fix(ai): recover stale Codex previous_response_id

[enieuwy]

Summary

• recover Codex websocket continuations when the cached previous_response_id expires server-side
• clear append/session metadata and retry the current turn with full context before any output has been emitted
• add regression coverage for the websocket delta -> previous_response_not_found -> full-context retry path

Fixes #925

Verification

bun test packages/ai/test/openai-codex-stream.test.ts -t "websocket continuation"

2 pass
28 filtered out
0 fail

Also ran:

bun run check

Biome passed. Type check is currently blocked in this checkout by missing workspace/dependency modules after pulling latest:

• @aws-sdk/credential-provider-node
• proxy-agent
• @oh-my-pi/pi-natives

[can1357]

ty!