[Discovery Engine] streamAnswer is typed as one AnswerQueryResponse, but REST returns frame arrays

### Description

`@googleapis/discoveryengine` exposes the REST `servingConfigs.streamAnswer` method as if the default parsed response is one `Schema$GoogleCloudDiscoveryengineV1AnswerQueryResponse`.

However, direct REST `streamAnswer` returns a JSON array of `AnswerQueryResponse` frames. With the default generated method, `res.data` is that array at runtime, while TypeScript and the generated example tell users to treat `res.data` as a single object. Typed code can therefore read `res.data.answerQueryToken` or `res.data.answer?.relatedQuestions` and get `undefined`, even though those fields are present in the returned frames.

This is not an answer-quality issue and does not require any live Google call to reproduce. The fixture below is a redacted HTTP 200 direct REST `streamAnswer` body from Discovery Engine / Vertex AI Search.

### Package / source

- Package: `@googleapis/discoveryengine@30.0.0`
- Repo commit checked: `9e92f535023f86df98d8a9dcbdf7777434e3124f`
- Generated method: `src/apis/discoveryengine/v1.ts`, `projects.locations.dataStores.servingConfigs.streamAnswer`
- Source lines: https://github.com/googleapis/google-api-nodejs-client/blob/9e92f535023f86df98d8a9dcbdf7777434e3124f/src/apis/discoveryengine/v1.ts#L57079-L57166

The generated comment says the method is streaming and returns multiple `AnswerQueryResponse` messages, but the default overload returns `Promise>`.

### Reproduction

Create these files and run one command:

```sh
npm install && npm run repro
```

`package.json`:

```json
{
"type": "module",
"scripts": {
"repro": "node repro.mjs && tsc --noEmit --strict --target es2022 --lib es2022 --module nodenext --moduleResolution nodenext typecheck.ts"
},
"dependencies": {
"@googleapis/discoveryengine": "30.0.0",
"@types/node": "24.10.1",
"nock": "14.0.10",
"typescript": "5.9.3"
}
}
```

`repro.mjs`:

```js
import fs from 'node:fs';
import nock from 'nock';
import {discoveryengine} from '@googleapis/discoveryengine';

const fixture = JSON.parse(fs.readFileSync('./fixture.json', 'utf8'));
const servingConfig =
'projects/testing-repos-489801/locations/global/collections/default_collection/dataStores/large-session-details-20260618-025044-m6sk/servingConfigs/default_search';

nock.disableNetConnect();
nock('https://discoveryengine.googleapis.com')
.post(`/v1/${servingConfig}:streamAnswer`)
.query(true)
.reply(200, fixture, {'content-type': 'application/json'});

const api = discoveryengine('v1');
const res = await api.projects.locations.collections.dataStores.servingConfigs.streamAnswer({
servingConfig,
requestBody: {query: {text: 'offline replay'}},
});

const framesWithRelatedQuestions = res.data.filter(
frame => frame.answer?.relatedQuestions?.length
);
const framesWithTokens = res.data.filter(frame => frame.answerQueryToken);

console.log(`Array.isArray(res.data): ${Array.isArray(res.data)}`);
console.log(`res.data.answerQueryToken: ${String(res.data.answerQueryToken)}`);
console.log(`res.data.answer?.relatedQuestions: ${String(res.data.answer?.relatedQuestions)}`);
console.log(`frame count: ${res.data.length}`);
console.log(`frames with answerQueryToken: ${framesWithTokens.length}`);
console.log(`frames with relatedQuestions: ${framesWithRelatedQuestions.length}`);
console.log(`first relatedQuestions count: ${framesWithRelatedQuestions[0]?.answer.relatedQuestions.length ?? 0}`);
```

`typecheck.ts`:

```ts
import {discoveryengine_v1} from '@googleapis/discoveryengine';

const api = new discoveryengine_v1.Discoveryengine({});
const servingConfig =
'projects/testing-repos-489801/locations/global/collections/default_collection/dataStores/large-session-details-20260618-025044-m6sk/servingConfigs/default_search';

async function main() {
const res =
await api.projects.locations.collections.dataStores.servingConfigs.streamAnswer({
servingConfig,
requestBody: {query: {text: 'offline replay'}},
});

// These compile because streamAnswer is typed as a single AnswerQueryResponse.
const token: string | null | undefined = res.data.answerQueryToken;
const relatedQuestions: string[] | undefined =
res.data.answer?.relatedQuestions ?? undefined;

// This is the runtime shape for valid REST streamAnswer output, but the
// generated default type rejects it.
// @ts-expect-error streamAnswer is typed as unary, not array-of-frame.
const frameCount: number = res.data.length;

console.log(token, relatedQuestions, frameCount);
}

void main();
```

fixture.json (redacted HTTP 200 direct REST streamAnswer body)

```json
[
{
"answer": {
"state": "STREAMING",
"steps": [
{
"state": "SUCCEEDED",
"description": "Rephrase the query and search.",
"actions": [
{
"searchAction": {
"query": "For sentinel large_session_include_details_large_session_include_details_20260618-025044_42p3u, what are the alpha, beta, gamma, and delta review requirements? Include citations."
},
"observation": {
"searchResults": [
{
"document": "projects/917493783080/locations/global/collections/default_collection/dataStores/large-session-details-20260618-025044-m6sk/branches/0/documents/large-session-include-details-doc",
"structData": {
"body": "Section 1: For sentinel large_session_include_details_large_session_include_details_20260618-025044_42p3u, alpha requires manual review, beta is automatically approved, gamma requires escalation, and delta requires a date-stamped audit note. The section owner is Search Credit QA 1; the support region is us-west; the effective date is 2026-06-11. Citations should point to this structured source and compare repeated facts across sections. Section 2: For sentinel large_session_include_details_large_session_include_details_20260618-025044_42p3u, alpha requires manual review, beta is automatically approved, gamma requires escalation, and delta requires a date-stamped audit note. The section owner is Search Credit QA 2; the support region is us-west; the effective date is 2026-06-12. Citations should point to this structured source and compare repeated facts across sections. Section 3: For sentinel large_session_include_details_large_session_include_details_20260618-025044_42p3u, alpha requires manual review, beta is automatically approved, gamma requires escalation, and delta requires a date-stamped audit note. The section owner is Search Credit QA 3; the support region is us-west; the effective date is 2026-06-13. Citations should point to this structured source and compare repeated facts across sections. Section 4: For sentinel large_session_include_details_large_session_include_details_20260618-025044_42p3u, alpha requires manual review, beta is automatically approved, gamma requires escalation, and delta requires a date-stamped audit note. The section owner is Search Credit QA 4; the support region is us-west; the effective date is 2026-06-14. Citations should point to this structured source and compare repeated facts across sections. Section 5: For sentinel large_session_include_details_large_session_include_details_20260618-025044_42p3u, alpha requires manual review, beta is automatically approved, gamma requires escalation, and delta requires a date-stamped audit note. The section owner is Search Credit QA 5; the support region is us-west; the effective date is 2026-06-15. Citations should point to this structured source and compare repeated facts across sections. Section 6: For sentinel large_session_include_details_large_session_include_details_20260618-025044_42p3u, alpha requires manual review, beta is automatically approved, gamma requires escalation, and delta requires a date-stamped audit note. The section owner is Search Credit QA 6; the support region is us-west; the effective date is 2026-06-16. Citations should point to this structured source and compare repeated facts across sections. Section 7: For sentinel large_session_include_details_large_session_include_details_20260618-025044_42p3u, alpha requires manual review, beta is automatically approved, gamma requires escalation, and delta requires a date-stamped audit note. The section owner is Search Credit QA 7; the support region is us-west; the effective date is 2026-06-17. Citations should point to this structured source and compare repeated facts across sections. Section 8: For sentinel large_session_include_details_large_session_include_details_20260618-025044_42p3u, alpha requires manual review, beta is automatically approved, gamma requires escalation, and delta requires a date-stamped audit note. The section owner is Search Credit QA 8; the support region is us-west; the effective date is 2026-06-18. Citations should point to this structured source and compare repeated facts across sections.",
"source_uri": "agent-search-test://large_session_include_details_20260618-025044_42p3u/large-session-include-details-doc",
"title": "Large session includeAnswerDetails parity sentinel",
"run_id": "large_session_include_details_20260618-025044_42p3u",
"unicode_notes": "Accents: cafe naive facade. Emoji: checkmark OK. Long dash: alpha -- beta. Greek: lambda pi. Japanese: テスト. Arabic: اختبار.",
"version": 1,
"sentinel_token": "large_session_include_details_large_session_include_details_20260618-025044_42p3u",
"facts": "The release code is R-ALPHA-77. The escalation owner is Search Credit QA. The support region is us-west. The policy labels are standard-search and advanced-generative-answer. Reviewers should verify manual review, automatic approval, escalation, and audit evidence."
}
}
]
}
}
]
}
]
},
"answerQueryToken": "NMwKDAiomezRBhDUgaihAhIkNmEzZGU2MjMtMDAwMC0yNTIwLTg0YzctMDg5ZTA4MmNlZmNj"
},
{
"answer": {
"state": "STREAMING",
"references": [
{
"structuredDocumentInfo": {
"document": "projects/917493783080/locations/global/collections/default_collection/dataStores/large-session-details-20260618-025044-m6sk/branches/0/documents/large-session-include-details-doc",
"structData": {},
"title": "Large session includeAnswerDetails parity sentinel"
}
}
]
},
"answerQueryToken": "NMwKDAiomezRBhDUgaihAhIkNmEzZGU2MjMtMDAwMC0yNTIwLTg0YzctMDg5ZTA4MmNlZmNj"
},
{
"answer": {
"state": "STREAMING",
"answerText": "For"
},
"answerQueryToken": "NMwKDAiomezRBhDUgaihAhIkNmEzZGU2MjMtMDAwMC0yNTIwLTg0YzctMDg5ZTA4MmNlZmNj"
},
{
"answer": {
"state": "STREAMING",
"answerText": " the sentinel `large_session_include_details_large_session_include_details_20"
},
"answerQueryToken": "NMwKDAiomezRBhDUgaihAhIkNmEzZGU2MjMtMDAwMC0yNTIwLTg0YzctMDg5ZTA4MmNlZmNj"
},
{
"answer": {
"state": "STREAMING",
"answerText": "260618-025044_42p3"
},
"answerQueryToken": "NMwKDAiomezRBhDUgaihAhIkNmEzZGU2MjMtMDAwMC0yNTIwLTg0YzctMDg5ZTA4MmNlZmNj"
},
{
"answer": {
"state": "STREAMING",
"answerText": "u`, the review requirements are as follows: alpha requires manual review, beta is automatically approved, gamma requires escalation, and delta requires a date"
},
"answerQueryToken": "NMwKDAiomezRBhDUgaihAhIkNmEzZGU2MjMtMDAwMC0yNTIwLTg0YzctMDg5ZTA4MmNlZmNj"
},
{
"answer": {
"state": "STREAMING",
"answerText": "-stamped audit note. "
},
"answerQueryToken": "NMwKDAiomezRBhDUgaihAhIkNmEzZGU2MjMtMDAwMC0yNTIwLTg0YzctMDg5ZTA4MmNlZmNj"
},
{
"answer": {
"state": "STREAMING",
"citations": [
{
"endIndex": "276",
"sources": [
{
"referenceId": "0"
}
]
}
]
},
"answerQueryToken": "NMwKDAiomezRBhDUgaihAhIkNmEzZGU2MjMtMDAwMC0yNTIwLTg0YzctMDg5ZTA4MmNlZmNj"
},
{
"answer": {
"state": "STREAMING",
"answerText": "The support region for this sentinel is us-west. "
},
"answerQueryToken": "NMwKDAiomezRBhDUgaihAhIkNmEzZGU2MjMtMDAwMC0yNTIwLTg0YzctMDg5ZTA4MmNlZmNj"
},
{
"answer": {
"state": "STREAMING",
"citations": [
{
"startIndex": "277",
"endIndex": "325",
"sources": [
{
"referenceId": "0"
}
]
}
]
},
"answerQueryToken": "NMwKDAiomezRBhDUgaihAhIkNmEzZGU2MjMtMDAwMC0yNTIwLTg0YzctMDg5ZTA4MmNlZmNj"
},
{
"answer": {
"state": "STREAMING",
"answerText": "The policy labels associated with this sentinel are standard-search and advanced-generative"
},
"answerQueryToken": "NMwKDAiomezRBhDUgaihAhIkNmEzZGU2MjMtMDAwMC0yNTIwLTg0YzctMDg5ZTA4MmNlZmNj"
},
{
"answer": {
"state": "STREAMING",
"answerText": "-answer. "
},
"answerQueryToken": "NMwKDAiomezRBhDUgaihAhIkNmEzZGU2MjMtMDAwMC0yNTIwLTg0YzctMDg5ZTA4MmNlZmNj"
},
{
"answer": {
"state": "STREAMING",
"citations": [
{
"startIndex": "326",
"endIndex": "425",
"sources": [
{
"referenceId": "0"
}
]
}
]
},
"answerQueryToken": "NMwKDAiomezRBhDUgaihAhIkNmEzZGU2MjMtMDAwMC0yNTIwLTg0YzctMDg5ZTA4MmNlZmNj"
},
{
"answer": {
"state": "STREAMING",
"answerText": "Reviewers should verify manual review, automatic approval, escalation, and audit evidence. "
},
"answerQueryToken": "NMwKDAiomezRBhDUgaihAhIkNmEzZGU2MjMtMDAwMC0yNTIwLTg0YzctMDg5ZTA4MmNlZmNj"
},
{
"answer": {
"state": "STREAMING",
"citations": [
{
"startIndex": "426",
"endIndex": "516",
"sources": [
{
"referenceId": "0"
}
]
}
]
},
"answerQueryToken": "NMwKDAiomezRBhDUgaihAhIkNmEzZGU2MjMtMDAwMC0yNTIwLTg0YzctMDg5ZTA4MmNlZmNj"
},
{
"answer": {
"state": "STREAMING",
"answerText": "The release code is R-ALPHA-77. "
},
"answerQueryToken": "NMwKDAiomezRBhDUgaihAhIkNmEzZGU2MjMtMDAwMC0yNTIwLTg0YzctMDg5ZTA4MmNlZmNj"
},
{
"answer": {
"state": "STREAMING",
"citations": [
{
"startIndex": "517",
"endIndex": "548",
"sources": [
{
"referenceId": "0"
}
]
}
]
},
"answerQueryToken": "NMwKDAiomezRBhDUgaihAhIkNmEzZGU2MjMtMDAwMC0yNTIwLTg0YzctMDg5ZTA4MmNlZmNj"
},
{
"answer": {
"state": "STREAMING",
"answerText": "The escalation owner is Search Credit QA.\n\n"
},
"answerQueryToken": "NMwKDAiomezRBhDUgaihAhIkNmEzZGU2MjMtMDAwMC0yNTIwLTg0YzctMDg5ZTA4MmNlZmNj"
},
{
"answer": {
"state": "STREAMING",
"citations": [
{
"startIndex": "549",
"endIndex": "590",
"sources": [
{
"referenceId": "0"
}
]
}
]
},
"answerQueryToken": "NMwKDAiomezRBhDUgaihAhIkNmEzZGU2MjMtMDAwMC0yNTIwLTg0YzctMDg5ZTA4MmNlZmNj"
},
{
"answer": {
"state": "STREAMING",
"answerText": "The section"
},
"answerQueryToken": "NMwKDAiomezRBhDUgaihAhIkNmEzZGU2MjMtMDAwMC0yNTIwLTg0YzctMDg5ZTA4MmNlZmNj"
},
{
"answer": {
"state": "STREAMING",
"answerText": " owner and effective date vary across different sections of the source:\n"
},
"answerQueryToken": "NMwKDAiomezRBhDUgaihAhIkNmEzZGU2MjMtMDAwMC0yNTIwLTg0YzctMDg5ZTA4MmNlZmNj"
},
{
"answer": {
"state": "STREAMING",
"answerText": "* Section 1: The section owner is Search Credit QA 1, and the effective date is 2026-06-11."
},
"answerQueryToken": "NMwKDAiomezRBhDUgaihAhIkNmEzZGU2MjMtMDAwMC0yNTIwLTg0YzctMDg5ZTA4MmNlZmNj"
},
{
"answer": {
"state": "STREAMING",
"answerText": "\n"
},
"answerQueryToken": "NMwKDAiomezRBhDUgaihAhIkNmEzZGU2MjMtMDAwMC0yNTIwLTg0YzctMDg5ZTA4MmNlZmNj"
},
{
"answer": {
"state": "STREAMING",
"citations": [
{
"startIndex": "675",
"endIndex": "768",
"sources": [
{
"referenceId": "0"
}
]
}
]
},
"answerQueryToken": "NMwKDAiomezRBhDUgaihAhIkNmEzZGU2MjMtMDAwMC0yNTIwLTg0YzctMDg5ZTA4MmNlZmNj"
},
{
"answer": {
"state": "STREAMING",
"answerText": "* Section 2: The section owner is Search Credit QA 2, and the effective date is 2026-06-12.\n"
},
"answerQueryToken": "NMwKDAiomezRBhDUgaihAhIkNmEzZGU2MjMtMDAwMC0yNTIwLTg0YzctMDg5ZTA4MmNlZmNj"
},
{
"answer": {
"state": "STREAMING",
"citations": [
{
"startIndex": "769",
"endIndex": "862",
"sources": [
{
"referenceId": "0"
}
]
}
]
},
"answerQueryToken": "NMwKDAiomezRBhDUgaihAhIkNmEzZGU2MjMtMDAwMC0yNTIwLTg0YzctMDg5ZTA4MmNlZmNj"
},
{
"answer": {
"state": "STREAMING",
"answerText": "* Section 3: The section owner is Search Credit QA 3, and the effective date is 2026-06"
},
"answerQueryToken": "NMwKDAiomezRBhDUgaihAhIkNmEzZGU2MjMtMDAwMC0yNTIwLTg0YzctMDg5ZTA4MmNlZmNj"
},
{
"answer": {
"state": "STREAMING",
"answerText": "-13.\n"
},
"answerQueryToken": "NMwKDAiomezRBhDUgaihAhIkNmEzZGU2MjMtMDAwMC0yNTIwLTg0YzctMDg5ZTA4MmNlZmNj"
},
{
"answer": {
"state": "STREAMING",
"citations": [
{
"startIndex": "863",
"endIndex": "956",
"sources": [
{
"referenceId": "0"
}
]
}
]
},
"answerQueryToken": "NMwKDAiomezRBhDUgaihAhIkNmEzZGU2MjMtMDAwMC0yNTIwLTg0YzctMDg5ZTA4MmNlZmNj"
},
{
"answer": {
"state": "STREAMING",
"answerText": "* Section 4: The section owner is Search Credit QA 4, and the effective date is 2026-06-14.\n"
},
"answerQueryToken": "NMwKDAiomezRBhDUgaihAhIkNmEzZGU2MjMtMDAwMC0yNTIwLTg0YzctMDg5ZTA4MmNlZmNj"
},
{
"answer": {
"state": "STREAMING",
"citations": [
{
"startIndex": "957",
"endIndex": "1050",
"sources": [
{
"referenceId": "0"
}
]
}
]
},
"answerQueryToken": "NMwKDAiomezRBhDUgaihAhIkNmEzZGU2MjMtMDAwMC0yNTIwLTg0YzctMDg5ZTA4MmNlZmNj"
},
{
"answer": {
"state": "STREAMING",
"answerText": "* Section 5: The section owner is Search Credit QA 5, and the effective date is 2"
},
"answerQueryToken": "NMwKDAiomezRBhDUgaihAhIkNmEzZGU2MjMtMDAwMC0yNTIwLTg0YzctMDg5ZTA4MmNlZmNj"
},
{
"answer": {
"state": "STREAMING",
"answerText": "026-06-15.\n"
},
"answerQueryToken": "NMwKDAiomezRBhDUgaihAhIkNmEzZGU2MjMtMDAwMC0yNTIwLTg0YzctMDg5ZTA4MmNlZmNj"
},
{
"answer": {
"state": "STREAMING",
"citations": [
{
"startIndex": "1051",
"endIndex": "1144",
"sources": [
{
"referenceId": "0"
}
]
}
]
},
"answerQueryToken": "NMwKDAiomezRBhDUgaihAhIkNmEzZGU2MjMtMDAwMC0yNTIwLTg0YzctMDg5ZTA4MmNlZmNj"
},
{
"answer": {
"state": "STREAMING",
"answerText": "* Section 6: The section owner is Search Credit QA 6, and the effective date is 2026-06-16.\n"
},
"answerQueryToken": "NMwKDAiomezRBhDUgaihAhIkNmEzZGU2MjMtMDAwMC0yNTIwLTg0YzctMDg5ZTA4MmNlZmNj"
},
{
"answer": {
"state": "STREAMING",
"citations": [
{
"startIndex": "1145",
"endIndex": "1238",
"sources": [
{
"referenceId": "0"
}
]
}
]
},
"answerQueryToken": "NMwKDAiomezRBhDUgaihAhIkNmEzZGU2MjMtMDAwMC0yNTIwLTg0YzctMDg5ZTA4MmNlZmNj"
},
{
"answer": {
"state": "STREAMING",
"answerText": "* Section 7: The section owner is Search Credit QA 7, and"
},
"answerQueryToken": "NMwKDAiomezRBhDUgaihAhIkNmEzZGU2MjMtMDAwMC0yNTIwLTg0YzctMDg5ZTA4MmNlZmNj"
},
{
"answer": {
"state": "STREAMING",
"answerText": " the effective date is 2026-06-17.\n"
},
"answerQueryToken": "NMwKDAiomezRBhDUgaihAhIkNmEzZGU2MjMtMDAwMC0yNTIwLTg0YzctMDg5ZTA4MmNlZmNj"
},
{
"answer": {
"state": "STREAMING",
"citations": [
{
"startIndex": "1239",
"endIndex": "1332",
"sources": [
{
"referenceId": "0"
}
]
}
]
},
"answerQueryToken": "NMwKDAiomezRBhDUgaihAhIkNmEzZGU2MjMtMDAwMC0yNTIwLTg0YzctMDg5ZTA4MmNlZmNj"
},
{
"answer": {
"state": "STREAMING",
"answerText": "* Section 8: The section owner is Search Credit QA 8, and the effective date is 2026-06-18."
},
"answerQueryToken": "NMwKDAiomezRBhDUgaihAhIkNmEzZGU2MjMtMDAwMC0yNTIwLTg0YzctMDg5ZTA4MmNlZmNj"
},
{
"answer": {
"state": "STREAMING",
"citations": [
{
"startIndex": "1333",
"endIndex": "1426",
"sources": [
{
"referenceId": "0"
}
]
}
]
},
"answerQueryToken": "NMwKDAiomezRBhDUgaihAhIkNmEzZGU2MjMtMDAwMC0yNTIwLTg0YzctMDg5ZTA4MmNlZmNj"
},
{
"answer": {
"state": "STREAMING",
"relatedQuestions": [
"What is the escalation process for gamma?",
"Who is the current section owner?",
"What is the latest effective date?",
"Where can I find this structured source?",
"Can I get more details on \"manual review\"?"
]
},
"answerQueryToken": "NMwKDAiomezRBhDUgaihAhIkNmEzZGU2MjMtMDAwMC0yNTIwLTg0YzctMDg5ZTA4MmNlZmNj"
},
{
"answer": {
"state": "SUCCEEDED",
"answerText": "For the sentinel `large_session_include_details_large_session_include_details_20260618-025044_42p3u`, the review requirements are as follows: alpha requires manual review, beta is automatically approved, gamma requires escalation, and delta requires a date-stamped audit note. The support region for this sentinel is us-west. The policy labels associated with this sentinel are standard-search and advanced-generative-answer. Reviewers should verify manual review, automatic approval, escalation, and audit evidence. The release code is R-ALPHA-77. The escalation owner is Search Credit QA.\n\nThe section owner and effective date vary across different sections of the source:\n* Section 1: The section owner is Search Credit QA 1, and the effective date is 2026-06-11.\n* Section 2: The section owner is Search Credit QA 2, and the effective date is 2026-06-12.\n* Section 3: The section owner is Search Credit QA 3, and the effective date is 2026-06-13.\n* Section 4: The section owner is Search Credit QA 4, and the effective date is 2026-06-14.\n* Section 5: The section owner is Search Credit QA 5, and the effective date is 2026-06-15.\n* Section 6: The section owner is Search Credit QA 6, and the effective date is 2026-06-16.\n* Section 7: The section owner is Search Credit QA 7, and the effective date is 2026-06-17.\n* Section 8: The section owner is Search Credit QA 8, and the effective date is 2026-06-18.",
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}
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"references": [
{
"structuredDocumentInfo": {
"document": "projects/917493783080/locations/global/collections/default_collection/dataStores/large-session-details-20260618-025044-m6sk/branches/0/documents/large-session-include-details-doc",
"structData": {},
"title": "Large session includeAnswerDetails parity sentinel"
}
}
],
"relatedQuestions": [
"What is the escalation process for gamma?",
"Who is the current section owner?",
"What is the latest effective date?",
"Where can I find this structured source?",
"Can I get more details on \"manual review\"?"
],
"steps": [
{
"state": "SUCCEEDED",
"description": "Rephrase the query and search.",
"actions": [
{
"searchAction": {
"query": "For sentinel large_session_include_details_large_session_include_details_20260618-025044_42p3u, what are the alpha, beta, gamma, and delta review requirements? Include citations."
},
"observation": {
"searchResults": [
{
"document": "projects/917493783080/locations/global/collections/default_collection/dataStores/large-session-details-20260618-025044-m6sk/branches/0/documents/large-session-include-details-doc",
"structData": {
"unicode_notes": "Accents: cafe naive facade. Emoji: checkmark OK. Long dash: alpha -- beta. Greek: lambda pi. Japanese: テスト. Arabic: اختبار.",
"run_id": "large_session_include_details_20260618-025044_42p3u",
"title": "Large session includeAnswerDetails parity sentinel",
"body": "Section 1: For sentinel large_session_include_details_large_session_include_details_20260618-025044_42p3u, alpha requires manual review, beta is automatically approved, gamma requires escalation, and delta requires a date-stamped audit note. The section owner is Search Credit QA 1; the support region is us-west; the effective date is 2026-06-11. Citations should point to this structured source and compare repeated facts across sections. Section 2: For sentinel large_session_include_details_large_session_include_details_20260618-025044_42p3u, alpha requires manual review, beta is automatically approved, gamma requires escalation, and delta requires a date-stamped audit note. The section owner is Search Credit QA 2; the support region is us-west; the effective date is 2026-06-12. Citations should point to this structured source and compare repeated facts across sections. Section 3: For sentinel large_session_include_details_large_session_include_details_20260618-025044_42p3u, alpha requires manual review, beta is automatically approved, gamma requires escalation, and delta requires a date-stamped audit note. The section owner is Search Credit QA 3; the support region is us-west; the effective date is 2026-06-13. Citations should point to this structured source and compare repeated facts across sections. Section 4: For sentinel large_session_include_details_large_session_include_details_20260618-025044_42p3u, alpha requires manual review, beta is automatically approved, gamma requires escalation, and delta requires a date-stamped audit note. The section owner is Search Credit QA 4; the support region is us-west; the effective date is 2026-06-14. Citations should point to this structured source and compare repeated facts across sections. Section 5: For sentinel large_session_include_details_large_session_include_details_20260618-025044_42p3u, alpha requires manual review, beta is automatically approved, gamma requires escalation, and delta requires a date-stamped audit note. The section owner is Search Credit QA 5; the support region is us-west; the effective date is 2026-06-15. Citations should point to this structured source and compare repeated facts across sections. Section 6: For sentinel large_session_include_details_large_session_include_details_20260618-025044_42p3u, alpha requires manual review, beta is automatically approved, gamma requires escalation, and delta requires a date-stamped audit note. The section owner is Search Credit QA 6; the support region is us-west; the effective date is 2026-06-16. Citations should point to this structured source and compare repeated facts across sections. Section 7: For sentinel large_session_include_details_large_session_include_details_20260618-025044_42p3u, alpha requires manual review, beta is automatically approved, gamma requires escalation, and delta requires a date-stamped audit note. The section owner is Search Credit QA 7; the support region is us-west; the effective date is 2026-06-17. Citations should point to this structured source and compare repeated facts across sections. Section 8: For sentinel large_session_include_details_large_session_include_details_20260618-025044_42p3u, alpha requires manual review, beta is automatically approved, gamma requires escalation, and delta requires a date-stamped audit note. The section owner is Search Credit QA 8; the support region is us-west; the effective date is 2026-06-18. Citations should point to this structured source and compare repeated facts across sections.",
"source_uri": "agent-search-test://large_session_include_details_20260618-025044_42p3u/large-session-include-details-doc",
"facts": "The release code is R-ALPHA-77. The escalation owner is Search Credit QA. The support region is us-west. The policy labels are standard-search and advanced-generative-answer. Reviewers should verify manual review, automatic approval, escalation, and audit evidence.",
"sentinel_token": "large_session_include_details_large_session_include_details_20260618-025044_42p3u",
"version": 1
}
}
]
}
}
]
}
]
},
"answerQueryToken": "NMwKDAiomezRBhDUgaihAhIkNmEzZGU2MjMtMDAwMC0yNTIwLTg0YzctMDg5ZTA4MmNlZmNj"
}
]

```

### Actual output

```text
Array.isArray(res.data): true
res.data.answerQueryToken: undefined
res.data.answer?.relatedQuestions: undefined
frame count: 43
frames with answerQueryToken: 43
frames with relatedQuestions: 2
first relatedQuestions count: 5
```

### Expected behavior

The generated REST surface should not expose the default parsed `streamAnswer` response as a single `AnswerQueryResponse` when valid REST output is an array of `AnswerQueryResponse` frames.

Possible fixes could be one of:

- Type the default parsed response as `Schema$GoogleCloudDiscoveryengineV1AnswerQueryResponse[]`.
- Document and type `streamAnswer` so callers must use `responseType: 'stream'` for this endpoint.
- Provide a higher-level accumulator that returns a final assembled Answer response and preserves terminal frame metadata such as `answerQueryToken` and `relatedQuestions`.

### Why the fixture is valid

The body is from a direct REST `streamAnswer` HTTP 200 response from `discoveryengine.googleapis.com`. The service returned a JSON array of `AnswerQueryResponse` frames. The raw service output is the ground truth here; the issue is only that the public Node REST client type/default wrapper presents that valid output as a unary object.

Start with the generated streamAnswer method in src/apis/discoveryengine/v1.ts at the referenced lines, then run the supplied reproduction with npm run repro. Verify the REST response is represented as an array of AnswerQueryResponse frames and that typecheck.ts accepts frame access while no longer presenting res.data as a single response object.

Written by the indexing model from the issue text.