ci: retry Mathlib cache fetches that drop a few transfers

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FYqwNMyPUHeTbFWg83GQq6

.gitea/scripts/prepare-mathlib.sh

@@ -27,7 +27,14 @@ else
   cd "$DIR"
   elan toolchain install "$(cat lean-toolchain)" >&2
   timeout 1800 lake update >&2
-  timeout 5400 lake exe cache get >&2
+  # The cache is ~9,000 files; a few transient transfer failures are normal, and a
+  # re-run fetches only what is still missing (downloads persist in ~/.cache/mathlib).
+  for attempt in 1 2 3 4; do
+    if timeout 5400 lake exe cache get >&2; then break; fi
+    [ "$attempt" -eq 4 ] && { echo "prepare-mathlib: cache get failed 4 times" >&2; exit 1; }
+    echo "prepare-mathlib: cache get attempt $attempt failed; retrying" >&2
+    sleep $((attempt * 15))
+  done
   start=$(date +%s)
   timeout 1200 lake env lean LeanBench.lean >&2 || {
     status=$?

docker/Dockerfile

@@ -46,7 +46,12 @@ RUN elan toolchain install "$(cat lean/lean-toolchain)" \
 RUN cd lean && timeout 1800 lake update
 
 # Mathlib's prebuilt artifacts. Slow, large, and cached as its own layer.
-RUN cd lean && timeout 5400 lake exe cache get
+# A handful of the ~9,000 transfers failing is normal; a re-run fetches only what is missing.
+RUN cd lean && for attempt in 1 2 3 4; do \
+      timeout 5400 lake exe cache get && break; \
+      [ "$attempt" -eq 4 ] && exit 1; \
+      echo "cache get attempt $attempt failed; retrying" >&2; sleep $((attempt * 15)); \
+    done
 
 # The honest check that this image can do its job, and it is exactly what
 # verification does at runtime: elaborate a file against Mathlib with `lake env lean`.