Bound persisted JSON string-list metadata parsing

[Widthdom]

Summary

• Bound persisted JSON string-list metadata parsing with raw-size, depth, item-count, and decoded-character caps.
• Keep unknown-extension writer samples within the reader budget so status metadata remains readable even with very long paths.
• Updated status contract docs and added a bilingual changelog fragment.

Validation

• Tests added or updated for changed behavior, or not needed because: JsonStringListCodecTests covers codec bounds and writer/reader integration.
• Relevant validation command(s) run:
  • dotnet build
  • dotnet test tests/CodeIndex.Tests/CodeIndex.Tests.csproj
  • dotnet test tests/CodeIndex.Tests/CodeIndex.Tests.csproj --filter "FullyQualifiedName~JsonStringListCodecTests|FullyQualifiedName~DocumentationStatusContractTests|FullyQualifiedName~McpAuditLogTests.ToolsCall_TruncatesAuditRequestId_Issue3237|FullyQualifiedName~UnknownExtension"
  • dotnet run --project tools/CodeIndex.Changelog -- check
  • dotnet format CodeIndex.sln --verify-no-changes
  • dotnet ./src/CodeIndex/bin/Debug/net8.0/cdidx.dll status --check --json
  • Codex adversarial review: no remaining blocking/actionable issues.

Documentation and changelog

• Documentation updated, or not needed because: README.md, DEVELOPER_GUIDE.md, and AGENT_GUIDE.md clarify the bounded unknown-extension sample contract.
• Changelog fragment added under changelog.d/unreleased/, or not needed because: changelog.d/unreleased/3045.security.md.
• Fragment follows .codex/workflows/changelog-fragment.md for category, issue front matter, and bilingual sections.

Issues

Fixes #3045

Follow-up issues

• McpAuditLog request-id truncation regression test writes no audit event #3304 was opened from an earlier full-test failure during validation; after merging latest origin/main, the targeted case and full test pass, so it is no longer reproducible and has been closed.