feat: graph-based targeted test selection for health checker (#1451)

[colehurwitz]

Summary

• Adds find_dependent_tests() to factory/graph.py — reverse-import BFS over the existing graph.json to compute which test files are transitively affected by changed source files
• Threads an optional test_paths parameter through PythonEvaluator → compute_hygiene_results() → run_eval() so pytest runs only the affected subset
• Adds factory eval --targeted CLI flag that computes changed files, resolves dependencies via the graph, and falls back to full suite when selection cannot be trusted
• Updates the health checker prompt to use --targeted by default

Safety design

• find_dependent_tests() returns None (not empty set) on any ambiguity → callers always fall back to full suite
• Hard-coded full-suite triggers: conftest.py, __init__.py, pyproject.toml, CI files
• Stale graph → full suite; unknown files → full suite; fan-out >80% → full suite
• Sacred Rule 9 / check_qa_execution() is unaffected (checks event presence, not pytest scope)

Files changed

• factory/graph.py — new find_dependent_tests() (122 lines)
• factory/eval/languages/python.py — test_paths param on run_tests_with_coverage() / run_tests()
• factory/eval/hygiene.py — thread test_paths through hygiene pipeline
• factory/eval/runner.py — thread test_paths through run_eval()
• factory/cli/eval_cmds.py — --targeted flag + _compute_targeted_test_paths()
• factory/cli/_parser_groups.py — argparse flag registration
• factory/agents/prompts/health_checker.md — one-line prompt update
• tests/test_targeted_tests.py — 21 tests covering all critical paths

Test plan

• 21 new tests pass (reverse BFS, multi-hop, staleness gates, exclusion triggers, fan-out threshold, test_paths threading)
• Full test suite: 2391 passed (no regressions)
• Lint clean, type check clean (1 pre-existing error in unrelated file)
• Adversarial testing: 35 edge cases verified with evidence
• Code review: 6/7 categories PASS, 1 important (CLI integration test gap, acceptable for v1)

Closes #1451

🤖 Generated with Claude Code

https://claude.ai/code/session_01YYiei7JyDnjMrt2Dg6jkJu

[colehurwitz]

Duplicate of #1454 — closing this one.