fix(analytics): drop browser-extension exception noise before ingestion

[posthog]

What does this PR do?

Adds a before_send filter to the shared PostHog init (packages/analytics) so exceptions injected by third-party browser extensions never reach error tracking. The trigger was an error-tracking inbox issue — 'Error' captured as exception with message: 'Invalid call to runtime.sendMessage(). Tab not found.' — which is thrown by a browser extension's injected content script, not by us. runtime.sendMessage is the WebExtension messaging API and we ship no chrome.runtime / browser.runtime usage anywhere in the repo, so nothing in our code path produces it.

The shared init previously had no before_send hook, so it ingested this class of extension noise as-is.

• Detection lives in a small, pure, unit-tested module (lib/before-send.ts) that drops $exception events whose message matches known extension messaging errors, or whose stack frames are served from extension URL schemes (chrome-extension://, moz-extension://, safari-web-extension://, …). All other events pass through untouched.
• The filter is exported from @trycompai/analytics so any app consuming it gets the same behavior.

Why: This exception is externally-injected browser-extension noise with no matching code in the repo — pure inbox clutter, no user-facing bug. The before_send hook stops this class of noise going forward.

Note on scope: The specific events that raised the issue occurred on the www.trycomp.ai landing page, which lives in a separate repo, so this monorepo change does not affect those exact events. Those have already been handled directly in error tracking (issue marked suppressed + a tightly-scoped ingestion suppression rule matching only the runtime.sendMessage message). This PR is the going-forward, defense-in-depth piece for the apps in this repo that use the shared PostHog provider.

• Fixes #XXXX (GitHub issue number) — N/A
• Fixes COMP-XXXX (Linear issue number) — N/A

Visual Demo (For contributors especially)

N/A — this only drops third-party browser-extension exceptions before they are sent to PostHog; there is no user-facing UI change.

Mandatory Tasks (DO NOT REMOVE)

• I have self-reviewed the code (A decent size PR without self-review might be rejected).
• I have updated the developer docs in /docs if this PR makes changes that would require a documentation change. If N/A, write N/A here and check the checkbox. — N/A
• I confirm automated tests are in place that prove my fix is effective or that my feature works.

How should this be tested?

• No environment variables required.
• cd packages/analytics && bun run test (or vitest run) exercises lib/before-send.test.ts, which covers: the runtime.sendMessage "Tab not found" message, extension-scheme stack frames, the flat $exception_message fallback, genuine app exceptions passing through, non-$exception events being ignored, and malformed/missing properties not throwing.
• Expected: extension-originated $exception events return null from before_send (dropped); all real events and non-exception events pass through unchanged.

Checklist

N/A

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Created with PostHog Code from this inbox report.

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Summary by cubic

Drops third‑party browser extension exception noise before ingestion by adding a PostHog before_send filter in @trycompai/analytics. This keeps error tracking clean by suppressing extension‑generated $exception events (e.g., WebExtension runtime.sendMessage “Tab not found”).

• Bug Fixes

  • Adds before_send: dropBrowserExtensionExceptions to the shared PostHog init.
  • Detects known extension messages and extension‑scheme stack frames; passes real events through.
  • Exports the filter from @trycompai/analytics and adds unit tests.

• Dependencies

  • Adds vitest and a minimal config to run analytics package tests.

^{Written for commit 06f222b. Summary will update on new commits.}

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