Sanitize replay diagnostic control characters

Co-authored-by: Shri Sukhani <shrisukhani@users.noreply.github.com>

Author: cursoragent

src/agent/__tests__/run-from-action-cache.test.ts

@@ -1316,6 +1316,31 @@ describe("runFromActionCache hardening", () => {
     expect(replay.steps[0]?.message).toContain("[truncated");
   });
 
+  it("sanitizes control characters in cached-step read diagnostics", async () => {
+    const agent = new HyperAgent({
+      llm: createMockLLM(),
+      cdpActions: false,
+    });
+    const page = {} as import("@/types/agent/types").HyperPage;
+    const cache = {
+      taskId: "cache-task",
+      createdAt: new Date().toISOString(),
+      status: TaskStatus.COMPLETED,
+      get steps(): unknown[] {
+        throw new Error(`steps\u0000\n${"x".repeat(2_000)}`);
+      },
+    } as unknown as ActionCacheOutput;
+
+    const replay = await agent.runFromActionCache(cache, page);
+
+    expect(replay.status).toBe(TaskStatus.FAILED);
+    const message = replay.steps[0]?.message ?? "";
+    expect(message).toContain("Failed to read cached steps");
+    expect(message).toContain("[truncated");
+    expect(message).not.toContain("\u0000");
+    expect(message).not.toContain("\n");
+  });
+
   it("fails replay step cleanly when page getter throws", async () => {
     const agent = new HyperAgent({
       llm: createMockLLM(),

src/agent/index.ts

@@ -1949,7 +1949,13 @@ export class HyperAgent<T extends BrowserProviders = "Local"> {
     const shouldWriteReplayDebug = (): boolean =>
       debug && this.isTaskLifecycleGenerationActive(replayLifecycleGeneration);
     const formatReplayDiagnostic = (value: unknown): string => {
-      const normalized = formatUnknownError(value).replace(/\s+/g, " ").trim();
+      const normalized = Array.from(formatUnknownError(value), (char) => {
+        const code = char.charCodeAt(0);
+        return (code >= 0 && code < 32) || code === 127 ? " " : char;
+      })
+        .join("")
+        .replace(/\s+/g, " ")
+        .trim();
       const fallback = normalized.length > 0 ? normalized : "unknown error";
       if (fallback.length <= HyperAgent.MAX_REPLAY_DIAGNOSTIC_CHARS) {
         return fallback;