Safari Technology Preview 250 adds Ruby overhang control, Explicit Resource Management, and ReadableStream fetch uploads

Safari Technology Preview 250 delivers a batch of CSS, JavaScript, and networking primitives that are still in flux across standards bodies. The `ruby-overhang: spaces` value and the `text-decoration-inset` property give typographers finer control over annotation placement, while the `white-space-trim` and `wrap-inside` properties address long-standing pain points in text wrapping. These additions are immediately testable but may still change before they ship in stable Safari, so teams should treat them as experimental rather than production-ready.

The JavaScript engine now implements the Explicit Resource Management proposal, including `using` declarations and `Symbol.dispose`. This lets developers replace manual cleanup patterns with deterministic disposal, reducing memory leaks in complex applications. The addition of `Iterator.zip()` and `Iterator.zipKeyed()` simplifies data pipeline code, but the feature flags mean engineers must opt in per-site, limiting its usefulness until it graduates to stable. WebAssembly gains relaxed SIMD and multiple memories, which improve performance for compute-heavy workloads but require recompilation of existing modules.

Networking changes are the most consequential for backend integration. Fetch now supports uploading a `ReadableStream` body with the `duplex` option, enabling streaming uploads without buffering the entire payload in memory. This is particularly useful for large file uploads or real-time data pipelines, but the requirement to set the `duplex` option means existing code must be updated to take advantage of it. The release also fixes a critical IndexedDB bug where a failed `put()` could delete both the old and new records, leaving the object store empty.

Accessibility and scrolling fixes address edge cases that could break user experience. VoiceOver no longer skips lines in textareas ending with a line break, and `scrollIntoView()` now correctly targets inline elements even when they share a line with taller content. These changes improve compatibility with existing sites but may require regression testing for applications that relied on the previous behavior. The removal of the non-standard `text` color value is a breaking change that could affect legacy code, though the replacement `canvastext` value is already widely supported.

WebDriver gains a new extension command to consume user activation, which helps test suites verify interactive behavior. Web Inspector now shows WebAssembly modules in the Sources tab, improving debugging for WebAssembly-heavy applications. These tooling improvements are incremental but reduce friction for engineers working with emerging web technologies. The release is available only for macOS Golden Gate and Tahoe, so teams targeting older macOS versions must continue using earlier previews.