context: count channels with activity, not raw messages

The count was dominated by noisy IRC channels (#bcache can drop
hundreds of lines in a day). "879 pending notifications" was a
false urgency signal that I kept ignoring. "3 channels have
notifications" tells me what to actually go look at.

Co-Authored-By: Proof of Concept <poc@bcachefs.org>

src/context.rs

@@ -4,16 +4,26 @@
 // in separately by the caller. Git context and IRC digest
 // are now available through where-am-i.md and the memory graph.
 
+use std::collections::HashSet;
+
 /// Build context string for a prompt.
 /// notification_text is passed in from the notify module.
 pub fn build(_include_irc: bool, notification_text: &str) -> String {
     // Keep nudges short — Claude checks notifications via
-    // `poc-daemon status` on its own. Just mention the count.
-    let count = notification_text.matches("[irc.").count()
-        + notification_text.matches("[telegram.").count();
-    if count > 0 {
-        format!("{count} pending notifications")
-    } else {
-        String::new()
+    // `poc-daemon status` on its own. Just mention how many channels
+    // have activity (not how many messages — one IRC channel can
+    // generate hundreds of lines).
+    let channels: HashSet<&str> = notification_text
+        .lines()
+        .filter_map(|l| l.strip_prefix('['))
+        .filter_map(|l| l.split_once(']'))
+        .map(|(ch, _)| ch)
+        .filter(|ch| ch.starts_with("irc.") || ch.starts_with("telegram."))
+        .collect();
+
+    match channels.len() {
+        0 => String::new(),
+        1 => "1 channel has notifications".to_string(),
+        n => format!("{n} channels have notifications"),
     }
 }