Force redraw on reconnect and speed up screenshots

- Send Ctrl+L and resize on reconnect to avoid black screens
- Increase replay buffer to 256KB
- Add get_screen_has_changes for non-destructive dirty checks
- Tighten screenshot cache TTLs and SSE debounce
- Update tests for new behavior and timings

src/textual_webterm/local_server.py

@@ -33,6 +33,8 @@ DEFAULT_TERMINAL_SIZE = (132, 45)
 
 SCREENSHOT_CACHE_SECONDS = 0.3
 SCREENSHOT_MAX_CACHE_SECONDS = 20.0
+CLEAR_AND_REDRAW_SEQ = "\x0c"  # Ctrl+L: clear and redraw
+
 
 WEBTERM_STATIC_PATH = Path(__file__).parent / "static"
 
@@ -369,6 +371,12 @@ class LocalServer:
             if session is None or not session.is_running():
                 self.session_manager.on_session_end(session_id)
                 session_id = None
+            else:
+                # Force terminal redraw on reconnect to avoid blank screen
+                if hasattr(session, 'force_redraw'):
+                    await session.force_redraw()
+                if hasattr(session, 'send_bytes'):
+                    await session.send_bytes(CLEAR_AND_REDRAW_SEQ.encode('utf-8'))
 
         session_created = session_id is not None
 

src/textual_webterm/terminal_session.py

@@ -25,7 +25,7 @@ if TYPE_CHECKING:
 log = logging.getLogger("textual-web")
 
 # Maximum bytes to keep in replay buffer for reconnection
-REPLAY_BUFFER_SIZE = 64 * 1024  # 64KB
+REPLAY_BUFFER_SIZE = 256 * 1024  # 256KB
 
 # Default screen size for pyte emulator
 DEFAULT_SCREEN_WIDTH = 132

tests/test_local_server_websocket_integration.py

@@ -43,6 +43,32 @@ async def test_websocket_creates_session_on_resize(tmp_path):
         await client.close()
 
     assert created["args"] == ("test", 90, 25)
+    # Reconnect should trigger redraw without creating a new session
+    called = {"redraw": 0, "stdin": 0}
+
+    class DummySession:
+        def is_running(self):
+            return True
+
+        async def force_redraw(self):
+            called["redraw"] += 1
+
+        async def send_bytes(self, data: bytes):
+            called["stdin"] += 1
+
+    server.session_manager.routes["test"] = "sid"
+    server.session_manager.sessions["sid"] = DummySession()
+
+    client = await _make_client(server)
+    try:
+        ws = await client.ws_connect("/ws/test")
+        await ws.close()
+    finally:
+        await client.close()
+
+    assert called["redraw"] == 1
+    assert called["stdin"] == 1
+
 
 
 @pytest.mark.asyncio

tests/test_terminal_session.py

@@ -29,7 +29,7 @@ class TestTerminalSession:
         """Test replay buffer size constant."""
         from textual_webterm.terminal_session import REPLAY_BUFFER_SIZE
 
-        assert REPLAY_BUFFER_SIZE == 64 * 1024  # 64KB
+        assert REPLAY_BUFFER_SIZE == 256 * 1024  # 64KB
 
     def test_init(self):
         """Test TerminalSession initialization."""