Add per-leaf mcpAllow flag for MCP visibility gating (default-deny)

src/lib/layout/tree.test.ts

@@ -12,6 +12,7 @@ import {
   setLeafShell,
   changeLabel,
   toggleBroadcast,
+  toggleMcpAllow,
   adjustFontSize,
   adjustAllFontSizes,
   resolveFontSize,
@@ -363,6 +364,27 @@ describe("toggleBroadcast", () => {
   });
 });
 
+describe("toggleMcpAllow", () => {
+  it("default-undefined toggles to true", () => {
+    const leaf = newLeaf();
+    expect(leaf.mcpAllow).toBeUndefined();
+    const on = toggleMcpAllow(leaf, leaf.id) as LeafNode;
+    expect(on.mcpAllow).toBe(true);
+  });
+
+  it("true toggles to false", () => {
+    const leaf = newLeaf({ mcpAllow: true });
+    const off = toggleMcpAllow(leaf, leaf.id) as LeafNode;
+    expect(off.mcpAllow).toBe(false);
+  });
+
+  it("MUST NOT swap the leaf id (metadata-only, no PTY respawn)", () => {
+    const leaf = newLeaf();
+    const next = toggleMcpAllow(leaf, leaf.id) as LeafNode;
+    expect(next.id).toBe(leaf.id);
+  });
+});
+
 describe("resolveFontSize", () => {
   it("returns the default when offset is undefined or 0", () => {
     expect(resolveFontSize(undefined)).toBe(DEFAULT_FONT_SIZE);