fix(browse): dblclick navigates; show virtual canonical folders at project root

#5 — Double-click on a folder no longer toggles collapse.

Root cause: the single-click handler called tree.render() immediately,
which replaced the clicked row element. The browser's double-click
detection requires the second click to land on the SAME target as the
first, so dblclick never fired for folders.

Fix: defer the single-click toggle by 220ms. A pending dblclick within
the window cancels the toggle and runs navigateIntoFolder instead.
Modifier-clicks (shift/alt for recursive) and ZIP expands skip the
deferral — they're never followed by a dblclick navigation.

#3 — Browse at /<project>/ now always shows the four canonical
folders (archive, working, staging, reviewing) even when they don't
yet exist on disk. Each missing folder is synthesized client-side as
a "virtual" row: muted icon + label + "(empty)" hint, double-clickable
to navigate. zddc-server already serves an empty listing for these
paths (commit 3fc3717), so navigation into a virtual folder works
without 404 and the user lands in a sensible empty workspace.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

browse/css/tree.css

@@ -313,6 +313,22 @@ html, body {
     font-weight: 500;
 }
 
+/* Virtual rows: synthesized client-side for folders that aren't on
+   disk yet (canonical project folders). Rendered muted so the user
+   reads them as "available but empty" rather than ordinary entries.
+   Hover/select states still apply; the hint sits to the right of the
+   label. */
+.tree-row--virtual .tree-name__icon,
+.tree-row--virtual .tree-name__label {
+    opacity: 0.65;
+}
+.tree-name__hint {
+    margin-left: 0.5rem;
+    font-size: 0.78rem;
+    color: var(--text-muted);
+    font-style: italic;
+}
+
 /* ── Grid view (Phase C) ─────────────────────────────────────────────────── */
 
 .grid-view {

browse/js/app.js

@@ -8,6 +8,47 @@
     var tree = window.app.modules.tree;
     var events = window.app.modules.events;
 
+    // Canonical folders that should appear at the root of a project
+     // view even if they don't yet exist on disk. Matches the four
+     // stage cards on the project landing page. zddc-server returns an
+     // empty listing for these paths (see commit 3fc3717), so
+     // navigating into a virtual folder works without 404.
+    var CANONICAL_PROJECT_FOLDERS = ['archive', 'working', 'staging', 'reviewing'];
+
+    // Decide whether `path` looks like a project root — i.e. exactly
+    // one path segment after the leading slash. /Project-1/ → yes;
+    // / → no; /Project-1/working/ → no.
+    function isProjectRoot(path) {
+        if (!path || path === '/') return false;
+        var trimmed = path.replace(/^\/+|\/+$/g, '');
+        if (!trimmed) return false;
+        return trimmed.indexOf('/') < 0;
+    }
+
+    // Merge virtual entries for any canonical folders absent from the
+    // server's listing. Each virtual entry is shaped like a normal
+    // directory entry so the tree renderer treats it the same way.
+    function withVirtualCanonicals(entries, path) {
+        if (!isProjectRoot(path)) return entries;
+        var present = Object.create(null);
+        entries.forEach(function (e) { if (e.isDir) present[e.name] = true; });
+        var augmented = entries.slice();
+        CANONICAL_PROJECT_FOLDERS.forEach(function (name) {
+            if (!present[name]) {
+                augmented.push({
+                    name: name,
+                    isDir: true,
+                    size: 0,
+                    modTime: null,
+                    ext: '',
+                    url: path.replace(/\/$/, '') + '/' + name + '/',
+                    virtual: true
+                });
+            }
+        });
+        return augmented;
+    }
+
     async function bootstrap() {
         events.init();
 
@@ -17,7 +58,8 @@
         // state with the "Select Directory" button.
         var detected = await loader.autoDetectServerMode();
         if (detected) {
-            tree.setRoot(detected.entries);
+            var entries = withVirtualCanonicals(detected.entries, detected.path);
+            tree.setRoot(entries);
             events.showBrowseRoot();
             tree.render();
             events.statusInfo('Loaded ' + detected.entries.length + ' item'

browse/js/events.js

@@ -183,11 +183,21 @@
 
         // Tree-row clicks (event delegation on the tree body).
         // Click semantics on a folder row:
-        //   - plain click  → toggle expand
+        //   - plain click  → toggle expand (deferred so dblclick wins)
         //   - shift-click  → recursive expand/collapse of the subtree
         //   - alt-click    → ALSO recursive
+        //   - dblclick     → navigate into the folder
         // File rows: plain click → preview in right pane; modifier-click
         // and middle-click open in new tab.
+        //
+        // The plain-click toggle for folders is intentionally deferred
+        // via setTimeout. Reason: toggling re-renders the tree, which
+        // replaces the clicked row element. The browser detects a
+        // double-click only when the second click lands on the same
+        // target element as the first; replacing the row breaks that
+        // continuity and the dblclick event never fires. The deferred
+        // toggle lets a pending dblclick cancel it.
+        var pendingFolderToggle = null;
         var treeBody = document.getElementById('treeBody');
         if (treeBody) {
             treeBody.addEventListener('click', function (e) {
@@ -202,11 +212,30 @@
                 if (isExpandable) {
                     e.preventDefault();
                     if (e.shiftKey || e.altKey) {
+                        // Modifier-click skips the dblclick race — it's
+                        // an explicit recursive toggle, never followed
+                        // by a dblclick.
                         if (node.expanded) tree.collapseSubtree(id);
                         else tree.expandSubtree(id);
-                    } else {
+                        return;
-                        tree.toggleFolder(id);
                     }
+                    // ZIPs don't navigate-into; toggle immediately.
+                    if (row.dataset.iszip === 'true') {
+                        tree.toggleFolder(id);
+                        return;
+                    }
+                    // Folder: defer the toggle so a pending dblclick
+                    // can pre-empt it.
+                    if (pendingFolderToggle) {
+                        clearTimeout(pendingFolderToggle.timer);
+                    }
+                    pendingFolderToggle = {
+                        id: id,
+                        timer: setTimeout(function () {
+                            pendingFolderToggle = null;
+                            tree.toggleFolder(id);
+                        }, 220)
+                    };
                     return;
                 }
 
@@ -247,6 +276,12 @@
                 var node = state.nodes.get(id);
                 if (!node) return;
                 e.preventDefault();
+                // Pre-empt the deferred single-click toggle so the user
+                // doesn't see a flicker of expand/collapse before nav.
+                if (pendingFolderToggle) {
+                    clearTimeout(pendingFolderToggle.timer);
+                    pendingFolderToggle = null;
+                }
                 navigateIntoFolder(node);
             });
         }

browse/js/tree.js

@@ -35,7 +35,11 @@
             isZip: isZip,
             zipFile: null,           // cached JSZip instance
             zipPath: raw.zipPath || null,  // path within zip (for virtual children)
-            zipParentId: raw.zipParentId || null  // ancestor zip's node id (for nested entries)
+            zipParentId: raw.zipParentId || null,  // ancestor zip's node id (for nested entries)
+            // True when this entry was synthesized client-side (e.g.
+            // canonical project folders that don't exist on disk yet).
+            // Rendered with a muted style + an "(empty)" hint.
+            virtual: !!raw.virtual
         };
         state.nodes.set(id, node);
         return node;
@@ -159,17 +163,23 @@
         var chevronClass = 'tree-name__chevron'
             + (expandable ? '' : ' tree-name__chevron--leaf');
         var selected = state.selectedId === node.id ? ' is-selected' : '';
+        var virtualCls = node.virtual ? ' tree-row--virtual' : '';
+        var virtualHint = node.virtual
+            ? '<span class="tree-name__hint" title="Folder not yet created on disk — opens an empty workspace">(empty)</span>'
+            : '';
         return ''
-            + '<div class="tree-row ' + (node.expanded ? 'expanded' : '') + selected
+            + '<div class="tree-row ' + (node.expanded ? 'expanded' : '') + selected + virtualCls
                 + '" data-id="' + node.id
                 + '" data-isdir="' + node.isDir
                 + '" data-iszip="' + node.isZip + '"'
+                + (node.virtual ? ' data-virtual="true"' : '')
                 + ' style="padding-left:' + indent + 'rem"'
                 + ' role="treeitem" tabindex="-1">'
             + '<span class="' + chevronClass + '"></span>'
             + '<span class="tree-name__icon">' + iconChar + '</span>'
             + '<span class="tree-name__label" title="' + escapeHtml(node.name) + '">'
                 + escapeHtml(node.name) + '</span>'
+            + virtualHint
             + '</div>';
     }