feat(leader): dynamic MLEADER text placement, grips, and consistent arrows

Reworks MLEADER text/leader geometry and grip editing, and aligns LEADER
to MLEADER's conventions (kept as separate entities).

Text & landing (render path):
- Text is side-anchored on the leader-facing edge and reads outward; the
  side, alignment and the horizontal landing are recomputed every frame
  from the text grip's position relative to the leader, so moving the
  arrow or the text re-mirrors the whole layout and the landing stays
  attached to the text's near edge.
- Fixes #49: text was centred on the leader endpoint regardless of side.

Grips:
- Text-location grip plus an MTEXT-style triangle wrap-width grip at the
  box's far edge; dragging it sets the MText wrap width.
- Multifunction grip menu restored and made functional: leader-line
  vertices offer Add Leader / Remove Leader (Add grabs the new arrow so it
  follows the cursor — click places, Esc removes it); the text grip offers
  Move Independent (text only) and Move with Leader (translates the whole
  multileader via a move-all sentinel grip).

Arrows:
- LEADER and MLEADER arrowheads now render at the same size (text height),
  matching previews.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

src/app/mod.rs

@@ -205,6 +205,10 @@ pub(super) struct OpenCADStudio {
     /// until dismissed (click outside, ESC, cursor leaves the grip).
     grip_popup: Option<GripPopup>,
     grip_pending: Option<GripPendingValue>,
+    /// A leader line just added via the "Add Leader" grip menu whose arrow is
+    /// being placed (follows the cursor). `(entity handle, new-arrow grip id)`.
+    /// Esc before the placement click removes it again.
+    grip_add_provisional: Option<(acadrust::Handle, usize)>,
     /// Open Quick Select panel state. `None` = panel closed. Filters are
     /// applied via `Message::QSelectApply`; the panel is dismissed on
     /// Apply / Cancel / Esc / outside-click.
@@ -980,6 +984,7 @@ impl OpenCADStudio {
             grip_hover: None,
             grip_popup: None,
             grip_pending: None,
+            grip_add_provisional: None,
             qselect: None,
             show_ucs_icon: true,
             show_viewcube: true,

src/app/update.rs

@@ -1283,6 +1283,19 @@ impl OpenCADStudio {
                 // A hot grip (click-move-click placement in progress) ends on
                 // Escape, leaving the entity at its last previewed position.
                 if self.tabs[self.active_tab].active_grip.take().is_some() {
+                    // An Add-Leader arrow being placed: Esc removes it again.
+                    if let Some((h, gid)) = self.grip_add_provisional.take() {
+                        let i = self.active_tab;
+                        use crate::entities::traits::EntityTypeOps;
+                        if let Some(e) = self.tabs[i].scene.document.get_entity_mut(h) {
+                            e.apply_grip_menu(
+                                gid,
+                                crate::scene::object::GripMenuAction::RemoveLeader,
+                            );
+                        }
+                        self.tabs[i].scene.bump_geometry();
+                        self.refresh_selected_grips();
+                    }
                     self.tabs[self.active_tab].snap_result = None;
                     self.refresh_properties();
                     return Task::none();
@@ -2516,6 +2529,8 @@ impl OpenCADStudio {
                         return Task::none();
                     }
                     self.tabs[i].active_grip = None;
+                    // Placement confirmed — keep the just-added leader.
+                    self.grip_add_provisional = None;
                     self.tabs[i].snap_result = None;
                     self.refresh_properties();
                     return Task::none();
@@ -3310,20 +3325,33 @@ impl OpenCADStudio {
                 };
                 use crate::entities::traits::EntityTypeOps;
                 use crate::scene::object::GripMenuAction;
-                if matches!(item.action, GripMenuAction::Stretch) {
-                    // Stretch = move this grip. Engage it so the next click
-                    // places it (click-move-click) — same as picking the grip
-                    // directly in the viewport. Without this the menu just
+                if matches!(
+                    item.action,
+                    GripMenuAction::Stretch
+                        | GripMenuAction::MoveWithLeader
+                        | GripMenuAction::MoveIndependent
+                ) {
+                    // Stretch / Move = grab this grip. Engage it so the next
+                    // click places it (click-move-click) — same as picking the
+                    // grip directly in the viewport. Without this the menu just
                     // closed and the grip never became hot (issue #48).
                     if let Some(g) = self.tabs[i]
                         .selected_grips
                         .iter()
                         .find(|g| g.id == popup.grip_id)
                     {
+                        // "Move with Leader" drags the whole multileader; the
+                        // others move just the picked grip.
+                        let (grip_id, is_translate) =
+                            if matches!(item.action, GripMenuAction::MoveWithLeader) {
+                                (crate::entities::multileader::MOVE_ALL_GRIP, true)
+                            } else {
+                                (popup.grip_id, g.is_midpoint)
+                            };
                         self.tabs[i].active_grip = Some(GripEdit {
                             handle: popup.handle,
-                            grip_id: popup.grip_id,
-                            is_translate: g.is_midpoint,
+                            grip_id,
+                            is_translate,
                             origin_world: g.world,
                             last_world: g.world,
                         });
@@ -3351,6 +3379,27 @@ impl OpenCADStudio {
                 }
                 // One-shot action — apply immediately.
                 self.push_undo_snapshot(i, item.label);
+                // For Add Leader, the new arrow becomes the last grip; remember
+                // its id so we can grab it for placement right after.
+                let add_leader_gid = if matches!(item.action, GripMenuAction::AddLeader) {
+                    self.tabs[i]
+                        .scene
+                        .document
+                        .get_entity(popup.handle)
+                        .and_then(|e| match e {
+                            acadrust::EntityType::MultiLeader(ml) => Some(
+                                ml.context
+                                    .leader_roots
+                                    .iter()
+                                    .flat_map(|r| r.lines.iter())
+                                    .map(|l| l.points.len())
+                                    .sum::<usize>(),
+                            ),
+                            _ => None,
+                        })
+                } else {
+                    None
+                };
                 if let Some(entity) = self
                     .tabs[i]
                     .scene
@@ -3363,6 +3412,22 @@ impl OpenCADStudio {
                 self.tabs[i].dirty = true;
                 self.refresh_selected_grips();
                 self.refresh_properties();
+                // Grab the new arrow so it follows the cursor (click places it,
+                // Esc removes it).
+                if let Some(new_gid) = add_leader_gid {
+                    if let Some(g) =
+                        self.tabs[i].selected_grips.iter().find(|g| g.id == new_gid)
+                    {
+                        self.tabs[i].active_grip = Some(GripEdit {
+                            handle: popup.handle,
+                            grip_id: new_gid,
+                            is_translate: false,
+                            origin_world: g.world,
+                            last_world: g.world,
+                        });
+                        self.grip_add_provisional = Some((popup.handle, new_gid));
+                    }
+                }
                 Task::none()
             }