mars: mirror luna's Obsidian vault to disk with livesync-bridge

Gives the Hermes agent a real directory of markdown for the luna_wiki
vault, at /var/lib/livesync-bridge/vault and mounted into her container at
/opt/data/vault (inside HERMES_WRITE_SAFE_ROOT, so she can write, not only
read). Obsidian itself is an Electron GUI with no headless mode, and an
agent wants files rather than an app.

livesync-bridge is Deno, not packaged, and publishes no image — upstream
ships only a `build: .` compose file. So it comes in as a pinned non-flake
input and runs under systemd. Two things that are not obvious:

  - The source is COPIED to a fixed path rather than run from /nix/store.
    Deno keys localStorage — where the bridge records per-file sync state —
    by the main module's origin. Verified by running one source tree from
    two paths against a single DENO_DIR: two origin directories appear. Run
    from the store, every input bump would silently reset both peers to a
    full rescan.
  - It runs as uid 986/gid 983, the same identity the hermes container
    uses. Two uids in a shared group only works while every file stays
    group-writable, and one 0644 file dropped by the agent would stall sync
    on that path.

Talks to CouchDB over the tailnet (jupiter.orbit.sol:5984), so neptun's
vhost, its TLS and its path allowlist are all out of the picture.

Verified before deploying: `deno check` passes on nixpkgs' 2.8.3 (upstream
pins 2.6.9), and the bridge starts, reads LSB_CONFIG, detects a file and
writes its health heartbeat. Both directions confirmed working on mars
afterwards.

Credentials are currently the `obsidian` admin account and the personal
vault's passphrase, which means mars can decrypt every vault database and
not just luna's. Deliberate reuse of what existed; hosts/mars/secrets.nix
records the two independent ways to narrow it.

⚠️ Upstream has three open, unanswered issues on the storage->couchdb
direction (#50, #23, #46) and all fail silently — the log reports the
upload and the database is never updated. Do not treat this directory as
durable storage for anything luna cannot regenerate.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TLN5nkLBtCciD3ZnUwtw2b

hosts/mars/secrets.nix

@@ -65,4 +65,36 @@
   # so they're visible inside the container at /opt/data/....
   # restartUnits re-provisions both on rotation, without a full mars deploy.
   sops.secrets.gitea_luna_token.restartUnits = [ "hermes-agent-prepare-dirs.service" ];
+
+  # livesync-bridge (livesync-bridge.nix) — luna's Obsidian vault, mirrored
+  # out of CouchDB on jupiter. Both values are consumed by the rendered
+  # config.json rather than read directly, so the sops default of root:root
+  # 0400 is correct here; only the TEMPLATE needs an owner (set where it is
+  # defined, next to the vault path it references).
+  #
+  # couchdb_luna_password holds jupiter's `obsidian` ADMIN password — the same
+  # value as secrets/jupiter.yaml's couchdb_admin_password — and
+  # obsidian_luna_passphrase is the same passphrase as the personal vault.
+  # That is a deliberate choice to reuse what already existed, but it is worth
+  # being clear about what it costs: mars can decrypt and read EVERY vault
+  # database, not just luna's, and mars is the box running an autonomous
+  # agent. The two are independent to fix, cheapest first:
+  #
+  #   1. A vault-specific passphrase (re-encrypts luna's remote database, but
+  #      leaves the personal vault's contents unreadable from here).
+  #   2. A CouchDB account scoped to luna's database via _security (three curl
+  #      calls, in README -> "Obsidian vaults"), which also stops mars from
+  #      reaching the other databases at all.
+  #
+  # Neither is required for the bridge to work; both shrink the blast radius
+  # if mars is ever compromised.
+  sops.secrets.couchdb_luna_password = { };
+
+  # The E2EE passphrase for luna's vault, as entered in the Obsidian plugin.
+  # Vault passphrases otherwise never leave the clients (see the note in
+  # services/dev/obsidian-livesync.nix) — this one has to be here because mars
+  # IS a client: it decrypts in order to write real markdown to disk. Path
+  # obfuscation uses the same passphrase in the plugin, so the bridge's
+  # separate obfuscatePassphrase field is fed from this one value.
+  sops.secrets.obsidian_luna_passphrase = { };
 }