Retry transient local provider connection failures (ECONNREFUSED) in session loop #15851

Describe the bug\nWhen using local OpenAI-compatible providers (for example llama.cpp), transient connection failures like ECONNREFUSED can appear during long-running sessions.\n\nThese failures are currently treated as non-retryable in some paths, so the session stops instead of recovering automatically.\n\n### Steps to reproduce\n1. Configure a local provider endpoint (for example http://127.0.0.1:8080/v1).\n2. Start a long session and trigger intermittent local server availability/connectivity interruptions.\n3. Observe that some connection failures abort the turn instead of retrying.\n\n### Expected behavior\nTransient local connectivity errors should be marked retryable so the existing session retry loop can recover automatically.\n\n### Additional context\nThis especially affects local/self-hosted flows where temporary restarts and socket hiccups are expected.