Qualify signed worker launch and broker boundary

[dovvnloading]

Summary

This PR advances the signed worker release gate and fixes the packaged-worker startup failure shown in the reported PyInstaller PKG archive dialog.

What changed

• Grant the newly-created AppContainer SID narrowly inherited read/execute access to the verified one-folder package root before CreateProcessW, then revoke that per-launch ACE during cleanup.
• Make the worker’s initial broker receive synchronous so startup acknowledgements are deterministic; retain the receiver thread only once a transform is active.
• Restrict Pillow startup to the allowlisted PNG/JPEG/WebP plugins and include those plugins explicitly in the PyInstaller closure.
• Add tools/execution_spikes/recipe_worker_e2e_qualification.py, a disposable signed end-to-end gate covering:
  • ephemeral Ed25519 signing and immutable installation;
  • active provenance verification;
  • AppContainer/job policy and live PID/SID broker binding;
  • authenticated prepare, input_chunk, input_complete, and collect protocol stages;
  • bounded timeout, redacted status, and exact worker cleanup.
• Update the ADR and execution-spike runbook with the evidence and the remaining release gate.
• Move the Win32 factory test to a temporary executable copy so it never mutates C:\Windows\System32.

Root cause and current gate

The reported embedded-PKG error was caused by the fresh AppContainer having no read/execute permission on the user-owned temporary package tree. That launch precondition is repaired and live-qualified.

The qualification run now passes signed installation, provenance, AppContainer/job identity binding, broker handshake, prepare, and input_chunk. It intentionally blocks at input_complete with worker_response_timeout while the packaged provider transform remains inside the worker. This PR therefore does not enable production provider execution or close the OS/provider lifecycle release gate.

Validation

• python -m pytest -q — 259 passed, 1 expected platform skip.
• Focused phase-2/native tests — 52 passed, 1 expected platform skip.
• Ruff, py_compile, compileall, and git diff --check passed.
• packaging/build_recipe_worker.ps1 — PyInstaller one-folder build completed successfully.
• Live disposable qualification — passed through input_chunk, fail-closed timeout at input_complete; no worker process remained after cleanup.

Risk and rollout

No application lifecycle or provider enablement is changed. The qualification helper is not imported by Cortex, accepts no user/model input, uses only an in-memory trust root, and cannot turn a timeout into a pass. The remaining provider-transform timeout is documented as a blocking release condition for the next stage.

[dovvnloading]

Remote verification complete: GitHub Actions Quality run 30112766530 passed all 20 steps in 3m1s, including headless tests, API contract generation, frontend lint/types/tests/build, launcher-managed bundle verification, signed WebView2 bootstrapper preparation, Windows one-folder package build, and packaged bootstrapper verification. The Node.js 20 deprecation annotation is informational only. The local signed-worker qualification remains intentionally blocked at the provider transform (worker_response_timeout); this PR does not enable that release gate.