bug(llc/tests): full-suite module pollution replaces sys.modules['llc.api'] — kills all llc.api.* route tests and masks regressions #9995

Discovered during

#9843 review — the reviewer found that in full-suite order, sys.modules['llc.api'] ends up replaced by a non-package module, so every llc.api.* route test errors at setup with ModuleNotFoundError: No module named 'llc.api.backlog'; 'llc.api' is not a package.

Impact

• ~30 setup ERRORs and several permanent failures in llc/tests full-suite runs (e.g. all of TestBacklogRoute, test_bulk_assign_sprint_calls_service)
• Masks real regressions: a genuinely-broken router test shows the same ERROR as the pollution, so diffs of full-suite results look 'identical' even when isolated runs regress (this exact masking hid a stale mock target during refactor(llc/api): consolidate duplicated per-router _service()/get_session() DI boilerplate #9843)

Likely cause

An earlier test's importlib.util.spec_from_file_location + direct sys.modules insertion — pattern at llc/tests/test_routine.py:268-281 — clobbers the package entry.

Fix direction

Restore sys.modules in a fixture/finally around the isolated-load pattern (save+restore the affected keys), or load under a synthetic module name that doesn't collide with the real package path.

Related: #9843 (PR #9994), umbrella #9923.