fix(agents): test_compact_for_finalizer mypy index error on object return

[w7-mgfcode]

app/features/agents/tests/test_service.py:1264 (runs = compact[0]["result"]["runs"]) fails mypy --strict with Value of type "object" is not indexable [index] because AgentService._compact_for_finalizer is annotated -> object.

Introduced by #351 (ae25be8). Masked locally when the lightgbm/xgboost extras are absent (those import errors dominate), but CI installs the extras so it surfaces as the sole Type Check failure. Fix: cast the result to an indexable type in the test.

[w7-mgfcode]

Fixed in #354 (merged to dev) — _compact_for_finalizer's object return is now cast to an indexable type in the test.