fix(abstract-utxo): align descriptor parse with multisig self-payment flow

Use a two-pass approach in parseOutputsWithPsbt to handle self-payments:
- Pass 1 (missing): check ALL outputs (including change/internal) against
  expected recipients so self-payments are not reported as missing
- Pass 2 (implicit): only flag EXTERNAL outputs (scriptId=undefined) not
  in the recipient list as implicit

Also adds isImplicitOutput helper to outputDifference.ts and tests for
both the helper and the self-payment scenarios.

Ticket: VL-5164

Author: gobi-wan-kenobi

modules/abstract-utxo/src/transaction/descriptor/parse.ts

@@ -7,7 +7,12 @@ import { getKeySignatures, toBip32Triple, UtxoNamedKeychains } from '../../keych
 import { getDescriptorMapFromWallet, getPolicyForEnv } from '../../descriptor';
 import { IDescriptorWallet } from '../../descriptor/descriptorWallet';
 import { fromExtendedAddressFormatToScript, toExtendedAddressFormat } from '../recipient';
-import { outputDifferencesWithExpected, OutputDifferenceWithExpected } from '../outputDifference';
+import {
+  getMissingOutputs,
+  isImplicitOutput,
+  outputDifference,
+  OutputDifferenceWithExpected,
+} from '../outputDifference';
 import { UtxoCoinName } from '../../names';
 import { sumValues, toWasmPsbt, UtxoLibPsbt } from '../../wasmUtil';
 
@@ -44,11 +49,30 @@ function parseOutputsWithPsbt(
     script: Buffer.from(output.script),
   }));
   const changeOutputs = outputs.filter((o) => o.scriptId !== undefined);
-  const outputDiffs = outputDifferencesWithExpected(outputs, recipientOutputs);
+
+  /**
+   * Two-pass approach to handle self-payments (outputs going to the sender's own wallet address):
+   *
+   * Pass 1 — missing outputs: Check all PSBT outputs (including change/internal) against the
+   * expected recipients. This ensures self-payments that are classified as change outputs by the
+   * descriptor wallet (isChange = true) are still matched against the intent recipients and do not
+   * appear as missing. This mirrors the multisig (fixedScript) flow where allOutputs includes
+   * both explanation.outputs and explanation.changeOutputs.
+   *
+   * Pass 2 — implicit outputs: Of the outputs NOT in the recipient list, only flag those that go
+   * to external addresses (scriptId = undefined) as implicit. Internal outputs (scriptId set) that
+   * are not in recipients are legitimate change outputs and should not be flagged.
+   */
+  const missingOutputs = getMissingOutputs(outputs, recipientOutputs);
+  const implicitOutputs = outputs.filter((o) => isImplicitOutput(o, recipientOutputs));
+  const explicitOutputs = outputDifference(outputs, implicitOutputs);
+
   return {
     outputs,
     changeOutputs,
-    ...outputDiffs,
+    explicitOutputs,
+    implicitOutputs,
+    missingOutputs,
   };
 }
 

modules/abstract-utxo/src/transaction/outputDifference.ts

@@ -50,6 +50,21 @@ export function getMissingOutputs<A extends ActualOutput, B extends ExpectedOutp
   return outputDifference(expectedOutputs, actualOutputs).filter((o) => !o.optional);
 }
 
+/**
+ * Returns true if the given output was not explicitly requested by the user (i.e., it is not in
+ * the list of expected outputs). This handles both external and internal (change/self-payment)
+ * outputs — an output is implicit regardless of whether it is going to a wallet address or not.
+ *
+ * Used to identify surprise outputs such as PayGo fees that were added by the server without
+ * being part of the original send intent.
+ */
+export function isImplicitOutput<A extends ActualOutput>(
+  output: A,
+  expectedOutputs: ExpectedOutput[]
+): boolean {
+  return !expectedOutputs.some((expected) => matchingOutput(output, expected));
+}
+
 export type OutputDifferenceWithExpected<TActual extends ActualOutput, TExpected extends ExpectedOutput> = {
   /** These are the external outputs that were expected and found in the transaction. */
   explicitOutputs: TActual[];

modules/abstract-utxo/test/unit/transaction/descriptor/parse.ts

@@ -160,5 +160,33 @@ describe('parse', function () {
         new AggregateValidationError([missingOutputError(recipient), implicitOutputError(psbtOutput0)])
       );
     });
+
+    describe('self-payment (recipient address is a wallet address)', function () {
+      it('should pass when both the external output and the self-payment are specified as recipients', function () {
+        // psbtOutput1 goes to descriptorSelf (own wallet) — this is a self-payment
+        // Both outputs are requested, so there are no missing or implicit external outputs
+        assert.doesNotThrow(() =>
+          assertExpectedOutputDifference(getBaseParsedTransaction(psbt, [psbtOutput0, psbtOutput1]))
+        );
+      });
+
+      it('should not report the self-payment as missing even though it is classified as an internal (change) output', function () {
+        // psbtOutput1 goes to descriptorSelf (own wallet) and is marked as internal/change by the
+        // descriptor wallet parser. Specifying it as a recipient should still find it in the PSBT
+        // outputs (two-pass approach: all outputs are checked, not just external ones).
+        const result = getBaseParsedTransaction(psbt, [psbtOutput0, psbtOutput1]);
+        assert.strictEqual(result.missingOutputs.length, 0);
+        assert.strictEqual(result.implicitExternalOutputs.length, 0);
+      });
+
+      it('should not report an unspecified internal output as an implicit external output', function () {
+        // psbtOutput1 goes to descriptorSelf (own wallet). When NOT specified as a recipient,
+        // it should NOT appear in implicitExternalOutputs because it is an internal/change output.
+        // Only psbtOutput0 (external) is requested, so psbtOutput1 is just unreported change.
+        const result = getBaseParsedTransaction(psbt, [psbtOutput0]);
+        assert.strictEqual(result.missingOutputs.length, 0);
+        assert.strictEqual(result.implicitExternalOutputs.length, 0);
+      });
+    });
   });
 });

modules/abstract-utxo/test/unit/transaction/outputDifference.ts

@@ -4,6 +4,7 @@ import {
   ActualOutput,
   ExpectedOutput,
   getMissingOutputs,
+  isImplicitOutput,
   matchingOutput,
   outputDifference,
   outputDifferencesWithExpected,
@@ -96,6 +97,20 @@ describe('outputDifference', function () {
     });
   });
 
+  describe('isImplicitOutput', function () {
+    it('returns true for outputs not in the expected list', function () {
+      assert.strictEqual(isImplicitOutput(a, []), true);
+      assert.strictEqual(isImplicitOutput(a, [b]), true);
+      assert.strictEqual(isImplicitOutput(a, [a2]), true);
+    });
+
+    it('returns false for outputs that match an expected output', function () {
+      assert.strictEqual(isImplicitOutput(a, [a]), false);
+      assert.strictEqual(isImplicitOutput(a, [b, a]), false);
+      assert.strictEqual(isImplicitOutput(a, [aMax]), false);
+    });
+  });
+
   describe('outputDifferencesWithExpected', function () {
     function test(
       outputs: ActualOutput[],