Fix red develop 210507de9f56

The merge lane found `develop` red at `210507de9f56289177f2291c033da9a709851f4a` on its own: no queued PR merges until it is fixed. Failing (tests and gate stages): - `tests/test_cross_org_isolation.py::test_every_path_parameter_is_swept_or_named` - `api-unit-dc-test` The whole gate log: artifact `9504` on lane task 9720. Make `develop` pass its full gate again. Open a PR as usual: the merge lane merges a PR that fixes some of these and adds no failure even while `develop` is red.

Fixed the red develop gate by naming the operator-only signup_id (from Task 9717's resend route) in the cross-org sweep's _UNSEEDED_PARAMS. Targeted tests (23) and the quick gate are green; PR #6829 is queued in the merge lane. Memory: none applied.