ASSERT_MY_TAPTREE, the cheap identity assert - #60
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The 2026-08-22 amendment, decided by Evan and recorded in the execution plan. Every puzzle spend so far paid 1,300,200 for ASSERT_MY_TAPROOT to re-derive a scriptPubKey that base consensus had already authenticated from the control block. VALIDATION.md changes: - The transaction view's execution identity becomes a triple: tapleaf, merkleRoot, and internalKey, the 32-byte x-only internal key the control block carries. Base consensus authenticates all three during every script-path spend. The view takes the triple as authenticated and derives nothing from it: no rule recomputes the scriptPubKey from the key and root. Rule 3's specifiers read tapleaf and merkleRoot, the self assert family reads internalKey and merkleRoot, and no specifier reads internalKey. Decision 26's decline of internal-key addressing stands for counterparts, where the control block proves no possession. A self assert over the spending input's own key claims no possession: it pins which tweak preimage the coin's scriptPubKey was built from. - Invariants: the lone-self-assert bullet covers multi-operand asserts, ASSERT_MY_TAPTREE's outcome is unchanged by the spent scriptPubKey, and on an input whose scriptPubKey is the taproot output of its identity (every input base consensus admits) ASSERT_MY_TAPTREE and ASSERT_MY_TAPROOT over equal operands produce identical outcomes, modulo a tweak collision. CONDITIONS.md changes: ASSERT_MY_TAPTREE at 0x38, the next code after the taproot assert, 0x34 to 0x36 staying the recorded decline gap. Two 32-byte atom operands, the internal key width-checked only (the view's key always lifts, so a non-point operand never matches and fails as unsatisfied, the same treatment the signature asserts give a pubkey operand), the merkle root never empty (the rule 3 operand's domain, the one parse-level difference from ASSERT_MY_TAPROOT). One condition over both fields rather than two single-field asserts: the pair is one fact, the tweak preimage, and mirroring ASSERT_MY_TAPROOT operand for operand makes a puzzle's adoption an opcode swap. Cost CONDITION_GENERIC_COST, stage 2, error unsatisfied_taptree_assert. The family preamble counts six conditions and states the internal key's content class. COSTS.md section 10: one sentence stating why the new assert charges the generic constant alone.
Implements the spec commit. ASSERT_MY_TAPTREE parses as two width-checked 32-byte atoms, the internal key then the merkle root, at CONDITION_GENERIC_COST. The internal key is not lifted: the field it is compared against always lifts, so a non-point operand fails as unsatisfied, the treatment the signature asserts give a pubkey operand. The root is never empty, the one parse-level difference from ASSERT_MY_TAPROOT. The transaction model's TxInput gains internal_key beside tapleaf and merkle_root, and the construction rule requires all three on a condition-carrying input. The model takes the triple as consensus-authenticated and never re-derives the scriptPubKey. check_self_asserts compares both operands against the carrying input's fields, raising the new unsatisfied_taptree_assert with both demanded and carried values in the message. Tooling follows: the runner's context loader accepts internal_key and the target input must carry the triple, the compiler's condition vocabulary gains the name (a reserved name, the same deliberate source-compatibility break every prior addition made), and the vector runner renders the parsed condition as its two operands with nothing derived.
Mechanical sweep, the spec commit authorizes every change: each of the 415 condition-carrying inputs in the validation corpus gains the now-required internal_key. The 82 honest puzzle instances in the vault and singleton files carry the NUMS point both puzzles curry, chosen by a checkable rule (the input's scriptPubKey equals the tweak of NUMS by its merkle root), the family suites and the two hostile foreign-script inputs carry fixed filler no case reads. Every pinned program, conditions payload, and signature is byte-identical to before. New conditions cases pin the parse surface: both operands at exactly 32 bytes, the empty root rejected (the one parse-level difference from ASSERT_MY_TAPROOT), a key that lifts to no curve point parsing (the width-only decision), arity and pair-operand rejections. The gap case moves from 0x38 to 0x39. The costs suite pins the 200 charge, its exact-budget pair, and the all-opcodes pair re-totaled. New validation cases pin the semantics: satisfied on an honest input, each operand mismatching alone, a non-point operand failing as unsatisfied rather than malformed, the assert ignoring the spent scriptPubKey (the model takes the identity as authenticated and derives nothing), agreement with ASSERT_MY_TAPROOT on an honest input, the covenant recreate pattern, duplication idempotence, and two inputs each asserting its own identity against a neighbor's. Every case executed at generation.
Every fixture constructing a condition-carrying input gains the internal_key the model now requires: fixed filler in the family suites and tool tests, per-input distinct values in the message invariants, and the NUMS point on the vault and singleton instance inputs, the key both puzzles curry. The self assert invariants now draw the input's execution identity from a small pool the taptree operands share, so satisfied and unsatisfied taptree asserts are both dense. AssertMyTaptree joins the strategy pool, which puts it under the environment-independence and lone-assert properties, and two properties are new: the taptree assert's outcome never depends on the spent scriptPubKey, and on an input whose scriptPubKey is the taproot output of its own identity the taptree and taproot asserts over equal operands are satisfied together and fail together. New coverage elsewhere: the model refuses a condition-carrying input missing any one of the three identity fields and an internal key at the wrong width, the corpus loader maps those to context errors, the runner refuses a target input missing any field, the cost table pins 200, and the compiler vocabulary table pins the name at 0x38 with its count.
The condition record gains decision 28 (the cheap identity assert: the internal key read by self asserts only and why decision 26's objection does not reach it, the view deriving nothing from the triple, the width-only operand with both sides steelmanned, the never-empty root, one condition over both fields as a stated exception to decision 20, opcode 0x38, the subsumption of ASSERT_MY_TAPROOT with its fate deferred to the rework PR) and divergence row C24. The register's rule 2 row names the taproot assert as the taptree assert's oracle through the agreement invariant. The comparison doc gains the self-assert row, the glossary the condition and the widened identity triple, the vectors README the internal_key input field and the parsed shape. The execution plan's amendment bullet records what landed and what the rework PR still owes.
…ding, one width rule Ten verified findings from the review pass, most severe first. The implementation commit had reformatted the five vendored Bitcoin Core oracle files through a formatter pass that omitted the third-party exclusion, breaking the verbatim guarantee their README records by sha256. The files are restored to main's blobs, the lint script's hint now carries the exclusion, and a new provenance check compares every file the README table lists against its recorded hash, so the guarantee is enforced rather than assumed. Nothing checked that an instance vector's identity triple derives its scriptPubKey, so the honest-key rule the sweep applied was prose only, and the forthcoming rework removes the taproot assert that would have caught a mis-set key. Both puzzle suites gain a closure test: every condition-carrying input's scriptPubKey is the tweak of its internal key by its merkle root, the leaf equals the root, and the vault file's two filler inputs are counted so the exemption cannot widen. Spec wording: the agreement invariant says the two asserts are satisfied together and fail together, each with its own error, rather than "identical outcomes", and the CONDITIONS.md entry carries the honest-input qualifier. The environment-independence invariant names the execution identity beside prevout data. Rule 3 no longer calls its two fields the view's execution identity, which is now a triple. The family preamble states the internal key's content class directly instead of pointing at a table that has no row for it. The language reference counts 27 condition names, and three docstrings that said pair now say triple. Code: one _fixed_width_atom helper replaces four hand-rolled copies of the exact-width atom check, so the operands decision 28 says share a domain share it in code. Vectors pin error codes only, so the unified messages change no expectation. Tests: AssertMyTaptree joins the rule 4 duplication pool and its idempotent set, the runner's render table pins its output, and the agreement property looks up precomputed tweaks instead of deriving two per example, which takes the suite from 120 to 102 seconds.
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Review pass (code-review skill, high, Fable finders, adversarial verify)Ten findings survived verification, all folded in commit
Dropped after verification: the costs.json all-opcodes re-pin (correct, +200), partial identity on non-condition inputs (pre-existing, no rule reads it), single error code for the conjunction (decision 28). Final: 815 tests, 1132 vector cases, lint clean including the new provenance check. |
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Lands the 2026-08-22 identity-assert amendment (decision by Evan, recorded in the execution plan): spec, implementation, vectors, tests, and the condition-record decision. The vault and singleton rework onto the new assert follows in its own PR, which also decides the fate of ASSERT_MY_TAPROOT.
What changed
(0x38 internal_key merkle_root), a sixth self assert atCONDITION_GENERIC_COST(200). It asserts the spending input's execution identity byte-exact: the internal key and merkle root base consensus authenticated from the control block. It proves what ASSERT_MY_TAPROOT proves at 1,300,200 by derivation, with no derivation.internalKeyjoinstapleafandmerkleRoot, validator-filled, required together on a condition-carrying input. Rule 3 reads the first two, the self asserts read the last two, no specifier reads the internal key. The view takes the triple as authenticated and derives nothing from it.unsatisfied_taptree_assert.internal_key: the NUMS point on the 82 honest vault and singleton instances, chosen by a checkable rule (the scriptPubKey equals the tweak of NUMS by the merkle root), filler elsewhere. Every pinned program, payload, and signature is byte-identical.Spec sections
CONDITIONS.md self asserts (the family preamble and the 0x38 entry), VALIDATION.md transaction view and invariants, COSTS.md section 10. Decision 28 and divergence row C24 in
docs/condition-record.md, with the width-only operand steelmanned both ways.Read the commits in this order
spec: ASSERT_MY_TAPTREE, the transaction view gains the internal keyconditions: ASSERT_MY_TAPTREE, the internal key on the transaction modelvectors: the corpus gains the internal key, the taptree casestests: the internal key on every fixture, taptree coveragedocs: decision 28, divergence C24, glossary and corpus shapereview fold-ins: oracle snapshot restored, identity closure, spec wording, one width rule(the review comment below lists the ten findings)Verify independently
The vault and singleton closure tests recompile both puzzles and recompute every pinned program and conditions payload, so the sweep of their instance inputs is checked against source. In the vector diff, every line the sweep touched is an added
internal_keyline (plus the comma the preceding line gains):git diff main -- vectors/validation | grep '^[-+] ' | grep -v internal_keyshows only themerkle_rootcomma lines outsideself-asserts.json. The VM diff harness is untouched (no operator change).Notes for review
taptree_ignores_scriptpubkeyvector, which shows a taptree assert satisfied over a P2WPKH filler script.ASSERT_MY_TAPTREEa reserved name, the same deliberate source-compatibility break as every prior vocabulary addition, pinned by the compiler vocabulary test.