fix(db): stamp the dialect into generated query files

The same generate command emitted ? one run and $1 the next, which looked
like non-determinism. It is not: postgres uses $1 placeholders where
sqlite and mysql use ?, and the driver comes from the active profile, so
building under a different profile rewrites this committed file.

The header now records the dialect it was generated for, making the flip
visible in the diff and explaining check:generated-types failures instead
of leaving them looking like random churn.

Worth deciding separately: a committed artifact whose contents depend on
the active profile will keep drifting. Either generate per dialect, or
stop committing it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

examples/basic-app/app/db/queries.gen.ts

@@ -1,4 +1,4 @@
-// AUTO-GENERATED by `wrnexus db generate` — do not edit.
+// AUTO-GENERATED by `wrnexus db generate` (dialect: sqlite) — do not edit.
 import type { Db, ExecResult } from "@wrnexus/db";
 import { users } from "./schema.ts";
 

packages/db/src/generate.ts

@@ -230,5 +230,12 @@ export function generateQueriesFile(
   if (usedModels.size > 0) {
     imports.push(`import { ${[...usedModels].sort().join(", ")} } from "./schema.ts";`);
   }
-  return `// AUTO-GENERATED by \`wrnexus db generate\` — do not edit.\n${imports.join("\n")}\n\n${blocks.join("\n\n")}\n`;
+  // The dialect is stamped into the header because it changes the emitted SQL:
+  // postgres uses $1 placeholders where sqlite and mysql use ?. Regenerating
+  // under a different profile therefore rewrites this committed file, and
+  // without the stamp the diff looks like unexplained churn.
+  return (
+    `// AUTO-GENERATED by \`wrnexus db generate\` (dialect: ${dialect}) — do not edit.\n` +
+    `${imports.join("\n")}\n\n${blocks.join("\n\n")}\n`
+  );
 }

packages/db/test/generate-dialect.test.ts

@@ -0,0 +1,23 @@
+import { expect, test } from "bun:test";
+import { generateQueriesFile, parseQueries } from "../src/generate.ts";
+
+const queries = parseQueries(`-- name: GetUser :one\nSELECT * FROM users WHERE email = :email;\n`);
+
+test("the generated header records the dialect it was built for", () => {
+  // The same command emits different SQL per dialect, so a build under another
+  // profile rewrites the committed file. The stamp makes that visible in the
+  // diff instead of looking like unexplained churn.
+  expect(generateQueriesFile(queries, [], "sqlite")).toContain("(dialect: sqlite)");
+  expect(generateQueriesFile(queries, [], "postgres")).toContain("(dialect: postgres)");
+});
+
+test("placeholder style follows the dialect", () => {
+  expect(generateQueriesFile(queries, [], "sqlite")).toContain("email = ?");
+  expect(generateQueriesFile(queries, [], "postgres")).toContain("email = $1");
+});
+
+test("generation is deterministic for a fixed dialect", () => {
+  const first = generateQueriesFile(queries, [], "postgres");
+  const second = generateQueriesFile(queries, [], "postgres");
+  expect(first).toBe(second);
+});