fix(auth): make users.hashed_password nullable

Better-Auth inserts into users without a hashed_password value (passwords
are stored in the accounts table). This was causing a NOT NULL constraint
violation and 422 FAILED_TO_CREATE_USER on sign-up.

Revision ID: 003_make_users_hashed_password_nullable
Resolves: CAR-172

Co-Authored-By: Paperclip <noreply@paperclip.ing>

api/alembic/versions/003_make_users_hashed_password_nullable.py

@@ -0,0 +1,26 @@
+"""Make users.hashed_password nullable.
+
+Better-Auth inserts users without hashed_password (passwords live in the
+accounts table). This column is now purely optional.
+
+Revision ID: 003_make_users_hashed_password_nullable
+Revises: 002_better_auth_tables
+Create Date: 2026-03-30
+"""
+
+import sqlalchemy as sa
+
+from alembic import op
+
+revision = "003_make_users_hashed_password_nullable"
+down_revision = "002_better_auth_tables"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.alter_column("users", "hashed_password", existing_type=sa.String(255), nullable=True)
+
+
+def downgrade() -> None:
+    op.alter_column("users", "hashed_password", existing_type=sa.String(255), nullable=False)

common/src/cartsnitch_common/models/user.py

@@ -21,7 +21,7 @@ class User(UUIDPrimaryKeyMixin, TimestampMixin, Base):
     __tablename__ = "users"
 
     email: Mapped[str] = mapped_column(String(255), nullable=False, unique=True)
-    hashed_password: Mapped[str] = mapped_column(String(255), nullable=False)
+    hashed_password: Mapped[str | None] = mapped_column(String(255), nullable=True)
     display_name: Mapped[str | None] = mapped_column(String(100))
     email_verified: Mapped[bool] = mapped_column(Boolean, nullable=False, server_default="false")
     image: Mapped[str | None] = mapped_column(Text, nullable=True)

src/lib/auth-client.ts

@@ -1,8 +1,36 @@
 import { createAuthClient } from "better-auth/react"
+import type { BetterFetchPlugin } from "@better-fetch/fetch"
+
+/**
+ * Maps 'name' -> 'display_name' in register requests to match the API's RegisterRequest schema.
+ */
+const displayNameMapper: BetterFetchPlugin = {
+  id: "display-name-mapper",
+  name: "display-name-mapper",
+  hooks: {
+    onRequest: async (context) => {
+      const url = typeof context.url === "string" ? context.url : context.url.pathname
+      if (
+        url.endsWith("/auth/register") &&
+        context.method === "POST" &&
+        context.body &&
+        "name" in context.body
+      ) {
+        context.body = {
+          ...context.body,
+          display_name: context.body.name as string,
+          name: undefined,
+        }
+      }
+      return context
+    },
+  },
+}
 
 export const authClient = createAuthClient({
-  baseURL: import.meta.env.VITE_AUTH_URL ?? "http://localhost:3001",
+  baseURL: import.meta.env.VITE_AUTH_URL || "",
   basePath: "/auth",
+  fetchPlugins: [displayNameMapper],
 })
 
 export const { useSession, signIn, signUp, signOut } = authClient