Harden event payload handling in log mirror workflow

Agent-Logs-Url: https://github.com/th30d4y/OpenLearnX/sessions/17fba2c8-4f49-4a78-9dc4-483acc8cc945

Co-authored-by: Stalin-143 <161853795+Stalin-143@users.noreply.github.com>

.github/workflows/mirror-repo-events-to-logs.yml

@@ -57,6 +57,11 @@ jobs:
           mkdir -p "$LOG_DIR"
           LOG_FILE="$LOG_DIR/events.jsonl"
 
+          if [ ! -r "$GITHUB_EVENT_PATH" ]; then
+            echo "GitHub event payload file is missing or unreadable: $GITHUB_EVENT_PATH"
+            exit 1
+          fi
+
           jq -cn \
             --arg timestamp "$(date -u +%Y-%m-%dT%H:%M:%SZ)" \
             --arg repository "$SOURCE_REPOSITORY" \