huskies: merge 1063

server/src/chat/transport/matrix/bot/messages/mod.rs

@@ -11,6 +11,27 @@ pub(super) fn format_user_prompt(sender: &str, message: &str) -> String {
     format!("{sender}: {message}")
 }
 
+/// Drain `lines` into a `<system-reminder>` block for injection at the head of
+/// the next LLM prompt. Returns an empty string when `lines` is empty.
+///
+/// At most 20 lines are shown verbatim; excess lines are replaced with a
+/// `…and N more` indicator to keep context size bounded.
+pub(in crate::chat::transport::matrix::bot) fn format_drained_events(lines: Vec<String>) -> String {
+    if lines.is_empty() {
+        return String::new();
+    }
+    const MAX_PIPELINE_EVENTS: usize = 20;
+    let total = lines.len();
+    let shown_count = total.min(MAX_PIPELINE_EVENTS);
+    let shown = lines[..shown_count].join("\n");
+    let tail = if total > MAX_PIPELINE_EVENTS {
+        format!("\n...and {} more", total - MAX_PIPELINE_EVENTS)
+    } else {
+        String::new()
+    };
+    format!("<system-reminder>\n{shown}{tail}\n</system-reminder>\n")
+}
+
 /// Matrix event handler for room messages. Each invocation spawns an
 #[cfg(test)]
 mod tests {
@@ -51,6 +72,49 @@ mod tests {
         assert!(crate::llm::oauth::extract_login_url_from_error(err).is_none());
     }
 
+    // -- format_drained_events ----------------------------------------------
+
+    #[test]
+    fn format_drained_events_empty_returns_empty_string() {
+        assert_eq!(format_drained_events(vec![]), String::new());
+    }
+
+    #[test]
+    fn format_drained_events_wraps_in_system_reminder() {
+        let result = format_drained_events(vec!["audit ts=2026 id=1 event=x".to_string()]);
+        assert!(result.starts_with("<system-reminder>\n"), "got: {result}");
+        assert!(result.ends_with("</system-reminder>\n"), "got: {result}");
+        assert!(
+            result.contains("audit ts=2026 id=1 event=x"),
+            "got: {result}"
+        );
+    }
+
+    #[test]
+    fn format_drained_events_caps_at_20_with_overflow_indicator() {
+        let lines: Vec<String> = (0..25).map(|i| format!("line {i}")).collect();
+        let result = format_drained_events(lines);
+        assert!(result.contains("...and 5 more"), "got: {result}");
+        assert!(
+            result.contains("line 19"),
+            "last shown line missing; got: {result}"
+        );
+        assert!(
+            !result.contains("line 20"),
+            "line 21 must be hidden; got: {result}"
+        );
+    }
+
+    #[test]
+    fn format_drained_events_exactly_20_no_overflow_indicator() {
+        let lines: Vec<String> = (0..20).map(|i| format!("line {i}")).collect();
+        let result = format_drained_events(lines);
+        assert!(
+            !result.contains("...and"),
+            "must not show overflow when exactly 20; got: {result}"
+        );
+    }
+
     // -- bot_name / system prompt -------------------------------------------
 
     #[test]