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

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Summary

PostHog showed new production volume on 2026-08-02 for Error: Script error. (5 occurrences / 2 users / 2 sessions), all Safari (desktop + iOS), all from the August email campaign (utm_source=email&utm_campaign=august), on /life and /week.

Every sample was synthetic, $exception_handled: false, and had no stack frames. Compass loads only same-origin /index.js as a module — real app exceptions report useful messages and frames. Opaque Script error. here is the browser sanitizing a cross-origin failure (extension / in-app browser / third-party inject), which matches the existing CefSharp / network-noise filter policy.

Also confirmed during triage: Selected event not found spiked earlier the same day and is already fixed/resolved by #2549 (merged ~3 minutes after last occurrence).

Change: drop $exception events whose value is exactly Script error. and that have no stack frames in filterPosthogBeforeSend. Keep any payload that somehow still has frames.

Simplicity

One exact-message check in the existing before_send filter, plus a frames guard so we never discard a stack-bearing event.

Automated validation

• Triaged active PostHog issues (7d / 48h / 30d; users + occurrences + first_seen).
• Sampled all 5 Script error events; reconstructed both affected session timelines.
• Confirmed production hosts only same-origin module scripts in index.html.
• Confirmed healthy traffic (~45 users on 2026-08-02).

Independent review

Focused diff review of the filter + tests: exact-message match, frames guard, no change to capture_console_errors / ApiError paths.

Test plan

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

Remaining risk

• Filter only applies after deploy; existing issue may still receive events until then — resolve/suppress after volume stops.
• If a future same-origin bug somehow surfaces only as Script error. with zero frames (should not happen for this app's script loading), it would be dropped; actionable app bugs still report real messages + frames.

Error signatures addressed

• Error: Script error. (issue)