fix(dashboard): draw jobq tree connectors with CSS lines instead of box-drawing chars

Replace the Unicode prefix string approach (└─ / ├─ / │  built up as text
in a single <span class="rqe-tree-indent">) with positioned DOM elements
that draw real lines:

- rqe-tree-guide: fixed-width ancestor column, optionally draws a full
  vertical border-left when the ancestor has siblings below it
  (.rqe-tree-guide-line).
- rqe-tree-connector: draws the L/T shape via ::before (vertical stem,
  top→center for last child, full height for mid child) and ::after
  (horizontal spur, center→right). .rqe-tree-connector-last vs
  .rqe-tree-connector-mid controls stem length.

renderTreeNode() now takes ancestorLines: boolean[] instead of a prefix
string. Each entry is true when the ancestor at that depth was not the
last child (so a vertical guide is still needed through that column).
childAncestorLines propagates depth === 0 correctly (root nodes have no
guide columns, so their children start with an empty array).

Lines are drawn with var(--border) so they follow the theme and work at
any font size without alignment drift. Addresses the review note on PR 2686.

frontend/packages/dashboard/src/builds.js

@@ -325,13 +325,24 @@ function renderQueueEntry(entry) {
   if (nodes.length) {
     const treeRoot = el('div', { class: 'rqe-nodes-tree' });
     const treeNodes = buildNodeTree(nodes);
-    function renderTreeNode(n, depth, isLast, prefix) {
+    function renderTreeNode(n, depth, isLast, ancestorLines) {
+      // ancestorLines: boolean[] where true = draw a vertical guide line at
+      // that ancestor depth level (the ancestor was not the last sibling, so
+      // its remaining siblings need a guide column below it).
       const row = el('div', { class: 'rqe-tree-row' });
       if (depth > 0) {
-        // prefix: the inherited connector string for ancestor columns
-        // isLast: whether this node is the last sibling (use └ vs ├)
-        row.append(el('span', { class: 'rqe-tree-indent' },
-          prefix + (isLast ? '└─ ' : '├─ ')));
+        // One guide column per ancestor level — draws a vertical line through
+        // columns where the ancestor still has siblings below it.
+        for (const hasLine of ancestorLines) {
+          row.append(el('span', {
+            class: 'rqe-tree-guide' + (hasLine ? ' rqe-tree-guide-line' : ''),
+          }));
+        }
+        // Connector: L-shaped for last child, T-shaped for mid child.
+        row.append(el('span', {
+          class: 'rqe-tree-connector'
+            + (isLast ? ' rqe-tree-connector-last' : ' rqe-tree-connector-mid'),
+        }));
       }
       const chip = el('span', {
         class: 'rqe-node rqe-node-' + n.state,
@@ -351,12 +362,14 @@ function renderQueueEntry(entry) {
         }, '⎙'));
       }
       treeRoot.append(row);
-      const childPrefix = depth > 0 ? prefix + (isLast ? '   ' : '│  ') : '';
+      // Propagate ancestor lines to children: inherit this node's columns,
+      // plus whether this node itself continues below (not the last sibling).
+      const childAncestorLines = depth === 0 ? [] : [...ancestorLines, !isLast];
       n._children.forEach((child, i) => {
-        renderTreeNode(child, depth + 1, i === n._children.length - 1, childPrefix);
+        renderTreeNode(child, depth + 1, i === n._children.length - 1, childAncestorLines);
       });
     }
-    treeNodes.forEach((n, i) => renderTreeNode(n, 0, i === treeNodes.length - 1, ''));
+    treeNodes.forEach((n, i) => renderTreeNode(n, 0, i === treeNodes.length - 1, []));
     li.append(treeRoot);
   }
   const failed = firstFailedNode(entry);

frontend/packages/dashboard/src/system-sections.css

@@ -142,6 +142,59 @@
   align-items: baseline;
   gap: 0.15em;
 }
+/* ─── jobq node tree (replaces .rqe-nodes for tree-structured payloads) ──── */
+.rqe-nodes-tree {
+  flex-basis: 100%;
+  margin: 0.25em 0 0 1.8em;
+  font-size: 0.85em;
+  display: flex;
+  flex-direction: column;
+  gap: 3px;
+}
+.rqe-tree-row {
+  display: flex;
+  align-items: center;
+  gap: 0;
+  min-height: 1.6em;
+}
+/* Guide column: fixed-width spacer that optionally draws a vertical guide
+   line through rows where a sibling of an ancestor continues below. */
+.rqe-tree-guide,
+.rqe-tree-connector {
+  flex-shrink: 0;
+  width: 1.1em;
+  align-self: stretch;
+  position: relative;
+}
+.rqe-tree-guide-line::before {
+  content: '';
+  position: absolute;
+  left: 50%;
+  top: 0;
+  bottom: 0;
+  border-left: 1px solid var(--border);
+}
+/* Connector: vertical stem from top, horizontal spur to the right.
+   Last child (└): stem goes top→center. Mid child (├): stem is full height. */
+.rqe-tree-connector::before {
+  content: '';
+  position: absolute;
+  left: 50%;
+  top: 0;
+  bottom: 50%;
+  border-left: 1px solid var(--border);
+}
+.rqe-tree-connector-mid::before {
+  bottom: 0;
+}
+.rqe-tree-connector::after {
+  content: '';
+  position: absolute;
+  top: 50%;
+  left: 50%;
+  right: 0;
+  border-top: 1px solid var(--border);
+}
 .rqe-node {
   padding: 0.05em 0.45em;
   border: 1px solid var(--border);