Show "Make substep of…" as a hover submenu listing all steps

Replaces the number-entry prompt with a scrollable side panel (so
large guides don't overflow the screen) listing every eligible step;
clicking one immediately re-parents the step. Context menus now
support submenu items in general via contextMenu().

app/renderer/editor.js

@@ -731,7 +731,18 @@ class GuideEditor {
           this.selectStep(step.stepId);
           contextMenu(e.clientX, e.clientY, [
             { label: 'Add substep', action: () => this.addSubstep(step.stepId) },
-            { label: 'Make substep of…', action: () => this.makeSubstepOf(step.stepId) },
+            {
+              label: 'Make substep of…',
+              submenu: () => {
+                const subtreeIds = new Set([step.stepId, ...this.getStepDescendantIds(step.stepId)]);
+                return this.steps
+                  .filter((s) => !subtreeIds.has(s.stepId))
+                  .map((s) => ({
+                    label: `${numbers.get(s.stepId)}  ${s.title || 'Untitled step'}`,
+                    action: () => this.makeSubstepOf(step.stepId, s.stepId),
+                  }));
+              },
+            },
             { label: 'Duplicate step', action: () => this.duplicateSelectedStep() },
             'sep',
             { label: 'Move up', action: () => this.moveSelectedStep(-1) },
@@ -1306,48 +1317,37 @@ class GuideEditor {
     return result;
   }
 
-  async makeSubstepOf(stepId) {
+  async makeSubstepOf(stepId, targetStepId) {
     const step = this.stepMap.get(stepId);
-    if (!step) return;
+    const target = this.stepMap.get(targetStepId);
+    if (!step || !target) return;
     const numbers = stepNumberMap(this.steps);
-    const input = await dialogs.promptText({
-      title: 'Make substep',
-      label: 'Make substep of step #',
-      placeholder: 'e.g. 2',
-    });
-    if (input == null) return;
-    const target = input.trim().replace(/^#/, '');
-    const targetId = this.steps.find((s) => numbers.get(s.stepId) === target)?.stepId;
-    if (!targetId) {
-      this.onToast(`No step numbered "${target}".`, { error: true });
-      return;
-    }
     const subtreeIds = new Set([stepId, ...this.getStepDescendantIds(stepId)]);
-    if (subtreeIds.has(targetId)) {
+    if (subtreeIds.has(targetStepId)) {
       this.onToast('A step cannot be made a substep of itself or one of its own substeps.', { error: true });
       return;
     }
-    if (step.parentStepId === targetId) {
+    if (step.parentStepId === targetStepId) {
-      this.onToast(`“${step.title || 'Untitled step'}” is already a substep of step ${target}.`);
+      this.onToast(`“${step.title || 'Untitled step'}” is already a substep of step ${numbers.get(targetStepId)}.`);
       return;
     }
 
-    step.parentStepId = targetId;
+    step.parentStepId = targetStepId;
     await api.step.save({ guideId: this.guideId, step });
 
     // Move the step (with its own substeps) to sit right after the target
     // step's existing substeps, so it becomes the target's last substep.
     const order = this.steps.map((s) => s.stepId);
     const remaining = order.filter((id) => !subtreeIds.has(id));
-    const targetSubtree = new Set([targetId, ...this.getStepDescendantIds(targetId)]);
+    const targetSubtree = new Set([targetStepId, ...this.getStepDescendantIds(targetStepId)]);
-    let insertAt = remaining.indexOf(targetId) + 1;
+    let insertAt = remaining.indexOf(targetStepId) + 1;
     while (insertAt < remaining.length && targetSubtree.has(remaining[insertAt])) insertAt++;
     const movedBlock = order.filter((id) => subtreeIds.has(id));
     remaining.splice(insertAt, 0, ...movedBlock);
     await api.step.reorder({ guideId: this.guideId, order: remaining });
 
     await this.reload(stepId);
-    this.onToast(`“${step.title || 'Untitled step'}” is now a substep of step ${target}.`);
+    this.onToast(`“${step.title || 'Untitled step'}” is now a substep of step ${numbers.get(targetStepId)}.`);
   }
 
   async duplicateSelectedStep() {

app/renderer/style.css

@@ -731,6 +731,25 @@ fieldset legend {
 }
 .ctx-menu .mi:hover { background: var(--panel-2); }
 .ctx-menu .mi.danger { color: var(--danger); }
+.ctx-menu .mi.disabled {
+  color: var(--muted);
+  cursor: default;
+}
+.ctx-menu .mi.disabled:hover { background: none; }
+.ctx-menu .mi.has-submenu {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  gap: 10px;
+}
+.ctx-menu .mi .submenu-arrow {
+  color: var(--muted);
+  font-size: 12px;
+}
+.ctx-submenu {
+  max-height: min(360px, calc(100vh - 24px));
+  overflow-y: auto;
+}
 .ctx-menu hr {
   margin: 6px 0;
   border: 0;

app/renderer/util.js

@@ -119,15 +119,55 @@ function promptDialog(title, { value = '', label = 'Name' } = {}) {
   });
 }
 
-/** Context menu at (x, y); items: [{label, danger, action}] or 'sep'. */
+/**
+ * Context menu at (x, y).
+ * items: [{label, danger, action}] | [{label, submenu}] | 'sep'.
+ * `submenu` is an array (or a function returning one) of the same item
+ * shapes, shown in a scrollable panel beside the item on hover.
+ */
 function contextMenu(x, y, items) {
   document.querySelectorAll('.ctx-menu').forEach((n) => n.remove());
   const menu = el('div.ctx-menu', { style: { left: `${x}px`, top: `${y}px` } });
+  let openSubmenu = null;
+  const closeSubmenu = () => {
+    if (openSubmenu) { openSubmenu.remove(); openSubmenu = null; }
+  };
+  const closeAll = () => { closeSubmenu(); menu.remove(); };
   for (const item of items) {
-    if (item === 'sep') { menu.append(el('hr')); continue; }
+    if (item === 'sep') { menu.append(el('hr', { onMouseEnter: closeSubmenu })); continue; }
+    if (item.submenu) {
+      const mi = el('div.mi.has-submenu', {
+        onMouseEnter: () => {
+          closeSubmenu();
+          const subItems = typeof item.submenu === 'function' ? item.submenu() : item.submenu;
+          const sub = el('div.ctx-menu.ctx-submenu');
+          if (!subItems.length) {
+            sub.append(el('div.mi.disabled', {}, 'Nothing else to choose'));
+          }
+          for (const subItem of subItems) {
+            if (subItem === 'sep') { sub.append(el('hr')); continue; }
+            sub.append(el('div.mi', {
+              className: `mi${subItem.danger ? ' danger' : ''}`,
+              onClick: () => { closeAll(); subItem.action(); },
+            }, subItem.label));
+          }
+          document.body.append(sub);
+          const miRect = mi.getBoundingClientRect();
+          sub.style.left = `${miRect.right + 2}px`;
+          sub.style.top = `${miRect.top}px`;
+          const subRect = sub.getBoundingClientRect();
+          if (subRect.right > innerWidth) sub.style.left = `${Math.max(6, miRect.left - subRect.width - 2)}px`;
+          if (subRect.bottom > innerHeight) sub.style.top = `${Math.max(6, innerHeight - subRect.height - 6)}px`;
+          openSubmenu = sub;
+        },
+      }, el('span', {}, item.label), el('span.submenu-arrow', {}, '›'));
+      menu.append(mi);
+      continue;
+    }
     menu.append(el('div.mi', {
       className: `mi${item.danger ? ' danger' : ''}`,
-      onClick: () => { menu.remove(); item.action(); },
+      onMouseEnter: closeSubmenu,
+      onClick: () => { closeAll(); item.action(); },
     }, item.label));
   }
   document.body.append(menu);
@@ -135,7 +175,7 @@ function contextMenu(x, y, items) {
   if (rect.right > innerWidth) menu.style.left = `${innerWidth - rect.width - 6}px`;
   if (rect.bottom > innerHeight) menu.style.top = `${innerHeight - rect.height - 6}px`;
   setTimeout(() => {
-    document.addEventListener('click', () => menu.remove(), { once: true });
+    document.addEventListener('click', () => closeAll(), { once: true });
   }, 0);
 }