ai-ollama: streamed chat() reports finishReason "stop" when done_reason is "length" #1852

TanStack AI version

@tanstack/ai 0.71.0, @tanstack/ai-ollama 0.12.2 (ollama 0.6.4)

Framework/Library version

Node.js 22, chat() on the server, no framework

Describe the bug and the steps to reproduce it

When Ollama stops at the token limit (options.num_predict), its last stream line has done: true and
done_reason: "length". The streamed chat() path still ends with RUN_FINISHED and finishReason: "stop", so a
cut-off answer looks complete.

The adapter sets the finish from whether tool calls were emitted and never reads done_reason
(packages/ai-ollama/src/adapters/text.ts#L440).
structuredOutput() already checks done_reason === 'length' (L263, from #1548), so only the streamed path is
affected.

Expected: finishReason: "length", as the Chat Completions adapter reports for finish_reason: "length".

Steps: save the script below as repro.mjs, then

npm init -y && npm pkg set type=module
npm install @tanstack/ai@0.71.0 @tanstack/ai-ollama@0.12.2
node repro.mjs

Output:

RUN_FINISHED stop

Your Minimal, Reproducible Example - (Sandbox Highly Recommended)

No Ollama server is needed: a custom fetch returns the NDJSON stream.

import { chat } from '@tanstack/ai';
import { createOllamaChat } from '@tanstack/ai-ollama';

// The last line is what Ollama sends when options.num_predict cuts the answer off.
const lines = [
  { model: 'qwen3.5:0.8b', created_at: '2026-10-21T09:00:00Z', message: { role: 'assistant', content: 'Saturn has more than' }, done: false },
  { model: 'qwen3.5:0.8b', created_at: '2026-10-21T09:00:01Z', message: { role: 'assistant', content: '' },
    done: true, done_reason: 'length', prompt_eval_count: 14, eval_count: 5 },
];
globalThis.fetch = async () => new Response(lines.map(line => JSON.stringify(line) + '\n').join(''),
  { headers: { 'content-type': 'application/x-ndjson' } });

for await (const event of chat({
  adapter: createOllamaChat('qwen3.5:0.8b'),
  messages: [{ role: 'user', content: 'How many moons does Saturn have?' }],
  modelOptions: { options: { num_predict: 5 } },
  debug: false,
})) {
  if (event.type === 'RUN_FINISHED') console.log('RUN_FINISHED', event.metadata?.tanstack?.finishReason);
  if (event.type === 'RUN_ERROR') console.log('RUN_ERROR', event.code);
}

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