diff --git a/crates/ui-egui/src/tools/vector_ui.rs b/crates/ui-egui/src/tools/vector_ui.rs
index 558d7a60f0..01ff55fce0 100644
--- a/crates/ui-egui/src/tools/vector_ui.rs
+++ b/crates/ui-egui/src/tools/vector_ui.rs
@@ -235,6 +235,9 @@ mod delete_anchor_options_bar_tests;
 #[cfg(test)]
 mod pen_enter_deselects_tests;
 
+#[cfg(test)]
+mod line_shift_snap_tests;
+
 #[cfg(test)]
 mod pen_mode_menu_tests;
 
diff --git a/crates/ui-egui/src/tools/vector_ui/line_shift_snap_tests.rs b/crates/ui-egui/src/tools/vector_ui/line_shift_snap_tests.rs
new file mode 100644
index 0000000000..867df50cef
--- /dev/null
+++ b/crates/ui-egui/src/tools/vector_ui/line_shift_snap_tests.rs
@@ -0,0 +1,131 @@
+//! #13243: ⇧ while dragging with the Line tool snaps to multiples of 45° as Photoshop does: a
+//! diagonal line ends at the shorter of the drag's two distances on both axes, a horizontal or
+//! vertical one keeps the full distance along its axis (and its 0.5 px centring on the pixel).
+//! The drag preview shows the same line as the layer, and ⇧ pressed after the start gives the
+//! same line as ⇧ held from the press.
+
+use egui::Modifiers;
+use photocraft_doc::{LayerContent, LiveShape};
+use serde_json::json;
+
+use super::shape_preview;
+use crate::PhotocraftApp;
+use crate::canvas::{ToolEvent, tool_event};
+use crate::state::Tool;
+
+/// The five measured drags from 400,300 and the line Photoshop draws for each: a flat line's
+/// ends move 0.5 px across it, onto the middle of the pixel.
+const CASES: [([f64; 2], [[f64; 2]; 2]); 5] = [
+    ([600.0, 400.0], [[400.0, 299.5], [600.0, 299.5]]),
+    ([600.0, 480.0], [[400.0, 300.0], [580.0, 480.0]]),
+    ([600.0, 520.0], [[400.0, 300.0], [600.0, 500.0]]),
+    ([300.0, 420.0], [[400.0, 300.0], [300.0, 400.0]]),
+    ([450.0, 500.0], [[399.5, 300.0], [399.5, 500.0]]),
+];
+
+const START: [f64; 2] = [400.0, 300.0];
+
+/// A new 800 × 600 document with the Line tool picked.
+fn app() -> PhotocraftApp {
+    let mut app = PhotocraftApp::new(photocraft_engine::Session::new(), crate::Services::default());
+    app.run("file.new", json!({"width": 800, "height": 600})).unwrap();
+    app.sync_views();
+    app.ui.tool = Tool::Line;
+    app
+}
+
+/// A drag from `from` to `to`, with `at_press` held at the press and `later` from the first move.
+fn drag(app: &mut PhotocraftApp, from: [f64; 2], to: [f64; 2], at_press: Modifiers, later: Modifiers) {
+    tool_event(app, ToolEvent::Down { x: from[0], y: from[1], pressure: 1.0 }, at_press);
+    tool_event(app, ToolEvent::Move { x: (from[0] + to[0]) / 2.0, y: (from[1] + to[1]) / 2.0, pressure: 1.0 }, later);
+    tool_event(app, ToolEvent::Move { x: to[0], y: to[1], pressure: 1.0 }, later);
+    tool_event(app, ToolEvent::Up { x: to[0], y: to[1] }, later);
+}
+
+/// The active layer's shape: its live line's ends, and its outline.
+fn line(app: &PhotocraftApp) -> ([f64; 2], [f64; 2], photocraft_doc::vector::Path) {
+    let st = app.session.active().unwrap();
+    match &st.doc.layer(st.active_layer.unwrap()).unwrap().content {
+        LayerContent::Shape(s) => match &s.live {
+            Some(LiveShape::Line { from, to, .. } | LiveShape::ArrowLine { from, to, .. }) => (*from, *to, s.path.clone()),
+            other => panic!("a live line, got {other:?}"),
+        },
+        _ => panic!("a shape layer"),
+    }
+}
+
+/// The measured ⇧-drags end where Photoshop ends them.
+#[test]
+fn shift_drags_end_where_photoshop_ends_them() {
+    for (to, want) in CASES {
+        let mut app = app();
+        drag(&mut app, START, to, Modifiers::SHIFT, Modifiers::SHIFT);
+        let (from, end, _) = line(&app);
+        assert_eq!([from, end], want, "⇧-drag 400,300 → {to:?}");
+    }
+}
+
+/// ⇧ pressed after the drag started constrains the line as ⇧ held from the press does.
+#[test]
+fn shift_pressed_after_the_start_gives_the_same_line() {
+    for (to, _) in CASES {
+        let mut held = app();
+        drag(&mut held, START, to, Modifiers::SHIFT, Modifiers::SHIFT);
+        let mut later = app();
+        drag(&mut later, START, to, Modifiers::NONE, Modifiers::SHIFT);
+        assert_eq!(line(&held), line(&later), "⇧ at the press or after it, → {to:?}");
+    }
+}
+
+/// The drag preview's outline is the outline of the layer the drag makes.
+#[test]
+fn the_preview_shows_the_line_the_drag_makes() {
+    for (to, _) in CASES {
+        let mut app = app();
+        let preview = shape_preview(&app, Tool::Line, START, to, Modifiers::SHIFT).expect("a preview");
+        drag(&mut app, START, to, Modifiers::NONE, Modifiers::SHIFT);
+        assert_eq!(preview.path, line(&app).2, "preview of → {to:?}");
+    }
+}
+
+/// Up-left, up-right and down-left drags snap the same way, mirrored.
+#[test]
+fn shift_snaps_every_direction() {
+    let o = app().ui.tool_options.clone();
+    for (to, want) in [([200.0, 180.0], [280.0, 180.0]), ([520.0, 100.0], [520.0, 180.0]), ([380.0, 100.0], [399.5, 100.0]), ([200.0, 310.0], [200.0, 299.5])] {
+        let g = super::shape_geometry(&o, Tool::Line, START, to, Modifiers::SHIFT).expect("a line");
+        assert_eq!(g["to"], json!(want), "⇧-drag 400,300 → {to:?}: {g}");
+    }
+}
+
+/// CodeRabbit on #13283: a short fractional ⇧-drag still draws a one-pixel diagonal. Snapped to
+/// 0.65 × 0.65 it is shorter than a pixel, but the drag itself is not, and its ends round to a
+/// whole-pixel 45° step.
+#[test]
+fn a_short_fractional_shift_drag_still_draws_a_diagonal() {
+    let o = app().ui.tool_options.clone();
+    let g = super::shape_geometry(&o, Tool::Line, [10.0, 10.0], [11.1, 10.65], Modifiers::SHIFT).expect("a line");
+    assert_eq!((g["from"].clone(), g["to"].clone()), (json!([10.0, 10.0]), json!([11.0, 11.0])), "{g}");
+}
+
+/// CodeRabbit on #13283: a short ⇧-drag near an axis still draws a one-pixel line. With
+/// Preferences › Tools › Snap Vector Tools and Transforms to Pixel Grid off, 0.96 × 0.30 snaps
+/// flat, and its 0.96 px along the axis would round both ends to x 201; the preview and the layer
+/// both show a line one pixel long.
+#[test]
+fn a_short_shift_drag_near_an_axis_still_draws_a_line() {
+    for (from, to, want) in [
+        ([200.51, 100.0], [201.47, 100.30], [[201.0, 99.5], [202.0, 99.5]]),
+        ([200.0, 100.51], [200.30, 101.47], [[199.5, 101.0], [199.5, 102.0]]),
+        ([201.47, 100.0], [200.51, 100.30], [[201.0, 99.5], [200.0, 99.5]]),
+    ] {
+        let mut app = app();
+        app.run("prefs.set", json!({"path": "tools.snapVectorToolsAndTransformsToPixelGrid", "value": false})).unwrap();
+        app.ui.views[0].zoom = 16.0;
+        let preview = shape_preview(&app, Tool::Line, from, to, Modifiers::SHIFT).expect("a preview");
+        drag(&mut app, from, to, Modifiers::SHIFT, Modifiers::SHIFT);
+        let (a, b, path) = line(&app);
+        assert_eq!([a, b], want, "⇧-drag {from:?} → {to:?}");
+        assert_eq!(preview.path, path, "preview of {from:?} → {to:?}");
+    }
+}
diff --git a/crates/ui-egui/src/tools/vector_ui/shapes.rs b/crates/ui-egui/src/tools/vector_ui/shapes.rs
index 4bf280dce0..184c7b2866 100644
--- a/crates/ui-egui/src/tools/vector_ui/shapes.rs
+++ b/crates/ui-egui/src/tools/vector_ui/shapes.rs
@@ -86,15 +86,28 @@ pub(super) fn align_line_edges(a: [f64; 2], b: [f64; 2], weight: f64, keep_angle
 pub(super) fn shape_geometry(o: &ToolOptions, tool: Tool, start: [f64; 2], end: [f64; 2], mods: egui::Modifiers) -> Option<Value> {
     Some(if tool == Tool::Line {
         let (mut dx, mut dy) = (end[0] - start[0], end[1] - start[1]);
-        if mods.shift {
-            // Snap to 45°.
-            let a = (dy.atan2(dx) / std::f64::consts::FRAC_PI_4).round() * std::f64::consts::FRAC_PI_4;
-            let len = dx.hypot(dy);
-            (dx, dy) = (len * a.cos(), len * a.sin());
-        }
+        // Too short a drag draws nothing. Measured before ⇧ shortens a diagonal, so a short
+        // fractional drag still reaches `align_line_edges`, which rounds it to whole pixels.
         if dx.hypot(dy) < 1.0 {
             return None;
         }
+        if mods.shift {
+            // Snap to a multiple of 45°, as Photoshop does (#13243): a horizontal or vertical
+            // line keeps the drag's distance along its axis, a diagonal one the shorter of the two
+            // distances on both axes. A drag within 30° of an axis snaps to it: Photoshop flattens
+            // a 26.6° drag and keeps a 39.8° one diagonal; the exact boundary is not measured.
+            // An axis line is at least a pixel long: a drag of a pixel or more can keep as little
+            // as 0.87 px along its axis, and `align_line_edges` could round both ends together.
+            let tan30 = std::f64::consts::FRAC_PI_6.tan();
+            (dx, dy) = if dy.abs() < dx.abs() * tan30 {
+                (dx.abs().max(1.0).copysign(dx), 0.0)
+            } else if dx.abs() < dy.abs() * tan30 {
+                (0.0, dy.abs().max(1.0).copysign(dy))
+            } else {
+                let m = dx.abs().min(dy.abs());
+                (m.copysign(dx), m.copysign(dy))
+            };
+        }
         let (from, to, weight) = align_line_edges(start, [start[0] + dx, start[1] + dy], f64::from(o.line_weight.max(1.0)), mods.shift)?;
         json!({"kind": "line", "from": from, "to": to, "weight": weight,
             "arrowStart": o.arrow_start, "arrowEnd": o.arrow_end,