feat(channels): list unread top-level mentions in sidebar Activity, and count only unread mentions on the Inbox card

docs/buzz-help.md

@@ -349,6 +349,9 @@ revokes all of them, and a pairing unused for 30 days expires.
   name, or **Open in channel** in the thread tab's menu, to open the thread in
   Channels beside its original message, which the channel history shows and
   highlights.
+- **Sidebar activity**: rest the pointer on a sidebar row to list its unread
+  mentions of you and its unread threads, mentions first. Open one or mark it
+  read from the list; just looking marks nothing read.
 - **Mute** is available from a channel or DM's sidebar context menu. Once
   confirmed, a crossed-out bell appears immediately after its name. New messages
   do not make muted channel or DM names bold.

docs/inbox.md

@@ -50,8 +50,11 @@ Resting a pointer on the sidebar's Activity row opens a card of recent conversat
 through the page contract's `preview`. It reads the same `session.unread.inbox()`
 and `session.inboxFeed` projection as the page, with All activity and Everyone,
 newest first and bounded to 50 rows after mixing conversations and reactions, as on the
-page. The header counts unread
-conversations once each, as a DM, mention or thread. Unread only is the card's own
+page. The header leads with the number of
+unread conversations, then counts each once by its most specific kind: DM, then
+mention, then thread. A mention counts only while it is unread, as Mentions with
+Unread only would list it; a Solo chat's flat row has no kind, so only the total
+counts it. Unread only is the card's own
 choice, saved on this device per account and community, and never changes the
 page's filters. A row opens its conversation directly, through the same
 conversation target as the page's fallback, and closes the card without opening

docs/unread.md

@@ -51,9 +51,11 @@ content does not qualify. Pane motion completion restarts observation after
 unchanged rows enter the viewport. Another pane, a dialog, background window,
 preload, and mounted virtualizer overscan do not qualify.
 
-Away from the bottom, observations mark individual fully visible messages. At the
-physical bottom, 300 ms visibility of the newest message's bottom edge also earns
-catch-up (including a message taller than the viewport):
+Away from the bottom, observations mark individual fully visible messages, to
+within a pixel: a reveal's whole-pixel scroll can leave a row a fraction of a
+pixel past the edge. At the physical bottom, 300 ms visibility of the newest
+message's bottom edge also earns catch-up (including a message taller than the
+viewport):
 
 - `activity:<channel>` uses the newest retained verified event timestamp at dwell
   completion, including replies newer than the visible top-level head. It reads
@@ -222,8 +224,8 @@ do not contribute to “N unread” offscreen counts or avatar previews, even fo
 mentions, manual unread or thread replies. Muted
 channel and DM sidebar rows show a crossed-out bell immediately after their names,
 even with no unread activity. They hide all unread dots, including
-thread activity dots. Thread activity remains available through the row's activity popover,
-and its unread count remains accessible to assistive technology. Unmute restores
+thread activity dots. Mentions and thread activity remain available through the row's activity
+popover, and their counts remain accessible to assistive technology. Unmute restores
 the dots from retained unread evidence. The promoted Bestie DM also hides muted
 unread dots; its label follows the same mute rule.
 Solo chat labels strengthen for any observed unread message, including mentions,
@@ -232,8 +234,17 @@ Ordinary unread renders no row marker. Unmuted DMs, mentions, broadcasts, and
 relevant thread replies add one accent dot; non-DM row numerals are omitted and DM
 avatars are reserved for promoted offscreen cues. Thread activity reuses that dot:
 its hover/focus/click popover groups unread replies by canonical thread root and
-opens the existing thread panel, so overlapping priority and thread activity never
-produce duplicate dots. Merely revealing the popover does not acknowledge a reply.
+opens the existing thread panel. Above the threads it lists unread top-level messages that
+mention the viewer, newest first; a mention opens at its message and is read like any
+visit. A reply's mention stays under its thread; DMs and broadcasts list no
+mentions. A row with only mentions keeps its priority dot, names them to
+assistive technology ("1 unread mention") and still opens the popover; with
+threads, the dot's label counts both ("1 unread mention, 1 unread thread").
+Overlapping priority, mention and thread activity never produce duplicate dots.
+Merely revealing the popover does not acknowledge a mention or reply.
+While Activity is still checking a mention's stored edits and deletions, its row
+shows "Preview updating…" instead of the text, or "Preview unavailable. Retry
+activity." if the check failed, as on the Activity page.
 A local manual-unread mark strengthens the label without fabricating priority; the
 underlying observed count remains available.
 Channel Settings → Diagnostics exposes explicit actions and Unread status/retry. Unknown and