Alpha-3: 4-Stage Curriculum + N-Step DQN + Pro Analytics

Alpha-3 — Full Training System Overhaul

4-Stage Curriculum with Dynamic Gamma

Stage	Name	Gamma	Promote Criteria
S1	FOOD_VECTOR	0.80	avg_food>=5 AND avg_steps>=50 (200 ep window)
S2	WALL_AVOID	0.90	avg_steps>=80 AND wall_death<3% (200 ep window)
S3	ENEMY_AVOID	0.95	avg_steps>=120 (200 ep window)
S4	MASS_MANAGEMENT	0.99	Final stage

Core Changes

• N-step returns (n=3) — reward signal propagates 3x faster
• Dynamic gamma per stage (effective horizon: 5→10→20→100 steps)
• Compound promotion — S1 requires BOTH food AND survival thresholds
• Tightened criteria — prevents premature stage advancement (previous run stuck at S3 after 8k eps)
• New rewards: enemy_approach_penalty, boost_penalty, expanded food_shaping clamp
• Softened S3 enemy penalties (2.0→1.0 proximity, 1.0→0.5 approach) to prevent paralysis

Professional Analytics Suite (13 Charts)

1. Main Dashboard (Bollinger bands, percentile steps, food SMA, loss, epsilon+LR, death area)
2. Curriculum Stage Progression (timeline with color bands)
3. Per-Stage Distributions (violin + box plots)
4. Hyperparameter Tracking (epsilon, LR, beta, loss EMA)
5. Correlation Scatter Matrix (12 plots with Pearson r + R² trend lines)
   5b. Correlation Heatmap + Ranked Strongest Correlations
6. Rolling Performance Percentile Bands (P10-P90)
7. Death Analysis (pie, grouped bars, histogram, rolling heatmap)
8. Food Efficiency (ratio tracking, cumulative, per-stage box)
9. Reward Distributions per Stage
10. Learning Detection (CDF early/late, volatility, segmented trends)
11. Goal Progress Gauges
12. HP Analysis (parallel coordinates, Epsilon×LR sweet spot heatmap, top 5% vs bottom 5%)

Breaking Changes

• Requires full training reset (new checkpoint format with n-step buffers + dynamic gamma)
• Old 3-stage curriculum replaced with 4-stage
• Old chart PNG files removed from repo

Previous Issues Fixed

• Bot stuck at Stage 3 after 8000+ episodes (avg_steps=42, 99.7% snake death, flat rewards)
• Root cause: S1 promoted after only 100 eps with trivial avg_food>=3 threshold
• S2→S3 promoted without real wall avoidance mastery