diff --git a/apps/web/app/api/google/linking/auth-url/route.ts b/apps/web/app/api/google/linking/auth-url/route.ts
index c39705123c..7d15bcec07 100644
--- a/apps/web/app/api/google/linking/auth-url/route.ts
+++ b/apps/web/app/api/google/linking/auth-url/route.ts
@@ -1,7 +1,10 @@
 import { NextResponse } from "next/server";
 import { withAuth } from "@/utils/middleware";
 import { getLinkingOAuth2Client } from "@/utils/gmail/client";
-import { GOOGLE_LINKING_STATE_COOKIE_NAME } from "@/utils/gmail/constants";
+import {
+  GOOGLE_LINKING_STATE_COOKIE_NAME,
+  GOOGLE_LINKING_STATE_RESULT_COOKIE_NAME,
+} from "@/utils/gmail/constants";
 import { SCOPES } from "@/utils/gmail/scopes";
 import {
   generateOAuthState,
@@ -31,6 +34,7 @@ export const GET = withAuth("google/linking/auth-url", async (request) => {
 
   const response = NextResponse.json({ url: authUrl });
 
+  response.cookies.delete(GOOGLE_LINKING_STATE_RESULT_COOKIE_NAME);
   response.cookies.set(
     GOOGLE_LINKING_STATE_COOKIE_NAME,
     state,
diff --git a/apps/web/app/api/google/linking/callback/route.ts b/apps/web/app/api/google/linking/callback/route.ts
index fba1e8fe44..ab93a6b452 100644
--- a/apps/web/app/api/google/linking/callback/route.ts
+++ b/apps/web/app/api/google/linking/callback/route.ts
@@ -1,18 +1,36 @@
-import { NextResponse } from "next/server";
 import { env } from "@/env";
 import prisma from "@/utils/prisma";
 import { getLinkingOAuth2Client } from "@/utils/gmail/client";
-import { GOOGLE_LINKING_STATE_COOKIE_NAME } from "@/utils/gmail/constants";
+import {
+  GOOGLE_LINKING_STATE_COOKIE_NAME,
+  GOOGLE_LINKING_STATE_RESULT_COOKIE_NAME,
+} from "@/utils/gmail/constants";
 import { withError } from "@/utils/middleware";
 import { validateOAuthCallback } from "@/utils/oauth/callback-validation";
 import { handleAccountLinking } from "@/utils/oauth/account-linking";
 import { mergeAccount } from "@/utils/user/merge-account";
 import { handleOAuthCallbackError } from "@/utils/oauth/error-handler";
+import {
+  checkOAuthCallbackDedupe,
+  buildOAuthSuccessRedirect,
+} from "@/utils/oauth/callback-helpers";
 
 export const GET = withError("google/linking/callback", async (request) => {
   const logger = request.logger;
 
+  const dedupeResponse = checkOAuthCallbackDedupe({
+    request,
+    stateCookieName: GOOGLE_LINKING_STATE_COOKIE_NAME,
+    resultCookieName: GOOGLE_LINKING_STATE_RESULT_COOKIE_NAME,
+    baseUrl: request.nextUrl.origin,
+  });
+
+  if (dedupeResponse) {
+    return dedupeResponse;
+  }
+
   const searchParams = request.nextUrl.searchParams;
+
   const storedState = request.cookies.get(
     GOOGLE_LINKING_STATE_COOKIE_NAME,
   )?.value;
@@ -30,10 +48,14 @@ export const GET = withError("google/linking/callback", async (request) => {
     return validation.response;
   }
 
+  const receivedState = searchParams.get("state");
+  if (!receivedState) {
+    throw new Error("Missing state parameter after validation");
+  }
+
   const { targetUserId, code } = validation;
-  const redirectUrl = new URL("/accounts", request.nextUrl.origin);
-  const response = NextResponse.redirect(redirectUrl);
-  response.cookies.delete(GOOGLE_LINKING_STATE_COOKIE_NAME);
+  const state = receivedState;
+  const baseRedirectUrl = new URL("/accounts", request.nextUrl.origin);
 
   const googleAuth = getLinkingOAuth2Client();
 
@@ -102,6 +124,10 @@ export const GET = withError("google/linking/callback", async (request) => {
     });
 
     if (linkingResult.type === "redirect") {
+      linkingResult.response.cookies.delete(GOOGLE_LINKING_STATE_COOKIE_NAME);
+      linkingResult.response.cookies.delete(
+        GOOGLE_LINKING_STATE_RESULT_COOKIE_NAME,
+      );
       return linkingResult.response;
     }
 
@@ -139,9 +165,12 @@ export const GET = withError("google/linking/callback", async (request) => {
         targetUserId,
         accountId: newAccount.id,
       });
-      redirectUrl.searchParams.set("success", "account_created_and_linked");
-      return NextResponse.redirect(redirectUrl, {
-        headers: response.headers,
+      return buildOAuthSuccessRedirect({
+        state,
+        params: { success: "account_created_and_linked" },
+        stateCookieName: GOOGLE_LINKING_STATE_COOKIE_NAME,
+        resultCookieName: GOOGLE_LINKING_STATE_RESULT_COOKIE_NAME,
+        baseUrl: request.nextUrl.origin,
       });
     }
 
@@ -173,16 +202,19 @@ export const GET = withError("google/linking/callback", async (request) => {
       mergeType,
     });
 
-    redirectUrl.searchParams.set("success", successMessage);
-    return NextResponse.redirect(redirectUrl, {
-      headers: response.headers,
+    return buildOAuthSuccessRedirect({
+      state,
+      params: { success: successMessage },
+      stateCookieName: GOOGLE_LINKING_STATE_COOKIE_NAME,
+      resultCookieName: GOOGLE_LINKING_STATE_RESULT_COOKIE_NAME,
+      baseUrl: request.nextUrl.origin,
     });
   } catch (error) {
     return handleOAuthCallbackError({
       error,
-      redirectUrl,
-      response,
+      redirectUrl: baseRedirectUrl,
       stateCookieName: GOOGLE_LINKING_STATE_COOKIE_NAME,
+      resultCookieName: GOOGLE_LINKING_STATE_RESULT_COOKIE_NAME,
       logger,
     });
   }
diff --git a/apps/web/app/api/outlook/linking/auth-url/route.ts b/apps/web/app/api/outlook/linking/auth-url/route.ts
index 86e3f8ffdc..acd1302d76 100644
--- a/apps/web/app/api/outlook/linking/auth-url/route.ts
+++ b/apps/web/app/api/outlook/linking/auth-url/route.ts
@@ -1,7 +1,10 @@
 import { NextResponse } from "next/server";
 import { withAuth } from "@/utils/middleware";
 import { getLinkingOAuth2Url } from "@/utils/outlook/client";
-import { OUTLOOK_LINKING_STATE_COOKIE_NAME } from "@/utils/outlook/constants";
+import {
+  OUTLOOK_LINKING_STATE_COOKIE_NAME,
+  OUTLOOK_LINKING_STATE_RESULT_COOKIE_NAME,
+} from "@/utils/outlook/constants";
 import {
   generateOAuthState,
   oauthStateCookieOptions,
@@ -24,6 +27,7 @@ export const GET = withAuth("outlook/linking/auth-url", async (request) => {
 
   const response = NextResponse.json({ url: authUrl });
 
+  response.cookies.delete(OUTLOOK_LINKING_STATE_RESULT_COOKIE_NAME);
   response.cookies.set(
     OUTLOOK_LINKING_STATE_COOKIE_NAME,
     state,
diff --git a/apps/web/app/api/outlook/linking/callback/route.ts b/apps/web/app/api/outlook/linking/callback/route.ts
index 45c3172a33..caeae4c1bd 100644
--- a/apps/web/app/api/outlook/linking/callback/route.ts
+++ b/apps/web/app/api/outlook/linking/callback/route.ts
@@ -1,13 +1,19 @@
-import { NextResponse } from "next/server";
 import { env } from "@/env";
 import prisma from "@/utils/prisma";
-import { OUTLOOK_LINKING_STATE_COOKIE_NAME } from "@/utils/outlook/constants";
+import {
+  OUTLOOK_LINKING_STATE_COOKIE_NAME,
+  OUTLOOK_LINKING_STATE_RESULT_COOKIE_NAME,
+} from "@/utils/outlook/constants";
 import { withError } from "@/utils/middleware";
 import { captureException, SafeError } from "@/utils/error";
 import { validateOAuthCallback } from "@/utils/oauth/callback-validation";
 import { handleAccountLinking } from "@/utils/oauth/account-linking";
 import { mergeAccount } from "@/utils/user/merge-account";
 import { handleOAuthCallbackError } from "@/utils/oauth/error-handler";
+import {
+  checkOAuthCallbackDedupe,
+  buildOAuthSuccessRedirect,
+} from "@/utils/oauth/callback-helpers";
 
 export const GET = withError("outlook/linking/callback", async (request) => {
   const logger = request.logger;
@@ -15,7 +21,19 @@ export const GET = withError("outlook/linking/callback", async (request) => {
   if (!env.MICROSOFT_CLIENT_ID || !env.MICROSOFT_CLIENT_SECRET)
     throw new SafeError("Microsoft login not enabled");
 
+  const dedupeResponse = checkOAuthCallbackDedupe({
+    request,
+    stateCookieName: OUTLOOK_LINKING_STATE_COOKIE_NAME,
+    resultCookieName: OUTLOOK_LINKING_STATE_RESULT_COOKIE_NAME,
+    baseUrl: request.nextUrl.origin,
+  });
+
+  if (dedupeResponse) {
+    return dedupeResponse;
+  }
+
   const searchParams = request.nextUrl.searchParams;
+
   const storedState = request.cookies.get(
     OUTLOOK_LINKING_STATE_COOKIE_NAME,
   )?.value;
@@ -33,10 +51,14 @@ export const GET = withError("outlook/linking/callback", async (request) => {
     return validation.response;
   }
 
+  const receivedState = searchParams.get("state");
+  if (!receivedState) {
+    throw new Error("Missing state parameter after validation");
+  }
+
   const { targetUserId, code } = validation;
-  const redirectUrl = new URL("/accounts", request.nextUrl.origin);
-  const response = NextResponse.redirect(redirectUrl);
-  response.cookies.delete(OUTLOOK_LINKING_STATE_COOKIE_NAME);
+  const state = receivedState;
+  const baseRedirectUrl = new URL("/accounts", request.nextUrl.origin);
 
   try {
     // Exchange code for tokens
@@ -136,6 +158,10 @@ export const GET = withError("outlook/linking/callback", async (request) => {
     });
 
     if (linkingResult.type === "redirect") {
+      linkingResult.response.cookies.delete(OUTLOOK_LINKING_STATE_COOKIE_NAME);
+      linkingResult.response.cookies.delete(
+        OUTLOOK_LINKING_STATE_RESULT_COOKIE_NAME,
+      );
       return linkingResult.response;
     }
 
@@ -210,9 +236,12 @@ export const GET = withError("outlook/linking/callback", async (request) => {
         targetUserId,
         accountId: newAccount.id,
       });
-      redirectUrl.searchParams.set("success", "account_created_and_linked");
-      return NextResponse.redirect(redirectUrl, {
-        headers: response.headers,
+      return buildOAuthSuccessRedirect({
+        state,
+        params: { success: "account_created_and_linked" },
+        stateCookieName: OUTLOOK_LINKING_STATE_COOKIE_NAME,
+        resultCookieName: OUTLOOK_LINKING_STATE_RESULT_COOKIE_NAME,
+        baseUrl: request.nextUrl.origin,
       });
     }
 
@@ -242,16 +271,19 @@ export const GET = withError("outlook/linking/callback", async (request) => {
       mergeType,
     });
 
-    redirectUrl.searchParams.set("success", successMessage);
-    return NextResponse.redirect(redirectUrl, {
-      headers: response.headers,
+    return buildOAuthSuccessRedirect({
+      state,
+      params: { success: successMessage },
+      stateCookieName: OUTLOOK_LINKING_STATE_COOKIE_NAME,
+      resultCookieName: OUTLOOK_LINKING_STATE_RESULT_COOKIE_NAME,
+      baseUrl: request.nextUrl.origin,
     });
   } catch (error) {
     return handleOAuthCallbackError({
       error,
-      redirectUrl,
-      response,
+      redirectUrl: baseRedirectUrl,
       stateCookieName: OUTLOOK_LINKING_STATE_COOKIE_NAME,
+      resultCookieName: OUTLOOK_LINKING_STATE_RESULT_COOKIE_NAME,
       logger,
     });
   }
diff --git a/apps/web/utils/gmail/constants.ts b/apps/web/utils/gmail/constants.ts
index debd3795cf..0c083cb935 100644
--- a/apps/web/utils/gmail/constants.ts
+++ b/apps/web/utils/gmail/constants.ts
@@ -14,3 +14,5 @@ export type LabelVisibility =
   (typeof labelVisibility)[keyof typeof labelVisibility];
 
 export const GOOGLE_LINKING_STATE_COOKIE_NAME = "google_linking_state";
+export const GOOGLE_LINKING_STATE_RESULT_COOKIE_NAME =
+  "google_linking_state_result";
diff --git a/apps/web/utils/oauth/callback-helpers.ts b/apps/web/utils/oauth/callback-helpers.ts
new file mode 100644
index 0000000000..0c875dbb8f
--- /dev/null
+++ b/apps/web/utils/oauth/callback-helpers.ts
@@ -0,0 +1,86 @@
+import { NextResponse } from "next/server";
+import type { NextRequest } from "next/server";
+import {
+  parseOAuthStateResultCookie,
+  encodeOAuthStateResultCookie,
+  oauthStateCookieOptions,
+} from "@/utils/oauth/state";
+
+interface CheckDedupeParams {
+  request: NextRequest;
+  stateCookieName: string;
+  resultCookieName: string;
+  baseUrl: string;
+}
+
+/**
+ * Checks if this OAuth callback has already been processed.
+ * If so, returns the cached redirect response.
+ * Otherwise, returns null to continue processing.
+ */
+export function checkOAuthCallbackDedupe({
+  request,
+  stateCookieName,
+  resultCookieName,
+  baseUrl,
+}: CheckDedupeParams): NextResponse | null {
+  const receivedState = request.nextUrl.searchParams.get("state");
+  const completedState = parseOAuthStateResultCookie(
+    request.cookies.get(resultCookieName)?.value,
+  );
+
+  if (
+    receivedState &&
+    completedState &&
+    completedState.state === receivedState &&
+    Object.keys(completedState.params).length > 0
+  ) {
+    const deduplicatedRedirect = new URL("/accounts", baseUrl);
+    for (const [key, value] of Object.entries(completedState.params)) {
+      deduplicatedRedirect.searchParams.set(key, value);
+    }
+    const deduplicatedResponse = NextResponse.redirect(deduplicatedRedirect);
+    deduplicatedResponse.cookies.delete(stateCookieName);
+    return deduplicatedResponse;
+  }
+
+  return null;
+}
+
+interface BuildSuccessRedirectParams {
+  state: string;
+  params: Record<string, string>;
+  stateCookieName: string;
+  resultCookieName: string;
+  baseUrl: string;
+}
+
+/**
+ * Builds a success redirect response with query params and sets the result cookie
+ * for deduplication on subsequent requests.
+ */
+export function buildOAuthSuccessRedirect({
+  state,
+  params,
+  stateCookieName,
+  resultCookieName,
+  baseUrl,
+}: BuildSuccessRedirectParams): NextResponse {
+  const redirectUrl = new URL("/accounts", baseUrl);
+  for (const [key, value] of Object.entries(params)) {
+    redirectUrl.searchParams.set(key, value);
+  }
+
+  const successResponse = NextResponse.redirect(redirectUrl);
+  successResponse.cookies.delete(stateCookieName);
+  successResponse.cookies.set(
+    resultCookieName,
+    encodeOAuthStateResultCookie({
+      state,
+      params,
+    }),
+    oauthStateCookieOptions,
+  );
+
+  return successResponse;
+}
diff --git a/apps/web/utils/oauth/error-handler.ts b/apps/web/utils/oauth/error-handler.ts
index f9ff5837c2..99b1c20727 100644
--- a/apps/web/utils/oauth/error-handler.ts
+++ b/apps/web/utils/oauth/error-handler.ts
@@ -4,23 +4,27 @@ import type { Logger } from "@/utils/logger";
 interface ErrorHandlerParams {
   error: unknown;
   redirectUrl: URL;
-  response: NextResponse;
   stateCookieName: string;
   logger: Logger;
+  resultCookieName?: string;
 }
 
 export function handleOAuthCallbackError({
   error,
   redirectUrl,
-  response,
   stateCookieName,
   logger,
+  resultCookieName,
 }: ErrorHandlerParams): NextResponse {
   logger.error("Error in OAuth linking callback:", { error });
   const errorMessage = error instanceof Error ? error.message : "Unknown error";
 
   redirectUrl.searchParams.set("error", "link_failed");
   redirectUrl.searchParams.set("error_description", errorMessage);
+  const response = NextResponse.redirect(redirectUrl);
   response.cookies.delete(stateCookieName);
-  return NextResponse.redirect(redirectUrl, { headers: response.headers });
+  if (resultCookieName) {
+    response.cookies.delete(resultCookieName);
+  }
+  return response;
 }
diff --git a/apps/web/utils/oauth/state.ts b/apps/web/utils/oauth/state.ts
index 05f3d56761..4ba6c3862e 100644
--- a/apps/web/utils/oauth/state.ts
+++ b/apps/web/utils/oauth/state.ts
@@ -47,3 +47,49 @@ export const getMcpPkceCookieName = (integration: IntegrationKey) =>
 
 export const getMcpOAuthStateType = (integration: IntegrationKey) =>
   `${integration}-mcp`;
+
+export interface OAuthStateResultCookieValue {
+  state: string;
+  params: Record<string, string>;
+}
+
+export function encodeOAuthStateResultCookie(
+  value: OAuthStateResultCookieValue,
+): string {
+  return Buffer.from(JSON.stringify(value)).toString("base64url");
+}
+
+export function parseOAuthStateResultCookie(
+  cookieValue: string | undefined,
+): OAuthStateResultCookieValue | null {
+  if (!cookieValue) {
+    return null;
+  }
+
+  try {
+    const parsed = JSON.parse(
+      Buffer.from(cookieValue, "base64url").toString("utf8"),
+    );
+
+    if (
+      !parsed ||
+      typeof parsed !== "object" ||
+      typeof parsed.state !== "string" ||
+      typeof parsed.params !== "object" ||
+      Array.isArray(parsed.params)
+    ) {
+      return null;
+    }
+
+    const params: Record<string, string> = {};
+    for (const [key, value] of Object.entries(parsed.params)) {
+      if (typeof key === "string" && typeof value === "string") {
+        params[key] = value;
+      }
+    }
+
+    return { state: parsed.state, params };
+  } catch {
+    return null;
+  }
+}
diff --git a/apps/web/utils/outlook/constants.ts b/apps/web/utils/outlook/constants.ts
index 9755f8d266..dc1f018993 100644
--- a/apps/web/utils/outlook/constants.ts
+++ b/apps/web/utils/outlook/constants.ts
@@ -1 +1,3 @@
 export const OUTLOOK_LINKING_STATE_COOKIE_NAME = "outlook_linking_state";
+export const OUTLOOK_LINKING_STATE_RESULT_COOKIE_NAME =
+  "outlook_linking_state_result";
diff --git a/version.txt b/version.txt
index a1109b5970..355aecc0ea 100644
--- a/version.txt
+++ b/version.txt
@@ -1 +1 @@
-v2.19.2
+v2.19.3