daily-fix: test_issue1315_dispatch pollutes the fu3 context registry — order-dependent Step 9c gate bounce

Goal

Fix the pre-existing order-dependent test pollution that can stochastically bounce any Step 9c test-verdict gate whose selection contains both files: tests/test_issue1315_dispatch.py:328-332 calls register_fu3_contexts() without restoring the registry, and tests/test_issue1090_fu3_dispatcher.py::test_conv_context_is_wildchat_family then fails its registry-cleanliness assert at entry under randomized ordering.

Context

Found during #2063's implementer round (constants-only diff; all involved files byte-identical to origin/main, so the bug is pre-existing on main). Deterministic reproduction:

uv run pytest -q -p no:randomly tests/test_issue1315_dispatch.py tests/test_issue1090_fu3_dispatcher.py

The polluter registers fu3 contexts into a module-global registry and never removes them; the victim asserts the registry is clean at entry. Under pytest-randomly, any ordering that runs the polluter first fails the victim — a fleet-wide stochastic Step 9c gate bounce for unrelated diffs (the gate selects both files whenever a diff touches the issue1090/1315 family or the pin-sweep pulls them in).

Fix sketch

Add registry restoration to the polluter (a try/finally popping the registered fu3 context keys, or a fixture with teardown — match the registry API in scripts/issue1090_fu3_worker.py / the module that owns register_fu3_contexts). Keep the victim's cleanliness assert (it is the detector, not the bug). Verify with the deterministic repro above run in BOTH orders plus a -p randomly seed sweep.