fix: answer osc 4 palette queries

refs #387

4 files changed, 199 insertions, 10 deletions

diff --git a/docs/next/CHANGELOG.md b/docs/next/CHANGELOG.md
index f8b405db..43a505de 100644
--- a/docs/next/CHANGELOG.md
+++ b/docs/next/CHANGELOG.md
@@ -11,6 +11,7 @@
 
 ### Fixed
 - Pane input no longer waits behind the PTY actor's idle read poll, restoring responsive typing at quiet shell prompts. (#379)
+- Pane apps that query OSC 4 ANSI palette colors now receive the active terminal palette response, so OpenCode and similar TUIs can enable system-theme behavior inside Herdr. (#387)
 
 ## [0.6.6] - 2026-05-31
 
diff --git a/src/ghostty/mod.rs b/src/ghostty/mod.rs
index 9eda90d7..e2b592d2 100644
--- a/src/ghostty/mod.rs
+++ b/src/ghostty/mod.rs
@@ -372,6 +372,7 @@ fn cell_color_from_style_color(color: ffi::GhosttyStyleColor) -> Option<CellColo
 pub struct RenderColors {
     pub background: RgbColor,
     pub foreground: RgbColor,
+    pub palette: [RgbColor; 256],
 }
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
@@ -1870,6 +1871,7 @@ impl RenderState {
         Ok(RenderColors {
             background: colors.background.into(),
             foreground: colors.foreground.into(),
+            palette: colors.palette.map(Into::into),
         })
     }
 
diff --git a/src/pane/osc.rs b/src/pane/osc.rs
index 217e0c86..1512f336 100644
--- a/src/pane/osc.rs
+++ b/src/pane/osc.rs
@@ -26,6 +26,7 @@ pub(super) enum DefaultColorEvent {
     Query(DefaultColorQuery),
     Set(DefaultColorQuery),
     Reset(DefaultColorQuery),
+    PaletteQuery(u8),
 }
 
 #[derive(Debug, Default)]
@@ -240,10 +241,24 @@ fn parse_default_color_event(body: &[u8]) -> Option<DefaultColorEvent> {
         b"11;?" => Some(DefaultColorEvent::Query(DefaultColorQuery::Background)),
         b"110" | b"110;" => Some(DefaultColorEvent::Reset(DefaultColorQuery::Foreground)),
         b"111" | b"111;" => Some(DefaultColorEvent::Reset(DefaultColorQuery::Background)),
-        _ => parse_default_color_set_event(body),
+        _ => parse_palette_color_query(body).or_else(|| parse_default_color_set_event(body)),
     }
 }
 
+fn parse_palette_color_query(body: &[u8]) -> Option<DefaultColorEvent> {
+    let index = body.strip_prefix(b"4;")?.strip_suffix(b";?")?;
+    if index.is_empty() || index.len() > 3 || !index.iter().all(|byte| byte.is_ascii_digit()) {
+        return None;
+    }
+    let mut value: u16 = 0;
+    for &digit in index {
+        value = value * 10 + u16::from(digit - b'0');
+    }
+    u8::try_from(value)
+        .ok()
+        .map(DefaultColorEvent::PaletteQuery)
+}
+
 fn parse_default_color_set_event(body: &[u8]) -> Option<DefaultColorEvent> {
     let separator = body.iter().position(|byte| *byte == b';')?;
     let query = match &body[..separator] {
@@ -576,13 +591,16 @@ mod tests {
     fn default_color_event_tracker_detects_queries_sets_and_resets() {
         let mut tracker = DefaultColorEventTracker::default();
 
-        tracker.observe(b"\x1b]10;?\x07\x1b]11;?\x1b\\\x1b]10;rgb:11/22/33\x07\x1b]111\x07");
+        tracker.observe(
+            b"\x1b]10;?\x07\x1b]11;?\x1b\\\x1b]4;0;?\x07\x1b]10;rgb:11/22/33\x07\x1b]111\x07",
+        );
 
         assert_eq!(
             tracker.drain_pending(),
             vec![
                 DefaultColorEvent::Query(DefaultColorQuery::Foreground),
                 DefaultColorEvent::Query(DefaultColorQuery::Background),
+                DefaultColorEvent::PaletteQuery(0),
                 DefaultColorEvent::Set(DefaultColorQuery::Foreground),
                 DefaultColorEvent::Reset(DefaultColorQuery::Background),
             ]
@@ -590,7 +608,7 @@ mod tests {
     }
 
     #[test]
-    fn default_color_event_tracker_handles_split_queries() {
+    fn default_color_event_tracker_handles_split_default_color_queries() {
         let mut tracker = DefaultColorEventTracker::default();
 
         tracker.observe(b"\x1b]11");
@@ -606,6 +624,39 @@ mod tests {
     }
 
     #[test]
+    fn default_color_event_tracker_handles_split_palette_color_queries() {
+        let mut tracker = DefaultColorEventTracker::default();
+
+        tracker.observe(b"\x1b]4;25");
+        assert!(tracker.drain_pending().is_empty());
+        tracker.observe(b"5;?\x1b");
+        assert!(tracker.drain_pending().is_empty());
+        tracker.observe(b"\\");
+
+        assert_eq!(
+            tracker.drain_pending(),
+            vec![DefaultColorEvent::PaletteQuery(255)]
+        );
+    }
+
+    #[test]
+    fn default_color_event_tracker_rejects_malformed_palette_color_queries() {
+        let mut tracker = DefaultColorEventTracker::default();
+
+        tracker.observe(b"\x1b]4;;?\x07");
+        tracker.observe(b"\x1b]4;-1;?\x07");
+        tracker.observe(b"\x1b]4;256;?\x07");
+        tracker.observe(b"\x1b]4;0;?;1;?\x07");
+        tracker.observe(b"\x1b]4;0;rgb:1111/2222/3333\x07");
+        tracker.observe(b"\x1b]4;0;?\x07");
+
+        assert_eq!(
+            tracker.drain_pending(),
+            vec![DefaultColorEvent::PaletteQuery(0)]
+        );
+    }
+
+    #[test]
     fn default_color_event_tracker_ignores_other_osc_and_dcs_payloads() {
         let mut tracker = DefaultColorEventTracker::default();
 
diff --git a/src/pane/terminal.rs b/src/pane/terminal.rs
index cc316bf7..db05d1fa 100644
--- a/src/pane/terminal.rs
+++ b/src/pane/terminal.rs
@@ -1305,6 +1305,11 @@ fn respond_to_default_color_events(
                     terminal_responses.push(response);
                 }
             }
+            DefaultColorEvent::PaletteQuery(index) => {
+                if let Some(response) = palette_color_query_response(index, core) {
+                    terminal_responses.push(response);
+                }
+            }
             DefaultColorEvent::Set(query) => mark_child_default_color_changed(core, query, true),
             DefaultColorEvent::Reset(query) => mark_child_default_color_changed(core, query, false),
         }
@@ -1321,13 +1326,36 @@ fn default_color_query_response(query: DefaultColorQuery, core: &GhosttyPaneCore
         }
         _ => None,
     }?;
-    let r = u16::from(color.r) * 257;
-    let g = u16::from(color.g) * 257;
-    let b = u16::from(color.b) * 257;
-    Some(Bytes::from(format!(
-        "\x1b]{};rgb:{r:04x}/{g:04x}/{b:04x}\x1b\\",
-        query.osc_number()
-    )))
+    Some(osc_rgb_response(
+        &query.osc_number().to_string(),
+        color.r,
+        color.g,
+        color.b,
+    ))
+}
+
+fn palette_color_query_response(index: u8, core: &mut GhosttyPaneCore) -> Option<Bytes> {
+    let GhosttyPaneCore {
+        terminal,
+        render_state,
+        ..
+    } = core;
+    render_state.update(terminal).ok()?;
+    let colors = render_state.colors().ok()?;
+    let color = colors.palette[usize::from(index)];
+    Some(osc_rgb_response(
+        &format!("4;{index}"),
+        color.r,
+        color.g,
+        color.b,
+    ))
+}
+
+fn osc_rgb_response(command: &str, r: u8, g: u8, b: u8) -> Bytes {
+    let r = u16::from(r) * 257;
+    let g = u16::from(g) * 257;
+    let b = u16::from(b) * 257;
+    Bytes::from(format!("\x1b]{command};rgb:{r:04x}/{g:04x}/{b:04x}\x1b\\"))
 }
 
 fn mark_child_default_color_changed(
@@ -1456,6 +1484,24 @@ mod tests {
         terminal.write(b"END");
     }
 
+    fn current_palette_color(pane: &GhosttyPaneTerminal, index: u8) -> crate::ghostty::RgbColor {
+        let mut core = pane.core.lock().unwrap();
+        let GhosttyPaneCore {
+            terminal,
+            render_state,
+            ..
+        } = &mut *core;
+        render_state.update(terminal).unwrap();
+        render_state.colors().unwrap().palette[usize::from(index)]
+    }
+
+    fn expected_osc_rgb_response(command: &str, color: crate::ghostty::RgbColor) -> Bytes {
+        let r = u16::from(color.r) * 257;
+        let g = u16::from(color.g) * 257;
+        let b = u16::from(color.b) * 257;
+        Bytes::from(format!("\x1b]{command};rgb:{r:04x}/{g:04x}/{b:04x}\x1b\\"))
+    }
+
     #[test]
     fn decscusr_cursor_shape_preserves_blinking_variants() {
         assert_eq!(
@@ -2318,6 +2364,95 @@ mod tests {
     }
 
     #[test]
+    fn process_pty_bytes_returns_palette_color_query_response_without_queuing_input() {
+        let (tx, mut rx) = mpsc::channel(4);
+        let terminal = crate::ghostty::Terminal::new(20, 5, 0).unwrap();
+        let pane = GhosttyPaneTerminal::new(terminal, tx.clone()).unwrap();
+        let pane_id = PaneId::from_raw(1);
+        let color = current_palette_color(&pane, 0);
+
+        let result = pane.process_pty_bytes(pane_id, 0, b"\x1b]4;0;?\x07", &tx);
+
+        assert_eq!(
+            result.terminal_responses,
+            vec![expected_osc_rgb_response("4;0", color)]
+        );
+        assert!(rx.try_recv().is_err());
+    }
+
+    #[test]
+    fn process_pty_bytes_returns_split_palette_color_query_response() {
+        let (tx, mut rx) = mpsc::channel(4);
+        let terminal = crate::ghostty::Terminal::new(20, 5, 0).unwrap();
+        let pane = GhosttyPaneTerminal::new(terminal, tx.clone()).unwrap();
+        let pane_id = PaneId::from_raw(1);
+        let color = current_palette_color(&pane, 255);
+
+        let result = pane.process_pty_bytes(pane_id, 0, b"\x1b]4;25", &tx);
+        assert!(result.terminal_responses.is_empty());
+        assert!(rx.try_recv().is_err());
+        let result = pane.process_pty_bytes(pane_id, 0, b"5;?\x1b", &tx);
+        assert!(result.terminal_responses.is_empty());
+        assert!(rx.try_recv().is_err());
+        let result = pane.process_pty_bytes(pane_id, 0, b"\\", &tx);
+
+        assert_eq!(
+            result.terminal_responses,
+            vec![expected_osc_rgb_response("4;255", color)]
+        );
+        assert!(rx.try_recv().is_err());
+    }
+
+    #[test]
+    fn process_pty_bytes_ignores_malformed_palette_color_queries() {
+        let (tx, mut rx) = mpsc::channel(4);
+        let terminal = crate::ghostty::Terminal::new(20, 5, 0).unwrap();
+        let pane = GhosttyPaneTerminal::new(terminal, tx.clone()).unwrap();
+        let pane_id = PaneId::from_raw(1);
+
+        let result = pane.process_pty_bytes(
+            pane_id,
+            0,
+            b"\x1b]4;;?\x07\x1b]4;-1;?\x07\x1b]4;256;?\x07\x1b]4;0;?;1;?\x07\x1b]4;0;rgb:1111/2222/3333\x07",
+            &tx,
+        );
+
+        assert!(result.terminal_responses.is_empty());
+        assert!(rx.try_recv().is_err());
+    }
+
+    #[test]
+    fn process_pty_bytes_orders_palette_reply_before_following_terminal_replies() {
+        let (tx, mut rx) = mpsc::channel(4);
+        let terminal = crate::ghostty::Terminal::new(20, 5, 0).unwrap();
+        let pane = GhosttyPaneTerminal::new(terminal, tx.clone()).unwrap();
+        let pane_id = PaneId::from_raw(1);
+        let color = current_palette_color(&pane, 0);
+        pane.apply_host_terminal_theme(crate::terminal_theme::TerminalTheme {
+            foreground: None,
+            background: Some(crate::terminal_theme::RgbColor {
+                r: 0x00,
+                g: 0x2b,
+                b: 0x36,
+            }),
+        });
+
+        let result = pane.process_pty_bytes(pane_id, 0, b"\x1b]4;0;?\x07\x1b]11;?\x07\x1b[c", &tx);
+
+        assert_eq!(result.terminal_responses.len(), 3);
+        assert_eq!(
+            result.terminal_responses[0],
+            expected_osc_rgb_response("4;0", color)
+        );
+        assert_eq!(
+            result.terminal_responses[1],
+            Bytes::from_static(b"\x1b]11;rgb:0000/2b2b/3636\x1b\\")
+        );
+        assert!(String::from_utf8_lossy(&result.terminal_responses[2]).contains('c'));
+        assert!(rx.try_recv().is_err());
+    }
+
+    #[test]
     fn process_pty_bytes_returns_default_color_query_responses_without_queuing_input() {
         let (tx, mut rx) = mpsc::channel(4);
         let terminal = crate::ghostty::Terminal::new(20, 5, 0).unwrap();