Model rules: who a chat's model may bring into a conversation

Rules read from the main model decide who it is offered as a crowd member,
a friend and on its roster; any-to-any with denies by default, or
none-to-none with allows. The crowd picker names what it holds back and
why, and a model held back only by a person's own rule -- or by anything,
with the new rules.override -- can still be added by hand. Another data
group is now a deny that an explicit rule opens. Admin -> Model rules and
a card in Settings, each with a matrix drawn by the enforcing function.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/lembas/services/settings_store.py

@@ -33,6 +33,7 @@ IMAGES = "images"
 SCHEDULES = "schedules"
 SUBAGENTS = "subagents"
 CROWD = "crowd"
+RULES = "rules"
 BRANDING = "branding"
 EXTRACTION = "extraction"
 
@@ -349,6 +350,16 @@ def _schedules_defaults() -> dict[str, Any]:
     }
 
 
+def _rules_defaults() -> dict[str, Any]:
+    """Who may talk to whom, instance-wide. See services/talk.py.
+
+    `open` is any model to any model, with deny rules; `closed` is none to none,
+    with allow rules. Open by default, so an instance that never looks behaves
+    exactly as it did before rules existed.
+    """
+    return {"mode": "open"}
+
+
 def _crowd_defaults() -> dict[str, Any]:
     """Several models answering one turn, in order, then again in reverse.
 
@@ -431,6 +442,7 @@ _DEFAULTS: dict[str, Any] = {
     SCHEDULES: _schedules_defaults,
     SUBAGENTS: _subagents_defaults,
     CROWD: _crowd_defaults,
+    RULES: _rules_defaults,
     # Whose instance this is. The defaults live in `services/branding.py`
     # beside the code that reads them, because every one of them is paired with
     # a label and a hint for the admin page and splitting the three across two
@@ -726,6 +738,13 @@ def crowd(db: DBSession) -> dict[str, Any]:
     return values
 
 
+def rules(db: DBSession) -> dict[str, Any]:
+    """The talk-rules group, with the mode clamped to the two that exist."""
+    values = get_group(db, RULES)
+    values["mode"] = "closed" if values.get("mode") == "closed" else "open"
+    return values
+
+
 def images_ready(db: DBSession) -> bool:
     """Whether image generation can actually happen.