feat(ui): render AI messages with streaming markdown

Messages store gains streamingIds set and startStream/appendStream/
endStream actions. Gateway store routes stream action payloads to
these new actions. Chat component switches to StreamingMarkdown
for in-progress messages, providing incremental block-level rendering.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

packages/store/src/gateway.ts

@@ -1,5 +1,5 @@
 import { create } from "zustand"
-import { GatewayClient, type ConnectionState, type DeviceInfo, type SendErrorResponse } from "@multica/sdk"
+import { GatewayClient, StreamAction, type ConnectionState, type DeviceInfo, type SendErrorResponse, type StreamPayload } from "@multica/sdk"
 import { useMessagesStore } from "./messages"
 
 const DEFAULT_GATEWAY_URL = "http://localhost:3000"
@@ -45,6 +45,32 @@ export const useGatewayStore = create<GatewayStore>()((set, get) => ({
     })
       .onStateChange((connectionState) => set({ connectionState }))
       .onMessage((msg) => {
+        // Handle streaming messages
+        if (msg.action === StreamAction) {
+          const payload = msg.payload as StreamPayload
+          const store = useMessagesStore.getState()
+          switch (payload.state) {
+            case "delta": {
+              const exists = store.messages.some((m) => m.id === payload.streamId)
+              if (!exists) {
+                store.startStream(payload.streamId, payload.agentId)
+              }
+              if (payload.content) {
+                store.appendStream(payload.streamId, payload.content)
+              }
+              break
+            }
+            case "final":
+              store.endStream(payload.streamId, payload.content ?? "")
+              break
+            case "error":
+              store.endStream(payload.streamId, `[error] ${payload.error}`)
+              break
+          }
+          return
+        }
+
+        // Fallback: complete message handling
         const payload = msg.payload as { agentId?: string; content?: string }
         if (payload?.agentId && payload?.content) {
           useMessagesStore.getState().addAssistantMessage(payload.content, payload.agentId)

packages/store/src/messages.ts

@@ -10,6 +10,7 @@ export interface Message {
 
 interface MessagesState {
   messages: Message[]
+  streamingIds: Set<string>
 }
 
 interface MessagesActions {
@@ -18,12 +19,16 @@ interface MessagesActions {
   updateMessage: (id: string, content: string) => void
   loadMessages: (agentId: string, msgs: Message[]) => void
   clearMessages: (agentId?: string) => void
+  startStream: (streamId: string, agentId: string) => void
+  appendStream: (streamId: string, content: string) => void
+  endStream: (streamId: string, content: string) => void
 }
 
 export type MessagesStore = MessagesState & MessagesActions
 
 export const useMessagesStore = create<MessagesStore>()((set, get) => ({
   messages: [],
+  streamingIds: new Set<string>(),
 
   addUserMessage: (content, agentId) => {
     set((s) => ({
@@ -54,4 +59,32 @@ export const useMessagesStore = create<MessagesStore>()((set, get) => ({
       messages: agentId ? s.messages.filter((m) => m.agentId !== agentId) : [],
     }))
   },
+
+  startStream: (streamId, agentId) => {
+    set((s) => {
+      const ids = new Set(s.streamingIds)
+      ids.add(streamId)
+      return {
+        messages: [...s.messages, { id: streamId, role: "assistant" as const, content: "", agentId }],
+        streamingIds: ids,
+      }
+    })
+  },
+
+  appendStream: (streamId, content) => {
+    set((s) => ({
+      messages: s.messages.map((m) => (m.id === streamId ? { ...m, content } : m)),
+    }))
+  },
+
+  endStream: (streamId, content) => {
+    set((s) => {
+      const ids = new Set(s.streamingIds)
+      ids.delete(streamId)
+      return {
+        messages: s.messages.map((m) => (m.id === streamId ? { ...m, content } : m)),
+        streamingIds: ids,
+      }
+    })
+  },
 }))

packages/ui/src/components/chat.tsx

@@ -6,6 +6,7 @@ import { Badge } from "@multica/ui/components/ui/badge";
 import { Button } from "@multica/ui/components/ui/button";
 import { ChatInput } from "@multica/ui/components/chat-input";
 import { MemoizedMarkdown } from "@multica/ui/components/markdown";
+import { StreamingMarkdown } from "@multica/ui/components/markdown/StreamingMarkdown";
 import { HugeiconsIcon } from "@hugeicons/react";
 import { UserIcon, Copy01Icon, CheckmarkCircle02Icon } from "@hugeicons/core-free-icons";
 import { toast } from "@multica/ui/components/ui/sonner";
@@ -27,6 +28,7 @@ export function Chat() {
   const gwState = useGatewayStore((s) => s.connectionState)
 
   const messages = useMessagesStore((s) => s.messages)
+  const streamingIds = useMessagesStore((s) => s.streamingIds)
   const filtered = useMemo(() => messages.filter(m => m.agentId === activeAgentId), [messages, activeAgentId])
 
   const handleSend = useCallback((text: string) => {
@@ -99,25 +101,32 @@ export function Chat() {
           </div>
         ) : (
           <div className="px-4 py-6 space-y-6 max-w-4xl mx-auto">
-            {filtered.map((msg) => (
-              <div
-                key={msg.id}
-                className={cn(
-                  "flex",
-                  msg.role === "user" ? "justify-end" : "justify-start"
-                )}
-              >
+            {filtered.map((msg) => {
+              const isStreaming = streamingIds.has(msg.id)
+              return (
                 <div
+                  key={msg.id}
                   className={cn(
-                    msg.role === "user" ? "bg-muted rounded-md max-w-[60%] p-1 px-2.5" : "w-full p-1 px-2.5"
+                    "flex",
+                    msg.role === "user" ? "justify-end" : "justify-start"
                   )}
                 >
-                  <MemoizedMarkdown mode="minimal" id={msg.id}>
-                    {msg.content}
-                  </MemoizedMarkdown>
+                  <div
+                    className={cn(
+                      msg.role === "user" ? "bg-muted rounded-md max-w-[60%] p-1 px-2.5" : "w-full p-1 px-2.5"
+                    )}
+                  >
+                    {isStreaming ? (
+                      <StreamingMarkdown content={msg.content} isStreaming={true} mode="minimal" />
+                    ) : (
+                      <MemoizedMarkdown mode="minimal" id={msg.id}>
+                        {msg.content}
+                      </MemoizedMarkdown>
+                    )}
+                  </div>
                 </div>
-              </div>
-            ))}
+              )
+            })}
           </div>
         )}
       </main>