fix(web): drop third-party browser extension exceptions

[posthog]

Problem

• Error tracking shows a junk issue, "Invalid call to runtime.sendMessage(). Tab not found.", that amend.sh did not cause — noise that hides real issues.
• The message is a Safari WebExtension API error thrown by a visitor's browser extension inside the page. amend.sh has no chrome.runtime or browser.runtime call anywhere in apps/web or packages/backend.
• getPostHogOptions() set capture_exceptions: true with no before_send filter, so posthog-js forwarded every unhandled window error, including third-party ones.

Changes

• Add a before_send hook to getPostHogOptions() that drops an $exception event when its message matches a known WebExtension messaging API and its stack carries no application frame.
• Keep the decision in a pure helper, isThirdPartyExtensionException(), with unit tests.

     autocapture: false,
     capture_exceptions: true,
+    before_send: (event) => {
+      if (event?.event === "$exception" && isThirdPartyExtensionException(event.properties)) {
+        return null;
+      }
+      return event;
+    },

Drop rule — both conditions must hold:

Condition	Reason
Message matches runtime/tabs.sendMessage/connect/onMessage/onConnect	Marks a WebExtension messaging error
No frame has in_app === true	Our own code always reports an application frame, so this spares real errors

Note

The filter is conservative: an error keeps flowing whenever any application frame is present, even if the message matches. Only frameless, synthetic extension errors are dropped.

Testing

• bun test scripts/posthog-exception-filter.test.ts — 5 pass (drops the reported error, keeps application errors and unrelated events).
• turbo -F web check-types, oxlint, and oxfmt --check pass on the changed files.

Agent context

• The PostHog signal routed to opencoredev/opentab, but that repo is a bare WXT scaffold with no PostHog setup. The real capture path lives here in amend.sh, so the fix lands here.
• After merge, suppress the existing error tracking issue so it does not reopen on the last event.

Why

A single Safari visit to https://amend.sh/#pricing filed a visitor extension error as an amend.sh issue. The impact is low, but this class of noise recurs for as long as the filter is missing.

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Created with PostHog Desktop from this inbox report.