penielgold-hub · Oct 6, 2026
@@ -1211,9 +1211,6 @@ export const buildFakeWitnessSet = (
       switch (script._tag) {
         case "NativeScript": {
           nativeScripts.push(script)
-          // Count required signers for this native script and add fake witnesses
-          const requiredSigners = addNativeScriptWitnesses(script)
-          yield* Effect.logDebug(`[buildFakeWitnessSet] Native script requires ${requiredSigners} signers`)
           break
         }
         case "PlutusV1":
@@ -1228,11 +1225,67 @@ export const buildFakeWitnessSet = (
       }
     }
 
-    // Also count required signers from scripts carried by reference or spent inputs
-    for (const utxo of [...state.referenceInputs, ...inputUtxos]) {
-      if (utxo.scriptRef && utxo.scriptRef._tag === "NativeScript") {
-        const requiredSigners = addNativeScriptWitnesses(utxo.scriptRef)
-        yield* Effect.logDebug(`[buildFakeWitnessSet] Input-carried native script requires ${requiredSigners} signers`)
+    // Count native-script signers only for scripts required by an actual transaction purpose.
+    const requiredScriptHashes = new Set<string>()
+    for (const utxo of state.selectedUtxos) {
+      if (utxo.address.paymentCredential._tag === "ScriptHash") {
+        requiredScriptHashes.add(ScriptHash.toHex(utxo.address.paymentCredential))
+      }
+    }
+    if (state.mint) {
+      for (const policyId of state.mint.map.keys()) {
+        requiredScriptHashes.add(PolicyId.toHex(policyId))
+      }
+    }
+    for (const certificate of state.certificates) {
+      let scriptHashHex = certScriptHashHex(certificate)
+      if (scriptHashHex === undefined) {
+        switch (certificate._tag) {
+          case "StakeRegistration":
+          case "StakeDeregistration":
+          case "StakeDelegation":
+          case "RegCert":
+          case "UnregCert":
+          case "VoteDelegCert":
+          case "StakeVoteDelegCert":
+          case "StakeRegDelegCert":
+          case "VoteRegDelegCert":
+          case "StakeVoteRegDelegCert":
+            if (certificate.stakeCredential._tag === "ScriptHash") {
+              scriptHashHex = ScriptHash.toHex(certificate.stakeCredential)
+            }
+            break
+        }
+      }
+      if (scriptHashHex !== undefined) requiredScriptHashes.add(scriptHashHex)
+    }
+    for (const [rewardAccount] of state.withdrawals) {
+      if (rewardAccount.stakeCredential._tag === "ScriptHash") {
+        requiredScriptHashes.add(ScriptHash.toHex(rewardAccount.stakeCredential))
+      }
+    }
+    for (const voter of state.votingProcedures?.procedures.keys() ?? []) {
+      const scriptHashHex = voterScriptHashHex(voter)
+      if (scriptHashHex !== undefined) requiredScriptHashes.add(scriptHashHex)
+    }
+    for (const procedure of state.proposalProcedures?.procedures ?? []) {
+      const scriptHashHex = proposalPolicyHashHex(procedure.governanceAction)
+      if (scriptHashHex !== undefined) requiredScriptHashes.add(scriptHashHex)
+    }
+
+    const isNativeScript = makeIsNativeScript(state)
+    for (const scriptHashHex of requiredScriptHashes) {
+      if (isNativeScript(scriptHashHex) !== true) continue
+
+      const script = state.scripts.get(scriptHashHex) ??
+        [...state.referenceInputs, ...state.selectedUtxos]
+          .map((utxo) => utxo.scriptRef)
+          .find((script) =>
+            script?._tag === "NativeScript" && ScriptHash.toHex(ScriptHash.fromScript(script)) === scriptHashHex
+          )
+      if (script?._tag === "NativeScript") {
+        const requiredSigners = addNativeScriptWitnesses(script)
+        yield* Effect.logDebug(`[buildFakeWitnessSet] Required native script requires ${requiredSigners} signers`)
       }
     }
 

@@ -0,0 +1,90 @@
+import { describe, expect, it } from "@effect/vitest"
+import { Effect, Ref } from "effect"
+
+import * as CoreAddress from "../src/Address.js"
+import * as CoreAssets from "../src/Assets.js"
+import * as Certificate from "../src/Certificate.js"
+import * as NativeScripts from "../src/NativeScripts.js"
+import * as ScriptHash from "../src/ScriptHash.js"
+import * as BuilderState from "../src/sdk/builders/internal/state.js"
+import { buildFakeWitnessSet } from "../src/sdk/builders/internal/txBuilder.js"
+import { makeTxBuilder, type TxBuilderConfig, type TxBuilderState,TxContext } from "../src/sdk/builders/TransactionBuilder.js"
+import { mainnet } from "../src/sdk/client/index.js"
+import * as TransactionHash from "../src/TransactionHash.js"
+import * as CoreUTxO from "../src/UTxO.js"
+import { createCoreTestUtxo } from "./utils/utxo-helpers.js"
+
+const PROTOCOL_PARAMS = {
+  minFeeCoefficient: 44n,
+  minFeeConstant: 155_381n,
+  coinsPerUtxoByte: 4_310n,
+  maxTxSize: 16_384
+}
+
+const CHANGE_ADDRESS =
+  "addr_test1qz2fxv2umyhttkxyxp8x0dlpdt3k6cwng5pxj3jhsydzer3n0d3vllmyqwsx5wktcd8cc3sq835lu7drv2xwl2wywfgs68faae"
+
+const baseConfig = { chain: mainnet } satisfies TxBuilderConfig
+
+const unusedNativeScript = NativeScripts.makeScriptPubKey(new Uint8Array(28).fill(0xcc))
+
+const scriptCarrier = (hash: string, scriptRef = unusedNativeScript) =>
+  new CoreUTxO.UTxO({
+    transactionId: TransactionHash.fromHex(hash),
+    index: 0n,
+    address: CoreAddress.fromBech32(CHANGE_ADDRESS),
+    assets: CoreAssets.fromLovelace(20_000_000n),
+    scriptRef
+  })
+
+const buildOptions = {
+  changeAddress: CoreAddress.fromBech32(CHANGE_ADDRESS),
+  availableUtxos: [
+    createCoreTestUtxo({
+      transactionId: "a".repeat(64),
+      index: 0,
+      address: CHANGE_ADDRESS,
+      lovelace: 100_000_000n
+    })
+  ],
+  protocolParameters: PROTOCOL_PARAMS
+}
+
+describe("TxBuilder native script signer estimation (#596)", () => {
+  it("does not count signers for an unrelated native script carried by a spent input", async () => {
+    const builder = await makeTxBuilder(baseConfig)
+      .collectFrom({ inputs: [scriptCarrier("b".repeat(64))] })
+      .build(buildOptions)
+
+    const fakeTx = await builder.toTransactionWithFakeWitnesses()
+    expect(fakeTx.witnessSet.vkeyWitnesses?.length ?? 0).toBe(1)
+  })
+
+  it("does not count signers for an unrelated native script carried by a reference input", async () => {
+    const builder = await makeTxBuilder(baseConfig)
+      .readFrom({ referenceInputs: [scriptCarrier("c".repeat(64))] })
+      .build(buildOptions)
+
+    const fakeTx = await builder.toTransactionWithFakeWitnesses()
+    expect(fakeTx.witnessSet.vkeyWitnesses?.length ?? 0).toBe(1)
+  })
+
+  it("counts signers for a native-script stake registration credential", async () => {
+    const requiredNativeScript = NativeScripts.makeScriptPubKey(new Uint8Array(28).fill(0xdd))
+    const scriptHash = ScriptHash.fromScript(requiredNativeScript)
+    const state: TxBuilderState = {
+      ...BuilderState.makeInitialTxBuilderState(),
+      certificates: [new Certificate.StakeRegistration({ stakeCredential: scriptHash })],
+      referenceInputs: [scriptCarrier("e".repeat(64), requiredNativeScript)]
+    }
+    const stateRef = await Effect.runPromise(Ref.make(state))
+    const input = buildOptions.availableUtxos[0]!
+
+    const fakeWitnessSet = await Effect.runPromise(
+      buildFakeWitnessSet([input]).pipe(Effect.provideService(TxContext, stateRef))
+    )
+
+    // One payment-key witness for the input and one signer for the stake credential.
+    expect(fakeWitnessSet.vkeyWitnesses?.length ?? 0).toBe(2)
+  })
+})
@@ -394,7 +394,7 @@ describe("TxBuilder propose with guardrail script: combinations", () => {
 
       // The wallet key and the guardrail's own signer both need a vkey witness
       const fakeTx = await signBuilder.toTransactionWithFakeWitnesses()
-      expect(fakeTx.witnessSet.vkeyWitnesses?.length ?? 0).toBeGreaterThanOrEqual(2)
+      expect(fakeTx.witnessSet.vkeyWitnesses?.length ?? 0).toBe(2)
     })
 
     it("drops a supplied redeemer", async () => {