The CI-watch and dep-update loaders collapsed a monorepo's cell-projects
to one canonical entry per repo (slug-sorted-first), so a repo whose cells
each carry their OWN ci_watch_workflow / dep_update_command had only the
canonical cell's workflow/command sampled — a red on another cell's
workflow or drift on another cell's lockfile was missed (under-count).
Refactor the shared one-per-repo collapse into _projects_one_per_key, keyed
by repo identity for external-PR discovery (unchanged: one review per PR per
repo), by (repo, effective workflow) for CI-watch, and by (repo, command)
for dep-update. Each distinct workflow/command is now sampled once; the
engines' per-git_url fix-task dedup still prevents duplicate fix tasks for
the same repo. _projects_one_per_repo now delegates to _projects_one_per_key.
key_fn uses a string annotation (Callable lives under TYPE_CHECKING, like
the existing Coroutine/Iterable annotations at lines 4193/5279).
Renn F
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