[ BOUNTY] Add diagnostic metadata diff tool (#5)

[xcapselx]

Summary

Add tools/diagnostic_diff.py — a diagnostic metadata diff tool that compares two build diagnostic JSON files and reports differences in module status, pass/fail counts, build metadata, and per-module output.

Changes

• tools/diagnostic_diff.py (new file):

  • diff_diagnostics(baseline, current) — compares commit, total_modules, passed, failed, chunked, and per-module status/elapsed/artifact/output
  • Detects added, removed, and modified modules
  • Summary with total changes, modules added/removed/modified, metadata changed, pass/fail delta
  • render_text() produces Markdown table output
  • --json flag for machine-readable output
  • --summary flag for summary-only output

• tests/test_diagnostic_diff.py (new file):

  • test_diff_detects_changed_fields — verifies commit, passed, failed changes
  • test_diff_detects_module_status_change — verifies module status FAIL->PASS detection
  • test_diff_identical_diagnostics_no_changes — verifies zero changes for identical inputs
  • test_diff_detects_added_module — verifies new module detection
  • test_diff_detects_removed_module — verifies removed module detection
  • test_render_text_produces_markdown — verifies Markdown output format
  • test_render_text_identical — verifies "No differences detected" message
  • test_load_diagnostic_file_not_found — verifies FileNotFoundError on missing file

Testing

python -m unittest tests.test_diagnostic_diff -v

Result:

Ran 8 tests in 0.001s
OK

Build diagnostic: diagnostic/build-94ad8d29.json

Checklist

• Relevant modules affected by these changes build locally
• Tests pass locally
• Diagnostic build log is committed in this PR
• Changes are scoped to the PR purpose
• Security, privacy, and error-handling implications have been considered

Closes #5

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: d20d5420-0226-43d0-8c9b-51e579836157

📥 Commits

Reviewing files that changed from the base of the PR and between 94e0fb0 and b337089.

📒 Files selected for processing (3)

• diagnostic/build-94ad8d29.json
• tests/test_diagnostic_diff.py
• tools/diagnostic_diff.py

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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