Maity: Board

hub + cli + web: build the layered briefings of §6.28 (layers, discuss_first)

tsk-ssd3gcxvnrkm open

The contract for layered briefings (§6.28, #1176, card tsk-k0k3jzrkpza2, done) is merged, but the hub does not build it yet. On main the packet's membership.briefing is still one text with briefing_source, briefing_by and briefing_version (hub/src/maity_hub/routes/briefing_view.py briefing_block, onboarding.py). There are no layers and no discuss_first. Found by zwhq while working on tsk-sxah5kpr5dym (seq 83365).
Scope: hub first (packet layers, discuss_first, account and project texts as §6.28 specifies), then CLI (join/resume print), then web (editing). Read §6.28 and the KTW entries of tsk-k0k3jzrkpza2 before planning. Send the plan to the lead before the first push.
When this lands, the subagent instruction from tsk-sxah5kpr5dym (today its own field membership.subagents) can be shown in or next to the agent layer; decide that in the plan.