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docs/store/synced.md

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+# Synced Store
+
+Utility for creating Svelte stores that automatically persist to and restore from localStorage.
+
+## Functions
+
+### synced(key, defaultValue)
+
+Creates a writable store that synchronizes with localStorage using JSON serialization.
+
+**Parameters:**
+- `key` - localStorage key to store the value under
+- `defaultValue` - Default value if nothing exists in localStorage
+
+**Returns:** Writable Svelte store that persists changes to localStorage
+
+The store automatically:
+- Loads initial value from localStorage on creation
+- Saves any changes back to localStorage
+- Falls back to defaultValue if localStorage is empty or invalid
+
+## Example
+
+```typescript
+import {synced} from "@welshman/store"
+
+// Create a store that persists user preferences
+const userPreferences = synced("user-prefs", {
+  theme: "dark",
+  notifications: true,
+  language: "en"
+})
+
+// Use like any writable store
+userPreferences.subscribe(prefs => {
+  console.log("Preferences:", prefs)
+})
+
+// Update the store - automatically saves to localStorage
+userPreferences.update(prefs => ({
+  ...prefs,
+  theme: "light"
+}))
+```