pkboost 2.2.0

Shannon-guided gradient boosting for extreme class imbalance with adaptive drift detection. Outperforms XGBoost/LightGBM on imbalanced data.
Documentation
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// Adaptive regression with drift detection and metamorphosis
// Regression equivalent of AdversarialLivingBooster

use crate::constants::*;
use crate::metabolism::FeatureMetabolism;
use crate::optimized_data::TransposedData;
use crate::regression::calculate_rmse;
use crate::regression::PKBoostRegressor;
use crate::tree::{OptimizedTreeShannon, TreeParams};
use ndarray::{Array1, Array2, ArrayView1, ArrayView2};
use rayon::prelude::*;
use std::collections::VecDeque;

#[derive(Debug, Clone, Copy, PartialEq)]
pub enum SystemState {
    Normal,
    Alert { checks_in_alert: usize },
    Metamorphosis,
}

pub struct RegressionVulnerability {
    pub error: f64,
    pub sample_idx: usize,
}

#[derive(Debug)]
pub struct DriftDiagnostics {
    pub error_entropy: f64,
    pub feature_entropy: Vec<f64>,
    pub drift_type: DriftType,
    pub residual_autocorrelation: f64,
    pub heteroscedasticity_score: f64,
}

#[derive(Debug, Clone, Copy)]
pub enum DriftType {
    Systemic,
    Localized,
    FeatureShift,
}

pub struct AdaptiveRegressor {
    primary: PKBoostRegressor,
    metabolism: FeatureMetabolism,
    state: SystemState,
    alert_trigger_threshold: usize,
    metamorphosis_trigger_threshold: usize,
    vulnerability_alert_threshold: f64,
    baseline_rmse: f64,
    consecutive_vulnerable_checks: usize,
    observations_count: usize,
    metamorphosis_count: usize,
    recent_x: VecDeque<Vec<f64>>, // Keep as Vec for streaming buffer
    recent_y: VecDeque<f64>,
    buffer_size: usize,
    metamorphosis_cooldown: usize,
    iterations_since_metamorphosis: usize,
    recent_rmse: VecDeque<f64>,
    recent_vulnerabilities: VecDeque<RegressionVulnerability>,
    vulnerability_ema: f64,
    ema_alpha: f64,
}

impl AdaptiveRegressor {
    /// Create new AdaptiveRegressor from ArrayView2 (zero-copy from Python)
    pub fn new(x_train: ArrayView2<'_, f64>, y_train: ArrayView1<'_, f64>) -> Self {
        let n_features = x_train.ncols();
        let n_samples = x_train.nrows();

        let (alert_thresh, meta_thresh) = if n_samples < 50_000 {
            (1, 2)
        } else if n_samples < 200_000 {
            (2, 3)
        } else {
            (3, 5)
        };

        let buffer_sz = if n_samples < 50_000 { 10000 } else { 15000 };
        let cooldown = if n_samples < 50_000 { 1000 } else { 5000 };

        println!("\n=== Adaptive Regressor Configuration ===");
        println!("Dataset: {} samples, {} features", n_samples, n_features);
        println!("Alert trigger: {} checks", alert_thresh);
        println!("Metamorphosis trigger: {} checks", meta_thresh);
        println!("Buffer size: {} samples", buffer_sz);
        println!("Cooldown: {} observations", cooldown);
        println!("=========================================\n");

        Self {
            primary: PKBoostRegressor::auto(x_train, y_train),
            metabolism: FeatureMetabolism::new(n_features),
            state: SystemState::Normal,
            alert_trigger_threshold: alert_thresh,
            metamorphosis_trigger_threshold: meta_thresh,
            vulnerability_alert_threshold: 0.5,
            baseline_rmse: 0.0,
            consecutive_vulnerable_checks: 0,
            observations_count: 0,
            metamorphosis_count: 0,
            recent_x: VecDeque::with_capacity(buffer_sz),
            recent_y: VecDeque::with_capacity(buffer_sz),
            buffer_size: buffer_sz,
            metamorphosis_cooldown: cooldown,
            iterations_since_metamorphosis: 0,
            recent_rmse: VecDeque::with_capacity(5),
            recent_vulnerabilities: VecDeque::with_capacity(5000),
            vulnerability_ema: 0.0,
            ema_alpha: VULNERABILITY_EMA_ALPHA,
        }
    }

    /// Initial training with ArrayView2 (zero-copy from Python)
    pub fn fit_initial(
        &mut self,
        x: ArrayView2<'_, f64>,
        y: ArrayView1<'_, f64>,
        eval_set: Option<(ArrayView2<'_, f64>, ArrayView1<'_, f64>)>,
        verbose: bool,
    ) -> Result<(), String> {
        if verbose {
            println!("\n=== INITIAL TRAINING (Adaptive Regressor) ===");
        }
        self.primary.fit(x, y, eval_set, verbose)?;

        // Validate model learned
        let train_preds = self.primary.predict(x)?;
        let train_preds_slice = train_preds.as_slice().unwrap();
        let y_slice = y.as_slice().ok_or("y must be contiguous")?;
        let train_rmse = calculate_rmse(y_slice, train_preds_slice);
        let y_mean = y_slice.iter().sum::<f64>() / y_slice.len() as f64;
        let y_std = (y_slice.iter().map(|yi| (yi - y_mean).powi(2)).sum::<f64>()
            / y_slice.len() as f64)
            .sqrt();

        if train_rmse > y_std * 0.95 || !train_rmse.is_finite() {
            return Err(format!(
                "Model failed to learn! RMSE: {:.4}, Baseline: {:.4}",
                train_rmse, y_std
            ));
        }

        if let Some((x_val, y_val)) = eval_set {
            let val_preds = self.primary.predict(x_val)?;
            let val_preds_slice = val_preds.as_slice().unwrap();
            let y_val_slice = y_val.as_slice().unwrap();
            self.baseline_rmse = calculate_rmse(y_val_slice, val_preds_slice);

            if self.baseline_rmse < 0.001 || !self.baseline_rmse.is_finite() {
                let val_mean = y_val_slice.iter().sum::<f64>() / y_val_slice.len() as f64;
                self.baseline_rmse = (y_val_slice
                    .iter()
                    .map(|y| (y - val_mean).powi(2))
                    .sum::<f64>()
                    / y_val_slice.len() as f64)
                    .sqrt();
                if verbose {
                    println!(
                        "⚠️  Invalid baseline, using Y std: {:.4}",
                        self.baseline_rmse
                    );
                }
            }

            self.vulnerability_alert_threshold = self.baseline_rmse * 1.5;

            if verbose {
                println!(
                    "Train RMSE: {:.4}, Baseline: {:.4}",
                    train_rmse, self.baseline_rmse
                );
                println!(
                    "Vulnerability threshold: {:.4}",
                    self.vulnerability_alert_threshold
                );
            }
        } else {
            self.baseline_rmse = train_rmse;
            self.vulnerability_alert_threshold = self.baseline_rmse * 1.5;
        }

        if verbose {
            println!("Initial training complete. Model ready for streaming.");
        }
        Ok(())
    }

    /// Process streaming batch with ArrayView2 (zero-copy from Python)
    pub fn observe_batch(
        &mut self,
        x: ArrayView2<'_, f64>,
        y: ArrayView1<'_, f64>,
        verbose: bool,
    ) -> Result<(), String> {
        let n_samples = x.nrows();
        let y_slice = y.as_slice().ok_or("y must be contiguous")?;

        self.observations_count += n_samples;
        self.iterations_since_metamorphosis += n_samples;

        // Maintain buffer
        for i in 0..n_samples {
            if self.recent_x.len() >= self.buffer_size {
                self.recent_x.pop_front();
                self.recent_y.pop_front();
            }
            self.recent_x.push_back(x.row(i).to_vec());
            self.recent_y.push_back(y_slice[i]);
        }

        let preds = self.primary.predict(x)?;
        let preds_slice = preds.as_slice().unwrap();
        let batch_rmse = calculate_rmse(y_slice, preds_slice);
        self.recent_rmse.push_back(batch_rmse);
        if self.recent_rmse.len() > 5 {
            self.recent_rmse.pop_front();
        }

        // Track vulnerabilities
        for (i, (&pred, &true_y)) in preds_slice.iter().zip(y_slice.iter()).enumerate() {
            let error = (pred - true_y).abs();
            if error > self.baseline_rmse {
                let vuln = RegressionVulnerability {
                    error,
                    sample_idx: i,
                };
                if self.recent_vulnerabilities.len() >= 5000 {
                    self.recent_vulnerabilities.pop_front();
                }
                self.recent_vulnerabilities.push_back(vuln);
                self.vulnerability_ema =
                    self.ema_alpha * error + (1.0 - self.ema_alpha) * self.vulnerability_ema;
            }
        }

        let usage = self.primary.get_feature_usage();
        self.metabolism.update(&usage, self.observations_count);

        if self.iterations_since_metamorphosis > self.metamorphosis_cooldown {
            self.update_state(verbose);
        }

        if let SystemState::Metamorphosis = self.state {
            if verbose {
                println!(
                    "\n=== METAMORPHOSIS TRIGGERED at observation {} ===",
                    self.observations_count
                );
            }
            self.execute_metamorphosis(verbose)?;
            self.iterations_since_metamorphosis = 0;
        }

        if verbose && self.observations_count % 5000 < n_samples {
            println!(
                "Status @ {}: RMSE: {:.4}, State: {:?}, Vuln: {:.4}",
                self.observations_count, batch_rmse, self.state, self.vulnerability_ema
            );
        }

        Ok(())
    }

    fn calculate_weighted_rmse(&self) -> Option<f64> {
        if self.recent_rmse.len() < 3 {
            return None;
        }
        let weights = vec![RMSE_WEIGHT_RECENT, RMSE_WEIGHT_MIDDLE, RMSE_WEIGHT_OLDEST];
        let weighted_sum: f64 = self
            .recent_rmse
            .iter()
            .rev()
            .zip(weights.iter())
            .map(|(r, w)| r * w)
            .sum();
        Some(weighted_sum / (RMSE_WEIGHT_RECENT + RMSE_WEIGHT_MIDDLE + RMSE_WEIGHT_OLDEST))
    }

    fn update_state(&mut self, verbose: bool) {
        let weighted_rmse = match self.calculate_weighted_rmse() {
            Some(r) => r,
            None => return,
        };

        let degradation = (weighted_rmse - self.baseline_rmse) / self.baseline_rmse;

        let adaptive_threshold =
            if self.vulnerability_ema > self.baseline_rmse * NOISE_DETECTION_MULTIPLIER {
                BASE_DEGRADATION_THRESHOLD * NOISY_DATA_THRESHOLD_MULTIPLIER
            } else {
                BASE_DEGRADATION_THRESHOLD
            };

        let is_vulnerable = degradation > adaptive_threshold
            || self.vulnerability_ema > self.vulnerability_alert_threshold;

        match self.state {
            SystemState::Normal => {
                if is_vulnerable {
                    self.consecutive_vulnerable_checks += 1;
                    if self.consecutive_vulnerable_checks >= self.alert_trigger_threshold {
                        if verbose {
                            println!(
                                "-- ALERT: RMSE degradation {:.1}% (threshold: {:.1}%) --",
                                degradation * 100.0,
                                adaptive_threshold * 100.0
                            );
                        }
                        self.state = SystemState::Alert { checks_in_alert: 1 };
                    }
                } else {
                    self.consecutive_vulnerable_checks = 0;
                }
            }
            SystemState::Alert { checks_in_alert } => {
                if is_vulnerable {
                    if checks_in_alert + 1 >= self.metamorphosis_trigger_threshold {
                        if verbose {
                            println!("-- METAMORPHOSIS: Persistent degradation --");
                        }
                        self.state = SystemState::Metamorphosis;
                    } else {
                        self.state = SystemState::Alert {
                            checks_in_alert: checks_in_alert + 1,
                        };
                    }
                } else {
                    if verbose {
                        println!("-- System returned to NORMAL --");
                    }
                    self.consecutive_vulnerable_checks = 0;
                    self.state = SystemState::Normal;
                }
            }
            SystemState::Metamorphosis => {}
        }
    }

    fn calculate_residual_autocorrelation(&self, errors: &[f64]) -> f64 {
        if errors.len() < 2 {
            return 0.0;
        }
        let mean = errors.iter().sum::<f64>() / errors.len() as f64;
        let mut numerator = 0.0;
        let mut denominator = 0.0;

        for i in 0..errors.len() - 1 {
            numerator += (errors[i] - mean) * (errors[i + 1] - mean);
        }
        for &e in errors {
            denominator += (e - mean).powi(2);
        }

        if denominator < EPSILON {
            0.0
        } else {
            numerator / denominator
        }
    }

    fn calculate_heteroscedasticity(&self, predictions: &[f64], errors: &[f64]) -> f64 {
        if predictions.len() < 10 {
            return 0.0;
        }

        let n_bins = 10.min(predictions.len() / 10);
        let mut pred_sorted: Vec<(f64, f64)> = predictions
            .iter()
            .zip(errors.iter())
            .map(|(&p, &e)| (p, e.abs()))
            .collect();
        pred_sorted.sort_by(|a, b| a.0.partial_cmp(&b.0).unwrap());

        let chunk_size = pred_sorted.len() / n_bins;
        let mut bin_vars = Vec::new();

        for chunk in pred_sorted.chunks(chunk_size) {
            let chunk_errors: Vec<f64> = chunk.iter().map(|(_, e)| *e).collect();
            let mean = chunk_errors.iter().sum::<f64>() / chunk_errors.len() as f64;
            let var = chunk_errors.iter().map(|e| (e - mean).powi(2)).sum::<f64>()
                / chunk_errors.len() as f64;
            bin_vars.push(var);
        }

        if bin_vars.is_empty() {
            return 0.0;
        }
        let mean_var = bin_vars.iter().sum::<f64>() / bin_vars.len() as f64;
        bin_vars
            .iter()
            .map(|v| (v - mean_var).powi(2))
            .sum::<f64>()
            .sqrt()
    }

    fn calculate_error_entropy(&self, errors: &[f64]) -> f64 {
        if errors.is_empty() {
            return 0.0;
        }

        let mut sorted_errors: Vec<f64> = errors
            .iter()
            .copied()
            .filter(|e| e.is_finite() && *e >= 0.0)
            .collect();

        if sorted_errors.is_empty() {
            return 0.0;
        }
        sorted_errors.sort_by(|a, b| a.partial_cmp(b).unwrap());

        let n_bins = 10.min(sorted_errors.len());
        let mut bins = vec![0; n_bins];
        let max_error = sorted_errors.last().unwrap() + EPSILON;

        for &err in &sorted_errors {
            let bin_idx = ((err / max_error) * n_bins as f64)
                .floor()
                .min((n_bins - 1) as f64) as usize;
            bins[bin_idx] += 1;
        }

        let total = sorted_errors.len() as f64;
        let entropy: f64 = bins
            .iter()
            .filter(|&&count| count > 0)
            .map(|&count| {
                let p = count as f64 / total;
                -p * p.log2()
            })
            .sum();

        entropy.max(0.0)
    }

    fn diagnose_drift(&self) -> DriftDiagnostics {
        let val_size = 2000.min(self.recent_x.len());
        let val_x: Vec<Vec<f64>> = self.recent_x.iter().rev().take(val_size).cloned().collect();
        let val_y: Vec<f64> = self.recent_y.iter().rev().take(val_size).cloned().collect();

        let val_x_arr = vec_to_array2(&val_x);
        let preds = self.primary.predict(val_x_arr.view()).unwrap_or_default();
        let preds_slice = preds.as_slice().unwrap_or(&[]);
        let errors: Vec<f64> = preds_slice
            .iter()
            .zip(val_y.iter())
            .map(|(p, y)| (p - y).abs())
            .collect();

        let error_entropy = self.calculate_error_entropy(&errors);

        let n_features = val_x.get(0).map_or(0, |row| row.len());
        let mut feature_entropy = Vec::new();

        for feat_idx in 0..n_features {
            let feat_vals: Vec<f64> = val_x.iter().map(|row| row[feat_idx]).collect();
            let feat_ent = self.calculate_error_entropy(&feat_vals);
            feature_entropy.push(feat_ent);
        }

        let drift_type = if error_entropy > SYSTEMIC_DRIFT_ENTROPY {
            DriftType::Systemic
        } else if error_entropy < LOCALIZED_DRIFT_ENTROPY {
            DriftType::Localized
        } else {
            DriftType::FeatureShift
        };

        let residual_autocorrelation = self.calculate_residual_autocorrelation(&errors);
        let heteroscedasticity_score = self.calculate_heteroscedasticity(preds_slice, &errors);

        DriftDiagnostics {
            error_entropy,
            feature_entropy,
            drift_type,
            residual_autocorrelation,
            heteroscedasticity_score,
        }
    }

    fn execute_metamorphosis(&mut self, verbose: bool) -> Result<(), String> {
        let checkpoint_trees = self.primary.trees.clone();

        let val_size = match self.recent_x.len() {
            0..=4000 => (self.recent_x.len() / 3)
                .max(MIN_VALIDATION_SIZE)
                .min(self.recent_x.len()),
            4001..=15000 => 2000,
            _ => ((self.recent_x.len() as f64 * 0.2) as usize).max(2000),
        };

        let val_x_vec: Vec<Vec<f64>> = self.recent_x.iter().rev().take(val_size).cloned().collect();
        let val_y: Vec<f64> = self.recent_y.iter().rev().take(val_size).cloned().collect();
        let val_x = vec_to_array2(&val_x_vec);

        let pre_preds = self.primary.predict(val_x.view())?;
        let checkpoint_rmse = calculate_rmse(&val_y, pre_preds.as_slice().unwrap());

        let diagnostics = self.diagnose_drift();

        let drifted_features: Vec<usize> = if self.recent_x.len() > 2000 {
            let n_features = self.recent_x.get(0).map_or(0, |r| r.len());
            (0..n_features)
                .filter(|&feat_idx| {
                    let recent: Vec<f64> = self
                        .recent_x
                        .iter()
                        .rev()
                        .take(1000)
                        .filter_map(|r| r.get(feat_idx).copied())
                        .collect();
                    let older: Vec<f64> = self
                        .recent_x
                        .iter()
                        .take(1000)
                        .filter_map(|r| r.get(feat_idx).copied())
                        .collect();

                    if recent.len() < 100 || older.len() < 100 {
                        return false;
                    }

                    let recent_mean = recent.iter().sum::<f64>() / recent.len() as f64;
                    let older_mean = older.iter().sum::<f64>() / older.len() as f64;
                    let drift_score =
                        (recent_mean - older_mean).abs() / older_mean.abs().max(EPSILON);

                    drift_score > FEATURE_DRIFT_THRESHOLD
                })
                .collect()
        } else {
            let avg_feat_entropy = diagnostics.feature_entropy.iter().sum::<f64>()
                / diagnostics.feature_entropy.len() as f64;
            diagnostics
                .feature_entropy
                .iter()
                .enumerate()
                .filter(|(_, &ent)| ent > avg_feat_entropy * 1.2)
                .map(|(i, _)| i)
                .collect()
        };

        if verbose {
            println!("  - Checkpointing {} trees", checkpoint_trees.len());
            println!(
                "  - Drift Analysis: Error Entropy: {:.3}, Type: {:?}",
                diagnostics.error_entropy, diagnostics.drift_type
            );
        }

        let buffer_x_vec: Vec<Vec<f64>> = self.recent_x.iter().cloned().collect();
        let buffer_y: Vec<f64> = self.recent_y.iter().cloned().collect();
        let buffer_x = vec_to_array2(&buffer_x_vec);
        let buffer_size = buffer_x.nrows();

        let predictions = self.primary.predict(buffer_x.view()).unwrap_or_default();
        let degradation = (checkpoint_rmse - self.baseline_rmse) / self.baseline_rmse;

        let error_variance: f64 = buffer_y
            .iter()
            .zip(predictions.iter())
            .map(|(y, p)| (y - p).powi(2))
            .sum::<f64>()
            / buffer_size as f64;

        let pred_mean = predictions.iter().sum::<f64>() / buffer_size as f64;
        let pred_variance: f64 = predictions
            .iter()
            .map(|p| (p - pred_mean).powi(2))
            .sum::<f64>()
            / buffer_size as f64;

        let complexity_score = error_variance + pred_variance * 0.5;
        let complexity_level = if complexity_score > HIGH_COMPLEXITY_THRESHOLD {
            "high"
        } else if complexity_score > MODERATE_COMPLEXITY_THRESHOLD {
            "moderate"
        } else {
            "low"
        };

        let temporal_score = diagnostics.residual_autocorrelation.abs();
        let variance_score =
            (diagnostics.heteroscedasticity_score / self.baseline_rmse.max(EPSILON)).min(1.0);
        let entropy_score = (diagnostics.error_entropy / 3.5).min(1.0);

        let combined_drift_score = DRIFT_WEIGHT_ENTROPY * entropy_score
            + DRIFT_WEIGHT_TEMPORAL * temporal_score
            + DRIFT_WEIGHT_VARIANCE * variance_score;

        let base_trees = if combined_drift_score > SEVERE_DRIFT_THRESHOLD {
            TREES_SEVERE_DRIFT
        } else if temporal_score > TEMPORAL_DRIFT_THRESHOLD {
            TREES_TEMPORAL_DRIFT
        } else if variance_score > VARIANCE_DRIFT_THRESHOLD {
            TREES_VARIANCE_DRIFT
        } else {
            TREES_LOCALIZED_DRIFT
        };

        let size_factor = if buffer_size < SMALL_BUFFER_THRESHOLD {
            SIZE_FACTOR_SMALL
        } else if buffer_size > LARGE_BUFFER_THRESHOLD {
            SIZE_FACTOR_LARGE
        } else {
            1.0
        };

        let complexity_factor = match complexity_level {
            "high" => COMPLEXITY_FACTOR_HIGH,
            "moderate" => 1.0,
            "low" => COMPLEXITY_FACTOR_LOW,
            _ => 1.0,
        };

        let severity_factor = if degradation > 1.5 {
            SEVERITY_FACTOR_VERY_SEVERE
        } else if degradation > 1.0 {
            SEVERITY_FACTOR_SEVERE
        } else if degradation < 0.3 {
            SEVERITY_FACTOR_MILD
        } else {
            1.0
        };

        let n_new_trees = ((base_trees as f64 * size_factor * complexity_factor * severity_factor)
            as usize)
            .clamp(MIN_TREES_PER_METAMORPHOSIS, MAX_TREES_PER_METAMORPHOSIS);

        let lr_adjustment = match complexity_level {
            "high" => LR_ADJUSTMENT_HIGH_COMPLEXITY,
            "moderate" => 1.0,
            "low" => LR_ADJUSTMENT_LOW_COMPLEXITY,
            _ => 1.0,
        };
        let lr_multiplier = BASE_LR_MULTIPLIER * lr_adjustment;

        let prune_threshold = match diagnostics.drift_type {
            DriftType::Systemic => 0.95,
            DriftType::FeatureShift => 0.90,
            DriftType::Localized => 1.0,
        };

        // Prune trees
        let pruned = if !drifted_features.is_empty() {
            let drift_prune_threshold = prune_threshold * 0.7;
            let pruned_count = self
                .primary
                .prune_trees(&drifted_features, drift_prune_threshold);
            let max_prune = (checkpoint_trees.len() * 30) / 100;
            pruned_count.min(max_prune)
        } else {
            0
        };

        if verbose {
            println!("  - Pruned {} trees, adding {} new", pruned, n_new_trees);
        }

        if self.recent_x.len() > 1000 {
            self.add_incremental_trees(n_new_trees, lr_multiplier, verbose)?;
        }

        // Validate
        if val_size >= 100 {
            let post_preds = self.primary.predict(val_x.view())?;
            let post_rmse = calculate_rmse(&val_y, post_preds.as_slice().unwrap());

            if post_rmse > checkpoint_rmse * METAMORPHOSIS_ROLLBACK_TOLERANCE {
                if verbose {
                    println!("  ⚠️  ROLLBACK: {:.4}{:.4}", checkpoint_rmse, post_rmse);
                }
                self.primary.trees = checkpoint_trees;
                self.state = SystemState::Normal;
                self.consecutive_vulnerable_checks = 0;
                return Ok(());
            }

            if verbose {
                println!("  ✅ ACCEPTED: {:.4}{:.4}", checkpoint_rmse, post_rmse);
            }

            if post_rmse < self.baseline_rmse * 1.1 {
                self.baseline_rmse = post_rmse;
            }
        }

        self.metamorphosis_count += 1;
        self.state = SystemState::Normal;
        self.consecutive_vulnerable_checks = 0;
        self.recent_vulnerabilities.clear();

        if verbose {
            println!("=== METAMORPHOSIS COMPLETE ===\n");
        }

        Ok(())
    }

    fn add_incremental_trees(
        &mut self,
        n_trees: usize,
        lr_multiplier: f64,
        verbose: bool,
    ) -> Result<usize, String> {
        let buffer_x_vec: Vec<Vec<f64>> = self.recent_x.iter().cloned().collect();
        let buffer_y: Vec<f64> = self.recent_y.iter().cloned().collect();

        if buffer_x_vec.len() < 1000 {
            return Err(format!(
                "Insufficient buffer: {} samples",
                buffer_x_vec.len()
            ));
        }

        let buffer_x = vec_to_array2(&buffer_x_vec);
        let n_samples = buffer_x.nrows();
        let n_features = buffer_x.ncols();

        let y_mean = buffer_y.iter().sum::<f64>() / buffer_y.len() as f64;
        let current_preds = self.primary.predict(buffer_x.view())?;
        let current_preds_slice = current_preds.as_slice().unwrap();
        let pred_mean = current_preds_slice.iter().sum::<f64>() / current_preds_slice.len() as f64;
        let pred_error = (pred_mean - y_mean).abs();

        let mut raw_preds = if pred_error > y_mean.abs() * 10.0 || !pred_mean.is_finite() {
            if verbose {
                println!("  ⚠️  Predictions far off, resetting to mean baseline");
            }
            vec![y_mean; n_samples]
        } else {
            current_preds_slice.to_vec()
        };

        let hb = self.primary.histogram_builder.as_ref().unwrap();
        let x_proc = hb.transform(buffer_x.view());
        let transposed = TransposedData::from_binned(x_proc);

        let feature_indices: Vec<usize> = (0..n_features).collect();
        let sample_indices: Vec<usize> = (0..n_samples).collect();

        let params = TreeParams {
            min_samples_split: self.primary.min_samples_split,
            min_child_weight: self.primary.min_child_weight,
            reg_lambda: self.primary.reg_lambda * 5.0,
            gamma: self.primary.gamma * 2.0,
            mi_weight: 0.3,
            n_bins_per_feature: feature_indices
                .iter()
                .map(|&i| hb.n_bins_per_feature[i])
                .collect(),
            feature_elimination_threshold: 0.01,
        };

        let adaptive_lr = (self.primary.learning_rate * lr_multiplier).min(0.05);
        let mut trees_added = 0;

        for tree_idx in 0..n_trees {
            let mut grad = self.primary.get_gradient(&buffer_y, &raw_preds);
            let hess = self.primary.get_hessian(&buffer_y, &raw_preds);

            let grad_norm: f64 = grad.iter().map(|g| g * g).sum::<f64>().sqrt();
            if grad_norm > GRADIENT_CRITICAL_THRESHOLD {
                let scale = GRADIENT_CRITICAL_THRESHOLD / grad_norm;
                grad = grad.iter().map(|&g| g * scale).collect();
            }

            if grad_norm > GRADIENT_CRITICAL_THRESHOLD * 5.0 {
                if verbose {
                    println!("  🛑 Stopping early: gradients too large");
                }
                break;
            }

            let mut tree = OptimizedTreeShannon::new(self.primary.max_depth);
            tree.fit_optimized(
                &transposed,
                &buffer_y,
                &grad,
                &hess,
                &sample_indices,
                &feature_indices,
                &params,
            );

            let tree_preds: Vec<f64> = (0..n_samples)
                .into_par_iter()
                .map(|i| tree.predict_from_transposed(&transposed, i))
                .collect();

            for (i, &tp) in tree_preds.iter().enumerate() {
                raw_preds[i] += adaptive_lr * tp;
                let y_range = y_mean.abs() * 100.0;
                raw_preds[i] = raw_preds[i].clamp(y_mean - y_range, y_mean + y_range);
            }

            self.primary.trees.push(tree);
            trees_added += 1;

            if verbose && (tree_idx + 1) % 5 == 0 {
                println!("    - Added tree {}/{}", tree_idx + 1, n_trees);
            }
        }

        Ok(trees_added)
    }

    /// Predict from ArrayView2 (zero-copy from Python)
    pub fn predict(&self, x: ArrayView2<'_, f64>) -> Result<Array1<f64>, String> {
        self.primary.predict(x)
    }

    pub fn get_state(&self) -> SystemState {
        self.state
    }

    pub fn get_metamorphosis_count(&self) -> usize {
        self.metamorphosis_count
    }

    pub fn get_vulnerability_score(&self) -> f64 {
        self.vulnerability_ema
    }

    pub fn predict_with_uncertainty(
        &self,
        x: ArrayView2<'_, f64>,
    ) -> Result<(Array1<f64>, Array1<f64>), String> {
        self.primary.predict_with_uncertainty(x)
    }
}

/// Helper to convert Vec<Vec<f64>> to Array2 (for internal buffer operations)
fn vec_to_array2(rows: &[Vec<f64>]) -> Array2<f64> {
    if rows.is_empty() {
        return Array2::zeros((0, 0));
    }
    let n_rows = rows.len();
    let n_cols = rows[0].len();
    let mut arr = Array2::zeros((n_rows, n_cols));
    for (i, row) in rows.iter().enumerate() {
        for (j, &val) in row.iter().enumerate() {
            arr[[i, j]] = val;
        }
    }
    arr
}