1 files changed, 27 insertions, 0 deletions
diff --git a/src/features/tabs/tabs.ts b/src/features/tabs/tabs.ts
index ff7bb4f..b2dad7d 100644
--- a/src/features/tabs/tabs.ts
+++ b/src/features/tabs/tabs.ts
@@ -13,6 +13,13 @@ export interface Tab {
    * renamed/removed. Absent for a raw model selection.
    */
   readonly snapshot?: NamedAgentSelectionSnapshot;
+  /**
+   * The EFFECTIVE tab group parent (backend `tabGroupParentId`): the
+   * conversation whose subagent group this tab is visually nested under in
+   * the tab grid. Purely presentational — distinct from the lineage
+   * `parentConversationId`. Absent = ungrouped (a top-level tab).
+   */
+  readonly tabGroupParentId?: string;
 }
 
 export interface TabsState {
@@ -120,6 +127,26 @@ export function setTitle(state: TabsState, conversationId: string, title: string
   return { tabs, activeConversationId: state.activeConversationId };
 }
 
+/**
+ * Set (string) or clear (null) a tab's tab group parent. Omits the key when
+ * cleared (`exactOptionalPropertyTypes`). No-op for an unknown tab.
+ */
+export function setTabGroupParent(
+  state: TabsState,
+  conversationId: string,
+  parentId: string | null,
+): TabsState {
+  const tabs = state.tabs.map((t) => {
+    if (t.conversationId !== conversationId) return t;
+    if (parentId !== null) return { ...t, tabGroupParentId: parentId };
+    if (!("tabGroupParentId" in t)) return t;
+    const { tabGroupParentId: _omit, ...rest } = t;
+    void _omit;
+    return rest;
+  });
+  return { tabs, activeConversationId: state.activeConversationId };
+}
+
 export function setWorkspaceId(
   state: TabsState,
   conversationId: string,