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Fix: Handle object-style finishReason for AI SDK v5/v6 compatibility (#695)
--------- Signed-off-by: Peter Wielander <mittgfu@gmail.com> Co-authored-by: Peter Wielander <mittgfu@gmail.com>
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‎.changeset/clean-parrots-search.md‎

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---
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"@workflow/ai": patch
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---
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Fix: Handle object-style finishReason for AI SDK v5/v6 compatibility

‎packages/ai/src/agent/do-stream-step.test.ts‎

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import { describe, expect, it } from 'vitest';
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import { normalizeFinishReason } from './do-stream-step.js';
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describe('normalizeFinishReason', () => {
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describe('string finish reasons', () => {
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it('should pass through "stop"', () => {
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expect(normalizeFinishReason('stop')).toBe('stop');
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});
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it('should pass through "tool-calls"', () => {
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expect(normalizeFinishReason('tool-calls')).toBe('tool-calls');
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});
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it('should pass through "length"', () => {
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expect(normalizeFinishReason('length')).toBe('length');
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});
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it('should pass through "content-filter"', () => {
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expect(normalizeFinishReason('content-filter')).toBe('content-filter');
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});
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it('should pass through "error"', () => {
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expect(normalizeFinishReason('error')).toBe('error');
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});
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it('should pass through "other"', () => {
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expect(normalizeFinishReason('other')).toBe('other');
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});
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it('should pass through "unknown"', () => {
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expect(normalizeFinishReason('unknown')).toBe('unknown');
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});
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});
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describe('object finish reasons', () => {
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it('should extract "stop" from object', () => {
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expect(normalizeFinishReason({ type: 'stop' })).toBe('stop');
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});
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it('should extract "tool-calls" from object', () => {
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expect(normalizeFinishReason({ type: 'tool-calls' })).toBe('tool-calls');
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});
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it('should extract "length" from object', () => {
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expect(normalizeFinishReason({ type: 'length' })).toBe('length');
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});
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it('should extract "content-filter" from object', () => {
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expect(normalizeFinishReason({ type: 'content-filter' })).toBe(
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'content-filter'
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);
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});
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it('should extract "error" from object', () => {
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expect(normalizeFinishReason({ type: 'error' })).toBe('error');
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});
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it('should extract "other" from object', () => {
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expect(normalizeFinishReason({ type: 'other' })).toBe('other');
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});
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it('should extract "unknown" from object', () => {
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expect(normalizeFinishReason({ type: 'unknown' })).toBe('unknown');
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});
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it('should return "unknown" for object without type property', () => {
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expect(normalizeFinishReason({})).toBe('unknown');
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});
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it('should return "unknown" for object with null type', () => {
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expect(normalizeFinishReason({ type: null })).toBe('unknown');
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});
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it('should return "unknown" for object with undefined type', () => {
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expect(normalizeFinishReason({ type: undefined })).toBe('unknown');
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});
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it('should handle object with additional properties', () => {
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expect(
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normalizeFinishReason({
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type: 'stop',
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reason: 'end_turn',
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metadata: { foo: 'bar' },
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})
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).toBe('stop');
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});
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});
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describe('edge cases', () => {
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it('should return "unknown" for undefined', () => {
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expect(normalizeFinishReason(undefined)).toBe('unknown');
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});
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it('should return "unknown" for null', () => {
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expect(normalizeFinishReason(null)).toBe('unknown');
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});
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it('should return "unknown" for number', () => {
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expect(normalizeFinishReason(42)).toBe('unknown');
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});
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it('should return "unknown" for boolean', () => {
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expect(normalizeFinishReason(true)).toBe('unknown');
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});
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it('should return "unknown" for array', () => {
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expect(normalizeFinishReason(['stop'])).toBe('unknown');
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});
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it('should handle empty string', () => {
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expect(normalizeFinishReason('')).toBe('');
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});
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});
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describe('bug reproduction', () => {
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it('should handle object format that caused [object Object] error', () => {
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const normalized = normalizeFinishReason({ type: 'stop' });
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expect(normalized).toBe('stop');
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expect(typeof normalized).toBe('string');
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});
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it('should handle tool-calls object format', () => {
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const normalized = normalizeFinishReason({ type: 'tool-calls' });
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expect(normalized).toBe('tool-calls');
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expect(typeof normalized).toBe('string');
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});
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});
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});

‎packages/ai/src/agent/do-stream-step.ts‎

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@@ -8,6 +8,7 @@ import type {
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} from '@ai-sdk/provider';
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import {
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gateway,
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type FinishReason,
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type StepResult,
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type StopCondition,
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type ToolChoice,
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448449
return { toolCalls, finish, step };
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}
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/**
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* Normalize the finish reason to the AI SDK FinishReason type.
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* AI SDK v6 may return an object with a 'type' property,
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* while AI SDK v5 returns a plain string. This function handles both.
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*
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* @internal Exported for testing
458+
*/
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export function normalizeFinishReason(rawFinishReason: unknown): FinishReason {
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// Handle object-style finish reason (possible in some AI SDK versions/providers)
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if (typeof rawFinishReason === 'object' && rawFinishReason !== null) {
462+
const objReason = rawFinishReason as { type?: string };
463+
return (objReason.type as FinishReason) ?? 'unknown';
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}
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// Handle string finish reason (standard format)
466+
if (typeof rawFinishReason === 'string') {
467+
return rawFinishReason as FinishReason;
468+
}
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return 'unknown';
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}
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// This is a stand-in for logic in the AI-SDK streamText code which aggregates
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// chunks into a single step result.
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function chunksToStep(
@@ -563,7 +584,7 @@ function chunksToStep(
563584
toolResults: [],
564585
staticToolResults: [],
565586
dynamicToolResults: [],
566-
finishReason: finish?.finishReason || 'unknown',
587+
finishReason: normalizeFinishReason(finish?.finishReason),
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usage: finish?.usage || { inputTokens: 0, outputTokens: 0, totalTokens: 0 },
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warnings: streamStart?.warnings,
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request: {

‎packages/ai/src/agent/durable-agent.ts‎

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});
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return {
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type: 'tool-result',
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type: 'tool-result' as const,
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toolCallId: toolCall.toolCallId,
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toolName: toolCall.toolName,
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output: {
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type: 'text',
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type: 'text' as const,
988988
value: JSON.stringify(toolResult) ?? '',
989989
},
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};

‎packages/ai/src/agent/stream-text-iterator.ts‎

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LanguageModelV2ToolResultPart,
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} from '@ai-sdk/provider';
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import type {
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FinishReason,
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StepResult,
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StreamTextOnStepFinishCallback,
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ToolChoice,
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lastStep = step;
260261
lastStepWasToolCalls = false;
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262-
if (finish?.finishReason === 'tool-calls') {
263+
// Normalize finishReason - AI SDK v6 returns { unified, raw }, v5 returns a string
264+
const finishReason = normalizeFinishReason(finish?.finishReason);
265+
266+
if (finishReason === 'tool-calls') {
263267
lastStepWasToolCalls = true;
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264269
// Add assistant message with tool calls to the conversation
265270
conversationPrompt.push({
266271
role: 'assistant',
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296301
done = true;
297302
}
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}
299-
} else if (finish?.finishReason === 'stop') {
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} else if (finishReason === 'stop') {
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// Add assistant message with text content to the conversation
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const textContent = step.content.filter(
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(item) => item.type === 'text'
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310315
}
311316

312317
done = true;
313-
} else if (finish?.finishReason === 'length') {
318+
} else if (finishReason === 'length') {
314319
// Model hit max tokens - stop but don't throw
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done = true;
316-
} else if (finish?.finishReason === 'content-filter') {
321+
} else if (finishReason === 'content-filter') {
317322
// Content filter triggered - stop but don't throw
318323
done = true;
319-
} else if (finish?.finishReason === 'error') {
324+
} else if (finishReason === 'error') {
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// Model error - stop but don't throw
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done = true;
322-
} else if (finish?.finishReason === 'other') {
327+
} else if (finishReason === 'other') {
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// Other reason - stop but don't throw
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done = true;
325-
} else if (finish?.finishReason === 'unknown') {
330+
} else if (finishReason === 'unknown') {
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// Unknown reason - stop but don't throw
327332
done = true;
328-
} else if (!finish?.finishReason) {
333+
} else if (!finishReason) {
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// No finish reason - this might happen on incomplete streams
330335
done = true;
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} else {
332-
throw new Error(`Unexpected finish reason: ${finish?.finishReason}`);
337+
throw new Error(
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`Unexpected finish reason: ${typeof finish?.finishReason === 'object' ? JSON.stringify(finish?.finishReason) : finish?.finishReason}`
339+
);
333340
}
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335342
if (onStepFinish) {
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toolResults: LanguageModelV2ToolResultPart[]
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) {
363370
'use step';
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365371
const writer = writable.getWriter();
366372
try {
367373
for (const result of toolResults) {
368374
await writer.write({
369-
type: 'tool-output-available',
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type: 'tool-output-available' as const,
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toolCallId: result.toolCallId,
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output: JSON.stringify(result) ?? '',
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});
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388394
}
389395
return filtered;
390396
}
397+
398+
/**
399+
* Normalize finishReason from different AI SDK versions.
400+
* - AI SDK v6: returns { unified: 'tool-calls', raw: 'tool_use' }
401+
* - AI SDK v5: returns 'tool-calls' string directly
402+
*/
403+
function normalizeFinishReason(raw: unknown): FinishReason | undefined {
404+
if (raw == null) return undefined;
405+
if (typeof raw === 'string') return raw as FinishReason;
406+
if (typeof raw === 'object') {
407+
const obj = raw as { unified?: FinishReason; type?: FinishReason };
408+
return obj.unified ?? obj.type ?? 'unknown';
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}
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return undefined;
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}

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