refactor: wave 3b — split api/routes.py (704 LOC) into a package

[ty13r]

Summary

Wave 3b — splits api/routes.py (704 LOC) into a package. Follows the same pattern as Wave 3a (queries split): decompose by concern, preserve every public URL, re-target test patches.

Submodule	LOC	Owns
__init__.py	22	Barrel: single APIRouter(prefix="/api") that includes the sub-routers
_helpers.py	126	classify_run_via_taxonomist — shared between evolve handlers, not a route itself
evolve.py	214	POST /api/evolve + POST /api/evolve/from-parent — endpoints that start runs
runs.py	402	POST /api/runs/{id}/cancel + every GET for reading run state

Largest submodule is 402 LOC — under the 500-LOC ceiling in docs/clean-code.md §2.

Also cleaned up

• classify_run_via_taxonomist was the last broad except Exception still using logger.warning(..., exc) with redundant exc formatting. Fixed to logger.exception(...) with a clear noqa rationale.
• _classify_run_via_taxonomist (module-private) renamed to classify_run_via_taxonomist since it's now cross-module.

Test patches

Tests that used patch("skillforge.api.routes.get_run", ...) etc. were patching the import side of the old monolith. Updated to target the new symbol location — ...routes.evolve.get_run for POST-endpoint tests, ...routes.runs.get_run for GET-endpoint tests. No test logic changed, just the patch target strings.

Test plan

• uv run ruff check skillforge — clean
• uv run mypy skillforge — 64 files pass
• uv run pytest tests/ — 403 passed, 2 skipped, 0 failed
• Frontend untouched, still green

What's next

Remaining hotspots (agents/spawner.py 805, agents/breeder.py 619, engine/variant_evolution.py 622, agents/managed_agents.py 605) are agent / engine logic — trickier than routes+queries. Those are being deferred so we can move to Wave 4 (frontend API layer with TanStack Query) which is a cleaner Pareto win than splitting well-tested agent code.

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