Fix theme hydration mismatch - #58
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The hook initialised state from localStorage and matchMedia during the first client render, so the server-rendered sun icon could differ from the client's moon icon and React reported a hydration error on every page. The pre-hydration script already puts the theme class on the html element, so the hook now treats that class as the single source of truth through useSyncExternalStore, rendering light on the server and reading the real theme once hydrated.
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Problem
React reported error 418 (text hydration mismatch) on every page.
useThemeinitialised its state from localStorage and matchMedia during the first client render, so the server-rendered ☀️ could differ from the client's 🌙.Fix
The pre-hydration
ThemeScriptalready puts thelight/darkclass on thehtmlelement before React runs. The hook now treats that class as the single source of truth viauseSyncExternalStore: it renderslighton the server, reads the real class once hydrated, and follows later class changes through a MutationObserver. Toggling writes the class and localStorage directly.Theme resolution logic (stored preference, then system preference) now lives only in
ThemeScript.Verification
theme=darkstored: no console errors on load, moon icon shown, toggle works both ways and persists🤖 Generated with Claude Code