3 files changed, 86 insertions, 0 deletions
diff --git a/src/adapters/ws/index.ts b/src/adapters/ws/index.ts
index 4dc0104..76d9e75 100644
--- a/src/adapters/ws/index.ts
+++ b/src/adapters/ws/index.ts
@@ -4,6 +4,7 @@ import type {
   ConversationCompactedMessage,
   ConversationOpenMessage,
   ConversationStatusChangedMessage,
+  ConversationTabGroupChangedMessage,
   ExtensionsChangedMessage,
   LayoutChangedMessage,
   TileLayoutChangedMessage,
@@ -30,6 +31,8 @@ export interface SurfaceSocketOptions {
   onConversationStatusChanged?: (msg: ConversationStatusChangedMessage) => void;
   /** Broadcast when a conversation's history has been compacted (reload needed). */
   onConversationCompacted?: (msg: ConversationCompactedMessage) => void;
+  /** Broadcast when a conversation's (visual) tab group parent changes. */
+  onConversationTabGroupChanged?: (msg: ConversationTabGroupChangedMessage) => void;
   /**
    * Broadcast after every plugin-manager mutation (plan 05 §11): every
    * connected frontend refetches its extension list (the server re-pushes the
@@ -93,6 +96,8 @@ export function createSurfaceSocket(opts: SurfaceSocketOptions): SurfaceSocketHa
           opts.onConversationOpen?.(msg as ConversationOpenMessage);
         } else if (msg.type === "conversation.statusChanged") {
           opts.onConversationStatusChanged?.(msg as ConversationStatusChangedMessage);
+        } else if (msg.type === "conversation.tabGroupChanged") {
+          opts.onConversationTabGroupChanged?.(msg as ConversationTabGroupChangedMessage);
         } else if (msg.type === "conversation.compacted") {
           opts.onConversationCompacted?.(msg as ConversationCompactedMessage);
         } else if (msg.type === "extensions-changed") {
diff --git a/src/adapters/ws/logic.test.ts b/src/adapters/ws/logic.test.ts
index 8fe2b5f..2179ad0 100644
--- a/src/adapters/ws/logic.test.ts
+++ b/src/adapters/ws/logic.test.ts
@@ -502,3 +502,63 @@ describe("parseServerMessage — layout (plan 02)", () => {
     expect(parseServerMessage(JSON.stringify({ type: "layout.unknown" }))).toBeNull();
   });
 });
+
+describe("parseServerMessage — subagent tab groups", () => {
+  it("forwards the effective tabGroupParentId on conversation.open", () => {
+    const result = parseServerMessage(
+      JSON.stringify({
+        type: "conversation.open",
+        conversationId: "child",
+        workspaceId: "w1",
+        tabGroupParentId: "parent",
+      }),
+    );
+    expect(result).toEqual({
+      type: "conversation.open",
+      conversationId: "child",
+      workspaceId: "w1",
+      tabGroupParentId: "parent",
+    });
+  });
+
+  it("omits a non-string/empty tabGroupParentId on conversation.open", () => {
+    for (const tabGroupParentId of ["", 42, null]) {
+      const result = parseServerMessage(
+        JSON.stringify({
+          type: "conversation.open",
+          conversationId: "c1",
+          workspaceId: "w1",
+          tabGroupParentId,
+        }),
+      );
+      expect(result).toEqual({
+        type: "conversation.open",
+        conversationId: "c1",
+        workspaceId: "w1",
+      });
+    }
+  });
+
+  it("parses conversation.tabGroupChanged with a parent id and with null (ungrouped)", () => {
+    for (const tabGroupParentId of ["parent", null]) {
+      const msg = {
+        type: "conversation.tabGroupChanged",
+        conversationId: "c1",
+        workspaceId: "w1",
+        tabGroupParentId,
+      };
+      expect(parseServerMessage(JSON.stringify(msg))).toEqual(msg);
+    }
+  });
+
+  it("rejects a malformed conversation.tabGroupChanged", () => {
+    const base = { type: "conversation.tabGroupChanged", conversationId: "c1", workspaceId: "w1" };
+    expect(parseServerMessage(JSON.stringify(base))).toBeNull(); // missing (undefined) parent
+    expect(parseServerMessage(JSON.stringify({ ...base, tabGroupParentId: "" }))).toBeNull();
+    expect(parseServerMessage(JSON.stringify({ ...base, tabGroupParentId: 1 }))).toBeNull();
+    const { workspaceId: _w, ...noWorkspace } = base;
+    expect(
+      parseServerMessage(JSON.stringify({ ...noWorkspace, tabGroupParentId: "p" })),
+    ).toBeNull();
+  });
+});
diff --git a/src/adapters/ws/logic.ts b/src/adapters/ws/logic.ts
index 4dbd173..cecc66c 100644
--- a/src/adapters/ws/logic.ts
+++ b/src/adapters/ws/logic.ts
@@ -4,6 +4,7 @@ import type {
   ConversationCompactedMessage,
   ConversationOpenMessage,
   ConversationStatusChangedMessage,
+  ConversationTabGroupChangedMessage,
   ExtensionsChangedMessage,
   LayoutChangedMessage,
   TileLayoutChangedMessage,
@@ -27,6 +28,7 @@ const VALID_SERVER_TYPES = new Set([
   "conversation.open",
   "conversation.statusChanged",
   "conversation.compacted",
+  "conversation.tabGroupChanged",
   "extensions-changed",
   "layout",
   "tile-layout",
@@ -126,11 +128,30 @@ export function parseServerMessage(data: string): WsServerMessage | null {
       // it, so a client can stamp the opened tab with the conversation's ACTUAL
       // model (fix-toolcall-duplicate-keys plan Part 4).
       const model = parsed.model;
+      // The EFFECTIVE tab group parent, so a summoned subagent's tab lands in
+      // its summoner's group immediately.
+      const tabGroupParentId = parsed.tabGroupParentId;
       const msg: ConversationOpenMessage = {
         type: "conversation.open",
         conversationId: parsed.conversationId,
         workspaceId: parsed.workspaceId,
         ...(typeof model === "string" && model.length > 0 ? { model } : {}),
+        ...(typeof tabGroupParentId === "string" && tabGroupParentId.length > 0
+          ? { tabGroupParentId }
+          : {}),
+      };
+      return msg;
+    }
+    case "conversation.tabGroupChanged": {
+      if (typeof parsed.conversationId !== "string") return null;
+      if (typeof parsed.workspaceId !== "string") return null;
+      const parent = parsed.tabGroupParentId;
+      if (parent !== null && (typeof parent !== "string" || parent.length === 0)) return null;
+      const msg: ConversationTabGroupChangedMessage = {
+        type: "conversation.tabGroupChanged",
+        conversationId: parsed.conversationId,
+        workspaceId: parsed.workspaceId,
+        tabGroupParentId: parent,
       };
       return msg;
     }