fix: anthropic tool call issues

.changeset/fix-anthropic-multi-turn-tool-calls.md

@@ -0,0 +1,35 @@
+---
+'@tanstack/ai': patch
+'@tanstack/ai-client': patch
+'@tanstack/ai-anthropic': patch
+'@tanstack/ai-gemini': patch
+---
+
+fix(ai, ai-client, ai-anthropic, ai-gemini): fix multi-turn conversations failing after tool calls
+
+**Core (@tanstack/ai):**
+
+- Lazy assistant message creation: `StreamProcessor` now defers creating the assistant message until the first content-bearing chunk arrives (text, tool call, thinking, or error), eliminating empty `parts: []` messages from appearing during auto-continuation when the model returns no content
+- Add `prepareAssistantMessage()` (lazy) alongside deprecated `startAssistantMessage()` (eager, backwards-compatible)
+- Add `getCurrentAssistantMessageId()` to check if a message was created
+- **Rewrite `uiMessageToModelMessages()` to preserve part ordering**: the function now walks parts sequentially instead of separating by type, producing correctly interleaved assistant/tool messages (text1 + toolCall1 → toolResult1 → text2 + toolCall2 → toolResult2) instead of concatenating all text and batching all tool calls. This fixes multi-round tool flows where the model would see garbled conversation history and re-call tools unnecessarily.
+- Deduplicate tool result messages: when a client tool has both a `tool-result` part and a `tool-call` part with `output`, only one `role: 'tool'` message is emitted per tool call ID
+
+**Client (@tanstack/ai-client):**
+
+- Update `ChatClient.processStream()` to use lazy assistant message creation, preventing UI flicker from empty messages being created then removed
+
+**Anthropic:**
+
+- Fix consecutive user-role messages violating Anthropic's alternating role requirement by merging them in `formatMessages`
+- Deduplicate `tool_result` blocks with the same `tool_use_id`
+- Filter out empty assistant messages from conversation history
+- Suppress duplicate `RUN_FINISHED` event from `message_stop` when `message_delta` already emitted one
+- Fix `TEXT_MESSAGE_END` incorrectly emitting for `tool_use` content blocks
+- Add Claude Opus 4.6 model support with adaptive thinking and effort parameter
+
+**Gemini:**
+
+- Fix consecutive user-role messages violating Gemini's alternating role requirement by merging them in `formatMessages`
+- Deduplicate `functionResponse` parts with the same name (tool call ID)
+- Filter out empty model messages from conversation history

examples/ts-group-chat/package.json

@@ -14,11 +14,11 @@
     "@tanstack/ai-client": "workspace:*",
     "@tanstack/ai-react": "workspace:*",
     "@tanstack/react-devtools": "^0.8.2",
-    "@tanstack/react-router": "^1.141.1",
-    "@tanstack/react-router-devtools": "^1.139.7",
-    "@tanstack/react-router-ssr-query": "^1.139.7",
-    "@tanstack/react-start": "^1.141.1",
-    "@tanstack/router-plugin": "^1.139.7",
+    "@tanstack/react-router": "^1.158.4",
+    "@tanstack/react-router-devtools": "^1.158.4",
+    "@tanstack/react-router-ssr-query": "^1.158.4",
+    "@tanstack/react-start": "^1.159.0",
+    "@tanstack/router-plugin": "^1.158.4",
     "capnweb": "^0.1.0",
     "react": "^19.2.3",
     "react-dom": "^19.2.3",

examples/ts-react-chat/package.json

@@ -20,14 +20,14 @@
     "@tanstack/ai-openrouter": "workspace:*",
     "@tanstack/ai-react": "workspace:*",
     "@tanstack/ai-react-ui": "workspace:*",
-    "@tanstack/nitro-v2-vite-plugin": "^1.141.0",
+    "@tanstack/nitro-v2-vite-plugin": "^1.154.7",
     "@tanstack/react-devtools": "^0.8.2",
-    "@tanstack/react-router": "^1.141.1",
-    "@tanstack/react-router-devtools": "^1.139.7",
-    "@tanstack/react-router-ssr-query": "^1.139.7",
-    "@tanstack/react-start": "^1.141.1",
+    "@tanstack/react-router": "^1.158.4",
+    "@tanstack/react-router-devtools": "^1.158.4",
+    "@tanstack/react-router-ssr-query": "^1.158.4",
+    "@tanstack/react-start": "^1.159.0",
     "@tanstack/react-store": "^0.8.0",
-    "@tanstack/router-plugin": "^1.139.7",
+    "@tanstack/router-plugin": "^1.158.4",
     "@tanstack/store": "^0.8.0",
     "highlight.js": "^11.11.1",
     "lucide-react": "^0.561.0",

examples/ts-react-chat/src/routeTree.gen.ts

@@ -39,7 +39,7 @@ export interface FileRoutesByFullPath {
   '/': typeof IndexRoute
   '/api/tanchat': typeof ApiTanchatRoute
   '/example/guitars/$guitarId': typeof ExampleGuitarsGuitarIdRoute
-  '/example/guitars': typeof ExampleGuitarsIndexRoute
+  '/example/guitars/': typeof ExampleGuitarsIndexRoute
 }
 export interface FileRoutesByTo {
   '/': typeof IndexRoute
@@ -60,7 +60,7 @@ export interface FileRouteTypes {
     | '/'
     | '/api/tanchat'
     | '/example/guitars/$guitarId'
-    | '/example/guitars'
+    | '/example/guitars/'
   fileRoutesByTo: FileRoutesByTo
   to: '/' | '/api/tanchat' | '/example/guitars/$guitarId' | '/example/guitars'
   id:
@@ -97,7 +97,7 @@ declare module '@tanstack/react-router' {
     '/example/guitars/': {
       id: '/example/guitars/'
       path: '/example/guitars'
-      fullPath: '/example/guitars'
+      fullPath: '/example/guitars/'
       preLoaderRoute: typeof ExampleGuitarsIndexRouteImport
       parentRoute: typeof rootRouteImport
     }

examples/ts-solid-chat/package.json

@@ -19,8 +19,8 @@
     "@tanstack/ai-openai": "workspace:*",
     "@tanstack/ai-solid": "workspace:*",
     "@tanstack/ai-solid-ui": "workspace:*",
-    "@tanstack/nitro-v2-vite-plugin": "^1.141.0",
-    "@tanstack/router-plugin": "^1.139.7",
+    "@tanstack/nitro-v2-vite-plugin": "^1.154.7",
+    "@tanstack/router-plugin": "^1.158.4",
     "@tanstack/solid-ai-devtools": "workspace:*",
     "@tanstack/solid-devtools": "^0.7.15",
     "@tanstack/solid-router": "^1.139.10",

packages/typescript/ai-anthropic/src/adapters/text.ts

@@ -247,6 +247,7 @@ export class AnthropicTextAdapter<
       const validKeys: Array<keyof InternalTextProviderOptions> = [
         'container',
         'context_management',
+        'effort',
         'mcp_servers',
         'service_tier',
         'stop_sequences',
@@ -450,7 +451,74 @@ export class AnthropicTextAdapter<
       })
     }
 
-    return formattedMessages
+    // Post-process: Anthropic requires strictly alternating user/assistant roles.
+    // Tool results are sent as role:'user' messages, which can create consecutive
+    // user messages when followed by a new user message. Merge them.
+    return this.mergeConsecutiveSameRoleMessages(formattedMessages)
+  }
+
+  /**
+   * Merge consecutive messages of the same role into a single message.
+   * Anthropic's API requires strictly alternating user/assistant roles.
+   * Tool results are wrapped as role:'user' messages, which can collide
+   * with actual user messages in multi-turn conversations.
+   *
+   * Also filters out empty assistant messages (e.g., from a previous failed request).
+   */
+  private mergeConsecutiveSameRoleMessages(
+    messages: InternalTextProviderOptions['messages'],
+  ): InternalTextProviderOptions['messages'] {
+    const merged: InternalTextProviderOptions['messages'] = []
+
+    for (const msg of messages) {
+      // Skip empty assistant messages (no content or empty string)
+      if (msg.role === 'assistant') {
+        const hasContent = Array.isArray(msg.content)
+          ? msg.content.length > 0
+          : typeof msg.content === 'string' && msg.content.length > 0
+        if (!hasContent) {
+          continue
+        }
+      }
+
+      const prev = merged[merged.length - 1]
+      if (prev && prev.role === msg.role) {
+        // Normalize both contents to arrays and concatenate
+        const prevBlocks = Array.isArray(prev.content)
+          ? prev.content
+          : typeof prev.content === 'string' && prev.content
+            ? [{ type: 'text' as const, text: prev.content }]
+            : []
+        const msgBlocks = Array.isArray(msg.content)
+          ? msg.content
+          : typeof msg.content === 'string' && msg.content
+            ? [{ type: 'text' as const, text: msg.content }]
+            : []
+        prev.content = [...prevBlocks, ...msgBlocks]
+      } else {
+        merged.push({ ...msg })
+      }
+    }
+
+    // De-duplicate tool_result blocks with the same tool_use_id.
+    // This can happen when the core layer generates tool results from both
+    // the tool-result part and the tool-call part's output field.
+    for (const msg of merged) {
+      if (Array.isArray(msg.content)) {
+        const seenToolResultIds = new Set<string>()
+        msg.content = msg.content.filter((block: any) => {
+          if (block.type === 'tool_result' && block.tool_use_id) {
+            if (seenToolResultIds.has(block.tool_use_id)) {
+              return false // Remove duplicate
+            }
+            seenToolResultIds.add(block.tool_use_id)
+          }
+          return true
+        })
+      }
+    }
+
+    return merged
   }
 
   private async *processAnthropicStream(
@@ -473,6 +541,9 @@ export class AnthropicTextAdapter<
     let stepId: string | null = null
     let hasEmittedRunStarted = false
     let hasEmittedTextMessageStart = false
+    let hasEmittedRunFinished = false
+    // Track current content block type for proper content_block_stop handling
+    let currentBlockType: string | null = null
 
     try {
       for await (const event of stream) {
@@ -488,6 +559,7 @@ export class AnthropicTextAdapter<
         }
 
         if (event.type === 'content_block_start') {
+          currentBlockType = event.content_block.type
           if (event.content_block.type === 'tool_use') {
             currentToolIndex++
             toolCallsMap.set(currentToolIndex, {
@@ -572,59 +644,68 @@ export class AnthropicTextAdapter<
             }
           }
         } else if (event.type === 'content_block_stop') {
-          const existing = toolCallsMap.get(currentToolIndex)
-          if (existing) {
-            // If tool call wasn't started yet (no args), start it now
-            if (!existing.started) {
-              existing.started = true
+          if (currentBlockType === 'tool_use') {
+            const existing = toolCallsMap.get(currentToolIndex)
+            if (existing) {
+              // If tool call wasn't started yet (no args), start it now
+              if (!existing.started) {
+                existing.started = true
+                yield {
+                  type: 'TOOL_CALL_START',
+                  toolCallId: existing.id,
+                  toolName: existing.name,
+                  model,
+                  timestamp,
+                  index: currentToolIndex,
+                }
+              }
+
+              // Emit TOOL_CALL_END
+              let parsedInput: unknown = {}
+              try {
+                const parsed = existing.input ? JSON.parse(existing.input) : {}
+                parsedInput = parsed && typeof parsed === 'object' ? parsed : {}
+              } catch {
+                parsedInput = {}
+              }
+
               yield {
-                type: 'TOOL_CALL_START',
+                type: 'TOOL_CALL_END',
                 toolCallId: existing.id,
                 toolName: existing.name,
                 model,
                 timestamp,
-                index: currentToolIndex,
+                input: parsedInput,
               }
             }
-
-            // Emit TOOL_CALL_END
-            let parsedInput: unknown = {}
-            try {
-              const parsed = existing.input ? JSON.parse(existing.input) : {}
-              parsedInput = parsed && typeof parsed === 'object' ? parsed : {}
-            } catch {
-              parsedInput = {}
-            }
-
-            yield {
-              type: 'TOOL_CALL_END',
-              toolCallId: existing.id,
-              toolName: existing.name,
-              model,
-              timestamp,
-              input: parsedInput,
+          } else {
+            // Emit TEXT_MESSAGE_END only for text blocks (not tool_use blocks)
+            if (hasEmittedTextMessageStart && accumulatedContent) {
+              yield {
+                type: 'TEXT_MESSAGE_END',
+                messageId,
+                model,
+                timestamp,
+              }
             }
           }
-
-          // Emit TEXT_MESSAGE_END if we had text content
-          if (hasEmittedTextMessageStart && accumulatedContent) {
+          currentBlockType = null
+        } else if (event.type === 'message_stop') {
+          // Only emit RUN_FINISHED from message_stop if message_delta didn't already emit one.
+          // message_delta carries the real stop_reason (tool_use, end_turn, etc.),
+          // while message_stop is just a completion signal.
+          if (!hasEmittedRunFinished) {
             yield {
-              type: 'TEXT_MESSAGE_END',
-              messageId,
+              type: 'RUN_FINISHED',
+              runId,
               model,
               timestamp,
+              finishReason: 'stop',
             }
           }
-        } else if (event.type === 'message_stop') {
-          yield {
-            type: 'RUN_FINISHED',
-            runId,
-            model,
-            timestamp,
-            finishReason: 'stop',
-          }
         } else if (event.type === 'message_delta') {
           if (event.delta.stop_reason) {
+            hasEmittedRunFinished = true
             switch (event.delta.stop_reason) {
               case 'tool_use': {
                 yield {