On-device worker: run pi-droid inside the phone (Termux)

[ArtemisAI]

Problem

Today pi-droid must run on an external host with the adb binary and reach the device over USB or WiFi. That excludes a useful topology: pi-droid running inside the phone itself, as a long-lived worker under Termux. Benefits:

• No host machine required — phone is self-sufficient
• No ADB authorization dialog / USB cable / WiFi reachability
• Phone can participate in the pi-agent mesh as a full node
• Fits the README's "inbound triggers from Telegram/Discord" pattern cleanly

Proposal

Implement OnDeviceTransport per the transport abstraction:

• shell(cmd) → direct child_process (no adb shell prefix)
• adb(args) → throws UnsupportedByTransport
• forward(local, remote) → Termux-API or socat
• screenshot() → termux-screenshot (or screencap -p if rooted; fallback if neither)
• capabilities.hostFs = "android", capabilities.adb = false, capabilities.screenMirror = "native"

Workspace on Termux

Same workspace resolution as other topologies — PI_DROID_HOME defaults to $HOME/.pi-droid inside Termux. An install script sets this env var and installs deps (pkg install nodejs python openssh).

Which tools degrade gracefully?

• ADB-required tools (tcpip, install, pm list packages via adb, port forward from another host): return UnsupportedByTransport.
• Shell-based tools (tap via input tap, key events, screencap, settings queries): work unchanged.
• Plugin flows (Ollama, Gmail): work because they use shell+CDP, not raw adb — once #10 migrates ollama-setup.ts:167 off direct execAsync.

Deliverables

1. src/transport/OnDeviceTransport.ts
2. scripts/install-termux.sh — one-line installer for Termux
3. Docs: Termux setup guide under docs/ON_DEVICE.md
4. Capability matrix: which of the ~36 tools work in on-device mode

Design doc

See docs/CONNECTIVITY.md § Topology C.

Depends on

• Transport abstraction: decouple tools from local ADB binary #10 (blocker)
• Workspace layout: move runtime data out of the repo into ~/.pi-droid/ #11 (needed for Termux config resolution)