ci: save the compiler cache from cancelled and failed builds too (#15668)

.github/workflows/build_orca.yml

@@ -106,6 +106,7 @@ jobs:
           job-summary: ''
 
       - name: Restore compiler cache
+        id: ccache_restore
         if: ${{ steps.ccache.outcome == 'success' }}
         uses: actions/cache/restore@v6
         with:
@@ -724,31 +725,40 @@ jobs:
           asset_content_type: application/octet-stream
           max_releases: 1
 
+      # The build has just touched everything it can use, so an object
+      # untouched for a week is dead, usually orphaned by a flag change.
       - name: Compiler cache statistics
         if: ${{ always() && steps.ccache.outcome == 'success' }}
         shell: bash
-        run: ccache -s -v || ccache -s
+        run: |
+          ccache --evict-older-than 7d
+          ccache -s -v || ccache -s
 
       # Entries are immutable, so the new one is saved first and the older
       # ones for this leg on this ref are dropped afterwards: a failed save
-      # leaves the previous entry in place.
+      # leaves the previous entry in place. A cancelled or failed build saves
+      # too, since what it compiled is still valid; a restore that did not
+      # finish does not, since the directory may be a truncated copy.
       - name: Save compiler cache
         id: ccache_save
-        if: ${{ steps.ccache.outcome == 'success' && github.event_name != 'pull_request' }}
+        if: ${{ always() && steps.ccache_restore.outcome == 'success' && github.event_name != 'pull_request' }}
         uses: actions/cache/save@v6
         with:
           path: ${{ github.workspace }}/.ccache
           key: ${{ env.CCACHE_ENTRY }}
 
       - name: Drop older compiler cache entries
-        if: ${{ steps.ccache_save.outcome == 'success' }}
+        if: ${{ always() && steps.ccache_save.outcome == 'success' }}
         # A read-only token (fork PRs) cannot delete; that only costs storage.
+        # Older means a lower run id, so two runs finishing close together keep
+        # the newer entry whichever of them cleans up last.
         continue-on-error: true
         shell: bash
         env:
           GH_TOKEN: ${{ github.token }}
         run: |
           gh cache list --ref "$GITHUB_REF" --key "ccache-$CCACHE_LEG-" --limit 100 --json id,key \
-            | jq -r --arg keep "$CCACHE_ENTRY" '.[] | select(.key != $keep) | .id' \
+            | jq -r --arg prefix "ccache-$CCACHE_LEG-" --argjson run "$GITHUB_RUN_ID" \
+                '.[] | select((.key | ltrimstr($prefix) | split("-")[0] | tonumber?) < $run) | .id' \
             | tr -d '\r' \
             | while read -r id; do gh cache delete "$id"; done