Safari Technology Preview 251 Engine & Regression Diagnostics

Subsystem Benchmark Suite READY

Active Subsystem Test Suite

Benchmark Cycles / Iterations (100 - 2000)

Live Micro-Timing Telemetry (ms per pass)

Micro-DOM Interactive Mutation Sandbox

Engine Performance Telemetry Idle

Compliance

99.4%

WebKit Core

Throughput Delta

+14.2%

vs Stable 18.2

Mean Latency

1.12 ms

892 ops/sec

Regression Verification & Resolved Fixes

Bug 288412 [RESOLVED]

Subgrid aspect-ratio re-calc cycle causing infinite layout cascade on container queries.

Bug 289104 [RESOLVED]

JSC Tier-2 DFG inline cache invalidation on repeated keyed dictionary lookups.

Bug 288921 [RESOLVED]

OffscreenCanvas zero-copy texture upload memory leak in multi-worker context.

Diagnostic Execution Logs

[INIT] STP 251 WebKit diagnostic harness initialized.

[READY] Ready for Subgrid & Masonry Layout Cycle benchmark.

WebKit Feature & Flag Baseline Comparison Safari Stable vs STP 251

Subsystem / Feature Flag	Safari 18.2 Stable	STP 251 (Current)	Status / Regression Delta
CSS Subgrid Container Queries	Partial (Recalc Loop Bug)	Fixed (STP 251)	PASSED +18.4% Frame Pacing
JSC DFG JIT Inline Caching	Deopt on Keyed Dictionary	Optimized (Tier-2)	PASSED +12.1% Execution Speed
Canvas Path2D GPU Batching	Serial Rasterization	Parallel Pipeline	PASSED +15.8% Draw Calls/sec
ARIA Live Region Tree Sync	Synchronous Mutation Block	Async Microtask Batch	PASSED -3.2ms Jank Reduced