feat(servers): export server list as mcp.json download (#1346) (#1351)

* feat(servers): export server list as mcp.json download (#1346)

Adds an Export button to the Servers screen, next to "Add Servers".
Clicking it downloads the current server list as a canonical mcp.json
file (2-space indent, same shape serializeStore writes), so the user
can hand it off, sync it to another machine, or symlink into Claude
Desktop / Cursor / Cline.

Wiring:
- ServerListControls: new Export Button (variant=default), disabled
  when serverCount === 0 (nothing to download).
- ServerListScreen / InspectorView: thread `onExport` / `onServerExport`
  through.
- App.tsx: onServerExport runs serverEntriesToMcpConfig on the in-memory
  servers list, JSON.stringify with 2-space indent, and triggers a Blob
  download via a temporary anchor (appended to body for Firefox
  compatibility, then removed; object URL revoked).

Tests:
- ServerListControls unit tests cover button-count (toggle hidden vs
  shown, Export always present), disabled-on-empty, click fires onExport.
- ServerListControls.stories grows play functions for both stories —
  WithServers asserts Export is enabled + click fires the spy in real
  Chromium, WithoutServers asserts Export is disabled.
- Existing screen + view tests / stories updated for the new prop.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* fix(servers): address PR #1351 review (extract helpers + exception safety + guard)

Substantive items from the review:

1. Serialization format parity (review #1): added
   `serializeMcpConfig(entries)` to core/mcp/serverList.ts — a
   browser-safe helper that runs `serverEntriesToMcpConfig` then
   stringifies with 2-space indent. Single source of truth for export
   formatting; can't drift from serializeStore's on-disk shape.

2. Exception safety on the anchor cleanup (review #2) + a direct test
   for the App.tsx download wiring (review #6): extracted
   `downloadJsonFile(filename, json)` to clients/web/src/lib/
   downloadFile.ts. removeChild + revokeObjectURL run in a `finally`
   so a thrown click() doesn't leak the DOM node or the object URL.
   Unit-tested under happy-dom with URL.createObjectURL mocked
   (happy-dom doesn't ship it).

3. Empty-list guard (review #5): App.tsx onServerExport bails when
   `servers.length === 0`. The button's disabled prop already prevents
   the UI path, but the handler is now locally correct against any
   future programmatic caller (storybook, keyboard shortcut, etc.).

Acknowledged but not changed:
- Tooltip on the disabled Export button (review #3) — Mantine's
  disabled-button + Tooltip wart wants a span wrapper + custom events
  config. Optional per the reviewer; deferred.
- Repeated exports → `mcp (1).json` browser suffix (review #4) — a
  deliberate trade-off since `mcp.json` is the conventional name a user
  would expect to symlink into Claude Desktop / Cursor / etc.

Tests: 1647 unit (+6) + 410 integration + 306 storybook = 2363 green.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

clients/web/src/test/core/mcp/serverList.test.ts

@@ -4,6 +4,7 @@ import {
   mcpConfigToServerEntries,
   normalizeServerType,
   serverEntriesToMcpConfig,
+  serializeMcpConfig,
 } from "@inspector/core/mcp/serverList.js";
 import type { MCPConfig, ServerEntry } from "@inspector/core/mcp/types.js";
 
@@ -169,6 +170,42 @@ describe("serverEntriesToMcpConfig", () => {
   });
 });
 
+describe("serializeMcpConfig", () => {
+  it("produces 2-space-indented canonical JSON", () => {
+    const json = serializeMcpConfig([
+      {
+        id: "alpha",
+        name: "alpha",
+        config: { type: "stdio", command: "node" },
+        connection: { status: "disconnected" },
+      },
+    ]);
+    expect(json).toBe(
+      `{\n  "mcpServers": {\n    "alpha": {\n      "type": "stdio",\n      "command": "node"\n    }\n  }\n}`,
+    );
+  });
+
+  it("strips runtime-only fields (connection, info, name) from the output", () => {
+    const json = serializeMcpConfig([
+      {
+        id: "alpha",
+        name: "Alpha (pretty)",
+        config: { type: "stdio", command: "node" },
+        connection: { status: "connected" },
+        info: { name: "alpha-impl", version: "1.0.0" },
+      },
+    ]);
+    const parsed = JSON.parse(json) as Record<string, unknown>;
+    expect(parsed).toEqual({
+      mcpServers: { alpha: { type: "stdio", command: "node" } },
+    });
+  });
+
+  it('returns `{ "mcpServers": {} }` for an empty list', () => {
+    expect(serializeMcpConfig([])).toBe(`{\n  "mcpServers": {}\n}`);
+  });
+});
+
 describe("DEFAULT_SEED_CONFIG", () => {
   it("contains the two canonical seed servers", () => {
     expect(Object.keys(DEFAULT_SEED_CONFIG.mcpServers)).toEqual([