Add REPL effect detection and input handling to pipeline runner

- Detect REPL effect in pipeline and enable interactive mode
- Enable raw terminal mode for REPL input capture
- Add keyboard input loop for REPL commands (return, up/down arrows, backspace)
- Process commands and handle pipeline mutations from REPL
- Fix lint issues in graph and REPL modules (type annotations, imports)

engine/app/pipeline_runner.py

@@ -433,6 +433,16 @@ def run_pipeline_mode(preset_name: str = "demo", graph_config: str | None = None
     ui_panel = None
     render_ui_panel_in_terminal = False
 
+    # Check for REPL effect in pipeline
+    repl_effect = None
+    for stage in pipeline.stages.values():
+        if isinstance(stage, EffectPluginStage) and stage._effect.name == "repl":
+            repl_effect = stage._effect
+            print(
+                "  \033[38;5;46mREPL effect detected - Interactive mode enabled\033[0m"
+            )
+            break
+
     if need_ui_controller:
         from engine.display import render_ui_panel
 
@@ -448,6 +458,10 @@ def run_pipeline_mode(preset_name: str = "demo", graph_config: str | None = None
         if hasattr(display, "set_raw_mode"):
             display.set_raw_mode(True)
 
+    # Enable raw mode for REPL if present and not already enabled
+    elif repl_effect and hasattr(display, "set_raw_mode"):
+        display.set_raw_mode(True)
+
         # Register effect plugin stages from pipeline for UI control
         for stage in pipeline.stages.values():
             if isinstance(stage, EffectPluginStage):
@@ -966,6 +980,38 @@ def run_pipeline_mode(preset_name: str = "demo", graph_config: str | None = None
                     else:
                         display.show(result.data, border=show_border)
 
+            # --- REPL Input Handling ---
+            if repl_effect and hasattr(display, "get_input_keys"):
+                # Get keyboard input (non-blocking)
+                keys = display.get_input_keys(timeout=0.0)
+
+                for key in keys:
+                    if key == "return":
+                        # Get command string before processing
+                        cmd_str = repl_effect.state.current_command
+                        if cmd_str:
+                            repl_effect.process_command(cmd_str, ctx)
+                            # Check for pending pipeline mutations
+                            pending = repl_effect.get_pending_command()
+                            if pending:
+                                _handle_pipeline_mutation(pipeline, pending)
+                                # Broadcast state update if WebSocket is active
+                                if web_control_active and isinstance(
+                                    display, WebSocketDisplay
+                                ):
+                                    state = display._get_state_snapshot()
+                                    if state:
+                                        display.broadcast_state(state)
+                    elif key == "up":
+                        repl_effect.navigate_history(-1)
+                    elif key == "down":
+                        repl_effect.navigate_history(1)
+                    elif key == "backspace":
+                        repl_effect.backspace()
+                    elif len(key) == 1:
+                        repl_effect.append_to_command(key)
+            # --- End REPL Input Handling ---
+
             if hasattr(display, "is_quit_requested") and display.is_quit_requested():
                 if hasattr(display, "clear_quit_request"):
                     display.clear_quit_request()