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(),
         });
     }