Database federation bridge: ArangoDB (game) + VerisimDB (levels)

Add 3 new Elixir modules to the sync server for database federation:
- ArangoClient: HTTP client for ArangoDB (document CRUD, AQL, graph traversal)
- VerisimClient: HTTP client for VerisimDB (hexad CRUD, text search, VQL)
- DatabaseBridge: coordination GenServer with schema validation, health
  monitoring, and graceful degradation (starts even if DBs are offline)

8 new REST endpoints under /db/ (health, players, topology, query, levels,
search). Req library added as sole new dependency. Design document with
full 4-tier database comparison table and glossary.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: hyperpolymath

idaptik-level-architect/docs/design/DESIGN-2026-02-27-database-tier-comparison.adoc

@@ -18,3 +18,20 @@ config :idaptik_sync_server, IDApixiTIK.SyncServerWeb.Endpoint,
 
 # Jason as default JSON library for Phoenix
 config :phoenix, :json_library, Jason
+
+# ---------------------------------------------------------------------------
+# Database Federation — ArangoDB (game data) + VerisimDB (level architect data)
+# Dev defaults — overridden by env vars in config/runtime.exs for production.
+# ---------------------------------------------------------------------------
+
+# ArangoDB: Joshua's live game data (players, sessions, network topology graph)
+config :idaptik_sync_server, IDApixiTIK.SyncServer.ArangoClient,
+  url: "http://localhost:8529",
+  database: "idaptik",
+  user: "root",
+  password: ""
+
+# VerisimDB: Level architect data (level hexads, version history, similarity search)
+config :idaptik_sync_server, IDApixiTIK.SyncServer.VerisimClient,
+  url: "http://localhost:8080/api/v1",
+  timeout: 30_000

idaptik-level-architect/idaptik-sync-server/config/config.exs

@@ -37,4 +37,17 @@ if config_env() == :prod do
     http: [port: port, ip: {0, 0, 0, 0}],
     url: [host: phx_host, port: port],
     secret_key_base: secret_key_base
+
+  # ── Database Federation ──────────────────────────────────────────────────
+  # ArangoDB: Joshua's game data (network topology, players, sessions)
+  config :idaptik_sync_server, IDApixiTIK.SyncServer.ArangoClient,
+    url: System.get_env("ARANGO_URL", "http://localhost:8529"),
+    database: System.get_env("ARANGO_DB", "idaptik"),
+    user: System.get_env("ARANGO_USER", "root"),
+    password: System.get_env("ARANGO_PASSWORD", "")
+
+  # VerisimDB: Level architect data (level hexads, version history, similarity)
+  config :idaptik_sync_server, IDApixiTIK.SyncServer.VerisimClient,
+    url: System.get_env("VERISIM_URL", "http://localhost:8080/api/v1"),
+    timeout: 30_000
 end

idaptik-level-architect/idaptik-sync-server/config/runtime.exs

@@ -18,6 +18,11 @@ defmodule IDApixiTIK.SyncServer.Application do
       IDApixiTIK.SyncServer.GameStore,
       IDApixiTIK.SyncServer.GameSessionRegistry,
 
+      # Database federation bridge — ArangoDB (game) + VerisimDB (levels)
+      # Must start after Cache (uses ETS) but before Endpoint (serves requests).
+      # Starts in degraded mode if either database is unavailable.
+      IDApixiTIK.SyncServer.DatabaseBridge,
+
       # Phoenix Endpoint — serves WebSocket (channels) + REST API
       IDApixiTIK.SyncServerWeb.Endpoint
     ]