diff --git a/apps/api/src/__tests__/seed-uat-credentials.test.ts b/apps/api/src/__tests__/seed-uat-credentials.test.ts
index 75eaffc..9bfccbf 100644
--- a/apps/api/src/__tests__/seed-uat-credentials.test.ts
+++ b/apps/api/src/__tests__/seed-uat-credentials.test.ts
@@ -67,6 +67,7 @@ let dbAccounts: AccountRow[] = [];
 let dbStaff: StaffRow[] = [];
 let insertedUsers: UserRow[] = [];
 let insertedAccounts: AccountRow[] = [];
+let updatedAccounts: Array<{ id: string; password: string }> = [];
 let updatedStaff: Array<{ id: string; userId: string }> = [];
 
 const originalEnv = { ...process.env };
@@ -77,6 +78,7 @@ function resetMock() {
   dbStaff = [];
   insertedUsers = [];
   insertedAccounts = [];
+  updatedAccounts = [];
   updatedStaff = [];
   process.env = { ...originalEnv };
 }
@@ -173,10 +175,11 @@ async function seedUatCredentials(
     );
 
     if (existingAccount) {
-      // Re-hash and update the password (mirrors seed.ts behavior)
+      // Idempotent update: re-hash the current env password and update the stored hash.
       const { hashPassword } = await import("better-auth/crypto");
       const passwordHash = await hashPassword(password);
       existingAccount.password = passwordHash;
+      updatedAccounts.push({ id: existingAccount.id, password: passwordHash });
     } else {
       // Use Better-Auth's hashPassword so test helper matches production seed.ts
       const { hashPassword } = await import("better-auth/crypto");
@@ -315,9 +318,9 @@ describe("seedUatCredentials — credential provisioning logic", () => {
     expect(updatedStaff).toHaveLength(0);
   });
 
-  // ── AC-5: idempotent — skips when user already exists ───────────────────────
+  // ── AC-5: idempotent — does not insert duplicate records ───────────────────
 
-  it("AC-5: re-running does not duplicate user or account records (idempotent)", async () => {
+  it("AC-5: re-running does not insert duplicate user or account records", async () => {
     process.env.SEED_UAT_CUSTOMER_PASSWORD = TEST_PASSWORD;
 
     const preExistingUsers: UserRow[] = [
@@ -333,25 +336,53 @@ describe("seedUatCredentials — credential provisioning logic", () => {
       },
     ];
 
-    // First call — nothing inserted (user + account pre-exist)
     await seedUatCredentials([UAT_ACCOUNTS[2]!], {
       users: preExistingUsers,
       accounts: preExistingAccounts,
       staff: [],
     });
 
+    // No inserts — user and account already exist
     expect(insertedUsers).toHaveLength(0);
     expect(insertedAccounts).toHaveLength(0);
+  });
+
+  // ── AC-5b: password rotation on re-seed ─────────────────────────────────────
+
+  it("AC-5b: re-running with a new password updates the stored credential hash", async () => {
+    const OLD_PASSWORD = "old-password-abc";
+    const NEW_PASSWORD = "new-password-xyz";
+    process.env.SEED_UAT_CUSTOMER_PASSWORD = NEW_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(OLD_PASSWORD),
+      },
+    ];
 
-    // Second call — still nothing inserted
     await seedUatCredentials([UAT_ACCOUNTS[2]!], {
       users: preExistingUsers,
       accounts: preExistingAccounts,
       staff: [],
     });
 
+    // No new records inserted
     expect(insertedUsers).toHaveLength(0);
     expect(insertedAccounts).toHaveLength(0);
+    // Password WAS updated to the new env value
+    expect(updatedAccounts).toHaveLength(1);
+    expect(updatedAccounts[0]!.id).toBe("pre-existing-acct");
+    // New hash is valid Better-Auth format (salt:key, each hex)
+    const newHashParts = updatedAccounts[0]!.password.split(":");
+    expect(Buffer.from(newHashParts[0]!, "hex")).toHaveLength(16);
+    expect(Buffer.from(newHashParts[1]!, "hex")).toHaveLength(64);
   });
 
   // ── AC-8: existing account password IS updated (not frozen at first-seed) ──
diff --git a/apps/api/src/db/seed.ts b/apps/api/src/db/seed.ts
index e5601d1..5b48dd6 100644
--- a/apps/api/src/db/seed.ts
+++ b/apps/api/src/db/seed.ts
@@ -602,7 +602,7 @@ async function seedKnownUsers() {
       await db.update(schema.account)
         .set({ password: passwordHash })
         .where(eq(schema.account.id, existingAccount.id));
-      console.log(`✓ Credential account for '${acct.email}' already exists — password updated`);
+      console.log(`✓ Updated credential account password for '${acct.email}'`);
     } 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