feat: fillet fit option reduces a radius too large for its edges (#388)

* feat(kernel): typed TooLarge refusal and fillet_max search

Blend refusals caused only by the size (larger than the neighbouring faces,
taller than the walls, longer than the next edge, larger than a corner
radius) now return KernelError::TooLarge, displayed as before. fillet_max
finds the largest radius below a request at which the fillet of the edges
works, to three significant digits, by building candidates; it is an explicit
call (up to 16 fillets), not run on every refusal.

A corner edge that doesn't run square to the edge is now reported as such
instead of as a blend larger than the neighbouring faces.

Refs #293

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01TWc1smHYwTSVrVc8SNvS44

* feat: fillet fit option reduces a radius too large for its edges

solid.fillet takes fit: exact (the default, as before: a radius too large
for the geometry around the edges is refused) or reduce: the radius is
reduced to the largest that works for all the picked edges (kernel
fillet_max, three significant digits, every candidate built). The feature
stores the requested radius, so it refits on every evaluation; when it
reduces, the feature's warning says so and the command returns
radius_applied. Pattern copies of the fillet use the same rule. The file
format writes fit only when it is reduce.

The Fillet dialog gets a Radius Fit row (Exact / Reduce to Fit, constant
radius) and, when the preview reduced the radius, an Applied Radius line;
editing the feature keeps the choice.

One radius for all edges for now; per-edge radii and taper follow.

Refs #293

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01TWc1smHYwTSVrVc8SNvS44

---------

Co-authored-by: Claude Opus 5.5 <[email protected]>
Co-authored-by: bherbruck <[email protected]>

crates/engine/src/cmd/features.rs

@@ -31,7 +31,7 @@ pub static COMMANDS: &[CommandSpec] = &[
         .at("SOLID", "MODIFY")
         .icon("fillet")
         .key("F")
-        .params("edges: [[x,y,z] point on edge | {body, index}]; radius: expr; body?; type?: constant|chord (radius is the width across)|variable (radius at the end nearest start, radius2 at the other); radius2?; start?: [x,y,z]; mid?: [[position 0…1 from start, radius expr], …] (variable radii between the ends); smooth?: bool (smooth instead of straight between the radii)"),
+        .params("edges: [[x,y,z] point on edge | {body, index}]; radius: expr; body?; type?: constant|chord (radius is the width across)|variable (radius at the end nearest start, radius2 at the other); radius2?; start?: [x,y,z]; mid?: [[position 0…1 from start, radius expr], …] (variable radii between the ends); smooth?: bool (smooth instead of straight between the radii); fit?: exact|reduce (exact, the default: a radius too large for the geometry around the edges is refused; reduce: it is reduced to the largest that fits all of them, returned as `radius_applied` and noted in the feature's warning)"),
     CommandSpec::new("solid.chamfer", "Chamfer", chamfer).at("SOLID", "MODIFY").icon("chamfer").params("edges: [[x,y,z] | {body, index}]; distance: expr; distance2?: expr (along the second face) | angle?: expr (from the first face); flip?: bool (which face is first: by default the one facing up most); body?"),
     CommandSpec::new("solid.combine", "Combine", combine).at("SOLID", "MODIFY").icon("combine").params("target: body; tools: [body]; operation?: join|cut|intersect; keep_tools?: bool; new_component?: bool (the result goes into a new component; component_name?)"),
     CommandSpec::new("solid.pattern.rectangular", "Rectangular Pattern", pattern_rect)
@@ -785,7 +785,19 @@ fn fillet(s: &mut Session, p: &Value) -> Result<Value> {
         }
         Some(o) => return Err(bad(cmd, format!("unknown fillet type `{o}` (constant, chord or variable)"))),
     };
-    add_feature(s, p, FeatureKind::Fillet { edges, radius, body: str_(p, "body").map(str::to_string), style })
+    let fit = match str_(p, "fit").map(str::to_ascii_lowercase).as_deref() {
+        None | Some("exact") => solvecraft_doc::FilletFit::Exact,
+        Some("reduce") => solvecraft_doc::FilletFit::Reduce,
+        Some(o) => return Err(bad(cmd, format!("unknown fit `{o}` (exact or reduce)"))),
+    };
+    let mut out = add_feature(s, p, FeatureKind::Fillet { edges, radius, body: str_(p, "body").map(str::to_string), style, fit })?;
+    // The radius the fillet used, when `fit: reduce` reduced it.
+    if let Some(id) = out.get("feature").and_then(Value::as_u64)
+        && let Some(r) = s.model.result(id).and_then(|res| res.state.fitted_radius(id))
+    {
+        out["radius_applied"] = serde_json::json!(r);
+    }
+    Ok(out)
 }
 
 fn chamfer(s: &mut Session, p: &Value) -> Result<Value> {