tests/fixtures/update_marker_corpus.json is read by pytest (update_lock),
cargo (marker_tests.rs), vitest (update-marker-corpus.test.ts) and the
marker.sh / marker.ps1 corpus tests. By path it selected only python, so a
corpus edit never ran the Rust, Electron or Windows PowerShell readers.
_SHARED_FIXTURE_CONSUMERS routes a fixture with its consumers' test lanes;
the routing test derives the consumers from the tree and replays the
classifier through the workflow files to each lane's job (review D14).
(cherry picked from commit 4893ef31833b5fcbdfc527beb70724ea63a3eb8f)
(cherry picked from commit 20c04a27b2a04ebaabb9a9df3693339243d9380e)
2d7307931d