test(migrate-ts): e2e reversible drop-column migration (up DROP / down ADD)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: dmealing

server/typescript/packages/migrate-ts/test/down/e2e-down.test.ts

@@ -0,0 +1,35 @@
+import { describe, test, expect } from "bun:test";
+import { MetaDataLoader, InMemoryStringSource } from "@metaobjectsdev/metadata";
+import type { MetaData } from "@metaobjectsdev/metadata";
+import { buildExpectedSchema } from "../../src/expected-schema.js";
+import { diff } from "../../src/diff/index.js";
+import { emit } from "../../src/emit/index.js";
+
+async function load(json: string): Promise<MetaData> {
+  return (await new MetaDataLoader().load([new InMemoryStringSource(json)])).root;
+}
+const ENTITY = (fields: string) => JSON.stringify({
+  "metadata.root": { children: [{
+    "object.entity": { name: "User", children: [
+      { "field.long": { name: "id" } },
+      ...JSON.parse(fields),
+      { "source.rdb": { name: "src", "@table": "users" } },
+      { "identity.primary": { name: "pk", "@fields": ["id"], "@generation": "increment" } },
+    ] },
+  }] },
+});
+
+describe("e2e: dropping a field yields a reversible migration", () => {
+  test("up drops the column; down re-adds it with the recorded type", async () => {
+    // snapshot (prior) has `email`; new metadata removes it
+    const prior = buildExpectedSchema(await load(ENTITY('[{"field.string":{"name":"email"}}]')), { dialect: "postgres" });
+    const next = buildExpectedSchema(await load(ENTITY('[]')), { dialect: "postgres" });
+    const r = await diff({ expected: next, actual: prior, allow: { dropColumn: true } });
+    const { up, down } = emit(r.changes, { dialect: "postgres" });
+    expect(up).toContain(`DROP COLUMN "email"`);
+    expect(down).toContain(`ADD COLUMN "email"`);
+    expect(down).toMatch(/column data is not restored/i);
+    // down is no longer a bare TODO stub
+    expect(down).not.toMatch(/TODO: re-add dropped column/i);
+  });
+});