fix: drop_fk op key + truncate overlong index names

- DiffEngine: emit 'fk_name' (not 'fk') for drop_fk operations so drivers
  can read it. Prevents 'Undefined array key fk_name' warning and empty
  DROP FOREIGN KEY statements.
- ModelScanner::addIndexes: truncate auto-generated index names that
  exceed MySQL's 64-char identifier limit, appending an 8-char md5
  suffix for uniqueness. Prevents 'Identifier name too long' errors on
  tables with long names + composite indexes.

Author: TimAnthonyAlexander

src/Database/Migrations/DiffEngine.php

@@ -258,23 +258,23 @@ private function diffForeignKeys(MigrationPlan $plan, TableDef $modelTable, Tabl
                 // Drop and recreate the foreign key
                 $plan->addOperation('drop_fk', [
                     'table' => $modelTable->name,
-                    'fk' => $fkName,
+                    'fk_name' => $fkName,
                     'destructive' => false
                 ]);
-                
+
                 $plan->addOperation('add_fk', [
                     'table' => $modelTable->name,
                     'fk' => $modelFk->toArray(),
                     'destructive' => false
                 ]);
             }
         }
-        
+
         // Drop removed foreign keys
         foreach ($fksToDrop as $fkName) {
             $plan->addOperation('drop_fk', [
                 'table' => $modelTable->name,
-                'fk' => $fkName,
+                'fk_name' => $fkName,
                 'destructive' => false
             ]);
         }

src/Database/Migrations/ModelScanner.php

@@ -417,36 +417,51 @@ private function addIndexes(TableDef $table, ReflectionClass $reflection): void
                     'fulltext' => 'ft_',
                     default => 'idx_'
                 };
-                $indexName = $prefix . $table->name . '_' . $key;
+                $indexName = $this->truncateIdentifier($prefix . $table->name . '_' . $key);
                 $table->indexes[$indexName] = new IndexDef($indexName, $key, $value);
             } elseif (is_array($value)) {
                 // Composite index: numeric key with array value
                 // Extract type if specified, otherwise default to 'index'
                 $type = 'index';
                 $columns = [];
-                
+
                 foreach ($value as $k => $v) {
                     if ($k === 'type') {
                         $type = $v;
                     } elseif (is_int($k)) {
                         $columns[] = $v;
                     }
                 }
-                
+
                 if ($columns !== []) {
                     $columnSuffix = implode('_', $columns);
                     $prefix = match ($type) {
                         'unique' => 'uniq_',
                         'fulltext' => 'ft_',
                         default => 'idx_'
                     };
-                    $indexName = $prefix . $table->name . '_' . $columnSuffix;
+                    $indexName = $this->truncateIdentifier($prefix . $table->name . '_' . $columnSuffix);
                     $table->indexes[$indexName] = new IndexDef($indexName, $columns, $type);
                 }
             }
         }
     }
 
+    /**
+     * Truncate an identifier to fit within MySQL's 64-character limit.
+     * When truncation is needed, append an 8-char hash of the full name to preserve uniqueness.
+     */
+    private function truncateIdentifier(string $name, int $maxLength = 64): string
+    {
+        if (strlen($name) <= $maxLength) {
+            return $name;
+        }
+
+        $hash = substr(md5($name), 0, 8);
+        $prefixLength = $maxLength - strlen($hash) - 1; // reserve space for '_' + hash
+        return substr($name, 0, $prefixLength) . '_' . $hash;
+    }
+
     /**
      * @param ReflectionClass<object> $reflection
      */