fix(ai-client): warn when receiving deprecated [DONE] sentinel

Old servers still emit `data: [DONE]\n\n` after the stream.  The client
already skips it, but now logs a deprecation warning so users know to
upgrade their @tanstack/ai server package.

Author: AlemTuzlak

packages/typescript/ai-client/src/connection-adapters.ts

@@ -312,7 +312,12 @@ export function fetchServerSentEvents(
         // Handle Server-Sent Events format
         const data = line.startsWith('data: ') ? line.slice(6) : line
 
-        if (data === '[DONE]') continue
+        if (data === '[DONE]') {
+          console.warn(
+            '[@tanstack/ai-client] Received [DONE] sentinel. This is deprecated — upgrade your @tanstack/ai server package. RUN_FINISHED is the stream terminator.',
+          )
+          continue
+        }
 
         try {
           const parsed: StreamChunk = JSON.parse(data)

packages/typescript/ai-client/src/sse-parser.ts

@@ -64,7 +64,12 @@ export async function* parseSSEResponse(
   for await (const line of readStreamLines(reader, abortSignal)) {
     const data = line.startsWith('data: ') ? line.slice(6) : line
 
-    if (data === '[DONE]') continue
+    if (data === '[DONE]') {
+      console.warn(
+        '[@tanstack/ai-client] Received [DONE] sentinel. This is deprecated — upgrade your @tanstack/ai server package. RUN_FINISHED is the stream terminator.',
+      )
+      continue
+    }
 
     try {
       const parsed: StreamChunk = JSON.parse(data)

packages/typescript/ai-client/tests/connection-adapters.test.ts

@@ -104,7 +104,9 @@ describe('connection-adapters', () => {
       expect(chunks).toHaveLength(1)
     })
 
-    it('should skip [DONE] markers', async () => {
+    it('should skip [DONE] markers and warn about deprecation', async () => {
+      const warnSpy = vi.spyOn(console, 'warn').mockImplementation(() => {})
+
       const mockReader = {
         read: vi
           .fn()
@@ -135,6 +137,11 @@ describe('connection-adapters', () => {
       }
 
       expect(chunks).toHaveLength(0)
+      expect(warnSpy).toHaveBeenCalledWith(
+        expect.stringContaining('[DONE] sentinel'),
+      )
+
+      warnSpy.mockRestore()
     })
 
     it('should handle malformed JSON gracefully', async () => {