Centralize review snapshot comparison and fallback

[timReynolds]

Review snapshot loading previously delegated patchset comparison back to the HTTP server, so callers had to assemble review behavior themselves. loadReviewSnapshot now owns indexed lookup, selected-head comparison, file projection and review-mark retention, and public fallback. The server supplies request parameters and GitHub client setup.

Comparison failures retain the indexed data with an explicit limitation, empty comparisons remain empty, and database failures propagate. Snapshot tests exercise the complete interface with a controlled index adapter and mocked GitHub transport, including rename marks, patch normalization, public fallback, and failure paths; redundant public-loader-only coverage was replaced.

Validation: npm run typecheck, npm run lint, npm test (170 tests), npm run format, and npm run build all pass.

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-13T21:54:23.738247Z	45167e8	PR opened

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[clearance-app-tr]

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Warnings

• examples/OWNERS.toml $.escalation.fallback_team: GitHub team @org/platform-leads was not found
• examples/OWNERS.toml $.rule[0].require[0].from: GitHub team @org/platform-eng was not found
• examples/OWNERS.toml $.rule[0].require_any[0].from: GitHub team @org/security-eng was not found
• examples/OWNERS.toml $.rule[0].require_any[1].from: GitHub team @org/compliance was not found
• examples/OWNERS.toml $.rule[1].require[0].from: GitHub team @org/platform-eng was not found
• examples/OWNERS.toml $.rule[1].require[1].from: GitHub team @org/security-eng was not found
• examples/OWNERS.toml $.notify[0].teams[0]: GitHub team @org/compliance was not found
• examples/OWNERS.toml $.override.teams[0]: GitHub team @org/repo-admins was not found