Per-channel unread message badge: multi-constellation rollup and auto-select clearing

[pskillen]

Type: enhancement | Area: Messages / unread

Follow-up gap from the #279 work (protocol-scoped + per-channel unread badges).

Context

The messages page renders one constellation and one channel at a time (ProtocolMessageHistoryPage.tsx). Per-channel unread badges are therefore only visible for channels in the currently selected constellation. Unread on channels in other constellations still contributes to the protocol nav badge but has no per-channel surface until the user switches constellation.

The system currently runs effectively one constellation per protocol, so this is acceptable for now and is being accepted as a known gap rather than blocking #279.

Gaps to address later

• Multi-constellation rollup: surface unread on constellation buttons (or a rollup badge) so unread in a non-active constellation is discoverable.
• Per-channel badges across constellations: decide whether channel badges should aggregate or remain scoped to the active constellation.
• Auto-select mark-as-read nuance: the messages page clears channel unread when auto-selecting the first channel. With a single constellation this is harmless, but with multiple constellations the channel auto-select effect (which also runs on constellation switch) must not blanket-clear unread for channels the user did not explicitly open. Scope markAsReadForChannel to genuine user selection + initial mount.

Related

• meshflow-ui #279 (protocol + per-channel unread badges, channel button row)
• Parent epic #341 (messages UI redesign)