fix(workflow): robust data branch fetch after force-push

Use explicit refspec for git fetch so origin/data tracking ref is
always created.  Replace rev-parse with actual file-existence check
so force-pushed branches with different history are detected.

Author: LeafCreeper

.github/workflows/check.yml

@@ -65,11 +65,12 @@ jobs:
       - name: Fetch database from data branch
         run: |
           mkdir -p data
-          git fetch origin data --depth=1 2>/dev/null || echo "No data branch yet."
-          if ! git rev-parse origin/data >/dev/null 2>&1; then
-            echo "No data branch, starting fresh."
-            exit 0
-          fi
+          git fetch --depth=1 origin refs/heads/data:refs/remotes/origin/data 2>/dev/null \
+            || { echo "No data branch, starting fresh."; exit 0; }
+          git show origin/data:data/icourse-index.enc >/dev/null 2>&1 \
+            || git show origin/data:data/icourse.db.gz.enc >/dev/null 2>&1 \
+            || git show origin/data:data/icourse.db.enc >/dev/null 2>&1 \
+            || { echo "No database found on data branch, starting fresh."; exit 0; }
           # Prefer the sharded layout (current).
           if git cat-file -e origin/data:data/icourse-index.enc 2>/dev/null; then
             mkdir -p data/sharded/shards

.github/workflows/single_run.yml

@@ -67,11 +67,12 @@ jobs:
       - name: Fetch database from data branch
         run: |
           mkdir -p data
-          git fetch origin data --depth=1 2>/dev/null || echo "No data branch yet."
-          if ! git rev-parse origin/data >/dev/null 2>&1; then
-            echo "No data branch, starting fresh."
-            exit 0
-          fi
+          git fetch --depth=1 origin refs/heads/data:refs/remotes/origin/data 2>/dev/null \
+            || { echo "No data branch, starting fresh."; exit 0; }
+          git show origin/data:data/icourse-index.enc >/dev/null 2>&1 \
+            || git show origin/data:data/icourse.db.gz.enc >/dev/null 2>&1 \
+            || git show origin/data:data/icourse.db.enc >/dev/null 2>&1 \
+            || { echo "No database found on data branch, starting fresh."; exit 0; }
           if git cat-file -e origin/data:data/icourse-index.enc 2>/dev/null; then
             mkdir -p data/sharded/shards
             git show origin/data:data/icourse-index.enc > data/sharded/icourse-index.enc