Add Ctrl+C quit handling to REPL

- Add _quit_requested flag to TerminalDisplay
- Add request_quit() method to TerminalDisplay
- Handle 'ctrl_c' key in REPL input loops in both pipeline_runner.py and main.py
- When Ctrl+C is pressed, request_quit() is called which sets the flag
- The main loop checks is_quit_requested() and raises KeyboardInterrupt

engine/app/main.py

@@ -550,7 +550,13 @@ def run_pipeline_mode_direct():
                 keys = display.get_input_keys(timeout=0.0)
 
                 for key in keys:
-                    if key == "return":
+                    if key == "ctrl_c":
+                        # Request quit when Ctrl+C is pressed
+                        if hasattr(display, "request_quit"):
+                            display.request_quit()
+                        else:
+                            raise KeyboardInterrupt()
+                    elif key == "return":
                         # Get command string before processing
                         cmd_str = repl_effect.state.current_command
                         if cmd_str:

engine/app/pipeline_runner.py

@@ -986,7 +986,13 @@ def run_pipeline_mode(preset_name: str = "demo", graph_config: str | None = None
                 keys = display.get_input_keys(timeout=0.0)
 
                 for key in keys:
-                    if key == "return":
+                    if key == "ctrl_c":
+                        # Request quit when Ctrl+C is pressed
+                        if hasattr(display, "request_quit"):
+                            display.request_quit()
+                        else:
+                            raise KeyboardInterrupt()
+                    elif key == "return":
                         # Get command string before processing
                         cmd_str = repl_effect.state.current_command
                         if cmd_str:

engine/display/backends/terminal.py

@@ -28,6 +28,7 @@ class TerminalDisplay:
         self._cached_dimensions: tuple[int, int] | None = None
         self._raw_mode_enabled: bool = False
         self._original_termios: list = []
+        self._quit_requested: bool = False
 
     def init(self, width: int, height: int, reuse: bool = False) -> None:
         """Initialize display with dimensions.
@@ -163,11 +164,15 @@ class TerminalDisplay:
 
     def is_quit_requested(self) -> bool:
         """Check if quit was requested (optional protocol method)."""
-        return False
+        return self._quit_requested
 
     def clear_quit_request(self) -> None:
         """Clear quit request (optional protocol method)."""
-        pass
+        self._quit_requested = False
+
+    def request_quit(self) -> None:
+        """Request quit (e.g., when Ctrl+C is pressed)."""
+        self._quit_requested = True
 
     def set_raw_mode(self, enable: bool = True) -> None:
         """Enable/disable raw terminal mode for input capture.