Collapses the five-call hand-assembly every sandbox-free surface repeats
(resolve model → build tool schemas → streamTurn → executeToolCall →
drive the loop) into one configured object: run()/stream() for an agent.
The model is always advertised the app tools, so it emits tool_calls and
the side effects fire — the failure that scored tool-driven agents zero
off-sandbox. Domain (taxonomy, handlers, system prompt) injected; no
sandbox, no DO, no agent-runtime import. The same core the Worker runs,
runnable in an eval/edge/Node. 5 tests, 176 total.