fix

.changeset/kysely-adapter-inline-capitalize.md

@@ -0,0 +1,9 @@
+---
+"@better-auth/kysely-adapter": patch
+---
+
+Drop the `@better-auth/core/utils/string` subpath import from the kysely adapter and inline the tiny `capitalizeFirstLetter` helper instead.
+
+When a stale `@better-auth/cli@1.4.x` is left in a project's dependencies (for example after upgrading `better-auth` without renaming the CLI to `auth`), package managers can hoist the older `@better-auth/core@1.4.x` (which the legacy CLI pins as a regular dependency) to the top of `node_modules`. That older core only declares `./utils` in its `exports` map; it lacks the `./utils/*` wildcard added in 1.5+. Resolving `@better-auth/core/utils/string` from the adapter therefore failed with `ERR_PACKAGE_PATH_NOT_EXPORTED` (Node) or `Module not found: Can't resolve '@better-auth/core/utils/string'` (Webpack/Turbopack). Inlining the helper removes the fragile subpath import so the adapter loads even when an older core is shadowed onto the resolution path.
+
+@see https://github.com/better-auth/better-auth/issues/9767

packages/kysely-adapter/src/kysely-adapter.test.ts

@@ -1,3 +1,5 @@
+import { readFileSync } from "node:fs";
+import path from "node:path";
 import { Kysely, SqliteDialect } from "kysely";
 import { describe, expect, it, vi } from "vitest";
 import { kyselyAdapter } from "./kysely-adapter";
@@ -60,4 +62,29 @@ describe("kysely-adapter", () => {
 		);
 		expect(deleteQuery.returningAll).toHaveBeenCalledTimes(1);
 	});
+
+	/**
+	 * Stale installs of `@better-auth/cli@1.4.x` pin `@better-auth/core@1.4.x`
+	 * as a regular dependency, so package managers can hoist that older core
+	 * to the top of `node_modules` and shadow the newer core this adapter is
+	 * compiled against. The 1.4.x core only exposes `./utils` (no wildcard),
+	 * so any `@better-auth/core/utils/<name>` subpath import here will throw
+	 * `ERR_PACKAGE_PATH_NOT_EXPORTED` at bundle/resolve time. Keep this
+	 * adapter free of `@better-auth/core/utils/*` imports.
+	 *
+	 * @see https://github.com/better-auth/better-auth/issues/9767
+	 */
+	it("does not import from @better-auth/core/utils/* subpaths", () => {
+		const source = readFileSync(
+			path.join(__dirname, "kysely-adapter.ts"),
+			"utf8",
+		);
+		const importLines = source
+			.split("\n")
+			.filter((line) => /^\s*import\b/.test(line));
+		const offenders = importLines.filter((line) =>
+			/@better-auth\/core\/utils\//.test(line),
+		);
+		expect(offenders).toEqual([]);
+	});
 });

packages/kysely-adapter/src/kysely-adapter.ts

@@ -9,7 +9,6 @@ import type {
 } from "@better-auth/core/db/adapter";
 import { createAdapterFactory } from "@better-auth/core/db/adapter";
 import { logger } from "@better-auth/core/env";
-import { capitalizeFirstLetter } from "@better-auth/core/utils/string";
 import type {
 	InsertQueryBuilder,
 	Kysely,
@@ -26,6 +25,17 @@ import {
 } from "./query-builders";
 import type { KyselyDatabaseType } from "./types";
 
+// Inlined locally to avoid relying on the `@better-auth/core/utils/*`
+// wildcard subpath export. When users have a stale `@better-auth/cli@1.4.x`
+// installed, package managers can hoist `@better-auth/core@1.4.x` (which
+// only exposes `./utils`, not `./utils/*`) to the top of `node_modules`,
+// shadowing the newer core that this adapter was built against and
+// breaking subpath imports at bundle/resolve time.
+// @see https://github.com/better-auth/better-auth/issues/9767
+function capitalizeFirstLetter(str: string) {
+	return str.charAt(0).toUpperCase() + str.slice(1);
+}
+
 interface KyselyAdapterConfig {
 	/**
 	 * Database type.