feat(swift): add x402 exact client

.gitignore

@@ -34,3 +34,5 @@ harness/go-client/go-client
 mpp-sdk-self-learning/
 .build/
 go/coverage.out
+notes/codex-review/
+notes/codex-review-*.md

harness/src/contracts.ts

@@ -1,11 +1,12 @@
 import type { CanonicalErrorCode } from "./canonical-codes";
 import { chargeScenarios } from "./intents/charge";
+import { x402ExactScenarios } from "./intents/x402-exact";
 
 export type { CanonicalErrorCode };
 
 export type AdapterKind = "client" | "server";
 
-export type InteropIntent = "charge";
+export type InteropIntent = "charge" | "x402-exact";
 
 export type InteropScenarioSplit = {
   recipientKey: string;
@@ -136,8 +137,10 @@ export type AdapterMessage = ReadyMessage | ClientRunResult;
 
 export { chargeCanonicalJsonVectors } from "./intents/charge";
 
-export const interopScenarios: readonly InteropScenario[] =
-  chargeScenarios;
+export const interopScenarios: readonly InteropScenario[] = [
+  ...chargeScenarios,
+  ...x402ExactScenarios,
+];
 
 export const interopScenario: InteropScenario = {
   ...(interopScenarios[0] as InteropScenario),
@@ -191,11 +194,18 @@ function selectScenarioIds(rawSelection: string | undefined): string[] {
   return selected;
 }
 
+// The legacy MPP charge runner predates the x402-exact intent. To keep
+// the existing CI matrix's default behaviour (charge-only) stable while
+// still surfacing the new intent through `selectInteropIntents("x402-exact")`,
+// the empty-selection default is restricted to "charge". Callers that
+// want the full intent set should pass the explicit list.
+const DEFAULT_INTENTS: readonly InteropIntent[] = ["charge"];
+
 export function selectInteropIntents(
   rawSelection: string | undefined,
 ): InteropIntent[] {
   if (!rawSelection || rawSelection.trim() === "") {
-    return [...supportedInteropIntents];
+    return [...DEFAULT_INTENTS];
   }
 
   const selected = rawSelection
@@ -209,8 +219,7 @@ export function selectInteropIntents(
   if (unsupported.length > 0) {
     throw new Error(
       `Unsupported MPP_INTEROP_INTENTS value(s): ${unsupported.join(", ")}. ` +
-        `Supported intents: ${supportedInteropIntents.join(", ")}. ` +
-        "Session and subscription scenarios are not implemented in this harness yet.",
+        `Supported intents: ${supportedInteropIntents.join(", ")}.`,
     );
   }
 

harness/src/fixtures/typescript/exact-client.ts

@@ -0,0 +1,225 @@
+// TypeScript reference x402 `exact` interop client.
+//
+// Shares the same `X402_INTEROP_*` env-var contract and ready/result
+// JSON protocol as the Rust spine (`rust/crates/x402/src/bin/
+// interop_client.rs`). Sends an unpaid GET, parses the base64
+// `PAYMENT-REQUIRED` envelope, selects an offer (`preferredCurrencies`
+// first) and resubmits with `PAYMENT-SIGNATURE`. Prints one result
+// JSON line to stdout.
+//
+// Scope: the fixture carries a stub credential payload (challenge id +
+// resource) so the harness wiring, negative-code classification, and
+// cross-server portability + idempotent-resubmit flows can run without
+// a full Solana signer. Real SVM PaymentProof construction (signed
+// VersionedTransaction or settled signature) lives in the Rust spine
+// and the TS SDK port; this client only pairs against the TS reference
+// server in the default matrix (see `test/x402-exact.e2e.test.ts`).
+
+import {
+  PAYMENT_REQUIRED_HEADER,
+  PAYMENT_SIGNATURE_HEADER,
+  readX402ClientEnvironment,
+} from "./exact-shared";
+
+type PaymentRequirement = {
+  scheme: string;
+  network: string;
+  resource?: string;
+  payTo: string;
+  asset: string;
+  maxAmountRequired: string;
+  extra?: { decimals?: number; tokenProgram?: string };
+};
+
+type PaymentRequiredEnvelope = {
+  x402Version: number;
+  accepts: PaymentRequirement[];
+  resource?: string;
+};
+
+const STABLECOIN_MINTS: Record<string, Record<string, string>> = {
+  USDC: {
+    "solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp":
+      "EPjFWdd5AufqSSqeM2qN1xzybapC8G4wEGGkZwyTDt1v",
+    "solana:EtWTRABZaYq6iMfeYKouRu166VU2xqa1":
+      "4zMMC9srt5Ri5X14GAgXhaHii3GnPAEERYPJgZJDncDU",
+  },
+  PYUSD: {
+    "solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp":
+      "2b1kV6DkPAnxd5ixfnxCpjxmKwqjjaYmCZfHsFu24GXo",
+  },
+};
+
+function resolveMint(currency: string, network: string): string {
+  const upper = currency.toUpperCase();
+  const byNetwork = STABLECOIN_MINTS[upper];
+  if (byNetwork && byNetwork[network]) {
+    return byNetwork[network];
+  }
+  return currency;
+}
+
+function pickOffer(
+  envelope: PaymentRequiredEnvelope,
+  preferred: string[],
+  network: string,
+): PaymentRequirement | undefined {
+  const supported = envelope.accepts.filter(
+    offer => offer.scheme === "exact" && offer.network === network,
+  );
+  if (supported.length === 0) {
+    return undefined;
+  }
+  if (preferred.length === 0) {
+    return supported[0];
+  }
+  for (const wanted of preferred) {
+    const wantedMint = resolveMint(wanted, network);
+    const match = supported.find(offer => offer.asset === wantedMint);
+    if (match) return match;
+  }
+  return supported[0];
+}
+
+function decodePaymentRequired(headerValue: string | null): PaymentRequiredEnvelope | null {
+  if (!headerValue) return null;
+  try {
+    const raw = Buffer.from(headerValue, "base64").toString("utf8");
+    return JSON.parse(raw) as PaymentRequiredEnvelope;
+  } catch {
+    return null;
+  }
+}
+
+async function readResponseBody(response: Response): Promise<unknown> {
+  const raw = await response.text();
+  try {
+    return JSON.parse(raw);
+  } catch {
+    return raw;
+  }
+}
+
+async function main() {
+  const env = readX402ClientEnvironment();
+
+  const firstResponse = await fetch(env.targetUrl);
+  const envelope = decodePaymentRequired(
+    firstResponse.headers.get(PAYMENT_REQUIRED_HEADER),
+  );
+
+  if (!envelope) {
+    console.log(
+      JSON.stringify({
+        type: "result",
+        implementation: "typescript",
+        role: "client",
+        ok: false,
+        status: firstResponse.status,
+        responseHeaders: Object.fromEntries(firstResponse.headers.entries()),
+        responseBody: await readResponseBody(firstResponse),
+        settlement: null,
+        error: "missing or unparseable PAYMENT-REQUIRED header",
+      }),
+    );
+    return;
+  }
+
+  const offer = pickOffer(envelope, env.preferredCurrencies, env.network);
+  if (!offer) {
+    console.log(
+      JSON.stringify({
+        type: "result",
+        implementation: "typescript",
+        role: "client",
+        ok: false,
+        status: firstResponse.status,
+        responseHeaders: Object.fromEntries(firstResponse.headers.entries()),
+        responseBody: await readResponseBody(firstResponse),
+        settlement: null,
+        error: `no offer matched network ${env.network}`,
+      }),
+    );
+    return;
+  }
+
+  // Credential payload mirrors the canonical x402 `exact` shape: an
+  // adapter-specific id plus the offer the client is committing to.
+  // A live SDK would also embed a signed Solana transaction here; the
+  // matrix runner uses the rust spine for the actual on-chain
+  // settlement assertions. The TS fixture's role is wire-level
+  // protocol compliance.
+  // Use the server-issued challenge id if present (TS reference server
+  // emits one in the `x-challenge-id` header on the 402). This lets the
+  // server verify the credential was issued against its own 402 — the
+  // cross-server portability scenario relies on this distinction.
+  const issuedChallengeId = firstResponse.headers.get("x-challenge-id");
+  const credentialId =
+    issuedChallengeId ??
+    `ts-x402-${Date.now().toString(36)}-${Math.random().toString(36).slice(2, 10)}`;
+  // Mirrors the Rust spine's PaymentPayload wire shape:
+  //   { x402Version, accepted: { scheme, network, asset, payTo, amount, extra? },
+  //     payload: { ... scheme-specific blob ... }, resource?: string }
+  // The `payload` field is required by Rust's parser. For the wire-only
+  // TS adapter the payload carries the credential id plus the route the
+  // client is committing to; a full SDK fixture would carry a signed
+  // Solana transaction here.
+  const credential = {
+    x402Version: envelope.x402Version,
+    accepted: {
+      scheme: offer.scheme,
+      network: offer.network,
+      asset: offer.asset,
+      payTo: offer.payTo,
+      amount: offer.maxAmountRequired,
+      extra: offer.extra ?? null,
+    },
+    payload: {
+      challengeId: credentialId,
+      resource: offer.resource ?? envelope.resource,
+    },
+    resource: offer.resource ?? envelope.resource,
+  };
+  const credentialHeader = Buffer.from(JSON.stringify(credential), "utf8").toString(
+    "base64",
+  );
+
+  const paidResponse = await fetch(env.targetUrl, {
+    headers: { [PAYMENT_SIGNATURE_HEADER]: credentialHeader },
+  });
+
+  const responseHeaders = Object.fromEntries(paidResponse.headers.entries());
+  // Echo the credential the client sent so the harness can replay it in
+  // cross-server portability + idempotent-resubmit scenarios. The credential
+  // is a request header so it is never reflected in the response on its own.
+  responseHeaders[`${PAYMENT_SIGNATURE_HEADER}-sent`] = credentialHeader;
+
+  console.log(
+    JSON.stringify({
+      type: "result",
+      implementation: "typescript",
+      role: "client",
+      ok: paidResponse.ok,
+      status: paidResponse.status,
+      responseHeaders,
+      responseBody: await readResponseBody(paidResponse),
+      settlement: paidResponse.headers.get(env.settlementHeader),
+    }),
+  );
+}
+
+void main().catch(error => {
+  console.log(
+    JSON.stringify({
+      type: "result",
+      implementation: "typescript",
+      role: "client",
+      ok: false,
+      status: 0,
+      responseHeaders: {},
+      responseBody: null,
+      settlement: null,
+      error: error instanceof Error ? error.message : String(error),
+    }),
+  );
+});