Fix #494: Pen + Cmd edits the path being drawn; Pen + Alt reshapes segments; handle drags fixed and fast

Reported: with the Pen there was no way to edit curves in place as Ctrl does in Illustrator on
Windows (Cmd on the Mac), segments couldn't be grabbed, and the curve-editing tools felt slow and
sometimes didn't take a handle.

- Cmd/Ctrl held at a press with any tool but a selection tool now borrows the selection tool in the
  engine (Session::pointer), not in the canvas: the selection tool chosen last, or Direct Selection
  for the Pen, Curvature and anchor tools until one is chosen. The tool lent to isn't deactivated,
  so the Pen goes on drawing its path after the release while that path stays selected; it no
  longer draws on another open path selected meanwhile. Agents reach it with pointer_gesture
  mods.cmd. With Cmd held the pointer is the borrowed tool's. Choosing a tool or switching
  documents mid-gesture gives the tool back first.
- Pen + Alt over a segment of a selected path reshapes it, as the Anchor Point tool does.
- The handles shown are the handles that drag (one helper for Direct Selection, the Anchor Point
  tool and Pen + Alt): Direct Selection now drags the handles of a path selected as a whole (as
  the Pen leaves it, so Cmd + drag of a handle while drawing works), the Anchor Point tool no
  longer grabs handles that Show handles when multiple anchors are selected hides, the nearest
  handle wins, and a handle shorter than the tolerance leaves its anchor to be picked. The anchor
  tools pick within Selection & Anchor Display > Tolerance instead of a fixed 4 px.
- path.reshapeSegment keeps a smooth anchor at either end smooth (its other handle turns with the
  moved one) instead of kinking it.
- A dragged handle gathered its smart guide targets from the whole document on every pointer move
  (21 ms per move on 20,000 paths): HandleSnap now gathers them once per drag (1 ms).
  vectorcraft-cli perf measures handle and segment drags on a 5,000-anchor path.
- catalog::is_selection_tool and catalog::edits_anchors replace the UI's own lists.
- Tests in tools, engine and MCP (headless pointer_gesture); docs/mcp.md, control-protocol.md,
  ROADMAP.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/vectorcraft-cli/src/perf.rs

@@ -70,6 +70,49 @@ fn load_average() -> Option<f64> {
     text.split_whitespace().map(|t| t.trim_matches(|c| c == '{' || c == '}')).find_map(|t| t.parse().ok())
 }
 
+/// Milliseconds per pointer move of a Direct Selection drag of a handle, then of a segment, of a
+/// 5,000-anchor wave of smooth anchors added on top of the synthetic `n`-path document.
+fn edit_drags(n: usize) -> Result<(f64, f64), String> {
+    use vectorcraft_engine::tools::{Mods, PointerEvent, PointerKind};
+    use vectorcraft_geom::{Anchor, PathData, SubPath, Vec2};
+    let mut doc = synthetic(n)?;
+    let l = doc.layers.first().map(|l| l.id);
+    let id = doc.alloc_id();
+    // Anchors 2 pt apart, up and down by 20 pt, their handles 0.6 pt long.
+    let anchor = |i: usize| {
+        let p = Point::new(i as f64 * 2.0, if i.is_multiple_of(2) { 500.0 } else { 520.0 });
+        Anchor::smooth(p, p + Vec2::new(0.6, 0.0))
+    };
+    let path = PathData::single(SubPath::new((0..5000).map(anchor).collect(), false));
+    doc.insert(l, usize::MAX, Node::path(id, path, Appearance::default_art())).map_err(|e| e.to_string())?;
+    let mut s = vectorcraft_engine::Session::new();
+    s.add_document(doc, None);
+    let view = vectorcraft_engine::ViewInfo { zoom: 8.0, ..Default::default() };
+    let err = |e: vectorcraft_engine::EngineError| e.to_string();
+    let mut drag = |down: Point| -> Result<f64, String> {
+        let ev = |kind, y: f64| PointerEvent { kind, pos: down + Vec2::new(0.0, y), mods: Mods::default(), pressure: 1.0 };
+        s.execute("select.anchors", &json!({"id": id.0, "anchors": [[0, 400]]})).map_err(err)?;
+        s.select_tool("directSelection", view).map_err(err)?;
+        let undo = s.doc().map_err(err)?.history.undo.len();
+        s.pointer(&ev(PointerKind::Down, 0.0), view).map_err(err)?;
+        let mut y = 0.0;
+        let ms = median_ms(9, || {
+            y += 3.0;
+            // A failed move shows as the missing undo step below.
+            let _ = s.pointer(&ev(PointerKind::Drag, y), view);
+        });
+        s.pointer(&ev(PointerKind::Up, y), view).map_err(err)?;
+        if s.doc().map_err(err)?.history.undo.len() != undo + 1 {
+            return Err(format!("the drag from {down:?} made no undo step"));
+        }
+        Ok(ms)
+    };
+    // Anchor 400 is at (800, 500): its outgoing handle's end, then its segment to anchor 401.
+    let handle = drag(Point::new(800.6, 500.0))?;
+    let segment = drag(Point::new(801.0, 510.0))?;
+    Ok((handle, segment))
+}
+
 pub fn run(args: &[String]) -> Result<(), String> {
     let mut n = 50_000usize;
     let mut it = args.iter();
@@ -145,6 +188,15 @@ pub fn run(args: &[String]) -> Result<(), String> {
         }
     });
     rows.push(("Pathfinder Unite, 1,000 paths", unite, 150.0));
+
+    // Path editing: one pointer move of a Direct Selection drag (the tool event and the preview it
+    // applies), on a 5,000-anchor path among the synthetic paths.
+    let (handle, segment) = edit_drags(n).unwrap_or_else(|e| {
+        failed = Some(e);
+        (0.0, 0.0)
+    });
+    rows.push(("handle drag, 5,000-anchor path (per move)", handle, 8.0));
+    rows.push(("segment drag, 5,000-anchor path (per move)", segment, 8.0));
     if let Some(e) = failed {
         return Err(e);
     }