fix(migrate-ts): review round 1 — comment/test-name accuracy, dialect arg

Three one-line fixes from review of the serial-identity default-diff fix:

- diff/index.ts: the replacement comment inverted its own causal clause
  ("Left undiffed, that surfaced as ... DROP DEFAULT" claims skipping the
  diff produced the bug -- the exact inverse; the bug was the case being
  left DIFFED). Fixed to "Left diffed".
- diff-uuid-identity-default.test.ts: the increment-PK regression-guard test
  name asserted "it never had a DEFAULT", the same false doctrine this
  change disproved. Renamed to "(no live default at all)".
- diff-serial-identity-default.test.ts: the new unit tests called diff()
  with no `dialect` for a Postgres-only bug. This repo's standing rule is
  that omitting `dialect` runs a different pipeline -- pass it always. Both
  diff() call sites now pass `dialect: "postgres"`, matching the
  integration test.

No production behavior change beyond the comment; the two test edits are
name/argument-only and do not change what either test asserts.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015TqsuDye2SfXGf43vuoD3n

Author: dmealing

server/typescript/packages/migrate-ts/src/diff/index.ts

@@ -398,7 +398,7 @@ function diffTableColumns(
     // but a legacy Postgres `serial`/`bigserial` column is historical sugar for
     // `integer` + a sequence + a REAL `DEFAULT nextval(...)` clause — introspection
     // correctly reads that back as a live default even though the expected side
-    // correctly declares none. Left undiffed, that surfaced as
+    // correctly declares none. Left diffed, that surfaced as
     // `ALTER COLUMN … DROP DEFAULT` with no replacement generation mechanism —
     // destructive against a live table, since every insert that doesn't supply the
     // PK explicitly then starts failing. So an `increment` PK skips the default-diff

server/typescript/packages/migrate-ts/test/unit/diff-serial-identity-default.test.ts

@@ -37,7 +37,7 @@ const expectedIncrementPk: ColumnDescriptor = {
 };
 
 async function defaultChanges(expected: ColumnDescriptor, actual: ColumnDescriptor) {
-  const r = await diff(snap(expected), snap(actual));
+  const r = await diff(snap(expected), snap(actual), { dialect: "postgres" });
   return r.changes.filter((c) => c.kind === "change-column-default");
 }
 
@@ -56,7 +56,7 @@ describe("diff — legacy Postgres serial PK default is not diffed as drift", ()
       ...expectedIncrementPk,
       default: { kind: "expr", value: "nextval('work_item_id_seq'::regclass)" },
     };
-    const r = await diff(snap(expectedIncrementPk), snap(actual));
+    const r = await diff(snap(expectedIncrementPk), snap(actual), { dialect: "postgres" });
     expect(r.changes).toEqual([]);
   });
 

server/typescript/packages/migrate-ts/test/unit/diff-uuid-identity-default.test.ts

@@ -53,7 +53,7 @@ describe("diff — uuid-identity PK default is not diffed", () => {
     expect(r.changes).toEqual([]);
   });
 
-  test("regression guard: increment-identity PK still no-ops (it never had a DEFAULT)", async () => {
+  test("regression guard: increment-identity PK still no-ops (no live default at all)", async () => {
     const inc: ColumnDescriptor = {
       name: "id", sqlType: { kind: "integer", bits: 64 }, nullable: false, identity: "increment",
     };