Add `mosaic fleet comms-block <role> [--host]` — an explicit-arg, comms-only
emitter wrapping a new resolveCommsBlock() over readFleetCommsBlock. Unlike the
launch-time reader (which returns '' on any miss so composeContract can no-op
silently), the emitter fails loud: unknown role / missing roster → stderr +
exit 1, so an operator can safely preview any peer's view and a typo is never
a silent no-op.
Add docs/fleet/FLEET-LAUNCH.md: the canonical roster-driven launch path
(worker + orchestrator .env fold via MOSAIC_AGENT_COMMAND, which short-circuits
the line-44 yolo hardcode), 3 launch gotchas (flag conflict, MOSAIC_AGENT_NAME
baking, launchRuntime guards), the #632 preserve-list note, and the North-Star
A→B→webUI launch-config arc.
PATH A of the orchestrator-launch fix; PATH B (roster-native launch-config:
yolo toggle + command/channels emission) tracked as #636.
TDD: 6 new resolveCommsBlock cases; 177 fleet+comms tests green; typecheck,
eslint, prettier clean.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EsgTQzV5YUGk1JtCLP4B83
