[kixelated]

back_to_back_groups_arrive_in_order fails under just rs loom on main with "second group": recv_group() returns Ok(None) instead of the second group.

This is a test bug, not a lost group. Since #5083, create_track(name, None) creates an untimed track. Per track::Consumer::subscribe, an unfloored subscriber on an untimed track starts at the latest group. Loom finds the interleaving where the publisher appends both groups before subscribe resolves. The cursor then starts at group 1, delivers it, and sees the finished track, so the test asked for something the API does not promise.

The fix subscribes from Position::group(0), which is what the test means: both groups, in order. The lock handoff it guards (waking group 1's waiters while group 2 is being written) is still exercised.

API / wire impact

None. Test-only change.

Verification

• Reproduced on main with RUSTFLAGS="--cfg loom" cargo test --locked --release -p moq-net --test loom back_to_back.
• just rs loom passes: kio 15/15, moq-net 13/13.

(Written by Claude Opus 5.5)

🤖 Generated with Claude Code

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Codex Review Summary

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-13T03:59:25.429981Z	9ef883c	PR opened

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• rs/moq-net/tests/loom.rs

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[kixelated]

Automated review by review (OpenAI)

Reviewed 9ef883c. No actionable findings. The explicit group-0 floor matches Cursor::new's untimed-track semantics and preserves the concurrent publisher/reader model and both delivery/order assertions. This is a focused test correction with no production API or wire changes.

Reviewed the full patch, surrounding model, subscription/cursor implementation, and existing reviews. Static GitHub-only review; I did not run tests. Loom coverage remains bounded by the existing preemption limit and instrumented kio primitives.

[kixelated]

Merge summary

• Test-only fix for the rs loom nightly failure in back_to_back_groups_arrive_in_order. Since feat(net)!: an undeclared Rust timescale means untimed #5083 an untimed track's unfloored subscriber starts at the latest group, so the model now subscribes from Position::group(0), which is what it asserts.
• Reproduced the failure locally by reverting the change (panics with "second group"), then confirmed just rs loom passes on the merged head: kio 15/15, moq-net 13/13.
• Merged main (no conflicts, no changes to the PR's file) and ran just check: passes.
• The OpenAI review of 9ef883c had no findings; the only commit since is the main merge.
• No API or wire impact. No open decisions or follow-ups.

(Written by Claude Opus 5.5)