ci(windows): diagnose flaky Runtime Host Local IPC startup failures #3237

Summary

Windows GitHub-hosted runners intermittently fail Runtime Host startup checks on identical source trees. The failure moves between the dedicated Local IPC trust-boundary workflow and the installed CLI first-run smoke, while reruns of the same code pass.

This currently makes PR checks non-deterministic and the CLI smoke exposes only INTERNAL_STARTUP_FAILURE, deleting the isolated data root before the underlying Host diagnostic can be inspected.

Evidence

Observed on #3183:

• Head bded591:
  • windows_recovery failed because the Runtime Host trust fixture exited with insecure_endpoint_directory while restricting the Windows Local IPC endpoint.
  • Installed CLI Windows validation passed, including first-run TUI setup, managed Runtime Host lifecycle, and a controlled model turn.
• Empty retrigger commit 5da258d has the exact same Git tree (b6cad43ab27a6dee887b7285877a097a5e84b875) as bded591:
  • windows_recovery passed.
  • Installed CLI Windows validation failed during the first-run TUI setup. Runtime Host recovery returned INTERNAL_STARTUP_FAILURE before the expected Set Up Provider marker.
• The failed CLI runner was windows-2025-vs2026 in westus; the immediately preceding successful Windows CLI run used the same image version in centralus.
• The only base change between the two PR merge refs was fix(ui): restore usable scrolling for one-line code blocks #3170, limited to Desktop/UI scrolling and selection files; it did not touch Runtime Host control endpoints, ACL handling, or CLI startup.
• The same contemporary main revision passed the dedicated Windows recovery workflow.

This rules out a deterministic #3183 code regression and points to a runner-sensitive Local IPC directory/ACL or startup race.

Expected outcome

• A failed installed-CLI smoke prints or uploads the underlying Runtime Host diagnostic instead of only INTERNAL_STARTUP_FAILURE.
• On Windows failure, capture the relevant storage/control paths, runner identity/region, directory owner and ACL state, and registration/service logs before the isolated root is deleted.
• Determine why prepareStorageRootControlDirectory or the subsequent first-run recovery intermittently fails on windows-2025 hosted runners.
• Stabilize the checks without weakening the Local IPC trust boundary or broadly retrying genuine product failures.

Reproduction status

Intermittent on GitHub-hosted Windows runners; not reproduced deterministically. Two identical PR trees produced disjoint failures in consecutive runs.