diff --git a/pmacs-gpu/src/main.rs b/pmacs-gpu/src/main.rs
index f1207ba..22b3acf 100644
--- a/pmacs-gpu/src/main.rs
+++ b/pmacs-gpu/src/main.rs
@@ -36,8 +36,8 @@ use loro::{ContainerTrait, ExportMode};
 use pmacs_protocol::{
     AdornmentContent, AdornmentPlacement, BufferId, ByteRange, CrdtOp, Decoration, DecorationKind,
     DecorationSegment, FrontendId, InlineAdornment, InstanceMessage, InstanceSignal,
-    Key as ProtocolKey, MenuPromptRow, Modifiers, PointerKind, SelectionSnapshot, StyleSegment,
-    StyleSpan,
+    Key as ProtocolKey, LineNumberMode, MenuPromptRow, Modifiers, PointerKind, SelectionSnapshot,
+    StyleSegment, StyleSpan,
     cell::{Color as CellColor, Style as CellStyle},
 };
 use wgpu::MultisampleState;
@@ -650,10 +650,12 @@ struct State {
     /// Minimap vertex bytes cached by [`MinimapCacheKey`] —
     /// rebuilding rescanned every line shape per frame.
     minimap_cache: Option<(MinimapCacheKey, Vec<u8>)>,
-    /// Line-number gutter toggle (UX gutter arc, GPU side). Frontend-local
-    /// (Q#UX5), set from the `--line-numbers` flag. Off ⇒ zero coordinate
-    /// change: `gutter_width_px()` is 0 and every shift site is a no-op.
-    line_numbers: bool,
+    /// Line-number gutter mode (UX gutter arc, GPU side). Shipped by the
+    /// daemon over `InstanceMessage::LineNumbers` (protocol v14). `Off` ⇒
+    /// zero coordinate change: `gutter_width_px()` is 0 and every shift site
+    /// is a no-op. Relative/Hybrid are rendered locally against the GPU's
+    /// own cursor line.
+    line_numbers: LineNumberMode,
     /// Shaped right-aligned line numbers, one per visible code line — its
     /// own text layer over the code, aligned row-for-row (same line height).
     gutter_buffer: Buffer,
@@ -1882,7 +1884,7 @@ impl State {
             mb_text_renderer,
             mb_bg_vertex_buffer: ReusableVertexBuffer::new(),
             minimap_cache: None,
-            line_numbers: false,
+            line_numbers: LineNumberMode::Off,
             gutter_buffer,
             gutter_text_renderer,
         }
@@ -2532,12 +2534,12 @@ impl State {
                 self.request_redraw();
                 None
             }
-            // UX gutter (protocol v13): the daemon owns the per-window
-            // line-number toggle (`M-x window.toggle-line-numbers`); apply
-            // it to our local gutter state and repaint on change.
-            InstanceMessage::LineNumbers { enabled, .. } => {
-                if self.line_numbers != enabled {
-                    self.line_numbers = enabled;
+            // UX gutter (protocol v14): the daemon owns the per-window
+            // line-number mode; apply it to our local gutter state and
+            // repaint on change.
+            InstanceMessage::LineNumbers { mode, .. } => {
+                if self.line_numbers != mode {
+                    self.line_numbers = mode;
                     self.request_redraw();
                 }
                 None
@@ -2812,7 +2814,7 @@ impl State {
     /// disabled (UX gutter arc, Q#UX3): `digits * advance + gap`. Mirrors
     /// the TUI's `Window::gutter_width`; the unit here is pixels.
     fn gutter_width_px(&self) -> f32 {
-        if !self.line_numbers {
+        if !self.line_numbers.is_on() {
             return 0.0;
         }
         let lines = self.current_line_starts.len().max(1);
@@ -2826,24 +2828,43 @@ impl State {
         TEXT_LEFT + self.gutter_width_px()
     }
 
+    /// The GPU's own cursor's 0-based buffer line, or `0` when there's no
+    /// own cursor in the displayed buffer (relative/hybrid then count from
+    /// the top — a rare transient). Derived from the whole-buffer line
+    /// table, so it's independent of the shaped slice.
+    fn cursor_line(&self) -> usize {
+        let byte = match self.own_cursor.as_ref() {
+            Some(c) if Some(c.buffer_id) == self.current_buffer_id => c.byte,
+            _ => 0,
+        };
+        self.current_line_starts
+            .partition_point(|&start| start <= byte)
+            .saturating_sub(1)
+    }
+
     /// Reshape the gutter buffer to the right-aligned line numbers for the
     /// currently-shaped code lines (UX gutter arc). One number per code
     /// line starting at `shaped_top`, so the two buffers align row-for-row
     /// at the same `top` and line height. No-op when the gutter is off.
     fn refresh_gutter_buffer(&mut self) {
         use std::fmt::Write as _;
-        if !self.line_numbers {
+        if !self.line_numbers.is_on() {
             return;
         }
         let digits = decimal_digits(self.current_line_starts.len().max(1)) as usize;
         let first = self.shaped_top;
+        // Relative/Hybrid measure distance from the cursor's buffer line;
+        // Absolute ignores it. Rebuilt every render, so it tracks the cursor.
+        let cursor_line = self.cursor_line();
+        let mode = self.line_numbers;
         let n = self.buffer.lines.len();
         let mut text = String::new();
         for i in 0..n {
             if i > 0 {
                 text.push('\n');
             }
-            let _ = write!(text, "{:>digits$}", first + i + 1);
+            let num = mode.number_for(first + i, cursor_line).unwrap_or(0);
+            let _ = write!(text, "{num:>digits$}");
         }
         self.gutter_buffer.set_text(
             &mut self.font_system,
@@ -4020,7 +4041,7 @@ impl State {
         // main-text clip-left. Computed here as locals — calling `self.*`
         // inside the `prepare` args would conflict with its `&mut` borrows.
         let text_left = self.text_left();
-        let gutter_clip_left = if self.line_numbers {
+        let gutter_clip_left = if self.line_numbers.is_on() {
             text_left.floor() as i32
         } else {
             0
@@ -4087,7 +4108,7 @@ impl State {
         // UX gutter: prepare the line-number layer in the reserved left
         // strip (empty when off → renders nothing). Same `top` + line
         // height as the code, so numbers align row-for-row.
-        let gutter_areas: Vec<TextArea> = if self.line_numbers {
+        let gutter_areas: Vec<TextArea> = if self.line_numbers.is_on() {
             vec![TextArea {
                 buffer: &self.gutter_buffer,
                 left: TEXT_LEFT,
@@ -4360,7 +4381,7 @@ impl State {
         vstart: u64,
         vend: u64,
     ) {
-        if !self.line_numbers {
+        if !self.line_numbers.is_on() {
             return;
         }
         let slice_len = vend - vstart;
@@ -7415,7 +7436,7 @@ mod tests {
         let off_px = off.render_offscreen();
         let mut on = State::new_headless(400, 300, "alpha\nbeta\ngamma\ndelta\n")
             .expect("adapter was just available");
-        on.line_numbers = true;
+        on.line_numbers = LineNumberMode::Absolute;
         let on_px = on.render_offscreen();
         assert_eq!(off_px.len(), on_px.len());
         let differing = off_px.iter().zip(&on_px).filter(|(a, b)| a != b).count();
@@ -7434,14 +7455,14 @@ mod tests {
         let Some(mut plain) = headless_or_skip(400, 300, text) else {
             return;
         };
-        plain.line_numbers = true;
+        plain.line_numbers = LineNumberMode::Absolute;
         plain.current_buffer_id = Some(BufferId::next());
         plain.view_range = (0, text.len() as u64);
         let plain_px = plain.render_offscreen();
 
         let mut with_diag =
             State::new_headless(400, 300, text).expect("adapter was just available");
-        with_diag.line_numbers = true;
+        with_diag.line_numbers = LineNumberMode::Absolute;
         with_diag.current_buffer_id = Some(BufferId::next());
         with_diag.view_range = (0, text.len() as u64);
         with_diag.current_decorations.push(Decoration {
@@ -7461,4 +7482,39 @@ mod tests {
             "the diagnostic sign bar should add ink ({differing} bytes differ)"
         );
     }
+
+    #[test]
+    fn headless_relative_mode_renders_differently_from_absolute() {
+        // Sub-arc 3: with the cursor on line 2, relative numbering
+        // (2,1,0,1,2) must differ from absolute (1,2,3,4,5) — proving the
+        // GPU renders the mode against its own cursor line.
+        let text = "alpha\nbeta\ngamma\ndelta\nepsilon\n";
+        let bid = BufferId::next();
+        let cursor = OwnCursor {
+            buffer_id: bid,
+            byte: 13, // inside "gamma" (buffer line 2)
+        };
+        let Some(mut abs) = headless_or_skip(400, 300, text) else {
+            return;
+        };
+        abs.current_buffer_id = Some(bid);
+        abs.view_range = (0, text.len() as u64);
+        abs.own_cursor = Some(cursor);
+        abs.line_numbers = LineNumberMode::Absolute;
+        let abs_px = abs.render_offscreen();
+
+        let mut rel = State::new_headless(400, 300, text).expect("adapter was just available");
+        rel.current_buffer_id = Some(bid);
+        rel.view_range = (0, text.len() as u64);
+        rel.own_cursor = Some(cursor);
+        rel.line_numbers = LineNumberMode::Relative;
+        let rel_px = rel.render_offscreen();
+
+        assert_eq!(abs_px.len(), rel_px.len());
+        let differing = abs_px.iter().zip(&rel_px).filter(|(a, b)| a != b).count();
+        assert!(
+            differing > 20,
+            "relative numbering must differ from absolute ({differing} bytes differ)"
+        );
+    }
 }
diff --git a/pmacs-protocol/src/lib.rs b/pmacs-protocol/src/lib.rs
index 5b2a123..fec34e3 100644
--- a/pmacs-protocol/src/lib.rs
+++ b/pmacs-protocol/src/lib.rs
@@ -49,8 +49,9 @@ pub use message::{
     AdornmentContent, AdornmentPlacement, AttachRequest, BlockAdornment, CursorState, Decoration,
     DecorationKind, DecorationSegment, FrontendCapabilities, FrontendEvent, GoodbyeReason, Hello,
     InlineAdornment, InstanceCapabilities, InstanceIdentity, InstanceMessage, InstanceSignal, Key,
-    KeyEvent, MenuPromptRow, Modifiers, MouseButton, MouseEvent, MouseKind, NegotiatedCapabilities,
-    PROTOCOL_VERSION, PointerKind, ResourceBody, SUPPORTED_PROTOCOL_VERSIONS, SelectionSnapshot,
-    StyleSegment, StyleSpan, is_supported_protocol_version, negotiate_capabilities,
+    KeyEvent, LineNumberMode, MenuPromptRow, Modifiers, MouseButton, MouseEvent, MouseKind,
+    NegotiatedCapabilities, PROTOCOL_VERSION, PointerKind, ResourceBody,
+    SUPPORTED_PROTOCOL_VERSIONS, SelectionSnapshot, StyleSegment, StyleSpan,
+    is_supported_protocol_version, negotiate_capabilities,
 };
 pub use transport::{MAX_FRAME_BYTES, TransportError, read_message, write_message};
diff --git a/pmacs-protocol/src/message.rs b/pmacs-protocol/src/message.rs
index 54d97b5..7ec8eb8 100644
--- a/pmacs-protocol/src/message.rs
+++ b/pmacs-protocol/src/message.rs
@@ -905,21 +905,68 @@ pub enum InstanceMessage {
         /// Total candidate count (the window is a slice of this).
         total: u32,
     },
-    /// UX gutter (protocol v13) — the per-window line-number gutter mode
-    /// for the frontend's active window. A semantic frontend renders line
-    /// numbers *locally* (it owns the text), but the on/off toggle lives
-    /// daemon-side (`M-x window.toggle-line-numbers`), so the daemon ships
-    /// the mode. Additive + daemon-gated `>= 13` — an older peer would
-    /// hard-error decoding it, so it stays off wires negotiated below 13.
+    /// UX gutter — the per-window line-number gutter *mode* for the
+    /// frontend's active window. A semantic frontend renders line numbers
+    /// *locally* (it owns the text + its own cursor line, so it can draw
+    /// relative/hybrid without a round trip), but the mode toggle lives
+    /// daemon-side, so the daemon ships which mode. Bumped 13 → 14: the
+    /// v13 shape carried a bare `enabled: bool` (off/absolute only); v14
+    /// carries the full [`LineNumberMode`] so relative/hybrid can ride the
+    /// same message. Daemon-gated `>= 14` — a v13 peer negotiates v13 and
+    /// receives no `LineNumbers` (its gutter stays off) rather than
+    /// mis-decoding the wider shape.
     LineNumbers {
         /// Buffer the active window shows (routing/consistency; the mode
         /// is a window property, not a buffer one).
         buffer_id: crate::BufferId,
-        /// Whether the line-number gutter is enabled for that window.
-        enabled: bool,
+        /// The line-number gutter mode for that window.
+        mode: LineNumberMode,
     },
 }
 
+/// Line-number gutter mode for a window (UX gutter arc). Shared across the
+/// wire, the daemon, and both frontends so the *number rule* — what value
+/// each line shows — is identical everywhere (Q#UX7). `pmacs` re-exports
+/// this as `crate::window::LineNumberMode`.
+#[derive(serde::Serialize, serde::Deserialize, Debug, Clone, Copy, PartialEq, Eq, Default)]
+pub enum LineNumberMode {
+    /// No gutter; zero layout change (the default, Emacs tradition).
+    #[default]
+    Off,
+    /// Absolute 1-based line numbers.
+    Absolute,
+    /// Distance from the cursor line (the cursor line shows `0`).
+    Relative,
+    /// Like `Relative`, but the cursor line shows its absolute 1-based
+    /// number instead of `0` (Vim `number` + `relativenumber`).
+    Hybrid,
+}
+
+impl LineNumberMode {
+    /// Whether this mode reserves a gutter at all (everything but `Off`).
+    #[must_use]
+    pub fn is_on(self) -> bool {
+        !matches!(self, Self::Off)
+    }
+
+    /// The displayed number for a 0-based buffer `line` given the cursor's
+    /// 0-based buffer line, or `None` in `Off`. `Relative`/`Hybrid` depend
+    /// on `cursor_line`; `Absolute` ignores it.
+    #[must_use]
+    pub fn number_for(self, line: usize, cursor_line: usize) -> Option<usize> {
+        match self {
+            Self::Off => None,
+            Self::Absolute => Some(line + 1),
+            Self::Relative => Some(line.abs_diff(cursor_line)),
+            Self::Hybrid => Some(if line == cursor_line {
+                line + 1
+            } else {
+                line.abs_diff(cursor_line)
+            }),
+        }
+    }
+}
+
 /// One row of an open menu on the wire ([`InstanceMessage::MenuPrompt`]).
 #[derive(serde::Serialize, serde::Deserialize, Debug, Clone, PartialEq, Eq)]
 pub struct MenuPromptRow {
@@ -1199,7 +1246,13 @@ pub enum ResourceBody {
 /// Daemon-gated `< 13`; a v12 peer negotiates v12 and receives no
 /// `LineNumbers` (its gutter simply stays off), like every prior additive
 /// bump.
-pub const PROTOCOL_VERSION: u32 = 13;
+///
+/// UX gutter modes: bumped 13 → 14 — `LineNumbers` swapped its `enabled:
+/// bool` for a [`LineNumberMode`] enum so relative/hybrid ride the same
+/// message. Encoding change to that variant; daemon-gated `< 14` (a v13
+/// peer negotiates v13 and receives no `LineNumbers` rather than
+/// mis-decoding the wider shape), same shape as the v10 `SearchPrompt` bump.
+pub const PROTOCOL_VERSION: u32 = 14;
 
 /// T M10.5: the set of protocol versions a v1.0 binary accepts on
 /// the wire. v0.1 binaries only accepted `[1]`; v1.0 binaries accept
@@ -1256,7 +1309,7 @@ pub const PROTOCOL_VERSION: u32 = 13;
 /// Q#MB1: extended to `[6, 7, 8, 9, 10, 11, 12]`.
 /// `InstanceMessage::MinibufferPrompt` is additive and daemon-gated per
 /// session, so the ladder resumes again.
-pub const SUPPORTED_PROTOCOL_VERSIONS: &[u32] = &[6, 7, 8, 9, 10, 11, 12, 13];
+pub const SUPPORTED_PROTOCOL_VERSIONS: &[u32] = &[6, 7, 8, 9, 10, 11, 12, 13, 14];
 
 /// T M10.5: predicate for the handshake check. Returns `true` if
 /// `peer_version` is in [`SUPPORTED_PROTOCOL_VERSIONS`].
diff --git a/src/daemon.rs b/src/daemon.rs
index df334da..8efa647 100644
--- a/src/daemon.rs
+++ b/src/daemon.rs
@@ -1050,11 +1050,12 @@ fn dispatcher_loop(
                 let peer_knows_minibuffer_prompt = session_registry
                     .session_state(*fid)
                     .is_some_and(|s| s.negotiated_protocol_version >= 12);
-                // UX gutter — `LineNumbers` is a v13 additive variant; a
-                // v12 peer keeps its gutter off rather than mis-decoding it.
+                // UX gutter — `LineNumbers` carries a `LineNumberMode` since
+                // v14 (was `enabled: bool` in v13); a peer below 14 keeps
+                // its gutter off rather than mis-decoding the wider shape.
                 let peer_knows_line_numbers = session_registry
                     .session_state(*fid)
-                    .is_some_and(|s| s.negotiated_protocol_version >= 13);
+                    .is_some_and(|s| s.negotiated_protocol_version >= 14);
                 for msg in &messages {
                     if !peer_knows_status_facts
                         && matches!(msg, InstanceMessage::StatusFacts { .. })
diff --git a/src/protocol.rs b/src/protocol.rs
index 01da2bd..1ece0e5 100644
--- a/src/protocol.rs
+++ b/src/protocol.rs
@@ -1683,7 +1683,7 @@ mod tests {
     // --- M5.5a handshake & postcard round-trips ---
 
     #[test]
-    fn protocol_version_is_thirteen_for_line_numbers() {
+    fn protocol_version_is_fourteen_for_line_number_modes() {
         // Pin the value: T M10.5 bumped 1→2 (v1.0 wire: CrdtOp /
         // PresenceUpdate). T M11.1 bumped 2→3 (v1.1 wire: the
         // SemanticFrame family + FrontendEvent::Viewport). T M11.6
@@ -1702,8 +1702,10 @@ mod tests {
         // `MenuPrompt`, all additive; the message daemon-gated). Q#MB1
         // bumped 11→12 (`InstanceMessage::MinibufferPrompt`, additive +
         // daemon-gated). UX gutter bumped 12→13
-        // (`InstanceMessage::LineNumbers`, additive + daemon-gated).
-        assert_eq!(PROTOCOL_VERSION, 13);
+        // (`InstanceMessage::LineNumbers`, additive + daemon-gated). UX
+        // gutter modes bumped 13→14 (`LineNumbers` swapped `enabled: bool`
+        // for a `LineNumberMode` enum — encoding change, still daemon-gated).
+        assert_eq!(PROTOCOL_VERSION, 14);
     }
 
     #[test]
@@ -1715,8 +1717,8 @@ mod tests {
         // Q#M4 / Q#S1 / Q#SR5 / Q#RX6 / Q#CM1 / Q#MB1 / UX gutter: the
         // ladder resumes above that floor — v7 (`TripleDown`), v8
         // (`StatusFacts`), v9 + v10 (`SearchPrompt` + regex/invalid), v11
-        // (the context menu), v12 (the GUI minibuffer), v13 (`LineNumbers`)
-        // all interoperate, so v6 through v13 talk.
+        // (the context menu), v12 (the GUI minibuffer), v13 (`LineNumbers`),
+        // v14 (`LineNumberMode`) all interoperate, so v6 through v14 talk.
         assert!(is_supported_protocol_version(6));
         assert!(is_supported_protocol_version(7));
         assert!(is_supported_protocol_version(8));
@@ -1725,10 +1727,11 @@ mod tests {
         assert!(is_supported_protocol_version(11));
         assert!(is_supported_protocol_version(12));
         assert!(is_supported_protocol_version(13));
-        for rejected in [0, 1, 2, 3, 4, 5, 14, u32::MAX] {
+        assert!(is_supported_protocol_version(14));
+        for rejected in [0, 1, 2, 3, 4, 5, 15, u32::MAX] {
             assert!(
                 !is_supported_protocol_version(rejected),
-                "v{rejected} must be rejected by a v13 binary"
+                "v{rejected} must be rejected by a v14 binary"
             );
         }
     }
diff --git a/src/semantic_render.rs b/src/semantic_render.rs
index 8356e3a..b99e331 100644
--- a/src/semantic_render.rs
+++ b/src/semantic_render.rs
@@ -157,11 +157,11 @@ pub struct SemanticRenderState {
     /// `(name, modified, diag_errors, diag_warnings)` last emitted as
     /// `StatusFacts` (Q#S1) — cached-compare suppression.
     last_status: HashMap<BufferId, (String, bool, u32, u32)>,
-    /// Last-emitted line-number gutter enabled-flag (UX gutter arc,
-    /// protocol v13) — cached-compare suppression. Seeded to `Some(false)`
-    /// (the frontend's default) so an off gutter never emits. Per-frontend
-    /// (one value), since this state carries one frontend's `frontend_id`.
-    last_line_numbers: Option<bool>,
+    /// Last-emitted line-number gutter mode (UX gutter arc, protocol v14) —
+    /// cached-compare suppression. Seeded to `Some(Off)` (the frontend's
+    /// default) so an off gutter never emits. Per-frontend (one value),
+    /// since this state carries one frontend's `frontend_id`.
+    last_line_numbers: Option<crate::window::LineNumberMode>,
     /// Last emitted `SearchPrompt` payload per buffer, for
     /// cached-compare suppression (see [`SearchPromptFacts`]).
     last_search_prompt: HashMap<BufferId, SearchPromptFacts>,
@@ -249,7 +249,7 @@ impl SemanticRenderState {
             // window never emits `LineNumbers`, so the common case adds no
             // traffic and the first frame is unchanged. Only an actual
             // toggle-on (or later toggle-off) ships a message.
-            last_line_numbers: Some(false),
+            last_line_numbers: Some(crate::window::LineNumberMode::Off),
             last_style_gate: HashMap::new(),
             diag_line_cache: HashMap::new(),
         }
@@ -698,26 +698,26 @@ impl SemanticRenderState {
     }
 
     /// The `LineNumbers` message for this frame, or `None` when the gutter
-    /// mode hasn't changed (UX gutter arc, protocol v13). The toggle lives
-    /// on this frontend's active window (`M-x window.toggle-line-numbers`);
-    /// a semantic frontend renders the gutter locally but the daemon owns
-    /// the on/off state, so it ships the mode. The daemon's write loop
-    /// keeps the variant off wires negotiated `< 13`.
+    /// mode hasn't changed (UX gutter arc, protocol v14). The mode lives on
+    /// this frontend's active window; a semantic frontend renders the gutter
+    /// locally (it owns the text + its cursor line, so relative/hybrid need
+    /// no round trip) but the daemon owns the mode, so it ships which one.
+    /// The daemon's write loop keeps the variant off wires negotiated `< 14`.
     fn line_numbers_msg(
         &mut self,
         state: &EditorState,
         buffer_id: BufferId,
     ) -> Option<InstanceMessage> {
-        let enabled = {
+        let mode = {
             let core = state.core.borrow();
             core.active_window_for(self.frontend_id)
-                .is_some_and(|w| w.line_numbers != crate::window::LineNumberMode::Off)
+                .map_or(crate::window::LineNumberMode::Off, |w| w.line_numbers)
         };
-        if self.last_line_numbers == Some(enabled) {
+        if self.last_line_numbers == Some(mode) {
             return None;
         }
-        self.last_line_numbers = Some(enabled);
-        Some(InstanceMessage::LineNumbers { buffer_id, enabled })
+        self.last_line_numbers = Some(mode);
+        Some(InstanceMessage::LineNumbers { buffer_id, mode })
     }
 
     /// The `InlineAdornments` message for this frame, or `None` when
@@ -1748,14 +1748,19 @@ mod tests {
             "off gutter must not emit LineNumbers"
         );
 
-        // Toggle the active window on → next frame emits enabled = true.
+        // Toggle the active window on → next frame emits the mode.
         state.core.borrow_mut().active_window_mut().line_numbers =
             crate::window::LineNumberMode::Absolute;
         let on = s.render_frame(&state);
         assert!(
-            on.iter()
-                .any(|m| matches!(m, InstanceMessage::LineNumbers { enabled: true, .. })),
-            "toggling the gutter on must emit LineNumbers {{ enabled: true }}"
+            on.iter().any(|m| matches!(
+                m,
+                InstanceMessage::LineNumbers {
+                    mode: crate::window::LineNumberMode::Absolute,
+                    ..
+                }
+            )),
+            "toggling the gutter on must emit LineNumbers with the mode"
         );
 
         // No further change → suppressed.
diff --git a/src/window.rs b/src/window.rs
index 9649166..316ecc4 100644
--- a/src/window.rs
+++ b/src/window.rs
@@ -130,46 +130,12 @@ pub struct Selection {
 }
 
 /// Line-number display mode for a window's left gutter (UX gutter arc).
-/// `Off` reserves no gutter at all — text starts at column 0, and every
-/// coordinate is unchanged (the default, matching the Emacs tradition).
-#[derive(Copy, Clone, Debug, PartialEq, Eq, Default)]
-pub enum LineNumberMode {
-    /// No gutter; zero layout change.
-    #[default]
-    Off,
-    /// Absolute 1-based line numbers, right-aligned in the gutter.
-    Absolute,
-    /// Distance from the cursor line (the cursor line shows `0`).
-    Relative,
-    /// Like `Relative`, but the cursor line shows its absolute 1-based
-    /// number instead of `0` (Vim `number` + `relativenumber`).
-    Hybrid,
-}
-
-impl LineNumberMode {
-    /// Whether this mode reserves a gutter at all (everything but `Off`).
-    #[must_use]
-    pub fn is_on(self) -> bool {
-        !matches!(self, Self::Off)
-    }
-
-    /// The displayed 0-or-1-based number for a buffer `line` given the
-    /// cursor's buffer line, or `None` in `Off`. `Relative`/`Hybrid` depend
-    /// on `cursor_line`; `Absolute` ignores it.
-    #[must_use]
-    pub fn number_for(self, line: usize, cursor_line: usize) -> Option<usize> {
-        match self {
-            Self::Off => None,
-            Self::Absolute => Some(line + 1),
-            Self::Relative => Some(line.abs_diff(cursor_line)),
-            Self::Hybrid => Some(if line == cursor_line {
-                line + 1
-            } else {
-                line.abs_diff(cursor_line)
-            }),
-        }
-    }
-}
+///
+/// Defined in `pmacs-protocol` so the wire, the daemon, and both frontends
+/// share one enum and one number rule ([`LineNumberMode::number_for`],
+/// Q#UX7); re-exported here so `crate::window::LineNumberMode` stays the
+/// in-crate path.
+pub use pmacs_protocol::LineNumberMode;
 
 /// Cells of horizontal padding the line-number gutter adds around the
 /// digit field: a leading and a trailing blank, so `gutter_w = digits +