Object.prototype stream key breaks the tool-call stream with an untyped defect

The tool-call accumulator in packages/llm/src/protocols/utils/tool-stream.ts stores pending calls in a plain object keyed by the provider's stream id:

type State<K extends StreamKey> = Partial<Record<K, PendingTool>>
const empty = () => ({})

On the OpenAI Responses protocol that key is event.item_id, a free-form string from the server (Schema.optional(Schema.String)). If it is an Object.prototype member name — toString, constructor, valueOf, hasOwnProperty — then tools[key] returns the inherited function instead of undefined, which is truthy. appendExisting, finish and finishWithInput therefore skip their if (!tool) return ... guards and build an event with id/name undefined.

The schema constructor then throws Expected string, got undefined synchronously, outside the Effect error channel, so the stream dies with a defect instead of yielding a typed provider-output error.

Reproduced against dev (3f2e0e8):

appendExisting("toString")  -> throw: Expected string, got undefined  (tool-stream.ts:89)
finish("constructor")       -> throw: Expected string, got undefined  (tool-stream.ts:171)
appendOrStart("toString")   -> OK (its id/name guard catches it)

The value comes from the remote provider response (any OpenAI-compatible server, proxy or gateway), not from local input.

Happy to send a PR: reading pending calls through an own-property check (Object.hasOwn) fixes it without changing the state shape.