Feature: ephemeral / read-only mode (e.g. Raspberry Pi with overlayfs)

[pskillen]

Motivation

When running the bot on a Raspberry Pi with a read-only root filesystem (e.g. raspi-config overlay or similar), the default setup is awkward: main.py expects a writable DATA_DIR for SQLite (user_prefs, user_cmds, node_db), node_info.json load/save, and optional failed-packet dumps.

In that deployment, the bot is effectively a gateway: forward packets (and related telemetry) into the Meshflow API. Anything stored locally can be ephemeral—it does not need to survive reboot.

Current behavior (summary)

• DATA_DIR is created and used for three SQLite databases and JSON round-trips for InMemoryNodeInfoStore.
• StorageAPIWrapper can already skip disk on API errors if failed_packets_dir is None.
• Optional packet JSON dumps only occur when DUMP_PACKETS_PORTNUMS is set.
• Runtime behavior already includes InMemoryNodeDB in tests; production main always wires SqliteNodeDB.

Proposed feature

Add a first-class ephemeral / read-only mode (name TBD), e.g. env var EPHEMERAL=1 or READONLY_FS=1, that:

1. Uses InMemoryNodeDB instead of SQLite for node cache (acceptable tradeoff: empty after restart until traffic is seen).
2. Uses no-op or in-memory AbstractCommandLogger and AbstractUserPrefsPersistence so admin history and prefs are not persisted (or document that admins should use tmpfs if they want SQLite until reboot).
3. Skips node_info.json load/save (or no-ops) so shutdown does not require a writable path.
4. Passes failed_packets_dir=None to StorageAPIWrapper so failed uploads are not written to disk.
5. Does not call os.makedirs for a persistent data directory when nothing needs it—or documents DATA_DIR on tmpfs as the supported path for users who still want SQLite until reboot without code changes.

Acceptance criteria (suggested)

• Bot starts and uploads packets to the API with no writes to the read-only root when ephemeral mode is enabled (aside from OS/Python temp if any).
• Document the mode in README / .env.example with a short Raspberry Pi + overlay note.
• Existing default behavior unchanged when the flag is off.

Workaround today

Point DATA_DIR at tmpfs (e.g. under /run or /tmp) so SQLite and JSON work on a volatile filesystem; optionally patch main to pass failed_packets_dir=None. This issue asks for built-in support so operators do not need a fork or manual wiring.

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Related context: packet ingestion does not inherently require SQLite; local DBs mainly support commands, !nodes, prefs, and admin history.