feat: enable permission-aware subagents

pi-subagents/src/abortable.ts

@@ -0,0 +1,43 @@
+/**
+ * abortable.ts — race a promise against an AbortSignal without cancelling the
+ * underlying work.
+ *
+ * Used by the `get_subagent_result` wait paths (top-level and nested): pressing
+ * Esc cancels only the caller's wait; the background child keeps running and its
+ * result stays unconsumed. The listener is removed on every settle path so the
+ * signal accumulates no handlers, and a late settlement of the wrapped promise
+ * after an abort is absorbed as a no-op (no unhandled rejection).
+ */
+
+/** Await a promise until it settles or the caller cancels, without aborting the underlying work. */
+export function abortable<T>(promise: Promise<T>, signal?: AbortSignal): Promise<T> {
+  if (!signal) return promise;
+  if (signal.aborted) return Promise.reject(signal.reason);
+
+  return new Promise<T>((resolve, reject) => {
+    let settled = false;
+    const cleanup = () => signal.removeEventListener("abort", onAbort);
+    const onAbort = () => {
+      if (settled) return;
+      settled = true;
+      cleanup();
+      reject(signal.reason);
+    };
+
+    signal.addEventListener("abort", onAbort, { once: true });
+    promise.then(
+      (value) => {
+        if (settled) return;
+        settled = true;
+        cleanup();
+        resolve(value);
+      },
+      (error: unknown) => {
+        if (settled) return;
+        settled = true;
+        cleanup();
+        reject(error);
+      },
+    );
+  });
+}