TASK-6e4ff870-a386-4a11-a59c-444ebc23732e: bound fence bootstrap reads

src/checks/candidate-execution-fence-init.mjs

@@ -1,3 +1,28 @@
 // Private init entrypoint. It is never a CLI surface: bootstrap is supplied only on inherited FD3 and acknowledgement only on FD4.
-import { closeSync, readFileSync, writeFileSync } from 'node:fs';
-export function readPrivateFenceBootstrapV2() { const frame = readFileSync(3, 'utf8'); if (Buffer.byteLength(frame, 'utf8') > 65_536) throw new Error('CANDIDATE_FENCE_FRAME_TOO_LARGE'); const value = JSON.parse(frame); if (!value?.nonce || !value?.generation) throw new Error('CANDIDATE_FENCE_FRAME_INVALID'); writeFileSync(4, JSON.stringify({ nonce: value.nonce, generation: value.generation })); closeSync(3); closeSync(4); return Object.freeze({ nonce: value.nonce, generation: value.generation, admissionFdsClosed: true }); }
+import { closeSync, readSync, writeFileSync } from 'node:fs';
+
+const MAX_BOOTSTRAP_FRAME_BYTES = 65_536;
+
+function readBoundedFrame(fd) {
+  const chunks = [];
+  let total = 0;
+  const buffer = Buffer.allocUnsafe(8_192);
+  while (true) {
+    const bytesRead = readSync(fd, buffer, 0, buffer.length, null);
+    if (bytesRead === 0) break;
+    total += bytesRead;
+    if (total > MAX_BOOTSTRAP_FRAME_BYTES) throw new Error('CANDIDATE_FENCE_FRAME_TOO_LARGE');
+    chunks.push(Buffer.from(buffer.subarray(0, bytesRead)));
+  }
+  return Buffer.concat(chunks, total).toString('utf8');
+}
+
+export function readPrivateFenceBootstrapV2() {
+  const frame = readBoundedFrame(3);
+  const value = JSON.parse(frame);
+  if (!value?.nonce || !value?.generation) throw new Error('CANDIDATE_FENCE_FRAME_INVALID');
+  writeFileSync(4, JSON.stringify({ nonce: value.nonce, generation: value.generation }));
+  closeSync(3);
+  closeSync(4);
+  return Object.freeze({ nonce: value.nonce, generation: value.generation, admissionFdsClosed: true });
+}