Evidence — the red run

Every test guarding this fix, run with the dispatcher change reverted (git stash push cli/the_loop/webhook/dispatcher.py) and the tests in place. Six fail; each failure is the defect itself, stated as an assertion.

Command

git stash push cli/the_loop/webhook/dispatcher.py
uv run --project cli python -m pytest \
  cli/tests/test_routing.py::test_dispatcher_still_routes_pr_events_that_are_not_close \
  cli/tests/test_routing.py::test_a_same_repo_pr_never_gets_a_session_even_once_it_has_a_record \
  cli/tests/test_routing.py::test_a_cross_repo_pr_without_a_workspace_is_declined_not_collided \
  cli/tests/test_workspace.py::test_a_cross_repo_pr_endpoint_spawns_in_its_own_checkout \
  cli/tests/test_webhook_routing_integration.py::test_pr_comment_reaches_the_linked_issues_work_item \
  cli/tests/test_webhook_routing_integration.py::test_pr_event_still_reaches_its_work_item_after_the_link_is_removed \
  -q -p no:randomly

Result

FAILED cli/tests/test_routing.py::test_dispatcher_still_routes_pr_events_that_are_not_close
FAILED cli/tests/test_routing.py::test_a_same_repo_pr_never_gets_a_session_even_once_it_has_a_record
FAILED cli/tests/test_routing.py::test_a_cross_repo_pr_without_a_workspace_is_declined_not_collided
FAILED cli/tests/test_workspace.py::test_a_cross_repo_pr_endpoint_spawns_in_its_own_checkout
FAILED cli/tests/test_webhook_routing_integration.py::test_pr_comment_reaches_the_linked_issues_work_item
FAILED cli/tests/test_webhook_routing_integration.py::test_pr_event_still_reaches_its_work_item_after_the_link_is_removed
6 failed in 21.55s

What each failure says

R1.1 / R1.3 — the ownership rule. The delivery never arrives, because a session is spawned for the pull request instead:

assert False
 +  where False = wait_until(<test_dispatcher_still_routes_pr_events_that_are_not_close.<locals>.<lambda>>)

R1.2 — a pre-existing endpoint keeps being fed. The event goes to the leftover conversation rather than the work item's:

AssertionError: assert 'github:octo/repo#16' == 'github:octo/repo#15'
  - github:octo/repo#15
  + github:octo/repo#16

R2.2 — a cross-repository pull request with no workspace collides instead of declining. The delivery never arrives, for the same reason: it spawned.

R2.1 — the endpoint's checkout is the work item's. This is the root cause printed verbatim: the spawn's cwd is octo/repo's worktree for work item 15, where the pull request's own would be octo/other's for pull request 16.

AssertionError: assert
  PosixPath('…/root/.worktrees/github.com/octo/repo/github-octo-repo-15')
       == PosixPath('…/root/.worktrees/github.com/octo/other/github-octo-other-16')

R1.1 / R1.4 at the webhook seam. Both integration scenarios fail on the same missing delivery — end to end from an HTTP delivery, the event still lands in a second session.