feat(pos): add tenant manager — provision DBs from template with sql.Identifier

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

pos/tenant_db.py

@@ -0,0 +1,31 @@
+# /home/Autopartes/pos/tenant_db.py
+"""Tenant DB connection manager. Gets a psycopg2 connection for a specific tenant."""
+
+import psycopg2
+from config import MASTER_DB_URL, TENANT_DB_URL_TEMPLATE
+
+
+def get_master_conn():
+    """Get connection to nexus_master DB."""
+    return psycopg2.connect(MASTER_DB_URL)
+
+
+def get_tenant_conn(tenant_id):
+    """Get connection to a tenant's DB by looking up db_name in nexus_master."""
+    master = get_master_conn()
+    cur = master.cursor()
+    cur.execute("SELECT db_name FROM tenants WHERE id = %s AND is_active = true", (tenant_id,))
+    row = cur.fetchone()
+    cur.close()
+    master.close()
+
+    if not row:
+        raise ValueError(f"Tenant {tenant_id} not found or inactive")
+
+    db_name = row[0]
+    return psycopg2.connect(TENANT_DB_URL_TEMPLATE.format(db_name=db_name))
+
+
+def get_tenant_conn_by_dbname(db_name):
+    """Get connection to a tenant DB directly by name."""
+    return psycopg2.connect(TENANT_DB_URL_TEMPLATE.format(db_name=db_name))