fix(mux): LOC video groups end with the duration marker

[kixelated]

Problem

Legacy video groups end with an empty frame that closes the last frame's duration, but the LOC producer never wrote it, so LOC groups could not close immediately.

Approach

container::loc::Wire implements Container::finish_group like the Legacy wire: for Kind::Video with a known end, it writes an empty-payload LOC frame at that timestamp. Producer already calls finish_group at cut and finish, and the catalog's Container::Loc already dispatches to it. Audio and data tracks write nothing.

Tests replace loc_cut_writes_no_duration_marker with LOC video (marker at the cut bound and at finish), audio, and data cases. Stale comments and docs (doc/concept/hang.md, doc/lib/rs/moq-mux.md) are updated, and the quest is deleted along with its quest/m1/README.md entry.

Impact

• Public API: none.
• Wire: Rust LOC video groups now end with an empty-payload LOC frame. The hang draft's loc section already gives empty video payloads the Legacy duration meaning, so no draft change (just drafts check passes).

Reader floor

Older LOC readers see the duration marker as an empty video frame. Readers skip it from moq-mux 0.10.0 (the skip landed in #3575) and @moq/loc 0.2.3.

Alternatives

None considered; this mirrors the Legacy contract.

Follow-ups

• The JS @moq/loc producer has no media kind, cut, or finish, so it writes no marker yet: quest/m2/js-loc-duration-marker.md (chore(quest): settle the PR-merge session's follow-ups #4468).

(Written by Claude Sonnet 5.5, edited by Claude Opus 5.5)

🤖 Generated with Claude Code

[kixelated]

Outcome: implemented and left as a draft. cargo test -p moq-mux (871 unit + 12 doc tests), cargo fmt, and cargo clippy -p moq-mux --all-targets are clean. I did not run just check (nix is off limits here).

Open decisions:

• JS @moq/loc producer: it has no media kind, cut, or finish, so it writes no marker. Recommend a follow-up quest once it does.
• Release note: older LOC consumers (before moq-mux 0.10.3 / @moq/loc 0.2.3) would see an empty video frame, so ship after those are the floor for LOC deployments.

(Written by Claude Sonnet 5.5)

[kixelated]

Decision: merge now. Both floors are published: moq-mux 0.10.3 (2026-09-25, now 0.10.8) and @moq/loc 0.2.3 (2026-09-23). Nothing concrete defines a "LOC minimum" to wait on. Before merging, note the reader floor in the PR body: moq-mux 0.10.0 (the skip landed in #3575) and @moq/loc 0.2.3. The JS producer is tracked separately as quest/m2/js-loc-duration-marker.md (#4468).

(written by Claude Opus 5.5)

[chatgpt-codex-connector]

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-29T13:24:21.008499Z	b11aac3	Draft marked ready

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📒 Files selected for processing (7)

• doc/concept/hang.md
• doc/lib/rs/moq-mux.md
• quest/m1/README.md
• quest/m1/loc-duration-marker.md
• rs/moq-mux/src/container/consumer.rs
• rs/moq-mux/src/container/loc/mod.rs
• rs/moq-mux/src/container/producer.rs

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[chatgpt-codex-connector]

💡 Codex Review

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Reviewed commit: b11aac3fe9

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[kixelated]

Recommendation: MERGE

Positive alignment fix: Legacy video groups already end with an empty duration-closing frame; LOC producers never wrote it, so LOC groups could not close immediately. Implementing finish_group for LOC video (only, with a known end) matches Legacy and is safe because consumers that skip empty LOC payloads already shipped. Tests cover video marker at cut/finish plus audio/data no-marker cases; docs updated. Low complexity, clear win—no better approach than the same marker Legacy uses.

This is an automated review, not the maintainer's decision
(Written by Grok)

[kixelated]

Merging per maintainer decision.

• Reader floor verified and added to the body: moq-mux 0.10.0 already dispatches Container::Loc(kind) to loc::Wire::end (identical at 0.10.3), and @moq/loc 0.2.3 (2026-09-23) is the first npm release after feat(hang)!: empty frames close the previous frame's duration #3575. The earlier 0.10.3 mention was corrected.
• Codex P2 (JS producer marker) replied to and resolved; tracked as quest/m2/js-loc-duration-marker.md (chore(quest): settle the PR-merge session's follow-ups #4468).
• No draft change: the hang draft loc section already gives empty video payloads the Legacy duration meaning. just drafts check passes.

(Written by Claude Opus 5.5)