feat(layout): plan 01 — tile engine + view registry

1 files changed, 60 insertions, 0 deletions

diff --git a/src/features/layout/logic/tree-query.ts b/src/features/layout/logic/tree-query.ts
new file mode 100644
index 0000000..aa8dfe9
--- /dev/null
+++ b/src/features/layout/logic/tree-query.ts
@@ -0,0 +1,60 @@
+/**
+ * Tree queries the chrome needs — pure walks over the layout tree.
+ */
+
+import type { LayoutNode, LayoutTree, PanelsNode, Path } from "@dispatch/layout-contract";
+
+/** The first panels node in the tree (the panel-selection owner), if any. */
+export function firstPanelsNode(tree: LayoutTree): { node: PanelsNode; path: Path } | null {
+  const seen: { node: PanelsNode; path: Path }[] = [];
+  const visit = (node: LayoutNode, path: Path): void => {
+    if (seen.length > 0) return;
+    if (node.kind === "panels") {
+      seen.push({ node, path });
+      return;
+    }
+    const kids: readonly LayoutNode[] =
+      node.kind === "split"
+        ? node.children.map((c) => c.node)
+        : node.kind === "stack"
+          ? node.children.map((c) => c.node)
+          : [];
+    for (const [i, child] of kids.entries()) visit(child, [...path, i]);
+  };
+  visit(tree.root, []);
+  return seen[0] ?? null;
+}
+
+/**
+ * The node id of the tree's FIRST collapsible split child — the one the chrome
+ * top bar's toggle reads/writes (`findById("side")` on the default tree;
+ * generically the first collapsible child, root-first then titlebar). Falls
+ * back to a path-derived key when the child's node has no id. Null → the tree
+ * has nothing collapsible (the toggle button hides).
+ */
+export function firstCollapsibleNodeId(tree: LayoutTree): string | null {
+  const visit = (node: LayoutNode, path: Path): string | null => {
+    if (node.kind === "split") {
+      for (const [i, child] of node.children.entries()) {
+        if (!child.collapsible) continue;
+        if (child.node.id !== undefined) return child.node.id;
+        return [...path, i].map((s) => String(s)).join(":");
+      }
+    }
+    const kids: readonly LayoutNode[] =
+      node.kind === "split"
+        ? node.children.map((c) => c.node)
+        : node.kind === "stack"
+          ? node.children.map((c) => c.node)
+          : [];
+    for (const [i, child] of kids.entries()) {
+      const found = visit(child, [...path, i]);
+      if (found !== null) return found;
+    }
+    return null;
+  };
+  const inRoot = visit(tree.root, []);
+  if (inRoot !== null) return inRoot;
+  if (tree.titlebar !== undefined) return visit(tree.titlebar, ["titlebar"]);
+  return null;
+}