feat(flatfile): warn on missing or mismatched log format-version

src/database_flatfile_parser.c

@@ -16,6 +16,7 @@
 #include <sys/stat.h>
 #include <glib.h>
 #include <glib/gstdio.h>
+#include <limits.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -338,6 +339,49 @@ ff_skip_bom(FILE* fp)
     return 0;
 }
 
+// Format-version helper
+// =========================================================================
+//
+// Scan leading '#' comment lines for `# format-version: <N>`. Stops at
+// the first non-comment line or after FF_VERSION_SCAN_MAX comments.
+// Restores fp to its position at entry, so callers can re-parse the
+// header normally afterwards.
+#define FF_VERSION_SCAN_MAX 16
+
+int
+ff_read_format_version(FILE* fp)
+{
+    long start = ftell(fp);
+    if (start < 0)
+        return -1;
+
+    int version = 0;
+    size_t prefix_len = strlen(FF_VERSION_PREFIX);
+
+    for (int i = 0; i < FF_VERSION_SCAN_MAX; i++) {
+        gboolean truncated = FALSE;
+        char* line = ff_readline(fp, &truncated);
+        if (!line)
+            break;
+        if (line[0] != '#') {
+            free(line);
+            break;
+        }
+        if (strncmp(line, FF_VERSION_PREFIX, prefix_len) == 0) {
+            char* endptr = NULL;
+            long v = strtol(line + prefix_len, &endptr, 10);
+            if (endptr != line + prefix_len && v > 0 && v <= INT_MAX)
+                version = (int)v;
+            free(line);
+            break;
+        }
+        free(line);
+    }
+
+    fseek(fp, start, SEEK_SET);
+    return version;
+}
+
 // Readline helper
 // =========================================================================
 //