[codex] Harden Pocket remote lifecycle

[nedtwigg]

Summary

• Ignore message/open/close events from superseded Pocket relay sockets after reconnecting.
• Mark restored exited terminal panes as exited in the registry so the directory reports them as non-attachable.
• Filter alive:false directory entries out of the Pocket wall picker and default attachment flow.

Impact

This prevents stale socket events from clearing an active reconnect and prevents Pocket from offering dead or restored-exited terminal panes as attach targets.

Root Cause

Pocket socket event handlers were not scoped to the current WebSocket instance, and restore wrote the exited-process message without updating the registry-level exited flag.

Validation

• pnpm --filter dormouse-lib test -- terminal-registry.alert.test.ts pocket-client.test.ts wall-model.test.ts