elizaos--eliza/plugins/plugin-native-bun-runtime

@elizaos/capacitor-bun-runtime

Native host package for the local agent runtime. The iOS Swift implementation can run in two modes:

• engine: "auto" / engine: "bun": uses the directly linked ElizaBunEngine.framework from @elizaos/bun-ios-runtime when the app was built with ELIZA_IOS_FULL_BUN_ENGINE=1. Store-distributed iOS local mode must use engine: "bun" and fail closed if the framework is missing.
• engine: "compat": hosts a JSContext compatibility bridge on a dedicated worker thread, installs the __ELIZA_BRIDGE__ host functions, and loads the staged iOS agent payload from public/agent/agent-bundle.js. This path is development/sideload-only.

The full Bun engine artifact is produced outside this package by the packages/native/bun-runtime build harness and an elizaos/bun fork.

The Android implementation delegates lifecycle and RPC calls to the host app's ElizaAgentService over its loopback API.

Install

bun add @elizaos/capacitor-bun-runtime

Capacitor 8 auto-discovers the plugin via the package metadata. Re-run pod install after adding it so the ElizaosCapacitorBunRuntime pod links into your iOS workspace. The pod depends on Capacitor and links system frameworks including JavaScriptCore (compat builds only), Network, Accelerate, Metal, MetalKit, MetalPerformanceShaders, Foundation, CoreML, and NaturalLanguage. When ELIZA_IOS_INCLUDE_LLAMA=1, it also depends on LlamaCpp and LlamaCppCapacitor for native llama.cpp symbols.

Bundle layout

The local iOS build stages these resources under App/public/agent/, which is copied into the app bundle by Capacitor's public folder resource:

• agent-bundle.js — the Bun-targeted agent bundle from packages/agent/dist-mobile-ios/. Required for the full backend path.
• pglite.wasm, initdb.wasm, pglite.data, vector.tar.gz, fuzzystrmatch.tar.gz — PGlite runtime assets used by the agent bundle.
• eliza-polyfill-prefix.js — the polyfill prefix that maps Bun.* / node:* onto __ELIZA_BRIDGE__ for the compatibility JSContext path. Optional; the runtime ships a minimal embedded fallback that just version-checks the bridge.

Usage

import { ElizaBunRuntime } from "@elizaos/capacitor-bun-runtime";

// Development/sideload only: auto-selects the full Bun engine when embedded,
// otherwise falls back to the JSContext compatibility bridge in DEBUG builds.
await ElizaBunRuntime.start({ engine: "auto" });

// Store iOS local mode: require the full Bun engine. This returns { ok: false }
// if the framework is not embedded in the app bundle.
await ElizaBunRuntime.start({
  engine: "bun",
  argv: ["bun", "public/agent/agent-bundle.js", "ios-bridge", "--stdio"],
});

// Round-trips a chat message through the agent's send_message handler,
// which must have been registered via bridge.ui_register_handler.
const { reply } = await ElizaBunRuntime.sendMessage({ message: "hello" });

// Generic dispatch into any handler the agent registered.
const { result } = await ElizaBunRuntime.call({
  method: "http_request",
  args: { method: "GET", path: "/api/health" },
});

// Check ready state, current model, throughput.
const status = await ElizaBunRuntime.getStatus();

// Tear down the runtime. Releases the JSContext or full Bun engine host.
await ElizaBunRuntime.stop();

Bridge contract

The full-engine ABI lives in packages/native/bun-runtime/BRIDGE_CONTRACT.md. The compatibility host still implements the Swift __ELIZA_BRIDGE__ v1 surface; breaking changes bump the version string emitted in globalThis.__ELIZA_BRIDGE_VERSION__.

In production full Bun mode, the Swift host calls the directly linked ElizaBunEngine ABI, starts agent-bundle.js ios-bridge --stdio, and forwards React requests through ElizaBunRuntime.call({ method: "http_request", args }). packages/ui/src/api/ios-local-agent-transport.ts uses that path first when the native plugin is available. The JSContext compatibility host is retained only for development/sideload builds; iOS store builds fail closed instead of falling back to it.

Llama backend

llama_* host functions delegate to LlamaBridgeImpl, which links against the same LlamaCpp.xcframework built by the iOS local-inference pipeline. The xcframework build also emits the small eliza_llama_* C helpers needed by the Swift direct bridge.

Events

The plugin emits two Capacitor events:

• eliza:ui — every bridge.ui_post_message(channel, payload) call. Subscribe with ElizaBunRuntime.addListener("eliza:ui", handler).
• eliza:runtime-exit — fired when the agent calls bridge.exit(code). Useful for surfacing crashes to the React shell.

Limitations (v1)

• Android requires the host app's ElizaAgentService loopback API.
• Full Bun is only used when ElizaBunEngine.framework is embedded. Outside iOS store local mode, engine: "auto" can fall back to the compatibility JSContext host for development/sideload builds.
• The full Bun bridge currently buffers HTTP response bodies over stdio. It is correct for API calls, but token-by-token streaming needs a follow-up stream envelope.
• No worker_threads.Worker support in the compatibility host.
• No child_process — sandboxed out.
• http_serve_* is disabled on iOS. Foreground and route traffic uses Capacitor/engine IPC instead of a WebView-visible localhost listener.
• bun:ffi.dlopen is forbidden. The only FFI surface is the llama bridge.