Sync 4: Retain complete stdout and stderr #40

Priority 4 of 5 runner fixes.

Runner failures currently leave bounded receipt evidence. The optional lane journal captures stdout only, and journal writes can fail without stopping the lane. That can leave too little evidence to debug a provider failure.

Port upstream's private stdout/stderr files beside the receipt. Retain complete streams on success and failure, and put their paths in the receipt. Reserve files without overwriting existing artifacts, reject path collisions, and close descriptors on every exit.

Keep the optional journal tap working. Check psf-monitor compatibility before changing receipt fields. Preserve the fork's gateway cost rules, OpenCode parsing, cancellation receipts, and explicit deadline. Use synthetic output in tests and never log provider key values.

Source: open-pstack PR #126.

Files: runner/run.ts, receipt types, and regression tests 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.