js/net: remaining capability gaps vs rs/moq-net (SETUP role, finish_at and final sequence, range controls, typed errors)

[kixelated]

Where js/net is a strict subset of the Rust model. The subscription-options model is tracked in #2155 and the announce Restart state in #2216; this covers the rest.

• SETUP role parameter: Rust encodes param 0x3 (Publisher/Subscriber/Both, derived from which origins the client wired up) and the draft documents it, but js/net/src/lite/setup.ts only implements probe and path. A JS client always presents as Both and a JS server cannot read a peer's role. Established.publish/consume usage can derive it just like Rust's Role::from_origins.
• Track end semantics: Rust distinguishes finish() (clean end at live edge), finish_at(final_sequence) (declare an end ahead of the live edge), and abort(err), and consumers can await finished() -> u64. JS collapses everything into close(abort?): no finishAt, and the SUBSCRIBE_END group number is discarded on the consuming side, so the JS model cannot express or observe lite-05 clean-end semantics. (Interacts with the SUBSCRIBE_END off-by-one bug, SUBSCRIBE_END is off-by-one: Rust sends exclusive, js/net and the draft say inclusive #2309, which should land first.)
• Range/cursor controls: start_at, end_at, get_group (wait for a live sequence), sync cache peek, and latest() have no JS equivalents. Some are relay-only and fine to omit, but startAt/endAt pair with the missing subscription range fields and a JS player implementing catch-up/DVR hits this wall.
• Typed errors: Rust has a #[non_exhaustive] enum with stable wire codes; JS throws bare Error with prose (only CacheFull is a class), so consumers string-match to distinguish NotFound from Unauthorized, and wire reset codes are not surfaced. At minimum add a stable code property before locking the API.
• Delete the dead SubscribeOptions export (js/net/src/track.ts): introduced by js/net: model subscription priority as an options object #2167, superseded by Subscription in moq-net + js/net: pre-merge API hardening for moq-lite-05 #2170, identical field-for-field, referenced nowhere. Two exported names for one concept invites drift.
• Frame field naming: JS uses payload for Datagram but data for both Frame types, and @moq/hang's container Frame is shaped differently from both @moq/net's and Rust's. Pick payload consistently (JS keyframe/duration are genuine WebCodecs needs and fine as additive fields).

Related: #2155, #2216, #2073.

(Written by Claude)

[coderabbitai]

🔗 Related PRs

#628 - draft-07 -> draft-14 compatibility [closed]
#1060 - Add draft-17 wire format to JS @moq/lite [closed]
#1108 - Add draft-17 JS support: connect, wire messages, tests [closed]
#1136 - Distinguish Parameters from Properties per moq-transport-17 [closed]
#1963 - feat(moq-net): hook up the rest of moq-lite-05 wire (TRACK_INFO, SUBSCRIBE_END, frame timestamps) [merged]

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