diff --git a/UAT_PLAYBOOK.md b/UAT_PLAYBOOK.md
index 68d6d25..8f3d171 100644
--- a/UAT_PLAYBOOK.md
+++ b/UAT_PLAYBOOK.md
@@ -28,6 +28,12 @@ GroomBook API is a Hono-based REST service (TypeScript/Node.js) powering the pet
 | TC-API-1.1 | Login via OIDC | POST to OIDC provider callback, verify JWT token issued | 200 OK, JWT returned with valid claims |
 | TC-API-1.2 | Session persistence | Make authenticated request, verify session token valid | 200 OK, request succeeds |
 | TC-API-1.3 | Logout | Call logout endpoint, verify token invalidated | 200 OK, subsequent requests return 401 |
+| TC-API-1.4 | Email+password login (UAT) | POST /api/auth/sign-in/email with uat-super@groombook.dev + SEED_UAT_SUPER_PASSWORD | 200 OK, session cookie returned |
+| TC-API-1.5 | Email+password login — groomer | POST /api/auth/sign-in/email with uat-groomer@groombook.dev + SEED_UAT_GROOMER_PASSWORD | 200 OK, session cookie returned |
+| TC-API-1.6 | Email+password login — customer | POST /api/auth/sign-in/email with uat-customer@groombook.dev + SEED_UAT_CUSTOMER_PASSWORD | 200 OK, session cookie returned |
+| TC-API-1.7 | Email+password login — tester | POST /api/auth/sign-in/email with uat-tester@groombook.dev + SEED_UAT_TESTER_PASSWORD | 200 OK, session cookie returned |
+| TC-API-1.8 | Email+password — invalid password | POST /api/auth/sign-in/email with wrong password | 400 Bad Request, error returned |
+| TC-API-1.9 | Email+password — unknown user | POST /api/auth/sign-in/email with non-existent email | 400 Bad Request, error returned |
 
 ### 4.2 Client Management
 
diff --git a/apps/api/src/__tests__/seed-uat-credentials.test.ts b/apps/api/src/__tests__/seed-uat-credentials.test.ts
new file mode 100644
index 0000000..7f954ae
--- /dev/null
+++ b/apps/api/src/__tests__/seed-uat-credentials.test.ts
@@ -0,0 +1,431 @@
+import { describe, it, expect, vi, beforeEach, afterEach } from "vitest";
+
+// ─── Test configuration constants (must match seed.ts) ─────────────────────────
+
+const UAT_ACCOUNTS = [
+  {
+    email: "uat-super@groombook.dev",
+    name: "UAT Super User",
+    passwordEnv: "SEED_UAT_SUPER_PASSWORD",
+    staffEmail: "uat-super@groombook.dev",
+  },
+  {
+    email: "uat-groomer@groombook.dev",
+    name: "UAT Staff Groomer",
+    passwordEnv: "SEED_UAT_GROOMER_PASSWORD",
+    staffEmail: "uat-groomer@groombook.dev",
+  },
+  {
+    email: "uat-customer@groombook.dev",
+    name: "UAT Customer",
+    passwordEnv: "SEED_UAT_CUSTOMER_PASSWORD",
+    staffEmail: null,
+  },
+  {
+    email: "uat-tester@groombook.dev",
+    name: "UAT Tester",
+    passwordEnv: "SEED_UAT_TESTER_PASSWORD",
+    staffEmail: "uat-tester@groombook.dev",
+  },
+];
+
+const TEST_PASSWORD = "test-password-123";
+
+// ─── Password hashing — must match better-auth/crypto (N=16384, r=16, p=1, dkLen=64, hex) ───
+
+async function hashPassword(password: string): Promise<string> {
+  const { hashPassword } = await import("better-auth/crypto");
+  return hashPassword(password);
+}
+
+// ─── Mock DB state ─────────────────────────────────────────────────────────────
+
+interface UserRow {
+  id: string;
+  email: string;
+  name: string;
+  emailVerified: boolean;
+}
+
+interface AccountRow {
+  id: string;
+  accountId: string;
+  providerId: string;
+  userId: string;
+  password: string | null;
+}
+
+interface StaffRow {
+  id: string;
+  email: string;
+  userId: string | null;
+  name: string;
+}
+
+let dbUsers: UserRow[] = [];
+let dbAccounts: AccountRow[] = [];
+let dbStaff: StaffRow[] = [];
+let insertedUsers: UserRow[] = [];
+let insertedAccounts: AccountRow[] = [];
+let updatedStaff: Array<{ id: string; userId: string }> = [];
+
+const originalEnv = { ...process.env };
+
+function resetMock() {
+  dbUsers = [];
+  dbAccounts = [];
+  dbStaff = [];
+  insertedUsers = [];
+  insertedAccounts = [];
+  updatedStaff = [];
+  process.env = { ...originalEnv };
+}
+
+// ─── Mock schema ───────────────────────────────────────────────────────────────
+
+function makeSchemaMock() {
+  const user = new Proxy({ _name: "user" }, {
+    get(_t, p) {
+      if (p === "_name") return "user";
+      if (p === "$inferSelect") return {};
+      return { table: "user", column: p };
+    },
+  });
+
+  const account = new Proxy({ _name: "account" }, {
+    get(_t, p) {
+      if (p === "_name") return "account";
+      if (p === "$inferSelect") return {};
+      return { table: "account", column: p };
+    },
+  });
+
+  const staff = new Proxy({ _name: "staff" }, {
+    get(_t, p) {
+      if (p === "_name") return "staff";
+      if (p === "$inferSelect") return {};
+      return { table: "staff", column: p };
+    },
+  });
+
+  return { user, account, staff };
+}
+
+const { user: mockUser, account: mockAccount, staff: mockStaff } = makeSchemaMock();
+
+function eq(col: unknown, val: unknown) {
+  return { __type: "eq" as const, col, val };
+}
+
+function and(...conds: unknown[]) {
+  return { __type: "and" as const, conds };
+}
+
+// ─── Seed logic helper ─────────────────────────────────────────────────────────
+// Inline the credential provisioning logic under test so we can call it directly.
+// This is the same logic as seed.ts lines 514-598.
+
+interface SeedAccount {
+  email: string;
+  name: string;
+  passwordEnv: string;
+  staffEmail: string | null;
+}
+
+let uuidCounter = 0;
+function mockUuid(): string {
+  return `mock-uuid-${++uuidCounter}`;
+}
+
+async function seedUatCredentials(
+  accounts: SeedAccount[],
+  opts: {
+    users?: UserRow[];
+    accounts?: AccountRow[];
+    staff?: StaffRow[];
+  }
+) {
+  const { users = dbUsers, accounts: accts = dbAccounts, staff: staffRows = dbStaff } = opts;
+
+  for (const acct of accounts) {
+    const password = process.env[acct.passwordEnv];
+    if (!password) {
+      console.warn(`⚠ Skipping ${acct.email} — ${acct.passwordEnv} not set`);
+      continue;
+    }
+
+    // 1. Find or create the Better-Auth user
+    const existingUser = users.find((u) => u.email === acct.email);
+
+    let userId: string;
+    if (existingUser) {
+      userId = existingUser.id;
+    } else {
+      userId = mockUuid();
+      const newUser: UserRow = { id: userId, name: acct.name, email: acct.email, emailVerified: true };
+      insertedUsers.push(newUser);
+      dbUsers.push(newUser);
+    }
+
+    // 2. Check if credential account already exists
+    const existingAccount = accts.find(
+      (a) => a.userId === userId && a.providerId === "credential"
+    );
+
+    if (existingAccount) {
+      // skip — already has credential account
+    } else {
+      // Use Better-Auth's hashPassword so test helper matches production seed.ts
+      const { hashPassword } = await import("better-auth/crypto");
+      const passwordHash = await hashPassword(password);
+
+      const newAccount: AccountRow = {
+        id: mockUuid(),
+        accountId: userId,
+        providerId: "credential",
+        userId,
+        password: passwordHash,
+      };
+      insertedAccounts.push(newAccount);
+      dbAccounts.push(newAccount);
+    }
+
+    // 3. Link staff record to Better-Auth user
+    if (acct.staffEmail) {
+      const existingStaff = staffRows.find((s) => s.email === acct.staffEmail);
+      if (existingStaff && !existingStaff.userId) {
+        existingStaff.userId = userId;
+        updatedStaff.push({ id: existingStaff.id, userId });
+      }
+    }
+  }
+}
+
+// ─── Tests ─────────────────────────────────────────────────────────────────────
+
+describe("seedUatCredentials — credential provisioning logic", () => {
+  beforeEach(() => {
+    resetMock();
+    uuidCounter = 0;
+  });
+
+  afterEach(() => {
+    process.env = { ...originalEnv };
+  });
+
+  // ── AC-1: creates user + account when neither exists ──────────────────────
+
+  it("AC-1: creates user and account for each UAT account with password env var set", async () => {
+    process.env.SEED_UAT_SUPER_PASSWORD = TEST_PASSWORD;
+    process.env.SEED_UAT_GROOMER_PASSWORD = TEST_PASSWORD;
+    process.env.SEED_UAT_CUSTOMER_PASSWORD = TEST_PASSWORD;
+    process.env.SEED_UAT_TESTER_PASSWORD = TEST_PASSWORD;
+
+    await seedUatCredentials(UAT_ACCOUNTS, { users: [], accounts: [], staff: [] });
+
+    // 4 users created (customer + tester have no staff, super + groomer do)
+    expect(insertedUsers).toHaveLength(4);
+    expect(insertedUsers.find((u) => u.email === "uat-super@groombook.dev")).toBeDefined();
+    expect(insertedUsers.find((u) => u.email === "uat-groomer@groombook.dev")).toBeDefined();
+    expect(insertedUsers.find((u) => u.email === "uat-customer@groombook.dev")).toBeDefined();
+    expect(insertedUsers.find((u) => u.email === "uat-tester@groombook.dev")).toBeDefined();
+
+    // 4 accounts created
+    expect(insertedAccounts).toHaveLength(4);
+    for (const acct of insertedAccounts) {
+      expect(acct.providerId).toBe("credential");
+      // Better-Auth uses hex encoding: saltHex:keyHex (both lowercase hex)
+      expect(acct.password).toMatch(/^[a-f0-9]+:[a-f0-9]+$/);
+      // Verify the hash is scrypt with correct params (N=16384, r=16, p=1, dkLen=64)
+      const parts = acct.password!.split(":");
+      const saltHex = parts[0]!;
+      const keyHex = parts[1]!;
+      const salt = Buffer.from(saltHex, "hex");
+      const storedHash = Buffer.from(keyHex, "hex");
+      expect(salt).toHaveLength(16);
+      expect(storedHash).toHaveLength(64);
+    }
+  });
+
+  // ── AC-2: emailVerified = true ─────────────────────────────────────────────
+
+  it("AC-2: created users have emailVerified = true", async () => {
+    process.env.SEED_UAT_CUSTOMER_PASSWORD = TEST_PASSWORD;
+
+    await seedUatCredentials(
+      [UAT_ACCOUNTS[2]!], // customer only
+      { users: [], accounts: [], staff: [] }
+    );
+
+    expect(insertedUsers[0]!.emailVerified).toBe(true);
+  });
+
+  // ── AC-3: providerId = credential, password is hashed ──────────────────────
+
+  it("AC-3: account records use providerId='credential' with properly formatted hashed password", async () => {
+    process.env.SEED_UAT_CUSTOMER_PASSWORD = TEST_PASSWORD;
+
+    await seedUatCredentials(
+      [UAT_ACCOUNTS[2]!],
+      { users: [], accounts: [], staff: [] }
+    );
+
+    const acct = insertedAccounts[0]!;
+    expect(acct.providerId).toBe("credential");
+    // Better-Auth uses hex: saltHex (32 chars) : keyHex (128 chars)
+    expect(acct.password).toMatch(/^[a-f0-9]+:[a-f0-9]+$/);
+    const parts = acct.password!.split(":");
+    const saltHex = parts[0]!;
+    const keyHex = parts[1]!;
+    expect(() => Buffer.from(saltHex, "hex")).not.toThrow();
+    expect(() => Buffer.from(keyHex, "hex")).not.toThrow();
+    const salt = Buffer.from(saltHex, "hex");
+    const storedHash = Buffer.from(keyHex, "hex");
+    expect(salt).toHaveLength(16);
+    expect(storedHash).toHaveLength(64);
+  });
+
+  // ── AC-4: staff.userId is linked ────────────────────────────────────────────
+
+  it("AC-4: links staff.userId to the Better-Auth user when staff record exists", async () => {
+    process.env.SEED_UAT_SUPER_PASSWORD = TEST_PASSWORD;
+    const staffRows: StaffRow[] = [
+      { id: "staff-super-1", email: "uat-super@groombook.dev", userId: null, name: "UAT Super User" },
+    ];
+
+    await seedUatCredentials([UAT_ACCOUNTS[0]!], { users: [], accounts: [], staff: staffRows });
+
+    expect(updatedStaff).toHaveLength(1);
+    expect(updatedStaff[0]!.id).toBe("staff-super-1");
+    expect(updatedStaff[0]!.userId).toBe("mock-uuid-1");
+    expect(staffRows[0]!.userId).toBe("mock-uuid-1");
+  });
+
+  it("AC-4b: does not update staff.userId if already set", async () => {
+    process.env.SEED_UAT_GROOMER_PASSWORD = TEST_PASSWORD;
+    const staffRows: StaffRow[] = [
+      { id: "staff-groomer-1", email: "uat-groomer@groombook.dev", userId: "already-linked", name: "UAT Groomer" },
+    ];
+
+    await seedUatCredentials([UAT_ACCOUNTS[1]!], { users: [], accounts: [], staff: staffRows });
+
+    expect(updatedStaff).toHaveLength(0);
+  });
+
+  // ── AC-5: idempotent — skips when user already exists ───────────────────────
+
+  it("AC-5: re-running does not duplicate user or account records (idempotent)", async () => {
+    process.env.SEED_UAT_CUSTOMER_PASSWORD = TEST_PASSWORD;
+
+    const preExistingUsers: UserRow[] = [
+      { id: "pre-existing-user", email: "uat-customer@groombook.dev", name: "UAT Customer", emailVerified: true },
+    ];
+    const preExistingAccounts: AccountRow[] = [
+      {
+        id: "pre-existing-acct",
+        accountId: "pre-existing-user",
+        providerId: "credential",
+        userId: "pre-existing-user",
+        password: await hashPassword(TEST_PASSWORD),
+      },
+    ];
+
+    // First call — nothing inserted (user + account pre-exist)
+    await seedUatCredentials([UAT_ACCOUNTS[2]!], {
+      users: preExistingUsers,
+      accounts: preExistingAccounts,
+      staff: [],
+    });
+
+    expect(insertedUsers).toHaveLength(0);
+    expect(insertedAccounts).toHaveLength(0);
+
+    // Second call — still nothing inserted
+    await seedUatCredentials([UAT_ACCOUNTS[2]!], {
+      users: preExistingUsers,
+      accounts: preExistingAccounts,
+      staff: [],
+    });
+
+    expect(insertedUsers).toHaveLength(0);
+    expect(insertedAccounts).toHaveLength(0);
+  });
+
+  // ── AC-6: missing env var skips with warning ────────────────────────────────
+
+  it("AC-6: missing SEED_UAT_*_PASSWORD env var skips that account (no error)", async () => {
+    // No env vars set at all
+    delete process.env.SEED_UAT_SUPER_PASSWORD;
+    delete process.env.SEED_UAT_GROOMER_PASSWORD;
+    delete process.env.SEED_UAT_CUSTOMER_PASSWORD;
+    delete process.env.SEED_UAT_TESTER_PASSWORD;
+
+    const warnSpy = vi.spyOn(console, "warn").mockReturnValue(undefined);
+
+    await seedUatCredentials(UAT_ACCOUNTS, { users: [], accounts: [], staff: [] });
+
+    // Nothing created
+    expect(insertedUsers).toHaveLength(0);
+    expect(insertedAccounts).toHaveLength(0);
+    // Warning logged for each of the 4 accounts
+    expect(warnSpy).toHaveBeenCalledTimes(4);
+    expect(warnSpy).toHaveBeenCalledWith(
+      "⚠ Skipping uat-super@groombook.dev — SEED_UAT_SUPER_PASSWORD not set"
+    );
+
+    warnSpy.mockRestore();
+  });
+
+  // ── AC-7: partial env var coverage ─────────────────────────────────────────
+
+  it("AC-7: only accounts with password env var set are provisioned", async () => {
+    process.env.SEED_UAT_SUPER_PASSWORD = TEST_PASSWORD;
+    // Only super has password set
+
+    const warnSpy = vi.spyOn(console, "warn").mockReturnValue(undefined);
+
+    await seedUatCredentials(UAT_ACCOUNTS, { users: [], accounts: [], staff: [] });
+
+    expect(insertedUsers).toHaveLength(1);
+    expect(insertedUsers[0]!.email).toBe("uat-super@groombook.dev");
+    expect(insertedAccounts).toHaveLength(1);
+    expect(insertedAccounts[0]!.accountId).toBe("mock-uuid-1");
+
+    // 3 warnings for missing accounts
+    expect(warnSpy).toHaveBeenCalledTimes(3);
+
+    warnSpy.mockRestore();
+  });
+});
+
+// ─── Password hash format verification ───────────────────────────────────────
+
+describe("password hash format — scrypt parameters", () => {
+  it("hashes use salt:hash format with 16-byte salt and 64-byte output", async () => {
+    const hash = await hashPassword("test-password");
+    const parts = hash.split(":");
+    const saltHex = parts[0]!;
+    const keyHex = parts[1]!;
+
+    expect(hash).toMatch(/^[a-f0-9]+:[a-f0-9]+$/);
+    expect(Buffer.from(saltHex, "hex")).toHaveLength(16);
+    expect(Buffer.from(keyHex, "hex")).toHaveLength(64);
+  });
+
+  it("same password produces different hashes (due to random salt)", async () => {
+    const hash1 = await hashPassword("same-password");
+    const hash2 = await hashPassword("same-password");
+
+    expect(hash1).not.toBe(hash2);
+    // Both are valid Better-Auth hex format
+    expect(hash1).toMatch(/^[a-f0-9]+:[a-f0-9]+$/);
+    expect(hash2).toMatch(/^[a-f0-9]+:[a-f0-9]+$/);
+  });
+
+  it("different passwords produce different hashes", async () => {
+    const hash1 = await hashPassword("password1");
+    const hash2 = await hashPassword("password2");
+
+    expect(hash1).not.toBe(hash2);
+  });
+});
\ No newline at end of file
diff --git a/apps/api/src/db/seed.ts b/apps/api/src/db/seed.ts
index 2ff67bf..566da17 100644
--- a/apps/api/src/db/seed.ts
+++ b/apps/api/src/db/seed.ts
@@ -18,7 +18,7 @@
 
 import postgres from "postgres";
 import { drizzle } from "drizzle-orm/postgres-js";
-import { eq, sql } from "drizzle-orm";
+import { eq, and, sql } from "drizzle-orm";
 import * as schema from "./schema.js";
 
 // ── Seed profile configuration ─────────────────────────────────────────────
@@ -511,6 +511,90 @@ async function seedKnownUsers() {
     }
   }
 
+  // ── Better-Auth email+password credentials for UAT accounts ──────────────────
+  // Provisions Better-Auth user + account records so UAT testers can log in
+  // via email+password (POST /api/auth/sign-in/email) instead of Authentik SSO.
+  const uatPasswordAccounts = [
+    { email: "uat-super@groombook.dev", name: "UAT Super User", passwordEnv: "SEED_UAT_SUPER_PASSWORD", staffEmail: "uat-super@groombook.dev" },
+    { email: "uat-groomer@groombook.dev", name: "UAT Staff Groomer", passwordEnv: "SEED_UAT_GROOMER_PASSWORD", staffEmail: "uat-groomer@groombook.dev" },
+    { email: "uat-customer@groombook.dev", name: "UAT Customer", passwordEnv: "SEED_UAT_CUSTOMER_PASSWORD", staffEmail: null },
+    { email: "uat-tester@groombook.dev", name: "UAT Tester", passwordEnv: "SEED_UAT_TESTER_PASSWORD", staffEmail: "uat-tester@groombook.dev" },
+  ];
+
+  for (const acct of uatPasswordAccounts) {
+    const password = process.env[acct.passwordEnv];
+    if (!password) {
+      console.warn(`⚠ Skipping ${acct.email} — ${acct.passwordEnv} not set`);
+      continue;
+    }
+
+    // 1. Find or create the Better-Auth user
+    const [existingUser] = await db
+      .select()
+      .from(schema.user)
+      .where(eq(schema.user.email, acct.email))
+      .limit(1);
+
+    let userId: string;
+    if (existingUser) {
+      userId = existingUser.id;
+      console.log(`✓ Better-Auth user '${acct.name}' already exists — skipping user creation`);
+    } else {
+      userId = uuid();
+      await db.insert(schema.user).values({
+        id: userId,
+        name: acct.name,
+        email: acct.email,
+        emailVerified: true,
+      });
+      console.log(`✓ Created Better-Auth user '${acct.name}' (${acct.email})`);
+    }
+
+    // 2. Check if credential account already exists
+    const [existingAccount] = await db
+      .select()
+      .from(schema.account)
+      .where(and(
+        eq(schema.account.userId, userId),
+        eq(schema.account.providerId, "credential")
+      ))
+      .limit(1);
+
+    if (existingAccount) {
+      console.log(`✓ Credential account for '${acct.email}' already exists — skipping`);
+    } else {
+      // Use Better-Auth's own hashPassword to guarantee parameter/encoding match.
+      // better-auth/crypto uses: N=16384, r=16, p=1, dkLen=64, salt as 16-byte random
+      // hex string, key hex-encoded, format saltHex:keyHex.
+      const { hashPassword } = await import("better-auth/crypto");
+      const passwordHash = await hashPassword(password);
+
+      await db.insert(schema.account).values({
+        id: uuid(),
+        accountId: userId,
+        providerId: "credential",
+        userId,
+        password: passwordHash,
+      });
+      console.log(`✓ Created credential account for '${acct.email}'`);
+    }
+
+    // 3. Link staff record to Better-Auth user (for accounts that have staff records)
+    if (acct.staffEmail) {
+      const [existingStaff] = await db
+        .select()
+        .from(schema.staff)
+        .where(eq(schema.staff.email, acct.staffEmail))
+        .limit(1);
+      if (existingStaff && !existingStaff.userId) {
+        await db.update(schema.staff)
+          .set({ userId })
+          .where(eq(schema.staff.id, existingStaff.id));
+        console.log(`✓ Linked staff '${acct.staffEmail}' → Better-Auth user`);
+      }
+    }
+  }
+
   // ── Services: idempotent upsert using name as unique key ─────────────────────
   // UNIQUE constraint on services.name (migration 0020) must exist first.
   // Uses b0000001-... IDs to match main seed servicesDef for same-named services.