Skip native frames in the third-party exception filter

[posthog]

Problem

• The third-party exception filter shipped this morning still lets vendor chunk-load errors through, so the team keeps triaging the same noise.
• The filter drops an exception only when every frame is identifiable third-party code. One native browser frame (Array.reduce, filename <anonymous>, in_app: false) matches no host and no vendor path, so it counts as unknown and keeps the whole exception.
• A new Loading chunk 7130 failed after 3 retries landed with five of six frames naming the Klaviyo onsite runtime and one native frame. The filter was live for ~4.5 hours before this event and still let it through.
• Cost is triage time, not user impact — one occurrence, one user, one session. This is the fifth exception of the same third-party class in four days (chunk 532, ResizeObserver, ProgressEvent, a max-call-stack case).

Changes

• Classify each frame as native, third-party, or first-party instead of only third-party vs unknown.
• Skip native and anonymous frames (<anonymous>, [native code], and non-in_app frames with no source).
• Drop the exception when at least one remaining frame is third-party and no frame is first-party.
• Unknown and first-party frames still keep the exception, so real first-party failures stay visible. Per-entry evaluation is unchanged, so a cause chain that touches our code is retained.

Stack	Before	After
All vendor frames	drop	drop
Vendor frames + one native frame	keep (bug)	drop
Vendor frames + one first-party frame	keep	keep
Unknown or missing origin	keep	keep

Tests

• Added a case to tests/analytics-third-party-filter.test.js for the chunk 7130 stack: five Klaviyo frames with an interleaved native Array.reduce frame, asserted dropped.
• node --test tests/analytics-third-party-filter.test.js — 14 pass.
• One unrelated pre-existing failure remains in scripts/generate-seo.test.mjs (fails on a clean checkout of main, untouched here).

---

Created with PostHog Desktop from this inbox report.

[Jingxi-Polymaker]

Superseded by #80, now merged. Both fixes suppress the reported Klaviyo stack with native Array.reduce. #80 requires explicit in_app: false and preserves conflicting source information, retaining unknown-origin and first-party exceptions that this implementation can suppress. It also adds regression coverage for native-only stacks, mixed frames, and exception causes.