feat(#1137): rich unread summary in loose ends and wake signal

- hive-sh4re: UnreadMatrix gains summary: String field (per-room breakdown)
- hive-matrix-mcp/protocol: add RoomUnread struct + UnreadSummary request
- hive-matrix-mcp/handlers: collect_unread() fetches per-room data;
  single-unread rooms include truncated last-message body + sender;
  multi-unread rooms carry count only
- hive-matrix-mcp/wake: format_unread_summary() builds wake body from
  RoomUnread slice; terse one-liner for single-room/single-message,
  bulleted list for multi-room; always appends read-hint
- hive-matrix-mcp/timeline: wake body now covers all rooms with unread
  at fire time, not just the triggering event; falls back to per-event
  teaser if notification counts haven't updated yet
- hive-ag3nt/mcp: matrix_unread_summary() replaces matrix_unread_rooms();
  UnreadMatrix loose end carries per-room summary lines; render shows
  room breakdown with sender: body for single-unread rooms

hive-matrix-mcp/src/wake.rs

@@ -72,10 +72,51 @@ pub fn format_wake_body(sender: &str, room: &str, text: &str) -> String {
     format!("[matrix] {sender} in {room}: {truncated}")
 }
 
+/// Format a wake-message body from a list of per-room unread summaries.
+/// Single-room / single-message case collapses to the terse one-liner
+/// format; multiple rooms expand to a bulleted list. Always appends a
+/// read-hint line so the agent knows which tools to reach for.
+#[must_use]
+pub fn format_unread_summary(rooms: &[crate::protocol::RoomUnread]) -> String {
+    use std::fmt::Write as _;
+    if rooms.is_empty() {
+        return String::new();
+    }
+    // Terse path: exactly one room, exactly one unread with body.
+    if rooms.len() == 1 {
+        let r = &rooms[0];
+        if r.count == 1 {
+            if let (Some(body), Some(sender)) = (&r.last_body, &r.last_sender) {
+                return format!(
+                    "[matrix] {sender} in {label}: {body} — use read_room to view, mark_read to clear",
+                    label = r.label
+                );
+            }
+        }
+        return format!(
+            "[matrix] {} unread in {} — use read_room to view, mark_read to clear",
+            r.count, r.label
+        );
+    }
+    // Multi-room path.
+    let mut out = String::from("[matrix] unread messages:");
+    for r in rooms {
+        if r.count == 1 {
+            if let (Some(body), Some(sender)) = (&r.last_body, &r.last_sender) {
+                let _ = write!(out, "\n- {}: {sender}: {body}", r.label);
+                continue;
+            }
+        }
+        let _ = write!(out, "\n- {}: {} unread", r.label, r.count);
+    }
+    out.push_str("\nUse list_rooms + read_room to view, mark_read to clear.");
+    out
+}
+
 /// Truncate `s` to `max` Unicode chars, appending `…` when cut.
 /// Char-based not byte-based so multi-byte content (most chat) doesn't
 /// get cut mid-codepoint.
-fn truncate_chars(s: &str, max: usize) -> String {
+pub fn truncate_chars(s: &str, max: usize) -> String {
     let mut end = s.len();
     for (count, (i, _)) in s.char_indices().enumerate() {
         if count == max {