feat: Add multi-layer CNN support with framebuffer capture and blend control

Implements automatic layer chaining and generic framebuffer capture API for
multi-layer neural network effects with proper original input preservation.

Key changes:
- Effect::needs_framebuffer_capture() - generic API for pre-render capture
- MainSequence: auto-capture to "captured_frame" auxiliary texture
- CNNEffect: multi-layer support via layer_index/total_layers params
- seq_compiler: expands "layers=N" to N chained effect instances
- Shader: @binding(4) original_input available to all layers
- Training: generates layer switches and original input binding
- Blend: mix(original, result, blend_amount) uses layer 0 input

Timeline syntax: CNNEffect layers=3 blend=0.7

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

1 files changed, 85 insertions, 105 deletions

diff --git a/workspaces/main/timeline.seq b/workspaces/main/timeline.seq
index 3670825..5947ff8 100644
--- a/workspaces/main/timeline.seq
+++ b/workspaces/main/timeline.seq
@@ -1,121 +1,101 @@
-# WORKSPACE: main
-# ============================================================================
-# DEMO SEQUENCE DEFINITION
-# ============================================================================
-# Defines the timeline and layering of visual effects for the demo.
-# Compiled by seq_compiler into src/generated/timeline.cc at build time.
-#
-# DOCUMENTATION: See doc/SEQUENCE.md for complete syntax reference
-#
-# QUICK REFERENCE:
-#   SEQUENCE <start> <priority> ["optional_name"] [optional_end]
-#     EFFECT <+|=|-> <ClassName> <start> <end>
-#
-#   Priority modifiers: + (increment), = (same), - (decrement/background)
-#   Time notation: 0b (beats), 0.0 (seconds)
-#   Optional name: Displayed in Gantt charts (e.g., "Opening Scene")
-#
-# VALIDATION & VISUALIZATION:
-#   ./build/seq_compiler assets/demo.seq                    # Validate only
-#   ./build/seq_compiler assets/demo.seq --gantt-html=t.html  # HTML Gantt
-#
-# ============================================================================
-
+# Demo Timeline
+# Generated by Timeline Editor
 # BPM 120
 
-SEQUENCE 0b 0
-  EFFECT - FlashCubeEffect .2 3       # Background cube (priority -1 = behind everything)
-  EFFECT + FlashEffect 0.0 1. color=1.0,0.5,0.5 decay=0.95  # Red-tinted flash
-  EFFECT + FadeEffect 0.1 1.          # Priority 1
-  EFFECT + SolarizeEffect 0 4b        # Priority 2 (was 3, now contiguous)
-  EFFECT + VignetteEffect 0 6 radius=0.6 softness=0.1
+SEQUENCE 0.00 0
+  EFFECT - FlashCubeEffect 0.00 2.44
+  EFFECT + FlashEffect 0.00 1.00 color=1.0,0.5,0.5 decay=0.95
+  EFFECT + FadeEffect 0.10 1.00
+  EFFECT + SolarizeEffect 0.00 2.00
+  EFFECT + VignetteEffect 0.00 2.50 radius=0.6 softness=0.1
+
+SEQUENCE 2.50 0 "rotating cube"
+  EFFECT + CircleMaskEffect 0.00 4.00 0.50
+  EFFECT + RotatingCubeEffect 0.00 4.00
+  EFFECT + GaussianBlurEffect 1.00 2.00 strength=1.0
+  EFFECT + GaussianBlurEffect 3.00 4.00 strength=2.0
+
+SEQUENCE 5.93 0
+  EFFECT - FlashCubeEffect 0.11 1.45
+  EFFECT + FlashEffect 0.00 0.20
 
-SEQUENCE 2.0 0
-  EFFECT + CircleMaskEffect 0.0 4.0 0.50        # Priority 0 mask generator
-  EFFECT + RotatingCubeEffect 0.0 4.0           # Priority 1 (renders inside circle)
-  EFFECT + GaussianBlurEffect 1.0 2.0 strength=1.0
-  EFFECT + GaussianBlurEffect 3.0 4.0 strength=2.0
+SEQUENCE 6.90 1 "spray"
+  EFFECT + ParticleSprayEffect 0.00 2.00
+  EFFECT + ParticlesEffect 0.00 3.00
+  EFFECT = GaussianBlurEffect 0.00 2.00 strength=3.0
 
-SEQUENCE 4b 0
-  EFFECT - FlashCubeEffect 0.1 3.     # Priority -1
-  EFFECT + FlashEffect 0.0 0.2        # Priority 0 (was 4, now contiguous)
+SEQUENCE 8.50 2
+  EFFECT + ThemeModulationEffect 0.00 2.00
+  EFFECT + HeptagonEffect 0.20 2.00
+  EFFECT + ParticleSprayEffect 0.00 2.00
+  EFFECT = ParticlesEffect 0.00 2.00
+  EFFECT + Hybrid3DEffect 0.00 2.00
+  EFFECT + GaussianBlurEffect 0.00 2.00
+  EFFECT + ChromaAberrationEffect 0.00 1.50 offset=0.01 angle=1.57
 
-SEQUENCE 6b 1
-  EFFECT + ParticleSprayEffect 0 4    # Priority 0 (spray particles)
-  EFFECT + ParticlesEffect 0 4        # Priority 1
-  EFFECT = GaussianBlurEffect 0 8 strength=3.0     # Priority 1 (stronger blur)
+SEQUENCE 10.50 0
+  EFFECT + HeptagonEffect 0.00 0.20
+  EFFECT + FadeEffect 0.10 1.00
 
-SEQUENCE 7b 0
-  EFFECT + HeptagonEffect 0.0 .2      # Priority 0
-  EFFECT + FadeEffect 0.1 1.0         # Priority 1 (was 5, now contiguous)
+SEQUENCE 10.50 0
+  EFFECT + Hybrid3DEffect 0.00 5.59
+  EFFECT + CNNEffect 0.54 4.97 layers=3 blend=0.2
 
-# Post-processing chain (priority 10 = applied after scene rendering)
-# Effects are applied in priority order: lower numbers first
-SEQUENCE 8b 3
-  EFFECT + ThemeModulationEffect 0 4     # Priority 0
-  EFFECT = HeptagonEffect 0.0 4.0        # Priority 0 (same layer)
-  EFFECT + GaussianBlurEffect 0 8 strength=1.5        # Priority 1 (subtle blur)
-  EFFECT + ChromaAberrationEffect 0 6 offset=0.03 angle=0.785    # Priority 2 (diagonal, stronger)
-  EFFECT + SolarizeEffect 0 10           # Priority 3
+SEQUENCE 16.14 3
+  EFFECT + ThemeModulationEffect 0.00 4.00
+  EFFECT = HeptagonEffect 0.00 4.00
+  EFFECT + GaussianBlurEffect 0.00 5.00 strength=1.5
+  EFFECT + ChromaAberrationEffect 0.00 5.00 offset=0.03 angle=0.785
+  EFFECT + SolarizeEffect 0.00 5.00
 
-SEQUENCE 12b 2
-  EFFECT - FlashCubeEffect .2 3          # Priority -1 (background)
-  EFFECT + HeptagonEffect 0 4            # Priority 0
-  EFFECT + ParticleSprayEffect 0 4       # Priority 1 (spray particles)
-  EFFECT + ParticlesEffect 0 4           # Priority 2
+SEQUENCE 21.00 2
+  EFFECT - FlashCubeEffect 0.20 1.50
+  EFFECT + HeptagonEffect 0.00 2.00
+  EFFECT + ParticleSprayEffect 0.00 2.00
+  EFFECT + ParticlesEffect 0.00 2.00
 
-SEQUENCE 15b 2
-  EFFECT - FlashCubeEffect .2 3          # Priority -1 (background)
-  EFFECT + FlashEffect 0.0 1             # Priority 0
+SEQUENCE 22.75 2
+  EFFECT - FlashCubeEffect 0.20 1.50
+  EFFECT + FlashEffect 0.00 1.00
 
-SEQUENCE 16b 10
-  EFFECT - FlashCubeEffect .2 3          # Priority -1 (background)
-  EFFECT + GaussianBlurEffect 0 8        # Priority 0
-  EFFECT + FlashEffect 0.0 0.2           # Priority 1
-  EFFECT = FlashEffect 1b 0.2            # Priority 1 (same layer)
+SEQUENCE 23.88 10
+  EFFECT - FlashCubeEffect 0.20 1.50
+  EFFECT + GaussianBlurEffect 0.00 2.00
+  EFFECT + FlashEffect 0.00 0.20
+  EFFECT = FlashEffect 0.50 0.20
 
-SEQUENCE 17b 2
-  EFFECT + ThemeModulationEffect 0 4     # Priority 0
-  EFFECT + HeptagonEffect 0.2 2.0        # Priority 1
-  EFFECT + ParticleSprayEffect 0 4       # Priority 2 (spray particles)
-  EFFECT = ParticlesEffect 0 4           # Priority 2 (same layer)
-  EFFECT + Hybrid3DEffect 0 4            # Priority 3
-  EFFECT + GaussianBlurEffect 0 8        # Priority 4
-  EFFECT + ChromaAberrationEffect 0 6 offset=0.01 angle=1.57    # Priority 5 (vertical, subtle)
+SEQUENCE 25.59 1
+  EFFECT + ThemeModulationEffect 0.00 8.00
+  EFFECT + HeptagonEffect 0.20 2.00
+  EFFECT + ParticleSprayEffect 0.00 8.00
+  EFFECT + Hybrid3DEffect 0.00 10.00
+  EFFECT + GaussianBlurEffect 0.00 8.00
+  EFFECT + ChromaAberrationEffect 0.00 10.00
+  EFFECT + SolarizeEffect 0.00 10.00
 
-SEQUENCE 24b 1
-  EFFECT + ThemeModulationEffect 0 8     # Priority 0
-  EFFECT + HeptagonEffect 0.2 2.0        # Priority 1
-  EFFECT + ParticleSprayEffect 0 8       # Priority 2 (spray particles - longer duration)
-  EFFECT + Hybrid3DEffect 0 20           # Priority 3
-  EFFECT + GaussianBlurEffect 0 8        # Priority 4
-  EFFECT + ChromaAberrationEffect 0 10   # Priority 5
-  EFFECT + SolarizeEffect 0 10           # Priority 6
+SEQUENCE 35.31 0
+  EFFECT + ThemeModulationEffect 0.00 4.00
+  EFFECT + HeptagonEffect 0.20 2.00
+  EFFECT + GaussianBlurEffect 0.00 8.00
+  EFFECT + SolarizeEffect 0.00 2.00
 
-SEQUENCE 32b 0
-  EFFECT + ThemeModulationEffect 0 4     # Priority 0
-  EFFECT + HeptagonEffect 0 16           # Priority 1
-  EFFECT + ChromaAberrationEffect 0 16   # Priority 2
-  EFFECT + GaussianBlurEffect 0 8        # Priority 3
+SEQUENCE 42.29 0
+  EFFECT + ThemeModulationEffect 0.00 6.00
+  EFFECT = HeptagonEffect 0.20 2.00
+  EFFECT + Hybrid3DEffect 0.00 4.00
+  EFFECT + ParticleSprayEffect 0.00 5.50
+  EFFECT + HeptagonEffect 0.00 8.00
+  EFFECT + ChromaAberrationEffect 0.00 7.50
+  EFFECT + GaussianBlurEffect 0.00 8.00
 
-SEQUENCE 48b 0
-  EFFECT + ThemeModulationEffect 0 4     # Priority 0
-  EFFECT + HeptagonEffect 0.2 2.0        # Priority 1
-  EFFECT + GaussianBlurEffect 0 8        # Priority 2
-  EFFECT + SolarizeEffect 0 2            # Priority 3
+SEQUENCE 50.02 0
+  EFFECT + ThemeModulationEffect 0.00 4.00
+  EFFECT + HeptagonEffect 0.00 9.50
+  EFFECT + ChromaAberrationEffect 0.00 9.00
+  EFFECT + GaussianBlurEffect 0.00 8.00
 
-SEQUENCE 56b 0
-  EFFECT + ThemeModulationEffect 0 8     # Priority 0
-  EFFECT = HeptagonEffect 0.2 2.0        # Priority 0 (same layer)
-  EFFECT + Hybrid3DEffect 0 4            # Priority 1
-  EFFECT + ParticleSprayEffect 0 8       # Priority 2 (spray particles)
-  EFFECT + HeptagonEffect 0 16           # Priority 3
-  EFFECT + ChromaAberrationEffect 0 16   # Priority 4
-  EFFECT + GaussianBlurEffect 0 8        # Priority 5
+SEQUENCE 31.00 0
+  EFFECT + ThemeModulationEffect 0.00 3.00
+  EFFECT + VignetteEffect 0.00 3.00 radius=0.6 softness=0.3
+  EFFECT + SolarizeEffect 0.00 3.00
 
-SEQUENCE 62b 0
-  EFFECT + ThemeModulationEffect 0 3     # Priority 0
-  EFFECT + VignetteEffect 0 3 radius=0.6 softness=0.3 # New effect
-  EFFECT + SolarizeEffect 0 3            # Priority 2
-# Demo automatically exits at this time (supports beat notation)
-END_DEMO 65b