feat: terminal backend abstraction — kitty, tmux, and plain backends

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/test_backends.py

@@ -0,0 +1,61 @@
+import os
+from unittest.mock import patch, MagicMock
+from kitty_workbench.backends import detect_backend, Backend
+from kitty_workbench.backends.kitty import KittyBackend
+from kitty_workbench.backends.tmux import TmuxBackend
+from kitty_workbench.backends.plain import PlainBackend
+
+
+def test_detect_kitty():
+    with patch.dict(os.environ, {"KITTY_PID": "12345"}, clear=False):
+        backend = detect_backend()
+        assert isinstance(backend, KittyBackend)
+
+def test_detect_tmux():
+    env = os.environ.copy()
+    env.pop("KITTY_PID", None)
+    env["TMUX"] = "/tmp/tmux-1000/default,12345,0"
+    with patch.dict(os.environ, env, clear=True):
+        backend = detect_backend()
+        assert isinstance(backend, TmuxBackend)
+
+def test_detect_plain():
+    env = os.environ.copy()
+    env.pop("KITTY_PID", None)
+    env.pop("TMUX", None)
+    with patch.dict(os.environ, env, clear=True):
+        backend = detect_backend()
+        assert isinstance(backend, PlainBackend)
+
+def test_kitty_image_protocol():
+    b = KittyBackend()
+    assert b.image_protocol() == "kitty"
+
+def test_tmux_image_protocol():
+    b = TmuxBackend()
+    with patch.dict(os.environ, {"TERM_PROGRAM": "unknown"}, clear=False):
+        assert b.image_protocol() in ("sixel", "none")
+
+def test_plain_image_protocol():
+    b = PlainBackend()
+    assert b.image_protocol() in ("sixel", "none")
+
+def test_kitty_launch_pane():
+    b = KittyBackend()
+    with patch("kitty_workbench.backends.kitty.subprocess") as mock_sp:
+        mock_sp.run.return_value = MagicMock(stdout="42", returncode=0)
+        pane_id = b.launch_pane(["kitty-workbench", "tui", "test"], "Test")
+        assert pane_id == 42
+        call_args = mock_sp.run.call_args[0][0]
+        assert "kitty" in call_args[0]
+        assert "--location=vsplit" in call_args
+
+def test_tmux_launch_pane():
+    b = TmuxBackend()
+    with patch("kitty_workbench.backends.tmux.subprocess") as mock_sp:
+        mock_sp.run.return_value = MagicMock(stdout="%5", returncode=0)
+        pane_id = b.launch_pane(["kitty-workbench", "tui", "test"], "Test")
+        assert pane_id == "%5"
+        call_args = mock_sp.run.call_args[0][0]
+        assert "tmux" in call_args[0]
+        assert "split-window" in call_args