# Web Performance Regression Investigation ## 1. Executive Regression Status Final Status: PERFORMANCE REGRESSION CONFIRMED Primary Regression: Checkout performance materially deteriorated under comparable supplied lab conditions. Affected Scope: Checkout route — supplied mobile lab profile. Baseline Quality: BASELINE VERIFIED Comparison Quality: COMPARABLE Largest Supported Delta: LCP +0.7 s Checkout JavaScript +230 KB Performance Budget / Target: NOT SUPPLIED Main Root Cause: New synchronous client dependency is a likely material contributor. Root-Cause Evidence State: INFERRED / LIKELY ## 3. Evidence Inventory VERIFIED / OBSERVED: - Baseline LCP: 1.8 s - Current LCP: 2.5 s - Baseline JS: 180 KB - Current JS: 410 KB - New synchronous dependency exists in supplied diff INFERRED / LIKELY: - The dependency growth materially contributes to the observed performance regression. NEEDS VERIFICATION: - Exact share of LCP deterioration attributable to the new dependency - Production field impact ## 5. Comparability Assessment Comparison Quality: COMPARABLE Aligned Factors: - same route - same mobile profile - same network - same CPU - same cold-cache condition ## 6. Performance Regression Map | Surface / Metric | Baseline | Current | Delta | Comparison | Regression State | Finding | |---|---:|---:|---:|---|---|---| | Checkout LCP | 1.8 s | 2.5 s | +0.7 s | COMPARABLE | REGRESSION OBSERVED | WPR-LCP-001 | | Checkout JS | 180 KB | 410 KB | +230 KB | COMPARABLE | REGRESSION OBSERVED | WPR-BUNDLE-001 | ## 8. High-Priority Findings | Finding ID | Title | Severity | Surface | Regression State | Impact | |---|---|---|---|---|---| | WPR-LCP-001 | Checkout LCP deterioration | HIGH | Checkout | REGRESSION OBSERVED | Slower primary-route rendering | | WPR-BUNDLE-001 | Route bundle growth | HIGH | Checkout | REGRESSION OBSERVED | More transfer and client execution | ## 9. Detailed Regression Findings ### WPR-BUNDLE-001 — Checkout Bundle Growth Domain: Bundle / JavaScript Severity: HIGH Evidence Status: VERIFIED / OBSERVED Affected Route: Checkout Baseline Evidence: Previous comparable bundle report. Current Evidence: Current comparable bundle report. Comparison Quality: COMPARABLE Baseline Measurement: 180 KB Current Measurement: 410 KB Absolute Delta: +230 KB Relative Delta: +127.8% Performance Budget / Target: NOT SUPPLIED Performance Change / Regression Evidence: Comparable route bundle evidence directly shows an increase from 180 KB to 410 KB. Regression State: REGRESSION OBSERVED Relevant Source / Change: New synchronous client dependency in supplied diff. Root Cause: The newly added dependency is a likely material contributor to increased client-side resource cost. Root-Cause Evidence State: INFERRED / LIKELY User Impact: More JavaScript must be transferred and processed on a primary route. Smallest Recommended Correction: Remove the accidental synchronous route-level import or restore justified code splitting without changing required checkout functionality. Correction Risk: Lazy-loading timing, dependency initialization and checkout functionality. Dependent Surfaces: Any route sharing the same client dependency. Re-Verification: Repeat the same route bundle analysis and comparable checkout lab test. ## 15. Targeted Correction Plan WPR-BUNDLE-001: Restore appropriate route-level loading behavior for the added dependency. WPR-LCP-001: Re-test LCP after the bundle correction before attributing the entire LCP delta to that change. ## 16. Correction Regression Risks Check: - checkout functionality - dependency initialization - loading-state behavior - shared routes - code-split chunk delivery ## 17. Re-Verification Plan Re-test using the same: - route - build mode - browser profile - device/emulation - network - CPU - cache condition One improved run alone should not be treated as production-wide resolution. ## 18. Unverified / Non-Comparable Areas Production field impact: NEEDS VERIFICATION Source-level contribution to the full LCP delta: NEEDS VERIFICATION beyond the current inference. ## 19. Final Regression Status PERFORMANCE REGRESSION CONFIRMED Comparable supplied evidence demonstrates material checkout deterioration. The regression is confirmed even though precise causal attribution remains partly inferred.