Bug: MCP auto-mount has no opt-out for Vite-plugin consumers

[dvcolomban]

Describe the bug

@devframes/hub@0.9.9 changed the aggregate MCP route's default from off to 'auto', mounting a Streamable-HTTP endpoint at <base>__mcp as soon as any agent-flagged action exists.

@vitejs/devtools's Vite plugin builds its initHub({...}) call from a fixed list of fields (base, context, ui, renderers, clientModuleResolution, auth, allowedOrigins, server/ws, host), unchanged from 0.6.1 through 0.7.1:

// dist/server-*.js
const hub = initHub({
  base: DEVTOOLS_MOUNT_PATH,
  context,
  ui: createViteDevToolsUi(options.ui),
  renderers: resolveDockRendererRegistrations(options.renderers),
  ...context.viteServer ? { clientModuleResolution: "/@id/{specifier}" } : {},
  auth: authDisabled ? false : getAuthHandler(context),
  ...allowedOrigins ? { allowedOrigins } : {},
  ...options.server ? { server: options.server } : { ws: ... },
  ...options.host ? { host: options.host } : {}
});

mcp never appears there, and none of DevToolsConfig, DevToolsPluginOptions, or DevToolsOptions/CreateDevToolsHubOptions expose a field for it. So a Vite-plugin consumer inherits the new auto-mount with no supported way to turn it off, even if they bridge MCP through something else already.

Maybe we should add mcp?: McpSetting to DevToolsOptions/DevToolsPluginOptions and forward it into initHub({...}) ?

Reproduction

No hosted repro, since this only shows up once a devframe-based Vite plugin is wired up with agent-flagged actions and something is watching /__devtools/__mcp. Steps:

1. pnpm add @vitejs/devtools@0.6.1 @devframes/hub@0.9.10 (or any hub >=0.9.9) in a project using the Vite plugin.
2. Register at least one action with agent: {...} metadata (any devframe capability that ships one works).
3. Run vite dev and request <devtools-base>__mcp.
4. It answers, and there's no option anywhere in the plugin's config to make it not.

System Info

System:
  OS: macOS 26.5.1
  CPU: (11) arm64 Apple M3 Pro
  Memory: 79.97 MB / 36.00 GB
  Shell: 5.9 - /bin/zsh
Binaries:
  Node: 24.20.0
  npm: 11.19.0
  pnpm: 11.22.0
  bun: 1.3.14
Browsers:
  Chrome: 152.0.7977.65
  Safari: 26.5

Used package manager

pnpm