createSwarm() composes named agents into one SwarmRunner: a router picks the
first agent; any agent hands control to a named peer via `HANDOFF: <name>`,
bounded by maxHandoffs. createLLMRouter() is a cheap-model router. Composes
with the rubric loop and HTTP handler since a swarm is itself a SwarmRunner.
6 new tests (routing, handoff, maxHandoffs cap, unknown-peer/unknown-route
fallbacks, empty-agents guard); 19/19 pass.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
