diff --git a/hermes_cli/main.py b/hermes_cli/main.py
index 6f205a1039f..f1f83333124 100644
--- a/hermes_cli/main.py
+++ b/hermes_cli/main.py
@@ -65,6 +65,39 @@ import os
 import sys
 
 
+# Mouse-tracking residue suppression — runs BEFORE every other import on the
+# TUI hot path so the terminal stops emitting SGR/X10 mouse reports while the
+# Python launcher is still doing imports (≈100–300ms in cooked + echo mode,
+# before the Node TUI takes stdin into raw mode). During that window any
+# incoming bytes are echoed straight back to the user's shell scrollback as
+# ``^[[<…M`` text. The TUI itself runs `resetTerminalModes()` again in
+# `entry.tsx`; this is just the earlier cousin. ``HERMES_TUI_NO_EARLY_DISABLE``
+# escapes the behaviour for diagnostics.
+def _suppress_mouse_residue_early() -> None:
+    if os.environ.get("HERMES_TUI_NO_EARLY_DISABLE") == "1":
+        return
+    if not (os.environ.get("HERMES_TUI") == "1" or "--tui" in sys.argv[1:]):
+        return
+    try:
+        # Skip when stdout is redirected (`hermes --tui … >log`, CI capture):
+        # the bytes can't reach the terminal anyway and would just pollute
+        # the log with raw CSI.
+        if not os.isatty(1):
+            return
+        # Disable every mouse-tracking variant we know about. Idempotent and
+        # safe to send even when no tracking is currently asserted.
+        os.write(
+            1,
+            b"\x1b[?1003l\x1b[?1002l\x1b[?1001l\x1b[?1000l\x1b[?9l"
+            b"\x1b[?1006l\x1b[?1005l\x1b[?1015l\x1b[?1016l\x1b[?2029l",
+        )
+    except OSError:
+        pass
+
+
+_suppress_mouse_residue_early()
+
+
 def _is_termux_startup_environment_fast() -> bool:
     """Tiny Termux check for pre-import startup shortcuts."""
     prefix = os.environ.get("PREFIX", "")
diff --git a/tests/hermes_cli/test_tui_mouse_residue_suppression.py b/tests/hermes_cli/test_tui_mouse_residue_suppression.py
new file mode 100644
index 00000000000..c8b646f38d1
--- /dev/null
+++ b/tests/hermes_cli/test_tui_mouse_residue_suppression.py
@@ -0,0 +1,92 @@
+"""Tests for the TUI-hot-path mouse-residue suppression.
+
+The Python launcher (`hermes --tui …`) has a ~100–300ms cold-start window
+where stdin is still in cooked + echo mode. If a previous Hermes session
+left DEC mouse-tracking asserted, any mouse motion during that window
+echoes literal ``^[[<…M`` text into the user's scrollback.
+
+`_suppress_mouse_residue_early()` writes the disable sequence to stdout
+before the heavy imports so the terminal stops emitting events ASAP.
+"""
+
+from __future__ import annotations
+
+import sys
+from unittest.mock import patch
+
+# Importing the module triggers `_suppress_mouse_residue_early()` at module
+# scope. Under the test runner argv (`pytest …`) it's a no-op, but we import
+# at file scope so individual tests don't race the import side-effect with
+# their `patch("os.write")` context.
+from hermes_cli.main import _suppress_mouse_residue_early
+
+EXPECTED = (
+    b"\x1b[?1003l\x1b[?1002l\x1b[?1001l\x1b[?1000l\x1b[?9l"
+    b"\x1b[?1006l\x1b[?1005l\x1b[?1015l\x1b[?1016l\x1b[?2029l"
+)
+
+
+class TestEarlyMouseDisable:
+    def test_writes_disable_sequence_when_tui_flag_in_argv(self, monkeypatch):
+        monkeypatch.setattr(sys, "argv", ["hermes", "--tui", "-c", "abc"])
+        monkeypatch.delenv("HERMES_TUI", raising=False)
+        monkeypatch.delenv("HERMES_TUI_NO_EARLY_DISABLE", raising=False)
+
+        with patch("os.isatty", return_value=True), patch("os.write") as mock_write:
+            _suppress_mouse_residue_early()
+
+        mock_write.assert_called_once_with(1, EXPECTED)
+
+    def test_writes_disable_sequence_when_hermes_tui_env_set(self, monkeypatch):
+        monkeypatch.setattr(sys, "argv", ["hermes"])
+        monkeypatch.setenv("HERMES_TUI", "1")
+        monkeypatch.delenv("HERMES_TUI_NO_EARLY_DISABLE", raising=False)
+
+        with patch("os.isatty", return_value=True), patch("os.write") as mock_write:
+            _suppress_mouse_residue_early()
+
+        mock_write.assert_called_once_with(1, EXPECTED)
+
+    def test_no_op_on_non_tui_invocation(self, monkeypatch):
+        monkeypatch.setattr(sys, "argv", ["hermes", "--version"])
+        monkeypatch.delenv("HERMES_TUI", raising=False)
+        monkeypatch.delenv("HERMES_TUI_NO_EARLY_DISABLE", raising=False)
+
+        with patch("os.write") as mock_write:
+            _suppress_mouse_residue_early()
+
+        mock_write.assert_not_called()
+
+    def test_respects_diagnostic_escape_hatch(self, monkeypatch):
+        monkeypatch.setattr(sys, "argv", ["hermes", "--tui"])
+        monkeypatch.delenv("HERMES_TUI", raising=False)
+        monkeypatch.setenv("HERMES_TUI_NO_EARLY_DISABLE", "1")
+
+        with patch("os.write") as mock_write:
+            _suppress_mouse_residue_early()
+
+        mock_write.assert_not_called()
+
+    def test_skips_when_stdout_is_not_a_tty(self, monkeypatch):
+        # `hermes --tui … >log` or CI capture: pipe is fd 1, not a TTY. The
+        # bytes can't reach a terminal and would just pollute the log.
+        monkeypatch.setattr(sys, "argv", ["hermes", "--tui"])
+        monkeypatch.delenv("HERMES_TUI", raising=False)
+        monkeypatch.delenv("HERMES_TUI_NO_EARLY_DISABLE", raising=False)
+
+        with patch("os.isatty", return_value=False), patch("os.write") as mock_write:
+            _suppress_mouse_residue_early()
+
+        mock_write.assert_not_called()
+
+    def test_oserror_is_swallowed(self, monkeypatch):
+        monkeypatch.setattr(sys, "argv", ["hermes", "--tui"])
+        monkeypatch.delenv("HERMES_TUI", raising=False)
+        monkeypatch.delenv("HERMES_TUI_NO_EARLY_DISABLE", raising=False)
+
+        def boom(*_a, **_k):
+            raise OSError("stdout closed")
+
+        with patch("os.isatty", return_value=True), patch("os.write", side_effect=boom):
+            # Must not propagate — startup hot path can never break.
+            _suppress_mouse_residue_early()