### Live delivery hardening: receipt chains, the receipts' binary form, room track names, proof of possession

- **A join's fill from the chain's first group.** [jwp-receipts](extensions/jwp-receipts.md)
  §3 step 3: below a join's anchor a group with a `null` parent is the chain's true start,
  `parent_not_held` and held as history until the group above it links back to it, not a
  second chain head (`chain_break`). A `null` parent outside such a gap, and a fork, are
  still `chain_break`. `wai-rs`, `jwp_verify.py` and two corpus vectors
  (`chain_join_fetch_from_group_0`, `chain_join_second_start_after_the_fill`, §5.9).
- **The receipts' binary form.** jwp-receipts §2.7 (new): group and object receipts, and a
  group's receipts together (`WJR1`), as bytes. A group is its canonical bytes (§3 step
  3), its link hash computed over them as received; an object its members in fixed widths.
  Reading yields the JSON form's members, and §3 applies to them unchanged; §2.7.4 says
  what does not read. [moq-streaming-format](extensions/moq-streaming-format.md) §4.1: a
  receipts-track object carries this form, not JSON. 20 vectors (procedure `binary`,
  §5.12), read and written byte for byte by `wai-rs` (`jwp_delivery::binary`),
  `jwp_verify.py` and `joule-moq`.
- **Room track names.** [live-rooms](extensions/live-rooms.md) §6.1 names a media track's
  receipts track (its name followed by `_receipts`) and a publisher's catalog track (the
  room and owner fields, Track Name `catalog`); §6.2 ties the catalog's
  `wai_receipts_track` to it; §10.2's `moqt` scopes admit both. The rooms corpus's scopes
  change accordingly.
- **Proof of possession.** live-rooms §10.5 (new): a grant is public, so every binding
  honours it only beside a `WRP1` proof by its principal over a fresh challenge the
  verifier chose and a context naming the endpoint (a verb and `//authority/path`). Over
  MOQT the relay's SETUP carries the challenge (`GRANT_CHALLENGE`) and the client's the
  grant and the proof (`GRANT_PROOF`); a SETUP whose grant has no proof that passes is
  closed `UNAUTHORIZED`. Over HTTP (WHIP and WHEP's Bearer token) the proof rides
  `WAI-Room-Proof`, and single-use challenges `WAI-Room-Challenge`. §10.5.4's checks
  add eight reasons to §11 (`pop_missing` to `pop_wrong_context`); the CAT mapping and
  §13 follow. The rooms corpus gains 17 proofs, MOQT and HTTP; `live_rooms_verify.py`
  checks them from the text.
- **Registry.** Wire identifiers `WJR1`, `WRP1`, the Setup Options `GRANT_CHALLENGE` and
  `GRANT_PROOF`, and the HTTP fields `WAI-Room-Proof` and `WAI-Room-Challenge` (two new
  kinds, `setup-option` and `http-header`), the last four proposed and not registered.

