the TCP listener by detecting fatal socket errors during accept and automatically rebuilding the listening socket so the host can recover without full process restart.
• Reduce duplication and make socket configuration explicit by centralizing listener creation and options.

Description

• Replace readonly _listener with a mutable socket and introduce CreateListenerSocket() to centralize socket construction and options previously in ConfigureListenerSocket().
• On Start() dispose the previous listener (if any) and recreate a fresh listener, then bind and listen before starting the accept pool.
• Add _listenerRestarting flag and logic in StartAccept(), OnAcceptCompleted() and ProcessAcceptInline() to detect fatal SocketError values via IsListenerFatalError() and trigger RebuildListenerAsync() which retries creating/binding a new listener and restarts accept loops.
• Return negative rearm values from ProcessAcceptInline() to indicate caller should stop rearming and handle restart scenarios, and adjust accept-queueing logic accordingly.

Testing

• No automated tests were executed as part of this change.

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Codex Task

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Dispose failed rebuilt listener before retry loop

When CreateListenerSocket()/Bind/Listen throws during RebuildListenerAsync, the catch (SocketException) block swallows the exception and immediately retries without disposing the just-created newListener. In a persistent failure (e.g., endpoint temporarily unavailable), this leaks one socket handle every 250ms, which can exhaust file descriptors and prevent the host from recovering.

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