feat: vendor permission system source

pi-permission-system/src/json-safe-stringify.ts

@@ -0,0 +1,54 @@
+/**
+ * JSON serialization that survives the values a permission log actually
+ * carries: `Error` instances, `bigint`s, and object graphs with cycles.
+ *
+ * Lives apart from the JSONL writer because both the log path and the
+ * permission-prompt path serialize tool input, and only one of them redacts.
+ */
+
+/**
+ * Rewrites a value before the standard JSON-safe handling runs.
+ * Returning a replacement short-circuits nothing — the replacement itself
+ * flows through the `Error` / `bigint` / cycle handling below.
+ */
+export type JsonValueTransform = (key: string, value: unknown) => unknown;
+
+/**
+ * Build a `JSON.stringify` replacer. Each call owns a fresh `seen` set, so a
+ * replacer must not be reused across `stringify` calls.
+ */
+export function createJsonSafeReplacer(
+  transform?: JsonValueTransform,
+): (key: string, value: unknown) => unknown {
+  const seen = new WeakSet<object>();
+
+  return (key: string, rawValue: unknown): unknown => {
+    const value = transform ? transform(key, rawValue) : rawValue;
+
+    if (value instanceof Error) {
+      return {
+        name: value.name,
+        message: value.message,
+        stack: value.stack,
+      };
+    }
+
+    if (typeof value === "bigint") {
+      return value.toString();
+    }
+
+    if (typeof value === "object" && value !== null) {
+      if (seen.has(value)) {
+        return "[Circular]";
+      }
+      seen.add(value);
+    }
+
+    return value;
+  };
+}
+
+/** Serialize `value` to JSON, tolerating errors, bigints, and cycles. */
+export function safeJsonStringify(value: unknown): string | undefined {
+  return JSON.stringify(value, createJsonSafeReplacer());
+}