Summary

• make the shell prompt setup uninterruptible until the assistant and running bash tool scaffolding exist
• finalize shell cancel fallback into a completed aborted bash result instead of reusing a running snapshot
• preserve partial streamed shell output when cancellation falls back to the interrupted path
• add regression coverage for ignored TERM and partial-output preservation

Why

After PR #36 merged, CI run #107 started failing in prompt-effect cancellation coverage. Early shell cancellation could race ahead of the normal finalization path, which either threw Impossible while looking up the last assistant message or reused a still-running bash tool snapshot. The fallback path also dropped already-streamed shell output.

Related Issue

Follow-up to #36. Triggered by CI run #107 after merge.

How To Verify

cd packages/opencode && bun test test/session/prompt-effect.test.ts --timeout 30000
cd packages/opencode && bun run typecheck
cd packages/opencode && bun run build

Screenshots or Recordings

N/A, no visible UI changes.

Checklist

• I ran the relevant verification steps
• I tested visible changes manually when needed
• I am targeting the dev branch