feat(graph): Add adapter to convert graphs to pipelines

Bridge the new graph abstraction with existing Stage-based pipeline
system for backward compatibility.

- Add GraphAdapter class to map nodes to Stage implementations
- Handle effect intensity configuration (sets global effect state)
- Map camera modes to Camera factory methods (feed, scroll, horizontal, etc.)
- Auto-inject required dependencies (render, camera_update) via pipeline capabilities
- Support for all major node types: source, camera, effect, position, display

The adapter ensures that graphs seamlessly integrate with the existing
pipeline architecture while providing a cleaner abstraction layer.

engine/pipeline/graph_adapter.py

@@ -0,0 +1,161 @@
+"""Adapter to convert Graph to Pipeline stages.
+
+This module bridges the new graph-based abstraction with the existing
+Stage-based pipeline system for backward compatibility.
+"""
+
+from typing import Dict, Any, List, Optional
+
+from engine.pipeline.graph import Graph, NodeType
+from engine.pipeline.controller import Pipeline, PipelineConfig
+from engine.pipeline.core import PipelineContext
+from engine.pipeline.params import PipelineParams
+from engine.pipeline.adapters import (
+    CameraStage,
+    DataSourceStage,
+    DisplayStage,
+    EffectPluginStage,
+    FontStage,
+    MessageOverlayStage,
+    PositionStage,
+    ViewportFilterStage,
+    create_stage_from_display,
+    create_stage_from_effect,
+)
+from engine.pipeline.adapters.positioning import PositioningMode
+from engine.display import DisplayRegistry
+from engine.effects import get_registry
+from engine.data_sources.sources import EmptyDataSource, HeadlinesDataSource
+from engine.camera import Camera
+
+
+class GraphAdapter:
+    """Converts Graph to Pipeline with existing Stage classes."""
+
+    def __init__(self, graph: Graph):
+        self.graph = graph
+        self.pipeline: Optional[Pipeline] = None
+        self.context: Optional[PipelineContext] = None
+
+    def build_pipeline(
+        self, viewport_width: int = 80, viewport_height: int = 24
+    ) -> Pipeline:
+        """Build a Pipeline from the Graph."""
+        # Create pipeline context
+        self.context = PipelineContext()
+        self.context.terminal_width = viewport_width
+        self.context.terminal_height = viewport_height
+
+        # Create params
+        params = PipelineParams(
+            viewport_width=viewport_width,
+            viewport_height=viewport_height,
+        )
+        self.context.params = params
+
+        # Create pipeline config
+        config = PipelineConfig()
+
+        # Create pipeline
+        self.pipeline = Pipeline(config=config, context=self.context)
+
+        # Map graph nodes to pipeline stages
+        self._map_nodes_to_stages()
+
+        # Build pipeline
+        self.pipeline.build()
+
+        return self.pipeline
+
+    def _map_nodes_to_stages(self) -> None:
+        """Map graph nodes to pipeline stages."""
+        for name, node in self.graph.nodes.items():
+            if not node.enabled:
+                continue
+
+            stage = self._create_stage_from_node(name, node)
+            if stage:
+                self.pipeline.add_stage(name, stage)
+
+    def _create_stage_from_node(self, name: str, node) -> Optional:
+        """Create a pipeline stage from a graph node."""
+        stage = None
+
+        if node.type == NodeType.SOURCE:
+            source_type = node.config.get("source", "headlines")
+            if source_type == "headlines":
+                source = HeadlinesDataSource()
+            elif source_type == "empty":
+                source = EmptyDataSource(
+                    width=self.context.terminal_width,
+                    height=self.context.terminal_height,
+                )
+            else:
+                source = EmptyDataSource(
+                    width=self.context.terminal_width,
+                    height=self.context.terminal_height,
+                )
+            stage = DataSourceStage(source, name=name)
+
+        elif node.type == NodeType.CAMERA:
+            mode = node.config.get("mode", "scroll")
+            speed = node.config.get("speed", 1.0)
+            # Map mode string to Camera factory method
+            mode_lower = mode.lower()
+            if hasattr(Camera, mode_lower):
+                camera_factory = getattr(Camera, mode_lower)
+                camera = camera_factory(speed=speed)
+            else:
+                # Fallback to scroll mode
+                camera = Camera.scroll(speed=speed)
+            stage = CameraStage(camera, name=name)
+
+        elif node.type == NodeType.DISPLAY:
+            backend = node.config.get("backend", "terminal")
+            positioning = node.config.get("positioning", "mixed")
+            display = DisplayRegistry.create(backend)
+            if display:
+                stage = DisplayStage(display, name=name, positioning=positioning)
+
+        elif node.type == NodeType.EFFECT:
+            effect_name = node.config.get("effect", "")
+            intensity = node.config.get("intensity", 1.0)
+            effect = get_registry().get(effect_name)
+            if effect:
+                # Set effect intensity (modifies global effect state)
+                effect.config.intensity = intensity
+                # Effects typically depend on rendered output
+                dependencies = {"render.output"}
+                stage = EffectPluginStage(effect, name=name, dependencies=dependencies)
+
+        elif node.type == NodeType.RENDER:
+            stage = FontStage(name=name)
+
+        elif node.type == NodeType.OVERLAY:
+            stage = MessageOverlayStage(name=name)
+
+        elif node.type == NodeType.POSITION:
+            mode_str = node.config.get("mode", "mixed")
+            try:
+                mode = PositioningMode(mode_str)
+            except ValueError:
+                mode = PositioningMode.MIXED
+            stage = PositionStage(mode=mode, name=name)
+
+        return stage
+
+
+def graph_to_pipeline(
+    graph: Graph, viewport_width: int = 80, viewport_height: int = 24
+) -> Pipeline:
+    """Convert a Graph to a Pipeline."""
+    adapter = GraphAdapter(graph)
+    return adapter.build_pipeline(viewport_width, viewport_height)
+
+
+def dict_to_pipeline(
+    data: Dict[str, Any], viewport_width: int = 80, viewport_height: int = 24
+) -> Pipeline:
+    """Convert a dictionary to a Pipeline."""
+    graph = Graph().from_dict(data)
+    return graph_to_pipeline(graph, viewport_width, viewport_height)