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/pipeline/stages/framebuffer.py

@@ -1,12 +1,12 @@
 """
 Frame buffer stage - stores previous frames for temporal effects.
 
-Provides:
-- frame_history: list of previous buffers (most recent first)
-- intensity_history: list of corresponding intensity maps
-- current_intensity: intensity map for current frame
+Provides (per-instance, using instance name):
+- framebuffer.{name}.history: list of previous buffers (most recent first)
+- framebuffer.{name}.intensity_history: list of corresponding intensity maps
+- framebuffer.{name}.current_intensity: intensity map for current frame
 
-Capability: "framebuffer.history"
+Capability: "framebuffer.history.{name}"
 """
 
 import threading
@@ -22,21 +22,32 @@ class FrameBufferConfig:
     """Configuration for FrameBufferStage."""
 
     history_depth: int = 2  # Number of previous frames to keep
+    name: str = "default"  # Unique instance name for capability and context keys
 
 
 class FrameBufferStage(Stage):
-    """Stores frame history and computes intensity maps."""
+    """Stores frame history and computes intensity maps.
+
+    Supports multiple instances with unique capabilities and context keys.
+    """
 
     name = "framebuffer"
     category = "effect"  # It's an effect that enriches context with frame history
 
-    def __init__(self, config: FrameBufferConfig | None = None, history_depth: int = 2):
-        self.config = config or FrameBufferConfig(history_depth=history_depth)
+    def __init__(
+        self,
+        config: FrameBufferConfig | None = None,
+        history_depth: int = 2,
+        name: str = "default",
+    ):
+        self.config = config or FrameBufferConfig(
+            history_depth=history_depth, name=name
+        )
         self._lock = threading.Lock()
 
     @property
     def capabilities(self) -> set[str]:
-        return {"framebuffer.history"}
+        return {f"framebuffer.history.{self.config.name}"}
 
     @property
     def dependencies(self) -> set[str]:
@@ -53,8 +64,9 @@ class FrameBufferStage(Stage):
 
     def init(self, ctx: PipelineContext) -> bool:
         """Initialize framebuffer state in context."""
-        ctx.set("frame_history", [])
-        ctx.set("intensity_history", [])
+        prefix = f"framebuffer.{self.config.name}"
+        ctx.set(f"{prefix}.history", [])
+        ctx.set(f"{prefix}.intensity_history", [])
         return True
 
     def process(self, data: Any, ctx: PipelineContext) -> Any:
@@ -70,16 +82,18 @@ class FrameBufferStage(Stage):
         if not isinstance(data, list):
             return data
 
+        prefix = f"framebuffer.{self.config.name}"
+
         # Compute intensity map for current buffer (per-row, length = buffer rows)
         intensity_map = self._compute_buffer_intensity(data, len(data))
 
         # Store in context
-        ctx.set("current_intensity", intensity_map)
+        ctx.set(f"{prefix}.current_intensity", intensity_map)
 
         with self._lock:
             # Get existing histories
-            history = ctx.get("frame_history", [])
-            intensity_hist = ctx.get("intensity_history", [])
+            history = ctx.get(f"{prefix}.history", [])
+            intensity_hist = ctx.get(f"{prefix}.intensity_history", [])
 
             # Prepend current frame to history
             history.insert(0, data.copy())
@@ -87,8 +101,8 @@ class FrameBufferStage(Stage):
 
             # Trim to configured depth
             max_depth = self.config.history_depth
-            ctx.set("frame_history", history[:max_depth])
-            ctx.set("intensity_history", intensity_hist[:max_depth])
+            ctx.set(f"{prefix}.history", history[:max_depth])
+            ctx.set(f"{prefix}.intensity_history", intensity_hist[:max_depth])
 
         return data
 
@@ -137,7 +151,8 @@ class FrameBufferStage(Stage):
         """Get frame from history by index (0 = current, 1 = previous, etc)."""
         if ctx is None:
             return None
-        history = ctx.get("frame_history", [])
+        prefix = f"framebuffer.{self.config.name}"
+        history = ctx.get(f"{prefix}.history", [])
         if 0 <= index < len(history):
             return history[index]
         return None
@@ -148,7 +163,8 @@ class FrameBufferStage(Stage):
         """Get intensity map from history by index."""
         if ctx is None:
             return None
-        intensity_hist = ctx.get("intensity_history", [])
+        prefix = f"framebuffer.{self.config.name}"
+        intensity_hist = ctx.get(f"{prefix}.intensity_history", [])
         if 0 <= index < len(intensity_hist):
             return intensity_hist[index]
         return None