[ci] Clear stale SSIM reference videos on container reuse

Modal containers and git clones can have stale or incomplete reference
videos (both legacy *_reference_videos/ and new reference_videos/).
conftest sees old .mp4 files, skips the HF download, and misses newly
added models. Fix by deleting both layouts after checkout to force a
fresh download from HF every time.

.buildkite/pipeline.yml

@@ -135,6 +135,10 @@ steps:
                 label: ":bar_chart: SSIM Tests"
                 env:
                   - TEST_TYPE=ssim
+                retry:
+                  automatic:
+                    - exit_status: 1
+                      limit: 2
                 agents:
                   queue: "default"
             - path:
@@ -195,6 +199,10 @@ steps:
                 label: ":test_tube: LoRA Training Tests"
                 env:
                   - TEST_TYPE=training_lora
+                retry:
+                  automatic:
+                    - exit_status: 1
+                      limit: 2
                 agents:
                   queue: "default"
             - path:
@@ -207,6 +215,10 @@ steps:
                 label: ":test_tube: Training Tests VSA"
                 env:
                   - TEST_TYPE=training_vsa
+                retry:
+                  automatic:
+                    - exit_status: 1
+                      limit: 2
                 agents:
                   queue: "default"
             - path:

fastvideo/tests/modal/ssim_test.py

@@ -455,16 +455,26 @@ def _prepare_ssim_workspace(
     set -euo pipefail
     source $HOME/.local/bin/env
     source /opt/venv/bin/activate
+    git_retry() {{
+      local attempt
+      for attempt in 1 2 3; do
+        if "$@"; then return 0; fi
+        echo "git command failed (attempt $attempt/3), retrying in 5s..."
+        sleep 5
+      done
+      "$@"
+    }}
     if [ -d {shlex.quote(repo_root)}/.git ]; then
       cd {shlex.quote(repo_root)}
       git remote set-url origin {shlex.quote(git_repo)} || true
-      git fetch --prune origin
+      git_retry git fetch --prune origin
     else
-      git clone {shlex.quote(git_repo)} {shlex.quote(repo_root)}
+      git_retry git clone {shlex.quote(git_repo)} {shlex.quote(repo_root)}
       cd {shlex.quote(repo_root)}
     fi
     {checkout_command}
-    git submodule update --init --recursive
+    rm -rf fastvideo/tests/ssim/reference_videos fastvideo/tests/ssim/*_reference_videos
+    git_retry git submodule update --init --recursive
     cd fastvideo-kernel
     ./build.sh
     cd ..