[kixelated]

Problem

A finite track read through a relay could lose its tail. A publisher declares end 4 and writes groups 0 through 3, but a reader through the relay received only some groups, then stalled or saw cancelled resets. The interop matrix stopped at its first frame and could not catch it.

Two causes, both reproduced deterministically:

1. The relay's moq-lite SubscribeServe dropped its track::Subscriber the moment the live edge reached the declared end, while still draining the group streams it had opened. The relay then cancelled its upstream subscription as idle and the publisher reset every group still on the wire.
2. The hosted Bun -> Rust lane got only group 3: the relay learned the end, then received group 3's stream before groups 0 through 2 (QUIC does not order streams). Its readers end at the boundary even with lower groups missing, so the relay finished the downstream subscription after group 3 alone.

Approach

• rs/moq-net/src/lite/publisher.rs: the Drain state holds the track subscriber until its group streams finish, so a subscription's demand lasts until its FIN.
• Private upstream-tail accounting (rs/moq-net/src/model/track.rs): a wire subscription marks its copy's tail pending from the declared end (lite SUBSCRIBE_END, IETF END_OF_TRACK) until the tail settles. While pending, a reader at the boundary waits only if a group between where the feed starts and the end has not arrived; the last producer going ends it regardless. A local track keeps ending at the boundary with missing lower groups (readers_end_at_the_boundary_with_missing_lower_groups is unchanged).
• An abort ends the wait for a pending tail. The hole count judges by the cache, so an evicted group or a datagram reads as a hole; an abort during the tail window now ends a reader that has everything cleanly, as before the hold, instead of with the abort. Only live-feed groups count: fetched backfill never reaches an arrival-order reader, so it neither fills a hole nor sets the floor.
• rs/moq-net/tests/finite_relay.rs: deterministic mock-time regressions over a relay, across lite 03/05/06/07 and IETF 14/17/22: held tails (cause 1) and newest-header-first delivery after the end (cause 2, new MockSession::release_newest_uni). Model unit tests cover the pending tail and the abort.
• Finite raw-track interop clients (Rust, Node, Bun) and five lanes: Rust-to-Rust, Rust-to-Node/Bun, Node/Bun-to-Rust. Readers verify every byte of four 256 KiB groups and a clean end at 4. just test interop --tail runs only these; --all runs them in the existing Interop CI step.
• Deletes the completed track-tail-interop quest and its references.

Impact

• No public API or wire change.
• Behavior: a moq-lite subscription's demand lasts until its in-flight groups drain. A Rust reader of a session-fed track waits at the declared end for a missing group until the upstream tail settles, or until the track aborts.
• Behavior on moq-lite 05/06: a lost datagram just below the end is indistinguishable from a reordered group, so its hole holds readers for the tail grace (it already held the subscription's routability). Deliberately skipped sequences no longer do: fix(net): name the groups a lite-05/06 subscription never got #5165 names them with SUBSCRIBE_DROP. moq-lite 07's stream count keeps that end prompt. a_lost_datagram_never_delays_the_end became a_lost_datagram_delays_the_end_only_without_a_stream_count.
• Behavior: an abort over a group that never arrived ends the reader cleanly, short of the end, as on main today. Telling it from an evicted group needs arrival accounting (open decision below).
• Test-only: --tail harness option (skipped by the wire-compat lanes, which run released binaries), interop-tail example in moq-cli, native-JS client type check.

Decisions

• Fix at the source (publisher drain keeps demand) (maintainer).
• Keep the five lanes strict, no XFAIL (maintainer).
• No separate CI step: the lanes run inside just test interop --all (maintainer).
• Publisher deadline is 2x the subscriber's (CodeRabbit finding).
• Reordered headers: ✅ private upstream-tail accounting, public reader semantics kept for local tracks (maintainer, 2026-10-07).
• Sub-agent picks (recommended options, flagged for review):
  • The hold applies to every reader of a session-fed copy, not only the relay's forwarding: the end reader's own copy can see the same reorder on the relay -> reader hop, so a forwarding-only hold would still fail the lane.
  • Holes only: with nothing missing below the end, readers end at once, so IETF PUBLISH flows (stream count 0) and complete tracks keep their prompt end.
  • Lite 05/06 lost datagram: lossless over prompt (above). The alternative keeps the old prompt end and leaves reordered groups lost on the default JS version (lite-06).
  • JS readers still end at the boundary with holes; mirroring is quest/m1/js-pending-tail.md.
  • Cache-judged holes (2026-10-10): ✅ an abort ends the wait, so a delivered track never turns into a failure; a happy-path hole from eviction or a datagram only delays the end until the session settles. A separate received-sequence record would remove that delay at the cost of new per-track state; not worth it for a bounded delay.

Open decision

Hole accounting: cache-judged (this PR) vs. an incremental per-track record of live arrivals. The record would make the owed count O(1) instead of a scan of the cached range on each end check once the live edge reached the end (Codex P2), and would let an abort over a never-arrived group surface the error instead of a clean truncated end (Grok). Cost: new per-track state that eviction must not touch, plus the fan-out benchmark AGENTS.md asks for. Recommendation: land as is, and plan the record as a follow-up quest.

Alternatives

Shrinking payloads, sleeps, or a zero start floor hide the race. Holding the relay's upstream subscription open while any group consumer exists blurs track demand with group reads. Holding readers only until the upstream FIN leaves the acknowledged-but-unread window open. Holding until the tail fully settles even without a hole delays every IETF published track by the grace.

Validation

• relay_waits_for_reordered_upstream_headers fails without the fix (lite-05 reads [3]; with the lite gate restored but the IETF one removed, moq-transport-14 reads [3]) and passes with it; relay_keeps_groups_in_flight_past_the_end still passes. an_abort_ends_a_pending_tail_cleanly fails without the abort change, and a_fetched_group_does_not_fill_a_pending_tail without the live-feed filter.
• The JS -> Rust tail lanes that failed after the 2026-10-10 main merge: the JS publisher sends START and END before any group header, so the relay held every 256 KiB group withheld for its first frame (fix(net): a relay's rejoin never shows an older cached group as the live edge #4914) while the end counted them as arrived. Main's fix(net): a group withheld for its first frame holds the end #5167 fixed that at the source; with it, all five tail lanes pass locally.
• moq-cli publish::tests::ts_passthrough_crosses_a_relay_through_a_flagged_jump passes with fix(net): name the groups a lite-05/06 subscription never got #5165 (3 of 3 runs, about 4 s), on lite-06 and moq-transport-14. The IETF path has no equivalent gap: its PUBLISH_DONE stream count settles the tail as soon as every opened stream arrived, and a skipped sequence opens none.
• just check passes. Hosted Interop on 91e9af89 passed the full matrix (all tail lanes and browser cells); only the TS compliance step failed (duration-fidelity), which also fails on main's scheduled run and is tracked in quest/m1/test-flakes-2/ts-duration-fidelity.md. Locally, just test interop --all: every cell, the refused-session case, and all five tail lanes pass locally; the C++ cells were unavailable on this host (no uniffi-bindgen-cpp).

Follow-ups

• Mirror the pending-tail reader hold in @moq/net (quest/m1/js-pending-tail.md).
• The lite-07 SUBSCRIBE_DROP case can extend this harness, tracked in quest/m1/subscribe-drop.md.

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-10T16:29:06.685029Z	5726689	New commits
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Walkthrough

Track completion now accounts for lower-numbered groups that may arrive after a declared end. Protocol handlers set and clear pending-tail state, and relay tests cover delayed and reordered group delivery. New Rust and native JavaScript clients exercise finite tracks through the interop harness, which checks delivered groups and clean-end acknowledgement. The harness also adds a tail-only mode and documentation for its runtime selection.

Priority: ➖ Normal

Merge Risk: ⚪ Minimal · up to 3ab01

Tail-only checks can run without ffmpeg, and no actionable merge-blocking risk introduced by this change remains.

Pre-merge checks | 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check		The title clearly summarizes a primary change: retaining a lite subscription's demand while its groups drain.
Description check		The description is directly related to the changeset and explains the tail-loss fixes, tests, interop coverage, and validation results.
Docstring Coverage		Docstring coverage is 80.56% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 36 functions across 10 files.
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

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Inline comments:
In `@test/interop/interop.sh`:
- Around line 743-752: Update the finite track tails block to treat the known
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[kixelated]

Automated review by review (OpenAI)

Reviewed commit: f0e73a3

No additional harness-correctness finding from the full nine-file review. The raw clients check exact payloads, every group, and end 4; keeping publishers alive until the reader's acknowledgement is a focused way to distinguish transport loss from premature publisher shutdown. The five lanes and existing harness reuse are proportionate. No production API/wire change.

The existing merge blocker is confirmed, not new: test/interop/interop.sh:743-752 adds known-failing tail lanes to normal --all. In the exact-head Interop run, four tail lanes passed but Bun-to-Rust received only [1, 3]; the resulting failure also skipped the later negative-control/media/TS/EIT steps. This supports the existing finding.

Recommendation: keep the strict regression and land it with the source-declared-start fix before enabling it in the normal gate. Blanket XFAIL would also hide unrelated missing-group failures and is weaker than fixing the tracked relay behavior. The retained quest correctly separates that fix from CLI drain design.

Verification: inspected the full diff, harness lifecycle, CI wiring and failure log. Exact-head Check passed; Interop failed as above. I did not run the matrix or reproduce the zero-floor diagnostic locally. The PR currently also reports merge conflicts.

(Written by review (OpenAI))

[kixelated]

Findings

1. High — Default Interop CI is red by design. Current checks: Interop fail. Log shows FAIL tail js-native-bun -> rust with wrong groups: [1, 3] (Rust←Bun), while Rust↔Rust and Rust→JS pass. The PR body intends that as the regression, and interop.sh runs the finite-tail lanes whenever --negative/--media are off — including the normal CI just test interop --all path. Landing this on main keeps the required Interop job failing until the relay start/floor fix lands.

   Fix: Keep --tail for local/quest reproduction, but do not fail the default matrix yet — e.g. only run the known-red lanes under an explicit flag / expected-fail annotation, or gate them behind the track-tail quest until the production fix merges. A diagnostic red lane is valuable; a permanently red required check is not.

2. Low — PR description vs CI. Body says Node/Bun→Rust both fail; this head’s CI run had js-native-node -> rust PASS and only Bun→Rust fail. Update the quest/PR text so the retained bug claim matches what CI actually reproduces (reorder-sensitive; may be intermittent).

Assessment

Harness shape is good: finite 256 KiB groups, declared end 4, stdin ack so the publisher does not tear down early, and no sleep standing in for drain. As a non-draft PR into main it still needs a green (or explicitly waived) Interop path.

Recommendation: ITERATE
Reviewed head: f0e73a3d29841b727dedaefe31f4fdacf1375b1d

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

[kixelated]

Re-review after push

Compared f0e73a3d29841b727dedaefe31f4fdacf1375b1d → 298e8826f19cb49a4ac49cc8932338edd39dbed8 (excluding the origin/main merge). Push-only delta: JS track.used → track.demand().used, Rust broadcast.finish() → broadcast.close() so the harness compiles against the post-merge APIs. That rename adapt looks correct and does not change harness intent.

Findings

1. High — still open — Default Interop CI is red by design. interop.sh still runs the finite-tail block whenever --negative/--media are off (including just test interop --all). Known-red Node/Bun→Rust lanes will keep the required Interop job failing until the relay start/floor fix lands.

   Fix: Keep --tail for local/quest reproduction; do not fail the default matrix yet (explicit flag / expected-fail / gate behind the track-tail quest).

2. Low — still open — PR text drift. Body still says the PR “remains a draft” and that Node/Bun→Rust both fail; the PR is ready (isDraft=false), and earlier CI only consistently failed Bun→Rust. Align description with current status and what CI actually reproduces.

Assessment

No new issues from the rename push itself. Open findings above still block a clean merge to main.

Recommendation: ITERATE
Reviewed head: 298e8826f19cb49a4ac49cc8932338edd39dbed8

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

[kixelated]

Automated review by review (OpenAI)

Reviewed commit: 298e882

No new actionable bugs found in the update. test/interop/clients/js-native/tail.ts:26-27 now waits through the current track.demand() API; test/interop/clients/rust/tail.rs:52 uses the current broadcast close() API after the reader acknowledgement. Both adaptations match the current implementations and preserve the strict four-group/clean-end assertions.

The earlier review recorded failing JS-to-Rust tail lanes in the normal gate. That gating and the assertions are unchanged; these API repairs do not themselves establish that the underlying loss is fixed. The current-head Interop run is queued at review time, so the old failure is not evidence of a failure on this head. Use the new run to establish whether the earlier finding is cleared; retain the strict regression rather than hiding arbitrary loss with blanket XFAIL.

Direction remains worthwhile: exact payload/end checks plus a reader acknowledgement isolate finite-tail behavior without inventing a CLI drain API. Verification was static review of the delta and current API definitions; no tests or matrix run locally. Rechecked open/non-draft state, head, and review history before submission.

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⚠️ Outside diff range comments (1)

🟡 Minor · Do not require ffmpeg for --tail. · interop.sh:178-179

test/interop/interop.sh:178-179
🎯 Functional Correctness | 🟡 Minor | ⚡ Quick win

Do not require ffmpeg for --tail.

When ffmpeg is absent, require_tools exits before a tail-only run starts. Tail-only mode uses raw-track clients and skips the media matrix. Require ffmpeg only for modes that run media publishers.

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only still-valid issues, skip the rest with a brief reason, keep changes
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Review comment at @test/interop/interop.sh around lines 178 - 179:
Update the tool checks in require_tools so tail-only mode does not require
ffmpeg, while modes that run media publishers continue to require it; preserve
the existing requirements for the other tools.

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Inline comments:
Review comments at @test/interop/interop.sh:
- Around line 653-655: Update the timeout handling in run_tail_pair so the tail
publisher receives a longer deadline than the subscriber, allowing for startup,
the subscriber’s full deadline, and acknowledgment. Apply the longer timeout to
the publisher commands for rust, js-native-node, and js-native-bun while
preserving the subscriber’s existing deadline.

---

Outside diff comments:
Review comments at @test/interop/interop.sh:
- Around line 178-179: Update the tool checks in require_tools so tail-only mode
does not require ffmpeg, while modes that run media publishers continue to
require it; preserve the existing requirements for the other tools.

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[kixelated]

Re-review after push

Compared 298e8826f19cb49a4ac49cc8932338edd39dbed8 → a231756bb2f15e74d8cd478e4af06cca962c637e, leaving out the origin/main merge 1fd7ef3e24. This push is the actual fix. SubscribeServe::Drain now holds the track::Subscriber until the in-flight GroupServe children finish (rs/moq-net/src/lite/publisher.rs:1226-1232, :1357-1372), so the relay's downstream demand lasts until FIN and the relay stops idle-cancelling upstream mid-drain. The push also adds a deterministic mock-transport regression test (rs/moq-net/tests/finite_relay.rs), gives the tail publisher 2× the subscriber's timeout, drops the ffmpeg requirement for --tail, and deletes the track-tail-interop quest.

The fix looks right to me. The state handoff only builds Drain { _track: Some(..) } from Run, and the Confirm placeholder _track: None gets overwritten before it can be polled. An error from poll_step returns through ? before the transition, so it can't leave a half-built state. Holding the subscriber also keeps the egress _stats_sub viewer count up through the drain, which is the right accounting.

Earlier findings

1. Default Interop red by design: fixed in code, not yet shown in CI. With the fix, the lanes are meant to pass strictly instead of reproducing a known bug. But Interop has not run on this head: the only checks are Quest (queued) and Auto-merge (skipped), because the PR is CONFLICTING. The last Interop run on this branch (298e8826, 2026-10-03) failed.
2. PR text drift: fixed. The body was rewritten to match the fix and the current status.

Findings

1. Blocking: merge conflict with main, so CI can't run. The branch is 6 commits behind. test(interop): a browser reads a refused session's close code #4819 (browser close code) added a close-code block to the end of the default matrix in test/interop/interop.sh and edited test/interop/README.md, test/justfile, and quest/m1/README.md, all of which this PR also touches. When you resolve it, put the close-code block inside the elif [[ "$TAIL_ONLY" -eq 0 ]] branch (around interop.sh:751) so --tail still runs only the five tail lanes and doesn't need Chromium. Then confirm the five finite track tails lanes pass in Interop.
2. Low: the "Interop on main is red independently" follow-up doesn't match the nightly. The PR body blames max_age_relay_javascript and the Python/Go publisher rows since nightly 11b28de07. But the scheduled Interop run on main at 11b28de0 (2026-10-05) concluded success, as did the four nightlies before it. If this PR's Interop goes red after the rebase, don't wave it off as a pre-existing failure without a failing main run to point to.
3. Low: test structure. relay_keeps_groups_in_flight_past_the_end loops over all seven versions in one #[tokio::test]. The first failing version hides the rest, and each round leaves its three origin drivers spawned for the rest of the test. A per-version test, or collecting failures and asserting once, would report the full matrix. Also, a group that ends cleanly with fewer than 2 frames is silently left out of seen instead of being reported. The final assert_eq! still catches it, but the message won't say which group was short.
4. Nit: no direct assertion on the root cause. The test catches the bug through a hang or a reset. A check that the relay's upstream subscription stays active, or that track.demand() stays used until the tails are written, would point at the regression directly if it comes back as something other than a hang.

Recommendation: MERGE after the rebase, once the five tail lanes pass in Interop.
Reviewed head: a231756bb2f15e74d8cd478e4af06cca962c637e

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

[kixelated]

Iterated on this PR after merging main (post #4741).

• The tail lanes still failed on merged main: Rust-publisher lanes stalled and Node-to-Rust lost groups. The relay log showed subscribe canceled (idle) 17 ms after the upstream subscribe.
• Root cause: the moq-lite SubscribeServe dropped its track::Subscriber when the live edge reached the declared end, while it was still draining the open group streams. The relay then saw no demand, cancelled upstream, and the publisher reset the groups still in flight. The Drain state now holds the subscriber until its groups finish. IETF already did this.
• Regression: rs/moq-net/tests/finite_relay.rs over the mock transport and a relay. It hangs without the fix and passes on every lite and IETF version with it. All five just test interop --tail lanes pass locally, run twice.
• CodeRabbit: --tail no longer requires ffmpeg. The tail publisher gets twice the subscriber's deadline. XFAIL is declined because the lanes pass now.
• Deleted the completed track-tail-interop quest.

CI: Interop is red from main, not from this PR. max_age_relay_javascript fails in the "Optional publisher retention" step, which skips the full matrix and its tail lanes. The Python/Go publisher rows have also been failing since nightly 11b28de. Another PR owns both. Check and Test are still queued. Local just check passes.

(Written by Claude Opus 5.5)

[kixelated]

Automated review by review (OpenAI)

Reviewed commit: 368a8fc.

The substantive change since my 298e882 review is a231756, separate from inherited main updates. rs/moq-net/src/lite/publisher.rs:1357–1377 moves the actual track subscriber into Drain together with its group tasks, retaining upstream demand until those tasks complete. This directly addresses the premature idle cancellation rather than hiding the tail-lane failure. The new finite_relay.rs regression holds group tails across the declared end and checks all four groups plus clean completion. The harness also removes tail-only ffmpeg dependence and extends publisher lifetime. No new actionable correctness finding in this focused follow-up.

Direction: source-level lifetime repair with strict interop assertions is the right correction. The old failing run is no longer evidence that this head loses tails. Conversely, the claimed local five-lane pass is not independently reproduced here: exact-head Interop run https://github.com/moq-dev/moq/actions/runs/37431880215 failed at Optional publisher retention and skipped the full matrix. Obtain a completed tail run on the eventual conflict-resolved head before treating cross-language verification as complete.

Verification limits: static fix/test/harness review and exact-head Actions job inspection; no local tests run. GitHub currently reports merge conflicts; Check was still running at inspection.

[kixelated]

Pushed 91e9af89: merged main (with #5165 and #5167), plus one fix and the test diagnostics.

Blockers from the last push

1. ts_passthrough_crosses_a_relay_through_a_flagged_jump: passes with fix(net): name the groups a lite-05/06 subscription never got #5165 (3 of 3 runs, about 4 s). The moq-transport-14 case has no equivalent gap: PUBLISH_DONE carries a stream count, so the tail settles as soon as every opened stream arrived, and a skipped sequence opens none.
2. JS -> Rust tail lanes: root cause found. The JS publisher sends START and END before any group header arrives, then four 256 KiB groups. Since fix(net): a relay's rejoin never shows an older cached group as the live edge #4914 a received group stays hidden until its first frame lands, but the end counted hidden groups as arrived. The relay's downstream reader ended with every group still hidden, dropped its demand, and the upstream was cancelled as idle. fix(net): a group withheld for its first frame holds the end #5167 on main fixed this at the source, so this PR takes main's withholds check unchanged. With it, all five tail lanes pass locally.

Review findings

• Medium, cache holes vs. arrival holes (awaits_tail): the abort half is fixed. An abort now ends the wait for a pending tail, and is_settled judges the end without the hole count. A reader that has every group ends cleanly, even after eviction, instead of getting the abort. an_abort_ends_a_pending_tail_cleanly fails without the change. On the happy path, an evicted group or a datagram below the end still delays the end until the session settles the tail. I'm leaving that delay: it's bounded, and removing it needs a received-sequence record per track.
• A tail that never settles holds readers forever: declined. Every terminal serve path ends the producer. Lite Finished clears the flag; Idle aborts (or keeps serving while still used); GiveBack aborts; the IETF error exits abort. With this push an abort also ends the wait for the tail, so no reader stays parked.
• awaits_tail is O(groups): it only runs once the live edge has reached the end, and it is bounded by the cache. Not changed.
• Evicted groups look like holes: now documented on awaits_tail, and the abort test covers the failure mode.
• JS readers: tracked in quest/m1/js-pending-tail.md.
• finite_relay.rs diagnostics: a failed head now ends the reader with its error, and the main task reports that error at once. Before, it showed up as a 10 s head timeout or "no group reached the subscriber".

Validation: just check passes (6,771 Rust tests). Locally, just test interop --all passes every cell, the refused session, and all five tail lanes. The C++ cells were unavailable on this host.

(Written by Claude Opus 5.5)

[kixelated]

Re-review after push

Compared cabc22e2 → 91e9af89, leaving out the two origin/main merges. The real delta is 7538bf29 (an abort ends the wait for a pending tail) and e7e3c91f (drops an unneeded mut). In model/track.rs, awaits_tail now returns false once abort is set, and is_settled no longer goes through is_complete, so an abort that lands while the tail is pending marks the track settled whenever every cached group below the end finished. There's a new unit test, an_abort_ends_a_pending_tail_cleanly, and finite_relay.rs now reports the reader's error instead of panicking on a failed head or a closed channel.

Earlier findings

1. A tail that never settles can hold readers: partly fixed. An abort now releases parked readers. A terminal path that neither aborts nor clears tail_pending (lite ServeEnd::GiveBack, or an upstream end while a relay or warm copy keeps the producer alive) still leaves awaits_tail true. There's still no finite_relay case where upstream errors after SUBSCRIBE_END with a hole open.
2. awaits_tail is O(groups) per end check: still open.
3. Evicted groups look like holes: addressed by the new doc comments on awaits_tail and is_settled.
4. JS readers end at the boundary with holes: still open as a follow-up.

New finding (non-blocking, but worth a decision)

1. An abort over a real hole now reads as a clean, complete track. Take start_at(0), finish_at_pending(2), where group 1 arrives and finishes but group 0 never does, and then upstream resets. is_settled sees edge() >= fin, and every cached group below fin is finished, so settled = true and is_complete returns true. The reader gets Ok(None) after receiving only group 1, which is exactly what the new unit test asserts. Before this push, the same reader ended with the abort error. That's the right call for an evicted group, but for a group that never arrived it's silent truncation: a VOD or recording consumer can't tell a partial track from a whole one, which is the failure this PR set out to fix. A possible fix is to keep evictions distinguishable (for example, a tombstone or an "ever cached" bitmap or counter in lookup) so that only evicted holes count as delivered, and a never-arrived hole under abort still surfaces the error. Or, if clean is intentional, say so in the PR's Impact section.

CI is still pending on 91e9af89.

Verdict: MERGE once CI is green (no blocking issues; new finding 1 is worth a deliberate choice before merge).
Reviewed head: 91e9af8984b4ce6b8c04430316918fac16949dbe

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

[chatgpt-codex-connector]

💡 Codex Review

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Reviewed commit: 91e9af8984

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[chatgpt-codex-connector]

Skip tail lanes during released compatibility cells

test/interop/compat.sh invokes this script repeatedly with RELAY_BIN and MOQ_BIN, so these calls are neither negative nor media and now enter the tail suite. However, build_relay_cli returns early for those overrides and compat.sh only builds the regular moq-cli binary, not the interop-tail example. Consequently, a clean standalone just test wire-compat fails every session cell when run_tail_pair tries to execute a nonexistent example; a cached example would instead add an unintended tail assertion against released implementations.

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[kixelated]

Fixed in 57266897: a run that swaps in released binaries or JS clients (IN_TREE=0, the same condition the idle-out check uses) skips the tail lanes, so wire-compat never needs the interop-tail example.

(Written by Claude Opus 5.5)

[chatgpt-codex-connector]

Ignore fetched slots when deciding the live tail is complete

When a group below fin is fetched while its live stream is still reordered, insert_group_request inserts it into lookup with visible = false, explicitly excluding it from arrival-order delivery. Counting every lookup entry therefore makes the hole appear filled, allowing recv_group() to return clean EOF after the high group even though the live lower stream has not arrived and the subscriber can never receive the fetched slot through that cursor. Tail completeness needs to count only groups delivered by the live feed, or use separate wire-tail accounting.

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[kixelated]

Fixed in 57266897: awaits_tail counts only live-feed slots (visible), and picks the no-start floor from them too, so fetched backfill neither fills a hole nor pulls the floor down. a_fetched_group_does_not_fill_a_pending_tail covers it.

(Written by Claude Opus 5.5)

[chatgpt-codex-connector]

Track tail holes without rescanning the full cache

For a large finite track whose highest group arrives before many lower streams, every post-boundary recv_group poll walks the entire cached range with count(). As lower groups arrive one at a time, each subscriber wakes and repeats that scan, producing O(M×N²) work across M readers and N groups in the exact reordering case this change handles. Maintain incremental outstanding-tail state, and benchmark both group and subscriber axes, rather than rescanning the table on each poll.

AGENTS.md reference: AGENTS.md:L37-L37

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[kixelated]

Agreed this is the remaining design question, and it ties to the abort-over-a-real-hole point in the latest review: both go away with incremental arrival accounting (a per-track record of live sequences that eviction does not touch, giving an O(1) owed count and telling a never-arrived hole from an evicted one). Not done in this push; I have flagged it for a maintainer decision rather than growing this PR further. Today the scan runs only once the live edge has reached the declared end, over the cached range below it.

(Written by Claude Opus 5.5)

[kixelated]

Pushed 57266897: merged main, plus fixes for the two Codex findings I agree with (wire-compat skips the tail lanes; fetched backfill doesn't count toward the tail).

On the re-review of 91e9af89:

• Tail that never settles: no reader stays parked. Lite ServeEnd::GiveBack calls serving.abort(err). It doesn't leave the flag set. An abort closes the track for every producer clone, so a relay or warm copy that still holds one doesn't keep a reader waiting either. awaits_tail now returns false once abort is set.
• An abort over a real hole reads as clean: intentional for now, now stated in the PR's Impact. Main behaves the same way today, since its end check doesn't look for holes. The alternative turned evicted groups into false errors. Telling the two apart needs per-track arrival accounting. That's the same change that would fix the O(groups) scan, so I've listed both under "Open decision" for the maintainer, recommending a follow-up quest.
• Hosted Interop on 91e9af89: the full matrix passed, including all five tail lanes and the browser cells. Only the TS compliance duration-fidelity step failed. It also fails on main's scheduled run and is tracked in quest/m1/test-flakes-2/ts-duration-fidelity.md.

(Written by Claude Opus 5.5)

[kixelated]

Re-review after push

Compared 91e9af89 → 57266897, leaving out the origin/main merge c086d50f. The real delta is 57266897: in model/track.rs, awaits_tail now only counts visible slots (fetched backfill no longer fills a pending tail, and the implicit floor is the lowest visible group), with a new unit test a_fetched_group_does_not_fill_a_pending_tail. interop.sh renames IDLE_CHECK to IN_TREE and skips the finite-tail lanes on wire-compat runs.

New finding

1. Blocking: a fetch that lands first can now park the reader forever. claim_sequence (track.rs ~1143) rejects a new group with Duplicate whenever covering_group finds a copy whose first frame is at or below frame_start, and covering_group (~659) ignores visible. So take start_at(0), finish_at_pending(2), group 1 arrives live, and a consumer fetches group 0 from frame 0 and it completes. When live group 0 then arrives, create_group/receive_group returns Duplicate, so slot 0 stays invisible. Before this push the fetched copy counted and the tail settled. Now awaits_tail stays true until an abort, so the reader hangs (and per the last review, an abort then ends it cleanly without group 0). On a relay this is plausible: a fetch for a just-missed group racing its live stream. Possible fixes: let a live insert over an invisible covering copy promote that slot to visible (push it onto arrival and call landed) instead of returning Duplicate, or make claim_sequence replace an invisible slot. Either way, extend the new test to deliver live group 0 after the fetch and assert the reader gets it and then ends.

Other notes

• The test only shows the reader waiting. It doesn't show it ever finishing, which is the case above.
• The wire-compat skip makes sense, but the finite-tail lanes now have no coverage against released relays at all. That's worth a line in the PR body.
• Is there JS parity? js/net has no matching change for fetched groups and pending tails. That's probably fine if JS still has no pending-tail wait (earlier finding 4).

Earlier findings

1. A tail that never settles can hold readers: still partly open, and the new finding adds another way in.
2. awaits_tail is O(groups): still open. The added find and filter keep it linear.
3. JS readers end at the boundary with holes: still open as a follow-up.
4. An abort over a real hole reads as a clean track: still open, with no decision recorded in the PR body.

CI is pending on 57266897.

Verdict: ITERATE. Fix the fetch-then-live hang, or confirm that live inserts can't hit Duplicate over an invisible copy.
Reviewed head: 5726689722eb345c8b4ae78b8fb9a3e44af62a81

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

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 5726689722

ℹ️ About Codex in GitHub

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[chatgpt-codex-connector]

Reject overridden tail-only runs instead of passing empty

When --tail is combined with any binary or client override that sets IN_TREE=0, TAIL_ONLY disables the regular matrix and this condition disables every tail lane, after which the script prints interop: all checks passed without running a test. This can produce a false-green result for an explicitly requested tail run; reject this unsupported combination or allow the applicable tail lanes to execute.

AGENTS.md reference: AGENTS.md:L15-L17

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[kixelated]

Fixed in 3ab018e1: --tail with any binary or client override now exits 2 with an error instead of passing empty.

(Written by Claude Opus 5.5)

[kixelated]

Merge decision for 3ab018e1:

• The Codex review of 57266897 (the last code change) raised one P2, --tail with overrides passing empty, which 3ab018e1 fixes (shell only). Every earlier Codex and Grok finding is fixed or answered in its thread.
• Missing groups at the tail stay judged from the cache. A per-track record of live arrivals (fixing the O(groups) end check and a clean-but-short end after an abort over a never-arrived group) is planned as a follow-up quest.
• Ordering with test(moq-cli): the TS passthrough jump test holds under load without pacing #5175: this lands first; test(moq-cli): the TS passthrough jump test holds under load without pacing #5175 reconciles its Drain removal against it.

Auto-merge is pinned to 3ab018e1da9c94d12be0b097a0d03bb59ab3edfa.

(Written by Claude Opus 5.5)