diff --git a/tests_v2/test_background_split_send_text_starts_terminal.py b/tests_v2/test_background_split_send_text_starts_terminal.py
new file mode 100644
index 000000000000..32f14688fbe1
--- /dev/null
+++ b/tests_v2/test_background_split_send_text_starts_terminal.py
@@ -0,0 +1,123 @@
+#!/usr/bin/env python3
+"""Regression: surface.send_text must start a background split terminal without selecting it."""
+
+from __future__ import annotations
+
+import logging
+import os
+import shlex
+import sys
+import tempfile
+import time
+from pathlib import Path
+
+sys.path.insert(0, str(Path(__file__).parent))
+from cmux import cmux, cmuxError
+
+
+SOCKET_PATH = os.environ.get("CMUX_SOCKET_PATH", "/tmp/cmux-debug.sock")
+
+
+def _must(cond: bool, msg: str) -> None:
+    if not cond:
+        raise cmuxError(msg)
+
+
+def _wait_for_file_text(path: Path, needle: str, timeout_s: float = 8.0) -> str:
+    deadline = time.time() + timeout_s
+    last_text = ""
+    while time.time() < deadline:
+        if path.exists():
+            last_text = path.read_text(encoding="utf-8", errors="replace")
+        if needle in last_text:
+            return last_text
+        time.sleep(0.1)
+    raise cmuxError(f"Timed out waiting for {needle!r} from background split terminal: {last_text!r}")
+
+
+def _first_terminal_surface_id(payload: dict) -> str:
+    surfaces = payload.get("surfaces") or []
+    for row in surfaces:
+        if row.get("type") == "terminal":
+            surface_id = str(row.get("id") or "")
+            if surface_id:
+                return surface_id
+    raise cmuxError(f"surface.list returned no terminal surface: {payload}")
+
+
+def main() -> int:
+    with cmux(SOCKET_PATH) as c:
+        baseline_workspace = c.current_workspace()
+        created_workspace = ""
+        marker_path = Path(tempfile.gettempdir()) / f"cmux-bg-split-send-{time.time_ns()}.txt"
+        try:
+            payload = c._call("workspace.create", {}) or {}
+            created_workspace = str(payload.get("workspace_id") or "")
+            _must(bool(created_workspace), f"workspace.create returned no workspace_id: {payload}")
+            _must(
+                c.current_workspace() == baseline_workspace,
+                "workspace.create should preserve selected workspace",
+            )
+
+            surfaces_payload = c._call("surface.list", {"workspace_id": created_workspace}) or {}
+            initial_surface = _first_terminal_surface_id(surfaces_payload)
+
+            split_payload = c._call(
+                "surface.split",
+                {
+                    "workspace_id": created_workspace,
+                    "surface_id": initial_surface,
+                    "direction": "right",
+                    "focus": False,
+                },
+            ) or {}
+            split_surface = str(split_payload.get("surface_id") or "")
+            _must(bool(split_surface), f"surface.split returned no surface_id: {split_payload}")
+            _must(
+                c.current_workspace() == baseline_workspace,
+                "surface.split in a background workspace should not steal workspace focus",
+            )
+
+            token = f"CMUX_BG_SPLIT_SEND_{time.time_ns()}"
+            command = (
+                "python3 -c "
+                + shlex.quote(
+                    f"from pathlib import Path; Path({marker_path.as_posix()!r}).write_text({token!r}, encoding='utf-8')"
+                )
+                + "\n"
+            )
+            send_payload = c._call(
+                "surface.send_text",
+                {
+                    "workspace_id": created_workspace,
+                    "surface_id": split_surface,
+                    "text": command,
+                },
+            ) or {}
+            _must(
+                str(send_payload.get("surface_id") or "") == split_surface,
+                f"surface.send_text returned unexpected surface_id: {send_payload}",
+            )
+
+            _wait_for_file_text(marker_path, token)
+            _must(
+                c.current_workspace() == baseline_workspace,
+                "surface.send_text should start the background terminal without selecting its workspace",
+            )
+        finally:
+            try:
+                marker_path.unlink()
+            except FileNotFoundError:
+                pass
+            if created_workspace:
+                try:
+                    c.close_workspace(created_workspace)
+                except Exception:
+                    logging.exception("Failed to clean up workspace %s", created_workspace)
+
+    print("PASS: background split surface.send_text starts the terminal without focus")
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())