Workspace layout: move runtime data out of the repo into ~/.pi-droid/

[ArtemisAI]

Problem

Runtime state currently lives inside the source tree:

• data/accounts.json — account credentials
• SSH keys, logs, screenshots — ad-hoc locations or absent
• No resolution convention for per-install state

This couples the agent to its checkout, makes plugin installs per-workspace awkward, and makes it hard to run pi-droid in topologies where the source tree isn't writable (e.g., a global install or on-device Termux).

The .pi-droid/ entry exists in .gitignore but is unused — the slot is reserved and we just haven't moved into it.

Proposal

One workspace directory, resolved per-process:

Resolution order

1. PI_DROID_HOME env var
2. $XDG_DATA_HOME/pi-droid (if set)
3. ~/.pi-droid/
4. ./.pi-droid/ in repo root (dev mode only, detected by pi-droid package.json in cwd)

Layout

<workspace>/
├── workspace.json       # device + transport config
├── accounts.json        # replaces data/accounts.json
├── ssh-keys/
├── plugins/             # installed marketplace plugins, per-workspace
├── state/               # resumable flow progress, locks
├── logs/flows/
├── screenshots/         # failure diagnostics only
└── cache/               # transient, e.g., CDP tokens

Permissions: 0700 on root, 0600 on secret-bearing files.

workspace.json schema

{
  "version": 1,
  "devices": {
    "s9-brain":  { "transport": "local-adb", "serial": "…" },
    "s9-remote": { "transport": "remote-adb", "ssh": "brain", "serial": "…" },
    "self":      { "transport": "on-device" }
  },
  "default": "s9-brain"
}

Back-compat

• ANDROID_SERIAL env var still works (short-circuits to local-adb).
• data/accounts.json still read as fallback with a one-time deprecation warning pointing at ~/.pi-droid/.
• ACCOUNTS_JSON env var still honored (wins over both).

Design doc

See docs/CONNECTIVITY.md § Workspace resolution.

Depends on / blocks

• Pairs with: Transport abstraction: decouple tools from local ADB binary #10 (uses workspace.json device definitions)
• Related: Issue 1 (standalone pidroid CLI) — CLI reads workspace to pick default device