Harden dom-capture callback diagnostics

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

Author: cursoragent

src/agent/shared/dom-capture.test.ts

@@ -115,4 +115,44 @@ describe("captureDOMState", () => {
       logSpy.mockRestore();
     }
   });
+
+  it("sanitizes and truncates onFrameChunk callback diagnostics", async () => {
+    getA11yDOM.mockImplementation(
+      async (
+        _page: Page,
+        _debug: boolean,
+        _enableVisualMode: boolean,
+        _debugStepDir: string | undefined,
+        options?: { onFrameChunk?: (chunk: { order: number; simplified: string }) => void }
+      ) => {
+        options?.onFrameChunk?.({ order: 0, simplified: " streamed chunk " });
+        return createDomState({
+          elements: new Map([["0-1", { name: "button" }]]),
+          domState: "fallback",
+        });
+      }
+    );
+
+    const warnSpy = jest.spyOn(console, "warn").mockImplementation(() => {});
+    const logSpy = jest.spyOn(console, "log").mockImplementation(() => {});
+    try {
+      const result = await captureDOMState(createPage(), {
+        enableStreaming: true,
+        onFrameChunk: () => {
+          throw new Error(`stream\u0000\n${"x".repeat(10_000)}`);
+        },
+        debug: true,
+      });
+
+      expect(result.domState).toBe("streamed chunk");
+      const diagnostic = String(warnSpy.mock.calls[0]?.[0] ?? "");
+      expect(diagnostic).toContain("[truncated");
+      expect(diagnostic).not.toContain("\u0000");
+      expect(diagnostic).not.toContain("\n");
+      expect(diagnostic.length).toBeLessThan(700);
+    } finally {
+      warnSpy.mockRestore();
+      logSpy.mockRestore();
+    }
+  });
 });

src/agent/shared/dom-capture.ts

@@ -6,6 +6,7 @@ import {
   type A11yDOMState,
 } from "@/context-providers/a11y-dom";
 import type { FrameChunkEvent } from "@/context-providers/a11y-dom/types";
+import { formatUnknownError } from "@/utils";
 import { waitForSettledDOM } from "@/utils/waitForSettledDOM";
 
 const DOM_CAPTURE_MAX_ATTEMPTS = 3;
@@ -26,6 +27,34 @@ export interface CaptureDOMOptions {
 }
 
 const MAX_DOM_CAPTURE_RETRIES = 10;
+const MAX_DOM_CAPTURE_DIAGNOSTIC_CHARS = 400;
+
+function sanitizeDomCaptureText(value: string): string {
+  if (value.length === 0) {
+    return value;
+  }
+  const withoutControlChars = Array.from(value, (char) => {
+    const code = char.charCodeAt(0);
+    return (code >= 0 && code < 32) || code === 127 ? " " : char;
+  }).join("");
+  return withoutControlChars.replace(/\s+/g, " ").trim();
+}
+
+function truncateDomCaptureDiagnostic(value: string): string {
+  if (value.length <= MAX_DOM_CAPTURE_DIAGNOSTIC_CHARS) {
+    return value;
+  }
+  const omittedChars = value.length - MAX_DOM_CAPTURE_DIAGNOSTIC_CHARS;
+  return `${value.slice(0, MAX_DOM_CAPTURE_DIAGNOSTIC_CHARS)}... [truncated ${omittedChars} chars]`;
+}
+
+function formatDomCaptureDiagnostic(value: unknown): string {
+  const normalized = sanitizeDomCaptureText(formatUnknownError(value));
+  if (normalized.length === 0) {
+    return "unknown callback error";
+  }
+  return truncateDomCaptureDiagnostic(normalized);
+}
 
 class DomChunkAggregator {
   private parts: string[] = [];
@@ -139,9 +168,9 @@ export async function captureDOMState(
                 } catch (error) {
                   if (debug) {
                     console.warn(
-                      `[DOM] onFrameChunk callback failed: ${
-                        error instanceof Error ? error.message : "unknown callback error"
-                      }`
+                      `[DOM] onFrameChunk callback failed: ${formatDomCaptureDiagnostic(
+                        error
+                      )}`
                     );
                   }
                 }