Fix: restore new chat startup flow

[xIGBClutchIx]

Summary

This restores responsive New chat startup in Pocodex by recognizing the current Codex bundle's new-conversation triggers and routing thread-prewarm-start responses back to the correct browser session instead of letting prewarm fall through to the timeout path.

What changed

• update the bootstrap new-conversation trigger detection to handle both older New thread labels and newer New chat labels, including shortcut-suffixed sidebar text
• preserve explicit ?thread= and initial-route deep links instead of overwriting them with the stored / route during bootstrap restore
• forward thread-prewarm-start through the app-server bridge on the same thread/start sanitization path used for normal MCP requests
• prefix prewarm request ids in the host routing layer so returning mcp-response messages resolve back to the originating browser session
• add focused regression coverage in test/bootstrap-script.test.ts, test/app-server-bridge-workers.test.ts, and test/request-id.test.ts

Root cause

• newer Codex bundles initiate New chat startup with a thread-prewarm-start request before the real thread handoff
• Pocodex still relied on older New thread trigger text in parts of the bootstrap flow and only rewrote host request ids for mcp-request
• that let stale thread restore state survive newer New chat controls and caused the prewarm response to be dropped instead of routed back to the browser
• once the response was dropped, the bundle waited for its prewarm timeout and only then issued a second real thread/start, which produced the long startup stall

Impact

• New chat no longer waits for the prewarm timeout before the real thread handoff can complete
• explicit thread deep links and initial-route launches are preserved instead of being replaced by the stored root route
• focused regression coverage now protects both the new-conversation trigger detection and the prewarm request-routing contract

Validation

• pnpm run check:commit
• pnpm exec vitest run test/request-id.test.ts test/app-server-bridge-workers.test.ts test/bootstrap-script.test.ts
• live local verification on http://127.0.0.1:8796/ showed about 10.2s on a cold run and about 1.0s on the immediate retry instead of the prior ~30s stall