fix(web): drop opaque script error exceptions in posthog

packages/web/src/auth/posthog/posthog-exception-filter.util.test.ts

@@ -3,7 +3,11 @@ import { filterPosthogBeforeSend } from "./posthog-exception-filter.util";
 import { describe, expect, it } from "bun:test";
 
 const exceptionEvent = (
-  entries: Array<{ type?: string; value?: string }>,
+  entries: Array<{
+    type?: string;
+    value?: string;
+    stacktrace?: { frames?: Array<Record<string, unknown>> };
+  }>,
 ): CaptureResult =>
   ({
     uuid: "test-uuid",
@@ -58,6 +62,27 @@ describe("filterPosthogBeforeSend", () => {
     ).toBeNull();
   });
 
+  it("drops opaque browser Script error. with no stack frames", () => {
+    expect(
+      filterPosthogBeforeSend(
+        exceptionEvent([{ type: "Error", value: "Script error." }]),
+      ),
+    ).toBeNull();
+  });
+
+  it("keeps Script error. when stack frames are present", () => {
+    const event = exceptionEvent([
+      {
+        type: "Error",
+        value: "Script error.",
+        stacktrace: {
+          frames: [{ filename: "/index.js", function: "boot" }],
+        },
+      },
+    ]);
+    expect(filterPosthogBeforeSend(event)).toBe(event);
+  });
+
   it("keeps ApiError exceptions", () => {
     const event = exceptionEvent([
       { type: "ApiError", value: "Request failed with status 500" },

packages/web/src/auth/posthog/posthog-exception-filter.util.ts

@@ -8,9 +8,20 @@ import { isTransientBrowserNetworkMessage } from "@web/api/util/backend-unavaila
 const CEFSHARP_SCANNER_MESSAGE =
   "Object Not Found Matching Id:1, MethodName:update, ParamCount:4";
 
+/**
+ * Browser-sanitized cross-origin `window.onerror` message. Same-origin app
+ * scripts (this app's `/index.js` module) report real messages + frames;
+ * "Script error." with no stack is almost always an extension, in-app browser,
+ * or other third-party script — never actionable from our code alone.
+ */
+const SCRIPT_ERROR_MESSAGE = "Script error.";
+
 type ExceptionEntry = {
   type?: unknown;
   value?: unknown;
+  stacktrace?: {
+    frames?: unknown[];
+  };
 };
 
 const readExceptionEntries = (
@@ -40,11 +51,22 @@ const readExceptionEntries = (
   }));
 };
 
+const hasStackFrames = (entry: ExceptionEntry): boolean => {
+  const frames = entry.stacktrace?.frames;
+  return Array.isArray(frames) && frames.length > 0;
+};
+
 const isDroppableException = (entry: ExceptionEntry): boolean => {
   if (typeof entry.value !== "string") return false;
 
   if (entry.value === CEFSHARP_SCANNER_MESSAGE) return true;
 
+  // Opaque cross-origin errors. Keep the rare case where frames somehow
+  // survived sanitization so a real stack is never discarded.
+  if (entry.value === SCRIPT_ERROR_MESSAGE && !hasStackFrames(entry)) {
+    return true;
+  }
+
   // SuperTokens/browser network blips that escape as unhandledrejections.
   // The app already treats these as expected unavailability; capturing them
   // only creates noise. SuperTokens' session fetch often rejects outside our

packages/web/src/auth/posthog/posthog.bootstrap.ts

@@ -36,7 +36,8 @@ export function initPosthog(): PostHog | undefined {
       capture_console_errors: false,
     },
     // Drop known-unactionable exception signatures (SuperTokens/browser
-    // network blips, CefSharp scanner noise) before they become issues.
+    // network blips, CefSharp scanner noise, opaque "Script error.") before
+    // they become issues.
     before_send: filterPosthogBeforeSend,
     opt_in_site_apps: true,
     person_profiles: "always",