fix(undo): grip-drag history entry + mid-command Ctrl+Z steps (#332)

Grip drags mutated the document without ever pushing history — dragging
a polyline vertex (or any grip) could not be undone. The release-commit
now swaps the pre-drag backup in, snapshots that PRE state as a "GRIP"
entry, swaps the dragged result back and clears the redo stack; the
Esc-cancel path is unchanged and a no-move engaging click records
nothing.

Ctrl+Z during a drawing command steps the command instead of the
document undo swallowing the in-progress object (which also killed the
active command): new CadCommand::on_undo_step hook, consulted before
undo_active_tab. PLINE pops its last vertex (shared with the U option),
LINE reverts the last committed segment and keeps drawing from the
previous point (rides its existing U/UndoDocument path), and ARC
Continue reverts the last arc and resumes from the prior anchor with
the correct tangent via a new anchor history. With nothing placed yet
each falls through to the document undo.

Also drops the two warnings the #336 work left behind (unused Entity
import, dead Snapper::override_active).

Closes #332

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/app/update/mod.rs

@@ -3709,6 +3709,17 @@ impl OpenCADStudio {
             Message::PspaceCommand => Task::done(Message::ExitViewport),
 
             Message::Undo => {
+                // Mid-command Ctrl+Z: a drawing command steps itself back
+                // (PLINE pops the last vertex) instead of the document undo
+                // swallowing the whole in-progress object.
+                let i = self.active_tab;
+                let step = self.tabs[i]
+                    .active_cmd
+                    .as_mut()
+                    .and_then(|c| c.on_undo_step());
+                if let Some(r) = step {
+                    return self.apply_cmd_result(r);
+                }
                 self.undo_active_tab();
                 Task::none()
             }

src/app/update/viewport.rs

@@ -1829,11 +1829,29 @@ pub(super) fn on_tick(&mut self, t: Instant) -> Task<Message> {
                         return Task::none();
                     }
                     self.tabs[i].active_grip = None;
-                    // Commit the grip drag: keep the doc's dragged geometry
-                    // (drop the cancel backup), un-hide the edited entity and
-                    // re-tessellate the base once, dropping the overlay preview.
+                    // Commit the grip drag: keep the doc's dragged geometry,
+                    // un-hide the edited entity and re-tessellate the base
+                    // once, dropping the overlay preview.
                     if let Some(h) = self.grip_preview_handle.take() {
-                        self.grip_original = None;
+                        // Undo entry for the drag (#332): the pre-drag backup
+                        // swaps in, the PRE state is snapshotted, then the
+                        // dragged result swaps back. Without this a grip edit
+                        // (e.g. reshaping a polyline vertex) was un-undoable —
+                        // the drag mutated the document without any history.
+                        if let Some(orig) = self.grip_original.take() {
+                            if let Some(e) = self.tabs[i].scene.document.get_entity_mut(h) {
+                                let dragged = std::mem::replace(e, orig);
+                                let snap = self.capture_history_snapshot(i, "GRIP");
+                                if let Some(e2) =
+                                    self.tabs[i].scene.document.get_entity_mut(h)
+                                {
+                                    *e2 = dragged;
+                                }
+                                self.tabs[i].history.undo_stack.push(snap);
+                                self.tabs[i].history.redo_stack.clear();
+                                self.tabs[i].dirty = true;
+                            }
+                        }
                         self.grip_text_verts = Vec::new();
                         self.grip_text_slide = false;
                         self.tabs[i].scene.hidden.remove(&h);

src/command.rs

@@ -1218,6 +1218,14 @@ pub trait CadCommand: Send {
     /// during TRIM and trims during EXTEND, #336). Default no-op.
     fn set_shift(&mut self, _shift: bool) {}
 
+    /// Mid-command Ctrl+Z: a multi-point drawing command can take the undo
+    /// itself (PLINE pops its last vertex) instead of the document undo
+    /// swallowing the whole in-progress object. `None` (default) lets the
+    /// normal document undo run.
+    fn on_undo_step(&mut self) -> Option<CmdResult> {
+        None
+    }
+
     /// Called when the user left-clicks in the viewport (point pick).
     fn on_point(&mut self, pt: DVec3) -> CmdResult;
 

src/modules/draw/draw/arc.rs

@@ -1334,6 +1334,10 @@ pub struct ArcContCommand {
     tangent: DVec3,
     /// Live Ctrl state (set via `set_ctrl`): flips the arc to the other way.
     ctrl: bool,
+    /// Anchor history for mid-command Ctrl+Z: the (start, tangent) each
+    /// committed arc was drawn from, so undoing a segment resumes the run
+    /// from the prior anchor instead of ending it.
+    history: Vec<(DVec3, DVec3)>,
 }
 
 impl ArcContCommand {
@@ -1342,6 +1346,7 @@ impl ArcContCommand {
             s,
             tangent,
             ctrl: false,
+            history: Vec::new(),
         }
     }
 }
@@ -1360,6 +1365,9 @@ impl CadCommand for ArcContCommand {
         match arc_continue(self.s, self.tangent, pt, self.ctrl) {
             Some((center, radius, sa, ea)) => {
                 let arc = make_arc(center, radius, sa, ea);
+                // Remember the anchor this arc was drawn from — mid-command
+                // Ctrl+Z reverts the commit and resumes from here.
+                self.history.push((self.s, self.tangent));
                 // Keep drawing: re-anchor at the arc just committed so the next
                 // click starts another tangent-continuing arc from its end,
                 // until the user ends the run with Enter/Esc (#327).
@@ -1374,6 +1382,15 @@ impl CadCommand for ArcContCommand {
             None => CmdResult::NeedPoint,
         }
     }
+    fn on_undo_step(&mut self) -> Option<CmdResult> {
+        // Ctrl+Z mid-run: revert the last committed arc and resume from the
+        // anchor it was drawn from. With none committed this run, the
+        // document undo takes over.
+        let (s, tangent) = self.history.pop()?;
+        self.s = s;
+        self.tangent = tangent;
+        Some(CmdResult::UndoDocument)
+    }
     fn on_enter(&mut self) -> CmdResult {
         CmdResult::Cancel
     }

src/modules/draw/draw/line.rs

@@ -198,6 +198,16 @@ impl CadCommand for LineCommand {
         }
     }
 
+    fn on_undo_step(&mut self) -> Option<CmdResult> {
+        // Ctrl+Z while drawing = the U option: revert the last committed
+        // segment and keep drawing from the previous point. With nothing
+        // placed yet the document undo takes over.
+        if self.points.is_empty() {
+            return None;
+        }
+        self.on_text_input("U")
+    }
+
     fn on_mouse_move(&mut self, pt: DVec3) -> Option<WireModel> {
         let last = *self.points.last()?;
         // With a deferred first tangent, slide the rubber band's start point

src/modules/draw/draw/polyline.rs

@@ -64,6 +64,36 @@ impl PlineCommand {
         }
     }
 
+    /// Drop the last placed vertex but keep drawing (#352): the U option and
+    /// mid-command Ctrl+Z both land here. Repeatable down to (and including)
+    /// the start point.
+    fn undo_last_vertex(&mut self) -> CmdResult {
+        if self.vertices.is_empty() {
+            return CmdResult::NeedPoint;
+        }
+        self.vertices.pop();
+        self.bulges.pop();
+        // Restore the exit tangent of the segment that is now last so a
+        // following Arc segment stays tangent-continuous.
+        let n = self.vertices.len();
+        self.last_tangent = if n >= 2 {
+            seg_exit_tangent(self.vertices[n - 2], self.vertices[n - 1], self.bulges[n - 2])
+        } else {
+            None
+        };
+        match n {
+            // Start point undone too — back to "Specify start point".
+            0 => CmdResult::NeedPoint,
+            // One vertex left: the live entity needs two, so it leaves the
+            // document until the next point re-creates it.
+            1 => match self.live_handle.take() {
+                Some(h) => CmdResult::RemoveLiveEntity(h),
+                None => CmdResult::NeedPoint,
+            },
+            _ => self.sync_live(false, false),
+        }
+    }
+
     /// Build the result that publishes the current vertices to the document:
     /// create the live entity at the 2nd vertex, then replace it in place as
     /// more vertices land. `finish` ends the command (used for close/done).
@@ -348,36 +378,21 @@ impl CadCommand for PlineCommand {
             // Undo: drop the last placed vertex but keep drawing (#352).
             // Repeatable — each U backs off one more segment, down to (and
             // including) the start point.
-            "U" | "UNDO" => {
-                if self.vertices.is_empty() {
-                    return Some(CmdResult::NeedPoint);
-                }
-                self.vertices.pop();
-                self.bulges.pop();
-                // Restore the exit tangent of the segment that is now last so
-                // a following Arc segment stays tangent-continuous.
-                let n = self.vertices.len();
-                self.last_tangent = if n >= 2 {
-                    seg_exit_tangent(self.vertices[n - 2], self.vertices[n - 1], self.bulges[n - 2])
-                } else {
-                    None
-                };
-                Some(match n {
-                    // Start point undone too — back to "Specify start point".
-                    0 => CmdResult::NeedPoint,
-                    // One vertex left: the live entity needs two, so it leaves
-                    // the document until the next point re-creates it.
-                    1 => match self.live_handle.take() {
-                        Some(h) => CmdResult::RemoveLiveEntity(h),
-                        None => CmdResult::NeedPoint,
-                    },
-                    _ => self.sync_live(false, false),
-                })
-            }
+            "U" | "UNDO" => Some(self.undo_last_vertex()),
             _ => None,
         }
     }
 
+    fn on_undo_step(&mut self) -> Option<CmdResult> {
+        // Ctrl+Z while drawing steps back one vertex; with nothing placed
+        // yet the document undo takes over.
+        if self.vertices.is_empty() {
+            None
+        } else {
+            Some(self.undo_last_vertex())
+        }
+    }
+
     fn on_mouse_move(&mut self, pt: DVec3) -> Option<WireModel> {
         let pt = pt.as_vec3();
         // The committed vertices already render as a real document entity, so

src/modules/draw/modify/trim.rs

@@ -2393,7 +2393,6 @@ fn fence_pieces(
     window: Option<[[f64; 2]; 2]>,
     extend: bool,
 ) -> Option<Vec<EntityType>> {
-    use acadrust::entities::Entity as _;
     // Sentinel handle: keeps the self-exclusion in *_seg_ts from matching any
     // real boundary geo while the piece is being re-picked.
     const TMP: u64 = u64::MAX - 7;

src/snap.rs

@@ -205,9 +205,6 @@ impl Snapper {
         }
     }
 
-    pub fn override_active(&self) -> bool {
-        self.override_saved.is_some()
-    }
 
     /// Whether temporary tracking points are being acquired and drawn: OTRACK
     /// on, or the Extension object snap on. Extension tracks a segment's line