added qdb_normalize_stable_key function to create stable identifiers from arbitrary key strings

common.php

@@ -441,12 +441,41 @@ function qdb_is_stable_key(string $s): bool {
     return $s !== '' && (bool)preg_match('/^[a-zA-Z][a-zA-Z0-9_]*$/', $s);
 }
 
+/**
+ * Coerce an arbitrary key string into a stable identifier (letters, digits, underscores;
+ * must start with a letter). Used on import and API writes so bundles are not limited to
+ * pre-validated keys (e.g. numeric option labels "1", "42").
+ */
+function qdb_normalize_stable_key(string $s): string {
+    $s = trim($s);
+    if ($s === '') {
+        return '';
+    }
+    if (qdb_is_stable_key($s)) {
+        return $s;
+    }
+    $out = preg_replace('/[^a-zA-Z0-9_]+/', '_', $s);
+    $out = preg_replace('/_+/', '_', $out ?? '');
+    $out = trim($out, '_');
+    if ($out === '') {
+        return 'k_' . substr(hash('crc32b', $s), 0, 8);
+    }
+    if (!preg_match('/^[a-zA-Z]/', $out)) {
+        $out = 'k_' . $out;
+    }
+    return qdb_is_stable_key($out) ? $out : 'k_' . substr(hash('crc32b', $s), 0, 8);
+}
+
 function qdb_validate_stable_key(string $s, string $label = 'Key'): string {
     $s = trim($s);
-    if (!qdb_is_stable_key($s)) {
-        json_error('INVALID_FIELD', "$label must match [a-zA-Z][a-zA-Z0-9_]*", 400);
+    if ($s === '') {
+        json_error('INVALID_FIELD', "$label is required", 400);
     }
-    return $s;
+    $normalized = qdb_normalize_stable_key($s);
+    if (!qdb_is_stable_key($normalized)) {
+        json_error('INVALID_FIELD', "$label could not be normalized to a valid key", 400);
+    }
+    return $normalized;
 }
 
 /** Resolve app lookup key for a question row. */