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Covenant parameter struct, an output-pinning helper covering both the P2TR and sub-dust OP_RETURN forms, an asset-lookup helper, the purchase covenant builder, and the four-leaf taptree assembler. Compiles clean under go vet. The covenants have never been executed: the integration suite shells out to the nigiri CLI for funding and block generation, which is unavailable here, so the purchase subtest remains a deliberate t.Fatal placeholder. Design: docs/superpowers/specs/2026-09-07-dust-free-transfer-covenant-design.md
Adds the recycle and refund covenant builders alongside purchase, a contract assembler that derives all three scripts and the four-leaf taptree from one parameter set, and the asset-packet helpers for issuance, merge and the shorted-amount rejection case. Covers both claim paths (receiver with and without a prior balance of the asset), the shared refund covenant under both its leaves, the bitcoin-payload variant, and five rejection cases. Two notes on what is and is not covered: Leaf 3 asserts the covenant only. The sender's signature is enforced by the tapscript closure, not by the arkade script, so both refund leaves execute the same covenant and are asserted identically. A foreign AssetID is deliberately not tested as a rejection case. The pinned lookup misses on every read, a miss returns (0, 0), and the sum clause degenerates to 0 == 0 + 0 -- so the covenant passes and arkd's asset-balance validation is what rejects the spend. The covenant-level case shorts the pinned asset's amount instead. Compiles under go vet and gofmt. Not executed: the suite drives regtest through the nigiri CLI, which is unavailable in this environment.
Moves the covenant builders out of the _test file into an importable test/covenant package and adds tests that drive them straight through arkade.NewEngine with a synthetic transaction. No arkd, emulator, regtest or nigiri: 21 subtests, about a second. This exists because TestMain in package test calls generateBlock() via the nigiri CLI and log.Fatalf's on failure, so every test in that package dies at startup where nigiri is unavailable. Splitting the builders out also gives a future operator service something to consume rather than reimplementing the scripts. Two defects surfaced by actually executing the covenants: OP_INSPECTINPUTSCRIPTPUBKEY reads FetchVtxoPrevOutPkScript, not FetchPrevOutput. A stub returning nil for it made the recycle covenant abort at its third instruction, so every rejection test passed without reaching the condition it claimed to test. Rejection tests now assert the error code and require an eval-false or verify-family failure. The foreign-AssetID case is not a covenant-level rejection and is recorded as such: the pinned lookup misses on all three reads, a miss returns (0, 0), and the clause degenerates to 0 == 0 + 0. Only arkd's asset-balance validation rejects that spend. Verified: go test ./test/covenant/ -count=1 passes; removing the numInputs guard makes reject_extra_input fail, confirming the guard carries the test. The live-stack test remains unexecuted.
A lookup miss returns (0, 0) -- amount and flag. Dropping the flag on every read meant a wrong AssetID missed everywhere, degenerating the sum clause to 0 == 0 + 0, so the covenant passed with the asset constraint silently unenforced. That covered both a deliberate substitution and an accidental byte-order slip on asset_txid. The flag is now OP_VERIFY'd where the asset must exist (the receiver's merged output, the covenant's own input) and dropped only for the receiver's prior balance, which may legitimately be zero -- the case that lets one script serve receivers with and without a holding. This inverts the severity of the byte-order trap. HTLC v3 records it as producing a silently unspendable contract, which is loud and safe; with a dropped flag it instead produced a vacuously-true asset clause, which is quiet and unsafe. Adds reject_foreign_asset_id and reject_reversed_asset_txid, and makes the test asset_txid non-palindromic so reversing it is meaningful. Verified: go test ./test/covenant/ -count=1 passes; disabling the flag verification makes both new tests accept a spend they must reject.
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WalkthroughThe changes add dust covenant scripts and test asset and Bitcoin purchase, recycle, refund, recovery, output pinning, balance conservation, and locktime flows through direct-engine and emulator tests. ChangesDust covenant flow
Estimated code review effort: 4 (Complex) | ~60 minutes Sequence Diagram(s)sequenceDiagram
participant CovenantTest
participant ReceiverWallet
participant Emulator
participant Indexer
CovenantTest->>ReceiverWallet: sign account and covenant inputs
ReceiverWallet->>Emulator: submit covenant spend
Emulator->>Indexer: register resulting outputs
Indexer-->>CovenantTest: expose accepted or rejected result
Suggested reviewers: Merge Risk: ⚪ Minimal · up to
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In `@test/covenant/covenant.go`:
- Around line 274-279: Update Params.Validate to reject Locktime values less
than or equal to zero, while preserving validation for valid positive locktimes
and the existing Build/VtxoScript behavior.
In `@test/dust_covenant_test.go`:
- Line 375: Update the test around submitToEmulator to assert the wrapped
txscript error has code ErrUnsatisfiedLockTime, rather than relying only on
require.Error, while retaining the gRPC rejection check as an additional
assertion if needed. Use the existing executeArkadeScripts error path and
covenant.LeafRecovery setup.
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📒 Files selected for processing (3)
test/covenant/covenant.gotest/covenant/covenant_test.gotest/dust_covenant_test.go
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Three fixes, two from the first CI run and one from review. The claim and refund transactions built their asset packet from the lockup txid. An asset's canonical AssetID is its issuance txid for the asset's whole life and does not change when the asset moves, so the covenant's pinned lookup missed and OP_VERIFY failed. Worth noting the found-flag verification added in the previous commit is what turned this into a loud failure; with the flag dropped it would have passed with the asset clause vacuous. The mint put the sender's share in its own output, but that output uses the same script buildWalletFundedTx sends change to. Two outputs with that script made findTaprootOutput resolve the wrong index on the next call and fail utils_test.go:560. The sender's share now rides on the change output, so only one output ever carries that script, and the lockup returns its balance as fresh change rather than burning it as fee. Params.Validate now rejects a zero Locktime, which would otherwise be always satisfied and make the recovery leaf spendable the moment the covenant is funded. recovery/rejected_before_locktime now asserts the covenant accepts before asserting the submission fails, isolating the rejection to the CLTV closure instead of passing for any unrelated reason.
The second CI run cleared the AssetID and output-index failures and surfaced the next layer: VTXO_ALREADY_SPENT and VTXO_NOT_FOUND. submitWithArkd submits straight to arkd, so the SDK's ListVtxos never observes the spend. buildWalletFundedTx picks its funding input from exactly that stale list, so every subtest after the first was handed a VTXO the previous subtest had already consumed. This is why the existing asset-account prototype calls buildWalletFundedTx once and threads inputs explicitly from there. Resolves the sender's account once via findAccountInput and threads it by hand. Every funding transaction now uses one layout -- receiver account, sender account holding the asset, sender change -- and re-points the tracked VTXO at its change output. Also puts the sender's asset on a dedicated dust output rather than on the change, so successive mints do not inherit unaccounted units from the previous asset, and lets the lockup spend that account whole. The sender's bitcoin commitment is then exactly one dust unit with no change, matching the prototype's phase 1.
The third CI run cleared the stale-vtxo failures and left a race: purchase passed end to end, every later subtest failed with VTXO_NOT_FOUND. arkd registers new VTXOs asynchronously, so spending one immediately after submitting the transaction that created it can lose the race. purchase won it; the rest did not. Uses the existing watchForPreconfirmedVtxos helper, which opens an indexer subscription before submission and blocks until the wanted outputs appear. The subscription must be opened after the outputs are final, since it reads their scriptPubKeys, and before submitting, or the event is missed.
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Tests-only PR (no emulator changes), but it contains three real bug fixes discovered during authorship, so this review treats those as findings in their own right. The rest is coverage and design commentary.
Bug fixes confirmed correct
FetchVtxoPrevOutPkScript was never delegated in test fetchers.
OP_INSPECTINPUTSCRIPTPUBKEY reads FetchVtxoPrevOutPkScript (pkg/arkade/opcode.go:2128), not FetchPrevOutput. The fix at test/covenant/covenant_test.go:336-342 correctly delegates to FetchPrevOutput, so input-inspecting rejection tests now reach the condition they claim to test. The requireRejected error-code allowlist (ErrEvalFalse, ErrVerify, ErrEqualVerify, ErrNumEqualVerify) correctly rejects aborts-before-condition: test/covenant/covenant_test.go:432-440. Good design.
Found-flag dropped everywhere made wrong AssetID pass vacuously.
appendAssetLookup (test/covenant/covenant.go:131-144) now calls OP_VERIFY on the flag wherever the asset must exist, and OP_DROP only for the receiver's prior balance (which may legitimately miss). The mutation tests reject_foreign_asset_id and reject_reversed_asset_txid in TestRecycle (test/covenant/covenant_test.go:574-595) confirm the fix is load-bearing. The non-palindromic txid construction at line 449-452 is a nice touch — reversing it produces a genuinely different value so the byte-order test has content.
Integration test was pinning lockup txid as AssetID.
The canonical AssetID for an asset is its issuance txid for life. Using the lockup txid as the group's AssetId would have caused OP_VERIFY to fail loudly (exactly because the found-flag was now hardened). The comment at test/dust_covenant_test.go:1037-1038 records this for future readers.
Findings requiring changes
1. TestPurchase is missing asset-constraint rejection tests
test/covenant/covenant_test.go:598-627
BuildPurchase enforces out[0].assetAmount == in[0].assetAmount via the same appendAssetLookup(required=true) pattern as BuildRecycle. The found-flag bug was the critical fix. TestPurchase has three subtests (valid, wrong value, wrong receiver) but none that exercise the asset constraint — no reject_foreign_asset_id, no reject_reversed_asset_txid, no reject_asset_amount_shorted. Given that the silent-pass mode was the exact failure mode this PR fixes, those paths should be covered explicitly for every script that uses the constraint. The code path is identical to recycle so the risk of an undetected regression here is lower, but the cost of adding the tests is negligible.
2. TestRefund is missing asset-constraint rejection tests
test/covenant/covenant_test.go:631-667
Same gap as above. BuildRefund enforces out[1].assetAmount == in[0].assetAmount. No rejection tests exist for a foreign asset ID or a shorted amount. The refund is a critical path (it's the operator and sender's recovery route), so this should be covered.
3. No unit test for the bitcoin-variant refund path
TestBitcoinVariant at test/covenant/covenant_test.go:671-705 covers only BuildRecycle with p.AssetID == nil. BuildRefund in bitcoin mode (no asset clauses) is untested. The sub-dust pinning logic for the refund outputs matters for that path too.
Design observations (no change required, but worth a decision)
BuildPurchase does not pin numInputs
test/covenant/covenant.go:195-210
BuildRecycle explicitly checks OP_INSPECTNUMINPUTS == 2 to prevent value inflation through extra inputs. BuildPurchase only pins the current input index to 0 and checks that out[0].value == in[0].value. An extra input doesn't let an attacker steal from the covenant (the output value is fixed), but the asymmetry is worth documenting so a future reader doesn't wonder if it was an oversight. If arkd's validation ensures value conservation over all outputs, the lack of a guard is safe; if there's any path where extra outputs could absorb unchecked sats, it matters. A comment in BuildPurchase stating the intent would resolve this.
Shared refund script between LeafRefundSender and LeafRecovery
test/covenant/covenant.go:280-291
The PR documents this: a pure-asset refund costs the operator one vtxoMinAmount because the shared script must pay the sender a standalone sub-dust output. Understood as a deliberate v1 trade. Worth tracking as a known inefficiency when splitting leaves in v2.
Package location test/covenant
Happy to defer to author's judgment. Keeping it under test/ avoids implying a supported API; pkg/covenant would be cleaner Go layout but raises the maintenance commitment. The current approach is a reasonable call for a first version.
Mechanics look correct
- Value conservation in
recycle:out[1].value == in[0].value + in[1].value - Topupandout[0].value == Topupare checked independently, soout[0] + out[1] == in[0] + in[1]holds. ✓ - Sub-dust pinning in
pinOutput: sha256 of the fullOP_RETURNscript is pushed (sincepushScriptPubKeyreports non-witness-program scripts as(sha256, -1)). Consistent with how the emulator surfaces that opcode. ✓ - Taptree leaf order is frozen by comment at
test/covenant/covenant.go:27-33. The order determines the merkle root and therefore the output address, so this is the right place to enforce it. ✓ - Integration test
senderFundingthreading: The closure variable is updated insidefundAccountsand is read sequentially (not.Parallel()in subtests). No race. ✓ lockupuses vin 0 for the asset packet (test/dust_covenant_test.go:999-1001, comment explains the vin-vs-output-index distinction). ✓mergePacketomits vin 1 whenpriorUnits == 0(test/dust_covenant_test.go:848-850), exercising the lookup-miss path in the emulator withrequired=false. Matches the covenant's intent. ✓recovery/rejected_before_locktimeasserts covenant acceptance before emulator rejection (test/dust_covenant_test.go:1167), which correctly isolates the CLTV closure as the source of rejection rather than the covenant script. Good test design.- Cross-repo impact: no SDK (ts, go, rust, dotnet) references
test/covenant. No public interface change.
The three findings above (missing rejection tests for purchase and refund asset constraints, and missing bitcoin-variant refund test) are the only blockers. The core design and the bug fixes are sound.
Two causes behind the fourth CI run, which failed with an invalid checkpoint signature and then a cascade of VTXO_ALREADY_SPENT. Sighash commits to the prevout amount, and the wallet resolves an input by script, so two outputs sharing a script in one transaction make it sign for the wrong amount. The funding transaction had the sender's dust account and the sender's change on the same script, since that is the only script the sender's wallet can sign; spending the change signed for the dust output's amount instead. purchase passed only because its lockup spends the first of the two, so the lookup happened to be right. Funding now comes from a separate identity, giving every output in a funding transaction a distinct script. This is the same defect as the findTaprootOutput failure two commits ago, in a different consumer -- never put two outputs with one script in a transaction. The merge claims also spend the receiver's own account, which needs the receiver's signature on both the arkade transaction and its checkpoints; the emulator supplies only the covenant input's. They now sign the way the asset-account prototype's phase 3 does. Covenant-only spends are unchanged, which is why purchase and recovery were unaffected.
The fifth CI run cleared the invalid checkpoint signature. What remained was the funding transaction after the first: submitWithArkd succeeded and its input was spent, but the vtxo subscription reported got 0/3 and timed out, and every later subtest then reused the stale input and saw VTXO_ALREADY_SPENT. The transaction was accepted, so the outputs existed and the subscription simply did not deliver. Each funding transaction opened a fresh subscription over scripts an earlier subscription had already registered and then removed on cleanup. Rather than depend on that behaviour, wait by polling the indexer for the transaction itself, which is the same call findAccountInput already relies on. Also emits asset outputs in vout order. Ranging the amounts map directly left the order to Go's randomised map iteration, so a packet with more than one output could differ between runs -- latent rather than the cause here, since the failing case was reproducible.
The sixth CI run showed the previous wait checked the wrong condition. GetVirtualTxs returns a transaction before arkd has registered its outputs as spendable, so the funding transaction was confirmed indexed and the lockup that spent one of its outputs still failed with VTXO_NOT_FOUND. Polls GetVtxos for the specific outpoints instead, requiring each to be present and unspent, which is the condition the next spend actually depends on. Also corrects the lockup's wait to its single output, and takes indexer and types from arkd/pkg/client-lib, which is where this tree gets them.
Addresses the three findings in arkana-ai-bot's review. Purchase and refund enforce the asset constraint with the same required-lookup pattern as recycle, but only recycle had rejection tests for it. Since a silently unenforced asset clause is the exact defect this design fixes, every script that enforces it now covers a foreign AssetID, a reversed asset_txid, and a shorted amount. Adds TestBitcoinVariantRefund. The refund path with no asset drops the asset clauses and still has to pin both sub-dust payouts, which TestRefund cannot reach because it runs with an asset. Also records why BuildPurchase does not pin the input count, which the review flagged as an unexplained asymmetry with BuildRecycle: purchase reads only in[0] and ties out[0] to it, so an extra input flows to the spender's own outputs and cannot divert the covenant. 30 subtests, up from 21. Mutation-checked: disabling the found-flag verification makes all six foreign-id and reversed-txid tests accept spends they must reject.
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Thanks — all three findings addressed in fe57a51. 1 & 2. Missing asset-constraint rejection tests on purchase and refund. Fair, and the reasoning is the one I should have applied myself: a silently unenforced asset clause is the precise defect this PR fixes, so every script enforcing it needs the coverage, not just the one where I happened to find the bug. Both now have 3. Bitcoin-variant refund untested. Added 30 subtests now, up from 21. All six new flag-dependent tests are mutation-checked — disabling the On On the shared refund script and One correction to the review's mechanics section, since it may matter to a later reader. It says the integration test's |
Seven runs in, the integration failure reduces to one reproducible difference. A funding transaction that spends a settled VTXO succeeds every time -- purchase has passed since run 3. A funding transaction that spends the previous funder's change, an output of an earlier arkade transaction, fails with an invalid signature in its checkpoint. The lockup spending the sender's dust account, also an arkade transaction output, succeeds, so it is the chaining that matters rather than the output's provenance. Why the chained case fails sits inside checkpoint construction and is not visible from the test side. Rather than keep guessing at it across ten minute CI cycles, this follows the pattern the suite demonstrably supports: the asset-account prototype also funds once and only ever spends that transaction's first output. Each fundAccounts call now settles its own funder and its change is never reused, which also removes the cross-subtest coupling behind the failures in runs 2 through 7.
The per-call funder took the integration test from one passing subtest to three: purchase and both recovery paths now pass end to end. The three that remain all use recycle, and two of them fail locally with "previous output not found" before any submission. PrevArkTxField is not set automatically. executeArkadeScripts and the emulator skip inputs that lack it, so FetchVtxoPrevOutPkScript returns nil and OP_INSPECTINPUTSCRIPTPUBKEY cannot resolve the input it inspects. cross_input_script_validation_test.go:345-346 sets it on both inputs for exactly this reason. This explains the failing set precisely. Recycle is the only covenant that inspects a second input; purchase reads input values instead, which resolve through FetchPrevOutput and the PSBT's witness UTXO, which is why it has been passing. recycle/receiver_holds_prior_balance also fails earlier, with an invalid checkpoint signature on its funding transaction. That one is not yet explained and is unaffected by this change.
Run nine reached five of six subtests passing. The one that remains, recycle/receiver_holds_prior_balance, differs from the passing receiver_holds_zero in exactly one way: its issuance packet has two asset outputs rather than one, and its funding transaction then fails to finalize with an invalid checkpoint signature. ark-lib places no limit on issuance output count, and multi-output transfers demonstrably work -- the asset-account prototype's routing packet splits across three outputs and that test is green on master. So this restructures around the shape already known to work rather than around a rule. The funding transaction now issues everything to a single output, the sender's account, funded with two dust units. The lockup splits that account into the covenant and the receiver's account in one transfer, which is also where the receiver's prior balance now comes from. Both dust units still come from the funder, so the sender's own bitcoin commitment is unchanged. Recycle's second input is consequently an output of the lockup rather than of the funding transaction, so both its inputs share one previous arkade transaction.
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CI is fully green as of c4e8288 — including all six integration subtests. @arkana-ai-bot the three findings from your review are addressed in fe57a51 and answered above; re-review welcome now that the branch is green. The last integration failure turned out to be a two-output issuance making the funding transaction fail to finalize with an invalid checkpoint signature. I have added a section to the PR description recording the non-obvious constraints this took several iterations to find — same-script outputs breaking signing, |
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Code Review — dust-free transfer covenant (PR #150)
Tests-only PR adding the dust-free transfer covenant: test/covenant/covenant.go (script builders), test/covenant/covenant_test.go (engine-level unit tests), and test/dust_covenant_test.go (live stack integration tests). No emulator code changes. Total diff: 1422 lines.
I re-derived everything from first principles as requested.
Protocol correctness — script algebra
BuildRecycle (covenant.go:161)
Value constraint: out[1].value == in[0].value + in[1].value − Topup. Traced through the OP_ADD / OP_SUB ordering — correct. Script pins in[1]'s scriptPubKey against ReceiverKey before using its value, preventing substitution.
Asset constraint in BuildRecycle (covenant.go:184–188)
appendAssetLookup(1, AssetID, output=true, required=true) // out[1] amount, flag OP_VERIFY'd
appendAssetLookup(0, AssetID, output=false, required=true) // in[0] amount, flag OP_VERIFY'd
appendAssetLookup(1, AssetID, output=false, required=false) // in[1] amount, flag OP_DROP'd
OP_ADD OP_EQUAL
Stack trace confirmed correct: out1_asset == in0_asset + in1_asset, with in1_asset = 0 on a lookup miss (receiver holds zero). The distinction between required=true (OP_VERIFY) and required=false (OP_DROP) on the receiver's prior balance is the key security invariant, and the PR's mutation-test argument — that disabling either OP_VERIFY causes rejections to pass vacuously — is sound.
BuildPurchase (covenant.go:200): out[0].asset == in[0].asset. Correct. The absence of a numInputs guard is deliberate and justified in the comment: in[0]'s value and asset amount fully constrain out[0], and extra inputs can only contribute to the spender's own outputs.
BuildRefund (covenant.go:222): out[1].asset == in[0].asset. Both operator and sender outputs are pinned by script and value. Sub-dust pinning via SHA256(raw script) is the correct path through pushScriptPubKey (opcode.go:2099–2104); confirmed against the -1 version sentinel.
popAssetID stack ordering (asset_opcodes.go:631): pops gidx then txid then idx; appendAssetLookup pushes idx / txid / Index in that order, so Index is on top — alignment confirmed.
Locktime zero guard (covenant.go:69): correct. A zero CLTV is always satisfied and would make LeafRecovery spendable at funding time.
RefundTopup boundary (covenant.go:82): when Topup == Dust, returns Dust − vtxoMinAmount; otherwise returns Topup unchanged. Correct in both directions.
Must-fix findings
M1 — LeafRefundSender has no integration test
test/dust_covenant_test.go covers LeafPurchase, LeafRecycle (×2), and LeafRecovery (×2). LeafRefundSender (covenant.go:287–289) — the 3-key path Multisig[server, sender, tweak(Refund)] — is exercised only at the script level in TestRefund. The end-to-end flow (sender signs, emulator signs, arkd validates, asset goes to sender's sub-dust output) is never exercised. A broken receiverWallet→senderWallet substitution, a PSBT field ordering issue, or an arkd asset-balance rejection specific to that closure structure would not be caught by the existing suite.
M2 — ForfeitClosures() returns all four leaves for this VTXO
arkd/pkg/ark-lib/script/vtxo_script.go:204–213 includes every MultisigClosure and CLTVMultisigClosure as a forfeit candidate. The covenant's taptree has four such closures, so forfeitClosures[0] (used by createAndSignForfeits, utils_test.go:298) resolves to Multisig[server, tweak(Recycle)]. A forfeit transaction built against that leaf carries outputs that do not satisfy the recycle covenant (wrong input count, wrong output addresses), meaning the emulator cannot sign a forfeit for this VTXO via the standard path. If the batch containing the lockup output reaches its sweep deadline before the receiver claims, the forfeit would fail. Please document the expected lifecycle — either that covenant VTXOs are always spent before batch expiry, or that the server handles them specially.
M3 — dustCovenantVtxoMinAmount = 1 is hardcoded and unvalidated
dust_covenant_test.go:888 hardcodes vtxoMinAmount = 1 with the comment "Not exposed by GetInfo." This value is passed directly to covenant.Build and p.RefundTopup; if the running emulator is configured differently, RefundTopup produces the wrong threshold, the covenant is built with wrong scripts, and the integration tests pass against a covenant that the production system would reject (or vice versa). At minimum, add a test assertion that the value matches expected behaviour, or expose it via GetInfo.
Should-fix findings
S1 — No bitcoin-mode purchase unit test
TestBitcoinVariant (covenant_test.go:779) exercises recycle-only. BuildPurchase with AssetID == nil terminates via finish(b, false) → OP_1; this code path is never executed in the test suite. It is simple and the asset-free recycle tests provide indirect confidence, but a two-line "valid" + "reject wrong value" case would close the gap.
S2 — No duplicate-key guard in Params.Validate
covenant.go:58. If SenderKey == ReceiverKey, refundSender allows the sender to route the asset back to themselves via a path that also requires their own signature — semantically that is fine, but ReceiverKey == OperatorKey would allow the operator to claim recycle output whilst also collecting the Topup repayment from themselves. No signature scheme catches this at script time. Recommend adding ReceiverKey != SenderKey && SenderKey != OperatorKey && ReceiverKey != OperatorKey checks (or at minimum documenting it as a caller precondition).
S3 — recovery leaf still requires server; "permissionless" is misleading
PR description says "permissionless after timeout." The closure is CLTVMultisigClosure{MultisigClosure{server, tweak(Refund)}, Locktime} — the server signature is required. The leaf is only sender-permissionless. Worth correcting in the PR description and any future doc reference to avoid an operator misunderstanding their exposure during server downtime.
Observations / no action required
O1 — requireRejected error-code filter (covenant_test.go:436–444): correctly distinguishes semantic covenant rejection (ErrEvalFalse, ErrVerify, ErrEqualVerify, ErrNumEqualVerify) from harness or stack errors that would give false-green rejection tests. Good design; the PR description's account of the OP_INSPECTINPUTSCRIPTPUBKEY / FetchVtxoPrevOutPkScript split matches what I see in opcode.go:2128.
O2 — assetID is intentionally non-palindromic (covenant_test.go:453): the byte-order trap test depends on this. Good.
O3 — recycle pins numInputs == 2 (covenant.go:164): noted as deliberate in PR description. Tested in reject_extra_input. Accepted as-is for a first version.
O4 — Leaf ordering fixes the merkle root (covenant.go:27): comment is correct and important; no action needed beyond the comment.
O5 — key(t, seed byte) uses buf[31] = seed (covenant_test.go:349): generates deterministic but structurally valid private keys. Fine for a test harness.
O6 — setPrevArkTxs(t, claimTx, lockTx, lockTx) (dust_covenant_test.go:1307): both inputs come from lockTx, so passing it twice is correct.
O7 — recovery/rejected_before_locktime with locktime − 1 = 499_999_999: both values are past unix timestamps; the test is testing the tx.nLockTime < CLTV_value comparison semantics, which is correct regardless of wall-clock time. Structure is sound.
Cross-repo impact
The new test/covenant package is not imported by any other repo (confirmed via grep across go-sdk, ts-sdk, rust-sdk, dotnet-sdk, arkd). No public API changes.
Summary
The script algebra is correct; the found-flag OP_VERIFY treatment is the critical invariant and it is properly tested with mutation checks. The three mandatory items above — missing integration test for LeafRefundSender (M1), the forfeit-closure incompatibility (M2), and the hardcoded vtxoMinAmount (M3) — need resolution before merge. M2 in particular touches protocol-level VTXO lifecycle.
Addresses the second arkana-ai-bot review. M1: LeafRefundSender had no integration coverage. It shares the refund covenant with LeafRecovery but not its closure, and it is the only leaf carrying a human key, so the end-to-end path -- sender signs the arkade transaction and its checkpoints, emulator signs, arkd accepts -- was never exercised. Added, with the sender signing the way the asset-account prototype's merge does. M3: the hardcoded vtxoMinAmount is now asserted rather than assumed. The refund reserves exactly that many sats for the sender's returned payload, so arkd accepting the recovery transaction is what validates the constant; a higher configured minimum would reject it. S1: BuildPurchase in bitcoin mode terminates through the asset-free branch, which no test reached -- the bitcoin recycle tests exercise a different script. Added valid and two rejection cases. S2: Params.Validate now requires the three keys to be distinct. Receiver equal to operator is the dangerous collapse: the operator could satisfy recycle while paying the top-up repayment to itself, collecting both sides. No signature check catches that, since each role's key is legitimately its own. 38 subtests in test/covenant, up from 30.
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Thanks — this is a much more useful review than the first, and the re-derivation of the script algebra is appreciated. All six addressed, in ad32d21 for the code and in the design doc for the two that are not code. M1 — M3 — hardcoded S1 — no bitcoin-mode purchase test. Added. You are right that the asset-free branch of S2 — no duplicate-key guard. Good catch, and the receiver-equals-operator case is the sharp one: the operator could satisfy S3 — "permissionless" is misleading. You are right and this was my error, repeated in the PR description, the design doc, and the commit messages. The closure is M2 — forfeit closure incompatibility. Confirmed, and I agree it is the most serious of the three because it is protocol-level rather than test-level. I have not fixed it, because I do not think it is fixable inside a tests-only PR, and the choice is not mine to make unilaterally. It is now recorded in the design doc's open questions with the three candidate resolutions: covenant VTXOs are guaranteed spent before batch expiry (which makes Happy to open a separate issue for M2 if that is the better home for it. |
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Status: Stale synchronize event — aaf9833 is an ancestor of my last checkpoint c4e8288; the diff c4e8288...aaf9833 contains 0 file changes. Actual PR HEAD is ad32d21 (+109 lines, 3 files). I'm closing the loop on my prior 6 findings using ad32d21 and the author's responses. 5 of 6 are resolved; M2 (forfeit lifecycle) remains open.
Prior-findings closure
M1 — LeafRefundSender had no integration test.
Fixed in ad32d21. refund/sender_signed subtest added in test/dust_covenant_test.go:519–560 with the dedicated submitSenderSigned helper. The sender wallet signs both the arkade transaction and its checkpoints before emulator.SubmitTx adds the server signature — matching the Multisig[server, sender, tweak(Refund)] closure. executeArkadeScripts is called before submission so script-level correctness is also verified. Coverage is complete.
M2 — ForfeitClosures() returns all four leaves; forfeiting the covenant VTXO via the standard path fails.
Still open. The author confirmed the diagnosis and documented three candidate resolutions in the design doc, but no code change was made and no tracking issue has been opened. The protocol gap is real: if a batch containing a covenant VTXO sweeps before the receiver claims, the emulator's forfeit builder selects forfeitClosures[0] = Multisig[server, ⊕recycle], builds a forfeit that cannot satisfy the recycle covenant (wrong input count, wrong output addresses), and the batch cannot be safely closed. This bounds the exposure not just by L but by the server being live and monitoring — a fact now noted in the design doc but not surfaced to the operator at runtime.
This is the only remaining blocker. A tests-only PR cannot resolve the underlying mechanism, but it can carry a concrete forcing function: I am requiring a GitHub issue be opened that (a) names the three candidate resolutions, (b) identifies which is chosen or explicitly defers the decision, and (c) is linked from this PR before merge. A comment in a design doc does not have the same accountability surface as a tracked issue.
M3 — vtxoMinAmount hardcoded and unvalidated.
Fixed in ad32d21 (test/dust_covenant_test.go:515–517). The require.Equal(t, dustCovenantVtxoMinAmount, dust-topup, ...) assertion documents the relationship. Note: this assertion proves a mathematical identity (since topup = RefundTopup(vtxoMinAmount) = dust - vtxoMinAmount when fully funded, dust - topup == vtxoMinAmount is trivially true); the actual live validation is that arkd accepts the recovery transaction with a dust-topup-sat output, which would fail if the emulator is configured differently. The assertion is weaker than it looks but the comment makes the contract clear, and a stronger assertion requires a GetInfo extension that is an arkd change. Accepted as-is.
S1 — No bitcoin-mode purchase unit test.
Fixed in ad32d21 (test/covenant/covenant_test.go:509–532). Three subtests: valid, reject_short_value, reject_wrong_receiver. The asset-free branch of BuildPurchase is now executed.
S2 — No duplicate-key guard in Params.Validate.
Fixed in ad32d21 (test/covenant/covenant.go:63–69). All three key pairings are rejected with a clear error and an explanatory comment. The dangerous collapse — ReceiverKey == OperatorKey lets the operator satisfy recycle while collecting the top-up repayment from itself — is explicitly called out. TestParamsValidation/rejects_reused_keys covers all three pairings.
S3 — "permissionless after timeout" was misleading.
Fixed per author's response (corrected in the design doc; the server signature is still required, so the leaf is sender-permissionless only, not fully permissionless). Not verifiable from code alone; taken on trust.
Incremental review of ad32d21
The three changed files contain only the changes described above; no new concerns from the incremental diff.
One minor observation on refund/sender_signed: it uses lockup(t, mintTx, c, units, 0) (zero prior receiver balance). The case where the receiver already holds a prior balance and the refund path is later taken is untested, but the asset-lookup difference is only in the required=false branch of appendAssetLookup for in[1], which is already covered by the recycle tests. No action needed.
Required before merge
Open a tracking issue (on arkade-os/emulator or arkade-os/arkd, whichever carries forfeit logic) documenting the ForfeitClosures incompatibility for covenant VTXOs. The issue should name the three candidate resolutions from the design doc and record which is chosen or mark the decision as explicitly deferred. Link the issue here. That is the only remaining change requested.
Review pointed out the assertion added for M3 is true by construction: once RefundTopup has been applied, dust-topup == vtxoMinAmount whenever the operator funded the whole dust unit, so the equality can never fail. The comment claimed it validated the constant, which it did not. What actually validates it is arkd accepting the recovery transaction with a dust-topup sat output, which a higher configured minimum would reject. The comment now says that, and the assertion checks the property that is not free: the payload is genuinely sub-dust.
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Tracking issue opened: #151 — It names the three candidate resolutions and records the decision as explicitly deferred, since each has consequences beyond this covenant design and the call is a maintainer's rather than mine. It also generalises the finding: the problem is not specific to this covenant, but applies to any VTXO whose taptree has more than one covenant-gated leaf, so You were also right about M3, and I have corrected it in 49ae96d. The assertion I added was true by construction — once On the observation about That should close out all six findings: five fixed in code, M2 tracked in #151. |
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Catchup from aaf9833 → ad32d21 (+384 net lines, 3 files). 5 of 6 prior findings fixed; M2 tracked in #151 per my earlier requirement. No new blocking issues. PR is clear to merge.
Prior-findings closure
M1 — LeafRefundSender had no integration test.
Fixed in ad32d21. refund/sender_signed subtest at test/dust_covenant_test.go runs executeArkadeScripts before submission (script-level), then submitSenderSigned which has senderWallet.SignTransaction applied before emulator.SubmitTx (closure-level). The Multisig[server, sender, tweak(Refund)] path is now fully covered end-to-end.
M2 — ForfeitClosures() returns all four leaves; forfeiting via the standard path fails.
Still open. Issue #151 is open with the problem stated, the three candidate resolutions recorded, and the decision explicitly marked as deferred. The PR body links #151 under "Known gap: forfeit." My prior review required exactly a tracked issue before merge; that condition is met. The gap is real — if the batch sweeps before the receiver claims, forfeit is unavailable and funds are lost rather than forfeited — but it cannot be resolved in a tests-only PR, and the risk is now surfaced to maintainers with the correct severity.
M3 — dustCovenantVtxoMinAmount hardcoded and unvalidated.
Fixed in ad32d21. The require.Equal(t, dustCovenantVtxoMinAmount, dust-topup, ...) assertion is present in recovery/after_locktime. The comment honestly states "arkd accepting this transaction is what validates the hardcoded vtxoMinAmount" — the assertion proves only the mathematical identity, not the live configuration, and it says so. That is the right level of honesty for a value that can't be fetched from GetInfo.
S1 — No bitcoin-mode purchase unit test.
Fixed in ad32d21. TestBitcoinVariant/purchase exercises the OP_1-terminating branch of BuildPurchase (asset-free path) with valid, reject_short_value, and reject_wrong_receiver cases.
S2 — No duplicate-key guard in Params.Validate.
Fixed in ad32d21. Params.Validate (covenant.go:63–69) rejects all three pairings. The dangerous collapse — ReceiverKey == OperatorKey lets the operator satisfy recycle while collecting both sides — is explicitly called out in the comment. TestParamsValidation/rejects_reused_keys covers all three.
S3 — "permissionless after timeout" was misleading.
Fixed in the design doc per author's response. Not verifiable in code; taken on trust, and the PR description table now reads sender-permissionless for recovery.
Incremental review of aaf9833...ad32d21
test/covenant/covenant.go (+13 lines)
Key-distinctness guard is placed after the nil check and the Topup range check, so p.ReceiverKey.IsEqual(...) is never called on a nil pointer. Switch-case ordering is safe. ✓
BuildPurchase comment is accurate: in[0]'s value and asset amount fully constrain out[0]; an extra input only adds to the spender's own outputs. ✓
test/covenant/covenant_test.go (+154 lines, −5 lines)
reversedAssetID refactoring is clean. The function is now shared across TestRecycle, TestPurchase, and TestRefund, eliminating three copies of the byte-flip loop.
Asset-constraint rejection tests for TestPurchase (reject_foreign_asset_id, reject_reversed_asset_txid, reject_asset_amount_shorted) — each mutates the packet rather than the covenant, which is the correct pattern: it confirms the built-in covenant correctly rejects a malformed spend, not that a malformed covenant fails to build. The requireRejected guard (ErrEvalFalse/ErrVerify/ErrEqualVerify/ErrNumEqualVerify) ensures these are semantic rejections, not harness aborts. ✓
Same three for TestRefund. The refund is the operator's and sender's recovery route; covering the found-flag OP_VERIFY path here is exactly the right extension. ✓
TestBitcoinVariantRefund: p.Topup = dust−payload = 280, vtxoMinAmount = 1, RefundTopup(1) = 280 (since capped = 329 > 280). Both outputs are sub-dust so both go through the SHA256 pinning path. Script trace:
out[0].value == 280EQUALVERIFY ✓pinOutput(0, OperatorKey, 280, 330)→ sub-dust: SHA256(SubDustScript(OperatorKey)) ✓out[1].value == 50EQUALVERIFY ✓pinOutput(1, SenderKey, 50, 330)→ sub-dust ✓finish(b, false)→OP_1✓
reject_p2tr_where_subdust_required correctly exploits the version mismatch: P2TR returns version=1 from OP_INSPECTOUTPUTSCRIPTPUBKEY, covenant pushes -1, EQUALVERIFY fires. ✓
test/dust_covenant_test.go (+217 lines, −70 lines)
issuancePacket sort-before-emit: Go map range order is non-deterministic; fixing this is a genuine correctness fix for multi-output issuance packets. ✓
transferPacket is correctly structured: total = sent + priorUnits, {0: sent, 1: priorUnits}. When priorUnits = 0, the zero-amount entry is skipped, giving {in[0]=sent, out[0]=sent} — drives the required=false lookup-miss path in BuildRecycle. ✓
Per-call fresh funder: each fundAccounts call creates a fresh identity, settles it, and uses it once. No shared funder VTXO to thread. Cross-subtest coupling is eliminated. ✓
awaitSpendable: require.Eventually with 30 s / 250 ms checks for len(res.Vtxos) == len(outpoints) and none spent. Handles partial registration. ✓
setPrevArkTxs(t, claimTx, lockTx, lockTx) in the recycle and bitcoin-variant cases: both inputs come from lockTx, so passing it twice is correct. Without this, OP_INSPECTINPUTSCRIPTPUBKEY on in[1] would call FetchVtxoPrevOutPkScript which returns nil, causing a pre-condition abort that would register as a false-green rejection test. The unit test harness fixed this with its own FetchVtxoPrevOutPkScript delegation; the integration tests now match. ✓
refund/sender_signed: createTransferAssetPacket(t, mintTx.TxHash(), 0, 0, 1, units) sends units to refundTx[1] (the sender's sub-dust output). The canonical AssetID is always the issuance txid, not the lockup txid — mintTx.TxHash() is correct. No locktime is set on the refund tx (unlike recovery/after_locktime), correctly modelling that LeafRefundSender has no CLTV requirement. ✓
receiverAccount input in recycleCase and bitcoin_variant now read from lockTx[1] instead of mintTx[0]/fundTx[0]. This is the correct source after the lockup restructuring — the receiver's account is created in the lockup split, not in the issuance/fund step. ✓
No new findings. The script algebra, asset accounting, sub-dust pinning, and test structure are all sound. M2 is tracked and the PR can merge.
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Status: One commit since my last pass (ad32d21 → 49ae96d). 11 lines changed, one file (test/dust_covenant_test.go). All prior findings remain in their last-reported state; none newly introduced or regressed. PR remains clear to merge.
Prior-findings closure
M1 — LeafRefundSender had no integration test.
Fixed (in ad32d21, refund/sender_signed subtest). Unchanged since my last pass. ✓
M2 — ForfeitClosures() incompatibility for covenant VTXOs.
Still open — protocol-level; tracked in #151. The incremental commit does not touch forfeit logic, and the issue's scope is an arkd/emulator mechanism change, not something this tests-only PR can carry. #151 records the three candidate resolutions and marks the decision explicitly deferred. That satisfies the accountability requirement from my last review. ✓
M3 — vtxoMinAmount hardcoded and assertion overclaimed.
Fixed in 49ae96d. The require.Equal(t, dustCovenantVtxoMinAmount, dust-topup, ...) assertion was tautologically true by construction: once RefundTopup is applied, dust - RefundTopup(...) == vtxoMinAmount is an algebraic identity, so it can never fail. The new assertion — require.Less(t, dust-topup, dust, "sender's payload must be sub-dust") — checks the property that is genuinely non-trivial: the sender's returned payload is sub-dust. This assertion fails if topup <= 0, catching the degenerate case where RefundTopup returns zero and the output would be dust-sized rather than sub-dust. The updated comment correctly states that the live validation of the hardcoded constant is arkd accepting the recovery transaction, not the in-test assertion. Accurate. ✓
S1, S2, S3 — bitcoin-mode purchase test, duplicate-key guard, "permissionless" wording.
Fixed in prior commits; unchanged. ✓
Incremental findings
None. The single-commit diff is a comment and assertion quality fix. No script logic, no protocol behaviour, no test coverage scope, and no cross-repo surface was changed.
Summary
All six findings from my reviews are resolved or tracked. M2 has a linked issue (#151) with an explicit deferral decision. The M3 correction in 49ae96d is accurate and strictly improves test documentation. No blocking issues.
Superseded for current Taxi/carrier work by #159, which contains this entire branch (merge base
49ae96d, 45 commits ahead and none behind at60f7cd43). This PR remains open as a frozen historical reference; its source, base and head are unchanged.Preserve this provenance branch while historical consumers are audited. Current Taxi main switched to compiler artifacts and V2 vectors in Taxi #37, removing the old Go-vector generator and copied fixtures. The separate forfeit-lifecycle issue #151 remains open and is not resolved by superseding this PR.
The original description and validation below are historical.
Adds the covenant scripts and tests for a dust-free transfer: a sender pays an
asset, or a sub-dust amount of bitcoin, without committing a dust unit of their
own. A service operator fronts the dust and an arkade covenant guarantees its
repayment.
Tests only — no changes to the emulator itself.
Why
Arkade already supports sub-dust outputs (
OP_RETURN <xonly>, value in[vtxoMinAmount, dust)), and the SDK routes below-dust sends into themautomatically. Two things stop that from being the answer:
resolveMinAmountssetsvtxoMinAmount = dustAmountwhen unset, making the sub-dust window empty.OP_RETURNis unspendable on-chain, so the receiverholds a VTXO they can never unilaterally exit. The SDK marks these
Swept.So the covenant's job is not "make sub-dust payments possible" — they already
are — but "let a receiver end up with a fully exitable VTXO without the sender
funding the dust."
Shape
Four leaves over three covenant scripts. Leaves 3 and 4 share
refundanddiffer only in closure.
recycleMultisig[server, ⊕recycle]purchaseMultisig[server, ⊕purchase]refundSenderMultisig[server, sender, ⊕refund]recoveryCLTV(L) + Multisig[server, ⊕refund]Leaf 4 needs no party signature once
Lpasses, but the server signature isstill required, as on every leaf. It is sender-permissionless, not
permissionless: the operator's exposure is bounded by
Land by serverliveness, which matters when sizing
L. An earlier revision of this descriptionsaid "permissionless after timeout" — that was wrong.
recycleenforces output value and asset amount as a sum over introspectedinputs rather than as constants, so the receiver's prior balance is irrelevant.
That is the improvement over the
TestAssetAccountCovenantprototype, whoseheader records that it must assume the receiver holds zero. Both cases are
covered end to end.
Deliberately does not use
OP_TUNNEL. It exists on master but not in thedeployed
v0.0.7emulator, so anOP_TUNNELcovenant would compile and thenfail against the emulator actually running.
Testing, in two layers
test/covenant— no stack required. The builders live in an importablepackage rather than a
_testfile, so they can be driven straight througharkade.NewEnginewith synthetic transactions. 38 subtests, about a second.Picked up by
make test, so it runs in theunitjob.test/dust_covenant_test.go— live stack. Covers what the above cannot:that the emulator signs, that arkd accepts, that the CLTV closure rejects a
premature recovery (the covenant does not read locktime; the closure does), and
that the bitcoin accounting holds end to end. All 7 subtests pass, covering
every leaf including
refundSender.Defects found by executing rather than reading
OP_INSPECTINPUTSCRIPTPUBKEYreadsFetchVtxoPrevOutPkScript(
pkg/arkade/opcode.go:2128), notFetchPrevOutput(:2070). A fetcher stubimplementing only the latter aborts every input-inspecting covenant at that
instruction — so every rejection test passed without ever reaching the condition
it claimed to test. Rejection tests now assert the script error code. The same
distinction reappeared in the integration layer:
PrevArkTxFieldmust be set perinput or that opcode cannot resolve the input it inspects.
Dropping the asset lookup's found-flag made the asset constraint optional. A
miss returns
(0, 0)— amount and flag. Dropping the flag everywhere meant awrong
AssetIDmissed on all three reads, the sum degenerated to0 == 0 + 0,and the covenant passed with the asset clause silently unenforced. The flag is
now
OP_VERIFY'd wherever the asset must exist, and dropped only for thereceiver's prior balance, which may legitimately be zero.
This inverts the severity of the byte-order trap the HTLC v3 design records.
There, reversing
asset_txidyields a silently unspendable contract: loud, andsafe. Under a dropped flag the same slip yielded a vacuously true asset clause:
quiet, and unsafe. It also caught a real bug in the integration test on its first
run, which had pinned the lockup txid instead of the issuance txid.
Every flag-dependent rejection test is mutation-checked: disabling the
OP_VERIFYmakes all six accept spends they must reject. Removing thenumInputsguard likewise makesreject_extra_inputfail.Known gap: forfeit — tracked in #151
ForfeitClosures()returns everyMultisig/CLTVclosure in a taptree, so forthis four-leaf tree
forfeitClosures[0]resolves toMultisig[server, ⊕recycle]and a forfeit built against it cannot satisfy the recycle covenant.
This affects none of the four spending paths, which is why every test here
passes without touching it. It bites at batch settlement: if the batch holding
the lockup output sweeps before the VTXO is spent, the forfeit path is
unavailable. That makes
Land the operator's recovery scheduling load-bearingfor fund safety, not merely for recovering the operator's advance.
Not fixable in a tests-only PR. Tracked in #151 with three candidate
resolutions and the decision explicitly deferred to a maintainer.
Notes for whoever writes the next integration test
Several constraints here are not obvious and cost several iterations:
commits to the prevout amount and the wallet resolves inputs by script, taking
the first match, so the second output signs for the wrong amount. This surfaces
as an invalid checkpoint signature, and separately breaks
findTaprootOutput.submitWithArkdbypasses the SDK's wallet, soListVtxosnever sees thespend and
buildWalletFundedTxwill hand back an already-spent input. Call itonce, or thread inputs explicitly.
GetVirtualTxsreturns atransaction before arkd has registered its outputs as spendable.
transaction fail to finalize with an invalid checkpoint signature; multi-output
transfers are fine, and the prototype's routing packet splits across three.
The lockup does the split here instead.
PrevArkTxFieldper input. It is not automatic, and without itOP_INSPECTINPUTSCRIPTPUBKEYcannot resolve the input it inspects.Worth a reviewer's opinion
test/covenantis a non-test package under a testdirectory, which is unusual. It is there so the covenants can be executed
without the
nigiri-dependentTestMainin packagetest, and so an operatorimplementation could consume them.
pkg/covenantwould imply a supportedpublic API that this is not yet. Happy to move it.
vtxoMinAmounton a sender-signed refund of a pure-asset payment, since theshared script must pay the sender a standalone sub-dust output. Splitting them
would let leaf 3 merge into the sender's account instead. Traded for one fewer
script to audit.
recyclepinsnumInputs == 2, so the receiver must merge from exactly oneaccount VTXO. Over-constrained on purpose for a first version.
one case: a foreign
AssetIDis now rejected by the covenant, but the covenantcannot detect an asset silently vanishing — arkd's balance validation does.
Params.Validaterequires the three keys distinct. Receiver equal tooperator would let the operator satisfy
recyclewhile paying the top-uprepayment to itself, collecting both sides, with no signature check to notice.
Design doc is not committed, per repo convention on
docs/superpowers/. Happy topaste it into an issue if useful.