fix(db2): Include identity offered a clause Db2 does not have

apps/web/src/frontend/lib/identity-insert-sql.test.ts

@@ -13,9 +13,12 @@ const build = (dialect: string, generation?: string) => {
 
 describe('explicit identity INSERT is shaped per dialect', () => {
   it('adds OVERRIDING SYSTEM VALUE where the engine demands it', () => {
-    // Postgres/Db2 reject an explicit GENERATED ALWAYS value without this
-    // (SQLSTATE 428C9 / SQL0798N).
-    for (const d of ['postgres', 'cockroachdb', 'yugabytedb', 'db2']) {
+    // The Postgres family rejects an explicit GENERATED ALWAYS value without
+    // this (SQLSTATE 428C9). Db2 is NOT one of them despite a similar error:
+    // verified on Db2 LUW 11.5, the clause itself is SQL0104N there, so a Db2
+    // GENERATED ALWAYS column is simply not writable — see the `unsupported`
+    // entry in dialect-identity-insert.
+    for (const d of ['postgres', 'cockroachdb', 'yugabytedb']) {
       expect(build(d, 'ALWAYS'), d).toContain('OVERRIDING SYSTEM VALUE');
       // It must sit between the column list and VALUES, not anywhere else.
       expect(build(d, 'ALWAYS'), d).toMatch(/\)\s+OVERRIDING SYSTEM VALUE\s+VALUES/);

apps/web/src/frontend/lib/rowDml.ts

@@ -303,8 +303,10 @@ export function buildPeekInsert(opts: {
   }
   if (Object.keys(row).length === 0) return { error: 'Nothing to insert.' };
 
-  // Postgres and Db2 refuse an explicit value for a GENERATED ALWAYS identity
-  // column unless the statement says so (SQLSTATE 428C9 / SQL0798N). The
+  // Postgres refuses an explicit value for a GENERATED ALWAYS identity column
+  // unless the statement says so (SQLSTATE 428C9). Db2 is *not* in this group
+  // despite the similar error: it has no overriding clause at all (SQL0798N,
+  // and SQL0104N if you try one), so its support entry is `unsupported`. The
   // clause comes from a fixed capability table, never from user input.
   const support = writeIdentityGeneration
     ? identityInsertFor(dialect, writeIdentityGeneration)

packages/sql/src/modules/dialect-identity-insert.test.ts

@@ -19,10 +19,15 @@ describe('identityInsertSupport — every registered dialect has an answer', ()
     for (const d of ['mysql', 'mariadb', 'tidb', 'sqlite']) {
       expect(identityInsertSupport(d).kind, d).toBe('native');
     }
-    for (const d of ['postgres', 'cockroachdb', 'yugabytedb', 'db2']) {
+    for (const d of ['postgres', 'cockroachdb', 'yugabytedb']) {
       expect(identityInsertSupport(d).kind, d).toBe('overriding');
       expect(identityInsertSupport(d).clause, d).toBe('OVERRIDING SYSTEM VALUE');
     }
+    // Db2 is deliberately not in that list. It looks like Postgres from the
+    // error message alone (both complain about GENERATED ALWAYS), but verified
+    // on Db2 LUW 11.5: OVERRIDING SYSTEM VALUE is SQL0104N in every position,
+    // so there is no ceremony that makes the write legal.
+    expect(identityInsertSupport('db2').kind).toBe('unsupported');
     for (const d of ['sqlserver', 'azuresql']) {
       expect(identityInsertSupport(d).kind, d).toBe('toggle');
     }
@@ -72,7 +77,16 @@ describe('identityInsertFor — how the column was declared', () => {
 
   it('keeps the overriding clause for ALWAYS', () => {
     expect(identityInsertFor('postgres', 'ALWAYS').kind).toBe('overriding');
-    expect(identityInsertFor('db2', 'ALWAYS').kind).toBe('overriding');
+  });
+
+  it('refuses a Db2 GENERATED ALWAYS identity outright', () => {
+    // Letting this through as `overriding` started the copy and then failed it
+    // mid-run with SQL0104N — the outcome this table exists to prevent.
+    const always = identityInsertFor('db2', 'ALWAYS');
+    expect(always.kind).toBe('unsupported');
+    expect(always.reason).toMatch(/GENERATED BY DEFAULT/i);
+    // BY DEFAULT is genuinely writable — confirmed against the live server.
+    expect(identityInsertFor('db2', 'BY DEFAULT').kind).toBe('native');
   });
 
   it('lets Oracle BY DEFAULT through', () => {

packages/sql/src/modules/dialect-identity-insert.ts

@@ -91,7 +91,21 @@ const SUPPORT: Record<string, IdentityInsertSupport> = {
   postgres: OVERRIDING,
   cockroachdb: OVERRIDING,
   yugabytedb: OVERRIDING,
-  db2: OVERRIDING,
+
+  // Not OVERRIDING: that clause is Postgres (and DB2 for i / z/OS). Verified on
+  // DB2 LUW 11.5 — `OVERRIDING SYSTEM VALUE` is SQL0104N in every position
+  // (before the column list, after it, and on INSERT … SELECT), and a plain
+  // insert into GENERATED ALWAYS is SQL0798N. There is no override, so listing
+  // DB2 as `overriding` let the copy start and then fail mid-run, which is the
+  // one outcome this table exists to prevent.
+  db2: {
+    kind: 'unsupported',
+    resyncSequence: true,
+    reason:
+      'Db2 has no overriding clause for a GENERATED ALWAYS identity column ' +
+      '(SQL0798N, and SQL0104N for OVERRIDING SYSTEM VALUE). Turn off Include ' +
+      'identity, or change the column to GENERATED BY DEFAULT.',
+  },
 
   sqlserver: TOGGLE,
   azuresql: TOGGLE,