diff --git a/crates/pipeline/src/curve.rs b/crates/pipeline/src/curve.rs
new file mode 100644
index 000000000..b2c2b0b14
--- /dev/null
+++ b/crates/pipeline/src/curve.rs
@@ -0,0 +1,238 @@
+//! The parametric tone curve model shared by the pipeline renderer and the UI curve editor.
+//!
+//! Lightroom-style tone curve parametric model: four regions (shadows, darks, lights, highlights)
+//! separated by three split points. Each region contributes a cosine-windowed bump, summed and
+//! forced monotone.
+
+use lightcraft_color::spline::Lut1;
+use lightcraft_develop::ToneCurve;
+
+/// The four shape controls of the parametric curve, in graph order: region 0 is the darkest.
+pub const PARAM_AMOUNTS: [&str; 4] = ["curve.shadows", "curve.darks", "curve.lights", "curve.highlights"];
+
+/// Resolution the parametric curve is sampled at, matching the renderer's LUT.
+pub const PARAM_LUT: usize = 1024;
+
+/// The parametric (region) curve of a [`ToneCurve`]: the four region amounts, each a cosine bump
+/// over its window between two splits, summed and then forced monotone.
+///
+/// This is the renderer's curve, not an approximation of it — both `curve_luts` in the pipeline
+/// and the curve editor in the UI use this struct so they can never disagree.
+#[derive(Clone, Debug)]
+pub struct ParametricCurve {
+    /// The curve, sampled and already forced monotone.
+    lut: [f32; PARAM_LUT],
+    /// The three region boundaries as fractions of the graph (0..1).
+    pub splits: [f64; 3],
+    /// The four region amounts, in graph order (0 = shadows, 3 = highlights).
+    pub amounts: [f64; 4],
+}
+
+impl ParametricCurve {
+    pub fn new(c: &ToneCurve) -> ParametricCurve {
+        let s0 = if c.split_shadows.is_nan() { 0.25 } else { (c.split_shadows / 100.0).clamp(0.0, 1.0) as f32 };
+        let s1 = if c.split_mid.is_nan() { 0.50_f32.max(s0) } else { (c.split_mid / 100.0).clamp(s0 as f64, 1.0) as f32 };
+        let s2 = if c.split_highlights.is_nan() { 0.75_f32.max(s1) } else { (c.split_highlights / 100.0).clamp(s1 as f64, 1.0) as f32 };
+        let clean_amt = |a: f64| if a.is_nan() { 0.0 } else { a.clamp(-100.0, 100.0) };
+        let (a0, a1, a2, a3) = (clean_amt(c.shadows), clean_amt(c.darks), clean_amt(c.lights), clean_amt(c.highlights));
+        let splits = [s0 as f64, s1 as f64, s2 as f64];
+        let amounts = [a0, a1, a2, a3];
+        let regions = [(0.0, s0, a0), (s0, s1, a1), (s1, s2, a2), (s2, 1.0, a3)];
+        let mut lut = [0.0_f32; PARAM_LUT];
+        let mut prev = 0.0_f32;
+        for (i, entry) in lut.iter_mut().enumerate() {
+            let x = i as f32 / (PARAM_LUT - 1) as f32;
+            let mut d = 0.0_f32;
+            for (a, b, amt) in regions {
+                if amt == 0.0 {
+                    continue;
+                }
+                let (ctr, half) = ((a + b) / 2.0, (b - a) * 0.75 + 0.05);
+                if half <= f32::EPSILON {
+                    continue;
+                }
+                let t = ((x - ctr) / half).clamp(-1.0, 1.0);
+                d += (amt / 100.0) as f32 * 0.22 * (0.5 + 0.5 * (t * std::f32::consts::PI).cos());
+            }
+            let y = (x + d * 4.0 * x * (1.0 - x)).clamp(0.0, 1.0);
+            prev = prev.max(y);
+            *entry = prev;
+        }
+        ParametricCurve { lut, splits, amounts }
+    }
+
+    /// Convert the evaluated parametric curve into a 1024-entry [`Lut1`].
+    pub fn to_lut(&self) -> Lut1 {
+        Lut1 { v: self.lut.to_vec() }
+    }
+
+    /// The curve at `x` (0 = black, 1 = white), read off the table (so it never overshoots the ends).
+    pub fn at(&self, x: f64) -> f64 {
+        let x = if x.is_nan() { 0.0 } else { x.clamp(0.0, 1.0) as f32 };
+        let at = x * (PARAM_LUT - 1) as f32;
+        let i = at.floor().clamp(0.0, (PARAM_LUT - 1) as f32) as usize;
+        let cur = self.lut.get(i).copied().unwrap_or(0.0);
+        let next = self.lut.get(i + 1).copied().unwrap_or(cur);
+        let f = at - i as f32;
+        (cur + (next - cur) * f) as f64
+    }
+
+    /// Where region `region`'s handle sits on the input axis: the middle of its own window, so a
+    /// handle never has to cross a split to be grabbed.
+    pub fn region_x(&self, region: usize) -> f64 {
+        let (a, b) = self.region_window(region);
+        (a + b) / 2.0
+    }
+
+    /// The window (two splits, as fractions of the graph) region `region` owns.
+    pub fn region_window(&self, region: usize) -> (f64, f64) {
+        let s0 = self.split_x(0);
+        let s1 = self.split_x(1);
+        let s2 = self.split_x(2);
+        match region {
+            0 => (0.0, s0),
+            1 => (s0, s1),
+            2 => (s1, s2),
+            _ => (s2, 1.0),
+        }
+    }
+
+    /// The half-width of region `region`'s own bump, as fraction of the graph.
+    pub fn region_half(&self, region: usize) -> f64 {
+        let (a, b) = self.region_window(region);
+        (b - a) * 0.75 + 0.05
+    }
+
+    /// The cosine window region `region` applies at `x` (1 at its centre, 0 at the window edges).
+    pub fn region_window_at(&self, region: usize, x: f64) -> f64 {
+        let ctr = self.region_x(region);
+        let half = self.region_half(region);
+        if half <= f64::EPSILON {
+            return 0.0;
+        }
+        let t = ((x - ctr) / half).clamp(-1.0, 1.0);
+        0.5 + 0.5 * (t * std::f64::consts::PI).cos()
+    }
+
+    /// The region that owns graph position `x`: the one whose own window contains it. The four
+    /// windows tile 0..1, so this is always defined and a drag anywhere on the curve moves exactly
+    /// one slider — the region under the pointer.
+    pub fn region_at(&self, x: f64) -> usize {
+        let x = if x.is_nan() { 0.0 } else { x.clamp(0.0, 1.0) };
+        let s0 = self.split_x(0);
+        let s1 = self.split_x(1);
+        let s2 = self.split_x(2);
+        if x <= s0 {
+            0
+        } else if x <= s1 {
+            1
+        } else if x <= s2 {
+            2
+        } else {
+            3
+        }
+    }
+
+    /// How much output level region `region`'s bump gains at `x` per unit of its slider: the bump is
+    /// linear in the amount, so this is a constant for a given `x`. A drag converts the pointer's
+    /// vertical motion into a slider change through it.
+    pub fn level_per_unit(&self, region: usize, x: f64) -> f64 {
+        let x = x.clamp(0.0, 1.0);
+        0.22 / 100.0 * self.region_window_at(region, x) * 4.0 * x * (1.0 - x)
+    }
+
+    /// The baseline level at `x` from the identity diagonal plus the contributions of all regions
+    /// *except* `region`. Used when inverting the model for `region` while holding the other three
+    /// regions fixed.
+    pub fn base_level_without(&self, region: usize, x: f64) -> f64 {
+        let x = x.clamp(0.0, 1.0);
+        let mut d = 0.0;
+        for i in 0..4 {
+            if i == region {
+                continue;
+            }
+            let amt = self.amounts.get(i).copied().unwrap_or(0.0);
+            if amt == 0.0 {
+                continue;
+            }
+            d += (amt / 100.0) * 0.22 * self.region_window_at(i, x);
+        }
+        x + d * 4.0 * x * (1.0 - x)
+    }
+
+    /// The curve level region `region` sits at when its slider holds `amount`, at graph position `x`,
+    /// holding the other regions fixed at their current settings.
+    pub fn handle_level_at(&self, region: usize, amount: f64, x: f64) -> f64 {
+        (self.base_level_without(region, x) + amount * self.level_per_unit(region, x)).clamp(0.0, 1.0)
+    }
+
+    /// The amount that puts region `region`'s curve at `level` at `x`, with the other three
+    /// regions held fixed — the inverse of [`Self::handle_level_at`]. A level the region cannot
+    /// reach saturates rather than jumping.
+    pub fn amount_at_level(&self, region: usize, level: f64, x: f64) -> f64 {
+        let per_unit = self.level_per_unit(region, x);
+        if per_unit.abs() <= f64::EPSILON {
+            return self.amounts.get(region).copied().unwrap_or(0.0);
+        }
+        let base = self.base_level_without(region, x);
+        ((level.clamp(0.0, 1.0) - base) / per_unit).clamp(-100.0, 100.0).round()
+    }
+
+    /// The graph position split `split` (0..=2) sits at, 0..1.
+    pub fn split_x(&self, split: usize) -> f64 {
+        self.splits.get(split).copied().unwrap_or(0.5)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn non_finite_or_inverted_splits_do_not_panic_or_poison_curve() {
+        let c = ToneCurve {
+            split_shadows: 80.0,
+            split_mid: 20.0,
+            split_highlights: f64::NAN,
+            shadows: f64::NAN,
+            lights: f64::INFINITY,
+            ..Default::default()
+        };
+        let model = ParametricCurve::new(&c);
+        assert!(model.at(0.5).is_finite());
+        assert!(model.at(f64::NAN).is_finite());
+        assert!(model.region_at(f64::NAN) < 4);
+        assert!((model.splits[0] - 0.8).abs() < 1e-6);
+        assert!((model.splits[1] - 0.8).abs() < 1e-6);
+        assert!((model.splits[2] - 0.8).abs() < 1e-6);
+    }
+
+    #[test]
+    fn horizontal_inversion_at_x_0_51_with_darks_60_preserves_zero_lights() {
+        let c = ToneCurve { darks: 60.0, lights: 0.0, ..Default::default() };
+        let model = ParametricCurve::new(&c);
+        assert_eq!(model.region_at(0.51), 2, "x=0.51 is inside the Lights region");
+        let level = model.at(0.51);
+        assert!((level - 0.5619).abs() < 0.001, "extracted model at 0.51 is ~0.5619: {level}");
+        // With other regions held fixed, inverting at level ~0.5619 must return Lights = 0, NOT 45!
+        let lights = model.amount_at_level(2, level, 0.51);
+        assert_eq!(lights, 0.0, "zero vertical delta preserves Lights=0: {lights}");
+    }
+
+    #[test]
+    fn a_curve_level_and_its_amount_are_inverses_with_other_regions_present() {
+        let c = ToneCurve { shadows: 20.0, darks: -30.0, lights: 40.0, highlights: -10.0, ..Default::default() };
+        let model = ParametricCurve::new(&c);
+        for region in 0..4 {
+            let centre = model.region_x(region);
+            let (_, upper) = model.region_window(region);
+            for x in [centre, centre + (upper - centre) * 0.5] {
+                for amount in [-100.0, -40.0, 0.0, 30.0, 100.0] {
+                    let level = model.handle_level_at(region, amount, x);
+                    let back = model.amount_at_level(region, level, x);
+                    assert!((back - amount).abs() <= 1.0, "region {region} at {x}: {amount} -> {level} -> {back}");
+                }
+            }
+        }
+    }
+}
diff --git a/crates/pipeline/src/finish.rs b/crates/pipeline/src/finish.rs
index b61b6a62c..c1e6a9bc2 100644
--- a/crates/pipeline/src/finish.rs
+++ b/crates/pipeline/src/finish.rs
@@ -29,31 +29,20 @@ fn curve_luts(c: &ToneCurve) -> Option<[Lut1; 3]> {
         return None;
     }
     const N: usize = 1024;
-    let (s1, s2, s3) = ((c.split_shadows / 100.0) as f32, (c.split_mid / 100.0) as f32, (c.split_highlights / 100.0) as f32);
-    let regions = [(0.0, s1, c.shadows), (s1, s2, c.darks), (s2, s3, c.lights), (s3, 1.0, c.highlights)];
-    let mut base = Lut1::from_fn(N, |x| {
-        let mut d = 0.0;
-        for (a, b, amt) in regions {
-            if amt == 0.0 {
-                continue;
-            }
-            let (ctr, half) = ((a + b) / 2.0, (b - a) * 0.75 + 0.05);
-            let t = ((x - ctr) / half).clamp(-1.0, 1.0);
-            let win = 0.5 + 0.5 * (t * std::f32::consts::PI).cos();
-            d += (amt / 100.0) as f32 * 0.22 * win;
-        }
-        (x + d * 4.0 * x * (1.0 - x)).clamp(0.0, 1.0)
-    });
-    // keep monotone
-    for i in 1..N {
-        base.v[i] = base.v[i].max(base.v[i - 1]);
-    }
+    let mut base = crate::curve::ParametricCurve::new(c).to_lut();
     let to_pts = |p: &[Point]| p.iter().map(|q| (q.x, q.y)).collect::<Vec<_>>();
     if master {
         base = MonotoneCurve::new(&to_pts(&c.master)).to_lut(N).compose(&base);
     }
     let per = [&c.red, &c.green, &c.blue];
-    Some(std::array::from_fn(|i| if chans[i] { MonotoneCurve::new(&to_pts(per[i])).to_lut(N).compose(&base) } else { base.clone() }))
+    Some(std::array::from_fn(|i| {
+        if chans.get(i).copied().unwrap_or(false) {
+            let pts = per.get(i).map(|&p| to_pts(p)).unwrap_or_default();
+            MonotoneCurve::new(&pts).to_lut(N).compose(&base)
+        } else {
+            base.clone()
+        }
+    }))
 }
 
 /// Vignette (post-crop) parameters.
diff --git a/crates/pipeline/src/lib.rs b/crates/pipeline/src/lib.rs
index 57cec33ec..8f2702760 100644
--- a/crates/pipeline/src/lib.rs
+++ b/crates/pipeline/src/lib.rs
@@ -27,6 +27,7 @@ pub mod auto;
 pub mod blemish;
 pub mod colorops;
 pub mod cull;
+pub mod curve;
 pub mod dust;
 pub mod finish;
 pub mod geometry;
@@ -44,6 +45,7 @@ pub mod transform;
 pub mod upright;
 pub mod visualize;
 
+pub use curve::{PARAM_AMOUNTS, PARAM_LUT, ParametricCurve};
 pub use output::{DeepImage, DeepSamples, DisplaySpace, OutputDepth, OutputSpace, OutputTrc, Proof, ProofLut, proof_profile, register_proof_profile};
 pub use visualize::{MaskView, Overlay};
 
diff --git a/crates/ui-egui/src/panels/edit.rs b/crates/ui-egui/src/panels/edit.rs
index b37c52604..2063580ae 100644
--- a/crates/ui-egui/src/panels/edit.rs
+++ b/crates/ui-egui/src/panels/edit.rs
@@ -6,6 +6,7 @@ use egui::{Align2, Color32, Pos2, Rect, RichText, Sense, Stroke, pos2, vec2};
 use lightcraft_catalog::PhotoId;
 use lightcraft_develop::{ControlSpec, DevelopSettings, Section, Track, WbMode, controls};
 use lightcraft_geom::Point;
+use lightcraft_pipeline::{PARAM_AMOUNTS, ParametricCurve};
 use lightcraft_raster::Histogram;
 use serde_json::{Value, json};
 
@@ -937,6 +938,115 @@ fn draw_curve_histogram(p: &egui::Painter, r: Rect, h: &lightcraft_raster::Histo
     p.add(mesh);
 }
 
+/// Segments the graph's curve line is drawn with.
+pub(crate) const CURVE_SAMPLES: i32 = 96;
+
+/// Close a graph drag's `develop` interaction, as one undo step.
+///
+/// It is closed when the drag ends *or* the pointer comes up without egui reporting `drag_stopped`
+/// for this widget (released outside the window, over a popup, or on a frame the widget does not
+/// run). A dangling interaction would make every later edit a silent preview — Undo would then
+/// appear to do nothing at all. Returns whether the drag is over, so the caller clears its state.
+fn commit_interaction(app: &mut LightcraftApp, ui: &egui::Ui, dragging: bool, stopped: bool) -> bool {
+    let released = ui.input(|i| i.pointer.any_released()) || !ui.input(|i| i.pointer.primary_down());
+    if !dragging || !(stopped || released) {
+        return false;
+    }
+    let _ = app.run("develop.endInteraction", json!({}));
+    true
+}
+
+/// How close (screen points) to the curve a press counts as grabbing it.
+const PARAM_GRAB: f32 = 14.0;
+
+/// The parametric curve's own drag: the graph shows the curve and nothing else, and dragging the
+/// line bends the region the pointer is over, with that region's slider following on the same frame.
+///
+/// The whole gesture runs inside one `develop` interaction, so it is one undo step (Ctrl+Z takes the
+/// gesture back, not the last frame of it), and every write goes through `develop.set`, so the
+/// slider, the curve and what is drawn are the same state rather than three things kept in step.
+fn param_drag(app: &mut LightcraftApp, ui: &mut egui::Ui, r: Rect, resp: &egui::Response, d: &DevelopSettings) {
+    if r.width() <= 1.0 || r.height() <= 1.0 {
+        return;
+    }
+    let t = Tokens::get(ui.ctx());
+    let model = ParametricCurve::new(&d.curve);
+    let to_screen = |x: f64, y: f64| pos2(r.left() + x as f32 * r.width(), r.bottom() - y as f32 * r.height());
+    let from_screen_x = |q: Pos2| ((q.x - r.left()) / r.width()).clamp(0.0, 1.0) as f64;
+    // the graph x of a point, and how far it is from the drawn curve (in screen points)
+    let near_curve = |q: Pos2| {
+        let x = from_screen_x(q);
+        to_screen(x, model.at(x)).distance(q)
+    };
+    let drag_id = egui::Id::new("curve-param-drag");
+    let cursor_id = egui::Id::new("curve-param-cursor");
+    // (region, x, initial_amount, start_y): the region being dragged, the graph x the drag is anchored
+    // at, the region's starting amount, and the starting screen Y position.
+    let mut dragged: Option<(usize, f64, f64, f32)> = ui.data(|dd| dd.get_temp::<Option<(usize, f64, f64, f32)>>(drag_id)).flatten();
+    let hovered = dragged.is_none() && resp.hover_pos().is_some_and(|q| near_curve(q) <= PARAM_GRAB);
+    let mut set: Option<(&'static str, f64)> = None;
+    // the press, not where the pointer is once the drag threshold has passed: a press slightly off
+    // the line is still a grab, and the pointer has usually left that spot by the time it starts
+    let press = ui.input(|i| i.pointer.press_origin()).or(resp.interact_pointer_pos());
+    if resp.drag_started()
+        && let Some(q) = press
+        && near_curve(q) <= PARAM_GRAB
+    {
+        let x = from_screen_x(q);
+        let _ = app.run("develop.beginInteraction", json!({"label": "Parametric Curve"}));
+        let region = model.region_at(x);
+        let initial_amount = model.amounts.get(region).copied().unwrap_or(0.0);
+        let start_pos = to_screen(x, model.at(x));
+        dragged = Some((region, x, initial_amount, start_pos.y));
+        ui.data_mut(|dd| dd.insert_temp(cursor_id, start_pos));
+    }
+    if let Some((region, x, initial_amount, start_y)) = dragged
+        && resp.dragged()
+    {
+        // Follow the pointer's motion from where the curve was grabbed, so the press itself moves
+        // nothing and the line tracks the hand. ⌥ = a tenth of the motion, as the point curve does.
+        let alt = ui.input(|i| i.modifiers.alt);
+        let dd = ui.input(|i| i.pointer.delta());
+        let step = if alt { vec2(dd.x * 0.1, dd.y * 0.1) } else { vec2(dd.x, dd.y) };
+        let cursor = ui.data(|d| d.get_temp::<Pos2>(cursor_id)).unwrap_or(pos2(0.0, start_y)) + step;
+        ui.data_mut(|d| d.insert_temp(cursor_id, cursor));
+        let delta_y = start_y - cursor.y;
+        let delta_level = (delta_y / r.height()) as f64;
+        let per_unit = model.level_per_unit(region, x);
+        let new_amount =
+            if per_unit.abs() > f64::EPSILON { (initial_amount + delta_level / per_unit).clamp(-100.0, 100.0).round() } else { initial_amount };
+        if let Some(&id) = PARAM_AMOUNTS.get(region) {
+            set = Some((id, new_amount));
+        }
+    }
+    if let Some((id, v)) = set {
+        let _ = app.run("develop.set", json!({"control": id, "value": v}));
+    }
+    let dropped = resp.drag_stopped();
+    if commit_interaction(app, ui, dragged.is_some(), dropped) {
+        dragged = None;
+        ui.data_mut(|d| {
+            d.remove::<Pos2>(cursor_id);
+            d.remove::<Option<(usize, f64, f64, f32)>>(drag_id);
+        });
+    }
+    ui.data_mut(|dd| dd.insert_temp(drag_id, dragged));
+    if dragged.is_some() {
+        ui.ctx().set_cursor_icon(egui::CursorIcon::Grabbing);
+    } else if hovered {
+        ui.ctx().set_cursor_icon(egui::CursorIcon::Grab);
+    }
+    // the region under the pointer (or the one in hand), named as its slider below reads it
+    let shown = dragged.map(|(region, ..)| region).or_else(|| hovered.then(|| resp.hover_pos()).flatten().map(|q| model.region_at(from_screen_x(q))));
+    if let Some(region) = shown
+        && let Some(&id) = PARAM_AMOUNTS.get(region)
+        && let Some(v) = set.and_then(|(s_id, v)| (s_id == id).then_some(v)).or_else(|| controls::get(d, id))
+    {
+        let name = controls::find(id).map_or("", |s| s.label);
+        ui.painter().text(r.left_top() + vec2(6.0, 4.0), Align2::LEFT_TOP, format!("{name} {v:.0}"), t.font(11.0), t.text_dim);
+    }
+}
+
 fn curve_editor(app: &mut LightcraftApp, ui: &mut egui::Ui, id: PhotoId, d: &DevelopSettings) {
     let t = Tokens::get(ui.ctx());
     // channel selector
@@ -1013,29 +1123,17 @@ fn curve_editor(app: &mut LightcraftApp, ui: &mut egui::Ui, id: PhotoId, d: &Dev
     let to_screen = |x: f64, y: f64| pos2(r.left() + x as f32 * r.width(), r.bottom() - y as f32 * r.height());
     let from_screen = |q: Pos2| (((q.x - r.left()) / r.width()).clamp(0.0, 1.0) as f64, ((r.bottom() - q.y) / r.height()).clamp(0.0, 1.0) as f64);
     if ch == "parametric" {
-        // draw the effective parametric curve by sampling the pipeline's region curve approximation
+        // The Effective curve: the model the renderer builds from the four region sliders, sampled
+        // here and rebuilt every frame. The graph holds no state of its own, so a slider moved by
+        // hand, a Reset or an Undo redraws it from the settings in the same frame it changes.
         let c = &d.curve;
-        let regions = [
-            (0.0, c.split_shadows / 100.0, c.shadows),
-            (c.split_shadows / 100.0, c.split_mid / 100.0, c.darks),
-            (c.split_mid / 100.0, c.split_highlights / 100.0, c.lights),
-            (c.split_highlights / 100.0, 1.0, c.highlights),
-        ];
-        let pts: Vec<Pos2> = (0..=64)
-            .map(|i| {
-                let x = i as f64 / 64.0;
-                let mut dd = 0.0;
-                for (a, b, amt) in regions {
-                    let (ctr, half) = ((a + b) / 2.0, (b - a) * 0.75 + 0.05);
-                    let tt = ((x - ctr) / half).clamp(-1.0, 1.0);
-                    dd += amt / 100.0 * 0.22 * (0.5 + 0.5 * (tt * std::f64::consts::PI).cos());
-                }
-                to_screen(x, (x + dd * 4.0 * x * (1.0 - x)).clamp(0.0, 1.0))
-            })
-            .collect();
+        let model = ParametricCurve::new(c);
+        let pts: Vec<Pos2> =
+            (0..=CURVE_SAMPLES).map(|i| to_screen(i as f64 / CURVE_SAMPLES as f64, model.at(i as f64 / CURVE_SAMPLES as f64))).collect();
         p.add(egui::Shape::line(pts, Stroke::new(2.0, Color32::from_gray(220))));
+        param_drag(app, ui, r, &resp, d);
         curve_footer(app, ui, d);
-        for c in ["curve.highlights", "curve.lights", "curve.darks", "curve.shadows"] {
+        for &c in PARAM_AMOUNTS.iter().rev() {
             control(app, ui, d, c, true);
         }
         control(app, ui, d, "curve.refineSaturation", true);
@@ -1167,9 +1265,11 @@ fn curve_editor(app: &mut LightcraftApp, ui: &mut egui::Ui, id: PhotoId, d: &Dev
         let arr: Vec<[f64; 2]> = v.iter().map(|p| [p.x, p.y]).collect();
         let _ = app.run("develop.curve", json!({"channel": ch, "points": arr}));
     }
-    if resp.drag_stopped() {
+    // the drag is over when egui says so, or when the pointer comes up without it saying so (a
+    // release outside the window would otherwise leave the interaction open, and every later edit a
+    // silent preview that Undo cannot take back)
+    if commit_interaction(app, ui, dragging.is_some(), resp.drag_stopped()) {
         dragging = None;
-        let _ = app.run("develop.endInteraction", json!({}));
     }
     ui.data_mut(|dd| dd.insert_temp(drag_id, dragging));
     curve_footer(app, ui, d);
diff --git a/crates/ui-egui/src/tests_curve.rs b/crates/ui-egui/src/tests_curve.rs
index 4d3b45702..a658ee9a8 100644
--- a/crates/ui-egui/src/tests_curve.rs
+++ b/crates/ui-egui/src/tests_curve.rs
@@ -6,6 +6,7 @@ use serde_json::json;
 
 use crate::headless::Headless;
 use crate::{LightcraftApp, Services};
+use lightcraft_pipeline::ParametricCurve;
 
 const T: Duration = Duration::from_secs(20);
 
@@ -221,3 +222,370 @@ fn curve_points_from_an_agent_are_stored_in_order() {
     let c = pts(&develop(&h).curve.green);
     assert!(c[1].0 < c[2].0, "dragged up to its neighbour, not past it: {c:?}");
 }
+
+/// The settings the parametric graph is drawn from: two neighbouring regions pushed opposite ways,
+/// where the raw sum of their bumps folds back on itself before the renderer's running maximum
+/// straightens it out.
+fn folded_regions() -> lightcraft_develop::ToneCurve {
+    lightcraft_develop::ToneCurve { shadows: 90.0, darks: -80.0, lights: -70.0, highlights: 60.0, ..Default::default() }
+}
+
+/// The bare sum of the four region bumps is not monotone, so the drawn curve needs the renderer's
+/// running maximum: this is the shape that made the graph disagree with the sliders.
+#[test]
+fn the_parametric_model_is_monotone_where_the_bare_sum_of_bumps_is_not() {
+    let c = folded_regions();
+    let raw = |x: f64| {
+        let s = [0.0, c.split_shadows / 100.0, c.split_mid / 100.0, c.split_highlights / 100.0, 1.0];
+        let amounts = [c.shadows, c.darks, c.lights, c.highlights];
+        let mut d = 0.0;
+        for i in 0..4 {
+            let (a, b) = (s[i], s[i + 1]);
+            let (ctr, half) = ((a + b) / 2.0, (b - a) * 0.75 + 0.05);
+            let t = ((x - ctr) / half).clamp(-1.0, 1.0);
+            d += amounts[i] / 100.0 * 0.22 * (0.5 + 0.5 * (t * std::f64::consts::PI).cos());
+        }
+        x + d * 4.0 * x * (1.0 - x)
+    };
+    assert!((0..=64).any(|i| raw(i as f64 / 64.0) > raw((i + 1) as f64 / 64.0)), "the shape folds back, or it proves nothing");
+    let model = ParametricCurve::new(&c);
+    let mut prev = f64::MIN;
+    for i in 0..=256 {
+        let y = model.at(i as f64 / 256.0);
+        assert!(y >= prev - 1e-12, "the model never folds back, at {i}: {y} < {prev}");
+        prev = y;
+    }
+}
+
+/// What the graph *paints* is the model the renderer computes from the sliders. They used to be two
+/// copies of the formula and the panel's copy was missing the renderer's monotone pass, so the drawn
+/// line could fold back while the renderer straightened it: the graph and the sliders below it
+/// disagreed. This reads the painted line itself, not the function behind it.
+#[test]
+fn the_parametric_graph_paints_the_model_the_renderer_uses() {
+    let mut h = curve_open("parametric");
+    let c = folded_regions();
+    for (control, value) in [("curve.shadows", c.shadows), ("curve.darks", c.darks), ("curve.lights", c.lights), ("curve.highlights", c.highlights)] {
+        exec(&mut h, "develop.set", json!({"control": control, "value": value}));
+    }
+    h.step();
+    h.step();
+    let settings = develop(&h).curve;
+    assert_eq!(settings, c, "the sliders hold the folded shape");
+    let graph = curve_graph_rect(&mut h);
+    let painted = painted_param_curve(&h, graph);
+    let model = ParametricCurve::new(&c);
+    let mut checked = 0;
+    for i in 0..=24 {
+        let x = i as f64 / 24.0;
+        let want = model.at(x);
+        let got = painted(x);
+        assert!((got - want).abs() < 0.02, "the painted curve is the renderer's at {x}: painted {got}, model {want}");
+        checked += 1;
+    }
+    assert_eq!(checked, 25);
+    // and the shape really does fold back before the monotone pass, so this proves something
+    assert!(model.at(0.6) > model.at(0.3), "the region bumps still bend the curve");
+}
+
+/// The graph rect as `[left, top, width, height]` plus a reader for the painted curve's height at a
+/// graph fraction (0 = the bottom of the graph, 1 = the top).
+fn curve_graph_rect(h: &mut Headless) -> [f32; 4] {
+    let r = h.request("ui.widgets", json!({"filter": "curve"}), T);
+    let w = r["result"].as_array().unwrap().iter().find(|w| w["id"] == "curve").cloned().unwrap_or_else(|| panic!("curve widget on screen: {r}"));
+    let v = w["rect"].as_array().unwrap();
+    std::array::from_fn(|i| v[i].as_f64().unwrap() as f32)
+}
+
+/// A reader for the height of the painted parametric curve at a graph fraction. The curve is the
+/// wide grey path the graph draws; the histogram is a mesh and the grid lines are single segments.
+fn painted_param_curve(h: &Headless, r: [f32; 4]) -> impl Fn(f64) -> f64 {
+    let points = h
+        .view
+        .painted_shapes()
+        .into_iter()
+        .find_map(|s| match s {
+            egui::Shape::Path(p) if p.points.len() > 32 && (p.stroke.width - 2.0).abs() < 0.1 => Some(p.points),
+            _ => None,
+        })
+        .unwrap_or_else(|| panic!("the parametric curve line is painted"));
+    move |x: f64| {
+        let want_x = r[0] + x as f32 * r[2];
+        let q = points
+            .iter()
+            .min_by(|a, b| (a.x - want_x).abs().total_cmp(&(b.x - want_x).abs()))
+            .copied()
+            .unwrap_or_else(|| panic!("the curve has points"));
+        ((r[1] + r[3] - q.y) / r[3]).clamp(0.0, 1.0) as f64
+    }
+}
+
+/// The tone the parametric graph paints at `x`, read by value from the painted line. Stepped first
+/// so the panel has drawn the state the command left behind.
+fn painted_tone(h: &mut Headless, x: f64) -> f64 {
+    h.step();
+    h.step();
+    let r = curve_graph_rect(h);
+    painted_param_curve(h, r)(x)
+}
+
+/// Where the midtones sit on a linear curve: a point well inside the Lights region, so lifting
+/// Lights bends the line there.
+const MID: f64 = 0.625;
+
+/// Reset restores the four sliders *and* puts the graph back to the straight diagonal, as one state.
+#[test]
+fn reset_clears_the_sliders_and_the_graph_together() {
+    let mut h = curve_open("parametric");
+    let straight = painted_tone(&mut h, MID);
+    assert!((straight - MID).abs() < 0.02, "a fresh parametric curve is the diagonal: {straight}");
+    exec(&mut h, "develop.set", json!({"control": "curve.lights", "value": 60}));
+    let bent = painted_tone(&mut h, MID);
+    assert!(bent > MID + 0.02, "the graph follows the slider up: {bent}");
+    let undo_before = h.app.session.undo.len();
+    click_widget(&mut h, "button:curveReset", 1);
+    let c = develop(&h).curve;
+    assert_eq!(c, lightcraft_develop::ToneCurve::default(), "Reset puts every slider and split back: {c:?}");
+    let flat = painted_tone(&mut h, MID);
+    assert!((flat - MID).abs() < 0.02, "and the graph is the diagonal again: {flat}");
+    assert_eq!(h.app.session.undo.len(), undo_before + 1, "Reset is one undo step");
+}
+
+/// Undo after a Reset brings back both the slider and the graph: the state the graph draws is the
+/// state Undo restores, so the two can never be left showing different things.
+#[test]
+fn undo_restores_the_slider_and_the_graph_together() {
+    let mut h = curve_open("parametric");
+    exec(&mut h, "develop.set", json!({"control": "curve.lights", "value": 60}));
+    let bent = painted_tone(&mut h, MID);
+    assert!(bent > MID + 0.02, "the graph is bent: {bent}");
+    click_widget(&mut h, "button:curveReset", 1);
+    assert_eq!(develop(&h).curve, lightcraft_develop::ToneCurve::default(), "reset first");
+    exec(&mut h, "edit.undo", json!({}));
+    let c = develop(&h).curve;
+    assert_eq!(c.lights, 60.0, "Undo brings the slider back: {c:?}");
+    let again = painted_tone(&mut h, MID);
+    assert!(again > MID + 0.02, "and the graph is bent with it, not left flat: {again}");
+    // redo puts the diagonal back, and the graph follows that too
+    exec(&mut h, "edit.redo", json!({}));
+    assert_eq!(develop(&h).curve, lightcraft_develop::ToneCurve::default(), "redo restores the reset");
+    let flat = painted_tone(&mut h, MID);
+    assert!((flat - MID).abs() < 0.02, "the graph is flat with the sliders: {flat}");
+}
+
+/// One graph drag that bends several regions at once is one undo step: Ctrl+Z takes back the whole
+/// gesture, not the last slider it happened to touch.
+#[test]
+fn one_graph_drag_that_moves_several_regions_is_one_undo_step() {
+    let mut h = curve_open("parametric");
+    exec(&mut h, "develop.set", json!({"control": "curve.lights", "value": 40}));
+    exec(&mut h, "develop.set", json!({"control": "curve.darks", "value": -40}));
+    let before = develop(&h).curve;
+    let undo_before = h.app.session.undo.len();
+    // drag the Lights slider's own track, the way a graph handle writes it: begin, live updates, end
+    exec(&mut h, "develop.beginInteraction", json!({"label": "Parametric Curve"}));
+    for v in [45, 55, 70, 85] {
+        exec(&mut h, "develop.set", json!({"control": "curve.lights", "value": v}));
+    }
+    exec(&mut h, "develop.endInteraction", json!({}));
+    let after = develop(&h).curve;
+    assert_eq!(after.lights, 85.0, "the drag ended at its last value: {after:?}");
+    assert_ne!(after, before, "the drag changed the state");
+    assert_eq!(h.app.session.undo.len(), undo_before + 1, "the whole drag is one step, not one per frame");
+    exec(&mut h, "edit.undo", json!({}));
+    assert_eq!(develop(&h).curve, before, "undo takes back the whole gesture at once");
+}
+
+/// The screen point where a drag should grab the curve: graph fraction `fx`, on the line itself.
+fn on_curve(r: [f32; 4], c: &lightcraft_develop::ToneCurve, fx: f32) -> [f32; 2] {
+    let y = ParametricCurve::new(c).at(fx as f64);
+    [r[0] + fx * r[2], r[1] + (1.0 - y as f32) * r[3]]
+}
+
+/// Dragging the curve itself bends the region under the pointer and moves that region's slider with
+/// it, live. The graph draws no handles, so the only thing to grab is the line.
+#[test]
+fn dragging_the_curve_moves_the_region_slider() {
+    let mut h = curve_open("parametric");
+    exec(&mut h, "develop.set", json!({"control": "curve.lights", "value": 60}));
+    h.step();
+    let r = curve_graph_rect(&mut h);
+    let c = develop(&h).curve;
+    let undo_before = h.app.session.undo.len();
+    // grab the line inside the Lights window (x = 0.625) and pull it down
+    let [x, y] = on_curve(r, &c, 0.625);
+    let d = h.request("ui.drag", json!({"x": x, "y": y, "toX": x, "toY": y + 0.08 * r[3], "steps": 8}), T);
+    assert_eq!(d["ok"], true, "{d}");
+    h.step();
+    let after = develop(&h).curve;
+    assert!(after.lights < 60.0, "the Lights slider follows the line down: {}", after.lights);
+    assert!(after.lights > 0.0, "and lands on a value, not at the bottom: {}", after.lights);
+    assert_eq!((after.shadows, after.darks, after.highlights), (0.0, 0.0, 0.0), "the other regions stay put: {after:?}");
+    assert_eq!(after.split_shadows, c.split_shadows, "and the splits are untouched");
+    assert_eq!(h.app.session.undo.len(), undo_before + 1, "one undo step for the whole drag");
+    // the graph really is redrawn below where the line was
+    let graph = curve_graph_rect(&mut h);
+    let painted = painted_param_curve(&h, graph)(0.625);
+    let before_level = ParametricCurve::new(&c).at(0.625);
+    assert!(painted < before_level - 0.02, "the painted line followed the drag down: {painted} vs before {before_level}");
+    // and Undo takes the whole gesture back to where it started
+    exec(&mut h, "edit.undo", json!({}));
+    assert_eq!(develop(&h).curve, c, "undo restores the value the drag started from");
+}
+
+/// A horizontal drag on the curve (zero vertical motion) changes no region amount, even when
+/// neighbouring regions contribute heavily to the curve at the grabbed position (AlexChambers report:
+/// Darks=60, Lights=0 grabbed at x=0.51 used to jump Lights to 45 with zero vertical motion).
+#[test]
+fn a_horizontal_drag_with_zero_vertical_motion_changes_nothing() {
+    let mut h = curve_open("parametric");
+    exec(&mut h, "develop.set", json!({"control": "curve.darks", "value": 60}));
+    h.step();
+    let before = develop(&h).curve;
+    assert_eq!(before.darks, 60.0);
+    assert_eq!(before.lights, 0.0);
+    let r = curve_graph_rect(&mut h);
+    let [x, y] = on_curve(r, &before, 0.51);
+    // Drag purely horizontally from x=0.51: dx = 20 px, dy = 0
+    let d = h.request("ui.drag", json!({"x": x, "y": y, "toX": x + 20.0, "toY": y, "steps": 6}), T);
+    assert_eq!(d["ok"], true, "{d}");
+    h.step();
+    let after = develop(&h).curve;
+    assert_eq!(after.lights, 0.0, "horizontal motion preserves Lights=0: {}", after.lights);
+    assert_eq!(after.darks, 60.0, "Darks is preserved: {}", after.darks);
+    assert_eq!(after, before, "horizontal drag changes nothing: {after:?}");
+}
+
+/// Dragging up bends the region the other way, so the gesture is not just "downwards works".
+#[test]
+fn dragging_the_curve_up_raises_the_region_slider() {
+    let mut h = curve_open("parametric");
+    let r = curve_graph_rect(&mut h);
+    let c = develop(&h).curve;
+    // x = 0.375 is inside the Darks window
+    let [x, y] = on_curve(r, &c, 0.375);
+    let d = h.request("ui.drag", json!({"x": x, "y": y, "toX": x, "toY": y - 0.08 * r[3], "steps": 8}), T);
+    assert_eq!(d["ok"], true, "{d}");
+    h.step();
+    let after = develop(&h).curve;
+    assert!(after.darks > 0.0, "the Darks slider follows the line up: {}", after.darks);
+    assert_eq!((after.shadows, after.lights, after.highlights), (0.0, 0.0, 0.0), "the other regions stay put: {after:?}");
+    assert!(ParametricCurve::new(&after).at(0.375) > ParametricCurve::new(&c).at(0.375), "the curve is drawn bent up at the Darks region");
+}
+
+/// Which region a drag moves is decided by where on the line it is grabbed: the same drag gesture
+/// four times over grabs four different sliders.
+#[test]
+fn the_region_dragged_is_the_one_under_the_pointer() {
+    for (fx, control, region) in
+        [(0.125_f32, "curve.shadows", 0usize), (0.375, "curve.darks", 1), (0.625, "curve.lights", 2), (0.875, "curve.highlights", 3)]
+    {
+        let mut h = curve_open("parametric");
+        let r = curve_graph_rect(&mut h);
+        let c = develop(&h).curve;
+        assert_eq!(ParametricCurve::new(&c).region_at(fx as f64), region, "x = {fx} belongs to {control}");
+        let [x, y] = on_curve(r, &c, fx);
+        let d = h.request("ui.drag", json!({"x": x, "y": y, "toX": x, "toY": y - 0.06 * r[3], "steps": 6}), T);
+        assert_eq!(d["ok"], true, "{d}");
+        h.step();
+        let after = develop(&h).curve;
+        let moved = after.shadows + after.darks + after.lights + after.highlights;
+        let want = match region {
+            0 => after.shadows,
+            1 => after.darks,
+            2 => after.lights,
+            _ => after.highlights,
+        };
+        assert!(want > 0.0, "grabbing at {fx} raises {control}: {after:?}");
+        assert!((moved - want).abs() < 1e-9, "and nothing else moved: {after:?}");
+    }
+}
+
+/// A drag that starts away from the line is not a graph gesture at all: nothing moves and no undo
+/// step is made (the graph is not a "click anywhere to bend" surface).
+#[test]
+fn a_parametric_drag_off_the_line_changes_nothing() {
+    let mut h = curve_open("parametric");
+    exec(&mut h, "develop.set", json!({"control": "curve.lights", "value": 40}));
+    h.step();
+    let before = develop(&h).curve;
+    let undo = h.app.session.undo.len();
+    let r = curve_graph_rect(&mut h);
+    // a corner of the graph, far above the line
+    let d = h.request(
+        "ui.drag",
+        json!({"x": r[0] + 0.06 * r[2], "y": r[1] + 0.06 * r[3], "toX": r[0] + 0.2 * r[2], "toY": r[1] + 0.3 * r[3], "steps": 6}),
+        T,
+    );
+    assert_eq!(d["ok"], true, "{d}");
+    h.step();
+    assert_eq!(develop(&h).curve, before, "no control moved");
+    assert_eq!(h.app.session.undo.len(), undo, "and no undo step was made");
+}
+
+/// Hovering the line names the region a press there would move (and offers the grab cursor), so the
+/// graph says which slider it is about to change before the drag starts.
+#[test]
+fn hovering_the_line_names_the_region_it_would_move() {
+    let mut h = curve_open("parametric");
+    exec(&mut h, "develop.set", json!({"control": "curve.lights", "value": 60}));
+    h.step();
+    let r = curve_graph_rect(&mut h);
+    let [x, y] = on_curve(r, &develop(&h).curve, 0.625);
+    let q = h.request("ui.move", json!({"x": x, "y": y}), T);
+    assert_eq!(q["ok"], true, "{q}");
+    h.step();
+    assert_eq!(h.last_cursor, egui::CursorIcon::Grab, "the line offers a grab: {:?}", h.last_cursor);
+    // the slider rows also paint "Lights", so compare with a frame away from the line
+    let lights = |h: &Headless| h.painted_text().iter().filter(|t| t.contains("Lights")).count();
+    let hovered = lights(&h);
+    // well above the line there is no grab and no name
+    let q = h.request("ui.move", json!({"x": x, "y": r[1] + 0.06 * r[3]}), T);
+    assert_eq!(q["ok"], true, "{q}");
+    h.step();
+    assert_eq!(h.last_cursor, egui::CursorIcon::Default, "away from the line there is nothing to grab: {:?}", h.last_cursor);
+    assert!(hovered > lights(&h), "hovering names the slider it would move: {hovered} vs {} away", lights(&h));
+}
+
+/// A point's level on the region's curve and its slider amount are inverses, so a drag puts the line
+/// exactly where the hand is, at whatever point on the graph it was grabbed. A level the region
+/// cannot reach saturates rather than jumping.
+#[test]
+fn a_curve_level_and_its_amount_are_inverses() {
+    let c = lightcraft_develop::ToneCurve { shadows: 20.0, lights: 40.0, ..Default::default() };
+    let model = ParametricCurve::new(&c);
+    for region in 0..4 {
+        let centre = model.region_x(region);
+        let (_, upper) = model.region_window(region);
+        // the region's window centre, and a point off-centre inside the same window
+        for x in [centre, centre + (upper - centre) * 0.5] {
+            for amount in [-100.0, -40.0, 0.0, 30.0, 100.0] {
+                let level = model.handle_level_at(region, amount, x);
+                let back = model.amount_at_level(region, level, x);
+                assert!((back - amount).abs() <= 1.0, "region {region} at {x}: {amount} → {level} → {back}");
+            }
+        }
+    }
+    let centre = model.region_x(3);
+    assert_eq!(model.amount_at_level(3, 1.0, centre), 100.0, "a level above the region's reach saturates high");
+    assert_eq!(model.amount_at_level(3, 0.0, centre), -100.0, "and one below saturates low");
+}
+
+/// The four regions tile the graph: every position belongs to exactly one of them, in order, so a
+/// drag anywhere on the line moves exactly one slider and the one the pointer is over.
+#[test]
+fn the_four_regions_tile_the_graph() {
+    let model = ParametricCurve::new(&lightcraft_develop::ToneCurve::default());
+    assert_eq!(model.region_at(0.0), 0, "black is the darkest region");
+    assert_eq!(model.region_at(1.0), 3, "white is the lightest");
+    assert_eq!(model.region_at(0.2), 0, "below the first split");
+    assert_eq!(model.region_at(0.3), 1, "between the first two splits");
+    assert_eq!(model.region_at(0.6), 2);
+    assert_eq!(model.region_at(0.8), 3);
+    let mut prev = model.region_at(0.0);
+    for i in 0..=100 {
+        let r = model.region_at(i as f64 / 100.0);
+        assert!(r >= prev, "the regions never go backwards: {r} after {prev}");
+        prev = r;
+    }
+}
diff --git a/docs/parity-checklist.md b/docs/parity-checklist.md
index 322d26530..3e453a15b 100644
--- a/docs/parity-checklist.md
+++ b/docs/parity-checklist.md
@@ -184,7 +184,7 @@ differences and missing bindings are in [ui-parity.md](ui-parity.md#shortcuts).
 | LR-EDIT-LIGHT-SHADOWS | Shadows | P0 | ✅ | `ctl:light.shadows` | From process V2, the same base as Highlights: dark areas keep their local contrast when lifted (#632) |
 | LR-EDIT-LIGHT-WHITES | Whites | P0 | ✅ | `ctl:light.whites` | |
 | LR-EDIT-LIGHT-BLACKS | Blacks | P0 | ✅ | `ctl:light.blacks` | |
-| LR-EDIT-LIGHT-CURVE-PARAM | Parametric curve | P0 | ✅ | `ctl:curve.highlights`, `ctl:curve.lights`, `ctl:curve.darks`, `ctl:curve.shadows`, `ctl:curve.split*` | |
+| LR-EDIT-LIGHT-CURVE-PARAM | Parametric curve | P0 | ✅ | `ctl:curve.highlights`, `ctl:curve.lights`, `ctl:curve.darks`, `ctl:curve.shadows`, `ctl:curve.split*`, `crates/pipeline/src/curve.rs` | the graph draws the renderer's own curve model; dragging the line moves the region under the pointer (one undo step) |
 | LR-EDIT-LIGHT-CURVE-POINT | Point curve | P0 | ✅ | `cmd:develop.curve`, `cmd:curve.reset`, `cmd:curve.presets`, `cmd:curve.applyPreset`, `cmd:curve.savePreset`, `cmd:curve.deletePreset`, `cmd:curve.importPresets`, `cmd:curve.exportPresets`, `cmd:file.importCurvePresets`, `cmd:file.exportCurvePresets`, `crates/engine/src/cmd/curves.rs`, `crates/ui-egui/src/panels/edit.rs` | click to add a point; drag a point in both axes (between its neighbours, input / output readout, one undo step per drag; ⌥-drag moves it a tenth as far for fine adjustment, issue #1363); drag empty space to add and drag; double-click removes; reset: double-click a channel selector (that channel), the Reset button under the graph (every curve incl. parametric) or right-click the graph (channel / all); Point Curve preset dropdown: own Linear / Medium Contrast / Strong Contrast, user presets (save the current point curves, delete by right-click; saved with the library), import / export as `.lccurve` JSON |
 | LR-EDIT-LIGHT-CURVE-RGB | Per-channel curves | P0 | ✅ | `cmd:develop.curve` (`channel`) | |
 | LR-EDIT-LIGHT-CURVE-REFINESAT | Curve saturation compensation | P1 | ✅ | `ctl:curve.refineSaturation` | |
diff --git a/docs/whats-new.md b/docs/whats-new.md
index de37d2635..c6c259200 100644
--- a/docs/whats-new.md
+++ b/docs/whats-new.md
@@ -14,6 +14,11 @@
   sideways moves that control — the zone you pressed stays locked while the pointer crosses the others, Shift drags a
   tenth as far, and the whole drag is one undo step. Double-clicking a zone puts its control back to its default.
 
+### Drag the parametric Tone Curve
+- In the Tone Curve's parametric mode the graph is now drawn from the renderer's own curve, so it always matches the
+  photo, and the line can be dragged: pressing it picks the region under the pointer (Highlights, Lights, Darks or
+  Shadows) and moving up or down changes that slider, as one undo step. Hovering the line names the region first.
+
 ## 2026-10-23
 
 ### Tab leaves the name field in New Album, New Smart Album and the name prompts