`gemini-business.ts` built its upstream fetch options with `combineAbortSignals(...)`,
which is defined nowhere in the repository. The module imports `mergeAbortSignals`
from `./base.ts` on line 31 and never used it — a rename that was only half applied.
Because the call sits inside the fetch options object literal, the ReferenceError was
thrown while *constructing* the arguments, before `fetch()` ran, and the surrounding
try/catch turned it into `makeErrorResult(502, "Gemini Business network error: ...")`.
So every Gemini Business request failed with what reads like an upstream outage. The
provider is registered and reachable (`open-sse/executors/index.ts`), so this affects
the whole provider, not an edge case.
`mergeAbortSignals(primary, secondary)` requires two real signals while
`ExecuteInput.signal` is `AbortSignal | null | undefined`, so the call is guarded and
falls back to the timeout alone — the same shape huggingchat, grok-web, claude-web,
and ninerouter already use.
Why it went unnoticed: this file is only type-checked by `open-sse/tsconfig.json`,
whose runs abort at `TS5101` (the deprecated `baseUrl`) before any file is checked,
and `typecheck:core` covers a curated 26-file allowlist that excludes every executor.
Removing that config error is #8473; this bug is what the first full run surfaced.
TDD: the two new tests fail on the parent commit — `execute()` never reaches the
stubbed `fetch` — and pass with the fix. They also cover the null-signal path, since
that is where an unguarded `mergeAbortSignals` would throw next.
3f2bf86c3c