diff --git a/crates/geometry/src/defeature.rs b/crates/geometry/src/defeature.rs
new file mode 100644
index 0000000..21d960f
--- /dev/null
+++ b/crates/geometry/src/defeature.rs
@@ -0,0 +1,417 @@
+//! Defeaturing for meshing: holes, fillets, chamfers and small bosses taken out of a design so they
+//! do not drive the mesh.
+//!
+//! A design opened from its timeline knows its features ([`Design::features`]), so a hole is
+//! removed by rebuilding the design with the hole's feature suppressed, exactly as SolidCraft
+//! would build it without it: the hole is filled, a fillet or chamfer goes back to its sharp edge,
+//! a boss is gone. The faces the other features made keep their persistent names, so sets, seeds
+//! and loads on them still resolve.
+//!
+//! A feature that cannot be suppressed on its own (a later feature needs it: a fillet along the
+//! hole's edge, a pattern of it), or whose suppression would take a body away, is kept in the
+//! B-rep and defeatured for meshing only instead, as virtual topology
+//! ([`crate::virtual_faces`]): its faces are merged into the neighbour they share the longest
+//! edges with, so the meshers see no edges around it (the material stays). Such a feature is
+//! listed with `virtual` in [`Design::defeat_report`].
+//!
+//! Defeatures live in the FieldCraft model by feature id (the `F<id>` of persistent names, stable
+//! across edits of the design) and are applied whenever the design is opened, before the
+//! partitions. [`Design::defeatured`] keeps the design as opened, so switching a feature back on
+//! rebuilds from it.
+
+use std::collections::{BTreeMap, BTreeSet};
+use std::sync::Arc;
+
+use serde::Serialize;
+use solidcraft_doc::FeatureKind;
+
+use crate::features::FeatureNode;
+use crate::virtual_faces::Merge;
+use crate::{Design, Error, FeatureError, Result};
+
+/// Most features all of a design's defeatures name together.
+pub const MAX_DEFEATURED: usize = 1024;
+/// Most rebuilds spent finding which features suppress on their own when suppressing them all
+/// at once breaks the design; the features past it are defeatured virtually.
+const MAX_TRIALS: usize = 64;
+
+/// Features of the design's timeline suppressed for meshing (`geometry.defeature`).
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct Defeature {
+    pub name: String,
+    /// Feature ids (`F<id>`).
+    pub features: Vec<u64>,
+}
+
+/// How a defeatured feature was taken out.
+#[derive(Debug, Clone, PartialEq, Eq, Serialize)]
+pub struct Defeated {
+    /// The defeature that names it.
+    pub defeature: String,
+    pub feature: u64,
+    /// `suppressed` (the design rebuilt without it) or `virtual` (its faces merged into a
+    /// neighbour for meshing; the B-rep keeps it).
+    pub method: &'static str,
+    /// Why it could not be suppressed, for a virtual one.
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub reason: Option<String>,
+}
+
+/// The defeatures applied to a design, and the design as opened.
+#[derive(Debug)]
+pub(crate) struct Applied {
+    /// The design as opened, before any defeature.
+    original: Design,
+    defeatures: Vec<Defeature>,
+    report: Vec<Defeated>,
+    /// The virtual defeatures, as merges applied with the model's own.
+    merges: Vec<Merge>,
+}
+
+/// A feature a mesh-prep pass may take out, and its size.
+#[derive(Debug, Clone, PartialEq, Serialize)]
+pub struct Candidate {
+    pub id: u64,
+    pub name: String,
+    /// The feature's definition type (`hole`, `extrude`, `fillet`, …).
+    #[serde(rename = "type")]
+    pub kind: String,
+    /// `hole`, `fillet`, `chamfer` or `boss`.
+    pub category: &'static str,
+    /// The size compared: a hole's diameter, a fillet's radius, a chamfer's distance, a boss's
+    /// height (mm).
+    pub size: f64,
+    /// The body's faces it made.
+    pub faces: Vec<String>,
+}
+
+/// Whether the feature `node` is a hole, fillet, chamfer or boss, and its size.
+pub fn candidate(node: &FeatureNode) -> Option<Candidate> {
+    let v = |k: &str| node.values.get(k).copied();
+    let op = node.operation.as_deref();
+    // A circular profile's diameter (an extrude of a circle).
+    let circle = || {
+        let p = node.sketch.as_ref()?.profiles.first()?;
+        match p.outer.as_slice() {
+            [crate::Curve::Circle { radius, .. }] if p.holes.is_empty() => Some(2.0 * radius),
+            _ => None,
+        }
+    };
+    let (category, size) = match (node.kind.as_str(), op) {
+        ("hole", _) => ("hole", v("diameter")?),
+        ("fillet", _) => ("fillet", v("radius")?),
+        ("chamfer", _) => ("chamfer", v("distance")?),
+        ("cylinder", Some("cut")) => ("hole", 2.0 * v("radius")?),
+        ("extrude", Some("cut")) => ("hole", circle()?),
+        ("extrude", Some("join")) => ("boss", v("distance")?.abs()),
+        ("cylinder" | "box", Some("join")) => ("boss", v("height")?.abs()),
+        _ => return None,
+    };
+    (size.is_finite() && size > 0.0).then(|| Candidate {
+        id: node.id,
+        name: node.name.clone(),
+        kind: node.kind.clone(),
+        category,
+        size,
+        faces: node.faces.clone(),
+    })
+}
+
+impl Design {
+    /// The design as opened, before its defeatures.
+    pub fn undefeatured(&self) -> &Design {
+        self.defeat.as_deref().map_or(self, |a| &a.original)
+    }
+
+    /// How each defeatured feature was taken out, in the defeatures' order.
+    pub fn defeat_report(&self) -> &[Defeated] {
+        self.defeat.as_deref().map_or(&[], |a| a.report.as_slice())
+    }
+
+    /// The design with `defeatures` applied, from the design as opened, and the merges that
+    /// defeature its features virtually (apply them with the model's own, [`Design::merged`]).
+    /// A defeature naming a feature the timeline lacks, or one that builds a body or a sketch, is
+    /// listed in [`Design::errors`] (`defeature <name>`) and the rest still apply. A design
+    /// without a timeline defeatures nothing (each is an error).
+    pub fn defeatured(&self, defeatures: &[Defeature]) -> Result<(Design, Vec<Merge>)> {
+        let base = self.undefeatured();
+        if defeatures.iter().all(|d| d.features.is_empty()) {
+            return Ok((base.clone(), Vec::new()));
+        }
+        if let Some(a) = self.defeat.as_deref().filter(|a| a.defeatures == defeatures) {
+            return Ok((self.clone(), a.merges.clone()));
+        }
+        if defeatures.iter().map(|d| d.features.len()).sum::<usize>() > MAX_DEFEATURED {
+            return Err(Error::Invalid(format!("a design takes at most {MAX_DEFEATURED} defeatured features")));
+        }
+        let mut errors = Vec::new();
+        let fail = |d: &Defeature, message: String| FeatureError { feature: format!("defeature {}", d.name), message, bodies: Vec::new() };
+        // The features to take out, each with the first defeature naming it.
+        let mut wanted: BTreeMap<u64, &str> = BTreeMap::new();
+        let mut order = Vec::new();
+        for d in defeatures {
+            for &id in &d.features {
+                let refused = match base.history.as_deref().map(|h| h.doc.feature(id)) {
+                    None => Some("the design has no feature timeline".to_string()),
+                    Some(None) => Some(format!("the design has no feature F{id}")),
+                    Some(Some(f)) if !suppressible(&f.kind) => {
+                        Some(format!("F{id} ({}) builds a body or a sketch; it is not a feature to defeature", f.name))
+                    }
+                    Some(Some(_)) => None,
+                };
+                match refused {
+                    Some(m) => errors.push(fail(d, m)),
+                    None if !wanted.contains_key(&id) => {
+                        wanted.insert(id, &d.name);
+                        order.push(id);
+                    }
+                    None => {}
+                }
+            }
+        }
+        // Suppress them all at once; when that breaks the design, one at a time, keeping those
+        // that rebuild cleanly.
+        let mut kept: BTreeSet<u64> = order.iter().copied().collect();
+        let mut rebuilt = rebuild_without(base, &kept)?.ok();
+        let mut reasons: BTreeMap<u64, String> = BTreeMap::new();
+        if rebuilt.is_none() {
+            kept.clear();
+            for (k, &id) in order.iter().enumerate() {
+                if k >= MAX_TRIALS {
+                    reasons.insert(id, format!("more than {MAX_TRIALS} features to try one at a time"));
+                    continue;
+                }
+                let mut next = kept.clone();
+                next.insert(id);
+                match rebuild_without(base, &next)? {
+                    Ok(d) => {
+                        kept = next;
+                        rebuilt = Some(d);
+                    }
+                    Err(why) => {
+                        reasons.insert(id, why);
+                    }
+                }
+            }
+        }
+        let mut design = match rebuilt {
+            Some(d) if !kept.is_empty() => d,
+            _ => base.clone(),
+        };
+        // The rest: their faces merged into a neighbour, body by body.
+        let mut merges = Vec::new();
+        let mut report = Vec::new();
+        let graph = if reasons.is_empty() { Vec::new() } else { base.features(None)? };
+        for &id in &order {
+            let defeature = wanted.get(&id).map_or_else(String::new, |n| n.to_string());
+            if kept.contains(&id) {
+                report.push(Defeated { defeature, feature: id, method: "suppressed", reason: None });
+                continue;
+            }
+            for b in &graph {
+                let Some(node) = b.features.iter().find(|f| f.id == id).filter(|f| !f.faces.is_empty()) else { continue };
+                match absorb(base, &b.body, &node.faces) {
+                    Ok(Some(into)) => {
+                        let mut faces = node.faces.clone();
+                        faces.push(into.clone());
+                        merges.push(Merge { name: format!("{defeature}-F{id}"), body: b.body.clone(), faces, into: Some(into) });
+                    }
+                    Ok(None) => {}
+                    Err(e) => errors.push(FeatureError {
+                        feature: format!("defeature {defeature}"),
+                        message: format!("F{id} on `{}`: {e}", b.body),
+                        bodies: vec![b.body.clone()],
+                    }),
+                }
+            }
+            report.push(Defeated { defeature, feature: id, method: "virtual", reason: reasons.get(&id).cloned() });
+        }
+        design.errors.extend(errors);
+        design.defeat = Some(Arc::new(Applied { original: base.clone(), defeatures: defeatures.to_vec(), report, merges: merges.clone() }));
+        Ok((design, merges))
+    }
+}
+
+/// Whether a feature of this kind may be taken out without taking a body or a sketch with it.
+fn suppressible(kind: &FeatureKind) -> bool {
+    use solidcraft_doc::Operation::NewBody;
+    match kind {
+        FeatureKind::Sketch { .. }
+        | FeatureKind::ConstructionPlane { .. }
+        | FeatureKind::ConstructionAxis { .. }
+        | FeatureKind::ConstructionPoint { .. }
+        | FeatureKind::Combine { .. }
+        | FeatureKind::Split { .. } => false,
+        FeatureKind::Extrude { operation, .. }
+        | FeatureKind::Revolve { operation, .. }
+        | FeatureKind::Sweep { operation, .. }
+        | FeatureKind::Loft { operation, .. }
+        | FeatureKind::Box { operation, .. }
+        | FeatureKind::Cylinder { operation, .. }
+        | FeatureKind::Sphere { operation, .. }
+        | FeatureKind::Torus { operation, .. } => *operation != NewBody,
+        _ => true,
+    }
+}
+
+/// `base` rebuilt with `ids` suppressed: `Err(why)` when that fails a feature that built in
+/// `base` or loses one of its bodies.
+fn rebuild_without(base: &Design, ids: &BTreeSet<u64>) -> Result<std::result::Result<Design, String>> {
+    let history = base.history.as_deref().ok_or_else(|| Error::Invalid("the design has no feature timeline".into()))?;
+    let mut doc = history.doc.clone();
+    for &id in ids {
+        if let Some(f) = doc.feature_mut(id) {
+            f.suppressed = true;
+        }
+    }
+    let design = crate::design::rebuild(&doc)?;
+    let failed: Vec<String> = design
+        .errors
+        .iter()
+        .filter(|e| !base.errors.iter().any(|b| b.feature == e.feature))
+        .map(|e| format!("{} no longer builds: {}", e.feature, e.message))
+        .collect();
+    if !failed.is_empty() {
+        return Ok(Err(failed.join("; ")));
+    }
+    let lost: Vec<&str> = base.source.iter().map(|b| b.name.as_str()).filter(|n| design.source.iter().all(|b| b.name != *n)).collect();
+    if !lost.is_empty() {
+        return Ok(Err(format!("body {} would be gone", lost.join(", "))));
+    }
+    Ok(Ok(design))
+}
+
+/// The face of `body` (in `base` as opened) outside `faces` that `faces` share the longest edges
+/// with; `None` when the body has none of them.
+fn absorb(base: &Design, body: &str, faces: &[String]) -> Result<Option<String>> {
+    let Some(shape) = base.source_body(body) else { return Ok(None) };
+    for f in faces {
+        if shape.faces_named(f).is_empty() {
+            continue;
+        }
+        // A face of the feature may border only the feature's own faces (the middle of a
+        // fillet chain): the next one finds the outside.
+        let mut probe = shape.clone();
+        let others: Vec<String> = faces.iter().filter(|g| *g != f && !shape.faces_named(g).is_empty()).cloned().collect();
+        if !others.is_empty() {
+            let mut all = vec![f.clone()];
+            all.extend(others);
+            match shape.merge_faces(f, &all) {
+                Ok(m) => probe = m,
+                Err(_) => continue,
+            }
+        }
+        if let Ok(n) = probe.absorbing_neighbour(f) {
+            return Ok(Some(n));
+        }
+    }
+    Err(Error::Invalid("its faces have no neighbour to merge into".into()))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::sample::{Plate, plate_design};
+
+    fn plate() -> Design {
+        crate::open_design(&plate_design(&Plate::default()).unwrap()).unwrap()
+    }
+
+    fn hole(d: &Design) -> u64 {
+        d.features(None).unwrap()[0].features.iter().filter_map(candidate).find(|c| c.category == "hole").unwrap().id
+    }
+
+    /// Suppressing the plate's hole fills it (the body is a solid block, its faces keep their
+    /// names); an empty list brings it back.
+    #[test]
+    fn the_plate_without_its_hole_is_a_block() {
+        let d = plate();
+        let id = hole(&d);
+        let c = d.features(None).unwrap()[0].features.iter().filter_map(candidate).next().unwrap();
+        assert_eq!((c.category, c.size), ("hole", Plate::default().hole_diameter));
+        let def = [Defeature { name: "Holes".into(), features: vec![id] }];
+        let (filled, merges) = d.defeatured(&def).unwrap();
+        assert!(merges.is_empty());
+        let p = Plate::default();
+        let v = filled.bodies[0].measure().unwrap().volume;
+        assert!((v - p.width * p.depth * p.thickness).abs() < 1e-6 * v, "{v}");
+        assert_eq!(filled.bodies[0].faces().len(), 6);
+        assert!(filled.bodies[0].faces().iter().all(|f| d.bodies[0].faces().iter().any(|g| g.name == f.name)));
+        assert_eq!(filled.defeat_report(), [Defeated { defeature: "Holes".into(), feature: id, method: "suppressed", reason: None }]);
+        // The feature graph of the defeatured design leaves the hole out; the design as opened keeps it.
+        assert_eq!(filled.features(None).unwrap()[0].features.len(), 1);
+        assert_eq!(filled.undefeatured().features(None).unwrap()[0].features.len(), 2);
+        // Applied again with the same list: the same design, no rebuild; with none: as opened.
+        let (again, _) = filled.defeatured(&def).unwrap();
+        assert_eq!(again.bodies[0].faces().len(), 6);
+        let (back, _) = filled.defeatured(&[]).unwrap();
+        assert_eq!(back.bodies[0].faces().len(), d.bodies[0].faces().len());
+        assert!(back.defeat_report().is_empty());
+    }
+
+    /// A feature the timeline lacks, or the base extrude, is an error of the defeature, not of
+    /// the call.
+    #[test]
+    fn unknown_and_body_features_are_listed_errors() {
+        let d = plate();
+        let base = d.features(None).unwrap()[0].features[0].id;
+        let (out, _) = d.defeatured(&[Defeature { name: "Bad".into(), features: vec![base, 999] }]).unwrap();
+        let errors: Vec<&str> = out.errors.iter().filter(|e| e.feature == "defeature Bad").map(|e| e.message.as_str()).collect();
+        assert_eq!(errors.len(), 2, "{errors:?}");
+        assert!(errors[0].contains("builds a body") && errors[1].contains("no feature F999"), "{errors:?}");
+        assert_eq!(out.bodies[0].faces().len(), d.bodies[0].faces().len());
+    }
+
+    /// The bracket's fillet is suppressed (back to a sharp corner) and listed as one.
+    #[cfg(feature = "scripts")]
+    #[test]
+    fn a_bracket_fillet_goes_back_to_its_sharp_edge() {
+        let script = r#"[
+            {"command": "sketch.create", "params": {"plane": "XY", "name": "Profile"}},
+            {"command": "sketch.line", "params": {"points": [[0, 0], [60, 0], [60, 8], [8, 8], [8, 50], [0, 50]], "closed": true}},
+            {"command": "sketch.finish", "params": {}},
+            {"command": "solid.extrude", "params": {"distance": 40, "body_name": "Bracket"}},
+            {"command": "solid.fillet", "params": {"edges": [[8, 8, 20]], "radius": 6}},
+            {"command": "solid.hole", "params": {"position": [40, 8, 20], "diameter": 8}}
+        ]"#;
+        let d = crate::open_design(&crate::script_design(script).unwrap()).unwrap();
+        let cands: Vec<Candidate> = d.features(None).unwrap()[0].features.iter().filter_map(candidate).collect();
+        assert_eq!(cands.iter().map(|c| (c.category, c.size)).collect::<Vec<_>>(), [("fillet", 6.0), ("hole", 8.0)]);
+        let fillet = cands[0].id;
+        let (sharp, merges) = d.defeatured(&[Defeature { name: "Small".into(), features: vec![fillet] }]).unwrap();
+        assert!(merges.is_empty());
+        let (before, after) = (d.bodies[0].measure().unwrap().volume, sharp.bodies[0].measure().unwrap().volume);
+        // The fillet's material comes out: (1 − π/4) r² × 40 in the inside corner.
+        let fill = (1.0 - std::f64::consts::FRAC_PI_4) * 36.0 * 40.0;
+        assert!((before - after - fill).abs() < 1e-3 * fill, "{before} {after}");
+        assert!(sharp.bodies[0].faces().iter().all(|f| !f.name.starts_with(&format!("F{fillet}:"))));
+    }
+
+    /// A hole whose rim a later fillet rounds cannot be suppressed alone (the fillet would lose
+    /// its edge): it is defeatured virtually, its faces merged into a neighbour, the B-rep kept.
+    #[cfg(feature = "scripts")]
+    #[test]
+    fn a_hole_a_fillet_needs_is_defeatured_virtually() {
+        let script = r#"[
+            {"command": "solid.box", "params": {"length": 40, "width": 40, "height": 10, "body_name": "Block"}},
+            {"command": "solid.hole", "params": {"position": [20, 20, 10], "diameter": 10}},
+            {"command": "solid.fillet", "params": {"edges": [[25, 20, 10]], "radius": 1}}
+        ]"#;
+        let d = crate::open_design(&crate::script_design(script).unwrap()).unwrap();
+        assert!(d.errors.is_empty(), "{:?}", d.errors);
+        let graph = d.features(None).unwrap();
+        let hole = graph[0].features.iter().find(|f| f.kind == "hole").unwrap();
+        let (out, merges) = d.defeatured(&[Defeature { name: "H".into(), features: vec![hole.id] }]).unwrap();
+        let report = out.defeat_report();
+        assert_eq!((report.len(), report[0].method), (1, "virtual"), "{report:?}");
+        assert!(report[0].reason.as_deref().is_some_and(|r| r.contains("no longer builds")), "{report:?}");
+        assert_eq!(merges.len(), 1, "{merges:?}");
+        let m = &merges[0];
+        assert!(m.into.as_ref().is_some_and(|i| !hole.faces.contains(i)) && m.faces.len() == hole.faces.len() + 1, "{m:?}");
+        // The B-rep is the design as opened; the merge applies.
+        assert_eq!(out.bodies[0].faces().len(), d.bodies[0].faces().len());
+        let merged = out.merged(&merges).unwrap();
+        assert!(merged.errors.is_empty(), "{:?}", merged.errors);
+        assert_eq!(merged.bodies[0].faces().len(), d.bodies[0].faces().len() - hole.faces.len());
+    }
+}
diff --git a/crates/geometry/src/design.rs b/crates/geometry/src/design.rs
index cf1152e..8af9c38 100644
--- a/crates/geometry/src/design.rs
+++ b/crates/geometry/src/design.rs
@@ -32,6 +32,8 @@ pub struct Design {
     pub(crate) opened: std::sync::Arc<Vec<Shape>>,
     /// The timeline the design was rebuilt from ([`Design::features`]).
     pub(crate) history: Option<std::sync::Arc<crate::features::History>>,
+    /// The defeatures applied ([`Design::defeatured`]) and the design as opened before them.
+    pub(crate) defeat: Option<std::sync::Arc<crate::defeature::Applied>>,
 }
 
 /// A feature of the design that failed to rebuild.
@@ -164,6 +166,7 @@ pub(crate) fn rebuild(doc: &Document) -> Result<Design> {
         errors,
         cuts: Vec::new(),
         history: Some(std::sync::Arc::new(history)),
+        defeat: None,
     })
 }
 
diff --git a/crates/geometry/src/lib.rs b/crates/geometry/src/lib.rs
index 43964c3..5d50858 100644
--- a/crates/geometry/src/lib.rs
+++ b/crates/geometry/src/lib.rs
@@ -18,6 +18,7 @@
 #![forbid(unsafe_code)]
 
 pub mod check;
+pub mod defeature;
 mod design;
 mod edges;
 pub mod face_split;
diff --git a/crates/geometry/src/partition.rs b/crates/geometry/src/partition.rs
index eb5ac8f..2402d21 100644
--- a/crates/geometry/src/partition.rs
+++ b/crates/geometry/src/partition.rs
@@ -178,6 +178,7 @@ impl Design {
             source: std::sync::Arc::clone(&self.source),
             opened: std::sync::Arc::clone(&self.source),
             history: self.history.clone(),
+            defeat: self.defeat.clone(),
         })
     }
 }