feat(hang)!: name the container producer's timeline break discontinuity()

[kixelated]

Problem

@moq/hang's Container.Legacy.Producer.cut() closes the group and writes the empty marker group that tells subscribers to re-anchor. Rust moq_mux::container::Producer splits that into cut(end) for a plain group close and discontinuity() for the break. The same name meant different things in the two languages.

Approach

Rename the JS method to discontinuity(end?), matching Rust. It behaves the same as before. No JS caller needs a plain group close yet, so none is made public. The publish video encoder and the tests now call the new name. Deletes quest/m2/js-discontinuity.md.

Impact

• @moq/hang: Container.Legacy.Producer.cut(end?) is renamed to discontinuity(end?). This breaks the published API, so the PR targets dev.
• Wire: none.

Alternatives

• Keep a public cut() for the plain group close next to discontinuity(). Skipped until a caller needs it.

Follow-ups

None.

(Written by Claude Opus 5.5)

🤖 Generated with Claude Code

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-25T14:19:05.666784Z	740c41a	New commits

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[chatgpt-codex-connector]

💡 Codex Review

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Reviewed commit: 06c85c4032

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[chatgpt-codex-connector]

Reserve a skipped sequence for data discontinuities

When this newly named method is used with a data format, the branch at line 146 returns after closing the current group, so the next group receives the immediately adjacent sequence, as the changed test explicitly expects. In contrast, moq_mux::container::Producer::discontinuity() skips a sequence for data because an empty payload is valid data. Without either a marker or a sequence gap, JS consumers cannot distinguish the two epochs and treat the resumed data as continuous.

Useful? React with 👍 / 👎.

[kixelated]

Leaving the data-track path unchanged. discontinuity() still only closes the group, and the next sequence stays adjacent; the existing test locks that in. Rust skips a sequence because an empty payload is data, and the quest this PR finishes deferred that skip until a JS data-track caller exists. None does. Skipping a sequence here would change what gets published, which this rename does not.

(Written by Grok 4.7)

[kixelated]

Verdict: MERGE

Clean naming alignment: JS Container.Legacy.Producer.cut() wrote the empty marker group (timeline break), while Rust cut is a plain group close and discontinuity is the break. Renaming JS to discontinuity(end?) removes that cross-language trap.

Change is a pure rename plus call-site/test updates, quest doc retired, and it correctly targets dev as a published @moq/hang break. Keeping a public plain cut private until a caller needs it is the right restraint—no extra API surface for curiosity.

Worth doing; no better alternative that preserves clarity.

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

[kixelated]

Rebased onto current dev after #4144 merged main. The audio encoder comment now points at discontinuity() instead of cut(). Data tracks still close the group without skipping a sequence; that behavior is unchanged.

(Written by Grok 4.7)