diff --git a/jevany/resume.py b/jevany/resume.py
index 7236837..ff5dbd2 100644
--- a/jevany/resume.py
+++ b/jevany/resume.py
@@ -120,6 +120,14 @@ def load_trainer_state(directory: str | Path, args: dict, dataset_sha256: str,
                          "(record content/order, media paths or local media contents)")
     if state["world_size"] != world_size or state["device"] != device:
         raise ValueError("--resume requires the original world size and device type")
+    required_rng = {"shuffle", "python", "numpy", "torch"}
+    if device in ("cuda", "mps"):
+        required_rng.add("device")
+    rank_rng = state.get("rank_rng")
+    if (not isinstance(rank_rng, list) or len(rank_rng) != world_size
+            or any(not isinstance(rng, dict) or not required_rng <= rng.keys() for rng in rank_rng)):
+        raise ValueError(f"{directory}: incomplete checkpoint RNG state; use a complete checkpoint "
+                         "or --init-from for a weights-only warm start")
     for name, expected in state["checkpoint_sha256"].items():
         if digest(directory / name) != expected:
             raise ValueError(f"{directory}: {name} differs from the saved trainer state")
diff --git a/tests/test_resume_checkpoints.py b/tests/test_resume_checkpoints.py
new file mode 100644
index 0000000..ea0e0ae
--- /dev/null
+++ b/tests/test_resume_checkpoints.py
@@ -0,0 +1,81 @@
+"""Checkpoint cadence, optimizer-step recovery and incomplete random state."""
+import json
+
+import pytest
+import torch
+from safetensors.torch import load_file
+
+from jevany.checkpoint import Checkpoint
+from jevany.train import main
+from test_backbones import make_base
+
+
+@pytest.mark.parametrize("objective", ["sft", "rlcr"])
+def test_checkpoint_cadence_and_each_unfinished_step_preserve_training(tmp_path, objective):
+    base = tmp_path / "base"
+    make_base(base, "llama")
+    data = tmp_path / "train.jsonl"
+    data.write_text("".join(json.dumps({"state": "state " * (2 + index), "questions": {
+        "q": {"type": "choice", "instructions": "choose",
+              "criteria": {"yes": None, "no": None, "other": None},
+              "label": ["yes", "no", "other"][index % 3]},
+    }}) + "\n" for index in range(5)))
+    args = ["--base", str(base), "--data", str(data), "--device", "cpu", "--lora", "2",
+            "--head-dim", "8", "--epochs", "2", "--batch", "1", "--accum", "2",
+            "--seed", "3", "--lr", "0.01", "--lora-dropout", "0.2"]
+    if objective == "rlcr":
+        args += ["--rlcr", "--rlcr-group-size", "4"]
+    plain = main(args + ["--out", str(tmp_path / "plain")])
+    assert not (plain / "checkpoints").exists()
+    full = main(args + ["--out", str(tmp_path / "full"), "--checkpoint-every-steps", "1"])
+
+    def weights(directory):
+        return load_file(directory / "adapter_model.safetensors"), Checkpoint(directory).meta.head
+
+    expected = weights(full)
+    for actual, reference in zip(weights(plain), expected):
+        assert actual.keys() == reference.keys()
+        assert all(torch.equal(actual[key], reference[key]) for key in reference)
+    states = sorted((full / "checkpoints").glob("step-*"))
+    assert [path.name for path in states] == [f"step-{index:06d}" for index in range(1, 7)]
+    metrics = json.loads((full / "training_metrics.json").read_text())
+    for state in states[:-1]:
+        resumed = main(["--resume", str(state), "--out", str(tmp_path / f"resumed-{state.name}")])
+        for actual, reference in zip(weights(resumed), expected):
+            assert actual.keys() == reference.keys()
+            for key in reference:
+                assert torch.equal(actual[key], reference[key]), (state.name, key)
+        resumed_metrics = json.loads((resumed / "training_metrics.json").read_text())
+        for key in ("optimizer_steps", "records_seen", "forward_tokens"):
+            assert resumed_metrics[key] == metrics[key], (state.name, key)
+        config = json.loads((resumed / "training_config.json").read_text())
+        assert config["resume_from"] == str(state.resolve())
+    with pytest.raises(ValueError, match="already finished"):
+        main(["--resume", str(states[-1]), "--out", str(tmp_path / "finished")])
+    assert not (tmp_path / "finished").exists()
+
+
+@pytest.mark.parametrize("missing", ["rank_rng", "rank", "rank_state", "torch"])
+def test_incomplete_rng_state_is_rejected_before_creating_output(tiny_run, tmp_path, missing):
+    root, _, _ = tiny_run
+    original = main([
+        "--base", str(root / "base"), "--data", str(root / "data" / "train.jsonl"),
+        "--out", str(tmp_path / "original"), "--device", "cpu", "--lora", "2",
+        "--head-dim", "8", "--lora-targets", "qv", "--max-steps", "2", "--accum", "1",
+        "--checkpoint-every-steps", "1",
+    ])
+    checkpoint = original / "checkpoints" / "step-000001"
+    state = torch.load(checkpoint / "trainer_state.pt", weights_only=True)
+    if missing == "rank_rng":
+        state.pop("rank_rng")
+    elif missing == "rank":
+        state["rank_rng"] = []
+    elif missing == "rank_state":
+        state["rank_rng"] = [None]
+    else:
+        state["rank_rng"][0].pop(missing)
+    torch.save(state, checkpoint / "trainer_state.pt")
+    output = tmp_path / "incomplete"
+    with pytest.raises(ValueError, match="incomplete.*RNG state"):
+        main(["--resume", str(checkpoint), "--out", str(output)])
+    assert not output.exists()