fix(ai): timeout Codex SSE header stalls

packages/ai/src/utils/abort-signals.ts

@@ -0,0 +1,41 @@
+export interface CombinedAbortSignal {
+	signal?: AbortSignal;
+	cleanup: () => void;
+}
+
+export function combineAbortSignals(signals: readonly (AbortSignal | undefined)[]): CombinedAbortSignal {
+	const activeSignals = signals.filter((signal): signal is AbortSignal => signal !== undefined);
+	if (activeSignals.length === 0) {
+		return { cleanup: () => {} };
+	}
+	if (activeSignals.length === 1) {
+		return { signal: activeSignals[0], cleanup: () => {} };
+	}
+
+	const controller = new AbortController();
+	const listeners: Array<{ signal: AbortSignal; listener: () => void }> = [];
+	const abort = (signal: AbortSignal) => {
+		if (!controller.signal.aborted) {
+			controller.abort(signal.reason);
+		}
+	};
+
+	for (const signal of activeSignals) {
+		if (signal.aborted) {
+			abort(signal);
+			break;
+		}
+		const listener = () => abort(signal);
+		signal.addEventListener("abort", listener, { once: true });
+		listeners.push({ signal, listener });
+	}
+
+	return {
+		signal: controller.signal,
+		cleanup: () => {
+			for (const { signal, listener } of listeners) {
+				signal.removeEventListener("abort", listener);
+			}
+		},
+	};
+}