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

flake.lock

@@ -176,6 +176,22 @@
         "url": "https://git.mgaction.town/darman/hypr-chrome.git"
       }
     },
+    "livesync-bridge": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1787571662,
+        "narHash": "sha256-btLnQNbFzCPaSVcY9rtiPdYeXrZjoK9AYvfA9+ovsIc=",
+        "owner": "vrtmrz",
+        "repo": "livesync-bridge",
+        "rev": "c3760beaa0851214da4860903445d7f6420ca025",
+        "type": "github"
+      },
+      "original": {
+        "owner": "vrtmrz",
+        "repo": "livesync-bridge",
+        "type": "github"
+      }
+    },
     "media-manager": {
       "flake": false,
       "locked": {
@@ -490,6 +506,7 @@
         "disko": "disko",
         "home-manager": "home-manager",
         "hypr-chrome": "hypr-chrome",
+        "livesync-bridge": "livesync-bridge",
         "mediamanager-nix": "mediamanager-nix",
         "nix-flatpak": "nix-flatpak",
         "nixos-anywhere": "nixos-anywhere",