diff --git a/apps/desktop/src/sdk/index.ts b/apps/desktop/src/sdk/index.ts
new file mode 100644
index 00000000000..c82ce4a0538
--- /dev/null
+++ b/apps/desktop/src/sdk/index.ts
@@ -0,0 +1,228 @@
+/**
+ * @hermes/plugin-sdk — THE plugin language. The vscode-module model: plugin
+ * authors import exactly one module and get everything — they never touch
+ * `@/…` internals (lint-fenced) and never need codebase access.
+ *
+ * Two delivery modes, one surface:
+ *  - bundled (`src/plugins/<name>/`): the import resolves here via alias;
+ *  - runtime-fetched (plugin host, next phase): the loader injects this same
+ *    object as `window.__HERMES_PLUGIN_SDK__` and maps the import to it, so a
+ *    published plugin builds against the types with the SDK marked external.
+ *
+ * Capability tiers (WoW-style):
+ *  - `host.state.*` — READONLY app state (nanostore atoms; `.get()` or
+ *    subscribe; `useValue` in React).
+ *  - `host.*` actions — curated, safe verbs (toast, haptic).
+ *  - `host.request` — the gateway JSON-RPC door; the plugin's real power,
+ *    and the future seam for per-plugin capability grants.
+ *  - `ui.*` — the design language, so plugin UI looks native by default.
+ */
+
+import { atom, type ReadableAtom } from 'nanostores'
+
+import { $narrowViewport } from '@/components/pane-shell/tree/store'
+import { onGatewayEvent } from '@/contrib/events'
+import { getLogs, getStatus } from '@/hermes'
+import { $gateway } from '@/store/gateway'
+import { notify, notifyError } from '@/store/notifications'
+import { $activeGatewayProfile } from '@/store/profile'
+import { $activeSessionId, $currentCwd, $currentModel, $gatewayState } from '@/store/session'
+import { runGatewayRestart } from '@/store/system-actions'
+
+// -- state: readonly views over the app's live atoms -------------------------
+
+const readonlyAtom = <T>(atomLike: ReadableAtom<T>): ReadableAtom<T> => atomLike
+
+/** Window geometry + the app's responsive posture, one readonly rect. */
+export interface ViewportRect {
+  width: number
+  height: number
+  /** Below the app's sidebar-collapse breakpoint (rails become overlays). */
+  narrow: boolean
+}
+
+const readViewport = (): ViewportRect => ({
+  width: typeof window === 'undefined' ? 0 : window.innerWidth,
+  height: typeof window === 'undefined' ? 0 : window.innerHeight,
+  narrow: $narrowViewport.get()
+})
+
+const $viewport = atom<ViewportRect>(readViewport())
+
+if (typeof window !== 'undefined') {
+  const refresh = () => $viewport.set(readViewport())
+  window.addEventListener('resize', refresh)
+  $narrowViewport.listen(refresh)
+}
+
+export const host = {
+  state: {
+    /** Runtime id of the active chat session (null on a fresh draft). */
+    activeSessionId: readonlyAtom<null | string>($activeSessionId),
+    /** Active workspace cwd ('' when detached). */
+    cwd: readonlyAtom<string>($currentCwd),
+    /** Gateway socket state: 'idle' | 'connecting' | 'open' | …. */
+    gateway: readonlyAtom<string>($gatewayState),
+    /** Current main model slug. */
+    model: readonlyAtom<string>($currentModel),
+    /** Profile the live gateway is routed to. */
+    profile: readonlyAtom<string>($activeGatewayProfile),
+    /** Window geometry ({ width, height, narrow }). */
+    viewport: readonlyAtom<ViewportRect>($viewport)
+  },
+
+  /** Toast into the app's notification stack. */
+  notify,
+  notifyError,
+
+  // NOTE: every host door is async-safe — wrapped so a sync throw from an
+  // internal helper (e.g. no desktop bridge in a plain browser) becomes a
+  // rejection a plugin's .catch() sees, never an error-boundary crash.
+
+  /** Tail an app log file (`agent` / `errors` / `gateway` / `gui` / …). */
+  logs: async (...args: Parameters<typeof getLogs>) => getLogs(...args),
+
+  /** Navigate the app router (hash routes, e.g. '/command-center?section=system'). */
+  navigate: (path: string) => {
+    window.location.hash = path.startsWith('#') ? path : `#${path}`
+  },
+
+  /** HEAR the gateway stream (message deltas, session lifecycle, tool
+   *  activity, …) by event type — `'*'` for everything. Returns a disposer.
+   *  Listeners are isolated; a throw can't affect app dispatch. */
+  onEvent: onGatewayEvent,
+
+  /** Restart the backend gateway (progress surfaces in the core statusbar). */
+  restartGateway: async () => runGatewayRestart(),
+
+  /** One-shot system status snapshot (platforms, versions, …). */
+  status: async () => getStatus(),
+
+  /** Gateway JSON-RPC — sessions, config, skills, cron, kanban, everything
+   *  the app itself uses. Lazy: resolves the LIVE socket per call. */
+  request: async <T>(method: string, params: Record<string, unknown> = {}): Promise<T> => {
+    const gateway = $gateway.get()
+
+    if (!gateway) {
+      throw new Error('Hermes gateway unavailable')
+    }
+
+    return gateway.request<T>(method, params)
+  }
+}
+
+// -- react bridge -------------------------------------------------------------
+
+// Every contribution surface, plugin-reachable: register keybinds, palette
+// commands, routes, themes, panes, composer extensions, and bar items with
+// the same area ids + payload types core uses.
+export { COMPOSER_AREAS, type ComposerAttachmentProvider, type ComposerMiddleware } from '@/app/chat/composer/contrib'
+
+// -- ui: the design language --------------------------------------------------
+
+export { PALETTE_AREA, type PaletteContribution } from '@/app/command-palette/contrib'
+export { type RouteContribution, ROUTES_AREA, SIDEBAR_NAV_AREA, type SidebarNavContribution } from '@/app/routes'
+export type { StatusbarItem } from '@/app/shell/statusbar-controls'
+
+export type { TitlebarTool } from '@/app/shell/titlebar-controls'
+export { StatusDot, type StatusTone } from '@/components/status-dot'
+export { Badge } from '@/components/ui/badge'
+export { Button } from '@/components/ui/button'
+export { Checkbox } from '@/components/ui/checkbox'
+export { Codicon } from '@/components/ui/codicon'
+export { ConfirmDialog } from '@/components/ui/confirm-dialog'
+export {
+  ContextMenu,
+  ContextMenuContent,
+  ContextMenuItem,
+  ContextMenuSeparator,
+  ContextMenuTrigger
+} from '@/components/ui/context-menu'
+export { CopyButton } from '@/components/ui/copy-button'
+export { DecodeText } from '@/components/ui/decode-text'
+export {
+  Dialog,
+  DialogContent,
+  DialogDescription,
+  DialogFooter,
+  DialogHeader,
+  DialogTitle,
+  DialogTrigger
+} from '@/components/ui/dialog'
+export {
+  DropdownMenu,
+  DropdownMenuContent,
+  DropdownMenuItem,
+  DropdownMenuSeparator,
+  DropdownMenuTrigger
+} from '@/components/ui/dropdown-menu'
+export { EmptyState } from '@/components/ui/empty-state'
+export { ErrorState } from '@/components/ui/error-state'
+export { GlyphSpinner } from '@/components/ui/glyph-spinner'
+export { Input } from '@/components/ui/input'
+export { Kbd, KbdGroup } from '@/components/ui/kbd'
+/** The app's canonical loader (animated curves; `lemniscate-bloom` for long
+ *  page loads) — the same one every core page uses. */
+export { Loader, type LoaderType } from '@/components/ui/loader'
+export { LogView } from '@/components/ui/log-view'
+export { Popover, PopoverContent, PopoverTrigger } from '@/components/ui/popover'
+export { ScrollArea } from '@/components/ui/scroll-area'
+export { SearchField } from '@/components/ui/search-field'
+export { SegmentedControl } from '@/components/ui/segmented-control'
+export { Select, SelectContent, SelectItem, SelectTrigger, SelectValue } from '@/components/ui/select'
+export { Separator } from '@/components/ui/separator'
+export { Skeleton } from '@/components/ui/skeleton'
+export { Switch } from '@/components/ui/switch'
+export { Tabs, TabsList, TabsTrigger } from '@/components/ui/tabs'
+export { Textarea } from '@/components/ui/textarea'
+export { Tip, Tooltip, TooltipContent, TooltipProvider, TooltipTrigger } from '@/components/ui/tooltip'
+export type { GatewayEventListener } from '@/contrib/events'
+export type { HermesPlugin, PluginContext, PluginContribution, PluginRestOptions, PluginStorage } from '@/contrib/plugin'
+
+// -- contracts ----------------------------------------------------------------
+
+/** Mount-scoped contribution: while the rendering component is mounted, its
+ *  children render in the target area's slot; unmount disposes it. Use for
+ *  page-owned chrome (a page's titlebar control leaves with the page) —
+ *  `ctx.register` stays the door for permanent contributions. Namespace the
+ *  id with your plugin slug (`kanban:board-switcher`). */
+export { Contribute, type ContributeProps } from '@/contrib/react/contribute'
+export type { Contribution } from '@/contrib/types'
+/** Localized copy — plugins reuse the app's strings (and stay translatable). */
+export { useI18n } from '@/i18n'
+export { triggerHaptic as haptic } from '@/lib/haptics'
+/** The app's lucide icon set (RefreshCw, LayoutDashboard, Activity, …). */
+export * as icons from '@/lib/icons'
+export { type KeybindContribution, KEYBINDS_AREA } from '@/lib/keybinds/actions'
+/** The app's deterministic identity color for a name (profiles, assignees,
+ *  authors) + its translucent tag fill — so plugin-rendered identities read
+ *  the same hue as everywhere else. */
+export { profileColor, profileColorSoft } from '@/lib/profile-color'
+/** The shared client itself, for invalidation OUTSIDE React (e.g. a
+ *  `ctx.socket` frame invalidating a query). Inside components keep using
+ *  `useQueryClient`. */
+export { queryClient } from '@/lib/query-client'
+
+export const PANES_AREA = 'panes'
+export const STATUSBAR_AREAS = { left: 'statusBar.left', right: 'statusBar.right' } as const
+export const TITLEBAR_AREAS = { center: 'titleBar.center', left: 'titleBar.left', right: 'titleBar.right' } as const
+
+/** The app's own gateway-readiness evaluation (setup.status +
+ *  setup.runtime_check, reconciled) — pass `host.request`. Don't hand-roll
+ *  readiness from raw RPC shapes. */
+export { evaluateRuntimeReadiness, type RuntimeReadinessResult } from '@/lib/runtime-readiness'
+/** Canonical time formatting — every timestamp/age string in the app comes
+ *  from these (localized `Intl` under the hood). Don't hand-roll "Xm ago". */
+export { coarseElapsed, fmtDateTime, fmtDayTime, relativeTime } from '@/lib/time'
+export { cn } from '@/lib/utils'
+export { THEMES_AREA } from '@/themes/user-themes'
+export type { RpcEvent, StatusResponse } from '@/types/hermes'
+/** Subscribe a component to a `host.state` atom. */
+export { useStore as useValue } from '@nanostores/react'
+/** The app's data-fetching layer. Plugins share the ONE QueryClient mounted at
+ *  the app root, so their queries cache, dedupe, poll (`refetchInterval`), and
+ *  invalidate exactly like core screens — no hand-rolled atoms or polls. */
+export { useMutation, useQuery, useQueryClient } from '@tanstack/react-query'
+/** Plugin-local reactive state (share between a trigger and its panel, poll
+ *  loops, cross-component signals) — the same primitive `host.state` uses. */
+export { atom, computed } from 'nanostores'
diff --git a/apps/desktop/src/sdk/runtime.ts b/apps/desktop/src/sdk/runtime.ts
new file mode 100644
index 00000000000..449b9060b05
--- /dev/null
+++ b/apps/desktop/src/sdk/runtime.ts
@@ -0,0 +1,54 @@
+/**
+ * Runtime SDK injection — the other half of the vscode-module model. Bundled
+ * plugins resolve `@hermes/plugin-sdk` through the vite alias; RUNTIME-loaded
+ * plugins (disk / fetched) import the same specifier and get the same object:
+ * the loader rewrites bare specifiers to shim modules that re-export the
+ * live namespaces installed here. React ships as the app's singletons —
+ * a second React instance would break hooks.
+ */
+
+import * as React from 'react'
+import * as jsxDevRuntime from 'react/jsx-dev-runtime'
+import * as jsxRuntime from 'react/jsx-runtime'
+
+import * as sdk from './index'
+
+const GLOBALS = {
+  __HERMES_PLUGIN_SDK__: sdk,
+  __HERMES_REACT__: React,
+  __HERMES_REACT_JSX__: jsxRuntime,
+  __HERMES_REACT_JSX_DEV__: jsxDevRuntime
+} as const
+
+export function installPluginSdk(): void {
+  Object.assign(globalThis, GLOBALS)
+}
+
+/** Build a shim ESM blob that re-exports a global namespace's live members.
+ *  Export names come from the namespace itself, so the list can't drift. */
+function shimUrl(globalKey: keyof typeof GLOBALS): string {
+  const names = Object.keys(GLOBALS[globalKey]).filter(name => name !== 'default' && /^[A-Za-z_$][\w$]*$/.test(name))
+
+  const source =
+    `const m = globalThis.${globalKey};\n` +
+    `export default m.default ?? m;\n` +
+    // Guard the destructuring: `export const {  } = m` is a syntax error, so
+    // only emit it when the namespace actually has named exports.
+    (names.length ? `export const { ${names.join(', ')} } = m;\n` : '')
+
+  return URL.createObjectURL(new Blob([source], { type: 'text/javascript' }))
+}
+
+let cached: Record<string, string> | null = null
+
+/** Specifier -> shim URL map for the runtime loader (longest keys first). */
+export function sdkImportMap(): Record<string, string> {
+  cached ??= {
+    '@hermes/plugin-sdk': shimUrl('__HERMES_PLUGIN_SDK__'),
+    'react/jsx-dev-runtime': shimUrl('__HERMES_REACT_JSX_DEV__'),
+    'react/jsx-runtime': shimUrl('__HERMES_REACT_JSX__'),
+    react: shimUrl('__HERMES_REACT__')
+  }
+
+  return cached
+}