1 files changed, 92 insertions, 0 deletions
diff --git a/src/training/checkpointing.py b/src/training/checkpointing.py
new file mode 100644
index 0000000..9ff02df
--- /dev/null
+++ b/src/training/checkpointing.py
@@ -0,0 +1,92 @@
+"""Checkpoint save/load for predictor + optimizer + schedule state.
+
+Only saves trainable components (predictor MLP, optimizer, schedule state).
+Frozen models (OLMo, Qwen) are not checkpointed — they load from HuggingFace.
+"""
+
+from __future__ import annotations
+
+import os
+from typing import Any, Optional
+
+import torch
+import torch.nn as nn
+import torch.optim as optim
+
+
+def save_checkpoint(
+    save_dir: str,
+    step: int,
+    predictor: nn.Module,
+    optimizer: optim.Optimizer,
+    scheduler: Any,
+    best_eval_nll: float,
+    extra: Optional[dict] = None,
+) -> str:
+    """Save training checkpoint.
+
+    Args:
+        save_dir: directory to save checkpoint
+        step: current global step
+        predictor: the structure predictor (only MLP params are saved)
+        optimizer: AdamW optimizer
+        scheduler: LR scheduler
+        best_eval_nll: best eval NLL so far
+        extra: any additional state to save
+
+    Returns:
+        path: path to saved checkpoint
+    """
+    os.makedirs(save_dir, exist_ok=True)
+    path = os.path.join(save_dir, f"checkpoint_step{step}.pt")
+
+    state = {
+        "step": step,
+        "predictor_state_dict": predictor.state_dict(),
+        "optimizer_state_dict": optimizer.state_dict(),
+        "scheduler_state_dict": scheduler.state_dict() if scheduler is not None else None,
+        "best_eval_nll": best_eval_nll,
+    }
+    if extra:
+        state.update(extra)
+
+    torch.save(state, path)
+    print(f"Checkpoint saved: {path}")
+    return path
+
+
+def load_checkpoint(
+    path: str,
+    predictor: nn.Module,
+    optimizer: Optional[optim.Optimizer] = None,
+    scheduler: Optional[Any] = None,
+    device: Optional[torch.device] = None,
+) -> dict:
+    """Load training checkpoint.
+
+    Args:
+        path: path to checkpoint file
+        predictor: structure predictor to load weights into
+        optimizer: optimizer to restore state (optional — skip for eval)
+        scheduler: LR scheduler to restore state (optional)
+        device: device to map tensors to
+
+    Returns:
+        state dict with step, best_eval_nll, and any extras
+    """
+    map_location = device if device is not None else "cpu"
+    state = torch.load(path, map_location=map_location)
+
+    predictor.load_state_dict(state["predictor_state_dict"])
+    print(f"Predictor state loaded from {path}")
+
+    if optimizer is not None and "optimizer_state_dict" in state:
+        optimizer.load_state_dict(state["optimizer_state_dict"])
+
+    if scheduler is not None and state.get("scheduler_state_dict") is not None:
+        scheduler.load_state_dict(state["scheduler_state_dict"])
+
+    return {
+        "step": state["step"],
+        "best_eval_nll": state.get("best_eval_nll", float("inf")),
+    }