[Bug] Nested field shapes bypass the #1219 frame guard and crash both adapter paths #1325

Client or integration

Not client-specific — reproduced by driving the adapters directly with a synthetic Response.

Area

Adapters · Streaming / SSE parsing · Non-streaming response parsing

Summary

#1219 / #1240 fixed the frame root: JSON.parse(payload) was cast to Record<string, unknown> and dereferenced, so data: null crashed the parser. The same "cast, then dereference" pattern survives one level deeper, on fields inside an otherwise well-formed frame. A frame that is a valid JSON object still crashes the adapter when a nested field has an unexpected shape.

These are found by audit, not from a live capture. Unlike data: null — which agentrouter.org demonstrably emits as padding — I have no evidence any provider sends these. Filing because the defect class and blast radius are identical to #1219 (an escaping TypeError mid-stream, which the surrounding try/catch cannot classify), and because the guards are cheap.

Verified on dev at 79831c90, with the #1240 fix already present.

D–F are in parseResponse, not parseStream — the non-streaming path has the same defect, so a fix confined to the streaming parsers would be incomplete.

In each case the cast asserts a shape that is never checked: root.candidates as {...}[] at google.ts:580 (!candidates?.length guards the array, not its elements), and delta.tool_calls as {...}[] / msg.tool_calls as {...}[] at openai-chat.ts:1038 and :1224.

Checked and clean — not every nested site is affected. google.ts:809 reads candidates?.[0]?.content?.parts with optional chaining, so the non-streaming Google path returns a normal done for {"candidates":[null]} rather than throwing. Google's non-stream path needs no change.

Reproduction

Save as tests/zz-nested-probe.test.ts on dev and run bun scripts/test.ts tests/zz-nested-probe.test.ts, then delete it.

import { test } from "bun:test";
import { createGoogleAdapter } from "../src/adapters/google";
import { createOpenAIChatAdapter } from "../src/adapters/openai-chat";
import { withTestTranslatorBudget } from "./helpers/translator-budget";

const g = { adapter: "google", baseUrl: "https://x.test", apiKey: "k", authMode: "key" } as any;
const o = { adapter: "openai-chat", baseUrl: "https://x.test/v1", apiKey: "k", authMode: "key" } as any;

async function stream(label: string, adapter: any, body: string) {
  try {
    const out: string[] = [];
    for await (const e of adapter.parseStream(new Response(body, { headers: { "content-type": "text/event-stream" } }))) out.push(e.type);
    console.log(`  ${label}: no throw -> [${out.join(",")}]`);
  } catch (e) { console.log(`  ${label}: THREW -> ${(e as Error).message}`); }
}
async function nonStream(label: string, adapter: any, body: unknown) {
  try {
    const ev = await adapter.parseResponse(new Response(JSON.stringify(body)));
    console.log(`  ${label}: no throw -> ${ev.map((e: any) => e.type).join(",")}`);
  } catch (e) { console.log(`  ${label}: THREW -> ${(e as Error).message}`); }
}

test("nested shape probe", async () => {
  await stream("A google candidates:[null]   ", withTestTranslatorBudget(createGoogleAdapter(g)), 'data: {"candidates":[null]}\n\n');
  await stream("B openai tool_calls object   ", withTestTranslatorBudget(createOpenAIChatAdapter(o)), 'data: {"choices":[{"delta":{"tool_calls":{"a":1}}}]}\n\n');
  await stream("C openai tool_calls [null]   ", withTestTranslatorBudget(createOpenAIChatAdapter(o)), 'data: {"choices":[{"delta":{"tool_calls":[null]}}]}\n\n');
  const oa = withTestTranslatorBudget(createOpenAIChatAdapter(o));
  await nonStream("D openai NS tool_calls object", oa, { choices: [{ message: { role: "assistant", tool_calls: { a: 1 } } }] });
  await nonStream("E openai NS tool_calls [null]", oa, { choices: [{ message: { role: "assistant", tool_calls: [null] } }] });
  await nonStream("F openai NS no .function    ", oa, { choices: [{ message: { role: "assistant", tool_calls: [{ id: "x" }] } }] });
  await nonStream("G google NS candidates:[null]", withTestTranslatorBudget(createGoogleAdapter(g)), { candidates: [null] });
});

Logs or error output

A google candidates:[null]   : THREW -> null is not an object (evaluating 'candidates[0].finishReason')
B openai tool_calls object   : THREW -> {} is not iterable
C openai tool_calls [null]   : THREW -> null is not an object (evaluating 'tc.index')
D openai NS tool_calls object: THREW -> {} is not iterable
E openai NS tool_calls [null]: THREW -> null is not an object (evaluating 'tc.id')
F openai NS no .function     : THREW -> undefined is not an object (evaluating 'tc.function.name')
G google NS candidates:[null]: no throw -> done          <- correctly guarded, no change needed

Version

dev at 79831c90 (with #1240 merged as 2f0dc7cb).

Operating system

Windows 11. Not platform-specific — the adapters are driven directly, no network and no config.

Provider and model

None. Reproduced adapter-locally for openai-chat and google.

Redacted configuration

Not applicable — synthetic Response objects, no config and no credentials.

Additional note on how to fix

Deliberately not opening a PR for this yet. The shape of the fix is a real decision, not a mechanical one, and it is yours to make:

• the #1240 precedent for the frame root was skip, do not terminate, because the frame turned out to be benign padding. For a malformed tool_calls the safer default is probably the opposite, since silently dropping a tool call can strand a turn — but that is a judgement about which failure is worse, and I would rather not guess it into the codebase;
• google.ts:809 shows the cheapest idiom already in use here (optional chaining), which may be all A needs.

Happy to write it once you say which way you want it, or to leave it entirely. Also happy for it to be closed as won't-fix given there is no field evidence — the audit is on the record either way.

Checks

• I searched existing issues and documentation.
• I removed secrets, tokens, account details, request credentials, and personal data.