feat(frost): finalize interactive signing over the first t responsive committers (7.3 t-of-included PR2/3)#4093
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mswilkison merged 2 commits intoJun 19, 2026
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… committers (7.3 t-of-included PR2/3) The interactive ROAST signing runner waited for ALL included members in round 1 and round 2, so one slow or offline member stalled the attempt to its ctx deadline -> fail -> ROAST retry. Make the attempt finalize over the first t responsive committers instead: - Coordinator: collectCommitments now collects until EXACTLY t (the threshold) and stops, builds the FROST package over that t-subset, and carries the chosen members in the package's signed signer_ids (PR1's field), ascending+distinct. - Non-coordinator signer (in signer_ids): runs round 2 and collects round-2 shares from the package's signer set, not the full included set. - Observer (committed in round 1 but not in signer_ids): does NOT run round 2; it aggregates the subset's broadcast shares publicly, marks the attempt succeeded, and returns the signature - and still aborts the engine session on success to drop its unconsumed round-1 nonces (the success path previously suppressed the abort, which leaked an observer's nonces). t-of-included stays inert until participant selection oversizes the included set past the threshold (it currently trims to exactly honestThreshold), so the machinery is harmless and dormant until MacLane enables oversizing. PR3 will make signingDoneCheck (pkg/tbtc) threshold/package-set aware. Also harden the runner constructor to reject threshold > included-set size, the new round-1 collection loop's termination invariant. All behind the frost_native pre-prod build tags. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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…tion evidence Fold of Codex review P2 on #4093. recordShareMessage filtered by the signer set before RecordShareSubmission, so an included member that is NOT in the chosen signing subset (an observer) had its share dropped before the collector could retain it. In a targeted coordinator-equivocation case where that member was handed a different package and broadcasts a divergent share, the collector is designed to keep it as EquivocationKindDivergentShare evidence for the f+1 blame/transition path - and the signer-set filter was discarding it. Split the membership gate: retain (hand to RecordShareSubmission) any INCLUDED member's well-formed share, but only COUNT signer-set shares toward the aggregate. The collector already enforces included-membership and keeps divergent shares separately; the runner now caches the included set (includedMembers) and gates retention by it, restoring the pre-subset evidence surface while keeping t-of-included counting. Added TestInteractiveSigningRunner_RetainsObserverDivergentShareAsEvidence: an included observer's divergent share is retained (EquivocationKindDivergentShare emitted) but not counted. Gemini approved the PR; this addresses the sole Codex finding. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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…f-included PR3/3) (#4094) ## What Completes RFC-21 Phase 7.3 t-of-included finalize. With PR2 (#4093) an interactive signing attempt finalizes over the first `t` responsive committers of an (optionally) oversized included set. The non-subset and offline members never broadcast a signing done check, so the outer `signingDoneCheck` — which required a confirmation from **every** attempt member — would hang an otherwise-successful attempt to its timeout and force a needless retry. This concludes the done check on a **deterministic threshold quorum**, keeping the legacy path byte-for-byte unchanged. ## Design (locked via a Codex + Gemini consult) My first cut completed on "the first `t` arrivals," which is **network-order-dependent**: the resulting `latestEndBlock` (a per-node max over a network-order-dependent subset) differs across honest nodes, and that value feeds batch scheduling (`signBatch`: `signingStartBlock = prev endBlock + interlude`) → the batch desyncs. The consult locked this design: - **Non-oversized (`included == honestThreshold`; today's selector output and the whole coarse path)**: the legacy all-members rule is **UNCHANGED** — wait for every attempt member, require all signatures equal, return `max(endBlock)`. - **Oversized (`included > honestThreshold`)**: bucket done checks **by signature**, conclude once a bucket holds `>= honestThreshold` distinct senders (the minimum that proves a valid threshold signature). **Minority buckets (divergent / adversarial signatures) are ignored, never fatal** — one bad done message can't fracture the group. The end block is the **deterministic `attemptTimeoutBlock`** (every honest node computes it identically), not a max over done messages. With honest majority (`t > groupSize/2`) at most one signature bucket can reach `t` — even under coordinator equivocation (two disjoint `t`-subsets can't coexist when `2t > n`) — so the quorum is unique. That means **no body-hash / proto change** is needed (bucket by the existing signature field), and **no `signBatch` change** (the oversized path feeds `attemptTimeoutBlock` through the existing return). The `>1`-quorum branch is unreachable and intentionally non-fatal (no noisy post-success failure). ## Inert until oversizing `included == honestThreshold` today, so the legacy branch is taken and behavior is identical to before; the quorum path only activates once selection oversizes the set (MacLane's policy knob). ## Tests (`signing_done_test.go`) - Legacy `TestSigningDoneCheck{,_MissingConfirmation,_AnotherSignature}` — unchanged, still green (they use an attempt-member set of size `honestThreshold`). - `TestSigningDoneCheck_ThresholdSubsetConcludes` — oversized; reporters carry different end blocks but the result is the deterministic `attemptTimeoutBlock`. - `TestSigningDoneCheck_OversizedIgnoresMinorityDivergentSignature` — `t` correct + 1 divergent → concludes on the quorum, ignores the minority (no error). - `TestSigningDoneCheck_OversizedSplitBelowQuorumTimesOut` — 2+2 split, no bucket reaches `t` → times out. Validated: build+vet across default / `frost_roast_retry` / `frost_native frost_roast_retry` / CGO; the done-check + signing-loop + roast-transition tests with `-race`; gofmt clean. The `signingDoneCheckStrategy` interface + `mockSigningDoneCheck` are untouched (only the constructor signature changed). 🤖 Generated with [Claude Code](https://claude.com/claude-code)
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What
RFC-21 Phase 7.3, the runner subset of t-of-included finalize. Today the interactive ROAST signing runner (
pkg/frost/signing/roast_runner_frost_native.go) waits for all included members in round 1 (collectCommitments) and round 2 (collectShares), so one slow or offline member stalls the attempt to its ctx deadline → fail → ROAST retry. This makes an attempt finalize over the firsttresponsive committers.Roles (decided by the package's signed
signer_ids, PR1's field #4092)collectCommitmentscollects until exactlyt(its own commitment seeded), proceeds the instantthave arrived, and builds the FROST package over thatt-subset. It setssigner_ids(ascending, distinct) insignSigningPackageto the chosen members. If fewer thantever commit, the ctx deadline fires and the run fails into the existing retry path.signer_ids) — runs round 2 and collects round-2 shares from the package's signer set, not the full included set.signer_ids) — does not run round 2. It aggregates the subset's broadcast shares publicly,MarkSucceeded, and returns the signature — and still aborts the engine session on success to drop its unconsumed round-1 nonces. The success path previously suppressed the abort, which leaked an observer's nonces; fixed via asignedRound2flag.A round-2-silent member among the chosen
tstill fails the attempt → retry (existing path). Only the elected coordinator builds the package, so there is no honest divergence (receivers already filtersender==elected+ attempt hash). The FROSTSigningPackageBytesremains the cryptographic source of truth, so a coordinator that lies insigner_idscauses only a liveness failure (aggregate fails closed), never a wrong signature or false blame.Inert until oversizing (MacLane's policy knob)
t-of-included is dormant until participant selection oversizes the included set past the threshold — it currently trims to exactly
honestThreshold(signing_loop_legacy_selector.go:91), so the chosen subset equals the full included set and every member signs (today's behavior). The machinery is harmless and inert until then.Hardening
The runner constructor now rejects
threshold > len(includedSet)— the new round-1 loop's termination invariant (a well-formed attempt always selects ≥ threshold members; fail fast rather than silently degrade into timeout-driven retries). Found by the inline adversarial review.Tests (all
frost_native, behind pre-prod tags)buildInteractiveSigningHarnesswithrunMembersto drive silence (a non-responsive member).FinalizesOverResponsiveThresholdSubset— a non-coordinator offline member is excluded; the two responsive members finalize overt; the coordinator's package omits the offline member.OversizedAllOnline_FinalizesOverThreshold— all online; exactlytsign (round-2 count),n−tobserve and abort their nonces, all reach Succeeded; the broadcast package carries exactlytascending signer ids.ObserverAggregatesAndAbortsWithoutSigning— focused observer: aggregates, Succeeded, 0 round-2 calls, 1 abort.UsesEngineDerivedFrostIdentifiersretargeted to a full-included (n==t) attempt for determinism.Validated: build+vet+test across the 5 tag combos (default /
frost_native/frost_roast_retry/frost_native frost_roast_retry/frost_native frost_tbtc_signerw/ CGO),-raceonpkg/frost/signing, thefrost_roast_retrydrive tests, repo-widefrost_nativevet,pkg/tbtcbuild, and gofmt — all clean.Follow-up (PR3, lands with/right after this)
signingDoneCheck(pkg/tbtc/signing_done.go:93, called fromsigning_loop.go:458) setsexpectedSignersCount = len(attemptMembersIndexes); once oversizing is enabled, a successful attempt that omitted an offline member would hang the outer done-check. PR3 makes it threshold/package-set aware.🤖 Generated with Claude Code