Fix red develop 833e0cfdc939

The merge lane found `develop` red at `833e0cfdc939e2f11bda73ff63a36e9effaf6907` on its own: no queued PR merges until it is fixed. Failing (tests and gate stages): - `tests/test_git_access.py::test_no_cookie_authenticated_get_mutates_state` - `api-unit-dc-test` The whole gate log: artifact `13177` on lane task 11892. 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 red develop: SameSite=Lax GET inventory now holds the /api/tasks/{id}/page composer to its parts' own GET scans (strips only its _isolation flush, guarded). test_git_access 63 passed, quick gate green; PR #7507 queued on the lane. Memory: none applied.