Relax post date check to allow front matter date newer than filename

Rather than requiring an exact match, only fail if the front matter
date is older than the filename date, which is the case that would
cause Jekyll to publish later than expected.

Assisted-by: Claude Sonnet 4.6 <noreply@anthropic.com>
Signed-off-by: Sam Barker <sam@quadrocket.co.uk>

Author: SamBarker

.github/workflows/pr-build.yml

@@ -39,6 +39,27 @@ jobs:
           CONTAINER_ENGINE: docker
           BUILD_IMAGE_SPEC: localhost:5000/kroxy-jekyll:latest
 
+      - name: Require post front matter date is not older than filename date
+        run: |
+          mismatches=()
+          for post in _posts/*.md; do
+            filename=$(basename "$post")
+            file_date=$(echo "$filename" | grep -oP '^\d{4}-\d{2}-\d{2}')
+            front_matter_date=$(grep -oP '^date:\s*\K\d{4}-\d{2}-\d{2}' "$post" || true)
+            if [[ -n "$file_date" && -n "$front_matter_date" && "$front_matter_date" < "$file_date" ]]; then
+              mismatches+=("$filename: filename date=$file_date, front matter date=$front_matter_date")
+            fi
+          done
+          if [[ ${#mismatches[@]} -gt 0 ]]; then
+            echo "Error: post front matter date is older than filename date:" >&2
+            for mismatch in "${mismatches[@]}"; do
+              echo "  $mismatch" >&2
+            done
+            exit 1
+          else
+            echo "Success: all post front matter dates are consistent with filename dates"
+          fi
+
       # Currently the image shas are not available when we create the release, they need to be manually
       # updated in the release PR before merge.
       - name: Require release manifests to contain non-placeholder container image SHAs