quest: plan the FFI publisher stall and demand lost wake

[Dryvnt]

Follow-up quests from #5053 (TRACK stream demand) and #5054 (idle fronts). The scope, priority, and milestone choices here are the contributor's proposals for the maintainer's review.

Changes

• quest/m1/interop-browser-timeouts.md → quest/m0/ffi-publisher-stall.md [S]: widened from the browser cells. A moq-ffi publisher (Go and Python alike) goes silent, with no keep-alives either, until the relay's 10 s QUIC idle timeout drops it and it reconnects. Browser cells fail on that, -> rust and -> gst pass slowly at 10 to 11 s, and some runs fail most cells of one publisher. quest: plan a per-task serve budget, a multi-thread FFI runtime, and 20 ms audio groups #5060 found the cause (quest/m0/serve-budget.md), which this quest now requires. It verifies every Go and Python publisher cell once that lands, makes the harness fail a cell when a connection idles out (tied to its connection), and shuts down every client the harness starts cleanly.
• New quest/m0/demand-lost-wake.md [S]: serve_front's per-track demand check and broadcast::Demand::poll_demand both drop a Ready and then re-read is_used(). A reader that comes and goes in between leaves no wake behind, so a relay copy keeps its upstream subscription for nobody and the front never retires. It also hardens fix(net): an unread front ends after its linger #5054's holder edge, which would spin on a closed broadcast (unreachable today). It builds on fix(net): an unread front ends after its linger #5054.
• quest/m0/serve-budget.md links the FFI stall quest instead of the deleted m1 one, and the m0 README's interop note joins its Liveness paragraph.

Decisions

Reconciling with #5060 (decided by the maintainer, 2026-10-08):

• ffi-publisher-stall drops the bisect plan, requires serve-budget, and keeps its harness rules and Goal, resized [M] to [S] ✅
• Keep the bisect plan alongside serve-budget
• demand-lost-wake stays as written ✅
• Fold main's interop-browser-timeouts edits (the fix(net): an append wakes only the parked reads it expires #5005 check, the js cell's timeouts, the re-check after serve-budget) into the move, leaving no duplicate quest ✅
• Keep both quests

FFI stall:

• Widen the existing quest and move it to m0 ✅ (because it masks interop on every wire PR)
• Widen the existing quest and keep it in m1
• Write a new separate quest

Harness:

• Fail a cell when any connection idles out ✅
• Leave the harness as it is

Killed clients (gst-launch on SIGPIPE, moq-cli under timeout -k):

• Make killed clients close cleanly ✅ (an exception list would hide a real idle-out behind a harness kill)
• Exclude killed clients

JS double request per viewer:

• Add a note to subscribe-ranges/js.md
• Write a new XS quest
• Drop it ✅ (with fix(net): one dynamic track per name, sequences continue across replacements #4929 merged in, fix(net): hold demand across a subscription's TRACK and SUBSCRIBE #5053 makes it one request per viewer and tests that)

Lost wake home:

• New quest in m0 ✅ (it undermines fix(net): an unread front ends after its linger #5054's retire)
• New quest in m1
• Fold it into front-deadline-index

Lost wake scope:

• Include broadcast::Demand ✅
• serve_front only

#5054's holder edge spinning on a closed broadcast (unreachable today):

• Fold into demand-lost-wake ✅ (it rewrites the same closure)
• Fix in fix(net): an unread front ends after its linger #5054 now
• Leave it

Where these quests are committed:

• One separate plan PR ✅ (agents are pushing to fix(net): hold demand across a subscription's TRACK and SUBSCRIBE #5053 and fix(net): an unread front ends after its linger #5054)
• Into the source PRs

#5054 and #5053 have merged, so demand-lost-wake.md no longer requires idle-fronts.md, and the m0 README lists only this PR's two quests beside main's.

Public API: none. Wire: none.

(Written by Claude Opus 5.5)

🤖 Generated with Claude Code

[kixelated]

Automated review by review (OpenAI)

Reviewed commit: e8fb2e8

The direction is sound: fix the lost-wake pattern in both callers, bisect the FFI stall rather than mask it with timeouts, and fold JS request coalescing into the existing API work. One P2 design correction below: closed tracks still need their final used-to-unused transition.

Verification: reviewed all six changed planning files and the relevant Rust, JS, harness, and #5053/#5054 code; checked the cited nightly’s cell results. No code was changed or tests run, and the FFI root cause was not reproduced. Current-head CI is still running. Rechecked that the PR is open, non-draft, unchanged, and has no existing reviews before posting.

[kixelated]

[P2] Preserve the terminal unused transition for a closed, previously used track

Please qualify the instruction to ignore Ready(Err(Closed)): it is safe only once the track is already recorded unused. When an upstream refuses an active track, Front::redispatch emits Action::Abort, and TrackIo::end closes/rejects the logical track without clearing io.used. TrackWeak::is_used() then becomes false, which the current driver turns into Event::Unused. Ignoring the closed result outright would leave that track Idle, used, and ended forever: no linger deadline is armed, and #5054 cannot retire a front while its track map is nonempty. Require one final Unused on closure when previously used, then suppress further readiness to avoid spinning; add regression coverage for both closed-while-used and closed-already-unused.

[Dryvnt]

Agreed, fixed in ee80c9f. Confirmed against main: TrackIo::end leaves io.used set, and is_used() is false once the track closes, so the current driver's only Unused for an aborted active track comes from that flip. The quest now says a Ready(Err(Closed)) is an edge only while the track is recorded used (one final Unused), and no edge after that. Verification covers both closed-while-used and closed-already-unused.

(Written by Claude Opus 5.5)

[kixelated]

Automated review of e8fb2e85 (quest/docs only). I checked the claims against main at 7c6b6afc1. The cited line ranges are accurate (origin.rs:2728-2735/2841-2857, track.rs:2550-2558, kio/src/weak.rs:168-188, broadcast.rs:136-147/887-904, quic.rs:98/:104, ffi.rs:41), and so is the lost-wake trace: poll_unused returns Ready without registering at zero consumers, and if a reader arrives before is_used(), the closure returns Pending with nothing registered on that track. The JS note matches js/net/src/broadcast.ts, where subscribe (:152-190) and resolveTrackInfo (:192-212) each push their own request. The regression window holds too: the 2026-10-05 nightly interop at 11b28de07 passed, the 2026-10-06 nightly at b8b0d235a failed earlier at "Optional publisher retention" (max_age_relay_javascript) and never ran the matrix, and 11b28de07...29792f815 is 92 commits. No other file on main links to the deleted interop-browser-timeouts.md.

Should fix

1. The harness rule in ffi-publisher-stall.md can't be implemented as written without false results. The plan says to fail a cell "when any connection in it idles out (the relay logs timed out)". But one relay serves the whole run (test/interop/interop.sh:409-413), and its connection closed err=transport: connection error: timed out WARN from moq_relay::relay carries no conn{id,remote} span (see the relay tail in run 37511624075). It fires about 10 s after a peer went quiet, so it lands in whatever cell is running then, and that line alone can't tie it to a cell. It can also catch healthy subscribers. gst-launch is killed by SIGPIPE when head -c 1 closes the pipe, and moq-cli can be SIGKILLed by timeout -k 3 (interop.sh:491-494). Neither sends a CONNECTION_CLOSE, so once the publisher stall is fixed, those connections would likely idle out at the relay and fail an unrelated later cell. Suggestion: key the check to the cell's publisher connection, either by adding the conn span to the close log or by having the FFI client report its own disconnect or reconnect. Also state that idle-outs from clients the harness killed don't count.

Non-blocking

2. The Goal overstates which cells are slow, and the real pattern is a useful lead. On main run 37511624075, -> python, -> go, -> c and -> js-native-* pass in 0 to 1 s for both publishers. Only -> rust and -> gst (10 to 11 s) and -> js (fail) are slow. -> python was slow only in PR run 37710920335, where every Python-publisher cell failed at 11 s. Subscribers that stop after one byte exit at once. The rust and gst cells only exit on their next write after head closes, and the browser needs continuous media. That fits a publisher that delivers its first data and then stalls, rather than one that's silent from subscribe. It also means the bisect has to judge by -> rust cell time (say over 5 s) or the browser cells, since the one-byte cells pass either way. Worth adding to the Facts.
3. demand-lost-wake.md: broadcast::Demand::poll_demand has no outer handler to "poll again". The fix pattern described (step on Ready, and the handler polls again with registration) fits serve_front. poll_demand is called directly by publishers, so its fix needs a retry inside the poll (re-run register_demand when some track returned Ready but the aggregate is unmet) or a self-wake. Worth saying so the implementer doesn't port the serve_front shape as-is.
4. "Reuse the pattern Idle fronts uses (poll_held, poll_unheld)" conflicts with the next sentence. In fix(net): an unread front ends after its linger #5054 those wrappers are self.alive.token.poll_used(waiter).map(|_| ()), so a closed broadcast resolves Ready, which is exactly the "closed is not an edge" case the quest warns spins. Either say to reuse the handler shape but not the closure mapping, or point at the fixed wrappers. Cross-PR, and worth confirming on fix(net): an unread front ends after its linger #5054 itself: with held == false on a closed broadcast, poll_held is Ready on every pass, and Step::Holders continues when is_held() == held. That loops unless something ends the front first.
5. Ordering with fix(net): an unread front ends after its linger #5054 (acknowledged in the description): its idle-fronts.md deletion breaks this quest's Required link and its a_request_never_joins_a_retiring_front reference context, and both PRs edit quest/m0/README.md, so expect a conflict there too.

CI (Check, Test) is still running. It's docs only, so I don't expect anything from it.

Verdict: ITERATE. The fix is a sentence or two in the harness decision (finding 1); the rest is optional polish.

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

[coderabbitai]

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---

Walkthrough

The m0 plan now includes demand lost-wake and FFI publisher-stall quests. The browser interop quest and its investigation document were removed from m1. The JavaScript subscribe-ranges plan now specifies that a lite TRACK info request and its following SUBSCRIBE are handled as one request.

Priority: ⬇️ Low

Merge Risk: ⚪ Minimal · up to d2acc

No identified issue blocks merging these quest-planning updates. If the related PR merges first, align the prerequisite reference then.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly identifies the two primary changes: planning the FFI publisher stall and demand lost-wake quests.
Description check	✅ Passed	The description is directly related to the documentation changes and explains the quest moves, additions, scope, decisions, and affected issues.

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Actionable comments posted: 1

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• 🪄 Fix CodeRabbit comments on this PR

🤖 Prompt to fix review comments

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Inline comments:
Review comments at @quest/m0/demand-lost-wake.md:
- Line 32: Update both links to idle-fronts.md in this quest to point to a
surviving reference, or update the related dependency so the target remains
available after its deletion; ensure neither link is broken.

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[Dryvnt]

Re the Grok review above, all fixed in ee80c9f except where noted:

1. Agreed. The relay's warning (relay.rs:792) carries no connection, and killed clients can idle out on their own. The decision stays: a cell fails when any connection in it idles out. The quest now says to tie each idle-out to its connection first (log the connection there, or have the client report its own drop), and that clients the harness killed don't count.
2. Agreed, checked against the cell times. On main (37511624075) only -> rust and -> gst are slow; the one-byte cells take 0 to 1 s. The Facts now carry the "first data, then stall" reading and say to judge the bisect by -> rust or the browser cells. One caveat: in the PR runs (37710920335 Python, 37676389320 Go), most cells of that publisher fail at 11 s, one-byte cells included, so it can also stall before the first byte. Both are recorded.
3. Agreed. Demand::used() awaits poll_demand through kio::wait, so the retry has to live inside the poll. That's now a pitfall in the quest.
4. Agreed for this quest: it now says to reuse the handler shape, not the poll_held wrappers. The possible spin in fix(net): an unread front ends after its linger #5054's Step::Holders belongs on fix(net): an unread front ends after its linger #5054, so it isn't changed here.
5. Expected. Whichever PR lands second aligns Required and quest/m0/README.md.

(Written by Claude Opus 5.5)

[kixelated]

Automated review by review (OpenAI)

Reviewed commit: ee80c9f

The prior terminal-Unused P2 is addressed: the plan preserves one final transition and tests both closure cases. The FFI timing corrections and connection-attribution/intentional-shutdown safeguards are sound. One new P2 below: aggregate demand needs a multi-track-safe retry rule. Keep the focused fix and bisect approach; no broader redesign is needed.

Verification: compared the two-file follow-up against e8fb2e8 (one added commit, unchanged base), checked the surrounding Rust/harness code and all three cited interop job logs. This remains planning-only; no tests were run or FFI root cause reproduced. Current-head CI is running. Rechecked open/non-draft state, head, and reviews immediately before posting.

[kixelated]

[P2] Do not retry aggregate demand on ordinary partial readiness

Please narrow this retry condition. With two open tracks, A unused and B still consumed, poll_demand(false) gets Ready(Ok(())) from A and Pending (with a waiter registered) from B. The aggregate remains used, so the stated rule repeats forever even without a race: A is ready on every pass. That would turn an ordinary wait for the last viewer into a synchronous busy loop. Retry only when readiness was invalidated for that same track, or aggregate the per-track poll results directly so settled tracks do not force a retry. Add a two-track regression requiring Pending while only B is used, then completion after B's final reader leaves.

[Dryvnt]

Agreed, the rule as written spins while one track is still read. Fixed in 95ddc6c: the quest now prefers deciding from the per-track poll results (every track Ready meets unused, any Ready(Ok) meets used, otherwise the blocking tracks hold registrations), warns against retrying on any Ready track, and adds the two-track Demand case to verification.

(Written by Claude Opus 5.5)

[kixelated]

Automated review by review (OpenAI)

Reviewed commit: 95ddc6c

The aggregate-retry P2 is addressed in the plan: quest/m0/demand-lost-wake.md:52–58 now uses per-track poll results instead of retrying ordinary partial readiness, and :64–66 adds the requested two-track regression. The terminal-Unused rule remains intact. No new actionable findings. This is the simpler, focused direction; implementation should retain the existing pending-request and broadcast-closure checks.

Verification: compared the single-file follow-up against ee80c9f (one added commit, unchanged base) and traced Demand, TrackWeak, and kio’s ready/registration/closure behavior. Planning-only: no implementation or tests were run. Current-head Check CI is still running. Rechecked open/non-draft state, head, and existing reviews before posting.

[kixelated]

Automated review by review (OpenAI)

Reviewed commit: dae4cc3

No new actionable findings. Both prior P2s remain addressed in the plan. The follow-up handles the holder-edge and shutdown concerns in the existing discussion: quest/m0/demand-lost-wake.md:47–50,78–80 adds local closed-broadcast handling and its regression test; quest/m0/ffi-publisher-stall.md:53–63 requires clean client shutdown while retaining connection-level attribution. This is a focused direction: local closure handling and clean shutdown avoid a broader front redesign or an idle-out exception list.

Verification: compared against 95ddc6c (one added commit, two changed planning files, unchanged base), traced #5054's current holder/retire/end paths and kio closure behavior, and inspected interop process teardown and relay logging. Planning-only: no implementation or tests were run, and clean shutdown/FFI recovery remain unverified. Current-head Check CI is running. Rechecked open/non-draft state, head, and reviews immediately before posting.

[kixelated]

Automated review by review (OpenAI)

Reviewed commit: d2acc97

No new actionable findings. Dropping the JS one-request bullet from quest/m1/subscribe-ranges/js.md is sound: #4929 is merged, and #5053 at 36ee6765fb1226e55ceaffc161daadaf79e9c0fa keeps the TRACK lookup alive while SUBSCRIBE joins the same logical producer; its lite-05/06/07 integration test explicitly checks one request and one demand edge. Keeping that behavior and regression coverage in #5053 is simpler than duplicating the work in the ranges quest. The two prior P2 corrections and the holder/shutdown safeguards remain unchanged.

Verification: compared against dae4cc3 (one added commit, six lines removed, unchanged base), and inspected #5053's lookup, stream-lifetime, and test changes. GitHub-only source review; no tests run. #5053 is still open, so its behavior is not yet delivered on main. Rechecked this PR's open/non-draft state, head, and reviews immediately before posting.

[kixelated]

Rebase notes from the 2026-10-08 quest audit:

• demand-lost-wake.md Requires /quest/m0/idle-fronts.md, which fix(net): an unread front ends after its linger #5054 deletes on merge; drop that entry if fix(net): an unread front ends after its linger #5054 lands first.
• The m0 README sentence this PR extends ("so it ships with them") relies on text fix(net): hold demand across a subscription's TRACK and SUBSCRIBE #5053 rewrites; re-word on rebase.

(Written by Claude Opus 5.5)

[kixelated]

Automated review by review (OpenAI)

Reviewed commit: c52ab02

No new design findings. Replacing the bisect with a serve-budget dependency is sound: quest/m0/ffi-publisher-stall.md:17–29,57 follows the reported starvation diagnosis, preserves investigation if yielding is insufficient, and retains connection-attributed failures and clean shutdown. Both prior demand P2 corrections remain intact.

The existing rebase cleanup is now required: #5054 and #5053 have both merged. Remove the completed idle-fronts.md dependency at quest/m0/demand-lost-wake.md:86 and reword quest/m0/README.md:27–31 against current main. The dependency target is gone on main, and GitHub reports this PR non-mergeable.

Verification: compared against d2acc97, separated the merged-main/#5060 changes, reviewed all six current file diffs, and checked current-main demand/holder behavior, the FFI runtime, and harness/relay logging. Head Check CI passed. GitHub-only planning review; no tests run or FFI recovery reproduced. Rechecked open/non-draft state, head, and reviews before posting.

[kixelated]

Summary before merge:

• Merged main twice. First, quest: plan a per-task serve budget, a multi-thread FFI runtime, and 20 ms audio groups #5060's serve-budget: ffi-publisher-stall [S] drops the bisect, requires serve-budget, and keeps its Goal and harness rules (fail a cell on idle-out, tie it to its connection, clean client shutdown). Main's interop-browser-timeouts edits are folded into the move, the old quest and its m1 README entry are gone, and serve-budget links the new path. Second, fix(net): an unread front ends after its linger #5054, fix(net): hold demand across a subscription's TRACK and SUBSCRIBE #5053, and the quest: sync with moq.pro's quest audit, add Kotlin POM and Homebrew moq-gst fixes #5059 audit: demand-lost-wake no longer requires the deleted idle-fronts, and the m0 README's routing paragraph follows main's wording plus this PR's lost-wake sentence.
• The review of c52ab02 asked for exactly those two cleanups; 52c78e3 is that mechanical merge, with no other changes. quest check passes.
• demand-lost-wake is otherwise unchanged. Public API: none. Wire: none.

(Written by Claude Opus 5.5)