Desktop catch-up escalates @channel markers from before the reader joined (badge-without-row)

[LordMelkor]

🤖 Filed by kray's AI agent on his behalf.

Deferred finding from the adversarial review of the #3197 late-joiner backfill fix. Depends on #3197.

Problem

The server-side mentions feed now bounds @channel rows to members who had already joined when the relay admitted the event (cm.joined_at <= e.received_at, cf5fd18). The desktop catch-up path has no equivalent bound:

• useUnreadChannels.ts fetches per-channel history with since = readAt + 1, and a channel with no read state — which is exactly the just-joined case — uses since: 0, pulling the full retained timeline.
• Classification runs each fetched event through shouldNotifyForEvent / isHighPriorityEventForUser, whose channelNotifyEscalates treats every ["notify","channel"] marker as mention-tier. It has no join-time input.

Net effect: a member who joins a channel gets mention-tier sidebar/app badges for @channel events sent before they joined — events the (now-correct) server feed deliberately excludes. Badge with no corresponding Inbox row.

@here is only marginally exposed (its 120s observation-time freshness window bounds retroactivity), but the same join-time question applies to an @here sent moments before the reader joined.

Fix directions

1. Join-time bound in the pure predicate (mirrors the server): extend ChannelNotifyContext (desktop/src/features/notifications/lib/channelNotifyEscalation.ts) with an optional joinedAtSeconds, and return false when event.created_at < joinedAtSeconds. Callers in the catch-up path pass the reader's own joinedAt (available on ChannelMember, desktop/src/shared/api/types.ts) — the cost is plumbing per-channel self-membership into useUnreadChannels, which today only holds membership sets. Note the client only has the client-authored created_at, not the relay's received_at, so the bound is skew-tolerant rather than exact — same trade-off class the server fix documents.
2. Feed-driven badges: treat the bounded mentions feed (which desktop now requests — see feat: @channel and @here channel-wide mentions (NIP-CM) #3197) as the authority for @channel mention-tier in catch-up, and stop escalating on the raw marker for historical fetches. Live-subscription escalation stays as-is (a live event is by definition post-join).

Option 1 is the smaller change; option 2 removes the client/server divergence class entirely.

Related

• feat: @channel and @here channel-wide mentions (NIP-CM) #3197 — @channel/@here (NIP-CM); server-side join bound in cf5fd18
• Inactive-community rail: count marker-only @channel/@here mentions #3235 — sibling finding: inactive-community rail counts mentions by #p only