feat(email-otp): add resendStrategy option to reuse existing OTP (#8560)

docs/content/docs/plugins/email-otp.mdx

@@ -411,6 +411,26 @@ export const auth = betterAuth({
 
 When the maximum attempts are exceeded, the `verifyOTP`, `signIn.emailOtp`, `verifyEmail`, and `resetPassword` methods will return an error with code `TOO_MANY_ATTEMPTS`.
 
+- `resendStrategy`: Controls what happens when a user requests a new OTP while an existing one is still valid. Defaults to `"rotate"`.
+  - `"rotate"`: Always generates a new OTP (default behavior).
+  - `"reuse"`: Resends the same OTP and extends its expiry. This prevents multiple valid codes from existing simultaneously when emails are delayed. Only works when the OTP is recoverable (`plain`, `encrypted`, or custom encrypt/decrypt). Falls back to `"rotate"` when the OTP is hashed. If the allowed attempts have been exhausted, a fresh OTP is generated instead of reusing the exhausted one.
+
+```ts title="auth.ts"
+import { betterAuth } from "better-auth"
+import { emailOTP } from "better-auth/plugins"
+
+export const auth = betterAuth({
+    plugins: [
+        emailOTP({
+            resendStrategy: "reuse", // [!code highlight]
+            async sendVerificationOTP({ email, otp, type }) {
+                // send the OTP
+            },
+        })
+    ]
+})
+```
+
 - `storeOTP`: The method used to transform the OTP before it is stored by Better Auth's verification layer, whether `encrypted`, `hashed` or `plain` text. Default is `plain` text.
 
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