Symptoms

• Pageviews ~1.6x baseline after SPA migration.
• DebugView shows duplicate page_view on route change.

Checks

1. GTM preview: multiple tags firing on historyChange and on a custom event.
2. Router: both pushState listener and route hook send events.

Fix

• Emit exactly one page_view per route.
• Debounce history changes; dedupe if same path within 500ms.

Validate

• Compare 7‑day pre/post; <5% drift accepted.
• Segment by route group to detect regressions.