fix(scroll): scope StyleCache.reset to the locked element

[blvdmitry]

Problem

StyleCache.reset() restored and cleared the entire cache, regardless of which element a given lock owned:

reset = () => {
  for (const [el, styles] of this.cache.entries()) Object.assign(el.style, styles);
  this.cache.clear();
};

lockStandardScroll and lockSafariScroll each use a module-level StyleCache shared across all their calls. So when two different elements are locked at once — e.g. an Overlay locking one container (useScrollLock({ containerRef })) while a ContextMenu locks another (useScrollLock({ originRef })) — restoring one lock wipes the saved originals of the other still-active lock. The survivor can no longer restore its styles (scroll lock leaks or releases early).

Note this is the cross-container case. The per-container guard in lockScroll (if (container.style.overflow === "hidden") return) only blocks re-locking the same element, so two different elements both land in the shared cache.

Fix

Make StyleCache a per-element lock registry:

• reset(el) is now required and scoped — it restores and removes only that element's entry, never touching other active locks.
• set(el, styles) is a no-op when the element is already cached — locking an already-locked element keeps the originals captured the first time, instead of merging.
• lockStandardScroll builds its styles into one object and calls set() once (overflow + optional scrollbar-gutter/paddingRight together), so all keys are captured atomically — required now that set() is idempotent per element.
• lockSafariScroll already does a single set(); its unlock now calls reset(document.body).

reset = (el: HTMLElement) => {
  const styles = this.cache.get(el);
  if (!styles) return;
  Object.assign(el.style, styles);
  this.cache.delete(el);
};

API note

reset() now requires an element (the global no-arg form is removed). The only callers are the two lock modules; both pass the element they locked.

Verification

• tsc --noEmit → 0 errors. oxlint → clean.
• StyleCache.test.ts updated for the new semantics (scoped reset, idempotent set, no-op reset for uncached element).
• Added an integration test in scroll/tests/lock.test.ts: unlocking one container does not affect another locked container — confirmed it fails against the old global-wipe reset() and passes with the scoped fix.
• Full css + scroll suites green (13 tests).

How to test

1. Lock scroll on two different containers (e.g. an Overlay container and a ContextMenu's scrollable region), then unlock one.
2. Before: the still-locked container loses its saved styles and can't restore on its own unlock. After: each unlock restores only its own element.

Found during a full package bug review. Part of the scroll-lock cluster.

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Generated by Claude Code

[github-actions]

size-limit report 📦

Path	Size	Loading time (3g)	Running time (snapdragon)	Total time
Library / JS	48.48 KB (0%)	970 ms (0%)	286 ms (-6.52% 🔽)	1.3 s
Library / CSS	22.18 KB (0%)	444 ms (0%)	0 ms (+100% 🔺)	444 ms
Theming / JS	7.81 KB (0%)	157 ms (0%)	121 ms (+348.38% 🔺)	277 ms
Theming with a default theme definition / JS	8.65 KB (0%)	174 ms (0%)	210 ms (+304.76% 🔺)	383 ms