Gate --only-changes on PRs only, add push retry in commit-cache

--only-changes must not run on master pushes: merge-base would diff
master against itself, find no changes, and skip all tests. Gate
behind GITHUB_EVENT_NAME == pull_request in all test scripts.

Add retry loop (3 attempts) for git push in commit-cache to handle
concurrent updates from simultaneous rebuild-cache completions.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: sbryngelson

.github/workflows/frontier/test.sh

@@ -18,12 +18,18 @@ if [ -n "$job_shard" ]; then
     shard_opts="--shard $job_shard"
 fi
 
+# Only prune tests on PRs; master pushes must run the full suite.
+prune_flag=""
+if [ "$GITHUB_EVENT_NAME" = "pull_request" ]; then
+    prune_flag="--only-changes"
+fi
+
 if [ "$job_device" = "gpu" ]; then
     rdma_opts=""
     if [ "$job_cluster" = "frontier" ]; then
         rdma_opts="--rdma-mpi"
     fi
-    ./mfc.sh test -v -a $rdma_opts --max-attempts 3 --only-changes -j $ngpus $device_opts $shard_opts -- -c $job_cluster
+    ./mfc.sh test -v -a $rdma_opts --max-attempts 3 $prune_flag -j $ngpus $device_opts $shard_opts -- -c $job_cluster
 else
-    ./mfc.sh test -v -a --max-attempts 3 --only-changes -j 32 --no-gpu $shard_opts -- -c $job_cluster
+    ./mfc.sh test -v -a --max-attempts 3 $prune_flag -j 32 --no-gpu $shard_opts -- -c $job_cluster
 fi

.github/workflows/frontier_amd/test.sh

@@ -18,12 +18,18 @@ if [ -n "$job_shard" ]; then
     shard_opts="--shard $job_shard"
 fi
 
+# Only prune tests on PRs; master pushes must run the full suite.
+prune_flag=""
+if [ "$GITHUB_EVENT_NAME" = "pull_request" ]; then
+    prune_flag="--only-changes"
+fi
+
 if [ "$job_device" = "gpu" ]; then
     rdma_opts=""
     if [ "$job_cluster" = "frontier" ]; then
         rdma_opts="--rdma-mpi"
     fi
-    ./mfc.sh test -v -a $rdma_opts --max-attempts 3 --only-changes -j $ngpus $device_opts $shard_opts -- -c $job_cluster
+    ./mfc.sh test -v -a $rdma_opts --max-attempts 3 $prune_flag -j $ngpus $device_opts $shard_opts -- -c $job_cluster
 else
-    ./mfc.sh test -v -a --max-attempts 3 --only-changes -j 32 --no-gpu $shard_opts -- -c $job_cluster
+    ./mfc.sh test -v -a --max-attempts 3 $prune_flag -j 32 --no-gpu $shard_opts -- -c $job_cluster
 fi

.github/workflows/phoenix/test.sh

@@ -62,4 +62,10 @@ if [ "$job_device" = "gpu" ]; then
     n_test_threads=`expr $gpu_count \* 2`
 fi
 
-./mfc.sh test -v --max-attempts 3 --only-changes -a -j $n_test_threads $device_opts -- -c phoenix
+# Only prune tests on PRs; master pushes must run the full suite.
+prune_flag=""
+if [ "$GITHUB_EVENT_NAME" = "pull_request" ]; then
+    prune_flag="--only-changes"
+fi
+
+./mfc.sh test -v --max-attempts 3 $prune_flag -a -j $n_test_threads $device_opts -- -c phoenix

.github/workflows/test.yml

@@ -211,7 +211,7 @@ jobs:
         run: |
           rm -f tests/failed_uuids.txt
           TEST_EXIT=0
-          /bin/bash mfc.sh test -v --max-attempts 3 -j "$(nproc)" --only-changes $TEST_ALL $TEST_PCT || TEST_EXIT=$?
+          /bin/bash mfc.sh test -v --max-attempts 3 -j "$(nproc)" $ONLY_CHANGES $TEST_ALL $TEST_PCT || TEST_EXIT=$?
 
           # Retry only if a small number of tests failed (sporadic failures)
           if [ -s tests/failed_uuids.txt ]; then
@@ -232,6 +232,7 @@ jobs:
         env:
           TEST_ALL: ${{ matrix.mpi == 'mpi' && '--test-all' || '' }}
           TEST_PCT: ${{ matrix.debug == 'debug' && '-% 20' || '' }}
+          ONLY_CHANGES: ${{ github.event_name == 'pull_request' && '--only-changes' || '' }}
 
   self:
     name: "${{ matrix.cluster_name }} (${{ matrix.device }}${{ matrix.interface != 'none' && format('-{0}', matrix.interface) || '' }}${{ matrix.shard != '' && format(' [{0}]', matrix.shard) || '' }})"
@@ -403,8 +404,11 @@ jobs:
             git commit -m "Regenerate gcov coverage cache
 
           Automatically rebuilt because cases.py changed."
-            git pull --rebase
-            git push
+            for i in 1 2 3; do
+              git pull --rebase && git push && break
+              echo "Push attempt $i failed, retrying in 5s..."
+              sleep 5
+            done
             echo "pushed=true" >> "$GITHUB_OUTPUT"
           fi