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Gateway lock

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Why

• Ensure only one gateway instance runs per base port on the same host; additional gateways must use isolated profiles and unique ports.
• Survive crashes/SIGKILL without leaving stale lock files.
• Fail fast with a clear error when the control port is already occupied.

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Mechanism

• The gateway binds the WebSocket listener (default ws://127.0.0.1:18789) immediately on startup using an exclusive TCP listener.
• If the bind fails with EADDRINUSE, startup throws GatewayLockError("another gateway instance is already listening on ws://127.0.0.1:<port>").
• The OS releases the listener automatically on any process exit, including crashes and SIGKILL—no separate lock file or cleanup step is needed.
• On shutdown the gateway closes the WebSocket server and underlying HTTP server to free the port promptly.

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Error surface

• If another process holds the port, startup throws GatewayLockError("another gateway instance is already listening on ws://127.0.0.1:<port>").
• Other bind failures surface as GatewayLockError("failed to bind gateway socket on ws://127.0.0.1:<port>: …").

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Operational notes

• If the port is occupied by another process, the error is the same; free the port or choose another with openclaw gateway --port <port>.
• The macOS app still maintains its own lightweight PID guard before spawning the gateway; the runtime lock is enforced by the WebSocket bind.