Allow transaction which returns only a change output

apps/extension/src/core/chains/liquid/adapters/smplx/assembleReviewedTransaction.ts

@@ -87,7 +87,12 @@ export async function assembleReviewedTransaction(
 		};
 	}
 
-	if (review.outputs.length === 0) {
+	// An empty `outputs` is only a document fault when nothing will be paid at all.
+	// A policy-asset "change" output is deliberately absent from `review.outputs` —
+	// its value is computed by `builder.addChange()` further down — so an action whose
+	// only output is change (e.g. a full withdrawal that sends the whole remaining
+	// balance to the beneficiary) pays perfectly well and must not be refused here.
+	if (review.outputs.length === 0 && !review.changeDeferred) {
 		return {
 			ok: false,
 			reason: `"${review.action}" pays nothing, so there is nothing to build.`,

packages/tx-manifest/src/review/covenantSpend.test.ts

@@ -221,6 +221,42 @@ describe("the transaction-level facts a covenant spend needs", () => {
 	test("carries none where the action declares none", async () => {
 		expect((await reviewed()).sequence).toBeUndefined();
 	});
+
+	test("carries a relative timelock where the covenant input is the only input", async () => {
+		const inputs = receiveInputs();
+
+		inputs[0] = { ...inputs[0], sequence: { relative_blocks: 10 } };
+
+		const outputs = [
+			{
+				amount_sat: 40_000,
+				asset: "lbtc",
+				description: "The reclaimed funds, sent to your wallet.",
+				destination: "wallet",
+				id: "received_out",
+			},
+		];
+		const review = await reviewed(spendRequest(withReceive([inputs[0]], outputs)));
+
+		expect(review.sequence).toBe(10);
+		expect(review.selected).toHaveLength(0);
+		expect(review.inputOrder).toHaveLength(1);
+	});
+
+	test("refuses a relative timelock a wallet fee input would inherit", async () => {
+		const inputs = receiveInputs();
+
+		inputs[0] = { ...inputs[0], sequence: { relative_blocks: 10 } };
+
+		const result = await reviewManifestAction(spendRequest(withReceiveInputs(inputs)), deps);
+
+		expect(isRefusal(result)).toBe(true);
+
+		if (isRefusal(result)) {
+			expect(result.reject).toBe("unimplemented-construct");
+			expect(result.reason).toContain("would inherit that wait");
+		}
+	});
 });
 
 describe("a covenant input that issues an asset", () => {

packages/tx-manifest/src/review/index.ts

@@ -101,6 +101,7 @@ export type AssetMovement = {
 export type ManifestReview = {
 	action: string;
 	changeBlinded: boolean;
+	changeDeferred?: boolean;
 	changeBlindedBy?: BlindingWord;
 	changeOverrode?: BlindingWord;
 	boundTo?: string;
@@ -624,6 +625,13 @@ export async function reviewManifestAction(
 	const outputAt = new Map<string, number>();
 	const returned = new Map<string, bigint>();
 	const changePaid = new Set<string>();
+	// Set when a policy-asset "change" output is left out of `outputs` below for the
+	// builder's `addChange()` to handle. Without this, an action whose only output is
+	// such a change output looks like an action with no outputs at all.
+	let changeDeferred = false;
+
+	for (const [at, planned] of plan.plan.outputs.entries()) {
+		const asset = ledger.outputs[at] ?? policyAsset;
 
 	for (const [at, planned] of plan.plan.outputs.entries()) {
 		const asset = ledger.outputs[at] ?? policyAsset;
@@ -635,6 +643,10 @@ export async function reviewManifestAction(
 					: (fundedFor.get(asset)?.changeSats ?? 0n);
 
 			if (surplus <= 0n) {
+				if (asset === policyAsset) {
+					changeDeferred = true;
+				}
+
 				continue;
 			}
 
@@ -861,6 +873,7 @@ export async function reviewManifestAction(
 		action: request.action,
 		...(action.boundTo === undefined ? {} : { boundTo: action.boundTo }),
 		changeBlinded: change.blinding === "blinded",
+		...(changeDeferred ? { changeDeferred: true } : {}),
 		...(change.blinding === "blinded"
 			? { changeBlindedBy: change.decidedBy }
 			: change.overrode === undefined