Investigate full-suite-only failure in global log report-hint test

[Widthdom]

Observed failure

While validating #5259 on macOS arm64 (repository SDK 9.0.301, base origin/main at b52ac0fc372a22eb9667ba409d3d204c153d3188), the full test run failed GlobalToolLogTests.TryStart_WritesInvariantUtcTimestampAndStackTrace on both net8.0 and net9.0. The same test passed on both frameworks when rerun alone with the same compiled assemblies.

The assertion at tests/CodeIndex.Tests/GlobalToolLogTests.cs:827 expected Run \cdidx report`in stderr, but stderr beganError: command failed before it could com...and did not contain that report hint. The test deliberately throws throughbeforeDispatchForTesting`, before query dispatch; #5259 changes batch result serialization and does not change the logging test or its implementation.

Commands

Full run:

dotnet test -p:UseSharedCompilation=false --settings tests/CodeIndex.Tests/CodeIndex.Tests.runsettings --blame-crash --blame-hang --blame-hang-timeout 5m

Passing focused retry:

dotnet test tests/CodeIndex.Tests/CodeIndex.Tests.csproj --no-build --no-restore --filter FullyQualifiedName~GlobalToolLogTests.TryStart_WritesInvariantUtcTimestampAndStackTrace

Investigation scope

Investigate order-dependent process state, configuration/environment provenance, and persistent-log session ownership around ProgramRunner.Run / GlobalToolLog.TryStart. The root cause is not established; do not weaken the expected report hint or classify the production behavior as a confirmed regression without a deterministic reproduction. Preserve culture-independent UTC timestamps and stack-trace coverage.

Acceptance: establish a deterministic reproduction of any interfering state, isolate/restore that state, and keep this test passing both alone and in the full net8.0/net9.0 suites.

Open-issue duplicate checks for the exact test name, GlobalToolLog, and global log report returned no existing issue.

[Widthdom]

Additional reproduction context: a local dogfood index refresh was running concurrently during the failing full-suite invocation. Later default-database query tests also encountered database-read failures during that refresh. The isolated log-test retries passed. Please distinguish concurrent repository-index activity from in-process test-state leakage when investigating; neither cause has been established yet. A final full-suite run without concurrent index mutation is being prepared.

[Widthdom]

Validation update: after the dogfood index refresh finished, a single focused retry covering every method that failed in the earlier full run passed all 47 selected cases on each of net8.0 and net9.0, including this log test. All GitHub CI lanes for #5265 also passed. The local full run itself was not clean; the concurrent-index/test-isolation interaction remains an investigation candidate rather than a confirmed production regression.

[Widthdom]

Work started on branch fix-issue5264. I will investigate deterministic interference around the global log report-hint test, distinguish concurrent repository-index activity from process-state leakage, and validate the fix on net8.0 and net9.0.