diff --git a/AGENTS.md b/AGENTS.md
index 08944062d..beb29caf5 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -31,7 +31,11 @@ inspector/
 │   ├── auth/                           # OAuth: providers, discovery, OAuthStorage + persist backends;
 │   │                                   #   mid-session recovery (challenge.ts WWW-Authenticate
 │   │                                   #   parsing, scopes.ts SEP-2350 scope union, oauthUx.ts
-│   │                                   #   shared copy, mcpAuth.ts force-reauthorization)
+│   │                                   #   shared copy, mcpAuth.ts force-reauthorization,
+│   │                                   #   issuerBinding.ts SEP-2352 callback-leg failure
+│   │                                   #   classification — separates a recoverable
+│   │                                   #   "lost authorization state" from a genuine
+│   │                                   #   cross-AS issuer mismatch — #1808)
 │   │   ├── browser/                    # Browser-side OAuth (sessionStorage, BrowserNavigation)
 │   │   ├── node/                       # Node-side OAuth (NodeOAuthStorage, OAuthCallbackServer,
 │   │   │                               #   runner-interactive-oauth loopback callback flow)
diff --git a/clients/web/src/App.test.tsx b/clients/web/src/App.test.tsx
index e8534fe36..0869d0d5d 100644
--- a/clients/web/src/App.test.tsx
+++ b/clients/web/src/App.test.tsx
@@ -1,5 +1,9 @@
 import { describe, it, expect, beforeEach, afterEach, vi } from "vitest";
-import { ProtocolErrorCode, ProtocolError } from "@modelcontextprotocol/client";
+import {
+  ProtocolErrorCode,
+  ProtocolError,
+  AuthorizationServerMismatchError,
+} from "@modelcontextprotocol/client";
 import { UrlElicitationLoopError } from "@inspector/core/mcp/urlElicitation.js";
 import { ToolCallCancelledError } from "@inspector/core/mcp/toolCallCancelledError.js";
 import {
@@ -47,6 +51,9 @@ vi.mock("@inspector/core/mcp/index.js", async (importOriginal) => {
   // When set, the next `connect()` rejects with this value (one-shot), so a test
   // can exercise the handshake-failure path. Cleared after it fires.
   let nextConnectRejection: unknown = null;
+  // Same one-shot arming for the `/oauth/callback` token exchange, so a test can
+  // exercise the callback-leg failure paths (#1808).
+  let nextResumeRejection: unknown = null;
   class FakeInspectorClient extends EventTarget {
     connect = vi.fn(() => {
       if (nextConnectRejection !== null) {
@@ -93,8 +100,16 @@ vi.mock("@inspector/core/mcp/index.js", async (importOriginal) => {
     getRoots = vi.fn().mockReturnValue([]);
     setRoots = vi.fn().mockResolvedValue(undefined);
     setServerSettings = vi.fn();
-    resumeAfterOAuth = vi.fn().mockResolvedValue(undefined);
+    resumeAfterOAuth = vi.fn(() => {
+      if (nextResumeRejection !== null) {
+        const err = nextResumeRejection;
+        nextResumeRejection = null;
+        return Promise.reject(err);
+      }
+      return Promise.resolve(undefined);
+    });
     checkAuthChallengeSatisfied = vi.fn().mockResolvedValue(true);
+    clearOAuthTokens = vi.fn().mockResolvedValue(undefined);
   }
   const instances: FakeInspectorClient[] = [];
   return {
@@ -110,6 +125,10 @@ vi.mock("@inspector/core/mcp/index.js", async (importOriginal) => {
     __rejectNextConnect: (err: unknown) => {
       nextConnectRejection = err;
     },
+    // Test-only: arm the next resumeAfterOAuth() to reject (callback-leg failure).
+    __rejectNextResumeAfterOAuth: (err: unknown) => {
+      nextResumeRejection = err;
+    },
   };
 });
 
@@ -563,9 +582,11 @@ import { useManagedRequestorTasks } from "@inspector/core/react/useManagedReques
 import { useMessageLog } from "@inspector/core/react/useMessageLog.js";
 import { useInspectorClient } from "@inspector/core/react/useInspectorClient.js";
 import { useSettingsDraft } from "@inspector/core/react/useSettingsDraft.js";
+import { useServers } from "@inspector/core/react/useServers.js";
 import type {
   InspectorServerSettings,
   MessageEntry,
+  ServerEntry,
 } from "@inspector/core/mcp/types.js";
 
 // Default useInspectorClient return — capabilities empty (no task tool calls).
@@ -590,6 +611,12 @@ const rejectNextConnect = (
   McpIndex as unknown as { __rejectNextConnect: (err: unknown) => void }
 ).__rejectNextConnect;
 
+const rejectNextResumeAfterOAuth = (
+  McpIndex as unknown as {
+    __rejectNextResumeAfterOAuth: (err: unknown) => void;
+  }
+).__rejectNextResumeAfterOAuth;
+
 const fetchLogInstances = (
   FetchLogModule as unknown as { __fetchLogInstances: EventTarget[] }
 ).__fetchLogInstances;
@@ -2154,6 +2181,159 @@ describe("App OAuth resume lifecycle", () => {
   });
 });
 
+// A callback that lands without recorded SEP-2352 discovery state used to
+// dead-end with the SDK's raw `AuthorizationServerMismatchError` text. It now
+// raises an explicit recovery affordance — but only for that case; a genuine
+// cross-authorization-server mismatch stays a security error. See #1808.
+describe("App OAuth callback issuer-binding failures (#1808)", () => {
+  const storage = new Map<string, string>();
+  const HTTP_SERVER: ServerEntry = {
+    id: "A",
+    name: "PlotRocket",
+    config: { type: "streamable-http", url: "https://mcp.example.com/mcp" },
+    connection: { status: "disconnected" },
+  };
+  const STDIO_SERVER: ServerEntry = {
+    id: "A",
+    name: "PlotRocket",
+    config: { type: "stdio", command: "node" },
+    connection: { status: "disconnected" },
+  };
+
+  /** Full `useServers` shape so the override typechecks like the real hook. */
+  const useServersResult = (
+    servers: ServerEntry[],
+  ): ReturnType<typeof useServers> => ({
+    servers,
+    loading: false,
+    error: undefined,
+    refresh: vi.fn().mockResolvedValue(undefined),
+    addServer: vi.fn().mockResolvedValue(undefined),
+    updateServer: vi.fn().mockResolvedValue(undefined),
+    updateServerSettings: updateServerSettingsSpy,
+    removeServer: vi.fn().mockResolvedValue(undefined),
+    reorderServers: vi.fn().mockResolvedValue(undefined),
+    importSource: vi.fn().mockResolvedValue({ servers: {} }),
+  });
+
+  // A real SDK error, not a look-alike: the SDK's `mcpBrand` is static, so a
+  // fabricated instance-branded object would exercise a shape that cannot occur.
+  const mismatchError = (recordedIssuer: string): Error =>
+    new AuthorizationServerMismatchError(
+      recordedIssuer,
+      "https://as.example.com",
+    );
+
+  const renderCallbackWithFailure = (err: Error) => {
+    writeOAuthResumeSnapshot({
+      version: 1,
+      serverId: "A",
+      activeTab: "Tools",
+      authKind: "reauth",
+      tabUi: {},
+    });
+    window.history.replaceState({}, "", `${OAUTH_CALLBACK_PATH}?code=test`);
+    rejectNextResumeAfterOAuth(err);
+    renderWithMantine(<App />);
+  };
+
+  beforeEach(() => {
+    clientInstances.length = 0;
+    storage.clear();
+    notificationsMock.show.mockClear();
+    vi.mocked(useInspectorClient).mockReturnValue({
+      ...DEFAULT_USE_INSPECTOR_CLIENT,
+      status: "disconnected",
+    });
+    vi.mocked(useServers).mockReturnValue(useServersResult([HTTP_SERVER]));
+    vi.stubGlobal("sessionStorage", {
+      getItem: (key: string) => storage.get(key) ?? null,
+      setItem: (key: string, value: string) => {
+        storage.set(key, value);
+      },
+      removeItem: (key: string) => {
+        storage.delete(key);
+      },
+    });
+    window.history.replaceState({}, "", "/");
+  });
+
+  afterEach(() => {
+    vi.unstubAllGlobals();
+    vi.mocked(useInspectorClient).mockReturnValue(DEFAULT_USE_INSPECTOR_CLIENT);
+    vi.mocked(useServers).mockReturnValue(useServersResult([STDIO_SERVER]));
+    window.history.replaceState({}, "", "/");
+  });
+
+  it("offers an explicit re-authorize affordance when the recorded state was lost", async () => {
+    renderCallbackWithFailure(
+      mismatchError(
+        "discoveryState was not available on the callback leg; ensure your provider persists discoveryState alongside codeVerifier",
+      ),
+    );
+
+    expect(
+      await screen.findByText("Authorization state was lost"),
+    ).toBeInTheDocument();
+    expect(
+      screen.getByRole("button", { name: "Authorize again" }),
+    ).toBeInTheDocument();
+    // The raw SDK wording never reaches the user.
+    expect(screen.queryByText(/discoveryState/)).not.toBeInTheDocument();
+    expect(screen.queryByText("Re-authentication required")).toBeNull();
+  });
+
+  it("clears the stale OAuth state and reconnects when the affordance is used", async () => {
+    const user = userEvent.setup();
+    renderCallbackWithFailure(
+      mismatchError("discoveryState was not available on the callback leg"),
+    );
+
+    const button = await screen.findByRole("button", {
+      name: "Authorize again",
+    });
+    await waitFor(() => expect(clientInstances).toHaveLength(1));
+    const callbackClient = clientInstances[0] as unknown as {
+      clearOAuthTokens: ReturnType<typeof vi.fn>;
+    };
+
+    await user.click(button);
+
+    await waitFor(() =>
+      expect(callbackClient.clearOAuthTokens).toHaveBeenCalled(),
+    );
+    // A fresh client is built for the retry connect.
+    await waitFor(() => expect(clientInstances.length).toBeGreaterThan(1));
+    expect(screen.queryByText("Authorization state was lost")).toBeNull();
+  });
+
+  it("treats a genuine issuer mismatch as a security error with no recovery button", async () => {
+    renderCallbackWithFailure(mismatchError("https://old.example.com"));
+
+    await waitFor(() =>
+      expect(notificationsMock.show).toHaveBeenCalledWith(
+        expect.objectContaining({
+          title: "Authorization server mismatch",
+          color: "red",
+        }),
+      ),
+    );
+    expect(screen.queryByText("Authorization state was lost")).toBeNull();
+    expect(
+      screen.queryByRole("button", { name: "Authorize again" }),
+    ).toBeNull();
+  });
+
+  it("falls back to the generic re-auth banner for an unrelated callback failure", async () => {
+    renderCallbackWithFailure(new Error("token endpoint exploded"));
+
+    expect(
+      await screen.findByText("Re-authentication required"),
+    ).toBeInTheDocument();
+    expect(screen.queryByText("Authorization state was lost")).toBeNull();
+  });
+});
+
 describe("App paginated list pagination toggle (#1721)", () => {
   beforeEach(() => {
     clientInstances.length = 0;
diff --git a/clients/web/src/App.tsx b/clients/web/src/App.tsx
index aa46f6518..6d162c7bd 100644
--- a/clients/web/src/App.tsx
+++ b/clients/web/src/App.tsx
@@ -197,12 +197,15 @@ import { clearServerOAuthState } from "./lib/clearServerOAuthState";
 import {
   authRecoveryRestoredMessage,
   isReAuthBannerReason,
+  issuerBindingFailureCopy,
+  lostAuthorizationStateActionLabel,
   oauthPreRedirectToastCopy,
   oauthResumeAbandonedMessage,
   reAuthBannerMessage,
   type OAuthPreRedirectContext,
   type OAuthRecoverySource,
 } from "./utils/oauthUx";
+import { findIssuerBindingFailure } from "@inspector/core/auth/issuerBinding.js";
 import {
   isBrowserTabVisible,
   onBrowserTabVisible,
@@ -879,6 +882,20 @@ function App() {
   const [reAuthBanner, setReAuthBanner] = useState<{
     serverId: string;
     message: string;
+    /**
+     * `lost_authorization_state` marks the SEP-2352 recovery case (#1808): the
+     * callback arrived with no recorded discovery state, so the banner offers
+     * "Authorize again", which drops the stale/partial OAuth state before
+     * starting a fresh authorization.
+     */
+    kind?: "lost_authorization_state";
+    /**
+     * Resolved at the point the banner is raised so `issuerBindingFailureCopy`
+     * stays the single source of the `kind → copy` mapping; both fall back to
+     * `ReAuthBanner`'s own defaults when absent.
+     */
+    title?: string;
+    actionLabel?: string;
   } | null>(null);
   const [pendingReauth, setPendingReauth] = useState<PendingReauth | null>(
     null,
@@ -2559,6 +2576,37 @@ function App() {
           });
           return;
         }
+        // SEP-2352 issuer binding (#1808). Two very different failures share
+        // one SDK error class, so classify before falling through to the
+        // generic re-auth banner (whose detail line would otherwise be the raw
+        // "AuthorizationServerMismatchError" text):
+        //  - no discovery state was recorded → recoverable bookkeeping loss,
+        //    surface the "Authorize again" affordance;
+        //  - a *different* issuer answered the callback → security signal, so
+        //    no one-click recovery is offered.
+        const issuerBindingFailure = findIssuerBindingFailure(err);
+        if (issuerBindingFailure) {
+          const copy = issuerBindingFailureCopy(issuerBindingFailure, {
+            serverName: server.name,
+          });
+          if (issuerBindingFailure.kind === "lost_authorization_state") {
+            setReAuthBanner({
+              serverId: server.id,
+              message: copy.message,
+              kind: "lost_authorization_state",
+              title: copy.title,
+              actionLabel: lostAuthorizationStateActionLabel(),
+            });
+          } else {
+            notifications.show({
+              title: copy.title,
+              message: copy.message,
+              color: "red",
+              autoClose: false,
+            });
+          }
+          return;
+        }
         queueMicrotask(() => {
           showReAuthBanner(server.id, err instanceof Error ? err : String(err));
         });
@@ -2839,8 +2887,45 @@ function App() {
   const onReauthenticateFromBanner = useCallback(() => {
     if (!reAuthBanner) return;
     const serverId = reAuthBanner.serverId;
+    const bannerKind = reAuthBanner.kind;
     setReAuthBanner(null);
 
+    // Lost-authorization-state recovery (#1808). The stale half of the flow
+    // (code verifier without discovery state, possibly a stale registration)
+    // would make a plain retry fail the same way, so drop the persisted OAuth
+    // state for this server first, then start a fresh authorization. This
+    // banner is only raised from the `/oauth/callback` failure path, where the
+    // session never reached "connected", so connecting is always the right
+    // toggle direction here.
+    if (bannerKind === "lost_authorization_state") {
+      void (async () => {
+        const server = serversRef.current.find((s) => s.id === serverId);
+        if (server) {
+          try {
+            await clearServerOAuthState({
+              config: server.config,
+              inspectorClient:
+                serverId === activeServerId ? inspectorClient : null,
+              isActiveConnection: serverId === activeServerId,
+              oauthStorage: webOAuthStorage,
+            });
+          } catch (err) {
+            notifications.show({
+              title: "Could not clear the stored authorization state",
+              message: err instanceof Error ? err.message : String(err),
+              color: "red",
+              // The banner is already dismissed and the flow is dead, so this
+              // is the only remaining explanation — don't time it out.
+              autoClose: false,
+            });
+            return;
+          }
+        }
+        await onToggleConnection(serverId);
+      })();
+      return;
+    }
+
     if (
       serverId === activeServerId &&
       connectionStatus === "connected" &&
@@ -2888,6 +2973,7 @@ function App() {
     servers,
     prepareOAuthRedirect,
     onToggleConnection,
+    webOAuthStorage,
   ]);
 
   // --- Action handlers that route directly to the InspectorClient. ---
@@ -4259,6 +4345,8 @@ function App() {
           <ReAuthBannerBar>
             <ReAuthBanner
               message={reAuthBanner.message}
+              title={reAuthBanner.title}
+              actionLabel={reAuthBanner.actionLabel}
               onReauthenticate={onReauthenticateFromBanner}
               onDismiss={() => setReAuthBanner(null)}
             />
diff --git a/clients/web/src/components/groups/ReAuthBanner/ReAuthBanner.stories.tsx b/clients/web/src/components/groups/ReAuthBanner/ReAuthBanner.stories.tsx
new file mode 100644
index 000000000..f5cbbd1c2
--- /dev/null
+++ b/clients/web/src/components/groups/ReAuthBanner/ReAuthBanner.stories.tsx
@@ -0,0 +1,44 @@
+import type { Meta, StoryObj } from "@storybook/react-vite";
+import { fn } from "storybook/test";
+import { ReAuthBanner } from "./ReAuthBanner";
+import {
+  lostAuthorizationStateActionLabel,
+  lostAuthorizationStateMessage,
+  lostAuthorizationStateTitle,
+  reAuthBannerMessage,
+} from "../../../utils/oauthUx";
+
+const meta: Meta<typeof ReAuthBanner> = {
+  title: "Groups/ReAuthBanner",
+  component: ReAuthBanner,
+  args: {
+    onReauthenticate: fn(),
+    onDismiss: fn(),
+  },
+};
+
+export default meta;
+type Story = StoryObj<typeof ReAuthBanner>;
+
+/** Degraded session: the stored token no longer works. */
+export const SessionNeedsAttention: Story = {
+  args: {
+    message: reAuthBannerMessage({
+      serverName: "PlotRocket",
+      detail: "Token expired.",
+    }),
+  },
+};
+
+/**
+ * SEP-2352 callback leg arrived with no recorded discovery state (#1808).
+ * Explains the loss in plain language and offers a one-click fresh
+ * authorization (which clears the stale state first).
+ */
+export const AuthorizationStateLost: Story = {
+  args: {
+    title: lostAuthorizationStateTitle(),
+    actionLabel: lostAuthorizationStateActionLabel(),
+    message: lostAuthorizationStateMessage({ serverName: "PlotRocket" }),
+  },
+};
diff --git a/clients/web/src/components/groups/ReAuthBanner/ReAuthBanner.test.tsx b/clients/web/src/components/groups/ReAuthBanner/ReAuthBanner.test.tsx
index 974dffb11..7f34e5fbe 100644
--- a/clients/web/src/components/groups/ReAuthBanner/ReAuthBanner.test.tsx
+++ b/clients/web/src/components/groups/ReAuthBanner/ReAuthBanner.test.tsx
@@ -27,4 +27,27 @@ describe("ReAuthBanner", () => {
     await user.click(closeButton);
     expect(onDismiss).toHaveBeenCalledOnce();
   });
+
+  it("renders a custom title and action label (lost-state recovery, #1808)", async () => {
+    const user = userEvent.setup();
+    const onReauthenticate = vi.fn();
+
+    renderWithMantine(
+      <ReAuthBanner
+        message="The stored authorization state was lost."
+        title="Authorization state was lost"
+        actionLabel="Authorize again"
+        onReauthenticate={onReauthenticate}
+        onDismiss={vi.fn()}
+      />,
+    );
+
+    expect(
+      screen.getByText("Authorization state was lost"),
+    ).toBeInTheDocument();
+    expect(screen.queryByText("Re-authentication required")).toBeNull();
+
+    await user.click(screen.getByRole("button", { name: "Authorize again" }));
+    expect(onReauthenticate).toHaveBeenCalledOnce();
+  });
 });
diff --git a/clients/web/src/components/groups/ReAuthBanner/ReAuthBanner.tsx b/clients/web/src/components/groups/ReAuthBanner/ReAuthBanner.tsx
index 38bd9bb44..817e19c30 100644
--- a/clients/web/src/components/groups/ReAuthBanner/ReAuthBanner.tsx
+++ b/clients/web/src/components/groups/ReAuthBanner/ReAuthBanner.tsx
@@ -1,16 +1,27 @@
 import { Alert, Button, Group, Text } from "@mantine/core";
 
+export const DEFAULT_REAUTH_BANNER_TITLE = "Re-authentication required";
+export const DEFAULT_REAUTH_BANNER_ACTION_LABEL = "Re-authenticate";
+
 export interface ReAuthBannerProps {
   message: string;
+  /** Heading; defaults to {@link DEFAULT_REAUTH_BANNER_TITLE}. */
+  title?: string;
+  /** Action button label; defaults to {@link DEFAULT_REAUTH_BANNER_ACTION_LABEL}. */
+  actionLabel?: string;
   onReauthenticate: () => void;
   onDismiss: () => void;
 }
 
+// `title` is intentionally not baked in here: the component always passes a
+// resolved `title`, whose parameter default is the single source of truth.
 const ReAuthAlert = Alert.withProps({
   color: "red",
   variant: "reauth",
-  title: "Re-authentication required",
   withCloseButton: true,
+  // Mantine's close button renders icon-only; without a label it has no
+  // accessible name (axe `button-name`).
+  closeButtonLabel: "Dismiss",
 });
 
 const BannerRow = Group.withProps({
@@ -32,14 +43,16 @@ const ReAuthButton = Button.withProps({
 
 export function ReAuthBanner({
   message,
+  title = DEFAULT_REAUTH_BANNER_TITLE,
+  actionLabel = DEFAULT_REAUTH_BANNER_ACTION_LABEL,
   onReauthenticate,
   onDismiss,
 }: ReAuthBannerProps) {
   return (
-    <ReAuthAlert onClose={onDismiss}>
+    <ReAuthAlert title={title} onClose={onDismiss}>
       <BannerRow>
         <MessageText>{message}</MessageText>
-        <ReAuthButton onClick={onReauthenticate}>Re-authenticate</ReAuthButton>
+        <ReAuthButton onClick={onReauthenticate}>{actionLabel}</ReAuthButton>
       </BannerRow>
     </ReAuthAlert>
   );
diff --git a/clients/web/src/test/core/auth/issuerBinding.test.ts b/clients/web/src/test/core/auth/issuerBinding.test.ts
new file mode 100644
index 000000000..5ebbe8552
--- /dev/null
+++ b/clients/web/src/test/core/auth/issuerBinding.test.ts
@@ -0,0 +1,191 @@
+import { describe, it, expect } from "vitest";
+import { AuthorizationServerMismatchError } from "@modelcontextprotocol/client";
+import { findIssuerBindingFailure } from "@inspector/core/auth/issuerBinding.js";
+
+/**
+ * Builds a **real** SDK `AuthorizationServerMismatchError`.
+ *
+ * This must stay the real class rather than a look-alike plain object. The SDK
+ * declares `mcpBrand` in a `static {}` block, so it sits on the constructor and
+ * is invisible from the instance; a fabricated fixture carrying an own
+ * `mcpBrand` property would pass against a classifier that reads
+ * `err.mcpBrand` — which no real thrown error would ever satisfy.
+ */
+function mismatchError(
+  recordedIssuer: string,
+  currentIssuer: string,
+): AuthorizationServerMismatchError {
+  return new AuthorizationServerMismatchError(recordedIssuer, currentIssuer);
+}
+
+/**
+ * Documents why the classifier must not test `err.mcpBrand`: the SDK declares
+ * that brand `static`, so it lives on the class and instances never carry it.
+ * If a future SDK moves it onto the instance, this fails and the note in
+ * `issuerBinding.ts` can be revisited.
+ */
+describe("SDK brand placement", () => {
+  it("keeps `mcpBrand` on the class, not the instance", () => {
+    const err = mismatchError("https://a.example.com", "https://b.example.com");
+    expect("mcpBrand" in err).toBe(false);
+    // The brand is defined at runtime via `Object.defineProperty` in a static
+    // block, so it is absent from the SDK's published type declarations — hence
+    // the cast to read it.
+    const brandOnClass = (
+      AuthorizationServerMismatchError as { mcpBrand?: unknown }
+    ).mcpBrand;
+    expect(brandOnClass).toBe("mcp.AuthorizationServerMismatchError");
+  });
+
+  it("matches via `isInstance`, which survives a foreign SDK copy", () => {
+    const err = mismatchError("https://a.example.com", "https://b.example.com");
+    expect(AuthorizationServerMismatchError.isInstance(err)).toBe(true);
+  });
+});
+
+/**
+ * An error that crossed a serialization boundary: neither the SDK's
+ * `Symbol.for()`-keyed brand set nor the prototype survives, but `name` does.
+ * This is the fallback arm of the classifier's predicate.
+ */
+function serializedMismatchError(
+  recordedIssuer: string,
+  currentIssuer: string,
+): Error {
+  const err = new Error(
+    "Authorization server changed between redirect and callback",
+  );
+  err.name = "AuthorizationServerMismatchError";
+  Object.assign(err, { recordedIssuer, currentIssuer });
+  return err;
+}
+
+const MISSING_STATE_SENTINEL =
+  "discoveryState was not available on the callback leg; ensure your provider persists discoveryState alongside codeVerifier";
+
+describe("findIssuerBindingFailure", () => {
+  it("classifies the missing-discovery-state sentinel as recoverable", () => {
+    const failure = findIssuerBindingFailure(
+      mismatchError(MISSING_STATE_SENTINEL, "https://as.example.com"),
+    );
+    expect(failure).toEqual({
+      kind: "lost_authorization_state",
+      currentIssuer: "https://as.example.com",
+    });
+  });
+
+  it("classifies non-URL prose in the recorded slot as recoverable", () => {
+    const failure = findIssuerBindingFailure(
+      mismatchError("nothing was recorded, sorry", "https://as.example.com"),
+    );
+    expect(failure?.kind).toBe("lost_authorization_state");
+  });
+
+  it("classifies a non-http(s) URL in the recorded slot as recoverable", () => {
+    const failure = findIssuerBindingFailure(
+      mismatchError("urn:example:not-an-issuer", "https://as.example.com"),
+    );
+    expect(failure?.kind).toBe("lost_authorization_state");
+  });
+
+  it("classifies two real issuers as a genuine mismatch", () => {
+    const failure = findIssuerBindingFailure(
+      mismatchError("https://old.example.com", "https://evil.example.com"),
+    );
+    expect(failure).toEqual({
+      kind: "issuer_mismatch",
+      recordedIssuer: "https://old.example.com",
+      currentIssuer: "https://evil.example.com",
+    });
+  });
+
+  it("accepts a plain http issuer as a genuine mismatch", () => {
+    const failure = findIssuerBindingFailure(
+      mismatchError("http://localhost:9000", "http://localhost:9001"),
+    );
+    expect(failure?.kind).toBe("issuer_mismatch");
+  });
+
+  it("walks the `cause` chain", () => {
+    const wrapped = new Error("negotiation failed", {
+      cause: mismatchError(MISSING_STATE_SENTINEL, "https://as.example.com"),
+    });
+    expect(findIssuerBindingFailure(wrapped)?.kind).toBe(
+      "lost_authorization_state",
+    );
+  });
+
+  it("walks `data.cause` (SdkError wrapper shape)", () => {
+    const wrapped = Object.assign(new Error("ERA_NEGOTIATION_FAILED"), {
+      data: {
+        cause: mismatchError("https://a.example.com", "https://b.example.com"),
+      },
+    });
+    expect(findIssuerBindingFailure(wrapped)?.kind).toBe("issuer_mismatch");
+  });
+
+  it("walks multiple levels", () => {
+    const wrapped = new Error("outer", {
+      cause: new Error("inner", {
+        cause: mismatchError(MISSING_STATE_SENTINEL, "https://as.example.com"),
+      }),
+    });
+    expect(findIssuerBindingFailure(wrapped)?.kind).toBe(
+      "lost_authorization_state",
+    );
+  });
+
+  it("ignores a non-object `data`", () => {
+    const wrapped = Object.assign(new Error("outer"), { data: "nope" });
+    expect(findIssuerBindingFailure(wrapped)).toBeUndefined();
+  });
+
+  it("ignores a null `data`", () => {
+    const wrapped = Object.assign(new Error("outer"), { data: null });
+    expect(findIssuerBindingFailure(wrapped)).toBeUndefined();
+  });
+
+  it("terminates on a cyclic cause chain", () => {
+    const outer: { cause?: unknown } = new Error("outer");
+    outer.cause = outer;
+    expect(findIssuerBindingFailure(outer)).toBeUndefined();
+  });
+
+  it("returns undefined for unrelated errors and non-objects", () => {
+    expect(findIssuerBindingFailure(new Error("boom"))).toBeUndefined();
+    expect(findIssuerBindingFailure(undefined)).toBeUndefined();
+    expect(findIssuerBindingFailure(null)).toBeUndefined();
+    expect(findIssuerBindingFailure("string")).toBeUndefined();
+  });
+
+  it("ignores a matching error missing the issuer fields", () => {
+    const err = new Error("half-shaped");
+    err.name = "AuthorizationServerMismatchError";
+    expect(findIssuerBindingFailure(err)).toBeUndefined();
+
+    const halfShaped = new Error("only recorded");
+    halfShaped.name = "AuthorizationServerMismatchError";
+    Object.assign(halfShaped, { recordedIssuer: "https://as.example.com" });
+    expect(findIssuerBindingFailure(halfShaped)).toBeUndefined();
+  });
+
+  it("classifies a serialized error via the `name` fallback", () => {
+    expect(
+      findIssuerBindingFailure(
+        serializedMismatchError(
+          MISSING_STATE_SENTINEL,
+          "https://as.example.com",
+        ),
+      )?.kind,
+    ).toBe("lost_authorization_state");
+  });
+
+  it("ignores a different SDK error carrying the same fields", () => {
+    const err = Object.assign(new Error("other"), {
+      recordedIssuer: "https://a.example.com",
+      currentIssuer: "https://b.example.com",
+    });
+    err.name = "IssuerMismatchError";
+    expect(findIssuerBindingFailure(err)).toBeUndefined();
+  });
+});
diff --git a/clients/web/src/test/core/auth/oauthUx.test.ts b/clients/web/src/test/core/auth/oauthUx.test.ts
index f209c9ab2..e11bb990f 100644
--- a/clients/web/src/test/core/auth/oauthUx.test.ts
+++ b/clients/web/src/test/core/auth/oauthUx.test.ts
@@ -19,6 +19,12 @@ import {
   stepUpInsufficientScopeMessage,
   stepUpModalTitle,
   stepUpAuthorizeActionLabel,
+  issuerBindingFailureCopy,
+  issuerMismatchMessage,
+  issuerMismatchTitle,
+  lostAuthorizationStateActionLabel,
+  lostAuthorizationStateMessage,
+  lostAuthorizationStateTitle,
 } from "@inspector/core/auth/oauthUx.js";
 import type { AuthChallenge } from "@inspector/core/auth/challenge.js";
 
@@ -334,3 +340,79 @@ describe("oauthUx re-auth banner", () => {
     expect(reAuthBannerMessage({})).toBe("Authentication needs attention.");
   });
 });
+
+describe("oauthUx issuer-binding copy", () => {
+  it("explains lost authorization state in plain language, with the server name", () => {
+    const withName = lostAuthorizationStateMessage({ serverName: "svc" });
+    expect(withName).toContain('"svc"');
+    expect(withName).toContain("was lost");
+    expect(withName).toContain("Authorize again");
+    // Never leaks the SDK's security-flavoured wording.
+    expect(withName).not.toContain("discoveryState");
+    expect(withName).not.toContain("AuthorizationServerMismatchError");
+    expect(lostAuthorizationStateMessage()).toContain("this server");
+    expect(lostAuthorizationStateTitle()).toBe("Authorization state was lost");
+    expect(lostAuthorizationStateActionLabel()).toBe("Authorize again");
+  });
+
+  it("names both issuers for a genuine mismatch and offers no retry nudge", () => {
+    const message = issuerMismatchMessage({
+      recordedIssuer: "https://old.example.com",
+      currentIssuer: "https://evil.example.com",
+      serverName: "svc",
+    });
+    expect(message).toContain('"svc"');
+    expect(message).toContain("https://old.example.com");
+    expect(message).toContain("https://evil.example.com");
+    expect(message).toContain("was not exchanged");
+    expect(message).not.toContain("Authorize again");
+    expect(
+      issuerMismatchMessage({
+        recordedIssuer: "https://old.example.com",
+        currentIssuer: "https://evil.example.com",
+      }),
+    ).toContain("this server");
+    expect(issuerMismatchTitle()).toBe("Authorization server mismatch");
+  });
+
+  it("bounds an overlong remote-supplied issuer in the mismatch copy", () => {
+    const overlong = `https://evil.example.com/${"a".repeat(400)}`;
+    const message = issuerMismatchMessage({
+      recordedIssuer: "https://old.example.com",
+      currentIssuer: overlong,
+    });
+    expect(message).not.toContain(overlong);
+    expect(message).toContain("…");
+    // The short issuer on the same call is passed through untouched.
+    expect(message).toContain("https://old.example.com");
+  });
+
+  it("issuerBindingFailureCopy dispatches on the failure kind", () => {
+    expect(
+      issuerBindingFailureCopy(
+        {
+          kind: "lost_authorization_state",
+          currentIssuer: "https://as.example.com",
+        },
+        { serverName: "svc" },
+      ),
+    ).toEqual({
+      title: lostAuthorizationStateTitle(),
+      message: lostAuthorizationStateMessage({ serverName: "svc" }),
+    });
+
+    expect(
+      issuerBindingFailureCopy({
+        kind: "issuer_mismatch",
+        recordedIssuer: "https://old.example.com",
+        currentIssuer: "https://evil.example.com",
+      }),
+    ).toEqual({
+      title: issuerMismatchTitle(),
+      message: issuerMismatchMessage({
+        recordedIssuer: "https://old.example.com",
+        currentIssuer: "https://evil.example.com",
+      }),
+    });
+  });
+});
diff --git a/clients/web/src/test/core/auth/runner-interactive-oauth.test.ts b/clients/web/src/test/core/auth/runner-interactive-oauth.test.ts
index d572e0bb7..b141c1cba 100644
--- a/clients/web/src/test/core/auth/runner-interactive-oauth.test.ts
+++ b/clients/web/src/test/core/auth/runner-interactive-oauth.test.ts
@@ -1,4 +1,5 @@
 import { describe, it, expect, vi, afterEach } from "vitest";
+import { AuthorizationServerMismatchError } from "@modelcontextprotocol/client";
 import {
   runRunnerInteractiveOAuth,
   type RunnerInteractiveOAuthClient,
@@ -249,6 +250,76 @@ describe("runRunnerInteractiveOAuth", () => {
     ).rejects.toThrow("token exchange failed");
   });
 
+  it("rewrites a lost-authorization-state callback failure into actionable copy (#1808)", async () => {
+    const redirectUrlProvider = { redirectUrl: "" };
+    // Real SDK error — its `mcpBrand` is static, so a fabricated
+    // instance-branded look-alike would not exercise the real shape.
+    const sdkError = new AuthorizationServerMismatchError(
+      "discoveryState was not available on the callback leg; ensure your provider persists discoveryState alongside codeVerifier",
+      "https://as.example",
+    );
+    const client = mockClient({
+      authenticate: vi.fn(async () => {
+        await simulateCallback(handlers.current);
+        return new URL("https://as.example/authorize");
+      }),
+      completeOAuthFlow: vi.fn(async () => {
+        throw sdkError;
+      }),
+    });
+
+    const failure = await runRunnerInteractiveOAuth({
+      client,
+      redirectUrlProvider,
+      callbackListen: {
+        hostname: "127.0.0.1",
+        port: 6276,
+        pathname: "/oauth/callback",
+      },
+      createCallbackServer: () => createMockCallbackServer(handlers),
+    }).catch((err: unknown) => err);
+
+    expect(failure).toBeInstanceOf(Error);
+    const message = (failure as Error).message;
+    expect(message).toContain("Authorization state was lost");
+    expect(message).toContain("Authorize again");
+    expect(message).not.toContain("discoveryState");
+    expect((failure as Error).cause).toBe(sdkError);
+  });
+
+  it("keeps the security wording for a genuine issuer mismatch (#1808)", async () => {
+    const redirectUrlProvider = { redirectUrl: "" };
+    const sdkError = new AuthorizationServerMismatchError(
+      "https://old.example",
+      "https://evil.example",
+    );
+    const client = mockClient({
+      authenticate: vi.fn(async () => {
+        await simulateCallback(handlers.current);
+        return new URL("https://as.example/authorize");
+      }),
+      completeOAuthFlow: vi.fn(async () => {
+        throw sdkError;
+      }),
+    });
+
+    const failure = await runRunnerInteractiveOAuth({
+      client,
+      redirectUrlProvider,
+      callbackListen: {
+        hostname: "127.0.0.1",
+        port: 6276,
+        pathname: "/oauth/callback",
+      },
+      createCallbackServer: () => createMockCallbackServer(handlers),
+    }).catch((err: unknown) => err);
+
+    const message = (failure as Error).message;
+    expect(message).toContain("Authorization server mismatch");
+    expect(message).toContain("https://evil.example");
+    expect(message).not.toContain("Authorize again");
+  });
+
   it("propagates OAuth callback errors from the authorization server", async () => {
     const redirectUrlProvider = { redirectUrl: "" };
     const client = mockClient({
diff --git a/clients/web/src/utils/oauthUx.ts b/clients/web/src/utils/oauthUx.ts
index 4485c48a4..ba86edf78 100644
--- a/clients/web/src/utils/oauthUx.ts
+++ b/clients/web/src/utils/oauthUx.ts
@@ -6,6 +6,12 @@ export {
   oauthResumeSuccessMessage,
   isReAuthBannerReason,
   reAuthBannerMessage,
+  issuerBindingFailureCopy,
+  lostAuthorizationStateActionLabel,
+  lostAuthorizationStateMessage,
+  lostAuthorizationStateTitle,
+  issuerMismatchMessage,
+  issuerMismatchTitle,
   type OAuthInteractiveAuthKind,
   type OAuthPreRedirectContext,
   type OAuthRecoverySource,
diff --git a/core/auth/index.ts b/core/auth/index.ts
index bf4a098f8..6086d7ac9 100644
--- a/core/auth/index.ts
+++ b/core/auth/index.ts
@@ -98,9 +98,20 @@ export {
   oauthPreRedirectToastCopy,
   isReAuthBannerReason,
   reAuthBannerMessage,
+  lostAuthorizationStateTitle,
+  lostAuthorizationStateMessage,
+  lostAuthorizationStateActionLabel,
+  issuerMismatchTitle,
+  issuerMismatchMessage,
+  issuerBindingFailureCopy,
   type OAuthInteractiveAuthKind,
 } from "./oauthUx.js";
 
+export {
+  findIssuerBindingFailure,
+  type IssuerBindingFailure,
+} from "./issuerBinding.js";
+
 // Discovery
 export { discoverScopes } from "./discovery.js";
 
diff --git a/core/auth/issuerBinding.ts b/core/auth/issuerBinding.ts
new file mode 100644
index 000000000..9314f17fa
--- /dev/null
+++ b/core/auth/issuerBinding.ts
@@ -0,0 +1,167 @@
+/**
+ * SEP-2352 issuer-binding failure classification.
+ *
+ * On the authorization-code callback leg the SDK compares the authorization
+ * server resolved by discovery against the one recorded in `discoveryState()`
+ * at redirect time, and throws `AuthorizationServerMismatchError` when the two
+ * cannot be reconciled. That single error class covers two very different
+ * situations:
+ *
+ * 1. **Lost authorization state** — no discovery state was recorded at all
+ *    (`recordedIssuer === undefined` inside the SDK). This is a *recoverable*
+ *    bookkeeping failure: the stored authorization state for the server was
+ *    dropped between the redirect and the callback (a new browser session, a
+ *    partially cleared store, a callback resumed in another tab). Nothing
+ *    suspicious happened — the user just has to authorize again.
+ * 2. **Genuine issuer mismatch** — a real issuer *was* recorded and the callback
+ *    resolved a different one. This is a security signal (RFC 7636: the
+ *    `authorization_code` and `code_verifier` are bound to the AS that minted
+ *    them; replaying them at another AS's token endpoint is a credential
+ *    exfiltration vector). It must never be papered over with a friendly
+ *    "just re-authorize" affordance.
+ *
+ * The SDK does not expose a discriminator, so we key off the shape of
+ * `recordedIssuer`: in the "lost state" case the SDK passes a human-readable
+ * sentence in the `recordedIssuer` slot ("discoveryState was not available on
+ * the callback leg; …"); a genuine mismatch always carries an absolute
+ * `http(s)` issuer URL there. We accept either signal — the sentinel phrase or
+ * "not a URL" — so a reworded SDK sentence still classifies correctly.
+ */
+
+import { AuthorizationServerMismatchError } from "@modelcontextprotocol/client";
+
+/** Phrase the SDK puts in the `recordedIssuer` slot when nothing was recorded. */
+const MISSING_DISCOVERY_STATE_PHRASE = "discoveryState was not available";
+
+/** Outcome of classifying a callback-leg issuer-binding failure. */
+export type IssuerBindingFailure =
+  | {
+      /** No discovery state was recorded — recoverable by authorizing again. */
+      kind: "lost_authorization_state";
+      /** Issuer resolved by discovery on the callback leg. */
+      currentIssuer: string;
+    }
+  | {
+      /** A different authorization server answered the callback — security signal. */
+      kind: "issuer_mismatch";
+      /** Issuer recorded at redirect time. */
+      recordedIssuer: string;
+      /** Issuer resolved by discovery on the callback leg. */
+      currentIssuer: string;
+    };
+
+interface AuthorizationServerMismatchShape {
+  recordedIssuer: string;
+  currentIssuer: string;
+}
+
+/**
+ * Recognize the SDK's `AuthorizationServerMismatchError`.
+ *
+ * Uses the SDK's own `isInstance` predicate, which is **cross-copy safe by
+ * construction**: the SDK stamps each instance with a brand set keyed by
+ * `Symbol.for("mcp.sdk.errorBrands")` and overrides `Symbol.hasInstance` to
+ * consult it, so an error thrown by a *different* bundled copy of the SDK still
+ * matches. (Note the brand constant itself is declared `static`, so it lives on
+ * the class and is never reachable as `err.mcpBrand` — checking that property on
+ * an instance always fails.)
+ *
+ * The `name` comparison is a deliberate fallback for a serialization boundary,
+ * where neither the brand set nor the prototype survives but `name` does.
+ */
+function isAuthorizationServerMismatchShape(
+  err: unknown,
+): err is AuthorizationServerMismatchShape {
+  if (err === null || typeof err !== "object") {
+    return false;
+  }
+  const candidate = err as {
+    recordedIssuer?: unknown;
+    currentIssuer?: unknown;
+    name?: unknown;
+  };
+  if (
+    typeof candidate.recordedIssuer !== "string" ||
+    typeof candidate.currentIssuer !== "string"
+  ) {
+    return false;
+  }
+  return (
+    AuthorizationServerMismatchError.isInstance(err) ||
+    candidate.name === "AuthorizationServerMismatchError"
+  );
+}
+
+/** True when `recordedIssuer` is the SDK's "nothing was recorded" placeholder. */
+function isMissingDiscoveryStatePlaceholder(recordedIssuer: string): boolean {
+  if (recordedIssuer.includes(MISSING_DISCOVERY_STATE_PHRASE)) {
+    return true;
+  }
+  // A genuine recorded issuer is always an absolute http(s) URL, so anything
+  // else in that slot is prose the SDK put there in place of an issuer.
+  try {
+    const url = new URL(recordedIssuer);
+    return url.protocol !== "http:" && url.protocol !== "https:";
+  } catch {
+    return true;
+  }
+}
+
+/**
+ * Find and classify a SEP-2352 issuer-binding failure anywhere in an error's
+ * `cause` / `data.cause` chain (era-negotiation and transport wrappers bury the
+ * original rejection, see `findNestedAuthError`).
+ */
+export function findIssuerBindingFailure(
+  err: unknown,
+): IssuerBindingFailure | undefined {
+  return findIssuerBindingFailureDeep(err, new Set());
+}
+
+function findIssuerBindingFailureDeep(
+  err: unknown,
+  seen: Set<unknown>,
+): IssuerBindingFailure | undefined {
+  if (err === null || typeof err !== "object" || seen.has(err)) {
+    return undefined;
+  }
+  seen.add(err);
+
+  if (isAuthorizationServerMismatchShape(err)) {
+    return classifyAuthorizationServerMismatch(err);
+  }
+
+  const nested = findIssuerBindingFailureDeep(
+    (err as { cause?: unknown }).cause,
+    seen,
+  );
+  if (nested) {
+    return nested;
+  }
+
+  const data = (err as { data?: unknown }).data;
+  if (data !== null && typeof data === "object") {
+    return findIssuerBindingFailureDeep(
+      (data as { cause?: unknown }).cause,
+      seen,
+    );
+  }
+
+  return undefined;
+}
+
+function classifyAuthorizationServerMismatch(
+  err: AuthorizationServerMismatchShape,
+): IssuerBindingFailure {
+  if (isMissingDiscoveryStatePlaceholder(err.recordedIssuer)) {
+    return {
+      kind: "lost_authorization_state",
+      currentIssuer: err.currentIssuer,
+    };
+  }
+  return {
+    kind: "issuer_mismatch",
+    recordedIssuer: err.recordedIssuer,
+    currentIssuer: err.currentIssuer,
+  };
+}
diff --git a/core/auth/node/runner-interactive-oauth.ts b/core/auth/node/runner-interactive-oauth.ts
index edbb394d0..ce0dd199e 100644
--- a/core/auth/node/runner-interactive-oauth.ts
+++ b/core/auth/node/runner-interactive-oauth.ts
@@ -1,4 +1,6 @@
 import type { AuthChallenge } from "../challenge.js";
+import { findIssuerBindingFailure } from "../issuerBinding.js";
+import { issuerBindingFailureCopy } from "../oauthUx.js";
 import {
   createOAuthCallbackServer,
   type OAuthCallbackServer,
@@ -40,6 +42,24 @@ export interface RunRunnerInteractiveOAuthOptions {
   callbackTimeoutMs?: number;
 }
 
+/**
+ * Replace an opaque SEP-2352 callback-leg failure with actionable copy (#1808).
+ *
+ * The runners have no banner to render, so their affordance is the message
+ * itself: it explains that the recorded authorization state was lost and that
+ * re-running authorization starts a fresh flow (the next `authenticate()`
+ * re-runs discovery and records new state). A *genuine* issuer mismatch gets
+ * the security-flavoured copy instead — never a "just try again" nudge.
+ */
+function toRunnerOAuthError(err: unknown): Error {
+  const failure = findIssuerBindingFailure(err);
+  if (failure) {
+    const copy = issuerBindingFailureCopy(failure);
+    return new Error(`${copy.title}. ${copy.message}`, { cause: err });
+  }
+  return err instanceof Error ? err : new Error(String(err));
+}
+
 /**
  * Run interactive OAuth for Node runners (TUI / CLI): loopback callback server,
  * browser redirect, authorization-code exchange via {@link completeOAuthFlow}.
@@ -70,7 +90,7 @@ export async function runRunnerInteractiveOAuth(
           await options.client.completeOAuthFlow(params.code, params.iss);
           flowResolve();
         } catch (err) {
-          flowReject(err instanceof Error ? err : new Error(String(err)));
+          flowReject(toRunnerOAuthError(err));
         }
       },
       onError: (params) => {
diff --git a/core/auth/oauthUx.ts b/core/auth/oauthUx.ts
index da2737223..184e5c5a6 100644
--- a/core/auth/oauthUx.ts
+++ b/core/auth/oauthUx.ts
@@ -1,4 +1,5 @@
 import type { AuthChallenge } from "./challenge.js";
+import type { IssuerBindingFailure } from "./issuerBinding.js";
 
 export type OAuthInteractiveAuthKind = "step_up" | "reauth";
 
@@ -224,6 +225,101 @@ export function isReAuthBannerReason(
   );
 }
 
+/** Banner/alert heading when the recorded authorization state was lost. */
+export function lostAuthorizationStateTitle(): string {
+  return "Authorization state was lost";
+}
+
+/**
+ * Plain-language explanation for a callback that arrived with no recorded
+ * discovery state (SEP-2352). Deliberately does not surface the SDK's
+ * `AuthorizationServerMismatchError` text — that wording reads like a security
+ * failure, and this case is ordinary bookkeeping loss.
+ */
+export function lostAuthorizationStateMessage(options?: {
+  serverName?: string;
+}): string {
+  const target = options?.serverName
+    ? `"${options.serverName}"`
+    : "this server";
+  return (
+    `The stored authorization state for ${target} was lost before the ` +
+    "authorization server sent you back, so the sign-in could not be " +
+    "completed. This usually means a new browser session, a different tab, or " +
+    "authorization state that was cleared while the flow was in progress. " +
+    "Authorize again to reconnect."
+  );
+}
+
+/** Action label for the lost-authorization-state recovery affordance. */
+export function lostAuthorizationStateActionLabel(): string {
+  return "Authorize again";
+}
+
+/** Heading for a genuine cross-authorization-server mismatch (a security signal). */
+export function issuerMismatchTitle(): string {
+  return "Authorization server mismatch";
+}
+
+/**
+ * Longest issuer we will echo back into user-facing copy.
+ *
+ * `currentIssuer` is remote-supplied (it comes from the configured server's AS
+ * metadata), so an overlong value could be used to abuse the notification
+ * layout. Rendering is escaped, so this is a presentation bound, not an
+ * injection defence.
+ */
+const MAX_DISPLAYED_ISSUER_LENGTH = 120;
+
+/** Bound an issuer for display, marking any truncation. */
+export function truncateIssuerForDisplay(issuer: string): string {
+  return issuer.length > MAX_DISPLAYED_ISSUER_LENGTH
+    ? `${issuer.slice(0, MAX_DISPLAYED_ISSUER_LENGTH)}…`
+    : issuer;
+}
+
+/**
+ * Copy for a genuine SEP-2352 issuer mismatch. This is *not* offered a
+ * one-click recovery: the authorization code and PKCE verifier are bound to the
+ * server that minted them, and a different server answering the callback is a
+ * credential-exfiltration signal the user must investigate.
+ */
+export function issuerMismatchMessage(options: {
+  recordedIssuer: string;
+  currentIssuer: string;
+  serverName?: string;
+}): string {
+  const target = options.serverName ? `"${options.serverName}"` : "this server";
+  return (
+    `Authorization for ${target} was stopped: the flow started at ` +
+    `${truncateIssuerForDisplay(options.recordedIssuer)} but the callback ` +
+    `resolved ${truncateIssuerForDisplay(options.currentIssuer)}. ` +
+    "The authorization code was not exchanged. " +
+    "Verify the server's authorization configuration before trying again."
+  );
+}
+
+/** Title + message for a callback-leg issuer-binding failure. */
+export function issuerBindingFailureCopy(
+  failure: IssuerBindingFailure,
+  options?: { serverName?: string },
+): { title: string; message: string } {
+  if (failure.kind === "lost_authorization_state") {
+    return {
+      title: lostAuthorizationStateTitle(),
+      message: lostAuthorizationStateMessage(options),
+    };
+  }
+  return {
+    title: issuerMismatchTitle(),
+    message: issuerMismatchMessage({
+      recordedIssuer: failure.recordedIssuer,
+      currentIssuer: failure.currentIssuer,
+      serverName: options?.serverName,
+    }),
+  };
+}
+
 export function reAuthBannerMessage(options: {
   serverName?: string;
   detail?: string;