Audit shared lifecycle state before claiming metric compatibility

Adding a separate analytics event does not preserve existing metrics when the new instrumentation also changes shared attempt state. Compare the old and new lifecycle boundaries, then intersect the emitted event changes with each saved chart's actual filters. Starting an attempt earlier can make previously ignored setup failures enter the old denominator and reduce apparent success without a product regression. Added completion records cannot affect charts restricted to attempts, and records missing experiment attributes cannot repair experiment-filtered charts. Preserve the legacy tracker independently when historical comparability is required; otherwise make the measurement boundary explicit. Source-level reproduction establishes the mechanism, not its production frequency.

Applies when: New journey instrumentation reuses counters or callbacks that feed existing dashboards. Keywords: analytics dashboard compatibility attempt lifecycle denominator completion experiment filters