fix(release): parse nested agent-run status JSON during drain

Non-greedy brace regex missed the queue object when worker status output contains nested JSON; scan balanced objects from the end instead.

Co-authored-by: Cursor <cursoragent@cursor.com>

release-gate/release-script.test.mjs

@@ -55,6 +55,7 @@ test('production stable release verifies canary promotion evidence before gate c
   assert.ok(impactIndex > 0, 'missing risk-based impact gate fallback');
   assert.doesNotMatch(source, /在同一候选完成 103 灰度验收且晋升证据校验落地前，禁止非 dry-run/);
   assert.match(source, /read_agent_run_status_json/);
+  assert.match(source, /starts\.length - 1/);
   assert.match(source, /obj\.queue/);
   assert.match(source, /for _ in \$\(seq 1 120\)/);
 });

scripts/release-portal-runtime-prod.sh

@@ -637,14 +637,28 @@ read_agent_run_status_json() {
 let s = "";
 process.stdin.on("data", (chunk) => { s += chunk; });
 process.stdin.on("end", () => {
-  let best = null;
-  for (const match of s.matchAll(/\{[\s\S]*?\}/g)) {
-    try {
-      const obj = JSON.parse(match[0]);
-      if (obj && typeof obj === "object" && obj.queue) best = JSON.stringify(obj);
-    } catch {}
+  const starts = [];
+  for (let i = 0; i < s.length; i += 1) {
+    if (s[i] === "{") starts.push(i);
+  }
+  for (let i = starts.length - 1; i >= 0; i -= 1) {
+    const start = starts[i];
+    let depth = 0;
+    for (let j = start; j < s.length; j += 1) {
+      if (s[j] === "{") depth += 1;
+      else if (s[j] === "}") depth -= 1;
+      if (depth !== 0) continue;
+      const chunk = s.slice(start, j + 1);
+      try {
+        const obj = JSON.parse(chunk);
+        if (obj && typeof obj === "object" && obj.queue) {
+          process.stdout.write(JSON.stringify(obj));
+          return;
+        }
+      } catch {}
+      break;
+    }
   }
-  if (best) process.stdout.write(best);
 });' || true
 }