diff --git a/bincio/edit/server.py b/bincio/edit/server.py
index 2f25567..c919bce 100644
--- a/bincio/edit/server.py
+++ b/bincio/edit/server.py
@@ -11,7 +11,7 @@ from typing import Any
 from fastapi import FastAPI, File, Form, HTTPException, Request, UploadFile
 from fastapi.middleware.cors import CORSMiddleware
 from fastapi.middleware.gzip import GZipMiddleware
-from fastapi.responses import HTMLResponse, JSONResponse, RedirectResponse, StreamingResponse
+from fastapi.responses import FileResponse, HTMLResponse, JSONResponse, RedirectResponse, StreamingResponse
 
 from bincio.edit.ops import SPORTS, STAT_PANELS, VALID_ACTIVITY_ID
 
@@ -467,6 +467,37 @@ async def recalculate_elevation_hysteresis_endpoint(activity_id: str) -> JSONRes
         raise HTTPException(422, str(e))
 
 
+@app.get("/api/wheel/version")
+async def wheel_version() -> JSONResponse:
+    """Public endpoint: current bincio wheel version for mobile app update checks."""
+    import importlib.metadata
+    try:
+        version = importlib.metadata.version("bincio")
+    except importlib.metadata.PackageNotFoundError:
+        version = "0.1.0"
+    return JSONResponse({
+        "version": version,
+        "url": f"/bincio-{version}-py3-none-any.whl",
+        "api_url": "/api/wheel/download",
+    })
+
+
+@app.get("/api/wheel/download")
+async def wheel_download() -> FileResponse:
+    """Serve the bincio wheel directly (used locally; in prod nginx serves /bincio-*.whl)."""
+    import importlib.metadata
+    try:
+        version = importlib.metadata.version("bincio")
+    except importlib.metadata.PackageNotFoundError:
+        version = "0.1.0"
+    wheel_name = f"bincio-{version}-py3-none-any.whl"
+    dist_dir = Path(__file__).parent.parent.parent / "dist"
+    wheel_path = dist_dir / wheel_name
+    if not wheel_path.exists():
+        raise HTTPException(status_code=404, detail=f"{wheel_name} not found in dist/")
+    return FileResponse(wheel_path, media_type="application/zip", filename=wheel_name)
+
+
 @app.post("/api/activity/{activity_id}/images")
 async def upload_image(activity_id: str, file: UploadFile = File(...)) -> JSONResponse:
     dd = _get_data_dir()
diff --git a/bincio/serve/server.py b/bincio/serve/server.py
index ff78399..492e0c1 100644
--- a/bincio/serve/server.py
+++ b/bincio/serve/server.py
@@ -23,7 +23,7 @@ from typing import Any, Optional
 log = logging.getLogger("bincio.serve")
 
 from fastapi import Cookie, FastAPI, File, Form, HTTPException, Request, Response, UploadFile
-from fastapi.responses import RedirectResponse, StreamingResponse
+from fastapi.responses import FileResponse, RedirectResponse, StreamingResponse
 from fastapi.middleware.cors import CORSMiddleware
 from fastapi.middleware.gzip import GZipMiddleware
 from fastapi.responses import JSONResponse
@@ -448,9 +448,27 @@ async def wheel_version() -> JSONResponse:
     return JSONResponse({
         "version": version,
         "url": f"/bincio-{version}-py3-none-any.whl",
+        "api_url": f"/api/wheel/download",
     })
 
 
+@app.get("/api/wheel/download")
+async def wheel_download() -> FileResponse:
+    """Serve the bincio wheel directly (used locally; in prod nginx serves /bincio-*.whl)."""
+    import importlib.metadata
+    try:
+        version = importlib.metadata.version("bincio")
+    except importlib.metadata.PackageNotFoundError:
+        version = "0.1.0"
+    wheel_name = f"bincio-{version}-py3-none-any.whl"
+    # Look in dist/ relative to repo root (two levels up from this file)
+    dist_dir = Path(__file__).parent.parent.parent / "dist"
+    wheel_path = dist_dir / wheel_name
+    if not wheel_path.exists():
+        raise HTTPException(status_code=404, detail=f"{wheel_name} not found in dist/")
+    return FileResponse(wheel_path, media_type="application/zip", filename=wheel_name)
+
+
 @app.post("/api/auth/login", response_model=LoginResponse)
 async def login(
     login_req: LoginRequest,
diff --git a/docs/mobile-app.md b/docs/mobile-app.md
index 3f0a3a2..1f7cb08 100644
--- a/docs/mobile-app.md
+++ b/docs/mobile-app.md
@@ -51,20 +51,53 @@ server uses. Any tool in any language can read them.
 
 ---
 
-## Setup
+## Development setup
+
+### Two build modes: Expo Go vs Development Build
+
+This is the most important thing to understand before starting.
+
+**Expo Go** is the Expo app available on the Play Store / App Store. It runs any
+Expo project by scanning a QR code — no compilation step. However, it only supports
+Expo's own built-in modules. It does **not** support third-party native modules.
+
+**Development Build** is a custom version of the Expo Go app compiled specifically
+for this project. It includes all third-party native modules (react-native-webview,
+maplibre). It is installed once on the device; after that, code changes still update
+instantly via Metro (the JS bundler) — no rebuild needed.
+
+| | Expo Go | Development Build |
+|---|---|---|
+| Setup | Scan QR, instant | Build APK once (local or EAS cloud) |
+| expo-sqlite | ✅ | ✅ |
+| expo-document-picker | ✅ | ✅ |
+| react-native-webview (Pyodide) | ✗ | ✅ |
+| @maplibre/maplibre-react-native | ✗ | ✅ |
+| Code changes | instant (Metro) | instant (Metro) |
+| Native changes | need new Expo Go release | rebuild APK |
+
+**Phase 0** only uses built-in Expo modules — Expo Go works. **Phase 1** (Pyodide)
+requires a Development Build because `react-native-webview` is a native module.
+
+The recommended setup from the start is a Development Build so you never hit a wall
+mid-phase.
+
+---
 
 ### Prerequisites
 
-| Tool | Minimum version | Notes |
+| Tool | Required for | Install |
 |---|---|---|
-| Node.js | 18 | 20 LTS recommended — install via [nodejs.org](https://nodejs.org) or `nvm` |
-| npm | ships with Node | |
-| Expo Go app | latest | Install on your phone — scan the QR code to run the app instantly during development |
-| Xcode | 15+ | **macOS only, iOS builds.** Install from the App Store, then `xcode-select --install` |
-| Android Studio | latest | **Android builds / emulator.** Includes the SDK and `adb` |
+| Node.js 20 LTS | everything | [nodejs.org](https://nodejs.org) or `nvm install 20` |
+| npm | everything | ships with Node |
+| Android Studio | Android dev build / emulator | [developer.android.com/studio](https://developer.android.com/studio) |
+| Xcode 15+ | iOS only, macOS only | App Store → `xcode-select --install` |
+| EAS CLI | cloud builds (optional) | `npm install -g eas-cli` |
 
-You do **not** need Xcode or Android Studio to start. Expo Go lets you run the app
-on your physical device by scanning a QR code — no native build required.
+You do **not** need a physical Android device to start. The Android emulator
+(AVD Manager inside Android Studio) works fine for development.
+
+---
 
 ### First-time setup
 
@@ -73,25 +106,153 @@ on your physical device by scanning a QR code — no native build required.
 bash mobile/setup.sh
 ```
 
-The script checks prerequisites, installs npm dependencies, and generates the
-required Expo type declarations. It prints next steps when done.
+The script checks Node, Android SDK, and Xcode availability; installs npm
+dependencies; and generates the required Expo type declarations.
 
-### Running the app
+---
+
+### Phase 0 — Expo Go (quickest start)
+
+Since Phase 0 uses only built-in Expo modules, you can start with Expo Go:
 
 ```bash
 cd mobile
-
-# Development server — scan QR with Expo Go on your phone
 npx expo start
+```
 
-# Run on a connected Android device or emulator
-npx expo run:android
+1. Install **Expo Go** on your Android phone from the Play Store.
+2. Scan the QR code printed in the terminal.
+3. The app loads instantly. Code changes in your editor appear on the phone
+   within a second or two.
 
-# Run on iOS simulator (macOS only)
-npx expo run:ios
+> **Limitation**: once you add the Pyodide WebView in Phase 1, you must switch to
+> a Development Build. Expo Go will show an error for `react-native-webview`.
 
-# Build a standalone APK for Karoo sideloading
-npx eas build -p android --profile preview
+---
+
+### Phase 1+ — Development Build
+
+#### Option A: local build (Android Studio required)
+
+Plug in an Android device via USB (or start an emulator in Android Studio), then:
+
+```bash
+cd mobile
+npx expo run:android          # builds APK, installs it, starts Metro
+```
+
+This compiles the full native project once (~3–5 min). After that, JS changes
+reflect instantly without rebuilding.
+
+For the emulator, create an AVD in Android Studio with API 33+ and start it before
+running the command.
+
+#### Option B: EAS Build (cloud, no Android Studio required)
+
+EAS (Expo Application Services) builds the APK in the cloud. You get a download
+link; install it on your device once.
+
+```bash
+npm install -g eas-cli
+eas login                         # Expo account needed
+eas build -p android --profile development
+```
+
+After install, start Metro locally:
+
+```bash
+cd mobile
+npx expo start --dev-client
+```
+
+Shake the device to open the dev menu and enter the Metro URL if needed.
+
+---
+
+### iOS development (macOS only)
+
+```bash
+cd mobile
+npx expo run:ios               # opens iOS simulator, builds, and runs
+```
+
+Requires Xcode 15+ and an active iOS simulator. Cloud builds via EAS:
+
+```bash
+eas build -p ios --profile development   # requires Apple Developer account ($99/yr)
+```
+
+---
+
+### Where Pyodide comes from
+
+The hidden WebView loads Pyodide from the **jsDelivr CDN** — the same source
+as the `/convert/` page on the web:
+
+```
+https://cdn.jsdelivr.net/pyodide/v0.26.4/full/pyodide.js  (~30 MB)
+```
+
+On first extraction after install, the WebView downloads and caches this
+runtime in `expo-file-system`'s document directory. Subsequent extractions use
+the cached copy — no internet required.
+
+The **bincio wheel** (~50 KB) is fetched from:
+
+```
+GET {instance_url}/api/wheel/version   → { version, url, api_url }
+GET {instance_url}/bincio-{version}-py3-none-any.whl   (nginx, prod)
+GET {instance_url}/api/wheel/download                  (FastAPI, local dev)
+```
+
+If no instance is configured, it falls back to `https://bincio.org`. The wheel
+is also cached locally and re-downloaded only when the version changes.
+
+**Local development** (before bincio is published to PyPI): the wheel is not on
+PyPI, so there is a bundled fallback at `mobile/assets/bincio.whl`. The
+extraction code loads it from the app bundle when no cached wheel exists yet.
+This bundled copy is updated manually by running:
+
+```bash
+uv build --wheel              # builds dist/bincio-*.whl
+cp dist/bincio-*.whl mobile/assets/bincio.whl
+```
+
+The server-side `GET /api/wheel/download` endpoint also serves the wheel
+directly from `dist/` — useful when running a local `bincio serve` instance on
+the same WiFi network as the test device and wanting to exercise the update flow.
+
+The **common packages** (`fitdecode`, `gpxpy`, `lxml`, `pyyaml`) are fetched from
+the Pyodide CDN via micropip on first use and cached by the WebView's internal
+storage.
+
+**Summary of what touches the network:**
+
+| Asset | Size | When | Cached |
+|---|---|---|---|
+| Pyodide runtime | ~30 MB | once (first extraction ever) | ✅ permanently |
+| Common packages | ~5 MB | once | ✅ permanently |
+| bincio wheel | ~50 KB | on version bump (bundled fallback in assets/) | ✅ until next update |
+| Map tiles | per-tile | on pan/zoom | ✅ by MapLibre |
+
+Everything else — the activity files, the extracted BAS JSON — stays on device.
+
+---
+
+### Distributing the app
+
+| Target | Method |
+|---|---|
+| Your own Android phone | `npx expo run:android` via USB, or EAS development build |
+| Karoo 2 | EAS production build → download APK → sideload via `adb install bincio.apk` or Karoo's app sideloader |
+| Other Android users | EAS build → share APK download link (no Play Store needed) |
+| Play Store | EAS production build → upload `.aab` to Play Console |
+| iOS users | EAS build → TestFlight (beta) or App Store |
+
+For Karoo sideloading:
+```bash
+eas build -p android --profile preview   # produces a standalone APK
+adb install /path/to/bincio.apk          # with Karoo connected via USB
 ```
 
 ---
diff --git a/mobile/assets/bincio.whl b/mobile/assets/bincio.whl
new file mode 100644
index 0000000..18bdd2e
Binary files /dev/null and b/mobile/assets/bincio.whl differ