app-server: use connection-specific thread unload delays

[euroelessar]

Why

Threads are eligible for unload after the last connection unsubscribes, but the appropriate grace period depends on the connection type. Local in-process and stdio clients can release immediately after the last subscriber leaves, while socket, TCP websocket, and remote-control clients should keep the existing 30-minute grace window to preserve reconnect behavior.

What changed

• Added per-origin unload delays on ConnectionOrigin.
• Carried each initialized connection delay into app-server thread subscription state.
• Made ThreadStateManager publish whether subscribers exist plus the winning unload delay, using the maximum delay among active subscribers and retaining that value once the thread becomes idle.
• Passed distinct unix socket and websocket origins through transport setup.
• Updated v2 unsubscribe tests and README notes for immediate stdio unload behavior.

Verification

• git diff --check ae863e72a27a283c08023dcf039871c917209120
• CARGO_TARGET_DIR=/tmp/codex-app-server-target cargo test -p codex-app-server connection_origin_sets_thread_unloading_delay
• CARGO_TARGET_DIR=/tmp/codex-app-server-target cargo test -p codex-app-server adding_connection_to_thread_updates_subscription_watcher
• CARGO_TARGET_DIR=/tmp/codex-app-server-target cargo test -p codex-app-server thread_unsubscribe_over_stdio
• CARGO_TARGET_DIR=/tmp/codex-app-server-target cargo test -p codex-app-server thread_unsubscribe_during_turn_keeps_turn_running

[chatgpt-codex-connector]

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[github-actions]

Closing this pull request because it has had no updates for more than 14 days. If you plan to continue working on it, feel free to reopen or open a new PR.