fix: time out stuck app-server RPCs and cancel before turn start

[goodjin]

Summary

• Writes to Codex app-server stdin now wait for backpressure and surface failures instead of being ignored, so a wedged pipe cannot look like a successful RPC.
• App-server JSON-RPC calls get a deadline (60s by default, 15s for turn/interrupt, override with CODEX_RPC_TIMEOUT_MS).
• session/cancel no longer waits for turn/start. It aborts the open prompt immediately; a late-started turn is still interrupted.

This showed up as a prompt that produced no session/update for minutes, with cancel also hanging until the adapter process was killed. Close already released a pending turn start; cancel did not, so both sides waited on each other.

Test plan

• npm run typecheck
• npm test (461 passed, 28 skipped)
• Confirm cancel returns while turn/start is still outstanding
• Confirm a later turn/start still gets turn/interrupt

Made with Cursor