feat(arc): keep ARC Continue drawing arcs until ended (#327)

The Continue option committed a single tangent-continuing arc and left
the command. Now each picked end point commits its arc and re-anchors at
that arc's free end, so the user keeps drawing tangent-continuing arcs
until ending the run with Enter/Esc. A degenerate (collinear) pick stays
active instead of cancelling.

Because arcs now commit via CmdResult::CommitEntity (repeating) rather
than CommitAndExit, advance the ARC_CONT continuation anchor in the
CommitEntity arm too — guarded to line/arc so non-continuable repeats
(point/ray/spline) leave it untouched. This also lets a LINE run feed a
following ARC Continue.

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

src/app/command_driver.rs

@@ -218,6 +218,17 @@ impl OpenCADStudio {
                 }
             }
             CmdResult::CommitEntity(entity) => {
+                // A line/arc drawn by a repeating command advances the ARC_CONT
+                // continuation anchor, so ending one run and launching another
+                // keeps continuing from the last segment (mirrors the
+                // CommitAndExit arm). Non-continuable repeats (point/ray/spline)
+                // leave the anchor untouched. (#327)
+                if matches!(
+                    entity,
+                    acadrust::EntityType::Line(_) | acadrust::EntityType::Arc(_)
+                ) {
+                    self.update_cont_anchor(&entity);
+                }
                 let label = self.history_label_from_active_cmd(i, "ENTITY");
                 self.push_undo_snapshot(i, label);
                 self.commit_entity(entity);

src/modules/draw/draw/arc.rs

@@ -1359,9 +1359,19 @@ impl CadCommand for ArcContCommand {
     fn on_point(&mut self, pt: DVec3) -> CmdResult {
         match arc_continue(self.s, self.tangent, pt, self.ctrl) {
             Some((center, radius, sa, ea)) => {
-                CmdResult::CommitAndExit(make_arc(center, radius, sa, ea))
+                let arc = make_arc(center, radius, sa, ea);
+                // 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).
+                if let Some((end, tangent)) = continue_anchor(&arc, Some(pt)) {
+                    self.s = end;
+                    self.tangent = tangent;
+                }
+                CmdResult::CommitEntity(arc)
             }
-            None => CmdResult::Cancel,
+            // A degenerate pick (no arc through these points) shouldn't end the
+            // whole run — stay active and wait for the next end point.
+            None => CmdResult::NeedPoint,
         }
     }
     fn on_enter(&mut self) -> CmdResult {