fix(ai): keep a successful tool-call part at input-complete

.changeset/fix-client-tool-call-input-complete.md

@@ -0,0 +1,6 @@
+---
+'@tanstack/ai': patch
+'@tanstack/ai-client': patch
+---
+
+Keep a successful tool-call part at `input-complete` after its result is applied. A client tool result set the tool-call part to `complete`, which raced the finalize-stream safety net and depended on async ordering (regressed in #1233). The tool-call part now stays at its terminal `input-complete` state, and the completed result stays on the separate tool-result part.

packages/ai/src/activities/chat/stream/processor.ts

@@ -434,12 +434,19 @@ export class StreamProcessor {
       return
     }
 
-    // Step 1: Update the tool-call part's output field (for UI rendering)
+    // Step 1: Update the tool-call part's output field (for UI rendering).
+    // A successful result keeps the tool-call part at its terminal
+    // 'input-complete' state (the model's request is complete); the result
+    // itself lives in the tool-result part created in Step 2. Setting the
+    // tool-call part to 'complete' here raced the finalize-stream safety net
+    // (completeToolCall), so the visible state flipped depending on async
+    // ordering (#1233). Only an execution error makes the tool-call part
+    // itself terminal with 'error'.
     let updatedMessages = updateToolCallWithOutput(
       this.messages,
       toolCallId,
       output,
-      error ? 'error' : undefined,
+      error ? 'error' : 'input-complete',
       error,
     )
 

packages/ai/tests/stream-processor.test.ts

@@ -1783,7 +1783,9 @@ describe('StreamProcessor', () => {
         (p) => p.type === 'tool-call',
       ) as ToolCallPart
       expect((toolCallPart as any).output).toEqual({ temp: 72 })
-      expect(toolCallPart.state).toBe('complete')
+      // The tool-call part stays at its terminal 'input-complete' state; the
+      // completed result lives in the separate tool-result part below.
+      expect(toolCallPart.state).toBe('input-complete')
 
       const toolResultPart = messages[0]!.parts.find(
         (p) => p.type === 'tool-result',
@@ -3849,7 +3851,9 @@ describe('StreamProcessor', () => {
         ?.parts.find(
           (p): p is ToolCallPart => p.type === 'tool-call' && p.id === 'tc-1',
         )
-      expect(updated?.state).toBe('complete')
+      // The tool-call part keeps its terminal 'input-complete' state; the
+      // result is carried by the tool-result part.
+      expect(updated?.state).toBe('input-complete')
       expect(updated?.output).toEqual({ temp: 72 })
 
       warn.mockRestore()