Fix PostgreSQL extraction and index completeness contracts

[Widthdom]

Summary

• parse PostgreSQL RETURNS TABLE (...) signatures with quote-aware balanced delimiters so defaults and quoted identifiers do not truncate returned columns;
• preserve successfully persisted graph rows when full or scoped indexing has per-file/discovery failures, expose structured partial-run diagnostics and --allow-partial, and recover unresolved failures through a normal full scan without requiring --rebuild;
• publish fixed reference-extraction safety limits and cap-hit completeness across status, language, graph, dependency, impact, and MCP contracts, including distinct guidance when legacy cap state is unavailable.

Validation

• dotnet restore CodeIndex.sln --disable-parallel
• dotnet build CodeIndex.sln -c Release --no-restore --disable-build-servers -m:1 -p:UseSharedCompilation=false (0 warnings, 0 errors)
• focused Release tests for the changed extraction, partial-index, CLI, JSON snapshot, reference, and documentation contracts on .NET 8 and .NET 9
• dotnet test CodeIndex.sln -c Release --no-restore --no-build --disable-build-servers -p:UseSharedCompilation=false (net8: 9,718 passed / 6 skipped; net9: 9,252 passed / 410 skipped; three unrelated parallel-isolation/timing failures all passed when rerun alone)
• make lint
• dotnet run --project tools/CodeIndex.Changelog -- check
• local cdidx index . --json and status --check --json (1,013 files, 0 errors, all readiness signals true, workspace matched)

Review

Two Codex adversarial-review rounds were completed. All actionable findings were addressed: scoped partial-index recovery, unavailable-cap-state guidance, mode-specific --allow-partial help, and state-specific status repair/explanation text.

Documentation and changelog

• Updated the bilingual user/developer/testing/compatibility documentation and AGENT_GUIDE.md for the new contracts.
• Added changelog.d/unreleased/4609.fixed.md, changelog.d/unreleased/4610.fixed.md, and changelog.d/unreleased/4620.fixed.md.
• AGENTS.md and CLAUDE.md were not changed.

Follow-up candidates

None.

Fixes #4609
Fixes #4610
Fixes #4620