feat: Replace WireGuard relay with Headscale for P2P mesh

[DarrenZal]

Summary

Replace the WireGuard star-topology relay with Headscale (self-hosted Tailscale) to remove the plaintext middlebox from the vault sync data path. Currently the relay decrypts/re-encrypts between peers — it can read all traffic. Headscale gives direct P2P WireGuard tunnels when NAT allows, with encrypted DERP fallback when it doesn't.

Companion to #18 (app-level E2EE). Together they provide defense-in-depth: no server can read payload contents.

Problem

In the current WireGuard star topology, the relay at poly@37.27.48.12 holds all peer keys and acts as a Layer 3 packet forwarder. It decrypts from Peer A and re-encrypts for Peer B — meaning the relay operator can read all plaintext IP packets including file contents, entity data, and federation events.

Proposed Solution

Phase 0: Deploy Headscale coordination server on poly (parallel with existing WG)

Phase 1: Migrate admin node (Darren's MacBook) to Tailscale

Phase 2: Migrate remaining peers (Shawn, NUC, friend-e2e)

Phase 3: Rewrite federation scripts (invite token schema, bootstrap flow, onboarding)

Phase 4: Extend E2EE to domain events (defense-in-depth, see #18)

Phase 5: MagicDNS + automated discovery (stretch)

Key Properties

• Zero KOI-net core code changes — protocol is transport-agnostic (HTTP POST to base_url)
• Zero-downtime migration — WireGuard and Tailscale run simultaneously
• Direct P2P when NAT allows — encrypted DERP fallback otherwise
• DERP relay can't decrypt — fundamentally different from current WG star topology
• Simpler onboarding — tailscale up --authkey=<key> vs ~15-step WG dance

Scripts to Modify

• setup-relay.sh → setup-headscale.sh
• activate-wireguard.sh → install-tailscale.sh
• bootstrap-node.sh — rewrite invite token schema (currently WG-shaped)
• create-invite.sh, approve-peer.sh, connect-peers.sh, validate-node.sh, remove-peer.sh
• smoke-vault-sync.sh, personal-env.template, lib.sh

Files Unchanged (transport-agnostic)

• api/koi_poller.py, api/koi_net_router.py, api/vault_sync.py
• api/koi_protocol.py, api/koi_envelope.py, api/event_queue.py
• api/koi_encryption.py, api/federation_events.py

Full Plan

See /plans/virtual-baking-cloud.md in the repo for the detailed implementation plan with code paths, DERP strategy options, and verification steps.

References

• Tailscale architecture
• Headscale DERP
• Headscale ACLs (HuJSON)
• feat: Application-level E2EE for vault sync #18 — App-level E2EE for vault sync