fix(engine): charge or hold the drain halts no retry can shed - #1320
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Three defects on the op-drain plane, all in the failure valve's classification of a refusal that repeats verbatim on every pass. An oversized authored head spun forever, uncharged and unsignalled. `classify_author` routed `AuthorError::HeadTooLarge` through `is_trust_refusal`, which answers `false`, so the refusal landed on `Halt::Unclassified` — the one arm that charges nothing, dequeues nothing and reports nothing. The condition is permanent for a given body: a fresh nonce moves the sealed bytes and never their count, so the same block length is refused tick after tick while the strict-FIFO head never advances. It now returns `Halt::UploadAttempt` directly, leaving `AuthorError::is_trust_refusal` alone so the rotation plane's retry rule does not move with it, and the doc comment no longer claims the budget bounds both branches. `Drain::nonce` filled 24 bytes straight off the entropy seam, the one unguarded draw in the crate and the highest-volume seal path in it. A seam reporting `Ok` having written nothing would seal every content body under one fixed nonce. It goes through `entropy::fresh_nonce` like every other draw. A BYO config refused before any request is built charged the attempt budget, so five ticks of a deterministic policy verdict ended in `AttemptsExhausted` releasing the version's staged blocks. The four `validate_byo_config` verdicts now take a new `Halt::HeldBySettings`, which holds the op and its reservation the way the over-quota hold does; its exit is the placement no longer reaching that verdict, not a timer. It surfaces as `SettingsHold` on `SessionStatus` and `SnapshotView`, naming the rule and never the endpoint or the bearer. Closes #1308 Closes #1304 Closes #1090
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This repository does not receive automatic reviews because it has fewer than 10 stars. ⚙️ Run configurationConfiguration used: Path: .coderabbit.yaml Review profile: CHILL Plan: Pro Plus Run ID: WalkthroughThe drain now holds operations rejected by deterministic provider settings, distinguishes oversized authored heads, and sources nonces through ChangesSettings hold and halt handling
Estimated code review effort: 4 (Complex) | ~45 minutes Merge Risk: 🟡 Moderate · up to The oversized-head path can preserve content while leaving a child name pinned without a parent reference, creating orphaned state and potential resource retention. Merge should wait until that child name is retired and the behavior is covered by a regression assertion. Sequence Diagram(s)sequenceDiagram
participant Drain
participant Placement
participant Engine
participant WASM
Placement->>Drain: classify_placement
Drain->>Engine: store SettingsHold
Engine->>WASM: project settingsHold
WASM-->>Engine: expose opId, node, check
Possibly related issues
Possibly related PRs
Suggested labels: 🚥 Pre-merge checks | ✅ 5✅ Passed checks (5 passed)
✨ Finishing Touches📝 Generate docstrings
🧪 Generate unit tests (beta)
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This was referenced Aug 19, 2026
The review gates on this branch found that routing `HeadTooLarge` to `Halt::UploadAttempt` bought a bounded spin at the cost of the user's content: exhausting the budget there runs `dead_letter` -> `abandon`, which retires the version's registry rows and releases its staged blocks, and the only copy of the version's content key rides the op record the same path dequeues. The trigger needs no attacker either -- a folder record inlines a child ref per child, so a folder past the block ceiling turns every upload into it into a write that lands and then erases itself five ticks later. The bound stays; what ending it costs does not. `Halt::HeadOversized` is charged like an attempt and dead-letters with the same `AttemptsExhausted` reason, but preserves the staged version the way a superseded edit's is kept, so the record is what is abandoned and not the bytes it would have named. The write-plane case is now content-bearing and asserts nothing is unpinned on the way out. Also from the gates: `classify_author` is an exhaustive match, so a new `AuthorError` cannot inherit the arm that retries free and forever; a raised hold clears the other, so the two hold cells cannot both claim one head; the repeated hold rationale is stated once at `SettingsHold`; `Drain::nonce` is inlined at its single call site rather than wrapping `fresh_nonce` behind a doc that restated it; and the boundary test's `SnapshotView` literal carries the new field, which the wasm32 leg catches and `--workspace` does not. Findings outside this diff's files are filed as #1326, #1327 and #1328.
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August 20, 2026 02:13
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| Filename | Overview |
|---|---|
| crates/engine/src/sync/drain.rs | Adds settings holds, bounded oversized-head handling, guarded nonce generation, and the associated drain classifications. |
| crates/engine/src/facade.rs | Stores and exposes the current settings hold through session status and snapshots. |
| crates/engine/tests/write_plane.rs | Adds integration coverage for oversized authored heads and silent entropy sources. |
| crates/wasm/src/lib.rs | Exposes settings-hold details through the WASM snapshot boundary. |
| crates/wasm/tests/boundary.rs | Verifies settings-hold values retain their expected JavaScript boundary shapes. |
Flowchart
%%{init: {'theme': 'neutral'}}%%
flowchart TD
D[Drain queue head] --> A{Placement admitted?}
A -->|Settings refusal| H[Hold by settings]
A -->|Admitted| P[Author and publish]
P -->|Head oversized| C[Charge attempt budget]
C -->|Budget remains| D
C -->|Budget exhausted| L[Dead-letter op and preserve staged version]
P -->|Nonce unavailable| R[Fail closed and retain queued op]
H -->|Settings change| D
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Inline comments:
In `@crates/engine/src/sync/drain.rs`:
- Around line 737-767: Update the Halt::HeadOversized branch in the halt
handling logic to retire the orphaned derived Create child name before
dequeue_op, while retaining preserve_dead_letter so the content CIDs remain
available. Add a regression assertion confirming the derived child name is
retired after the parent hits HeadTooLarge.
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crates/engine/src/content/provider.rscrates/engine/src/facade.rscrates/engine/src/lib.rscrates/engine/src/sync/drain.rscrates/engine/src/sync/mod.rscrates/engine/tests/write_plane.rscrates/wasm/src/lib.rscrates/wasm/tests/boundary.rs
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An oversized parent head halts after publish_create confirmed the child record, so the derived write name is registered while no published record references it. Dead-lettering on Halt::HeadOversized dequeued the op without owing that name back, leaving a pin row charged forever. Retire the name half of registered_by on that path and keep the content, so the staged version stays openable while the unreachable name is reclaimed. State the oversized-head terms once on Halt::HeadOversized and cross-reference them from the valve arm and classify_author.
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Three defects on the op-drain plane, all in how the failure valve classifies a refusal that repeats verbatim on every pass. They share
crates/engine/src/sync/drain.rs, so they land together.An oversized authored head spun forever, uncharged and unsignalled
classify_authorroutedAuthorError::HeadTooLargethroughis_trust_refusal, which answersfalse, so it landed onHalt::Unclassified— the one valve arm that charges nothing, dequeues nothing and writes nothing toDrainReport. The condition is permanent for a given body: a fresh nonce moves the sealed bytes and never their count, soencoderecomputes the same block length tick after tick while the strict-FIFO queue head never advances.The classification stays as it is.
AuthorError::is_trust_refusalstill answersfalseforHeadTooLarge— it also decidesWriteRotateError::is_retryable, and the blueprint forbids a permanent attacker-influenced size refusal on the produce side. Only the valve's own verdict moves, to a newHalt::HeadOversized: charged against the same budget, dead-lettering with the sameAttemptsExhaustedreason, so the spin is bounded and every op behind it drains.What the security gate changed here. The obvious route —
Halt::UploadAttempt, which is what the issue proposed — bounds the spin by destroying the content. Exhausting the budget there runsdead_letter->abandon, which retires the version's registry rows and releases its staged blocks, and the version's only content key rides the op record the same path dequeues. The trigger needs no attacker: a folder record inlines a child ref per child, so a folder past the 2 MiB ceiling turns every upload into it into a write that lands and then erases itself five ticks later.Halt::HeadOversizedtherefore preserves the staged version the way a superseded edit's is kept — only the record was over the ceiling; the bytes it would have named are whole. Reverting that one arm makes the write-plane test fail on a non-empty retire batch.classify_authoris also now an exhaustive match, so a newAuthorErrorvariant cannot silently inherit the arm that retries free and forever.Drain::noncebypassed the all-zero refusalIt filled 24 bytes straight off the entropy seam, on the highest-volume seal path in the engine. A seam reporting
Okhaving written nothing would seal every content body under one fixed nonce, and two seals under one key at one nonce is a confidentiality break. The draw now goes throughentropy::fresh_nonce, mapped onto the drain's existing fail-closed arm.The issue's claim that this was "the one unguarded draw" is false — the crypto gate found four more, including the HPKE ephemeral for every op record. They live in files this PR does not own, and are filed as #1326.
A BYO config refused before the request is built spent the op's budget
classify_placement's_fallthrough caught the four verdictsvalidate_byo_configreaches before any request exists —InvalidEndpoint,InsecureTransport,BlockedAddress,InvalidCredential. Every retry reproduces them, so five ticks ended inAttemptsExhaustedreleasing the version's staged blocks over a config a member could have edited.They now take
Halt::HeldBySettings, which holds the op and its staging reservation the way the over-quota hold does. Its exit is a settings change, not a timer:settings_admit_the_held_headreleases the head as soon as the placement stops reaching the same verdict. It is surfaced asSettingsHoldonSessionStatus,SnapshotViewand the wasm view, naming the rule that refused — never the endpoint or the bearer. Raising either hold clears the other, so the two cells cannot both claim one head.What is not covered, and why
The BYO issue's end-to-end case is not constructible. It asks for an invalid endpoint holding an op in
crates/engine/tests/write_plane.rs, released by a corrected settings record. Both directions of the settings plane already runvalidate_byo_config:settings.rs::validaterefuses the publish, anddecode_settings_bodyrefuses the read-back on both the resolved and the cached path. So noPlacement::Externalthe drain can see carries a configplace_blockwill reject; that call is defence in depth. The classification was still wrong — a deterministic verdict that destroys staged content on a timer — and the fix is the one the issue specifies, covered by unit tests on the classifier, on the hold's exit predicate, and on the read surfaces.settingsHoldis not threaded to the TypeScript worker.blockedis, throughengineWasm.ts/protocol.ts/commandCodec.ts. Wiring a second descriptor for a state the engine cannot currently reach is scope this PR declines; the Rust and wasm surfaces carry it, and a host adds the branch when the state can occur.Adjacent findings, filed rather than folded in:
net/rotation.rsand the facade identity path. Both files belong to feat(engine): give CreateInviteLink a production mint path #1321.PlacementRefusalstill charges the budget while the comment above it claims it holds. Left out deliberately:SettingsUnavailableis a transient load failure and does not want the settings-change exit the other two variants do.An entropy-seam outage still spends the attempt budget, which the crypto gate argued should be uncharged. Left as it is: it is pre-existing on
main, and the issue asks for the existing fail-closed arm.Tests
an_authored_head_over_the_block_ceiling_dead_letters_with_its_version_intact— a child name past the ceiling makes the parent record unauthorable on every pass; the op dead-letters withAttemptsExhaustedin more than one pass, leaves the queue, and unpins nothing. Revertingclassify_authorhangs it at the harness's 50-pass ceiling; reverting only theHeadOversizedrouting fails it on the retire batch.a_seam_that_draws_a_silent_nonce_publishes_no_record— a seeded source silenced mid-scenario; no record publishes and the op keeps its place. RevertingDrain::noncepublishes under the all-zero nonce.a_config_refused_before_the_request_holds_the_op_rather_than_spending_its_budgetanda_settings_hold_lets_go_only_once_the_placement_stops_refusing— the classification and its exit condition.a_settings_refused_hold_reaches_both_read_surfaces— the hold reachessnapshotandstatus.only_a_refusal_a_rebase_cannot_shed_is_charged_against_the_attempt_budget— the existingclassify_authorcase, updated rather than deleted.SnapshotViewliterals — the--all-targetswasm32 leg catches that, and--workspacedoes not.All run in existing CI gates.
Closes #1308
Closes #1304
Closes #1090
Note
Hold or charge drain halts so retry can't shed them in
sync::drainHalt::HeldBySettings(ProviderError)andHalt::HeadOversizedtoDrain::pass; settings refusals hold the queue head without spending attempts, while oversized record heads spend attempts and dead-letter with the staged version preservedSettingsHold(op_id, node, refusingProviderError) surfaced throughEngine::status,Engine::snapshot, and the WASMSnapshotViewso clients can observe settings-based holdsclassify_placementto treatInvalidEndpoint,InsecureTransport,BlockedAddress, andInvalidCredentialas holds rather than attempt charges; rewritesclassify_authorsoHeadTooLargemaps toHeadOversizedand seal errors map to free-retryUnclassifiedDrain::noncewithfresh_nonceinpublish_record; a failed nonce draw halts before PUT as an upload attempt instead of proceedingclassify_placementandclassify_authornow classify errors differently — BYO settings failures (ProviderError) no longer spend attempts, andHeadTooLargeauthor errors now consume attempts until dead-letter; consumers readingSessionStatusorSnapshotViewmust handle the newsettings_holdfieldMacroscope summarized f9091c3.
Summary by CodeRabbit
New Features
Bug Fixes