the contribution funnel is `PRIORITIES.md`

Renamed from the file that held it, and reframed with it. The document says what the program wants done next, in the maintainer's order — not an inventory of everything unsolved. An item's absence means nobody has asked for it. Difficulty tags are unchanged, and the frozen consolidation's own list keeps its name, since frozen trees are not renamed.

Three code paths read the file — checkers/registry.py, checkers/run.py, tests/path_gate.py. The registry's lookup had the failure mode the rename was most likely to trigger: a missing file produced an empty item set and every answers_item check then skipped itself while the gate stayed green. It is now a hard failure, and both cases are permanent self-test cases.