feat(go): Add Go stdlib remote registry loader with lazy caching (PR-03)

[shivasurya]

Summary

• Add GoStdlibRegistryRemote implementing the core.GoStdlibLoader interface
• Lazy per-package loading: only download packages when first accessed
• SHA256 checksum verification of each package against the manifest
• Thread-safe double-check locking (sync.RWMutex) prevents duplicate downloads under concurrency
• 30s HTTP timeout; versioned CDN URL pattern ({baseURL}/go{version}/stdlib/v1/)
• Helper methods: CacheSize, ClearCache, IsManifestLoaded, GoVersion

Test plan

• TestLoadManifest_* — success, HTTP error, network error, invalid JSON, bad URL, body read error
• TestGetPackage_* — cache hit (fast path), download, not found, HTTP error, network error, invalid JSON, checksum mismatch, checksum skip, body read error
• TestFetchPackageLocked_DoubleCheckCacheHit — deterministic double-check path coverage
• TestValidateStdlibImport_*, TestGetFunction_*, TestGetType_*, TestPackageCount_*
• TestConcurrentGetPackage — race detector clean
• 100% coverage on go_stdlib_remote.go, 0 lint issues, all 20 packages pass

Stacked on

PR-21 (shiva/go-stdlib-support-pr02) — Go stdlib extraction tool

🤖 Generated with Claude Code

[safedep]

SafeDep Report Summary

No dependency changes detected. Nothing to scan.

_{This report is generated by SafeDep Github App}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.22%. Comparing base (e8dac45) to head (4ba4dff).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #549      +/-   ##
==========================================
+ Coverage   83.09%   83.22%   +0.12%     
==========================================
  Files         141      142       +1     
  Lines       17531    17660     +129     
==========================================
+ Hits        14568    14697     +129     
  Misses       2422     2422              
  Partials      541      541              

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[shivasurya]

• feat(go): Replace hardcoded stdlib set with GoImportResolver struct (PR-09) #557
• feat(go): Add stdlib metadata to MCP call graph tool responses (PR-08) #556
• feat(go): Close stdlib type inference gap in GetReturnType (PR-07b) #555
• feat(go): Resolve stdlib return types in variable extraction (PR-07) #554
• feat(go): Wire stdlib loader into builder pipeline (PR-06) #553
• feat(go): Add Go version detection and stdlib loader init (PR-05) #552
• feat(go): Add Go stdlib R2 publishing pipeline (PR-04) #551
• feat(go): Add Go stdlib remote registry loader with lazy caching (PR-03) #549 👈 (View in Graphite)
• feat(go): Add Go stdlib extraction tool for registry generation (PR-02) #548
• feat(go): Add Go stdlib registry data structures and types (PR-01) #546
• main

This stack of pull requests is managed by Graphite. Learn more about stacking.

[shivasurya]

Merge activity

• Feb 25, 3:17 AM UTC: A user started a stack merge that includes this pull request via Graphite.
• Feb 25, 3:21 AM UTC: Graphite rebased this pull request as part of a merge.
• Feb 25, 3:21 AM UTC: @shivasurya merged this pull request with Graphite.

[github-actions]

Code Pathfinder Security Scan

No security issues detected.

Metric	Value
Files Scanned	2
Rules	38

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