fix(desktop): populate last_message_at in channel browser (#951)

Signed-off-by: Will Pfleger <wpfleger@squareup.com>
Co-authored-by: npub1mn7jgtj4w2pd0g0zeuhxsa6jy6p0rewxz4kujt98my82ahfmp72sxjexk7 <dcfd242e557282d7a1e2cf2e6877522682f1e5c6156dc92ca7d90eaedd3b0f95@sprout-oss.stage.blox.sqprod.co>

desktop/src-tauri/src/commands/channels.rs

@@ -156,6 +156,51 @@ pub async fn get_channels(state: State<'_, AppState>) -> Result<Vec<ChannelInfo>
         }
     }
 
+    // Populate last_message_at by fetching the most recent human message per
+    // channel. Uses per-channel filters (single #h value each) so the relay can
+    // push the query to its indexed channel_id column. Multi-value #h is NOT
+    // SQL-pushed and would silently drop quieter channels under the global limit.
+    let channel_ids: Vec<String> = channels.iter().map(|c| c.id.clone()).collect();
+    if !channel_ids.is_empty() {
+        let filters: Vec<serde_json::Value> = channel_ids
+            .iter()
+            .map(|id| {
+                serde_json::json!({
+                    "kinds": [9, 40002],
+                    "#h": [id],
+                    "limit": 1
+                })
+            })
+            .collect();
+
+        let message_events = query_relay(&state, &filters).await.unwrap_or_default();
+
+        let mut last_message_by_channel: std::collections::HashMap<String, u64> =
+            std::collections::HashMap::new();
+        for ev in &message_events {
+            if let Some(ch_id) = ev.tags.iter().find_map(|t| {
+                let s = t.as_slice();
+                (s.len() >= 2 && s[0] == "h").then(|| s[1].clone())
+            }) {
+                let ts = ev.created_at.as_secs();
+                last_message_by_channel
+                    .entry(ch_id)
+                    .and_modify(|existing| {
+                        if ts > *existing {
+                            *existing = ts;
+                        }
+                    })
+                    .or_insert(ts);
+            }
+        }
+
+        for channel in &mut channels {
+            if let Some(&ts) = last_message_by_channel.get(&channel.id) {
+                channel.last_message_at = Some(nostr_convert::timestamp_to_iso(ts));
+            }
+        }
+    }
+
     // NIP-DV: drop DMs the viewer has hidden. The relay maintains a per-viewer
     // parameterized-replaceable snapshot (kind:30622, d=my pubkey) whose `h`
     // tags list currently-hidden DM channel ids. The snapshot also carries

desktop/src-tauri/src/nostr_convert.rs

@@ -533,7 +533,7 @@ pub fn relay_members_from_event(event: &Event) -> Value {
 // ── Time helpers ────────────────────────────────────────────────────────────
 
 /// Convert a unix-seconds timestamp to a UTC RFC-3339 string.
-fn timestamp_to_iso(secs: u64) -> String {
+pub(crate) fn timestamp_to_iso(secs: u64) -> String {
     use std::time::{Duration, SystemTime, UNIX_EPOCH};
     let dt = UNIX_EPOCH + Duration::from_secs(secs);
     // Format manually as RFC-3339 — the `time` crate is already a transitive