Fix dimension text rendering upside-down when drawn right-to-left

Normalize the dimension direction in both the SVG writer and the viewport
decorator so text always reads left-to-right (or bottom-to-top for vertical
dims) regardless of which anchor was placed first. Also guards against a
pre-existing crash when two dimension endpoints project to the same screen
position (zero-length vector passed to angle_signed).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/bonsai/bonsai/bim/module/drawing/decoration.py

@@ -740,6 +740,10 @@ class DimensionDecorator(BaseDecorator):
             text_dir = p1 - p0
             if text_dir.length < 1:
                 continue
+            # Normalize so text always reads left-to-right (or bottom-to-top for
+            # vertical dims) regardless of which end was drawn first.
+            if text_dir.x < 0 or (abs(text_dir.x) < 1e-6 and text_dir.y < 0):
+                text_dir = -text_dir
             perpendicular = Vector((-text_dir.y, text_dir.x)).normalized()
             text_offset = perpendicular * text_offset_value
 
@@ -748,7 +752,7 @@ class DimensionDecorator(BaseDecorator):
                 "multiline": True,
                 "text_dir": text_dir,
             }
-            base_pos = p1 if is_ordinate else p0 + text_dir * 0.5
+            base_pos = p1 if is_ordinate else (p0 + p1) / 2
 
             if not show_description_only:
                 segment_length = (v1 - v0).length

src/bonsai/bonsai/bim/module/drawing/svgwriter.py

@@ -1588,8 +1588,10 @@ class SvgWriter:
         end = (offset + v1.xy * Vector((1, -1))) * self.svg_scale
         mid = ((end - start) / 2) + start
         vector = end - start
+        sheet_dimension = vector.length
+        if sheet_dimension < 1e-6:
+            return
         perpendicular = Vector((vector.y, -vector.x)).normalized()
-        sheet_dimension = (end - start).length
 
         # if annotation can't fit offset text to the right of marker
         if distance_override is not None:
@@ -1597,6 +1599,13 @@ class SvgWriter:
         else:
             text_position = mid if sheet_dimension > 5 else (end + (3 * vector.normalized()))
         angle = math.degrees(vector.angle_signed(Vector((1, 0))))
+        # Keep text readable regardless of draw direction: if the dimension runs
+        # right-to-left the raw angle is near ±180° which renders text upside-down.
+        # Flip both angle and perpendicular so text always reads left-to-right and
+        # stays on the same side of the dimension line.
+        if abs(angle) > 90:
+            angle += 180
+            perpendicular = -perpendicular
 
         line = self.svg.line(start=start, end=end, class_=" ".join(classes))
         self.svg.add(line)