Bind MCP indexing to authorized filesystem identities

[Widthdom]

Summary

• Bind MCP index authorization to retained no-follow root and opened entry identities.
• Enumerate directories relative to retained handles on Linux, macOS, and Windows, and reject link or identity swaps at the actual open boundary.
• Confine language-map and pattern configuration to an authorization-scoped project snapshot, normalize Windows long paths, and preserve the checked root identity in results and audit failures.
• Preserve the latest main language-detection contracts while routing ambiguous .m / .pl prefix reads and project-marker enumeration through the same authorized identity boundary.
• Stabilize the Windows CI transaction and isolated-hook timing contracts with restored test-only budgets tracked by Stabilize Windows CI timing contracts for shared-writer and hook-worker tests #4687.

Root cause

MCP authorized a canonical pathname before traversal, but later filesystem operations and configuration discovery reopened pathnames without binding every read and directory enumeration to the checked filesystem identity and authorization scope.

The latest main language detection added early content and project-marker probes for ambiguous extensions; the conflict resolution preserves those probes while ensuring MCP indexing supplies its identity-bound read and enumeration delegates.

The Windows test lane also used the production 5-second transaction contention timeout in a non-fair semaphore stress test and a 250 ms isolated-worker startup/callback budget, so hosted-runner scheduling variance could be misclassified as a transaction leak or healthy-hook timeout.

Impact

This prevents symlink, reparse-point, directory, file, and sidecar swaps from redirecting network-triggered MCP indexing outside the approved CWD/client roots or importing configuration cached under a wider scope.

The CI-only timing changes do not alter production defaults. They preserve dedicated timeout coverage while avoiding false failures on loaded Windows runners.

Validation

• dotnet format CodeIndex.sln --no-restore
• dotnet restore CodeIndex.sln --locked-mode
• dotnet build CodeIndex.sln -c Release --no-restore -p:UseSharedCompilation=false — 0 warnings, 0 errors
• Issue Bind MCP indexing authorization to the directory identity used for traversal #4606 and DB-lock coverage — net8.0: 14/14; net9.0: 14/14
• Merge-resolution authorization tests — net8.0: 4/4; net9.0: 4/4
• FileIndexer and issue Bind MCP indexing authorization to the directory identity used for traversal #4606 affected coverage after merging latest main — net8.0: 585/585; net9.0: 585/585
• FileIndexer, FileContentLoader, and ExtractorPluginRegistry affected coverage before the latest main merge — net8.0: 598/598; net9.0: 598/598
• Final ExtractorPluginRegistry coverage — net8.0: 52/52; net9.0: 52/52
• AuditLogSink coverage — net8.0: 64/64; net9.0: 64/64
• Issue Stabilize Windows CI timing contracts for shared-writer and hook-worker tests #4687 focused tests — net8.0: 2/2 across three consecutive runs; net9.0: 1/1 with the production-only hook test skipped
• ConcurrencyTests and PostExtractionHookTests — net8.0: 34/34; net9.0: 20 passed, 14 production-only skips
• dotnet run --project tools/CodeIndex.Changelog --no-restore -- check — 79 fragments validated
• cdidx status --check --json — workspace matches index
• Two Codex adversarial-review rounds completed for Bind MCP indexing authorization to the directory identity used for traversal #4606; all findings were addressed and self-validated within the two-round workflow limit
• Codex adversarial review of the Stabilize Windows CI timing contracts for shared-writer and hook-worker tests #4687 CI stabilization — no blocking/actionable issues found
• Codex adversarial review after resolving the latest origin/main conflicts — no blocking/actionable issues found

Documentation and changelog

• Updated README.md, DEVELOPER_GUIDE.md, and TESTING_GUIDE.md in English and Japanese for Bind MCP indexing authorization to the directory identity used for traversal #4606.
• Documented the ambiguous-language authorization regression test in both language sections of TESTING_GUIDE.md.
• Documented the restored Windows CI timing contracts in both language sections of TESTING_GUIDE.md for Stabilize Windows CI timing contracts for shared-writer and hook-worker tests #4687.
• Added/updated changelog.d/unreleased/4606.security.md; no additional changelog fragment was needed for the test-only Stabilize Windows CI timing contracts for shared-writer and hook-worker tests #4687 stabilization or the merge-only conflict resolution.

Follow-up candidates

None.

Fixes #4606
Fixes #4687