Optimize test suite and release validation

[Widthdom]

Summary

• streamline the release validation matrix so the full .NET 8 suite runs once while publish-only lanes use the production SDK and restore path
• retain runtime-specific smoke coverage for the produced Linux, Windows, and macOS artifacts
• move independent database fixtures and parser-only checks out of oversized non-parallel test collections, with explicit console and SQLite isolation where shared state requires it
• scale TRX telemetry to handle the full suite efficiently and deduplicate CI matrix contract assertions
• document the resulting parallelism boundaries in the bilingual testing guide and add internal changelog fragments

Why

The suite was paying for redundant release lanes and serializing independent tests behind broad SQLite pool-sensitive classes. The TRX telemetry reader also retained a smaller file-size ceiling and repeatedly sorted its slow-test list. Together these increased CI/release wall-clock time and limited useful full-suite telemetry.

Impact

The full Release/net8 suite improved from 24m 08s to 21m 07s, a reduction of 3m 01s (about 12.5%), while preserving all 11,355 test outcomes and runtime artifact smoke validation.

During full-suite validation, concurrent MCP request diagnostics exposed a stderr ownership gap. The emitting MCP audit integration tests are now explicitly console-sensitive, and nested batch captures retain their own non-parallel boundary.

Validation

• dotnet build CodeIndex.sln --configuration Debug -p:UseSharedCompilation=false --nologo — 0 warnings, 0 errors
• full Release/net8 suite — 11,348 passed, 7 skipped, 0 failed (11,355 total) in 21m 07s
• focused net9 changed/workflow suite — 258 passed, 2 skipped, 0 failed
• changelog validation — 15 fragments validated
• git diff --check origin/main...HEAD
• repository CodeIndex status check — fresh and matched to HEAD
• separate-agent adversarial review — no blocking/actionable issues found