feat: auth screen with auto-redirect, sync favorites/history with backend

.agents/skills/vercel-composition-patterns/rules/state-decouple-implementation.md

@@ -0,0 +1,113 @@
+---
+title: Decouple State Management from UI
+impact: MEDIUM
+impactDescription: enables swapping state implementations without changing UI
+tags: composition, state, architecture
+---
+
+## Decouple State Management from UI
+
+The provider component should be the only place that knows how state is managed.
+UI components consume the context interface—they don't know if state comes from
+useState, Zustand, or a server sync.
+
+**Incorrect (UI coupled to state implementation):**
+
+```tsx
+function ChannelComposer({ channelId }: { channelId: string }) {
+  // UI component knows about global state implementation
+  const state = useGlobalChannelState(channelId)
+  const { submit, updateInput } = useChannelSync(channelId)
+
+  return (
+    <Composer.Frame>
+      <Composer.Input
+        value={state.input}
+        onChange={(text) => sync.updateInput(text)}
+      />
+      <Composer.Submit onPress={() => sync.submit()} />
+    </Composer.Frame>
+  )
+}
+```
+
+**Correct (state management isolated in provider):**
+
+```tsx
+// Provider handles all state management details
+function ChannelProvider({
+  channelId,
+  children,
+}: {
+  channelId: string
+  children: React.ReactNode
+}) {
+  const { state, update, submit } = useGlobalChannel(channelId)
+  const inputRef = useRef(null)
+
+  return (
+    <Composer.Provider
+      state={state}
+      actions={{ update, submit }}
+      meta={{ inputRef }}
+    >
+      {children}
+    </Composer.Provider>
+  )
+}
+
+// UI component only knows about the context interface
+function ChannelComposer() {
+  return (
+    <Composer.Frame>
+      <Composer.Header />
+      <Composer.Input />
+      <Composer.Footer>
+        <Composer.Submit />
+      </Composer.Footer>
+    </Composer.Frame>
+  )
+}
+
+// Usage
+function Channel({ channelId }: { channelId: string }) {
+  return (
+    <ChannelProvider channelId={channelId}>
+      <ChannelComposer />
+    </ChannelProvider>
+  )
+}
+```
+
+**Different providers, same UI:**
+
+```tsx
+// Local state for ephemeral forms
+function ForwardMessageProvider({ children }) {
+  const [state, setState] = useState(initialState)
+  const forwardMessage = useForwardMessage()
+
+  return (
+    <Composer.Provider
+      state={state}
+      actions={{ update: setState, submit: forwardMessage }}
+    >
+      {children}
+    </Composer.Provider>
+  )
+}
+
+// Global synced state for channels
+function ChannelProvider({ channelId, children }) {
+  const { state, update, submit } = useGlobalChannel(channelId)
+
+  return (
+    <Composer.Provider state={state} actions={{ update, submit }}>
+      {children}
+    </Composer.Provider>
+  )
+}
+```
+
+The same `Composer.Input` component works with both providers because it only
+depends on the context interface, not the implementation.