test(coverage): enforce branch-aware 90% policy

[Brad-Edwards]

Summary

Replace the superseded coverage design from PR #1139 with a minimal branch-aware policy: Coverage.py owns Python semantics, canonical verification enforces the repository’s fixed 90% aggregate line floor, and branch data remains visible without a manual ratchet or 100% changed-code gate.

Requirement UIDs

• (none — bug/refactor/maintenance run; see Traceability section below)

Related Issues

Closes #1104

ADR Impact

• ADR-103
• ADR-014
• ADR-015

Changes

• Adopt ADR-103 to define coverage scope, the 90% line floor, branch visibility, and the ADR-015 accidental-regression trust boundary.
• Measure repository-owned Python with Coverage.py branch collection and publish canonical XML and JSON reports.
• Enforce line coverage directly from Coverage.py totals without a semantic diff checker or manual ratchet.
• Allow requirement-free quickfix policy and hook paths to skip only requirement governance while retaining all repository checks.
• Supersede the implementation approach proposed in PR test(coverage): require 100% coverage for changed Python code #1139.

Test Plan

• Unit tests pass
• Integration tests pass if applicable
• Configured completion command passes
• No coverage regression

Canonical quickfix verification and repository policy passed. The combined report measured 76,656 of 85,111 executable lines (90.066%) and 20,234 of 26,566 branches (76.165%).

Ground Control Checks

• Configured repository policy command passes
• Pre-push code review and test-quality review completed; all findings fixed or dispositioned

Traceability

• IMPLEMENTS: ADR-103 ← implementations/python/pyproject.toml, ADR-103 ← noxfile.py, ADR-014 ← .github/workflows/ci.yml
• TESTS: ADR-103 ← implementations/python/tests/test_repo_policy_tools.py

Checklist

• Code follows the project's coding standards
• Changelog: owned by Release Please (generated from the Conventional Commit PR title; no per-PR fragment)
• Architectural docs updated if stack, package structure, or key behaviors changed

Documentation

Updated: see diff.