Place a peg's pivot with ⌃/⌘ rather than ⌥

⌥-drag does not survive the trip. Most Linux window managers grab Alt-drag to
move the window, so the page never sees the pointer and the gesture is simply
absent — on the machine it is absent from, with no error and nothing to find.
Reported from one.

⌃ (⌘ on a Mac) now places the pivot, which is the modifier the rest of this
stage already reaches for. ⌥ keeps working for anyone whose desktop leaves it
alone; ⇧ is deliberately not it, since it means CONSTRAIN everywhere else here —
uniform scale, 15° turn steps — and is what a snap to the child's corners will
want when this drag grows one.

The menu row says so, because a modifier nothing mentions is a modifier nobody
finds: "add peg · ⌃/⌘-drag its cross to place the pivot".

`peg.mjs` now asserts each modifier through real pointer events instead of
reading the handler, which is the only way this class of bug shows up — all
three place the pivot with a child drift of 0, and an unmodified drag still
translates.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HkinzDz1VtahZVsujAGRBD

frontend/src/arthur/ui/stage.cljs

@@ -325,9 +325,20 @@
             ;; to 8.8 from the middle, so the disc has to stop short of 5.2.
             [:circle.peg-grab
              {:cx px :cy py :r 5
-              ;; ⌥ moves the PIVOT instead of the peg, which is the pan-behind
+              ;; ⌃/⌘ moves the PIVOT instead of the peg, which is the pan-behind
               ;; split: a plain drag writes `pos` and carries the children with
               ;; it, and that is a translate, not a new pivot.
+              ;;
+              ;; NOT ⌥, which this was and which does not survive the trip. Most
+              ;; Linux window managers grab Alt-drag to move the window, so the
+              ;; page never sees the pointer at all and the gesture is simply
+              ;; missing — on the machine it is missing from, with no error. ⌥ is
+              ;; still accepted for anyone whose desktop leaves it alone, and the
+              ;; command key is the one the rest of this stage already reaches for.
+              ;;
+              ;; ⇧ is deliberately NOT it: it means CONSTRAIN everywhere else
+              ;; here — uniform scale, 15° turn steps — and it is what a snap to
+              ;; the child's corners would want when this drag grows one.
               :on-pointer-down
               (fn [^js event]
                 (.stopPropagation event)
@@ -335,7 +346,7 @@
                 (let [svg (.-ownerSVGElement (.-currentTarget event))
                       p   (xy svg event (:w ctx) (:h ctx))]
                   (.setPointerCapture svg (.-pointerId event))
-                  (if (.-altKey event)
+                  (if (or (.-ctrlKey event) (.-metaKey event) (.-altKey event))
                     (reset! repivot {:path path :p p})
                     (begin! ctx :move path p))))}]
             [:line.knob-arm {:x1 px :y1 (- py r) :x2 px :y2 (- py r 8)}]

frontend/src/arthur/ui/topbar.cljs

@@ -95,7 +95,7 @@
                  ;; measured part by hand — which is what `gesture/refusal` tells
                  ;; you to do, so it has to be reachable from somewhere.
                  {:label "add peg"
-                  :sub "A transform node over the selection, to pivot, turn and key from"
+                  :sub "A transform node over the selection · ⌃/⌘-drag its cross to place the pivot"
                   :disabled? (nil? one-node)
                   :on-click #(rf/dispatch [::ui/peg one-node])}]}]
        [snapshots/view]

frontend/test/browser/peg.mjs

@@ -201,45 +201,88 @@ try {
      String(dom2.cornerHit));
 
   if (dom2.grab) {
-    const before2 = await evalJS(`
+    // Every modifier that has to place the pivot. CDP modifiers: 1=alt, 2=ctrl,
-      const c = cljs.core, k = c.keyword, v = c.vector;
+    // 4=meta. ⌥ alone was the whole gesture once, and on a desktop whose window
-      const db = c.deref(re_frame.db.app_db);
+    // manager grabs Alt-drag the page never sees it — so each is asserted
-      const e = arthur.footage.store.entry(c.get(db, k('clip/current')));
+    // through real pointer events rather than by reading the handler.
-      const doc = c.get(e, k('clip'));
-      const res = arthur.domain.clip.resolver(doc, k('main'), c.get(e,k('store')),
-                                              arthur.domain.palette.index_of, null);
-      return Array.from(c.get(c.first(res.call(null, 0)), k('pts')));
-    `);
     const { x, y } = dom2.grab;
-    const steps = [['mousePressed', 0, 0], ['mouseMoved', -40, 25], ['mouseMoved', -80, 50],
+    let after2;
-                   ['mouseReleased', -80, 50]];
+    for (const [name, modifiers, sign] of [['alt', 1, -1], ['ctrl', 2, 1], ['meta', 4, -1]]) {
-    for (const [type, dx, dy] of steps) {
+      const pre = await evalJS(`
-      await send('Input.dispatchMouseEvent', {
+        const c = cljs.core, k = c.keyword, v = c.vector;
-        type, x: x + dx, y: y + dy, button: 'left', buttons: 1, clickCount: 1,
+        const db = c.deref(re_frame.db.app_db);
-        pointerType: 'mouse', modifiers: 1, // alt
+        const e = arthur.footage.store.entry(c.get(db, k('clip/current')));
-      });
+        const doc = c.get(e, k('clip'));
-      await sleep(90);
+        const nodes = c.get_in(doc, v(k('symbols'), k('main'), k('nodes')));
+        const pegId = c.get(c.get(nodes, k('shape')), k('parent'));
+        const res = arthur.domain.clip.resolver(doc, k('main'), c.get(e,k('store')),
+                                                arthur.domain.palette.index_of, null);
+        return {pts: Array.from(c.get(c.first(res.call(null, 0)), k('pts'))),
+                pos: c.clj__GT_js(c.get_in(nodes, v(pegId, k('channels'), v(k('xform'),k('pos')), k('value'))))};
+      `);
+      // Where the cross is NOW, since the previous modifier already moved it.
+      const g = await evalJS(`
+        const q = document.querySelector('.paint-overlay .handles .peg-grab');
+        const r = q && q.getBoundingClientRect();
+        return r ? {x: r.x + r.width/2, y: r.y + r.height/2} : null;
+      `);
+      const dx = 30 * sign, dy = 20 * sign;
+      for (const [type, fx, fy] of [['mousePressed', 0, 0], ['mouseMoved', dx/2, dy/2],
+                                    ['mouseMoved', dx, dy], ['mouseReleased', dx, dy]]) {
+        await send('Input.dispatchMouseEvent', {
+          type, x: g.x + fx, y: g.y + fy, button: 'left', buttons: 1, clickCount: 1,
+          pointerType: 'mouse', modifiers,
+        });
+        await sleep(90);
+      }
+      await sleep(450);
+      const post = await evalJS(`
+        const c = cljs.core, k = c.keyword, v = c.vector;
+        const db = c.deref(re_frame.db.app_db);
+        const e = arthur.footage.store.entry(c.get(db, k('clip/current')));
+        const doc = c.get(e, k('clip'));
+        const nodes = c.get_in(doc, v(k('symbols'), k('main'), k('nodes')));
+        const pegId = c.get(c.get(nodes, k('shape')), k('parent'));
+        const res = arthur.domain.clip.resolver(doc, k('main'), c.get(e,k('store')),
+                                                arthur.domain.palette.index_of, null);
+        return {pts: Array.from(c.get(c.first(res.call(null, 0)), k('pts'))),
+                pos: c.clj__GT_js(c.get_in(nodes, v(pegId, k('channels'), v(k('xform'),k('pos')), k('value'))))};
+      `);
+      const drift = Math.max(...pre.pts.map((b, i) => Math.abs(b - post.pts[i])));
+      const moved = Math.hypot(post.pos[0] - pre.pos[0], post.pos[1] - pre.pos[1]);
+      ok(drift < 1e-6, `${name}-drag places the pivot and moves NOTHING under the peg`,
+         `drift ${drift}`);
+      ok(moved > 2, `${name}-drag actually moved the pivot`, `by ${moved.toFixed(2)}`);
+      after2 = post;
+    }
+    // And a plain drag still translates, which is the other half of the split.
+    {
+      const g = await evalJS(`
+        const q = document.querySelector('.paint-overlay .handles .peg-grab');
+        const r = q && q.getBoundingClientRect();
+        return r ? {x: r.x + r.width/2, y: r.y + r.height/2} : null;
+      `);
+      const pre = after2;
+      for (const [type, fx] of [['mousePressed', 0], ['mouseMoved', 12], ['mouseReleased', 12]]) {
+        await send('Input.dispatchMouseEvent', {
+          type, x: g.x + fx, y: g.y, button: 'left', buttons: 1, clickCount: 1, pointerType: 'mouse',
+        });
+        await sleep(90);
+      }
+      await sleep(450);
+      const post = await evalJS(`
+        const c = cljs.core, k = c.keyword, v = c.vector;
+        const db = c.deref(re_frame.db.app_db);
+        const e = arthur.footage.store.entry(c.get(db, k('clip/current')));
+        const res = arthur.domain.clip.resolver(c.get(e, k('clip')), k('main'), c.get(e,k('store')),
+                                                arthur.domain.palette.index_of, null);
+        return Array.from(c.get(c.first(res.call(null, 0)), k('pts')));
+      `);
+      ok(Math.abs(post[0] - pre.pts[0]) > 2, 'and an UNMODIFIED drag still translates the child',
+         `dx=${(post[0] - pre.pts[0]).toFixed(2)}`);
     }
-    await sleep(500);
-    const after2 = await evalJS(`
-      const c = cljs.core, k = c.keyword, v = c.vector;
-      const db = c.deref(re_frame.db.app_db);
-      const e = arthur.footage.store.entry(c.get(db, k('clip/current')));
-      const doc = c.get(e, k('clip'));
-      const nodes = c.get_in(doc, v(k('symbols'), k('main'), k('nodes')));
-      const pegId = c.get(c.get(nodes, k('shape')), k('parent'));
-      const res = arthur.domain.clip.resolver(doc, k('main'), c.get(e,k('store')),
-                                              arthur.domain.palette.index_of, null);
-      return {pos: c.clj__GT_js(c.get_in(nodes, v(pegId, k('channels'), v(k('xform'),k('pos')), k('value')))),
-              pts: Array.from(c.get(c.first(res.call(null, 0)), k('pts'))),
-              refusal: c.clj__GT_js(c.get_in(db, v(k('ui'), k('refusal'))))};
-    `);
-    const drift = Math.max(...before2.map((b, i) => Math.abs(b - after2.pts[i])));
-    console.log('after alt-drag: peg pos', JSON.stringify(after2.pos), 'child drift', drift);
-    ok(drift < 1e-6, 'alt-dragging the cross moved NOTHING under the peg', `drift ${drift}`);
-    ok(Math.abs(after2.pos[0] - made.pegPos[0]) > 2, 'but the pivot did move',
-       `${JSON.stringify(made.pegPos)} -> ${JSON.stringify(after2.pos)}`);
   }
+
   console.log(failures ? `\n${failures} FAILED` : '\nPASS: a peg can be made, moved, and have its pivot placed');
 } finally {
   if (ws) ws.close();