test(windows): diagnose intermittent concurrent lane capture failure

[nstranquist]

Observed on 2026-08-17:

• PR build(deps): bump actions/checkout from 6.0.2 to 7.0.1 #2 Windows job https://github.com/nstranquist/wip-commit/actions/runs/31997441235/job/95291516565 failed in TestConcurrentSharedLanesCaptureDisjointPaths.
• The test output hid the typed error behind a pointer value.
• The push-run Windows job passed on the same commit.
• Attempt 2 job https://github.com/nstranquist/wip-commit/actions/runs/31997441235/job/95292060903 also passed on the same commit.

Acceptance:

• Print the complete typed error code, message, recovery data, and result data on failure.
• Stress the exact concurrent test on hosted Windows.
• Identify and fix the timing, lock, Git, or test-harness cause.
• Keep every current HEAD, index, foreign-stage, lease, and ref assertion.
• Do not classify the dependency update as safe from one passing rerun.

[nstranquist]

Root cause and fix are now identified.

The diagnostic stress run reproduced the failure on hosted Windows in attempt 3. The complete error showed a Windows sharing violation while an operational read opened a lease JSON file during another lane heartbeat's atomic replacement.

Commit 11e1915 fences operational lane and lease reads, archive candidate reads, and RecordCommit with the state registry lock. Private locked helpers prevent reentrant locking. The code documents the lane-lock-before-registry-lock order.

A deterministic regression test now proves that Load, LoadLease, Current, Status, ActivePaths, ArchiveCandidates, and RecordCommit wait for the registry fence.

Local evidence on the fixed source:

• exact concurrent capture test: 100 repetitions passed
• complete race suite: 3 repetitions passed
• complete unit, vet, actionlint, golangci-lint, gitleaks, and strict Git object checks passed

Hosted evidence:

• fixed-source push run: all jobs passed, including the Windows stress job
• fixed-source pull-request run, attempt 2: all jobs passed, including the Windows stress job
• latest documented head Windows stress: attempt 1, attempt 2, and attempt 3 all passed
• latest documented head push run, attempt 2: all source-bearing jobs passed, including the Windows stress job

PR #7 contains the fix and its operating documentation. This issue remains open until the fix lands on main.