02. Tech Stack

1. Stack table

Layer	Tech	Baseline	Notes
Desktop shell	Electron	latest stable (pin at impl)	app shell
UI	React 19 + TypeScript	modern stable	English-first UI
Bundler	electron-vite / Vite	stable	multi-entry build
Styling	Tailwind CSS 4	stable	utility-first
State	Zustand	stable	UI state
Host backend	Rust	stable Rust toolchain	tools/plugins/permissions/persistence adapters
Rust async	tokio	stable	host services
Host RPC	stdio JSON-RPC (NDJSON)	frozen (D001)	Electron main ↔ Rust host
Agent engine	@earendil-works/pi-agent-core	1.4.0	agent loop
Model API	@earendil-works/pi-ai	1.4.0	provider adapters, OAuth, and stream handling
Model catalog	models.dev + Pi Providers/Models	bundled models.dev + pinned Pi 1.4.0	models.dev chat metadata; Pi account IDs, wire capabilities, and typed operations

models.dev owns published chat metadata; pi-ai owns transports and auth. Host persists Desktop account rows, credentials, and explicit binding overrides. Agent Runtime owns desktop context projection and checkpoint compaction. The transitional pi-coding-agent dependency is confined to native Pi session continuation and the trusted-extension compatibility shim; it is not the desktop agent loop, compaction, or durable session store. See the pi runtime dependency boundary.

| Node runtime | Node.js | >= 22.19 | pi requirement | | DB | SQLite | Rust host-core via rusqlite | sessions/settings | | Packaging | electron-builder | stable | macOS arm64 and Intel x64, Windows x64, and Linux x64 and arm64 release lanes | | Package manager | pnpm | 11.18.x | JS monorepo | | Lint/test | style-token checker (scripts/check-style-tokens.mjs) + vitest + cargo test; general JS linter still open (biome vs oxlint) | stable | dual stack quality | | Schema (TS) | typebox | frozen (D011) | shared contracts | | i18n | i18next + react-i18next | frozen (D012) | English source locale |

2. Language policy in engineering

• Product strings: English source
• Specs/ADRs: English primary
• Code identifiers: English
• Commits/issues/PRs: English preferred

3. Why Rust host core

• stronger sandboxing foundation
• better process/fs control
• long-term native performance and safety
• cleaner privilege separation from UI and model runtime

4. Why keep pi in Node/TS

• mature multi-provider support
• existing agent event model
• skills/extensions ecosystem leverage
• avoid rewriting agent framework

5. Dependency boundaries

Allowed

• official pi packages
• mainstream Electron/React ecosystem
• Rust crates for fs/process/sqlite/rpc/serde

Careful

• heavy native node addons
• multiple competing RPC frameworks
• large editor stacks too early (Monaco)

Not in MVP

• remote gateway frameworks
• marketplace backend
• custom LLM provider SDK replacing pi-ai

Production packaging boundary

• Renderer-only libraries are development/build dependencies because Vite bundles their runtime code and lazy assets into out/renderer.
• Electron Main bundles pure-JS workspace packages. Packages that require runtime module resolution or a native ABI remain production dependencies; the current external set includes only electron-updater.
• Resources/agent-runtime/sidecar.js is the only independent pi sidecar bundle. The complete @pi-desktop/agent-runtime package tree must not be copied into ASAR as a second runtime.
• The desktop package has no interactive PTY dependency. Agent Bash remains a non-interactive runtime capability owned by the agent sidecar.
• Dependency source maps, tests, examples, and declarations are build inputs, not release assets. License and notice files remain distributable.
• Lazy renderer capabilities such as Mermaid, KaTeX, and Shiki remain local assets; package-size optimization must not introduce runtime CDN fetches.

6. Build matrix (MVP)

• JS workspace build (pnpm)
• Rust host build (cargo)
• integration smoke (pnpm dev boots all layers)