fix(scene): correct MIRROR of TEXT under MIRRTEXT (commit + preview)

Root cause: the glyph tessellator advanced the pen by advance*width_factor
while the transform already scales the pen position by the width factor, so
a backward (negative width factor) run kept its word order and grew on the
same side of the anchor instead of mirroring across it. Advance in unscaled
glyph units to match text_local_bounds; the transform applies the factor once.

On top of that:
- The renderer honours the entity's own text-generation flags (DXF 71: bit 2
  backward / bit 4 upside-down) XOR the text style's flags, and signs the
  horizontal anchor by the width factor so Center/Right backward text mirrors
  about its anchor.
- MIRRTEXT on: a MIRROR toggles both group-71 bits so the reflected rotation
  renders a true glyph mirror (backward-upright for a vertical axis, flipped
  for a horizontal one).
- MIRRTEXT off: the text flips left<->right and lands mirror-symmetric to the
  source (right-reading) instead of hugging the axis.
- The MIRROR preview re-derives text ghosts to match the commit; mirrored()
  now reflects the double-single residual too.

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

src/scene/model/wire_model.rs

@@ -232,6 +232,14 @@ impl WireModel {
             p[0] = p1.x + 2.0 * t * ax - dx;
             p[1] = p1.y + 2.0 * t * ay - dy;
         }
+        // World position is the double-single sum `points + points_low` (text /
+        // UTM wires split it), so the residual must reflect too — as a direction
+        // (linear reflection about the axis, no `p1` offset).
+        for p in &mut out.points_low {
+            let t = (p[0] * ax + p[1] * ay) / len2;
+            p[0] = 2.0 * t * ax - p[0];
+            p[1] = 2.0 * t * ay - p[1];
+        }
         out
     }
 

src/scene/modify.rs

@@ -32,13 +32,24 @@ fn capture_text_orient(e: &EntityType) -> Option<TextOrient> {
     }
 }
 
-/// Re-apply a captured orientation after a transform (the position stays
-/// mirrored, only the rotation / oblique / x-scale are restored).
+/// MIRRTEXT off: after the mirror reflects a text's points and rotation, put
+/// the glyphs back to right-reading. Restores the captured rotation / oblique /
+/// x-scale, and for single-line TEXT also flips the horizontal justification
+/// (left ↔ right) so the box lands mirror-symmetric to the source instead of
+/// hugging the axis — AutoCAD's behaviour. Center/Middle/Aligned/Fit are already
+/// symmetric about their (reflected) anchor, so they stay.
 fn restore_text_orient(e: &mut EntityType, o: &TextOrient) {
     match e {
         EntityType::Text(t) => {
             t.rotation = o.rotation;
             t.oblique_angle = o.oblique;
+            use acadrust::entities::TextHorizontalAlignment as HA;
+            t.horizontal_alignment = match t.horizontal_alignment {
+                HA::Left => HA::Right,
+                HA::Right => HA::Left,
+                other => other,
+            };
+            crate::entities::text::sync_text_alignment_point(t);
         }
         EntityType::MText(m) => {
             m.rotation = o.rotation;
@@ -52,6 +63,19 @@ fn restore_text_orient(e: &mut EntityType, o: &TextOrient) {
     }
 }
 
+/// MIRRTEXT on: a real MIRROR makes text a true glyph mirror. `apply_transform`
+/// already reflects the baseline rotation; toggling *both* group-71 bits
+/// (backward `0x2` + upside-down `0x4`) then renders the exact geometric
+/// reflection (the renderer XORs these flags into the effective width-factor
+/// sign / 180° flip). Toggling — not setting — keeps a double mirror an
+/// involution. Only single-line TEXT carries group 71; MTEXT / Shape keep the
+/// reflected rotation (readable-but-rotated), which is standard-conforming.
+fn mirror_true_text_flags(e: &mut EntityType) {
+    if let EntityType::Text(t) = e {
+        t.generation_flags ^= 0x2 | 0x4;
+    }
+}
+
 impl Scene {
     // ── Modify (transform / copy) ─────────────────────────────────────────
 
@@ -67,6 +91,10 @@ impl Scene {
         // transform and re-apply afterwards.
         let preserve_text_orientation =
             matches!(t, EntityTransform::Mirror { .. }) && !self.document.header.mirror_text;
+        // MIRRTEXT on: toggle the group-71 flags after the reflect so text
+        // becomes a true glyph mirror (see `mirror_true_text_flags`).
+        let mirror_true =
+            matches!(t, EntityTransform::Mirror { .. }) && self.document.header.mirror_text;
         let mut text_orient_backup: Vec<(Handle, TextOrient)> = Vec::new();
         if preserve_text_orientation {
             for &h in handles {
@@ -106,6 +134,9 @@ impl Scene {
         for &h in handles {
             if let Some(entity) = self.document.get_entity_mut(h) {
                 view::dispatch::apply_transform(entity, t);
+                if mirror_true {
+                    mirror_true_text_flags(entity);
+                }
             }
             if self.hatches.contains_key(&h) {
                 let existing_color = self.hatches[&h].color;
@@ -245,6 +276,8 @@ impl Scene {
         // header flag is off.
         let preserve_text_orientation =
             matches!(t, EntityTransform::Mirror { .. }) && !self.document.header.mirror_text;
+        let mirror_true =
+            matches!(t, EntityTransform::Mirror { .. }) && self.document.header.mirror_text;
         let mut new_handles = Vec::with_capacity(clones.len());
         for mut entity in clones {
             let text_orient = if preserve_text_orientation {
@@ -256,6 +289,9 @@ impl Scene {
             if let Some(o) = &text_orient {
                 restore_text_orient(&mut entity, o);
             }
+            if mirror_true {
+                mirror_true_text_flags(&mut entity);
+            }
             // A dimension draws from its baked `*D` block; give the copy its own
             // transformed block so it lands at the copy position rather than
             // rendering on top of the source. (#161)

src/scene/preview.rs

@@ -42,6 +42,55 @@ impl Scene {
             .collect()
     }
 
+    /// Split a MIRROR selection into plain ghost wires (reflected wholesale) and
+    /// text ghosts paired with their bounding-box centre. Lets the preview match
+    /// the commit for TEXT: MIRRTEXT on → true glyph mirror (full reflection, same
+    /// as plain geometry); MIRRTEXT off → right-reading at the mirror-symmetric
+    /// position (reflect the centre, translate) instead of hugging the axis.
+    pub fn mirror_preview_parts(
+        &self,
+        handles: &[Handle],
+    ) -> (Vec<WireModel>, Vec<(WireModel, glam::DVec3)>) {
+        let mut plain: Vec<WireModel> = Vec::new();
+        let mut texts: Vec<(WireModel, glam::DVec3)> = Vec::new();
+        for h in handles {
+            let Some(e) = self.document.entities().find(|e| e.common().handle == *h) else {
+                continue;
+            };
+            if matches!(e, EntityType::Text(_)) {
+                let wires = self.tessellate_one(e);
+                let mut lo = [f64::INFINITY; 2];
+                let mut hi = [f64::NEG_INFINITY; 2];
+                for w in &wires {
+                    for (i, p) in w.points.iter().enumerate() {
+                        if !p[0].is_finite() || !p[1].is_finite() {
+                            continue;
+                        }
+                        // Reconstruct f64 world from the double-single pair (the
+                        // low residual may be absent on some wires).
+                        let l = w.points_low.get(i).copied().unwrap_or([0.0; 3]);
+                        let (x, y) = (p[0] as f64 + l[0] as f64, p[1] as f64 + l[1] as f64);
+                        lo[0] = lo[0].min(x);
+                        lo[1] = lo[1].min(y);
+                        hi[0] = hi[0].max(x);
+                        hi[1] = hi[1].max(y);
+                    }
+                }
+                let center = if lo[0] <= hi[0] {
+                    glam::DVec3::new((lo[0] + hi[0]) * 0.5, (lo[1] + hi[1]) * 0.5, 0.0)
+                } else {
+                    glam::DVec3::ZERO
+                };
+                for w in wires {
+                    texts.push((w, center));
+                }
+            } else {
+                plain.extend(self.tessellate_one(e));
+            }
+        }
+        (plain, texts)
+    }
+
     /// Boundary outline wire for a hatch, reconstructed from its cached
     /// `HatchModel` (offsets from `world_origin`). Used only for edit previews —
     /// the normal render shows the fill, not this outline.

src/scene/text/lff.rs

@@ -420,18 +420,22 @@ pub fn tessellate_text_run(
                 emit_glyph(out, &g.strokes, *cursor_x);
                 emit_fill(fill_tris, &g.fill_tris, *cursor_x);
             }
-            *cursor_x += run.advance * wf;
+            // Advance the pen in unscaled glyph units — the `xform` scales the
+            // pen position by `wf`, so multiplying the advance here too would
+            // apply the width factor twice (and reverse a backward run's word
+            // order onto the wrong side). Matches `text_local_bounds`.
+            *cursor_x += run.advance;
         } else {
             for ch in seg.chars() {
                 match face.glyph(ch) {
                     Some(glyph) => {
                         emit_glyph(out, &glyph.strokes, *cursor_x);
                         emit_fill(fill_tris, &glyph.fill_tris, *cursor_x);
-                        *cursor_x += (glyph.advance + face.letter_spacing() * tracking) * wf;
+                        *cursor_x += glyph.advance + face.letter_spacing() * tracking;
                     }
                     None => {
                         warn_missing_glyph(font_name, ch);
-                        *cursor_x += (6.0 + face.letter_spacing() * tracking) * wf;
+                        *cursor_x += 6.0 + face.letter_spacing() * tracking;
                     }
                 }
             }
@@ -456,17 +460,17 @@ pub fn tessellate_text_run(
                         Some(glyph) => {
                             emit_glyph(&mut out, &glyph.strokes, cursor_x);
                             emit_fill(&mut fill_tris, &glyph.fill_tris, cursor_x);
-                            cursor_x += (glyph.advance + face.letter_spacing() * tracking) * wf;
+                            cursor_x += glyph.advance + face.letter_spacing() * tracking;
                         }
                         None => {
                             warn_missing_glyph(font_name, *c);
-                            cursor_x += (6.0 + face.letter_spacing() * tracking) * wf;
+                            cursor_x += 6.0 + face.letter_spacing() * tracking;
                         }
                     }
                 }
             }
             Tok::Space => cursor_x += face.word_spacing(),
-            Tok::Missing => cursor_x += (6.0 + face.letter_spacing() * tracking) * wf,
+            Tok::Missing => cursor_x += 6.0 + face.letter_spacing() * tracking,
             Tok::Deco(deco, op) => {
                 let (slot, y) = match deco {
                     Deco::Under => (&mut underline, UNDER_Y),