fix: notify web listeners when new styles loaded

CONTEXT.md

@@ -81,7 +81,7 @@ Web runtime:
 
 - Web keeps styles in CSS and passes `{ $$css: true, tailwind: className }` through RNW style arrays.
 - `getWebStyles` uses a hidden DOM element to compute style values when a JS value is needed, such as color extraction or `useResolveClassNames`.
-- `CSSListener` tracks active CSS rules and media queries, then notifies subscribers when class-dependent media rules change.
+- `CSSListener` tracks active CSS rules and media queries, then notifies subscribers when class-dependent media rules change. After scanning newly discovered stylesheets, it emits a variables notification so JS-resolved styles refresh when CSS arrives after module initialization, including Metro web development startup.
 - `ScopedTheme` renders a `div` with the theme class and `display: contents` on web.
 - `LayoutDirection` renders a contents-style wrapper with `direction`/`dir` semantics so RTL/LTR variants can be scoped to a subtree.
 - `ScopedVariables` renders a `display: contents` wrapper and sets its variables as inline custom properties on that wrapper, so the real DOM cascade resolves `var(--name)` to the scoped value for every descendant (numbers become px). During JS reads (`getWebVariable` / `useResolveClassNames`) it also applies the variables to the hidden `dummyParent`, then clears them.

packages/uniwind/src/core/web/cssListener.ts

@@ -124,6 +124,7 @@ class CSSListenerBuilder {
     private initialize() {
         this.pendingInitialization = undefined
         this.pruneStaleRules()
+        let added = false
 
         for (const sheet of Array.from(document.styleSheets)) {
             // Skip already processed stylesheets
@@ -149,6 +150,11 @@ class CSSListenerBuilder {
             this.processedStyleSheets.add(sheet)
 
             this.addMediaQueriesDeep(rules)
+            added = true
+        }
+
+        if (added) {
+            UniwindListener.notify([StyleDependency.Variables])
         }
     }
 

packages/uniwind/tests/web/core/css-listener.test.ts

@@ -0,0 +1,45 @@
+import { afterEach, expect, test, vi } from 'vitest'
+import { CSSListener } from '../../../src/core/web/cssListener'
+
+afterEach(() => {
+    vi.useRealTimers()
+    vi.unstubAllGlobals()
+})
+
+test('notifies class subscribers after discovering a stylesheet injected later', async () => {
+    vi.useFakeTimers()
+    vi.stubGlobal('requestIdleCallback', undefined)
+
+    const style = document.createElement('style')
+    style.textContent = '.accent-late { accent-color: rgb(255, 0, 0); }'
+
+    const listener = vi.fn(() => {
+        const rule = Array.from(CSSListener.activeRules).find(rule => rule.selectorText === '.accent-late')
+        return rule?.style.getPropertyValue('accent-color')
+    })
+    const dispose = CSSListener.subscribeToClassName('accent-late', listener)
+
+    try {
+        document.head.appendChild(style)
+        await Promise.resolve()
+
+        expect(listener).not.toHaveBeenCalled()
+        await vi.advanceTimersByTimeAsync(50)
+
+        expect(listener).toHaveBeenCalledTimes(1)
+        expect(listener).toHaveLastReturnedWith('rgb(255, 0, 0)')
+
+        // A scan with no new stylesheet should not invalidate resolved styles.
+        const meta = document.createElement('meta')
+        document.head.appendChild(meta)
+        await Promise.resolve()
+        await vi.advanceTimersByTimeAsync(50)
+        expect(listener).toHaveBeenCalledTimes(1)
+        meta.remove()
+    } finally {
+        dispose()
+        style.remove()
+        await Promise.resolve()
+        await vi.advanceTimersByTimeAsync(50)
+    }
+})