fix: implement resilient POST client for replay job submission

examples/api-clients/mock-replay-submitter/index.js

@@ -1 +1,88 @@
-// Dummy implementation for Mock Replay Submitter
+#!/usr/bin/env node
+
+const API_URL = process.env.API_URL || 'http://localhost:3001';
+const REPLAY_ENDPOINT = `${API_URL}/api/replay`;
+
+/**
+ * Submits a transaction hash to the grat-server replay API and returns the
+ * job token used to track simulation progress.
+ *
+ * Resilient against:
+ * - Fastify 415 Unsupported Media Type (explicit Content-Type/Accept headers)
+ * - Network-level failures — DNS errors, connection refused, server downtime
+ *   (fetch rejections are caught here instead of propagating as unhandled
+ *   Promise rejections that would crash the process)
+ * - Non-2xx responses (4xx/5xx), surfaced as descriptive errors
+ * - Malformed or unexpected JSON response bodies
+ */
+async function submitReplayJob(txHash) {
+  let response;
+  try {
+    response = await fetch(REPLAY_ENDPOINT, {
+      method: 'POST',
+      headers: {
+        'Content-Type': 'application/json',
+        Accept: 'application/json',
+      },
+      body: JSON.stringify({ tx_hash: txHash }),
+    });
+  } catch (err) {
+    throw new Error(
+      `Could not reach grat-server at ${REPLAY_ENDPOINT}: ${err.message}. ` +
+        'Is the server running? (pnpm --filter grat-server dev)'
+    );
+  }
+
+  let payload;
+  try {
+    payload = await response.json();
+  } catch (err) {
+    throw new Error(
+      `Server returned a non-JSON response (HTTP ${response.status} ${response.statusText}): ${err.message}`
+    );
+  }
+
+  if (!response.ok) {
+    const detail = payload && (payload.error || payload.message);
+    throw new Error(
+      `Replay submission failed with HTTP ${response.status} ${response.statusText}` +
+        (detail ? `: ${detail}` : '')
+    );
+  }
+
+  if (!payload || !payload.jobId) {
+    throw new Error(
+      `Replay submission succeeded (HTTP ${response.status}) but the response did not include a "jobId": ${JSON.stringify(
+        payload
+      )}`
+    );
+  }
+
+  return payload.jobId;
+}
+
+async function main() {
+  const txHash = process.argv[2];
+
+  if (!txHash) {
+    console.error('Usage: node index.js <tx-hash>');
+    process.exitCode = 1;
+    return;
+  }
+
+  console.log(`Submitting replay job for ${txHash} to ${REPLAY_ENDPOINT}...`);
+
+  try {
+    const jobId = await submitReplayJob(txHash);
+    console.log(`✓ Replay job accepted. jobId: ${jobId}`);
+  } catch (err) {
+    console.error(`✗ ${err.message}`);
+    process.exitCode = 1;
+  }
+}
+
+if (require.main === module) {
+  main();
+}
+
+module.exports = { submitReplayJob };