A2Web — Web App Agent System

A2Web lets you launch web applications in native windows and connect them to AI agents. Web apps register tools and send observations via the WebMCP polyfill. Sub-agents (created via pi's SDK) receive observations automatically and proactively invoke tools.

How It Works

Pi Agent ──JSON WS──► Harness ──CRDT──► Web Host ──wry──► Webviews
│ │ (native windows)
│ observations │
└── forwarded ───────┘
│
▼
Sub-Agent (pi SDK session)
- Receives observations via followUp prompts
- Invokes registered web app tools proactively

• Pi Extension (.pi/extensions/a2web/) — registers tools (start_sub_agent, launch_webview, invoke_webapp_tool), creates sub-agent sessions, forwards observations
• Harness (harness/) — Rust binary bridging pi ↔ web-host via JSON WebSocket (port 2341) and samod CRDT sync (port 2342)
• Web Host (web-host/) — Rust binary using wry + tao for native webview windows, injects the WebMCP polyfill and bridge JS
• WebMCP Polyfill (web-host/src/webmcp.js) — implements document.modelContext with registerTool, sendObservation, getTools

Quick Start

# 1. Build Rust binaries
cargo build -p shared -p harness -p web-host
# 2. Install extension dependenciescd .pi/extensions/a2web && npm install &&cd ../..
# 3. Run pi in this directory
pi
# 4. In pi, create a sub-agent and launch apps# (see AGENTS.md for examples)

Example

Create a counter app and a todo list, both linked to the same sub-agent:

/reload
start_sub_agent session_id="demo-session"
launch_webview app_id="counter" html="..." session_id="demo-session"
launch_webview app_id="todos" html="..." session_id="demo-session"

The sub-agent sees observations from both apps. Add a todo like "increment counter to 10" — the sub-agent will call increment until the counter reaches 10, then mark the todo as done.

Project Structure

a2web/
AGENTS.md # Architecture, tools, data flow, patterns
Cargo.toml # Rust workspace
shared/src/lib.rs # CRDT document types (AgentDoc)
harness/src/main.rs # Bridge: pi JSON WS + samod CRDT server
web-host/
src/main.rs # wry/tao webview host
src/webmcp.js # WebMCP polyfill injected into webviews
.pi/extensions/a2web/
index.ts # Extension entry: registers tools, lifecycle
tools.ts # Tool implementations + sub-agent system
types.ts # TypeScript types for harness messages
doc-bridge.ts # WebSocket connection to harness
harness.ts # Harness process management

License

MIT