Problem

When altimate-code crashes (TUI mode), session traces are lost. Users starting a new session cannot find logs from the previous crash.

Root cause: The TUI worker holds all trace data in memory. Bun Workers don't receive OS signals (SIGINT/SIGTERM/SIGHUP), so the worker dies silently when the main thread exits — no crash handlers flush traces to disk.

Upstream context: sst/opencode has 60+ open crash-related issues including:

• Sessions permanently stuck after server restart or stream interruption — no startup recovery for orphaned messages/tool parts anomalyco/opencode#19023 — Sessions permanently stuck after crash (no startup recovery)
• Session not saved to current project when opencode process terminates unexpectedly. anomalyco/opencode#14291 — Session not saved on unexpected termination
• [BUG] Opencode process survives terminal close — missing SIGHUP handler causes orphaned process accumulation anomalyco/opencode#12767 — Missing SIGHUP handler causes orphaned processes

Expected Behavior

Trace files should be persisted to ~/.local/share/altimate-code/traces/ with status: "crashed" when the process exits unexpectedly.

Reported in

#588