fix: address review findings on merged #293/#292 hatch+snap

Three defects found reviewing the just-merged PRs:

- PLOTWINDOW forced corner snap (#293) only ran in the on_tick preview
  path, so the marker highlighted an endpoint but the click committed a
  plain snap — with the global OSNAP master (or Endpoint mode) off the
  corner landed at the raw cursor, defeating the feature. Apply the same
  snap_forced_corners branch at the click-commit recompute.

- build_dxf_pattern (#292) wrote the pattern line's LOCAL step into the
  world-frame HatchPatternLine.offset. The new prebaked reader
  inverse-rotates offset assuming world frame, so app-created hatches
  (HATCH command) collapsed their spacing by cos(angle) — ANSI31 at 45deg
  rendered 2.245 instead of 3.175 on both viewport and PDF/plot export.
  Rotate the local step into world here so it round-trips and the stored
  offset is format-correct for other CAD apps.

- far_from_origin_pattern_hatch_still_fills placed its offset ALONG the
  45deg lines (projects to k~0), so it never exercised the span-cap fix and
  passed even with the old absolute-index clamp restored. Move the offset
  perpendicular to the lines so |k| >> the cap. Add
  app_created_hatch_roundtrips_catalog_spacing to guard the offset-frame
  fix (verified: fails at 2.245 without it, passes at 3.175 with it).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/update/viewport.rs

@@ -1828,7 +1828,23 @@ pub(super) fn on_tick(&mut self, t: Instant) -> Task<Message> {
                         } else {
                             let (go, gr) = self.tabs[i].ucs_grid_basis();
                             self.snapper.from_point = self.last_point;
-                            self.snapper.snap(snap_cursor, p, &all_wires[..], view_rot, eye, bounds, go, gr)
+                            // Mirror the preview path (see on_tick): a command that
+                            // forces corner snap (PLOTWINDOW) must commit the forced
+                            // Endpoint hit, not a plain snap — otherwise the marker
+                            // promises an endpoint the click places at the raw cursor
+                            // whenever the global OSNAP master (or Endpoint mode) is off.
+                            let force_corners = self.tabs[i]
+                                .active_cmd
+                                .as_ref()
+                                .map(|c| c.forces_endpoint_snap())
+                                .unwrap_or(false);
+                            if force_corners {
+                                self.snapper.snap_forced_corners(
+                                    snap_cursor, p, &all_wires[..], view_rot, eye, bounds, go, gr,
+                                )
+                            } else {
+                                self.snapper.snap(snap_cursor, p, &all_wires[..], view_rot, eye, bounds, go, gr)
+                            }
                         };
                         // Snap runs in model space; the result is already model.
                         let mut pt = snap_hit.map(|s| s.world).unwrap_or(raw);

src/scene/model/hatch_patterns.rs

@@ -45,10 +45,20 @@ pub fn build_dxf_pattern(entry: &PatternEntry) -> DxfPattern {
     pat.description = entry.description.clone();
     for ln in &entry.pat_lines {
         let angle_rad = (ln.angle_deg as f64).to_radians();
+        // The catalog stores the step (dx = shift along the line, dy =
+        // perpendicular spacing) in the pattern LINE-LOCAL frame. The DWG
+        // `HatchPatternLine.offset` is a WORLD-space vector — that is how real
+        // files store it and how `family_from_stored_line` reads it back (it
+        // inverse-rotates by the line angle). Emitting the raw local step here
+        // made the reader recover a rotated, too-dense spacing (e.g. ANSI31 at
+        // 45° collapsed 3.175 → 2.245). Rotate local → world by the line angle
+        // so the offset is format-correct and round-trips to the exact spacing.
+        let (ca, sa) = (angle_rad.cos(), angle_rad.sin());
+        let (ldx, ldy) = (ln.dx as f64, ln.dy as f64);
         pat.lines.push(HatchPatternLine {
             angle: angle_rad,
             base_point: Vector2::new(ln.x0 as f64, ln.y0 as f64),
-            offset: Vector2::new(ln.dx as f64, ln.dy as f64),
+            offset: Vector2::new(ldx * ca - ldy * sa, ldx * sa + ldy * ca),
             dash_lengths: ln.dashes.iter().map(|&d| d as f64).collect(),
         });
     }

tests/block_hatch_export.rs

@@ -134,9 +134,13 @@ fn pattern_hatch_uses_stored_line_spacing() {
 #[test]
 fn far_from_origin_pattern_hatch_still_fills() {
     let mut scene = Scene::new();
-    // Spacing 0.3 at ~4000 units out → k ≈ 4000/0.3·√2 ≈ 18000, well past the
-    // 4096 clamp on both ends.
-    scene.add_entity(EntityType::Hatch(ansi31_stored_at(0.3, 1.0, 4000.0, 4000.0)));
+    // The offset must be PERPENDICULAR to the 45° hatch lines to drive k far
+    // from 0 — a diagonal offset (e.g. (4000,4000)) lies ALONG the lines and
+    // projects to k≈0, so it would not exercise the clamp at all. At (4000,0)
+    // the perpendicular index is |k| ≈ 4000·sin45°/0.3 ≈ 9400, well past the
+    // 4096 clamp on both ends; the old absolute-index clamp inverts the range
+    // (k_lo > k_hi) there and emits nothing.
+    scene.add_entity(EntityType::Hatch(ansi31_stored_at(0.3, 1.0, 4000.0, 0.0)));
     scene.populate_hatches_from_document();
 
     let hatches = scene.paper_canvas_hatches();
@@ -199,3 +203,65 @@ fn textbox_boundary_path_is_not_filled() {
          would paint a phantom bar"
     );
 }
+
+// A hatch created in-app (HATCH command -> Scene::add_hatch) stores its pattern
+// through build_dxf_pattern and is then rebuilt via hatch_model_from_dxf. The
+// rebuilt spacing must equal the catalog's own spacing — not a rotated,
+// too-dense value. Regression: build_dxf_pattern wrote the pattern line-LOCAL
+// step into the world-frame `offset`, so the prebaked reader inverse-rotated it
+// and ANSI31 at 45° collapsed its spacing by cos(45°) (3.175 -> 2.245) on both
+// the viewport and the PDF/plot export.
+#[test]
+fn app_created_hatch_roundtrips_catalog_spacing() {
+    use std::sync::Arc;
+
+    use OpenCADStudio::scene::model::hatch_model::{HatchModel, PatFamily};
+    use OpenCADStudio::scene::model::hatch_patterns;
+
+    // Effective perpendicular spacing of a family, exactly as pattern_segments
+    // computes it: rotate the local step out by the angle, project onto the
+    // line-perpendicular direction.
+    fn perp_spacing(f: &PatFamily, scale: f32) -> f32 {
+        let a = f.angle_deg.to_radians();
+        let (ca, sa) = (a.cos(), a.sin());
+        let step_x = (f.dx * ca - f.dy * sa) * scale;
+        let step_y = (f.dx * sa + f.dy * ca) * scale;
+        (step_x * -sa + step_y * ca).abs()
+    }
+
+    let entry = hatch_patterns::find("ANSI31").expect("ANSI31 in catalog");
+    let HatchPattern::Pattern(cat_fams) = &entry.gpu else {
+        panic!("ANSI31 is a line pattern")
+    };
+    let expected = perp_spacing(&cat_fams[0], 1.0);
+
+    // Build the model the way the HATCH command does: catalog family, scale 1.
+    let mut scene = Scene::new();
+    let boundary: Vec<[f32; 2]> = vec![[0.0, 0.0], [10.0, 0.0], [10.0, 10.0], [0.0, 10.0]];
+    let model = HatchModel {
+        world_origin: [0.0, 0.0],
+        boundary: Arc::new(boundary),
+        pattern: entry.gpu.clone(),
+        name: "ANSI31".into(),
+        color: [0.75, 0.75, 0.75, 0.85],
+        angle_offset: 0.0,
+        scale: 1.0,
+        vp_scissor: None,
+        draw_depth: 0.0,
+    };
+    scene.add_hatch(model);
+    scene.populate_hatches_from_document();
+
+    let hatches = scene.paper_canvas_hatches();
+    let m = hatches
+        .iter()
+        .find(|m| matches!(m.pattern, HatchPattern::Pattern(_)))
+        .expect("pattern hatch present after round-trip");
+    let HatchPattern::Pattern(fams) = &m.pattern else { unreachable!() };
+    let got = perp_spacing(&fams[0], m.scale);
+    assert!(
+        (got - expected).abs() < expected * 0.02,
+        "app-created ANSI31 round-tripped to spacing {got}, expected ~{expected} \
+         — build_dxf_pattern must store the world-frame offset, not the local step"
+    );
+}