fix: detect agent state from terminal tail instead of viewport

2 files changed, 43 insertions, 2 deletions

diff --git a/README.md b/README.md
index c539453b..69d16f01 100644
--- a/README.md
+++ b/README.md
@@ -294,7 +294,7 @@ herdr does not require hooks or agent-side configuration for its built-in detect
 
 1. identifying the foreground process of each pane's pty via `/proc` on linux or `proc_pidinfo` on macos
 2. matching the process name against known agents
-3. reading terminal screen content and applying per-agent heuristics to determine state
+3. reading the live bottom of the terminal buffer and applying per-agent heuristics to determine state
 
 this means detection works with any supported agent, installed any way, with zero setup. if it runs in a terminal, herdr can see it.
 
diff --git a/src/pane.rs b/src/pane.rs
index 9552e1c6..a578eb33 100644
--- a/src/pane.rs
+++ b/src/pane.rs
@@ -19,6 +19,7 @@ use crate::layout::PaneId;
 
 const CLAUDE_WORKING_HOLD: std::time::Duration = std::time::Duration::from_millis(1200);
 const RELEASE_REACQUIRE_SUPPRESSION: std::time::Duration = std::time::Duration::from_secs(1);
+const DEFAULT_DETECTION_ROWS: usize = 24;
 
 #[derive(Debug, Clone, Copy)]
 struct PendingAgentRelease {
@@ -342,6 +343,10 @@ impl PaneTerminal {
         self.ghostty.visible_text()
     }
 
+    fn detection_text(&self) -> String {
+        self.ghostty.detection_text()
+    }
+
     fn recent_text(&self, lines: usize) -> String {
         self.ghostty.recent_text(lines)
     }
@@ -646,6 +651,14 @@ impl GhosttyPaneTerminal {
             .unwrap_or_default()
     }
 
+    fn detection_text(&self) -> String {
+        self.core
+            .lock()
+            .ok()
+            .and_then(|core| ghostty_detection_text(&core).ok())
+            .unwrap_or_default()
+    }
+
     fn recent_text(&self, lines: usize) -> String {
         self.core
             .lock()
@@ -1054,6 +1067,16 @@ fn ghostty_visible_text(core: &mut GhosttyPaneCore) -> Result<String, crate::gho
     Ok(lines_to_text(lines))
 }
 
+fn ghostty_detection_text(core: &GhosttyPaneCore) -> Result<String, crate::ghostty::Error> {
+    let lines = core
+        .terminal
+        .rows()
+        .ok()
+        .map(|rows| usize::from(rows).max(1))
+        .unwrap_or(DEFAULT_DETECTION_ROWS);
+    ghostty_recent_text(core, lines)
+}
+
 fn ghostty_recent_text(
     core: &GhosttyPaneCore,
     lines: usize,
@@ -1572,7 +1595,7 @@ impl PaneRuntime {
                         }
                     }
 
-                    let content = terminal.visible_text();
+                    let content = terminal.detection_text();
                     let raw_state = detect::detect_state(agent, &content);
                     let new_state = stabilize_agent_state(
                         agent,
@@ -2126,6 +2149,24 @@ mod tests {
     }
 
     #[test]
+    fn detection_text_stays_at_bottom_when_viewport_is_scrolled() {
+        let (tx, _rx) = mpsc::channel(4);
+        let mut terminal = crate::ghostty::Terminal::new(80, 3, 100).unwrap();
+        write_numbered_lines(&mut terminal, 10);
+        let pane = GhosttyPaneTerminal::new(terminal, tx).unwrap();
+
+        let bottom_snapshot = pane.detection_text();
+        assert_eq!(bottom_snapshot, pane.recent_text(3));
+        assert!(bottom_snapshot.contains("000009"));
+
+        let before = pane.scroll_metrics().expect("scroll metrics before scroll");
+        pane.set_scroll_offset_from_bottom(before.max_offset_from_bottom);
+
+        assert!(pane.visible_text().contains("000000"));
+        assert_eq!(pane.detection_text(), bottom_snapshot);
+    }
+
+    #[test]
     fn recent_unwrapped_text_ignores_soft_wraps() {
         let (tx, _rx) = mpsc::channel(4);
         let mut terminal = crate::ghostty::Terminal::new(5, 3, 100).unwrap();