Sync 1: Isolate Bun startup #37

Priority 1 of 5 runner fixes.

The current pstack-runner starts Bun directly. Project .env files, Bun configuration, and inherited startup options can affect it before its routing and credential checks run.

Port upstream's startup isolation: clear BUN_OPTIONS and NODE_OPTIONS, disable automatic env-file loading, and start Bun without project configuration. Preserve normal parent-provided variables, including provider keys and parent identity. Keep the existing explicit-deadline semantics and cancellation behavior.

Cover individual and combined startup inputs with synthetic fixtures. Verify that project preloads never execute, project dotenv values do not reach the runner, and intentionally exported variables still reach the right child.

Sources:

• open-pstack PR #113
• Pinned launcher

Files: runner/pstack-runner, the new entry module if needed, and launcher regression tests. These paths are under plugins/pstack/skills/poteto-mode/scripts/.

Done when

• The focused regression checks pass, along with bash scripts/check.sh.
• The exact candidate is installed and the changed behavior passes from each affected parent app. Record the version, action, and observed result in the PR. Keep it draft until that evidence is complete.