fix(server): summarize Buffer values in stored and API JSON

Stop dumping every byte as a number in event I/O, workflow test results, and script dry-runs.

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

packages/server/json-preview.js

@@ -0,0 +1,43 @@
+const BUFFER_PREVIEW_BYTES = 16;
+
+/**
+ * @param {unknown} value
+ */
+export function isBinary(value) {
+  return (
+    Buffer.isBuffer(value) ||
+    ArrayBuffer.isView(value) ||
+    value instanceof ArrayBuffer
+  );
+}
+
+/**
+ * Compact stand-in for JSON (Buffer.toJSON dumps every byte as a number).
+ * @param {Buffer | ArrayBufferView | ArrayBuffer} value
+ */
+export function summarizeBinary(value) {
+  const buf = Buffer.isBuffer(value)
+    ? value
+    : value instanceof ArrayBuffer
+      ? Buffer.from(value)
+      : Buffer.from(value.buffer, value.byteOffset, value.byteLength);
+  const take = Math.min(buf.length, BUFFER_PREVIEW_BYTES);
+  return {
+    type: "Buffer",
+    length: buf.length,
+    preview: buf.subarray(0, take).toString("hex"),
+    truncated: buf.length > take,
+  };
+}
+
+/**
+ * JSON.stringify replacer. Must be a real function so `this` is the holder:
+ * Buffer#toJSON already ran on `value`, but `this[key]` is still the Buffer.
+ * @param {string} key
+ * @param {unknown} value
+ */
+export function jsonPreviewReplacer(key, value) {
+  const raw = this[key];
+  if (isBinary(raw)) return summarizeBinary(raw);
+  return value;
+}