kandev/docs/plans/plugins/PLUGIN-API.md

Kandev Plugin API contract (native JS UI plugins — "option C")

This is the frozen interface every frontend + example task builds against. Do not diverge without updating this file.

Loading model

1. Backend boot payload gains plugins: ActivePlugin[] where ActivePlugin = { id: string; name: string; bundleUrl: string; styleUrls?: string[] }. bundleUrl = /api/plugins/{id}/bundle — kandev serves this directly from the extracted package directory on local disk (~/.kandev/plugins/<id>/<version>/ui/..., per manifest ui.bundle). There is no reverse proxy and no live upstream request: the plugin subprocess does not need to be running to serve the UI bundle, since installation already extracted the file.
2. On SPA boot, the plugin host (apps/web/lib/plugins/host.ts) iterates bootPayload.plugins, injects any styleUrls as <link>, and dynamically import(/* @vite-ignore */ bundleUrl) each bundle as a native ES module.
3. Each bundle, when evaluated, calls the global:

   window.registerKandevPlugin(pluginId, {
     initialize(registry, host): void | Promise<void>,
     destroy?(): void,
   })
   

4. After the module resolves, the host calls initialize(registry, host). On plugin disable/uninstall the host calls destroy?.() and unregisters everything that plugin added (registrations are tracked per pluginId).

Global entry point

window.registerKandevPlugin(id: string, plugin: KandevPlugin) — defined by the host before any bundle loads. Bundles are authored with React as an external; they must use host.React (NOT bundle their own React) to share the host instance.

host: PluginHostApi

interface PluginHostApi {
  pluginId: string;
  React: typeof import("react");            // host React instance (shared)
  jsx: typeof React.createElement;          // convenience alias (h)
  store: {                                   // kandev app store (zustand StoreApi)
    getState(): AppState;
    setState(partial): void;
    subscribe(listener): () => void;
  };
  api: {
    // fetch scoped to this plugin's backend via kandev proxy:
    // GET/POST {method} /api/plugins/{id}/... ; returns parsed JSON
    fetch(path: string, init?: RequestInit): Promise<Response>;
    // Backend API origin ("" when SPA and API share an origin) — for reaching
    // first-party kandev REST endpoints without re-deriving the split-origin
    // dev/desktop base URL from window internals.
    baseUrl: string;
  };
  ui: Record<string, unknown>;              // curated @kandev/ui components + app UI (see below)
  theme: "light" | "dark";
  // Soft SPA navigation (history push/replace + SPA re-render) — same code
  // path as the app router, so plugin pages can link into native routes
  // (e.g. /t/{taskId}) without a full reload.
  navigate(href: string, options?: { replace?: boolean }): void;
}

host.ui contents: shadcn primitives (Alert*, Badge, Button, Card*, Checkbox, Dialog*, DropdownMenu*, Input, Label, Pagination*, ScrollArea, Select*, Separator, Sheet*, Skeleton, Spinner, Switch, Table*, Tabs*, Textarea, Tooltip*) plus first-party app UI: PageTopbar (the kandev title bar, for routes that opt out of the default chrome and own their layout), TaskCreateDialog (kandev's real create-task modal, prefilled via initialValues), and Combobox (the app's Command+Popover picker). The authoritative list is apps/web/lib/plugins/host-api.ts (PLUGIN_UI).

Plugins must use these host instances — bundling copies of anything Radix/portal/context-based would split React context across instances and break refs/asChild. Pure-React libs (e.g. @tabler/icons-react) bundle fine.

registry: PluginRegistry

// icon: curated icon name (apps/web/lib/plugins/icons.ts — "ticket", "chart",
// "robot", "database", ...); unknown/missing names render a puzzle glyph in
// the sidebar.
// section: "main" (default) renders as a top-level sidebar entry;
// "integrations" renders inside the sidebar's Integrations section alongside
// the first-party integration links (GitHub, Jira, ...). Hosts predating a
// section value simply don't render items targeting it (additive change).
interface NavItem { id: string; label: string; path: string; icon?: string; section?: "main" | "settings" | "integrations"; }

// Configuration for the kandev-style title bar the host renders above a plugin
// route. All fields optional; defaults are derived (see registerRoute below).
interface PluginPageChrome {
  title?: string;      // default: nav-item label for the same path, else plugin name
  subtitle?: string;   // muted text next to the title
  icon?: string;       // curated icon name; default: matching nav item's icon
  backHref?: string;   // back-link target (host default "/")
  backLabel?: string;  // back-link label (host default "Kandev")
  actions?: React.ComponentType; // rendered on the right side of the topbar
}

interface PluginRouteOptions {
  // Default: enabled with derived title. Object → configure; false → render the
  // route full-bleed and own the chrome (e.g. with host.ui.PageTopbar).
  topbar?: boolean | PluginPageChrome;
}

interface PluginRegistry {
  // Top-level SPA route, e.g. "/jira". Component rendered by the SPA route resolver
  // when window.location path === path (exact match; trailing segments via ":param" not
  // required for v1 — exact + startsWith("/plugins/{id}") allowed). The host wraps the
  // page in kandev chrome (PageTopbar + scrollable content area) by default —
  // configure or opt out via options.topbar.
  registerRoute(path: string, Component: React.ComponentType, options?: PluginRouteOptions): void;

  // Sidebar/main nav entry. Rendered by <PluginNavItems/> in the app sidebar,
  // with item.icon resolved against the curated icon map (fallback: puzzle).
  registerNavItem(item: NavItem): void;

  // Route under /settings/plugins/{id}/... rendered inside settings shell.
  // The settings shell already provides its own topbar chrome — no options here.
  registerSettingsRoute(path: string, Component: React.ComponentType): void;

  // Named slot injection. Host renders all components registered for a slot via
  // <PluginSlot name="..." props={...}/>. Initial slots: "task-sidebar",
  // "settings-nav", "main-nav-footer", "chat-input-actions". The last renders
  // icon buttons in the chat composer toolbar (beside the model picker, mic,
  // and send) and forwards `{ taskId, taskTitle, activeSessionId, sessionIds }`
  // as `slotProps` — the active session plus every kandev session id on the
  // task. Resolving a session id to an agent/ACP transcript id (e.g. to key
  // tokscale cost data on a session) is the plugin's job, done server-side in
  // the plugin backend via the Host data API; the host only propagates ids.
  registerComponent(slot: string, Component: React.ComponentType<{ slotProps?: unknown }>): void;

  // WS action handler. Bridged into the existing lib/ws dispatch; called with the
  // decoded message payload for that action string.
  registerWsHandler(action: string, handler: (payload: unknown) => void): void;
}

Registry internals (host side)

apps/web/lib/plugins/registry.ts holds a singleton PluginRegistry whose data is reactive (a small zustand store or event emitter) so host React components re-render when registrations change. Every registration records the owning pluginId so the host can bulk-unregister on disable. Exposes read selectors: getRoutes() (each entry carries pluginId + options), getNavItems(), getSettingsRoutes(), getSlotComponents(slot), getWsHandlers(action), and getPluginName(pluginId) (display name recorded by forPlugin(id, name), used for derived page-chrome titles).

Plugin top-level routes render inside PluginPageFrame (apps/web/components/plugins/plugin-page.tsx): a PageTopbar title bar above a scrollable content area, resolved from options.topbar with derived defaults, or the bare component when the route opted out (topbar: false).

Integration points the app must add (task-19)

• src/spa-routes.tsx: after the static route switch, before the not-found fallback, consult registry.getRoutes() for a matching path and render it inside the normal app shell.
• src/settings-routes.tsx: consult registry.getSettingsRoutes() for /settings/plugins/{id}/* paths.
• App sidebar (grep the nav list component): render <PluginNavItems/> reading registry.getNavItems().
• lib/ws/router.ts / lib/ws/client.ts: after built-in dispatch, forward the message to any registry.getWsHandlers(action).
• components/plugins/plugin-slot.tsx: <PluginSlot name props/> renders all slot components; drop into task detail sidebar + settings nav as initial hosts. The chat composer toolbar (components/task/chat/chat-input-toolbar-desktop.tsx and -mobile.tsx, via chat-input-plugin-actions.tsx) hosts the chat-input-actions slot, passing { taskId, taskTitle, activeSessionId, sessionIds }.

Security posture (documented, enforced where cheap)

Plugin JS runs in the kandev origin with store access — this is the accepted tradeoff of option C. v1 mitigations: only active, operator-installed plugins load; bundles are served by kandev from the extracted package directory (same-origin, no third-party CDN, no upstream network hop); host wraps initialize in try/catch so a broken plugin can't crash boot; registrations namespaced + bulk-revocable per plugin. No credentials are ever displayed to the operator — installing a plugin (via URL or upload) has nothing to copy or reveal, unlike the old register flow's one-time API key/webhook secret. Sandboxing plugin JS (worker/realms) is explicit future work.

Example plugin must (task-21)

Ship a bundle that on initialize registers: a nav item "Hello" → route /plugins/hello rendering a native page (uses host.jsx + host.ui), a task-sidebar slot component, and a WS handler for task.created that updates a counter in its page via the plugin's own module state. No bundled React.