diff --git a/roundtable/core/settings.py b/roundtable/core/settings.py
index e6568f8..e924565 100644
--- a/roundtable/core/settings.py
+++ b/roundtable/core/settings.py
@@ -36,6 +36,9 @@ _DEFAULT_WEBHOOK_TEMPLATE = (
 # All recognised settings and their defaults.
 # Plugin settings are stored as "plugin.<name>" and handled separately.
 DEFAULTS: dict[str, Any] = {
+    # General — external URL for install scripts, share links, alert deep-links.
+    # Empty = fall back to the current request's Host header.
+    "general.public_base_url": "",
     "session.lifetime_hours": 8,
     "data.retention_days": 90,
     "monitors.poll_interval_seconds": 60,