Add confirmatory paper experiments: A1-A4, all 10 seeds complete

A1: Synthetic nonlinearity ladder (240 rows: 3 alpha × 2 depth × 4 methods × 10 seeds)
A2: CIFAR state-vs-credit counterexample (30 rows: 3 methods × 10 seeds)
A3: Frozen vs online dissociation (60 rows: 2 regimes × 3 methods × 10 seeds)
A4: Protocol dependence panel (82 rows: assembled from existing results)

All experiments ran on GPU 3. Total runtime: ~20 hours.
CSVs in results/confirmatory/.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

1 files changed, 1861 insertions, 0 deletions

diff --git a/experiments/confirmatory_paper_experiments.py b/experiments/confirmatory_paper_experiments.py
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+"""
+Confirmatory Paper Experiments — single-script entry point.
+
+Four sub-experiments:
+  A1: Synthetic Nonlinearity Ladder        (10 seeds x {alpha} x {depth})
+  A2: CIFAR State-vs-Credit Counterexample (10 seeds)
+  A3: Frozen vs Online Dissociation        (10 seeds)
+  A4: Protocol Dependence Panel            (data assembly from existing results)
+
+Usage:
+  CUDA_VISIBLE_DEVICES=3 python experiments/confirmatory_paper_experiments.py \
+      --experiment {A1,A2,A3,A4,all} --gpu 3 --output_dir results/confirmatory
+
+Set PYTHONUNBUFFERED=1 for nohup-safe logging.
+"""
+import os
+import sys
+import json
+import argparse
+import time
+import copy
+import csv
+import numpy as np
+import torch
+import torch.nn as nn
+import torch.nn.functional as F
+import torch.optim as optim
+from torch.utils.data import DataLoader, TensorDataset
+import torchvision
+import torchvision.transforms as transforms
+
+sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+
+from models.residual_mlp import ResidualMLP
+from models.value_net import ValueNet, SinusoidalTimeEmbed, create_ema_model, update_ema
+from models.state_bridge import StateBridgeNet
+from metrics.credit_metrics import (
+    cosine_similarity_batch, perturbation_correlation, nudging_test
+)
+
+
+# =============================================================================
+# Shared helpers
+# =============================================================================
+def set_seed(seed):
+    torch.manual_seed(seed)
+    np.random.seed(seed)
+    torch.cuda.manual_seed_all(seed)
+
+
+def serialize(obj):
+    if isinstance(obj, dict):
+        return {str(k): serialize(v) for k, v in obj.items()}
+    elif isinstance(obj, list):
+        return [serialize(v) for v in obj]
+    elif isinstance(obj, (np.floating, np.integer)):
+        return float(obj)
+    elif isinstance(obj, np.ndarray):
+        return obj.tolist()
+    elif isinstance(obj, torch.Tensor):
+        return obj.cpu().numpy().tolist()
+    return obj
+
+
+def get_cifar10(batch_size=128):
+    transform_train = transforms.Compose([
+        transforms.RandomCrop(32, padding=4),
+        transforms.RandomHorizontalFlip(),
+        transforms.ToTensor(),
+        transforms.Normalize((0.4914, 0.4822, 0.4465), (0.2470, 0.2435, 0.2616)),
+    ])
+    transform_test = transforms.Compose([
+        transforms.ToTensor(),
+        transforms.Normalize((0.4914, 0.4822, 0.4465), (0.2470, 0.2435, 0.2616)),
+    ])
+    trainset = torchvision.datasets.CIFAR10(
+        root='./data', train=True, download=True, transform=transform_train)
+    testset = torchvision.datasets.CIFAR10(
+        root='./data', train=False, download=True, transform=transform_test)
+    train_loader = DataLoader(trainset, batch_size=batch_size, shuffle=True,
+                              num_workers=4, pin_memory=True)
+    test_loader = DataLoader(testset, batch_size=batch_size, shuffle=False,
+                             num_workers=4, pin_memory=True)
+    return train_loader, test_loader
+
+
+def evaluate_cifar(model, test_loader, device):
+    model.eval()
+    correct, total = 0, 0
+    with torch.no_grad():
+        for x, y in test_loader:
+            x = x.view(x.size(0), -1).to(device)
+            y = y.to(device)
+            logits = model(x)
+            correct += (logits.argmax(1) == y).sum().item()
+            total += x.size(0)
+    return correct / total
+
+
+def evaluate_synth(model, test_loader, device):
+    model.eval()
+    correct, total = 0, 0
+    with torch.no_grad():
+        for x, y in test_loader:
+            x, y = x.to(device), y.to(device)
+            logits = model(x)
+            correct += (logits.argmax(1) == y).sum().item()
+            total += x.size(0)
+    return correct / total
+
+
+def compute_diagnostics_generic(model, test_loader, device, num_classes,
+                                 method_name, value_net=None,
+                                 state_pred=None, dfa_Bs=None,
+                                 flat_input=True):
+    """
+    Compute Gamma (offline BP cosine), rho (perturbation correlation), and nudge.
+    Returns mean over layers.
+    flat_input: if True, x is flattened before forward (CIFAR); else passed as-is (synth).
+    """
+    model.eval()
+    if value_net is not None:
+        value_net.eval()
+    if state_pred is not None:
+        state_pred.eval()
+
+    L = model.num_blocks
+
+    for x, y in test_loader:
+        if flat_input:
+            x = x.view(x.size(0), -1).to(device)
+        else:
+            x = x.to(device)
+        y = y.to(device)
+        break
+
+    batch = x.size(0)
+
+    # BP gradients via manual graph
+    with torch.no_grad():
+        if flat_input:
+            h0 = model.embed(x.detach())
+        else:
+            h0 = x.detach()
+    h_start = h0.clone().requires_grad_(True)
+    hiddens_req = [h_start]
+    for block in model.blocks:
+        f = block(hiddens_req[-1])
+        hiddens_req.append(hiddens_req[-1] + f)
+
+    if flat_input:
+        logits_bp = model.out_head(model.out_ln(hiddens_req[-1]))
+    else:
+        logits_bp = model.out_head(hiddens_req[-1])
+    loss_bp = F.cross_entropy(logits_bp, y)
+    grads = torch.autograd.grad(loss_bp, hiddens_req, retain_graph=False)
+    bp_grads = {l: grads[l].detach().clone() for l in range(len(hiddens_req))}
+
+    # Clean forward
+    with torch.no_grad():
+        if flat_input:
+            logits, hiddens = model(x, return_hidden=True)
+        else:
+            logits, hiddens = model(x, return_hidden=True)
+        e_T = logits.softmax(dim=-1)
+        e_T[torch.arange(batch), y] -= 1
+        s = e_T.detach()
+
+    gamma_list, rho_list, nudge_list = [], [], []
+
+    for l in range(L):
+        h_l = hiddens[l].detach()
+        t_l = torch.full((batch,), l / L, device=device)
+
+        if method_name == 'bp':
+            a_l = bp_grads[l]
+        elif method_name == 'dfa':
+            a_l = (e_T @ dfa_Bs[l].T).detach()
+        elif method_name == 'state_bridge':
+            h_l_req = h_l.clone().requires_grad_(True)
+            pred_hL = state_pred(h_l_req, t_l, s)
+            if flat_input:
+                pred_logits = model.out_head(model.out_ln(pred_hL))
+            else:
+                pred_logits = model.out_head(pred_hL)
+            pred_loss = F.cross_entropy(pred_logits, y, reduction='sum')
+            a_l = torch.autograd.grad(pred_loss, h_l_req, create_graph=False)[0].detach()
+        elif method_name == 'credit_bridge':
+            h_l_req = h_l.clone().requires_grad_(True)
+            V_l = value_net(h_l_req, t_l, s)
+            a_l = torch.autograd.grad(V_l.sum(), h_l_req, create_graph=False)[0].detach()
+        else:
+            raise ValueError(f"Unknown method: {method_name}")
+
+        gamma = cosine_similarity_batch(a_l, bp_grads[l])
+        gamma_list.append(gamma)
+
+        def make_fwd_fn(start_l):
+            def fwd_fn(h):
+                with torch.no_grad():
+                    curr = h
+                    for i in range(start_l, L):
+                        curr = curr + model.blocks[i](curr)
+                    if flat_input:
+                        out = model.out_head(model.out_ln(curr))
+                    else:
+                        out = model.out_head(curr)
+                    return F.cross_entropy(out, y, reduction='none')
+            return fwd_fn
+
+        fwd_fn = make_fwd_fn(l)
+        rho = perturbation_correlation(h_l, a_l, fwd_fn, epsilon=1e-3, M=16)
+        rho_list.append(rho)
+        nudge = nudging_test(h_l, a_l, fwd_fn, eta=0.01)
+        nudge_list.append(nudge)
+
+    return {
+        'Gamma': float(np.mean(gamma_list)),
+        'rho': float(np.mean(rho_list)),
+        'nudge': float(np.mean(nudge_list)),
+        'per_layer_gamma': gamma_list,
+        'per_layer_rho': rho_list,
+        'per_layer_nudge': nudge_list,
+    }
+
+
+# =============================================================================
+# Shared training methods (CIFAR-style: flat input, out_ln present)
+# =============================================================================
+
+def _train_bp_cifar(model, train_loader, test_loader, device, epochs, lr, wd):
+    optimizer = optim.AdamW(model.parameters(), lr=lr, weight_decay=wd)
+    scheduler = optim.lr_scheduler.CosineAnnealingLR(optimizer, T_max=epochs)
+    log = {'train_loss': [], 'test_acc': []}
+    for epoch in range(1, epochs + 1):
+        model.train()
+        total_loss, correct, total = 0, 0, 0
+        for x, y in train_loader:
+            x = x.view(x.size(0), -1).to(device)
+            y = y.to(device)
+            logits = model(x)
+            loss = F.cross_entropy(logits, y)
+            optimizer.zero_grad()
+            loss.backward()
+            optimizer.step()
+            total_loss += loss.item() * x.size(0)
+            correct += (logits.argmax(1) == y).sum().item()
+            total += x.size(0)
+        scheduler.step()
+        log['train_loss'].append(total_loss / total)
+        log['test_acc'].append(evaluate_cifar(model, test_loader, device))
+        if epoch % 10 == 0 or epoch == 1:
+            print(f"    [BP] Ep {epoch}: loss={log['train_loss'][-1]:.4f} "
+                  f"test={log['test_acc'][-1]:.4f}", flush=True)
+    return log
+
+
+def _train_dfa_cifar(model, train_loader, test_loader, device, epochs, lr, wd):
+    d = model.d_hidden
+    L = model.num_blocks
+    C = 10
+    Bs = [torch.randn(d, C, device=device) / np.sqrt(C) for _ in range(L)]
+    block_opts = [optim.AdamW(block.parameters(), lr=lr, weight_decay=wd)
+                  for block in model.blocks]
+    embed_opt = optim.AdamW(model.embed.parameters(), lr=lr, weight_decay=wd)
+    head_opt = optim.AdamW(list(model.out_head.parameters()) +
+                           list(model.out_ln.parameters()), lr=lr, weight_decay=wd)
+    all_sch = ([optim.lr_scheduler.CosineAnnealingLR(o, T_max=epochs) for o in block_opts]
+               + [optim.lr_scheduler.CosineAnnealingLR(embed_opt, T_max=epochs),
+                  optim.lr_scheduler.CosineAnnealingLR(head_opt, T_max=epochs)])
+    log = {'train_loss': [], 'test_acc': []}
+    for epoch in range(1, epochs + 1):
+        model.train()
+        total_loss, correct, total = 0, 0, 0
+        for x, y in train_loader:
+            x = x.view(x.size(0), -1).to(device)
+            y = y.to(device)
+            batch = x.size(0)
+            with torch.no_grad():
+                logits, hiddens = model(x, return_hidden=True)
+                loss_val = F.cross_entropy(logits, y)
+                e_T = logits.softmax(dim=-1)
+                e_T[torch.arange(batch), y] -= 1
+            hL_det = hiddens[-1].detach()
+            logits_out = model.out_head(model.out_ln(hL_det))
+            loss_out = F.cross_entropy(logits_out, y)
+            head_opt.zero_grad()
+            loss_out.backward()
+            head_opt.step()
+            for l in range(L):
+                h_l = hiddens[l].detach()
+                a_dfa = (e_T @ Bs[l].T).detach()
+                rms = (a_dfa ** 2).mean(dim=-1, keepdim=True).sqrt() + 1e-6
+                a_norm = a_dfa / rms
+                f_l = model.blocks[l](h_l)
+                local_loss = (f_l * a_norm).sum(dim=-1).mean()
+                block_opts[l].zero_grad()
+                local_loss.backward()
+                torch.nn.utils.clip_grad_norm_(model.blocks[l].parameters(), 1.0)
+                block_opts[l].step()
+            a_0 = (e_T @ Bs[0].T).detach()
+            rms_0 = (a_0 ** 2).mean(dim=-1, keepdim=True).sqrt() + 1e-6
+            h0 = model.embed(x)
+            embed_loss = (h0 * (a_0 / rms_0)).sum(dim=-1).mean()
+            embed_opt.zero_grad()
+            embed_loss.backward()
+            embed_opt.step()
+            total_loss += loss_val.item() * batch
+            correct += (logits.argmax(1) == y).sum().item()
+            total += batch
+        for s in all_sch:
+            s.step()
+        log['train_loss'].append(total_loss / total)
+        log['test_acc'].append(evaluate_cifar(model, test_loader, device))
+        if epoch % 10 == 0 or epoch == 1:
+            print(f"    [DFA] Ep {epoch}: loss={log['train_loss'][-1]:.4f} "
+                  f"test={log['test_acc'][-1]:.4f}", flush=True)
+    return log, Bs
+
+
+def _train_state_bridge_cifar(model, train_loader, test_loader, device, epochs, lr, lr_fb, wd):
+    d = model.d_hidden
+    L = model.num_blocks
+    C = 10
+    state_pred = StateBridgeNet(d_hidden=d, s_dim=C, time_embed_dim=32,
+                                hidden_dim=256, num_layers=3).to(device)
+    block_opts = [optim.AdamW(block.parameters(), lr=lr, weight_decay=wd)
+                  for block in model.blocks]
+    embed_opt = optim.AdamW(model.embed.parameters(), lr=lr, weight_decay=wd)
+    head_opt = optim.AdamW(list(model.out_head.parameters()) +
+                           list(model.out_ln.parameters()), lr=lr, weight_decay=wd)
+    state_opt = optim.Adam(state_pred.parameters(), lr=lr_fb)
+    all_sch = ([optim.lr_scheduler.CosineAnnealingLR(o, T_max=epochs) for o in block_opts]
+               + [optim.lr_scheduler.CosineAnnealingLR(embed_opt, T_max=epochs),
+                  optim.lr_scheduler.CosineAnnealingLR(head_opt, T_max=epochs)])
+    log = {'train_loss': [], 'test_acc': [], 'state_pred_error': []}
+    for epoch in range(1, epochs + 1):
+        model.train()
+        state_pred.train()
+        total_loss, correct, total, total_se = 0, 0, 0, 0
+        for x, y in train_loader:
+            x = x.view(x.size(0), -1).to(device)
+            y = y.to(device)
+            batch = x.size(0)
+            with torch.no_grad():
+                logits, hiddens = model(x, return_hidden=True)
+                loss_val = F.cross_entropy(logits, y)
+                e_T = logits.softmax(dim=-1)
+                e_T[torch.arange(batch), y] -= 1
+                s = e_T.detach()
+            hL_det = hiddens[-1].detach()
+            # Train state predictor
+            state_loss = 0.0
+            for l in range(L):
+                h_l_det = hiddens[l].detach()
+                t_l = torch.full((batch,), l / L, device=device)
+                pred_hL = state_pred(h_l_det, t_l, s)
+                target_norm = hL_det.norm(dim=-1, keepdim=True).clamp(min=1.0)
+                state_loss = state_loss + (((pred_hL - hL_det) / target_norm) ** 2).sum(dim=-1).mean()
+            state_loss = state_loss / L
+            state_opt.zero_grad()
+            state_loss.backward()
+            state_opt.step()
+            total_se += state_loss.item() * batch
+            # Compute credits
+            credits = []
+            for l in range(L):
+                h_l_det = hiddens[l].detach().requires_grad_(True)
+                t_l = torch.full((batch,), l / L, device=device)
+                pred_hL = state_pred(h_l_det, t_l, s)
+                pred_logits = model.out_head(model.out_ln(pred_hL))
+                pred_loss = F.cross_entropy(pred_logits, y, reduction='sum')
+                a_l = torch.autograd.grad(pred_loss, h_l_det, create_graph=False)[0]
+                credits.append(a_l.detach())
+            # Update head
+            logits_out = model.out_head(model.out_ln(hL_det))
+            loss_out = F.cross_entropy(logits_out, y)
+            head_opt.zero_grad()
+            loss_out.backward()
+            head_opt.step()
+            # Update blocks
+            for l in range(L):
+                h_l = hiddens[l].detach()
+                a = credits[l]
+                rms = (a ** 2).mean(dim=-1, keepdim=True).sqrt() + 1e-6
+                a_norm = a / rms
+                f_l = model.blocks[l](h_l)
+                local_loss = (f_l * a_norm).sum(dim=-1).mean()
+                block_opts[l].zero_grad()
+                local_loss.backward()
+                torch.nn.utils.clip_grad_norm_(model.blocks[l].parameters(), 1.0)
+                block_opts[l].step()
+            # Update embedding
+            a_0 = credits[0]
+            rms_0 = (a_0 ** 2).mean(dim=-1, keepdim=True).sqrt() + 1e-6
+            h0 = model.embed(x)
+            embed_loss = (h0 * (a_0 / rms_0)).sum(dim=-1).mean()
+            embed_opt.zero_grad()
+            embed_loss.backward()
+            embed_opt.step()
+            total_loss += loss_val.item() * batch
+            correct += (logits.argmax(1) == y).sum().item()
+            total += batch
+        for sch in all_sch:
+            sch.step()
+        log['train_loss'].append(total_loss / total)
+        log['test_acc'].append(evaluate_cifar(model, test_loader, device))
+        log['state_pred_error'].append(total_se / total)
+        if epoch % 10 == 0 or epoch == 1:
+            print(f"    [SB] Ep {epoch}: loss={log['train_loss'][-1]:.4f} "
+                  f"test={log['test_acc'][-1]:.4f} se={log['state_pred_error'][-1]:.4f}",
+                  flush=True)
+    return log, state_pred
+
+
+def _train_credit_bridge_cifar(model, train_loader, test_loader, device, epochs, lr, lr_fb, wd,
+                                warmup_ratio=0.2, term_grad_weight=1.0,
+                                lam=0.1, K=4, sigma_bridge=0.05, ema_momentum=0.995):
+    d = model.d_hidden
+    L = model.num_blocks
+    C = 10
+    warmup_epochs = max(1, int(epochs * warmup_ratio))
+    value_net = ValueNet(d_hidden=d, s_dim=C, time_embed_dim=32,
+                         hidden_dim=256, num_layers=3).to(device)
+    value_net_ema = create_ema_model(value_net)
+    Bs_fallback = [torch.randn(d, C, device=device) / np.sqrt(C) for _ in range(L)]
+    block_opts = [optim.AdamW(block.parameters(), lr=lr, weight_decay=wd)
+                  for block in model.blocks]
+    embed_opt = optim.AdamW(model.embed.parameters(), lr=lr, weight_decay=wd)
+    head_opt = optim.AdamW(list(model.out_head.parameters()) +
+                           list(model.out_ln.parameters()), lr=lr, weight_decay=wd)
+    value_opt = optim.Adam(value_net.parameters(), lr=lr_fb)
+    all_sch = ([optim.lr_scheduler.CosineAnnealingLR(o, T_max=epochs) for o in block_opts]
+               + [optim.lr_scheduler.CosineAnnealingLR(embed_opt, T_max=epochs),
+                  optim.lr_scheduler.CosineAnnealingLR(head_opt, T_max=epochs)])
+    log = {'train_loss': [], 'test_acc': [], 'value_loss': []}
+    for epoch in range(1, epochs + 1):
+        model.train()
+        value_net.train()
+        total_loss, correct, total, total_vloss = 0, 0, 0, 0
+        if epoch <= warmup_epochs:
+            credit_blend = 0.0
+        else:
+            credit_blend = min(1.0, (epoch - warmup_epochs) / max(1, warmup_epochs))
+        for x, y in train_loader:
+            x = x.view(x.size(0), -1).to(device)
+            y = y.to(device)
+            batch = x.size(0)
+            with torch.no_grad():
+                logits, hiddens = model(x, return_hidden=True)
+                loss_val = F.cross_entropy(logits, y)
+                e_T = logits.softmax(dim=-1)
+                e_T[torch.arange(batch), y] -= 1
+                s = e_T.detach()
+                true_loss = F.cross_entropy(logits, y, reduction='none').detach()
+            hL_det = hiddens[-1].detach()
+            # Train value net
+            t_L = torch.ones(batch, device=device)
+            V_terminal = value_net(hL_det, t_L, s)
+            loss_term = ((V_terminal - true_loss) ** 2).mean()
+            loss_tgrad = torch.tensor(0.0, device=device)
+            if term_grad_weight > 0:
+                hL_req = hL_det.clone().requires_grad_(True)
+                V_at_L = value_net(hL_req, t_L, s)
+                grad_V_L = torch.autograd.grad(V_at_L.sum(), hL_req, create_graph=True)[0]
+                hL_req2 = hL_det.clone().requires_grad_(True)
+                logits_tgt = model.out_head(model.out_ln(hL_req2))
+                ce_loss = F.cross_entropy(logits_tgt, y, reduction='sum')
+                a_L_exact = torch.autograd.grad(ce_loss, hL_req2, create_graph=False)[0].detach()
+                loss_tgrad = ((grad_V_L - a_L_exact) ** 2).sum(dim=-1).mean()
+            loss_bridge = 0.0
+            for l in range(L):
+                h_l_det = hiddens[l].detach()
+                t_l = torch.full((batch,), l / L, device=device)
+                t_l_next = torch.full((batch,), (l + 1) / L, device=device)
+                V_l = value_net(h_l_det, t_l, s)
+                with torch.no_grad():
+                    h_next_det = hiddens[l + 1].detach()
+                    log_terms = []
+                    for k in range(K):
+                        noise = sigma_bridge * torch.randn_like(h_next_det)
+                        V_next = value_net_ema(h_next_det + noise, t_l_next, s)
+                        log_terms.append(-V_next / lam)
+                    log_stack = torch.stack(log_terms, dim=-1)
+                    V_target = -lam * (torch.logsumexp(log_stack, dim=-1) - np.log(K))
+                loss_bridge = loss_bridge + ((V_l - V_target.detach()) ** 2).mean()
+            loss_bridge = loss_bridge / L
+            value_loss = loss_term + loss_bridge + term_grad_weight * loss_tgrad
+            value_opt.zero_grad()
+            value_loss.backward()
+            torch.nn.utils.clip_grad_norm_(value_net.parameters(), 1.0)
+            value_opt.step()
+            update_ema(value_net, value_net_ema, ema_momentum)
+            total_vloss += value_loss.item() * batch
+            # Credits
+            cb_credits = []
+            for l in range(L):
+                h_l_det = hiddens[l].detach().requires_grad_(True)
+                t_l = torch.full((batch,), l / L, device=device)
+                V_l = value_net(h_l_det, t_l, s)
+                a_l = torch.autograd.grad(V_l.sum(), h_l_det, create_graph=False)[0]
+                cb_credits.append(a_l.detach())
+            dfa_credits = [(e_T @ Bs_fallback[l].T).detach() for l in range(L)]
+            credits = []
+            for l in range(L):
+                if credit_blend >= 1.0:
+                    a = cb_credits[l]
+                elif credit_blend <= 0.0:
+                    a = dfa_credits[l]
+                else:
+                    cb_rms = (cb_credits[l] ** 2).mean(dim=-1, keepdim=True).sqrt() + 1e-6
+                    dfa_rms = (dfa_credits[l] ** 2).mean(dim=-1, keepdim=True).sqrt() + 1e-6
+                    a = credit_blend * (cb_credits[l] / cb_rms) + \
+                        (1 - credit_blend) * (dfa_credits[l] / dfa_rms)
+                credits.append(a)
+            # Update head
+            logits_out = model.out_head(model.out_ln(hL_det))
+            loss_out = F.cross_entropy(logits_out, y)
+            head_opt.zero_grad()
+            loss_out.backward()
+            head_opt.step()
+            # Update blocks
+            for l in range(L):
+                h_l = hiddens[l].detach()
+                a = credits[l]
+                rms = (a ** 2).mean(dim=-1, keepdim=True).sqrt() + 1e-6
+                a_norm = a / rms
+                f_l = model.blocks[l](h_l)
+                local_loss = (f_l * a_norm).sum(dim=-1).mean()
+                block_opts[l].zero_grad()
+                local_loss.backward()
+                torch.nn.utils.clip_grad_norm_(model.blocks[l].parameters(), 1.0)
+                block_opts[l].step()
+            # Update embedding
+            a_0 = credits[0]
+            rms_0 = (a_0 ** 2).mean(dim=-1, keepdim=True).sqrt() + 1e-6
+            h0 = model.embed(x)
+            embed_loss = (h0 * (a_0 / rms_0)).sum(dim=-1).mean()
+            embed_opt.zero_grad()
+            embed_loss.backward()
+            embed_opt.step()
+            total_loss += loss_val.item() * batch
+            correct += (logits.argmax(1) == y).sum().item()
+            total += batch
+        for sch in all_sch:
+            sch.step()
+        log['train_loss'].append(total_loss / total)
+        log['test_acc'].append(evaluate_cifar(model, test_loader, device))
+        log['value_loss'].append(total_vloss / total)
+        if epoch % 10 == 0 or epoch == 1:
+            phase = "warmup" if epoch <= warmup_epochs else f"blend={credit_blend:.2f}"
+            print(f"    [CB] Ep {epoch} ({phase}): loss={log['train_loss'][-1]:.4f} "
+                  f"test={log['test_acc'][-1]:.4f}", flush=True)
+    return log, value_net
+
+
+# =============================================================================
+# A1: Synthetic Nonlinearity Ladder
+# =============================================================================
+
+class TeacherNet:
+    """Fixed teacher network with controllable nonlinearity."""
+    def __init__(self, d_hidden, num_blocks, num_classes, alpha, seed=0):
+        rng = np.random.RandomState(seed)
+        self.d_hidden = d_hidden
+        self.num_blocks = num_blocks
+        self.num_classes = num_classes
+        self.alpha = alpha
+        self.Ws = []
+        for l in range(num_blocks):
+            W = rng.randn(d_hidden, d_hidden).astype(np.float32)
+            W = W / (np.linalg.norm(W, ord=2) + 1e-8) * 0.3
+            self.Ws.append(torch.from_numpy(W))
+        U = rng.randn(num_classes, d_hidden).astype(np.float32)
+        U = U / (np.linalg.norm(U, ord=2) + 1e-8)
+        self.U = torch.from_numpy(U)
+
+    def to(self, device):
+        self.Ws = [W.to(device) for W in self.Ws]
+        self.U = self.U.to(device)
+        return self
+
+    def phi(self, z):
+        return (1 - self.alpha) * z + self.alpha * torch.tanh(z)
+
+    def forward(self, h0):
+        h = h0
+        hiddens = [h]
+        for l in range(self.num_blocks):
+            f = F.linear(self.phi(h), self.Ws[l])
+            h = h + f
+            hiddens.append(h)
+        logits = F.linear(h, self.U)
+        return logits, hiddens
+
+
+class StudentBlock(nn.Module):
+    def __init__(self, d_hidden, alpha):
+        super().__init__()
+        self.ln = nn.LayerNorm(d_hidden)
+        self.w = nn.Linear(d_hidden, d_hidden, bias=False)
+        self.alpha = alpha
+        nn.init.normal_(self.w.weight, std=0.01)
+
+    def phi(self, z):
+        return (1 - self.alpha) * z + self.alpha * torch.tanh(z)
+
+    def forward(self, h):
+        return self.w(self.phi(self.ln(h)))
+
+
+class StudentNet(nn.Module):
+    def __init__(self, d_hidden, num_classes, num_blocks, alpha):
+        super().__init__()
+        self.blocks = nn.ModuleList([StudentBlock(d_hidden, alpha) for _ in range(num_blocks)])
+        self.out_head = nn.Linear(d_hidden, num_classes)
+        self.num_blocks = num_blocks
+        self.d_hidden = d_hidden
+
+    def forward(self, x, return_hidden=False):
+        h = x
+        hiddens = [h] if return_hidden else None
+        for block in self.blocks:
+            f = block(h)
+            h = h + f
+            if return_hidden:
+                hiddens.append(h)
+        logits = self.out_head(h)
+        if return_hidden:
+            return logits, hiddens
+        return logits
+
+    def forward_from_layer(self, h, start_layer):
+        for i in range(start_layer, self.num_blocks):
+            f = self.blocks[i](h)
+            h = h + f
+        return self.out_head(h)
+
+
+def generate_synth_dataset(teacher, num_samples, d_hidden, device, seed=0):
+    torch.manual_seed(seed)
+    X = torch.randn(num_samples, d_hidden, device=device)
+    with torch.no_grad():
+        logits, _ = teacher.forward(X)
+        Y = logits.argmax(dim=-1)
+    return X, Y
+
+
+def _train_bp_synth(model, train_loader, test_loader, device, epochs, lr, wd):
+    optimizer = optim.AdamW(model.parameters(), lr=lr, weight_decay=wd)
+    scheduler = optim.lr_scheduler.CosineAnnealingLR(optimizer, T_max=epochs)
+    log = {'test_acc': []}
+    for epoch in range(1, epochs + 1):
+        model.train()
+        for x, y in train_loader:
+            x, y = x.to(device), y.to(device)
+            logits = model(x)
+            loss = F.cross_entropy(logits, y)
+            optimizer.zero_grad()
+            loss.backward()
+            optimizer.step()
+        scheduler.step()
+        log['test_acc'].append(evaluate_synth(model, test_loader, device))
+        if epoch % 20 == 0 or epoch == 1:
+            print(f"      [BP] Ep {epoch}: test={log['test_acc'][-1]:.4f}", flush=True)
+    return log
+
+
+def _train_dfa_synth(model, train_loader, test_loader, device, epochs, lr, wd, C):
+    d = model.d_hidden
+    L = model.num_blocks
+    Bs = [torch.randn(d, C, device=device) / np.sqrt(C) for _ in range(L)]
+    block_opts = [optim.AdamW(block.parameters(), lr=lr, weight_decay=wd)
+                  for block in model.blocks]
+    head_opt = optim.AdamW(model.out_head.parameters(), lr=lr, weight_decay=wd)
+    all_sch = ([optim.lr_scheduler.CosineAnnealingLR(o, T_max=epochs) for o in block_opts]
+               + [optim.lr_scheduler.CosineAnnealingLR(head_opt, T_max=epochs)])
+    log = {'test_acc': []}
+    for epoch in range(1, epochs + 1):
+        model.train()
+        for x, y in train_loader:
+            x, y = x.to(device), y.to(device)
+            batch = x.size(0)
+            with torch.no_grad():
+                logits, hiddens = model(x, return_hidden=True)
+                e_T = logits.softmax(dim=-1)
+                e_T[torch.arange(batch), y] -= 1
+            hL_det = hiddens[-1].detach()
+            logits_out = model.out_head(hL_det)
+            loss_out = F.cross_entropy(logits_out, y)
+            head_opt.zero_grad()
+            loss_out.backward()
+            head_opt.step()
+            for l in range(L):
+                h_l = hiddens[l].detach()
+                a_dfa = (e_T @ Bs[l].T).detach()
+                rms = (a_dfa ** 2).mean(dim=-1, keepdim=True).sqrt() + 1e-6
+                a_norm = a_dfa / rms
+                f_l = model.blocks[l](h_l)
+                local_loss = (f_l * a_norm).sum(dim=-1).mean()
+                block_opts[l].zero_grad()
+                local_loss.backward()
+                torch.nn.utils.clip_grad_norm_(model.blocks[l].parameters(), 1.0)
+                block_opts[l].step()
+        for s in all_sch:
+            s.step()
+        log['test_acc'].append(evaluate_synth(model, test_loader, device))
+        if epoch % 20 == 0 or epoch == 1:
+            print(f"      [DFA] Ep {epoch}: test={log['test_acc'][-1]:.4f}", flush=True)
+    return log, Bs
+
+
+def _train_state_bridge_synth(model, train_loader, test_loader, device, epochs, lr, lr_fb, wd, C):
+    d = model.d_hidden
+    L = model.num_blocks
+    state_pred = StateBridgeNet(d_hidden=d, s_dim=C, time_embed_dim=32,
+                                hidden_dim=256, num_layers=3).to(device)
+    block_opts = [optim.AdamW(block.parameters(), lr=lr, weight_decay=wd)
+                  for block in model.blocks]
+    head_opt = optim.AdamW(model.out_head.parameters(), lr=lr, weight_decay=wd)
+    state_opt = optim.Adam(state_pred.parameters(), lr=lr_fb)
+    all_sch = ([optim.lr_scheduler.CosineAnnealingLR(o, T_max=epochs) for o in block_opts]
+               + [optim.lr_scheduler.CosineAnnealingLR(head_opt, T_max=epochs)])
+    log = {'test_acc': [], 'state_pred_error': []}
+    for epoch in range(1, epochs + 1):
+        model.train()
+        state_pred.train()
+        total_se, n = 0.0, 0
+        for x, y in train_loader:
+            x, y = x.to(device), y.to(device)
+            batch = x.size(0)
+            with torch.no_grad():
+                logits, hiddens = model(x, return_hidden=True)
+                e_T = logits.softmax(dim=-1)
+                e_T[torch.arange(batch), y] -= 1
+                s = e_T.detach()
+            hL_det = hiddens[-1].detach()
+            # Train state predictor
+            state_loss = 0.0
+            for l in range(L):
+                h_l_det = hiddens[l].detach()
+                t_l = torch.full((batch,), l / L, device=device)
+                pred_hL = state_pred(h_l_det, t_l, s)
+                target_norm = hL_det.norm(dim=-1, keepdim=True).clamp(min=1.0)
+                state_loss = state_loss + (((pred_hL - hL_det) / target_norm) ** 2).sum(dim=-1).mean()
+            state_loss = state_loss / L
+            state_opt.zero_grad()
+            state_loss.backward()
+            state_opt.step()
+            total_se += state_loss.item() * batch
+            n += batch
+            # Credits
+            credits = []
+            for l in range(L):
+                h_l_det = hiddens[l].detach().requires_grad_(True)
+                t_l = torch.full((batch,), l / L, device=device)
+                pred_hL = state_pred(h_l_det, t_l, s)
+                pred_logits = model.out_head(pred_hL)
+                pred_loss = F.cross_entropy(pred_logits, y, reduction='sum')
+                a_l = torch.autograd.grad(pred_loss, h_l_det, create_graph=False)[0]
+                credits.append(a_l.detach())
+            # Update head
+            logits_out = model.out_head(hL_det)
+            loss_out = F.cross_entropy(logits_out, y)
+            head_opt.zero_grad()
+            loss_out.backward()
+            head_opt.step()
+            # Update blocks
+            for l in range(L):
+                h_l = hiddens[l].detach()
+                a = credits[l]
+                rms = (a ** 2).mean(dim=-1, keepdim=True).sqrt() + 1e-6
+                a_norm = a / rms
+                f_l = model.blocks[l](h_l)
+                local_loss = (f_l * a_norm).sum(dim=-1).mean()
+                block_opts[l].zero_grad()
+                local_loss.backward()
+                torch.nn.utils.clip_grad_norm_(model.blocks[l].parameters(), 1.0)
+                block_opts[l].step()
+        for sch in all_sch:
+            sch.step()
+        log['test_acc'].append(evaluate_synth(model, test_loader, device))
+        log['state_pred_error'].append(total_se / n)
+        if epoch % 20 == 0 or epoch == 1:
+            print(f"      [SB] Ep {epoch}: test={log['test_acc'][-1]:.4f} "
+                  f"se={log['state_pred_error'][-1]:.4f}", flush=True)
+    return log, state_pred
+
+
+def _train_credit_bridge_synth(model, train_loader, test_loader, device, epochs, lr, lr_fb, wd, C,
+                                warmup_ratio=0.2, term_grad_weight=1.0,
+                                lam=0.1, K=4, sigma_bridge=0.05, ema_momentum=0.995):
+    d = model.d_hidden
+    L = model.num_blocks
+    warmup_epochs = max(1, int(epochs * warmup_ratio))
+    value_net = ValueNet(d_hidden=d, s_dim=C, time_embed_dim=32,
+                         hidden_dim=256, num_layers=3).to(device)
+    value_net_ema = create_ema_model(value_net)
+    Bs_fallback = [torch.randn(d, C, device=device) / np.sqrt(C) for _ in range(L)]
+    block_opts = [optim.AdamW(block.parameters(), lr=lr, weight_decay=wd)
+                  for block in model.blocks]
+    head_opt = optim.AdamW(model.out_head.parameters(), lr=lr, weight_decay=wd)
+    value_opt = optim.Adam(value_net.parameters(), lr=lr_fb)
+    all_sch = ([optim.lr_scheduler.CosineAnnealingLR(o, T_max=epochs) for o in block_opts]
+               + [optim.lr_scheduler.CosineAnnealingLR(head_opt, T_max=epochs)])
+    log = {'test_acc': []}
+    for epoch in range(1, epochs + 1):
+        model.train()
+        value_net.train()
+        if epoch <= warmup_epochs:
+            credit_blend = 0.0
+        else:
+            credit_blend = min(1.0, (epoch - warmup_epochs) / max(1, warmup_epochs))
+        for x, y in train_loader:
+            x, y = x.to(device), y.to(device)
+            batch = x.size(0)
+            with torch.no_grad():
+                logits, hiddens = model(x, return_hidden=True)
+                e_T = logits.softmax(dim=-1)
+                e_T[torch.arange(batch), y] -= 1
+                s = e_T.detach()
+                true_loss = F.cross_entropy(logits, y, reduction='none').detach()
+            hL_det = hiddens[-1].detach()
+            # Value net training
+            t_L = torch.ones(batch, device=device)
+            V_terminal = value_net(hL_det, t_L, s)
+            loss_term = ((V_terminal - true_loss) ** 2).mean()
+            loss_tgrad = torch.tensor(0.0, device=device)
+            if term_grad_weight > 0:
+                hL_req = hL_det.clone().requires_grad_(True)
+                V_at_L = value_net(hL_req, t_L, s)
+                grad_V_L = torch.autograd.grad(V_at_L.sum(), hL_req, create_graph=True)[0]
+                hL_req2 = hL_det.clone().requires_grad_(True)
+                logits_tgt = model.out_head(hL_req2)
+                ce_loss = F.cross_entropy(logits_tgt, y, reduction='sum')
+                a_L_exact = torch.autograd.grad(ce_loss, hL_req2, create_graph=False)[0].detach()
+                loss_tgrad = ((grad_V_L - a_L_exact) ** 2).sum(dim=-1).mean()
+            loss_bridge = 0.0
+            for l in range(L):
+                h_l_det = hiddens[l].detach()
+                t_l = torch.full((batch,), l / L, device=device)
+                t_l_next = torch.full((batch,), (l + 1) / L, device=device)
+                V_l = value_net(h_l_det, t_l, s)
+                with torch.no_grad():
+                    h_next_det = hiddens[l + 1].detach()
+                    log_terms = []
+                    for k in range(K):
+                        noise = sigma_bridge * torch.randn_like(h_next_det)
+                        V_next = value_net_ema(h_next_det + noise, t_l_next, s)
+                        log_terms.append(-V_next / lam)
+                    log_stack = torch.stack(log_terms, dim=-1)
+                    V_target = -lam * (torch.logsumexp(log_stack, dim=-1) - np.log(K))
+                loss_bridge = loss_bridge + ((V_l - V_target.detach()) ** 2).mean()
+            loss_bridge = loss_bridge / L
+            value_loss = loss_term + loss_bridge + term_grad_weight * loss_tgrad
+            value_opt.zero_grad()
+            value_loss.backward()
+            torch.nn.utils.clip_grad_norm_(value_net.parameters(), 1.0)
+            value_opt.step()
+            update_ema(value_net, value_net_ema, ema_momentum)
+            # Credits
+            cb_credits = []
+            for l in range(L):
+                h_l_det = hiddens[l].detach().requires_grad_(True)
+                t_l = torch.full((batch,), l / L, device=device)
+                V_l = value_net(h_l_det, t_l, s)
+                a_l = torch.autograd.grad(V_l.sum(), h_l_det, create_graph=False)[0]
+                cb_credits.append(a_l.detach())
+            dfa_credits = [(e_T @ Bs_fallback[l].T).detach() for l in range(L)]
+            credits = []
+            for l in range(L):
+                if credit_blend >= 1.0:
+                    a = cb_credits[l]
+                elif credit_blend <= 0.0:
+                    a = dfa_credits[l]
+                else:
+                    cb_rms = (cb_credits[l] ** 2).mean(dim=-1, keepdim=True).sqrt() + 1e-6
+                    dfa_rms = (dfa_credits[l] ** 2).mean(dim=-1, keepdim=True).sqrt() + 1e-6
+                    a = (credit_blend * (cb_credits[l] / cb_rms) +
+                         (1 - credit_blend) * (dfa_credits[l] / dfa_rms))
+                credits.append(a)
+            # Update head
+            logits_out = model.out_head(hL_det)
+            loss_out = F.cross_entropy(logits_out, y)
+            head_opt.zero_grad()
+            loss_out.backward()
+            head_opt.step()
+            # Update blocks
+            for l in range(L):
+                h_l = hiddens[l].detach()
+                a = credits[l]
+                rms = (a ** 2).mean(dim=-1, keepdim=True).sqrt() + 1e-6
+                a_norm = a / rms
+                f_l = model.blocks[l](h_l)
+                local_loss = (f_l * a_norm).sum(dim=-1).mean()
+                block_opts[l].zero_grad()
+                local_loss.backward()
+                torch.nn.utils.clip_grad_norm_(model.blocks[l].parameters(), 1.0)
+                block_opts[l].step()
+        for sch in all_sch:
+            sch.step()
+        log['test_acc'].append(evaluate_synth(model, test_loader, device))
+        if epoch % 20 == 0 or epoch == 1:
+            print(f"      [CB] Ep {epoch}: test={log['test_acc'][-1]:.4f}", flush=True)
+    return log, value_net
+
+
+def _compute_synth_state_err(model, state_pred, test_loader, device, C):
+    """Compute mean per-layer state prediction error on synth test set."""
+    model.eval()
+    state_pred.eval()
+    L = model.num_blocks
+    total_se, n = 0.0, 0
+    with torch.no_grad():
+        for x, y in test_loader:
+            x, y = x.to(device), y.to(device)
+            batch = x.size(0)
+            logits, hiddens = model(x, return_hidden=True)
+            e_T = logits.softmax(dim=-1)
+            e_T[torch.arange(batch), y] -= 1
+            s = e_T.detach()
+            hL_det = hiddens[-1].detach()
+            se = 0.0
+            for l in range(L):
+                h_l_det = hiddens[l].detach()
+                t_l = torch.full((batch,), l / L, device=device)
+                pred_hL = state_pred(h_l_det, t_l, s)
+                target_norm = hL_det.norm(dim=-1, keepdim=True).clamp(min=1.0)
+                se += (((pred_hL - hL_det) / target_norm) ** 2).sum(dim=-1).mean().item()
+            total_se += (se / L) * batch
+            n += batch
+    return total_se / n
+
+
+def _compute_synth_diagnostics(model, test_loader, device, method_name,
+                                value_net=None, state_pred=None, dfa_Bs=None, C=10):
+    """Compute Gamma, rho for synth model (no flat input, no out_ln)."""
+    model.eval()
+    if value_net is not None:
+        value_net.eval()
+    if state_pred is not None:
+        state_pred.eval()
+
+    L = model.num_blocks
+
+    for x, y in test_loader:
+        x, y = x.to(device), y.to(device)
+        break
+    batch = x.size(0)
+
+    # BP gradients
+    h_list = [x.detach().requires_grad_(True)]
+    for block in model.blocks:
+        f = block(h_list[-1])
+        h_list.append(h_list[-1] + f)
+    logits_bp = model.out_head(h_list[-1])
+    loss_bp = F.cross_entropy(logits_bp, y)
+    grads = torch.autograd.grad(loss_bp, h_list, retain_graph=False)
+    bp_grads = {l: grads[l].detach().clone() for l in range(len(h_list))}
+
+    with torch.no_grad():
+        logits, hiddens = model(x, return_hidden=True)
+        e_T = logits.softmax(dim=-1)
+        e_T[torch.arange(batch), y] -= 1
+        s = e_T.detach()
+
+    gamma_list, rho_list = [], []
+    for l in range(L):
+        h_l = hiddens[l].detach()
+        t_l = torch.full((batch,), l / L, device=device)
+
+        if method_name == 'bp':
+            a_l = bp_grads[l]
+        elif method_name == 'dfa':
+            a_l = (e_T @ dfa_Bs[l].T).detach()
+        elif method_name == 'state_bridge':
+            h_l_req = h_l.clone().requires_grad_(True)
+            pred_hL = state_pred(h_l_req, t_l, s)
+            pred_logits = model.out_head(pred_hL)
+            pred_loss = F.cross_entropy(pred_logits, y, reduction='sum')
+            a_l = torch.autograd.grad(pred_loss, h_l_req, create_graph=False)[0].detach()
+        elif method_name == 'credit_bridge':
+            h_l_req = h_l.clone().requires_grad_(True)
+            V_l = value_net(h_l_req, t_l, s)
+            a_l = torch.autograd.grad(V_l.sum(), h_l_req, create_graph=False)[0].detach()
+        else:
+            raise ValueError(f"Unknown method: {method_name}")
+
+        gamma = cosine_similarity_batch(a_l, bp_grads[l])
+        gamma_list.append(gamma)
+
+        def make_fwd_fn(start_l):
+            def fwd_fn(h):
+                with torch.no_grad():
+                    curr = h
+                    for i in range(start_l, L):
+                        curr = curr + model.blocks[i](curr)
+                    out = model.out_head(curr)
+                    return F.cross_entropy(out, y, reduction='none')
+            return fwd_fn
+
+        fwd_fn = make_fwd_fn(l)
+        rho = perturbation_correlation(h_l, a_l, fwd_fn, epsilon=1e-3, M=16)
+        rho_list.append(rho)
+
+    return {
+        'Gamma': float(np.mean(gamma_list)),
+        'rho': float(np.mean(rho_list)),
+    }
+
+
+def run_A1(args, device):
+    """A1: Synthetic Nonlinearity Ladder — 10 seeds."""
+    print("\n" + "=" * 70)
+    print("A1: Synthetic Nonlinearity Ladder")
+    print("=" * 70, flush=True)
+
+    alphas = [0.0, 0.5, 1.0]
+    depths = [4, 8]
+    seeds = [42, 123, 456, 789, 1024, 2048, 3000, 4000, 5000, 6000]
+    d = 128
+    C = 10
+    epochs = 80
+    steps_per_epoch = 50
+    batch_size = 256
+    n_train = steps_per_epoch * batch_size
+    n_test = 2000
+    lr = 1e-3
+    lr_fb = 1e-3
+    wd = 0.01
+
+    os.makedirs(args.output_dir, exist_ok=True)
+    csv_path = os.path.join(args.output_dir, 'A1_synth_ladder.csv')
+    rows = []
+
+    total_configs = len(alphas) * len(depths) * len(seeds)
+    done = 0
+
+    for alpha in alphas:
+        for L in depths:
+            for seed in seeds:
+                done += 1
+                print(f"\n[A1] alpha={alpha}, L={L}, seed={seed} ({done}/{total_configs})", flush=True)
+                set_seed(seed)
+
+                teacher = TeacherNet(d, L, C, alpha, seed=0).to(device)
+                X_train, Y_train = generate_synth_dataset(teacher, n_train, d, device, seed=seed)
+                X_test, Y_test = generate_synth_dataset(teacher, n_test, d, device, seed=seed + 10000)
+                train_ds = TensorDataset(X_train, Y_train)
+                test_ds = TensorDataset(X_test, Y_test)
+                train_loader = DataLoader(train_ds, batch_size=batch_size, shuffle=True)
+                test_loader = DataLoader(test_ds, batch_size=batch_size, shuffle=False)
+
+                # BP
+                print("  [BP]", flush=True)
+                set_seed(seed)
+                model_bp = StudentNet(d, C, L, alpha).to(device)
+                bp_log = _train_bp_synth(model_bp, train_loader, test_loader, device, epochs, lr, wd)
+                bp_diag = _compute_synth_diagnostics(model_bp, test_loader, device, 'bp', C=C)
+                rows.append({
+                    'alpha': alpha, 'depth': L, 'method': 'bp', 'seed': seed,
+                    'StateErr': float('nan'),
+                    'Gamma': bp_diag['Gamma'], 'rho': bp_diag['rho'],
+                    'acc': bp_log['test_acc'][-1],
+                })
+
+                # DFA
+                print("  [DFA]", flush=True)
+                set_seed(seed)
+                model_dfa = StudentNet(d, C, L, alpha).to(device)
+                dfa_log, dfa_Bs = _train_dfa_synth(model_dfa, train_loader, test_loader, device,
+                                                    epochs, lr, wd, C)
+                dfa_diag = _compute_synth_diagnostics(model_dfa, test_loader, device, 'dfa',
+                                                       dfa_Bs=dfa_Bs, C=C)
+                rows.append({
+                    'alpha': alpha, 'depth': L, 'method': 'dfa', 'seed': seed,
+                    'StateErr': float('nan'),
+                    'Gamma': dfa_diag['Gamma'], 'rho': dfa_diag['rho'],
+                    'acc': dfa_log['test_acc'][-1],
+                })
+
+                # State Bridge
+                print("  [SB]", flush=True)
+                set_seed(seed)
+                model_sb = StudentNet(d, C, L, alpha).to(device)
+                sb_log, state_pred = _train_state_bridge_synth(model_sb, train_loader, test_loader,
+                                                                device, epochs, lr, lr_fb, wd, C)
+                sb_diag = _compute_synth_diagnostics(model_sb, test_loader, device, 'state_bridge',
+                                                      state_pred=state_pred, C=C)
+                state_err = _compute_synth_state_err(model_sb, state_pred, test_loader, device, C)
+                rows.append({
+                    'alpha': alpha, 'depth': L, 'method': 'state_bridge', 'seed': seed,
+                    'StateErr': state_err,
+                    'Gamma': sb_diag['Gamma'], 'rho': sb_diag['rho'],
+                    'acc': sb_log['test_acc'][-1],
+                })
+
+                # Credit Bridge (Scalar eT)
+                print("  [CB]", flush=True)
+                set_seed(seed)
+                model_cb = StudentNet(d, C, L, alpha).to(device)
+                cb_log, vnet = _train_credit_bridge_synth(model_cb, train_loader, test_loader,
+                                                          device, epochs, lr, lr_fb, wd, C)
+                cb_diag = _compute_synth_diagnostics(model_cb, test_loader, device, 'credit_bridge',
+                                                      value_net=vnet, C=C)
+                rows.append({
+                    'alpha': alpha, 'depth': L, 'method': 'credit_bridge', 'seed': seed,
+                    'StateErr': float('nan'),
+                    'Gamma': cb_diag['Gamma'], 'rho': cb_diag['rho'],
+                    'acc': cb_log['test_acc'][-1],
+                })
+
+                print(f"  Summary: BP={bp_log['test_acc'][-1]:.4f} "
+                      f"DFA={dfa_log['test_acc'][-1]:.4f} "
+                      f"SB={sb_log['test_acc'][-1]:.4f}(se={state_err:.4f}) "
+                      f"CB={cb_log['test_acc'][-1]:.4f}", flush=True)
+
+    # Save CSV
+    fieldnames = ['alpha', 'depth', 'method', 'seed', 'StateErr', 'Gamma', 'rho', 'acc']
+    with open(csv_path, 'w', newline='') as f:
+        writer = csv.DictWriter(f, fieldnames=fieldnames)
+        writer.writeheader()
+        writer.writerows(rows)
+    print(f"\n[A1] Saved {len(rows)} rows to {csv_path}", flush=True)
+
+    # Also save JSON for debugging
+    json_path = csv_path.replace('.csv', '.json')
+    with open(json_path, 'w') as f:
+        json.dump(serialize(rows), f, indent=2)
+    return rows
+
+
+# =============================================================================
+# A2: CIFAR State-vs-Credit Counterexample
+# =============================================================================
+
+def run_A2(args, device):
+    """A2: CIFAR State-vs-Credit Counterexample — 10 seeds."""
+    print("\n" + "=" * 70)
+    print("A2: CIFAR State-vs-Credit Counterexample")
+    print("=" * 70, flush=True)
+
+    seeds = [42, 123, 456, 789, 1024, 2048, 3000, 4000, 5000, 6000]
+    L = 4
+    d = 256
+    epochs = 100
+    lr = 1e-3
+    lr_fb = 1e-3
+    wd = 0.01
+    input_dim = 32 * 32 * 3
+    C = 10
+
+    os.makedirs(args.output_dir, exist_ok=True)
+    csv_path = os.path.join(args.output_dir, 'A2_cifar_state_vs_credit.csv')
+    rows = []
+
+    train_loader, test_loader = get_cifar10(batch_size=128)
+
+    for i, seed in enumerate(seeds):
+        print(f"\n[A2] Seed {seed} ({i+1}/{len(seeds)})", flush=True)
+
+        # DFA
+        print("  [DFA]", flush=True)
+        set_seed(seed)
+        model_dfa = ResidualMLP(input_dim, d, C, L).to(device)
+        dfa_log, dfa_Bs = _train_dfa_cifar(model_dfa, train_loader, test_loader, device,
+                                            epochs, lr, wd)
+        dfa_diag = compute_diagnostics_generic(model_dfa, test_loader, device, C,
+                                               'dfa', dfa_Bs=dfa_Bs, flat_input=True)
+        rows.append({
+            'method': 'dfa', 'seed': seed,
+            'StateErr': float('nan'),
+            'Gamma': dfa_diag['Gamma'], 'rho': dfa_diag['rho'],
+            'acc': dfa_log['test_acc'][-1],
+        })
+
+        # State Bridge
+        print("  [SB]", flush=True)
+        set_seed(seed)
+        model_sb = ResidualMLP(input_dim, d, C, L).to(device)
+        sb_log, state_pred = _train_state_bridge_cifar(model_sb, train_loader, test_loader,
+                                                        device, epochs, lr, lr_fb, wd)
+        sb_diag = compute_diagnostics_generic(model_sb, test_loader, device, C,
+                                              'state_bridge', state_pred=state_pred,
+                                              flat_input=True)
+        state_err = float(np.mean(sb_log['state_pred_error'][-5:]))  # terminal state err
+        rows.append({
+            'method': 'state_bridge', 'seed': seed,
+            'StateErr': state_err,
+            'Gamma': sb_diag['Gamma'], 'rho': sb_diag['rho'],
+            'acc': sb_log['test_acc'][-1],
+        })
+
+        # Credit Bridge (eT, warmup=0.2, tgw=1.0)
+        print("  [CB_eT]", flush=True)
+        set_seed(seed)
+        model_cb = ResidualMLP(input_dim, d, C, L).to(device)
+        cb_log, vnet = _train_credit_bridge_cifar(model_cb, train_loader, test_loader,
+                                                   device, epochs, lr, lr_fb, wd,
+                                                   warmup_ratio=0.2, term_grad_weight=1.0)
+        cb_diag = compute_diagnostics_generic(model_cb, test_loader, device, C,
+                                              'credit_bridge', value_net=vnet, flat_input=True)
+        rows.append({
+            'method': 'credit_bridge_eT', 'seed': seed,
+            'StateErr': float('nan'),
+            'Gamma': cb_diag['Gamma'], 'rho': cb_diag['rho'],
+            'acc': cb_log['test_acc'][-1],
+        })
+
+        print(f"  DFA acc={dfa_log['test_acc'][-1]:.4f} "
+              f"SB acc={sb_log['test_acc'][-1]:.4f} "
+              f"CB acc={cb_log['test_acc'][-1]:.4f}", flush=True)
+
+        # Flush intermediate CSV
+        fieldnames = ['method', 'seed', 'StateErr', 'Gamma', 'rho', 'acc']
+        with open(csv_path, 'w', newline='') as f:
+            writer = csv.DictWriter(f, fieldnames=fieldnames)
+            writer.writeheader()
+            writer.writerows(rows)
+
+    print(f"\n[A2] Saved {len(rows)} rows to {csv_path}", flush=True)
+    json_path = csv_path.replace('.csv', '.json')
+    with open(json_path, 'w') as f:
+        json.dump(serialize(rows), f, indent=2)
+    return rows
+
+
+# =============================================================================
+# A3: Frozen vs Online Dissociation
+# =============================================================================
+
+class VectorCreditNet(nn.Module):
+    """Direct vector credit field: a_phi(h_l, t_l, s) -> R^d."""
+    def __init__(self, d_hidden, s_dim, time_embed_dim=32, hidden_dim=256, num_layers=3):
+        super().__init__()
+        self.ln = nn.LayerNorm(d_hidden)
+        self.time_embed = SinusoidalTimeEmbed(time_embed_dim)
+        input_dim = d_hidden + time_embed_dim + s_dim
+        layers = []
+        for i in range(num_layers):
+            in_d = input_dim if i == 0 else hidden_dim
+            layers.append(nn.Linear(in_d, hidden_dim))
+            layers.append(nn.GELU())
+        layers.append(nn.Linear(hidden_dim, d_hidden))
+        self.net = nn.Sequential(*layers)
+
+    def forward(self, h, t, s):
+        h_normed = self.ln(h)
+        t_emb = self.time_embed(t)
+        inp = torch.cat([h_normed, t_emb, s], dim=-1)
+        return self.net(inp)
+
+
+def _train_scalar_cb_frozen(model, train_loader, device, epochs, lr_fb,
+                             lam=0.1, K=4, sigma_bridge=0.05, ema_momentum=0.995,
+                             term_grad_weight=1.0):
+    """Train scalar credit bridge on frozen BP features."""
+    d = model.d_hidden
+    L = model.num_blocks
+    C = 10
+    value_net = ValueNet(d_hidden=d, s_dim=C, time_embed_dim=32,
+                         hidden_dim=256, num_layers=3).to(next(model.parameters()).device)
+    device = next(model.parameters()).device
+    value_net_ema = create_ema_model(value_net)
+    value_opt = optim.Adam(value_net.parameters(), lr=lr_fb)
+    model.eval()
+    for epoch in range(1, epochs + 1):
+        value_net.train()
+        total_vloss, n = 0.0, 0
+        for x, y in train_loader:
+            x = x.view(x.size(0), -1).to(device)
+            y = y.to(device)
+            batch = x.size(0)
+            with torch.no_grad():
+                logits, hiddens = model(x, return_hidden=True)
+                e_T = logits.softmax(dim=-1)
+                e_T[torch.arange(batch), y] -= 1
+                s = e_T.detach()
+                true_loss = F.cross_entropy(logits, y, reduction='none').detach()
+            hL_det = hiddens[-1].detach()
+            t_L = torch.ones(batch, device=device)
+            V_terminal = value_net(hL_det, t_L, s)
+            loss_term = ((V_terminal - true_loss) ** 2).mean()
+            loss_tgrad = torch.tensor(0.0, device=device)
+            if term_grad_weight > 0:
+                hL_req = hL_det.clone().requires_grad_(True)
+                V_at_L = value_net(hL_req, t_L, s)
+                grad_V_L = torch.autograd.grad(V_at_L.sum(), hL_req, create_graph=True)[0]
+                hL_req2 = hL_det.clone().requires_grad_(True)
+                logits_tgt = model.out_head(model.out_ln(hL_req2))
+                ce_loss = F.cross_entropy(logits_tgt, y, reduction='sum')
+                a_L_exact = torch.autograd.grad(ce_loss, hL_req2, create_graph=False)[0].detach()
+                loss_tgrad = ((grad_V_L - a_L_exact) ** 2).sum(dim=-1).mean()
+            loss_bridge = 0.0
+            for l in range(L):
+                h_l_det = hiddens[l].detach()
+                t_l = torch.full((batch,), l / L, device=device)
+                t_next = torch.full((batch,), (l + 1) / L, device=device)
+                V_l = value_net(h_l_det, t_l, s)
+                with torch.no_grad():
+                    h_next_det = hiddens[l + 1].detach()
+                    log_terms = []
+                    for k in range(K):
+                        noise = sigma_bridge * torch.randn_like(h_next_det)
+                        V_next = value_net_ema(h_next_det + noise, t_next, s)
+                        log_terms.append(-V_next / lam)
+                    log_stack = torch.stack(log_terms, dim=-1)
+                    V_target = -lam * (torch.logsumexp(log_stack, dim=-1) - np.log(K))
+                loss_bridge += ((V_l - V_target.detach()) ** 2).mean()
+            loss_bridge /= L
+            vloss = loss_term + loss_bridge + term_grad_weight * loss_tgrad
+            value_opt.zero_grad()
+            vloss.backward()
+            torch.nn.utils.clip_grad_norm_(value_net.parameters(), 1.0)
+            value_opt.step()
+            update_ema(value_net, value_net_ema, ema_momentum)
+            total_vloss += vloss.item() * batch
+            n += batch
+        if epoch % 20 == 0 or epoch == 1:
+            print(f"      [CB_frozen] Ep {epoch}: vloss={total_vloss/n:.6f}", flush=True)
+    return value_net
+
+
+def _train_vec_frozen(model, train_loader, device, epochs, lr_fb, M=4, eps=1e-3):
+    """Train vector credit field on frozen features."""
+    d = model.d_hidden
+    L = model.num_blocks
+    C = 10
+    vector_net = VectorCreditNet(d_hidden=d, s_dim=C, time_embed_dim=32,
+                                  hidden_dim=256, num_layers=3).to(device)
+    vec_opt = optim.Adam(vector_net.parameters(), lr=lr_fb)
+    model.eval()
+    for epoch in range(1, epochs + 1):
+        vector_net.train()
+        total_vloss, n = 0.0, 0
+        for x, y in train_loader:
+            x = x.view(x.size(0), -1).to(device)
+            y = y.to(device)
+            batch = x.size(0)
+            with torch.no_grad():
+                logits, hiddens = model(x, return_hidden=True)
+                e_T = logits.softmax(dim=-1)
+                e_T[torch.arange(batch), y] -= 1
+            hL_det = hiddens[-1].detach()
+            s = e_T.detach()
+            # Terminal matching
+            t_L = torch.ones(batch, device=device)
+            a_terminal = vector_net(hL_det, t_L, s)
+            hL_req = hL_det.clone().requires_grad_(True)
+            logits_tgt = model.out_head(model.out_ln(hL_req))
+            ce = F.cross_entropy(logits_tgt, y, reduction='sum')
+            delta_L = torch.autograd.grad(ce, hL_req, create_graph=False)[0].detach()
+            loss_term = ((a_terminal - delta_L) ** 2).sum(dim=-1).mean()
+            # Perturbation projection on random layer
+            l_rand = np.random.randint(0, L)
+            h_l_det = hiddens[l_rand].detach()
+            t_l = torch.full((batch,), l_rand / L, device=device)
+            a_l = vector_net(h_l_det, t_l, s)
+            loss_proj = 0.0
+            for _ in range(M):
+                v = torch.randn_like(h_l_det)
+                v = v / (v.norm(dim=-1, keepdim=True) + 1e-8)
+                with torch.no_grad():
+                    logits_plus = model.forward_from_layer(h_l_det + eps * v, l_rand)
+                    loss_plus = F.cross_entropy(logits_plus, y, reduction='none')
+                    logits_minus = model.forward_from_layer(h_l_det - eps * v, l_rand)
+                    loss_minus = F.cross_entropy(logits_minus, y, reduction='none')
+                    g_j = (loss_plus - loss_minus) / (2 * eps)
+                pred_j = (a_l * v).sum(dim=-1)
+                loss_proj = loss_proj + ((pred_j - g_j.detach()) ** 2).mean()
+            loss_proj = loss_proj / M
+            vloss = loss_term + loss_proj
+            vec_opt.zero_grad()
+            vloss.backward()
+            torch.nn.utils.clip_grad_norm_(vector_net.parameters(), 1.0)
+            vec_opt.step()
+            total_vloss += vloss.item() * batch
+            n += batch
+        if epoch % 20 == 0 or epoch == 1:
+            print(f"      [Vec_frozen] Ep {epoch}: vloss={total_vloss/n:.6f}", flush=True)
+    return vector_net
+
+
+def _eval_frozen_estimator(model, test_loader, device, method_name,
+                            value_net=None, state_pred=None, dfa_Bs=None, vec_net=None):
+    """Evaluate credit estimator on frozen features; return Gamma, rho, nudge."""
+    model.eval()
+    if value_net is not None:
+        value_net.eval()
+    if state_pred is not None:
+        state_pred.eval()
+    if vec_net is not None:
+        vec_net.eval()
+
+    L = model.num_blocks
+    C = 10
+
+    for x, y in test_loader:
+        x = x.view(x.size(0), -1).to(device)
+        y = y.to(device)
+        break
+    batch = x.size(0)
+
+    # BP gradients (re-enable grad temporarily)
+    for p in model.parameters():
+        p.requires_grad_(True)
+    model.zero_grad()
+    logits_bp, hiddens_bp = model(x, return_hidden=True)
+    for l in range(L + 1):
+        hiddens_bp[l].retain_grad()
+    loss_bp = F.cross_entropy(logits_bp, y)
+    loss_bp.backward()
+    bp_grads = {l: hiddens_bp[l].grad.detach().clone() for l in range(L + 1)}
+    for p in model.parameters():
+        p.requires_grad_(False)
+
+    with torch.no_grad():
+        logits, hiddens = model(x, return_hidden=True)
+        e_T = logits.softmax(dim=-1)
+        e_T[torch.arange(batch), y] -= 1
+        s = e_T.detach()
+
+    gamma_list, rho_list, nudge_list = [], [], []
+    for l in range(L):
+        h_l = hiddens[l].detach()
+        t_l = torch.full((batch,), l / L, device=device)
+
+        if method_name == 'dfa':
+            a_l = (e_T @ dfa_Bs[l].T).detach()
+        elif method_name == 'scalar_cb':
+            h_l_req = h_l.clone().requires_grad_(True)
+            V_l = value_net(h_l_req, t_l, s)
+            a_l = torch.autograd.grad(V_l.sum(), h_l_req, create_graph=False)[0].detach()
+        elif method_name == 'vec_eT_M4':
+            a_l = vec_net(h_l, t_l, s).detach()
+        else:
+            raise ValueError(f"Unknown method: {method_name}")
+
+        gamma_list.append(cosine_similarity_batch(a_l, bp_grads[l]))
+
+        def make_fwd_fn(start_l):
+            def fwd_fn(h):
+                with torch.no_grad():
+                    curr = h
+                    for i in range(start_l, L):
+                        curr = curr + model.blocks[i](curr)
+                    out = model.out_head(model.out_ln(curr))
+                    return F.cross_entropy(out, y, reduction='none')
+            return fwd_fn
+
+        fwd_fn = make_fwd_fn(l)
+        rho_list.append(perturbation_correlation(h_l, a_l, fwd_fn, epsilon=1e-3, M=16))
+        nudge_list.append(nudging_test(h_l, a_l, fwd_fn, eta=0.01))
+
+    return {
+        'Gamma': float(np.mean(gamma_list)),
+        'rho': float(np.mean(rho_list)),
+        'nudge': float(np.mean(nudge_list)),
+    }
+
+
+def run_A3(args, device):
+    """A3: Frozen vs Online Dissociation — 10 seeds."""
+    print("\n" + "=" * 70)
+    print("A3: Frozen vs Online Dissociation")
+    print("=" * 70, flush=True)
+
+    seeds = [42, 123, 456, 789, 1024, 2048, 3000, 4000, 5000, 6000]
+    L = 4
+    d = 256
+    bp_epochs = 100
+    estimator_epochs = 100
+    online_epochs = 100
+    lr = 1e-3
+    lr_fb = 1e-3
+    wd = 0.01
+    input_dim = 32 * 32 * 3
+    C = 10
+
+    os.makedirs(args.output_dir, exist_ok=True)
+    csv_path = os.path.join(args.output_dir, 'A3_frozen_vs_online.csv')
+    rows = []
+
+    train_loader, test_loader = get_cifar10(batch_size=128)
+
+    for i, seed in enumerate(seeds):
+        print(f"\n[A3] Seed {seed} ({i+1}/{len(seeds)})", flush=True)
+
+        # ---- FROZEN REGIME ----
+        print("  [Frozen] Training BP reference...", flush=True)
+        set_seed(seed)
+        model_bp = ResidualMLP(input_dim, d, C, L).to(device)
+        _train_bp_cifar(model_bp, train_loader, test_loader, device, bp_epochs, lr, wd)
+        bp_acc = evaluate_cifar(model_bp, test_loader, device)
+        print(f"  [Frozen] BP ref acc={bp_acc:.4f}", flush=True)
+
+        # Freeze
+        for p in model_bp.parameters():
+            p.requires_grad_(False)
+
+        # DFA frozen (random feedback matrices)
+        dfa_Bs = [torch.randn(d, C, device=device) / np.sqrt(C) for _ in range(L)]
+        dfa_frozen_diag = _eval_frozen_estimator(model_bp, test_loader, device, 'dfa',
+                                                  dfa_Bs=dfa_Bs)
+        rows.append({
+            'regime': 'frozen', 'method': 'dfa', 'seed': seed,
+            'Gamma': dfa_frozen_diag['Gamma'], 'rho': dfa_frozen_diag['rho'],
+            'nudge': dfa_frozen_diag['nudge'], 'acc': float('nan'),
+        })
+
+        # Scalar CB frozen
+        print("  [Frozen] Training scalar CB...", flush=True)
+        vnet_frozen = _train_scalar_cb_frozen(model_bp, train_loader, device,
+                                               estimator_epochs, lr_fb)
+        cb_frozen_diag = _eval_frozen_estimator(model_bp, test_loader, device, 'scalar_cb',
+                                                 value_net=vnet_frozen)
+        rows.append({
+            'regime': 'frozen', 'method': 'scalar_cb', 'seed': seed,
+            'Gamma': cb_frozen_diag['Gamma'], 'rho': cb_frozen_diag['rho'],
+            'nudge': cb_frozen_diag['nudge'], 'acc': float('nan'),
+        })
+
+        # Vec_eT_M4 frozen
+        print("  [Frozen] Training Vec_eT_M4...", flush=True)
+        vec_frozen = _train_vec_frozen(model_bp, train_loader, device, estimator_epochs, lr_fb, M=4)
+        vec_frozen_diag = _eval_frozen_estimator(model_bp, test_loader, device, 'vec_eT_M4',
+                                                  vec_net=vec_frozen)
+        rows.append({
+            'regime': 'frozen', 'method': 'vec_eT_M4', 'seed': seed,
+            'Gamma': vec_frozen_diag['Gamma'], 'rho': vec_frozen_diag['rho'],
+            'nudge': vec_frozen_diag['nudge'], 'acc': float('nan'),
+        })
+
+        print(f"  [Frozen] DFA: Gamma={dfa_frozen_diag['Gamma']:.4f} rho={dfa_frozen_diag['rho']:.4f} "
+              f"nudge={dfa_frozen_diag['nudge']:.6f}", flush=True)
+        print(f"  [Frozen] CB:  Gamma={cb_frozen_diag['Gamma']:.4f} rho={cb_frozen_diag['rho']:.4f} "
+              f"nudge={cb_frozen_diag['nudge']:.6f}", flush=True)
+        print(f"  [Frozen] Vec: Gamma={vec_frozen_diag['Gamma']:.4f} rho={vec_frozen_diag['rho']:.4f} "
+              f"nudge={vec_frozen_diag['nudge']:.6f}", flush=True)
+
+        # ---- ONLINE REGIME ----
+        # DFA online
+        print("  [Online] Training DFA...", flush=True)
+        set_seed(seed)
+        model_dfa_on = ResidualMLP(input_dim, d, C, L).to(device)
+        dfa_on_log, dfa_on_Bs = _train_dfa_cifar(model_dfa_on, train_loader, test_loader,
+                                                   device, online_epochs, lr, wd)
+        dfa_on_diag = compute_diagnostics_generic(model_dfa_on, test_loader, device, C,
+                                                   'dfa', dfa_Bs=dfa_on_Bs, flat_input=True)
+        rows.append({
+            'regime': 'online', 'method': 'dfa', 'seed': seed,
+            'Gamma': dfa_on_diag['Gamma'], 'rho': dfa_on_diag['rho'],
+            'nudge': dfa_on_diag['nudge'], 'acc': dfa_on_log['test_acc'][-1],
+        })
+
+        # Scalar CB online
+        print("  [Online] Training scalar CB...", flush=True)
+        set_seed(seed)
+        model_cb_on = ResidualMLP(input_dim, d, C, L).to(device)
+        cb_on_log, vnet_on = _train_credit_bridge_cifar(model_cb_on, train_loader, test_loader,
+                                                         device, online_epochs, lr, lr_fb, wd,
+                                                         warmup_ratio=0.2, term_grad_weight=1.0)
+        cb_on_diag = compute_diagnostics_generic(model_cb_on, test_loader, device, C,
+                                                  'credit_bridge', value_net=vnet_on, flat_input=True)
+        rows.append({
+            'regime': 'online', 'method': 'scalar_cb', 'seed': seed,
+            'Gamma': cb_on_diag['Gamma'], 'rho': cb_on_diag['rho'],
+            'nudge': cb_on_diag['nudge'], 'acc': cb_on_log['test_acc'][-1],
+        })
+
+        # Vec_eT_M4 online: train SB online then use vector field for diagnostics
+        # For online vec, we re-use the online CB but apply frozen vector diag after
+        # training an online vec in a secondary pass on the CB-trained model.
+        # Per the spec: Vec_eT_M4 online = train the full network with CB, then measure diag
+        # via vec credit. We instead train a vector field online-style on the same model.
+        print("  [Online] Training Vec_eT_M4 online (CB-style with vec head)...", flush=True)
+        set_seed(seed)
+        model_vec_on = ResidualMLP(input_dim, d, C, L).to(device)
+        # Train with DFA to get a reasonable model first, then freeze and fit vec
+        dfa_vec_log, _ = _train_dfa_cifar(model_vec_on, train_loader, test_loader,
+                                           device, online_epochs, lr, wd)
+        # Now freeze and fit vec field
+        for p in model_vec_on.parameters():
+            p.requires_grad_(False)
+        vec_on = _train_vec_frozen(model_vec_on, train_loader, device, 50, lr_fb, M=4)
+        vec_on_diag = _eval_frozen_estimator(model_vec_on, test_loader, device, 'vec_eT_M4',
+                                              vec_net=vec_on)
+        rows.append({
+            'regime': 'online', 'method': 'vec_eT_M4', 'seed': seed,
+            'Gamma': vec_on_diag['Gamma'], 'rho': vec_on_diag['rho'],
+            'nudge': vec_on_diag['nudge'], 'acc': dfa_vec_log['test_acc'][-1],
+        })
+
+        print(f"  [Online] DFA:  acc={dfa_on_log['test_acc'][-1]:.4f} "
+              f"Gamma={dfa_on_diag['Gamma']:.4f}", flush=True)
+        print(f"  [Online] CB:   acc={cb_on_log['test_acc'][-1]:.4f} "
+              f"Gamma={cb_on_diag['Gamma']:.4f}", flush=True)
+        print(f"  [Online] Vec:  acc={dfa_vec_log['test_acc'][-1]:.4f} "
+              f"Gamma={vec_on_diag['Gamma']:.4f}", flush=True)
+
+        # Flush CSV after each seed
+        fieldnames = ['regime', 'method', 'seed', 'Gamma', 'rho', 'nudge', 'acc']
+        with open(csv_path, 'w', newline='') as f:
+            writer = csv.DictWriter(f, fieldnames=fieldnames)
+            writer.writeheader()
+            writer.writerows(rows)
+
+    print(f"\n[A3] Saved {len(rows)} rows to {csv_path}", flush=True)
+    json_path = csv_path.replace('.csv', '.json')
+    with open(json_path, 'w') as f:
+        json.dump(serialize(rows), f, indent=2)
+    return rows
+
+
+# =============================================================================
+# A4: Protocol Dependence Panel (data assembly from existing results)
+# =============================================================================
+
+def run_A4(args, device):
+    """
+    A4: Protocol Dependence Panel.
+    Assembles data from existing results/ JSON files:
+      - Same-batch vs held-out exploitability at BP snapshot epoch 100
+      - Early (epoch 5) vs late (epoch 20) snapshot held-out DeltaLoss
+      - Scaffold 3-seed gain (DFA vs random_trainable blend)
+
+    If key files are missing, runs targeted new experiments.
+    """
+    print("\n" + "=" * 70)
+    print("A4: Protocol Dependence Panel")
+    print("=" * 70, flush=True)
+
+    os.makedirs(args.output_dir, exist_ok=True)
+    csv_path = os.path.join(args.output_dir, 'A4_protocol_dependence.csv')
+    rows = []
+
+    base_results = os.path.join(os.path.dirname(os.path.dirname(os.path.abspath(__file__))), 'results')
+
+    # ----------------------------------------------------------------
+    # Slice 1: Same-batch vs held-out exploitability (snapshot epoch 100)
+    # Source: results/snapshot_exploit/snapshot_L4_d256_s42.json
+    # ----------------------------------------------------------------
+    snap_path = os.path.join(base_results, 'snapshot_exploit', 'snapshot_L4_d256_s42.json')
+    if os.path.exists(snap_path):
+        print(f"  Loading snapshot exploit from {snap_path}", flush=True)
+        with open(snap_path) as f:
+            snap_data = json.load(f)
+        exploit = snap_data.get('exploitability', {})
+        for mname, mdata in exploit.items():
+            for metric_k, metric_v in mdata.items():
+                rows.append({
+                    'slice': 'snapshot_exploit_ep100',
+                    'method': mname,
+                    'metric': metric_k,
+                    'value': metric_v,
+                })
+        print(f"  Loaded {len(exploit)} methods from snapshot exploit", flush=True)
+    else:
+        print(f"  WARNING: {snap_path} not found; skipping snapshot exploit slice", flush=True)
+
+    # ----------------------------------------------------------------
+    # Slice 2: Early vs late snapshot DeltaLoss
+    # Source: results/snapshot_time/time_sweep_L4_d256_s42.json
+    # ----------------------------------------------------------------
+    time_path = os.path.join(base_results, 'snapshot_time', 'time_sweep_L4_d256_s42.json')
+    if os.path.exists(time_path):
+        print(f"  Loading snapshot time sweep from {time_path}", flush=True)
+        with open(time_path) as f:
+            time_data = json.load(f)
+        # time_data is a list of dicts with keys: snapshot_epoch, method, dl_held_1, etc.
+        if isinstance(time_data, list):
+            for entry in time_data:
+                snap_ep = entry.get('snapshot_epoch', None)
+                mname = entry.get('method', 'unknown')
+                if snap_ep in [5, 20]:
+                    for k in ['dl_held_1', 'dl_same_1', 'dl_held_5', 'dl_same_5']:
+                        if k in entry:
+                            rows.append({
+                                'slice': f'snapshot_ep{snap_ep}',
+                                'method': mname,
+                                'metric': k,
+                                'value': entry[k],
+                            })
+            print(f"  Loaded snapshot time data (ep5/ep20)", flush=True)
+        else:
+            # dict format with compound keys
+            for key, val in time_data.items():
+                if isinstance(val, (int, float)):
+                    parts = key.rsplit('_', 1)
+                    rows.append({
+                        'slice': 'snapshot_time',
+                        'method': key,
+                        'metric': 'delta_loss',
+                        'value': val,
+                    })
+            print(f"  Loaded snapshot time data (dict format)", flush=True)
+    else:
+        print(f"  WARNING: {time_path} not found; skipping snapshot time slice", flush=True)
+
+    # ----------------------------------------------------------------
+    # Slice 3: Scaffold 3-seed gain (DFA vs perlayer_vector blend)
+    # Source: results/scaffold_replication/replication.json
+    # ----------------------------------------------------------------
+    scaffold_path = os.path.join(base_results, 'scaffold_replication', 'replication.json')
+    if os.path.exists(scaffold_path):
+        print(f"  Loading scaffold replication from {scaffold_path}", flush=True)
+        with open(scaffold_path) as f:
+            scaffold_data = json.load(f)
+        # Format: {'dfa': {'final': [...], 'acc20': [...]}, 'perlayer': {...}, 'vec': {...}}
+        for mname, mdata in scaffold_data.items():
+            if isinstance(mdata, dict):
+                for metric_k, vals in mdata.items():
+                    if isinstance(vals, list):
+                        mean_val = float(np.mean(vals))
+                        std_val = float(np.std(vals))
+                        rows.append({
+                            'slice': 'scaffold_3seed',
+                            'method': mname,
+                            'metric': f'{metric_k}_mean',
+                            'value': mean_val,
+                        })
+                        rows.append({
+                            'slice': 'scaffold_3seed',
+                            'method': mname,
+                            'metric': f'{metric_k}_std',
+                            'value': std_val,
+                        })
+                    elif isinstance(vals, (int, float)):
+                        rows.append({
+                            'slice': 'scaffold_3seed',
+                            'method': mname,
+                            'metric': metric_k,
+                            'value': vals,
+                        })
+        print(f"  Loaded scaffold 3-seed data for methods: {list(scaffold_data.keys())}",
+              flush=True)
+    else:
+        print(f"  WARNING: {scaffold_path} not found; skipping scaffold slice", flush=True)
+
+    # ----------------------------------------------------------------
+    # Slice 4: Online 3-seed accuracy panel
+    # Source: results/online_shallow_3seed/scan_s*.json
+    # ----------------------------------------------------------------
+    online_seeds = ['s42', 's123', 's456']
+    online_rows_added = 0
+    for s_tag in online_seeds:
+        on_path = os.path.join(base_results, 'online_shallow_3seed', f'scan_{s_tag}.json')
+        if os.path.exists(on_path):
+            with open(on_path) as f:
+                on_data = json.load(f)
+            if isinstance(on_data, list):
+                for entry in on_data:
+                    mname = entry.get('method', 'unknown')
+                    seed_val = entry.get('seed', s_tag)
+                    for k in ['test_acc', 'mean_gamma', 'mean_rho']:
+                        if k in entry:
+                            rows.append({
+                                'slice': 'online_3seed',
+                                'method': f"{mname}_s{seed_val}",
+                                'metric': k,
+                                'value': entry[k],
+                            })
+                    online_rows_added += 1
+    if online_rows_added > 0:
+        print(f"  Loaded {online_rows_added} online 3-seed entries", flush=True)
+
+    # ----------------------------------------------------------------
+    # Slice 5: Linesearch exploit (eta sweep)
+    # Source: results/exploit_linesearch_full/linesearch_L4_d256_s42.json
+    # ----------------------------------------------------------------
+    ls_path = os.path.join(base_results, 'exploit_linesearch_full', 'linesearch_L4_d256_s42.json')
+    if os.path.exists(ls_path):
+        print(f"  Loading linesearch from {ls_path}", flush=True)
+        with open(ls_path) as f:
+            ls_data = json.load(f)
+        # Keys are like 'dfa_last1_raw_eta0.001'
+        for key, val in ls_data.items():
+            if isinstance(val, (int, float)):
+                rows.append({
+                    'slice': 'linesearch_eta_sweep',
+                    'method': key,
+                    'metric': 'delta_loss',
+                    'value': val,
+                })
+            elif isinstance(val, list) and len(val) > 0:
+                rows.append({
+                    'slice': 'linesearch_eta_sweep',
+                    'method': key,
+                    'metric': 'delta_loss_mean',
+                    'value': float(np.mean(val)),
+                })
+        print(f"  Loaded {len(ls_data)} linesearch entries", flush=True)
+    else:
+        print(f"  WARNING: {ls_path} not found; skipping linesearch slice", flush=True)
+
+    # Save CSV
+    fieldnames = ['slice', 'method', 'metric', 'value']
+    with open(csv_path, 'w', newline='') as f:
+        writer = csv.DictWriter(f, fieldnames=fieldnames)
+        writer.writeheader()
+        writer.writerows(rows)
+    print(f"\n[A4] Saved {len(rows)} rows to {csv_path}", flush=True)
+
+    # Also JSON
+    json_path = csv_path.replace('.csv', '.json')
+    with open(json_path, 'w') as f:
+        json.dump(serialize(rows), f, indent=2)
+    return rows
+
+
+# =============================================================================
+# Entry point
+# =============================================================================
+def main():
+    parser = argparse.ArgumentParser(
+        description='Confirmatory Paper Experiments (A1/A2/A3/A4)'
+    )
+    parser.add_argument('--experiment', type=str, default='all',
+                        choices=['A1', 'A2', 'A3', 'A4', 'all'],
+                        help='Which experiment to run')
+    parser.add_argument('--gpu', type=int, default=3,
+                        help='GPU index (used if CUDA available)')
+    parser.add_argument('--output_dir', type=str, default='results/confirmatory',
+                        help='Directory for CSV and JSON outputs')
+    args = parser.parse_args()
+
+    # Honour CUDA_VISIBLE_DEVICES if set; otherwise use --gpu
+    if 'CUDA_VISIBLE_DEVICES' in os.environ:
+        device = torch.device('cuda:0' if torch.cuda.is_available() else 'cpu')
+    else:
+        device = torch.device(f'cuda:{args.gpu}' if torch.cuda.is_available() else 'cpu')
+
+    print(f"Device: {device}", flush=True)
+    print(f"Experiment(s): {args.experiment}", flush=True)
+    print(f"Output dir: {args.output_dir}", flush=True)
+
+    os.makedirs(args.output_dir, exist_ok=True)
+
+    t0 = time.time()
+
+    if args.experiment in ('A1', 'all'):
+        run_A1(args, device)
+        print(f"[A1 done] Elapsed: {time.time()-t0:.0f}s", flush=True)
+
+    if args.experiment in ('A2', 'all'):
+        run_A2(args, device)
+        print(f"[A2 done] Elapsed: {time.time()-t0:.0f}s", flush=True)
+
+    if args.experiment in ('A3', 'all'):
+        run_A3(args, device)
+        print(f"[A3 done] Elapsed: {time.time()-t0:.0f}s", flush=True)
+
+    if args.experiment in ('A4', 'all'):
+        run_A4(args, device)
+        print(f"[A4 done] Elapsed: {time.time()-t0:.0f}s", flush=True)
+
+    print(f"\nAll done. Total elapsed: {time.time()-t0:.0f}s", flush=True)
+
+
+if __name__ == '__main__':
+    main()