feat: Complete pipeline hot-rebuild implementation with acceptance tests

- Implements pipeline hot-rebuild with state preservation (issue #43)
- Adds auto-injection of MVP stages for missing capabilities
- Adds radial camera mode for polar coordinate scanning
- Adds afterimage and motionblur effects using framebuffer history
- Adds comprehensive acceptance tests for camera modes and pipeline rebuild
- Updates presets.toml with new effect configurations

Related to: #35 (Pipeline Mutation API epic)
Closes: #43, #44, #45

engine/app/pipeline_runner.py

@@ -45,8 +45,19 @@ def run_pipeline_mode(preset_name: str = "demo"):
     print(f"  \033[38;5;245mPreset: {preset.name} - {preset.description}\033[0m")
 
     params = preset.to_params()
-    params.viewport_width = 80
-    params.viewport_height = 24
+    # Use preset viewport if available, else default to 80x24
+    params.viewport_width = getattr(preset, "viewport_width", 80)
+    params.viewport_height = getattr(preset, "viewport_height", 24)
+
+    if "--viewport" in sys.argv:
+        idx = sys.argv.index("--viewport")
+        if idx + 1 < len(sys.argv):
+            vp = sys.argv[idx + 1]
+            try:
+                params.viewport_width, params.viewport_height = map(int, vp.split("x"))
+            except ValueError:
+                print("Error: Invalid viewport format. Use WxH (e.g., 40x15)")
+                sys.exit(1)
 
     pipeline = Pipeline(
         config=PipelineConfig(
@@ -156,25 +167,12 @@ def run_pipeline_mode(preset_name: str = "demo"):
         list_source = ListDataSource(items, name=preset.source)
         pipeline.add_stage("source", DataSourceStage(list_source, name=preset.source))
 
-    # Add FontStage for headlines/poetry (default for demo)
-    if preset.source in ["headlines", "poetry"]:
-        from engine.pipeline.adapters import FontStage, ViewportFilterStage
-
-        # Add viewport filter to prevent rendering all items
-        pipeline.add_stage(
-            "viewport_filter", ViewportFilterStage(name="viewport-filter")
-        )
-        pipeline.add_stage("font", FontStage(name="font"))
-    else:
-        # Fallback to simple conversion for other sources
-        pipeline.add_stage("render", SourceItemsToBufferStage(name="items-to-buffer"))
-
-    # Add camera stage if specified in preset (after font/render stage)
+    # Add camera state update stage if specified in preset (must run before viewport filter)
+    camera = None
     if preset.camera:
         from engine.camera import Camera
-        from engine.pipeline.adapters import CameraStage
+        from engine.pipeline.adapters import CameraClockStage, CameraStage
 
-        camera = None
         speed = getattr(preset, "camera_speed", 1.0)
         if preset.camera == "feed":
             camera = Camera.feed(speed=speed)
@@ -190,9 +188,35 @@ def run_pipeline_mode(preset_name: str = "demo"):
             camera = Camera.floating(speed=speed)
         elif preset.camera == "bounce":
             camera = Camera.bounce(speed=speed)
+        elif preset.camera == "radial":
+            camera = Camera.radial(speed=speed)
+        elif preset.camera == "static" or preset.camera == "":
+            # Static camera: no movement, but provides camera_y=0 for viewport filter
+            camera = Camera.scroll(speed=0.0)  # Speed 0 = no movement
+            camera.set_canvas_size(200, 200)
 
         if camera:
-            pipeline.add_stage("camera", CameraStage(camera, name=preset.camera))
+            # Add camera update stage to ensure camera_y is available for viewport filter
+            pipeline.add_stage(
+                "camera_update", CameraClockStage(camera, name="camera-clock")
+            )
+
+    # Add FontStage for headlines/poetry (default for demo)
+    if preset.source in ["headlines", "poetry"]:
+        from engine.pipeline.adapters import FontStage, ViewportFilterStage
+
+        # Add viewport filter to prevent rendering all items
+        pipeline.add_stage(
+            "viewport_filter", ViewportFilterStage(name="viewport-filter")
+        )
+        pipeline.add_stage("font", FontStage(name="font"))
+    else:
+        # Fallback to simple conversion for other sources
+        pipeline.add_stage("render", SourceItemsToBufferStage(name="items-to-buffer"))
+
+    # Add camera stage if specified in preset (after font/render stage)
+    if camera:
+        pipeline.add_stage("camera", CameraStage(camera, name=preset.camera))
 
     for effect_name in preset.effects:
         effect = effect_registry.get(effect_name)
@@ -451,7 +475,7 @@ def run_pipeline_mode(preset_name: str = "demo"):
                 # Add camera if specified
                 if new_preset.camera:
                     from engine.camera import Camera
-                    from engine.pipeline.adapters import CameraStage
+                    from engine.pipeline.adapters import CameraClockStage, CameraStage
 
                     speed = getattr(new_preset, "camera_speed", 1.0)
                     camera = None
@@ -468,8 +492,19 @@ def run_pipeline_mode(preset_name: str = "demo"):
                         camera = Camera.floating(speed=speed)
                     elif cam_type == "bounce":
                         camera = Camera.bounce(speed=speed)
+                    elif cam_type == "radial":
+                        camera = Camera.radial(speed=speed)
+                    elif cam_type == "static" or cam_type == "":
+                        # Static camera: no movement, but provides camera_y=0 for viewport filter
+                        camera = Camera.scroll(speed=0.0)
+                        camera.set_canvas_size(200, 200)
 
                     if camera:
+                        # Add camera update stage to ensure camera_y is available for viewport filter
+                        pipeline.add_stage(
+                            "camera_update",
+                            CameraClockStage(camera, name="camera-clock"),
+                        )
                         pipeline.add_stage("camera", CameraStage(camera, name=cam_type))
 
                 # Add effects
@@ -637,10 +672,11 @@ def run_pipeline_mode(preset_name: str = "demo"):
     ctx.set("pipeline_order", pipeline.execution_order)
     ctx.set("camera_y", 0)
 
-    current_width = 80
-    current_height = 24
+    current_width = params.viewport_width
+    current_height = params.viewport_height
 
-    if hasattr(display, "get_dimensions"):
+    # Only get dimensions from display if viewport wasn't explicitly set
+    if "--viewport" not in sys.argv and hasattr(display, "get_dimensions"):
         current_width, current_height = display.get_dimensions()
         params.viewport_width = current_width
         params.viewport_height = current_height
@@ -687,7 +723,7 @@ def run_pipeline_mode(preset_name: str = "demo"):
                     display.clear_quit_request()
                 raise KeyboardInterrupt()
 
-            if hasattr(display, "get_dimensions"):
+            if "--viewport" not in sys.argv and hasattr(display, "get_dimensions"):
                 new_w, new_h = display.get_dimensions()
                 if new_w != current_width or new_h != current_height:
                     current_width, current_height = new_w, new_h