chore(web): move App.tsx's module-level block into files (#2127)

Phase 0 of #2126. Lines 239-668 of clients/web/src/App.tsx were already at
module scope — helpers, formatters, constants, and the toast subcomponents,
none of which close over component state — so the whole block moves verbatim
into files. App.tsx drops from 5,303 to 4,892 lines with no behavior change.

Placement follows the lib-vs-utils rule in AGENTS.md: pure computation to
utils/, anything touching the environment to lib/.

EMPTY_SETTINGS and the two loose toast ids deliberately do NOT land in a new
top-level src/constants.ts, which the issue suggested: the web coverage
include is a whitelist naming components/hooks/theme/lib/utils/server, so a
module there would have fallen out of the >=90 gate silently. They go under
utils/ instead.

ReAuthBannerBar is in the block but not in the issue's table — it was added
after the issue was written (#2108). It moves to components/groups/ReAuthBanner/,
beside the banner it wraps.

Every new module is at 100% on all four coverage dimensions. Two v8 ignores,
each justified in place: getAuthToken's typeof-window guard (a happy-dom
inherent path) and replayProtocolRequest's provably-dead default case.

Signed-off-by: cliffhall <cliff@futurescale.com>

clients/web/src/components/elements/Toasts/FetchBodyDroppedToastMessage.tsx

@@ -0,0 +1,38 @@
+import { List, Stack, Text } from "@mantine/core";
+import { ToastCauseList, ToastLinkButton } from "./ToastPrimitives";
+
+// Body of the "response body dropped" warning toast: a one-line summary of what
+// happened, the likely causes, and a link that opens this server's settings
+// (on the Options section) so the user can raise the Network Log Size if it's
+// just a high-traffic server. Surfaces the otherwise-invisible rotation drop
+// described in #1390.
+export const FetchBodyDroppedToastMessage = ({
+  maxFetchRequests,
+  onAdjust,
+}: {
+  maxFetchRequests: number;
+  onAdjust: () => void;
+}) => (
+  <Stack gap={4}>
+    <Text size="sm">
+      A response body arrived after its Network log entry had already rotated
+      out (the log hit its {maxFetchRequests}-request limit), so the body
+      couldn&apos;t be shown. This usually indicates:
+    </Text>
+    <ToastCauseList>
+      <List.Item>
+        a chatty or misbehaving server (notification storms, rapid polling)
+      </List.Item>
+      <List.Item>an SSE/transport reconnect or retry storm</List.Item>
+      <List.Item>
+        a slow streaming call racing against high request volume
+      </List.Item>
+      <List.Item>
+        the Network Log Size set too low for this server&apos;s traffic
+      </List.Item>
+    </ToastCauseList>
+    <ToastLinkButton onClick={onAdjust}>
+      Adjust Network Log Size for this server
+    </ToastLinkButton>
+  </Stack>
+);

clients/web/src/components/elements/Toasts/OutputValidationToastMessage.tsx

@@ -0,0 +1,22 @@
+import { Stack, Text } from "@mantine/core";
+import { ToastLinkButton } from "./ToastPrimitives";
+
+// Body of the output-schema-mismatch warning toast: a one-line summary plus a
+// link that opens the full validation details in a modal (the raw error is far
+// too long for a toast).
+export const OutputValidationToastMessage = ({
+  onViewDetails,
+}: {
+  onViewDetails: () => void;
+}) => (
+  <Stack gap={4}>
+    <Text size="sm">
+      The tool result&apos;s structuredContent doesn&apos;t match the
+      tool&apos;s outputSchema. The inspector renders it anyway, but strict MCP
+      clients may not.
+    </Text>
+    <ToastLinkButton onClick={onViewDetails}>
+      View validation details
+    </ToastLinkButton>
+  </Stack>
+);

clients/web/src/components/elements/Toasts/ToastPrimitives.tsx

@@ -0,0 +1,13 @@
+import { Anchor, List } from "@mantine/core";
+
+// Shared "list of likely causes" styling for the warning-toast bodies.
+export const ToastCauseList = List.withProps({ size: "sm", spacing: 2 });
+
+// The "open the relevant settings/details" link rendered at the bottom of each
+// warning-toast body. Same static shape across all three toasts; each passes
+// its own `onClick`.
+export const ToastLinkButton = Anchor.withProps({
+  component: "button",
+  type: "button",
+  size: "sm",
+});

clients/web/src/components/elements/Toasts/Toasts.stories.tsx

@@ -0,0 +1,34 @@
+import type { Meta, StoryObj } from "@storybook/react-vite";
+import { fn } from "storybook/test";
+import { FetchBodyDroppedToastMessage } from "./FetchBodyDroppedToastMessage";
+import { OutputValidationToastMessage } from "./OutputValidationToastMessage";
+import { UrlElicitationErrorToastMessage } from "./UrlElicitationErrorToastMessage";
+
+// The bodies rendered inside a Mantine notification. They are shown here on
+// their own so the copy and the affordance can be reviewed without provoking
+// the failure that raises each one.
+const meta: Meta = {
+  title: "Elements/Toasts",
+};
+
+export default meta;
+
+/** #1390 — a response body arrived after its Network log entry rotated out. */
+export const FetchBodyDropped: StoryObj<typeof FetchBodyDroppedToastMessage> = {
+  render: (args) => <FetchBodyDroppedToastMessage {...args} />,
+  args: { maxFetchRequests: 250, onAdjust: fn() },
+};
+
+/** A tool result whose `structuredContent` doesn't match its `outputSchema`. */
+export const OutputValidation: StoryObj<typeof OutputValidationToastMessage> = {
+  render: (args) => <OutputValidationToastMessage {...args} />,
+  args: { onViewDetails: fn() },
+};
+
+/** A non-spec `-32042` carrying no `elicitations`, so there is no URL to open. */
+export const UrlElicitationError: StoryObj<
+  typeof UrlElicitationErrorToastMessage
+> = {
+  render: (args) => <UrlElicitationErrorToastMessage {...args} />,
+  args: { onViewDetails: fn() },
+};

clients/web/src/components/elements/Toasts/Toasts.test.tsx

@@ -0,0 +1,87 @@
+import { describe, expect, it, vi } from "vitest";
+import { screen } from "@testing-library/react";
+import userEvent from "@testing-library/user-event";
+import { renderWithMantine } from "../../../test/renderWithMantine";
+import { FetchBodyDroppedToastMessage } from "./FetchBodyDroppedToastMessage";
+import { OutputValidationToastMessage } from "./OutputValidationToastMessage";
+import { UrlElicitationErrorToastMessage } from "./UrlElicitationErrorToastMessage";
+import { ToastCauseList, ToastLinkButton } from "./ToastPrimitives";
+
+describe("ToastPrimitives", () => {
+  it("renders the shared cause list and link button", () => {
+    const onClick = vi.fn();
+    renderWithMantine(
+      <>
+        <ToastCauseList>
+          <li>a cause</li>
+        </ToastCauseList>
+        <ToastLinkButton onClick={onClick}>Do the thing</ToastLinkButton>
+      </>,
+    );
+    expect(screen.getByText("a cause")).toBeInTheDocument();
+    expect(
+      screen.getByRole("button", { name: "Do the thing" }),
+    ).toBeInTheDocument();
+  });
+});
+
+describe("FetchBodyDroppedToastMessage", () => {
+  it("names the limit that dropped the body and lists the likely causes", () => {
+    renderWithMantine(
+      <FetchBodyDroppedToastMessage
+        maxFetchRequests={250}
+        onAdjust={vi.fn()}
+      />,
+    );
+    expect(screen.getByText(/250/)).toBeInTheDocument();
+    expect(
+      screen.getByText(/an SSE\/transport reconnect or retry storm/),
+    ).toBeInTheDocument();
+  });
+
+  it("calls onAdjust from the settings link", async () => {
+    const onAdjust = vi.fn();
+    renderWithMantine(
+      <FetchBodyDroppedToastMessage
+        maxFetchRequests={10}
+        onAdjust={onAdjust}
+      />,
+    );
+    await userEvent.click(
+      screen.getByRole("button", {
+        name: "Adjust Network Log Size for this server",
+      }),
+    );
+    expect(onAdjust).toHaveBeenCalledTimes(1);
+  });
+});
+
+describe("OutputValidationToastMessage", () => {
+  it("summarizes the mismatch and opens the details modal", async () => {
+    const onViewDetails = vi.fn();
+    renderWithMantine(
+      <OutputValidationToastMessage onViewDetails={onViewDetails} />,
+    );
+    expect(screen.getByText(/outputSchema/)).toBeInTheDocument();
+    await userEvent.click(
+      screen.getByRole("button", { name: "View validation details" }),
+    );
+    expect(onViewDetails).toHaveBeenCalledTimes(1);
+  });
+});
+
+describe("UrlElicitationErrorToastMessage", () => {
+  it("explains the empty elicitations list and opens the details modal", async () => {
+    const onViewDetails = vi.fn();
+    renderWithMantine(
+      <UrlElicitationErrorToastMessage onViewDetails={onViewDetails} />,
+    );
+    expect(
+      screen.getByText(/listed no required\s+elicitations/),
+    ).toBeInTheDocument();
+    await userEvent.click(
+      screen.getByRole("button", { name: "View error details" }),
+    );
+    expect(onViewDetails).toHaveBeenCalledTimes(1);
+  });
+});

clients/web/src/components/elements/Toasts/UrlElicitationErrorToastMessage.tsx

@@ -0,0 +1,21 @@
+import { Stack, Text } from "@mantine/core";
+import { ToastLinkButton } from "./ToastPrimitives";
+
+// Body of the non-spec URLElicitationRequired toast: the server returned a
+// -32042 error with no `elicitations` list, so there's no URL to open. We keep
+// the toast short and link to a modal with the raw error body.
+export const UrlElicitationErrorToastMessage = ({
+  onViewDetails,
+}: {
+  onViewDetails: () => void;
+}) => (
+  <Stack gap={4}>
+    <Text size="sm">
+      The server reported a URLElicitationRequired error but listed no required
+      elicitations, so there&apos;s nothing to open.
+    </Text>
+    <ToastLinkButton onClick={onViewDetails}>
+      View error details
+    </ToastLinkButton>
+  </Stack>
+);