ci: nanochat smoke on ailab gpu runner

- scripts/smoke.sh: end-to-end nanochat pipeline (dataset → tokenizer
  → tiny d=6 base_train, 50 iters); idempotent, caches under
  /data/nanochat-smoke (venv, uv-cache, shards).
- CN mirrors baked in: aliyun PyPI, sjtu pytorch-wheels/cu128, hf-mirror.
- workflow targets gpu label (ailab). drop earlier dummy workflow.

scripts/smoke.sh

@@ -0,0 +1,65 @@
+#!/bin/bash
+# End-to-end smoke for upstream nanochat: dataset → tokenizer → tiny base_train.
+# Idempotent: caches venv, uv-cache, and dataset shards under /data/nanochat-smoke/.
+# Targets ailab (CN, RTX 5090). Uses CN mirrors for PyPI / pytorch wheels / HuggingFace.
+set -euo pipefail
+export PATH="$HOME/.local/bin:$PATH"
+
+CACHE_ROOT=${CACHE_ROOT:-/data/nanochat-smoke}
+NANOCHAT_DIR=$CACHE_ROOT/nanochat
+export NANOCHAT_BASE_DIR=$CACHE_ROOT/cache
+export UV_CACHE_DIR=$CACHE_ROOT/uv-cache
+export UV_DEFAULT_INDEX=${UV_DEFAULT_INDEX:-https://mirrors.aliyun.com/pypi/simple/}
+export UV_INDEX_STRATEGY=unsafe-best-match
+export HF_ENDPOINT=${HF_ENDPOINT:-https://hf-mirror.com}
+export OMP_NUM_THREADS=1
+
+mkdir -p "$CACHE_ROOT" "$NANOCHAT_BASE_DIR"
+
+if [ ! -d "$NANOCHAT_DIR" ]; then
+    echo "Cloning nanochat into $NANOCHAT_DIR"
+    git clone https://github.com/karpathy/nanochat.git "$NANOCHAT_DIR" \
+        || git clone https://ghfast.top/https://github.com/karpathy/nanochat.git "$NANOCHAT_DIR"
+fi
+
+cd "$NANOCHAT_DIR"
+
+# CN mirror patches — idempotent: sed only matches the upstream URLs.
+sed -i \
+    -e "s|https://download.pytorch.org/whl/cu128|https://mirror.sjtu.edu.cn/pytorch-wheels/cu128|g" \
+    -e "s|https://download.pytorch.org/whl/cpu|https://mirror.sjtu.edu.cn/pytorch-wheels/cpu|g" \
+    pyproject.toml uv.lock
+sed -i \
+    -e "s|https://huggingface.co/datasets/karpathy/climbmix-400b-shuffle|https://hf-mirror.com/datasets/karpathy/climbmix-400b-shuffle|" \
+    nanochat/dataset.py
+
+[ -d .venv ] || uv venv
+uv sync --extra gpu --index-strategy unsafe-best-match
+
+source .venv/bin/activate
+
+echo "=== [1/4] download 1 climbmix shard ==="
+time python -m nanochat.dataset -n 1
+
+echo "=== [2/4] train tokenizer (50M chars) ==="
+time python -m scripts.tok_train --max-chars=50000000
+
+echo "=== [3/4] tok_eval ==="
+time python -m scripts.tok_eval
+
+echo "=== [4/4] base_train d=6 50 iters ==="
+time python -m scripts.base_train \
+    --depth=6 \
+    --head-dim=64 \
+    --window-pattern=L \
+    --max-seq-len=512 \
+    --device-batch-size=8 \
+    --total-batch-size=4096 \
+    --eval-every=25 \
+    --eval-tokens=131072 \
+    --core-metric-every=-1 \
+    --sample-every=25 \
+    --num-iterations=50 \
+    --run=dummy
+
+echo "=== smoke done ==="