diff --git a/packages/app/e2e/workspace-pane-remount.spec.ts b/packages/app/e2e/workspace-pane-remount.spec.ts
new file mode 100644
index 000000000..ef1c2be5a
--- /dev/null
+++ b/packages/app/e2e/workspace-pane-remount.spec.ts
@@ -0,0 +1,64 @@
+import { buildHostAgentDetailRoute } from "@/utils/host-routes";
+import { expect, test } from "./fixtures";
+import {
+  archiveAgentFromDaemon,
+  connectArchiveTabDaemonClient,
+  createIdleAgent,
+} from "./helpers/archive-tab";
+import { expectComposerVisible } from "./helpers/composer";
+import { createTempGitRepo } from "./helpers/workspace";
+import { waitForWorkspaceTabsVisible } from "./helpers/workspace-tabs";
+
+test.describe("Workspace pane mounting", () => {
+  test("opening the first split pane keeps the existing agent composer mounted", async ({
+    page,
+  }) => {
+    test.setTimeout(90_000);
+    const serverId = process.env.E2E_SERVER_ID;
+    if (!serverId) {
+      throw new Error("E2E_SERVER_ID is not set.");
+    }
+
+    const client = await connectArchiveTabDaemonClient();
+    const repo = await createTempGitRepo("pane-remount-");
+    let agentId: string | null = null;
+
+    try {
+      const agent = await createIdleAgent(client, {
+        cwd: repo.path,
+        title: `pane-remount-${Date.now()}`,
+      });
+      agentId = agent.id;
+
+      await page.goto(buildHostAgentDetailRoute(serverId, agent.id, agent.cwd));
+      await page.waitForURL(
+        (url) => url.pathname.includes("/workspace/") && !url.searchParams.has("open"),
+        { timeout: 60_000 },
+      );
+      await waitForWorkspaceTabsVisible(page);
+      await expectComposerVisible(page);
+
+      const originalComposer = await page
+        .getByTestId("message-input-root")
+        .filter({ visible: true })
+        .first()
+        .elementHandle();
+      expect(originalComposer).not.toBeNull();
+
+      await page.getByRole("button", { name: "Split pane right" }).first().click();
+      await expect(page.getByTestId("message-input-root").filter({ visible: true })).toHaveCount(
+        2,
+        { timeout: 30_000 },
+      );
+
+      const originalStillConnected = await originalComposer!.evaluate((node) => node.isConnected);
+      expect(originalStillConnected).toBe(true);
+    } finally {
+      if (agentId) {
+        await archiveAgentFromDaemon(client, agentId).catch(() => undefined);
+      }
+      await client.close().catch(() => undefined);
+      await repo.cleanup();
+    }
+  });
+});
diff --git a/packages/app/src/components/split-container-pane-focus.test.ts b/packages/app/src/components/split-container-pane-focus.test.ts
index 7e5f4541b..461364677 100644
--- a/packages/app/src/components/split-container-pane-focus.test.ts
+++ b/packages/app/src/components/split-container-pane-focus.test.ts
@@ -23,4 +23,13 @@ describe("shouldFocusPaneFromEventTarget", () => {
     ).toBe(true);
     expect(shouldFocusPaneFromEventTarget(null)).toBe(true);
   });
+
+  it("returns true for composer text inputs so focusing the composer focuses the pane", () => {
+    expect(
+      shouldFocusPaneFromEventTarget({
+        closest: (selector: string) =>
+          selector.includes("input") ? ({ tagName: "INPUT" } as Element) : null,
+      } as unknown as EventTarget),
+    ).toBe(true);
+  });
 });
diff --git a/packages/app/src/components/split-container-pane-focus.ts b/packages/app/src/components/split-container-pane-focus.ts
index c3cb53b7b..a63823f1f 100644
--- a/packages/app/src/components/split-container-pane-focus.ts
+++ b/packages/app/src/components/split-container-pane-focus.ts
@@ -1,9 +1,7 @@
 const INTERACTIVE_TARGET_SELECTOR = [
   "a",
   "button",
-  "input",
   "select",
-  "textarea",
   "[role='button']",
   "[role='link']",
   "[contenteditable='true']",
diff --git a/packages/app/src/components/split-container.tsx b/packages/app/src/components/split-container.tsx
index 00f999f0b..ba6111bf8 100644
--- a/packages/app/src/components/split-container.tsx
+++ b/packages/app/src/components/split-container.tsx
@@ -406,6 +406,7 @@ export function SplitContainer({
     }
     return { kind: "pane" as const, pane: focusedPane };
   }, [focusModeEnabled, layout.root, layout.focusedPaneId, panesById]);
+  const renderRoot = useMemo(() => wrapRootPaneForStableMount(effectiveRoot), [effectiveRoot]);
 
   const handleDragStart = useCallback((event: DragStartEvent) => {
     const data = asWorkspaceTabDragData(event.active.data.current);
@@ -560,7 +561,7 @@ export function SplitContainer({
       onDragEnd={handleDragEnd}
     >
       <SplitNodeView
-        node={effectiveRoot}
+        node={renderRoot}
         workspaceKey={workspaceKey}
         uiTabs={uiTabs}
         focusedPaneId={layout.focusedPaneId}
@@ -1071,6 +1072,22 @@ function getNodeKey(node: SplitNode): string {
   return node.group.id;
 }
 
+function wrapRootPaneForStableMount(node: SplitNode): SplitNode {
+  if (node.kind === "group") {
+    return node;
+  }
+
+  return {
+    kind: "group",
+    group: {
+      id: `root:${node.pane.id}`,
+      direction: "horizontal",
+      children: [node],
+      sizes: [1],
+    },
+  };
+}
+
 const styles = StyleSheet.create((theme) => ({
   group: {
     flex: 1,