feat(fleet): comms-block emitter + FLEET-LAUNCH runbook (#633)

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

docs/TASKS.md

@@ -86,3 +86,7 @@ Active workstream is **W1 — Federation v1**. Workers should:
 ## #631 — re-seed preserves user fleet data (CRITICAL) — fix/631-reseed-preserves-fleet-data
 
 - Status: implemented + tested. PRIMARY: install.sh PRESERVE_PATHS += fleet/\*.yaml + fleet/agents + fleet/run (glob-aware cp-fallback); TS parity. SECONDARY: refreshActiveFleetUnits propagates unit fixes to ~/.config/systemd/user on mosaic update. bash F6 + TS + unit tests green. Detail: scratchpads/631-reseed-preserves-fleet.md.
+
+## #633 — comms-block emitter + FLEET-LAUNCH runbook — feat/633-comms-block-runbook
+
+- Status: implemented + tested (TDD). `mosaic fleet comms-block <role> [--host]` wraps resolveCommsBlock → readFleetCommsBlock; fails loud (stderr + exit 1) on unknown role / missing roster instead of silent empty. docs/fleet/FLEET-LAUNCH.md runbook: worker path + orchestrator .env fold (MOSAIC_AGENT_COMMAND; line-41 [-z] short-circuits line-44 yolo hardcode) + 3 launch gotchas + #632 preserve note + North-Star 4-field arc (harness ✅/model ✅ roster-native today; yolo + command/channels = PATH B #636). 177 fleet+comms tests green (6 new resolveCommsBlock cases). PATH A of the A→B→webUI arc. Detail: scratchpads/633-comms-block-runbook.md.