feat: add spacetimedb json migration tooling

scripts/spacetime-export-migration-json.mjs

@@ -0,0 +1,55 @@
+#!/usr/bin/env node
+
+import { writeFile } from 'node:fs/promises';
+import path from 'node:path';
+import {
+  callSpacetimeProcedureAuto,
+  ensureParentDir,
+  ensureProcedureOk,
+  parseArgs,
+} from './spacetime-migration-common.mjs';
+
+try {
+  const options = parseArgs(process.argv.slice(2));
+  if (!options.out) {
+    throw new Error('必须传入 --out。');
+  }
+
+  const input = {
+    include_tables: options.includeTables,
+  };
+  const result = await callSpacetimeProcedureAuto(
+    options,
+    'export_database_migration_to_file',
+    input,
+  );
+  ensureProcedureOk(result);
+
+  if (typeof result.migration_json !== 'string' || result.migration_json.trim() === '') {
+    throw new Error('导出 procedure 没有返回 migration_json。');
+  }
+
+  const outPath = path.resolve(options.out);
+  await ensureParentDir(outPath);
+  await writeFile(outPath, result.migration_json, 'utf8');
+
+  console.log(`[spacetime:migration:export] 已写入 ${outPath}`);
+  printTableStats(result.table_stats);
+} catch (error) {
+  console.error(
+    `[spacetime:migration:export] ${error instanceof Error ? error.message : String(error)}`,
+  );
+  process.exit(1);
+}
+
+function printTableStats(tableStats) {
+  if (!Array.isArray(tableStats) || tableStats.length === 0) {
+    return;
+  }
+
+  const rows = tableStats.map((stat) => ({
+    table: stat.table_name,
+    exported: stat.exported_row_count,
+  }));
+  console.table(rows);
+}