Helpers on another model, chosen by logic rather than by the model

A helper still runs on the chat's own model by default. Other models are
designated per main model -- offered to it, or by hand only -- by the
instance or, with helpers.designate, by a person. subagent_run gains a
model argument whose enum is exactly the candidates that passed two
checks: capacity (a model that serves one request at a time cannot be
its own helper; a connection that holds one model at a time cannot serve
a helper on another of its models) and the model rules. A helper on
another model takes that model's own effort and data group. The composer
gains a Helpers picker; the model page, the connection form and Settings
gain their switches and lists.

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

CHANGELOG.md

@@ -16,6 +16,76 @@ for 1.0.0 have something to be assembled from.
 
 ## Unreleased
 
+## 1.12.0
+
+Helpers on another model. This is the last of the three releases.
+
+- **A helper can run on a different model.** A helper is still the chat's own
+  model by default. On each model's page, **Helpers** lists other models this
+  one may send helpers to. Each is either *offered to the model*, so it can
+  choose that model itself, or *by hand only*, so it is used once somebody adds
+  it to a chat. When there is more than one choice, `subagent_run` gains a
+  `model` argument limited to exactly those models, and the model is told what
+  each is for. A helper on another model runs with that model's own default
+  reasoning effort, never the parent's, which it might refuse. It reads its own
+  data group's memories and notes.
+- **The composer's Helpers button** lists the models designated for the chat's
+  model. Tick one to add it to this chat, on the new-chat screen as well.
+- **Capacity is decided by logic, not by the model.** Two new switches, both off
+  by default, so nothing changes until they are set:
+  - **Serves one request at a time**, on a model. It cannot be its own helper,
+    because the helper would wait behind the reply that is waiting for it.
+  - **Holds one model at a time**, on a connection (llama-swap in front of one
+    GPU). Its models may still be their own helpers, but never send one to
+    another model on the same connection, because loading it would unload the
+    model whose reply is waiting.
+
+  A model with no helper it can use is no longer offered `subagent_run` at all,
+  instead of being offered a tool that refuses every call. Asking a friend and
+  the crowd are not affected: both are sequential, and the wait for a model to
+  load is accepted there.
+- **The model rules apply to helpers too.** A designation the model chooses
+  itself must be allowed by the rules. One added to a chat by hand needs what a
+  crowd member added by hand needs. A model in another data group needs a rule
+  that allows it.
+- **Your own helper models.** With the new *Choose their own helper models*
+  permission (off by default), Settings → Models lets a person designate helpers
+  for their models. These are added to the instance's, and a row of theirs for
+  the same pair replaces the instance's.
+
+## 1.11.0
+
+Rules for which model may talk to which. This is the second of three releases;
+the third adds helpers on a different model.
+
+- **Model rules.** The new **Admin → Model rules** page sets who a chat's model
+  may bring into the conversation: as a crowd member, as a friend it asks, and
+  on its list of other models. A rule names two models, or *any model* on either
+  side, and allows or forbids. The starting point is either *any model may talk
+  to any other* (the default, so nothing changes) or *no model may talk to
+  another*. The most specific rule wins. The page ends with a table of every
+  model against every other, drawn by the same rules that are enforced.
+- **A rule is read from the chat's own model.** If gpt-oss may not talk to
+  qwen38, then in a gpt-oss chat qwen38 is not on its list of other models, it
+  cannot be asked as a friend, and the crowd picker does not offer it. Members
+  of a crowd are not checked against each other.
+- **The crowd picker names what it holds back, and why.** Models the rules do
+  not offer are listed under *Not offered to this model* with the reason. You
+  can still tick one by hand when the rule holding it back is your own, or when
+  you may override the instance's rules. A member added by hand keeps speaking
+  when the round runs; one the instance later forbids is skipped and shown
+  crossed out, as a member that cannot be reached always was.
+- **Your own rules.** Settings → Models has a card for your own starting point
+  and rules, and the same table for you. Anybody can narrow the instance's
+  rules for themselves. With the new *Override the model rules for themselves*
+  permission (off by default), your rules and starting point win over the
+  instance's, and you can add any model to a crowd by hand.
+- **Another data group is a rule, not a wall.** In 1.10.0 a model from another
+  data group could never join a conversation. Now it is not offered unless a
+  rule explicitly allows it: the instance's, or your own with the override.
+  When it does join, it reads its own group's memories and notes, never the
+  chat's.
+
 ## 1.10.0
 
 Data groups: a provider's models read only the data of the group their

scripts/shoot.py

@@ -324,6 +324,12 @@ def build_client():
         owner = db.query(User).first()
         db.add(Note(owner_id=owner.id, title="A note at home", body="x", data_group_id="default"))
         db.add(Note(owner_id=owner.id, title="A hosted note", body="x", data_group_id="hosted"))
+        # A rule and a designation, so the rules page, the matrix and the
+        # model page's Helpers card render with something in them.
+        from lembas.db.models import HelperDesignation, TalkRule
+
+        db.add(TalkRule(from_model="gemma4-moe", to_model="qwen3-coder", effect="deny"))
+        db.add(HelperDesignation(main_model="gemma4-moe", helper_model="qwen3-coder"))
         local = db.query(Connection).filter_by(name="local").first()
         db.add(
             Chat(

src/lembas/__init__.py

@@ -1,3 +1,3 @@
 """LLeMbas - a Middle-earth themed web UI for OpenAI-compatible LLM endpoints."""
 
-__version__ = "1.10.0"
+__version__ = "1.12.0"

src/lembas/api/admin.py

@@ -177,8 +177,10 @@ async def update_connection(
     unload_method: str = Form("POST"),
     extra_headers: str = Form(""),
     data_group_id: str = Form(""),
+    one_model_at_a_time: bool = Form(False),
 ) -> Response:
     connection = _connection(db, connection_id)
+    connection.one_model_at_a_time = one_model_at_a_time
     # Which of the instance's data groups this provider reads. Empty is "not
     # submitted" -- an older page -- and leaves it alone; a personal group is
     # somebody else's arrangement and cannot be chosen here.

src/lembas/api/admin_models.py

@@ -14,6 +14,7 @@ from sqlalchemy.orm import Session as DBSession
 from lembas.api.deps import AdminUser, Db, RequiredUser
 from lembas.db.models import AUTHOR_USER, Connection, Group, Model, PersonaRevision
 from lembas.services import chat as chat_service
+from lembas.services import helpers as helpers_service
 from lembas.services import personas as personas_service
 from lembas.services import settings_store, uploads
 from lembas.services.llm.openai_client import MAX_CONTEXT
@@ -209,6 +210,16 @@ async def model_detail(
             # and undo what a model wrote *before* they switched it off, which is
             # exactly when they would come looking.
             "persona": personas_service.get(db, model.model_id, None),
+            # Helpers designated for this model by the instance, and every other
+            # model id that could be one.
+            "designations": [
+                d for d in helpers_service.own_designations(db, None)
+                if d.main_model == model.model_id
+            ],
+            "helper_choices": sorted(
+                {m.model_id for m in chat_service.available_models(db, user)}
+                - {model.model_id}
+            ),
             "persona_limit": personas_service.MAX_PERSONA_CHARS,
             "position_of": index + 1,
             "total": len(ordered),
@@ -261,6 +272,7 @@ async def update_model(
     enabled: bool = Form(False),
     pinned: bool = Form(False),
     public: bool = Form(False),
+    single_session: bool = Form(False),
     position: str = Form(""),
     context_length: str = Form(""),
     default_effort: str = Form(""),
@@ -284,6 +296,7 @@ async def update_model(
     model.enabled = enabled
     model.pinned = pinned
     model.public = public
+    model.single_session = single_session
 
     # Merged rather than rebuilt, unlike the capabilities below: params_json
     # holds whatever sampling defaults an administrator has set and this form
@@ -338,6 +351,35 @@ async def update_model(
     )
 
 
+@router.post("/admin/models/{model_id}/helpers")
+async def add_helper(
+    db: Db,
+    user: AdminUser,
+    model_id: str,
+    helper_model: str = Form(""),
+    offer: bool = Form(False),
+) -> Response:
+    """Designate a model this one may send helpers to, for everybody.
+
+    Its own form, for the persona's reason: a list edited row by row, not a field
+    carried by the big save.
+    """
+    model = _model(db, model_id)
+    helpers_service.set_designation(db, None, model.model_id, helper_model, offer=offer)
+    return RedirectResponse(
+        f"/admin/models/{model.id}/edit?saved=Helpers+updated.", status_code=303
+    )
+
+
+@router.post("/admin/models/{model_id}/helpers/{designation_id}/delete")
+async def remove_helper(db: Db, user: AdminUser, model_id: str, designation_id: str) -> Response:
+    model = _model(db, model_id)
+    helpers_service.delete_designation(db, None, designation_id)
+    return RedirectResponse(
+        f"/admin/models/{model.id}/edit?saved=Helpers+updated.", status_code=303
+    )
+
+
 @router.post("/admin/models/{model_id}/persona")
 async def update_persona(
     db: Db,

src/lembas/api/admin_rules.py

@@ -0,0 +1,85 @@
+"""Model rules: which model may bring which into a conversation.
+
+The instance's layer. A person's own rules and mode are on their settings page
+(`api/preferences.py`), and `services/talk.py` is where the two are combined.
+
+The page ends in a matrix -- every main model against every other -- drawn by
+`talk.matrix`, which calls the same `decide` that enforces the rules. A preview
+computed any other way would be a second copy of the logic, and a preview that
+disagrees with enforcement is worse than none: it is believed.
+"""
+
+from __future__ import annotations
+
+from fastapi import APIRouter, Form, Request, Response, status
+from fastapi.responses import RedirectResponse
+
+from lembas.api.deps import AdminUser, Db
+from lembas.api.pages import describe_verdict
+from lembas.db.models import ANY_MODEL, EFFECT_ALLOW, EFFECT_DENY
+from lembas.services import chat as chat_service
+from lembas.services import settings_store, talk
+from lembas.web.templating import render
+
+router = APIRouter(prefix="/admin/rules", tags=["admin-rules"])
+
+
+def model_ids(db, user) -> list[str]:
+    """Every model id this person can reach, once each, in the admin's order."""
+    seen: list[str] = []
+    for model in chat_service.available_models(db, user):
+        if model.model_id not in seen:
+            seen.append(model.model_id)
+    return seen
+
+
+@router.get("")
+async def rules_page(request: Request, db: Db, user: AdminUser, saved: str = ""):
+    models = chat_service.available_models(db, user)
+    return render(
+        request,
+        "admin/rules.html",
+        {
+            "mode": settings_store.rules(db)["mode"],
+            "rules": talk.rules_of(db, None),
+            "model_ids": model_ids(db, user),
+            "any_model": ANY_MODEL,
+            "allow": EFFECT_ALLOW,
+            "deny": EFFECT_DENY,
+            "matrix_models": models,
+            # The instance's own view: no person's layer and no override, which
+            # is what somebody without `rules.override` gets unless they narrow.
+            "matrix": talk.matrix(db, None, models),
+            "describe_verdict": describe_verdict,
+            "saved": saved,
+        },
+    )
+
+
+@router.post("/mode")
+async def save_mode(db: Db, user: AdminUser, mode: str = Form(talk.MODE_OPEN)) -> Response:
+    settings_store.update(
+        db,
+        {"mode": talk.MODE_CLOSED if mode == talk.MODE_CLOSED else talk.MODE_OPEN},
+        key=settings_store.RULES,
+    )
+    return RedirectResponse("/admin/rules?saved=1", status_code=status.HTTP_303_SEE_OTHER)
+
+
+@router.post("")
+async def add_rule(
+    db: Db,
+    user: AdminUser,
+    from_model: str = Form(ANY_MODEL),
+    to_model: str = Form(ANY_MODEL),
+    effect: str = Form(EFFECT_DENY),
+    both: bool = Form(False),
+) -> Response:
+    talk.set_rule(db, None, from_model, to_model, effect, both=both)
+    return RedirectResponse("/admin/rules?saved=1", status_code=status.HTTP_303_SEE_OTHER)
+
+
+@router.post("/{rule_id}/delete")
+async def delete_rule(db: Db, user: AdminUser, rule_id: str) -> Response:
+    talk.delete_rule(db, None, rule_id)
+    return RedirectResponse("/admin/rules?saved=1", status_code=status.HTTP_303_SEE_OTHER)

src/lembas/api/chats.py

@@ -37,6 +37,7 @@ from lembas.services import compaction as compaction_service
 from lembas.services import data_groups, interaction, settings_store, sse
 from lembas.services import files as files_service
 from lembas.services import generation as generation_service
+from lembas.services import helpers as helpers_service
 from lembas.services import metrics as metrics_service
 from lembas.services import prompts as prompts_service
 from lembas.services import reports as reports_service
@@ -309,6 +310,7 @@ async def start_chat(
     # -- the same mechanism the scope switches above use, and the reason the control
     # lives inside the composer's form rather than in the topbar.
     crowd_model_ids: list[str] = Form(default=[]),
+    helper_model_ids: list[str] = Form(default=[]),
 ) -> Response:
     """Create a chat from its first message.
 
@@ -343,6 +345,7 @@ async def start_chat(
     )
 
     _apply_crowd(db, chat, user, crowd_model_ids)
+    helpers_service.apply_chat_helpers(db, chat, user, helper_model_ids)
 
     _adopt_draft(db, user, draft_id, chat)
 
@@ -1546,15 +1549,15 @@ def _apply_crowd(db: DBSession, chat: Chat, user: User, values: list[str]) -> No
     and a model offered by two connections is two rows with different capabilities.
     """
     from lembas.db.models import CrowdMember
+    from lembas.services import talk
 
     settings = settings_store.crowd(db)
-    # Only models in the chat's own data group: a member is sent the whole
-    # conversation, so one from another group would carry it to that provider.
+    # What this person may add by hand, by the talk rules from the chat's main
+    # model. A member is sent the whole conversation, so one in another data
+    # group comes in only when a rule explicitly lets it.
     reachable = {
         model.model_id: model
-        for model in chat_service.available_models(
-            db, user, data_groups.for_chat(db, chat)
-        )
+        for model in talk.addable(db, user, chat.model_id, data_groups.for_chat(db, chat))
     }
     wanted: list[str] = []
     for value in values:
@@ -2200,6 +2203,10 @@ async def update_chat(request: Request, db: Db, user: RequiredUser, chat_id: str
         # every box clears the crowd.
         _apply_crowd(db, chat, user, form.getlist("crowd_model_ids"))
 
+    if "helper_model_ids" in form:
+        # The helpers picker, the same shape again.
+        helpers_service.apply_chat_helpers(db, chat, user, form.getlist("helper_model_ids"))
+
     submitted_params = {name: form[name] for name in _PARAM_RANGES if name in form}
     if submitted_params:
         if not allowed.get("chat.params"):

src/lembas/api/pages.py

@@ -100,6 +100,7 @@ def _chat_context(db: DBSession, user: User, chat: Chat | None) -> dict:
         **_crowd_context(
             db, user, chat, in_group, current.model_id if current is not None else ""
         ),
+        **_helper_context(db, user, chat, current.model_id if current is not None else ""),
         # What *this* model takes, not the three every model used to be assumed
         # to take. The vocabulary is per model -- gpt-oss has no `xhigh` and
         # Bonsai has no `high`, and sending the wrong one does not degrade, it
@@ -213,6 +214,43 @@ def _scope_context(db: DBSession, user: User, chat: Chat | None) -> dict:
     }
 
 
+def _talk_settings(db: DBSession, user: User) -> dict:
+    """The person's own talk rules, and the matrix as it applies to them."""
+    from lembas.api.admin_rules import model_ids
+    from lembas.db.models import ANY_MODEL, EFFECT_ALLOW, EFFECT_DENY
+    from lembas.services import talk
+
+    models = chat_service.available_models(db, user)
+    return {
+        "talk_mode": talk.user_mode(user),
+        "talk_override": talk.may_override(db, user),
+        "talk_rules": talk.rules_of(db, user),
+        "talk_matrix_models": models,
+        "talk_matrix": talk.matrix(db, user, models),
+        "model_ids": model_ids(db, user),
+        "any_model": ANY_MODEL,
+        "allow": EFFECT_ALLOW,
+        "deny": EFFECT_DENY,
+        "describe_verdict": describe_verdict,
+        **_helper_settings(db, user),
+    }
+
+
+def _helper_settings(db: DBSession, user: User) -> dict:
+    """The person's own helper designations, and whether they may add any."""
+    from lembas.services import helpers as helpers_service
+
+    may = helpers_service.may_designate(db, user)
+    shown = bool(settings_store.subagents(db).get("enabled")) and permissions.has(
+        db, user, "tools.subagent"
+    )
+    return {
+        "helper_settings_shown": shown,
+        "may_designate": may,
+        "own_designations": helpers_service.own_designations(db, user),
+    }
+
+
 def _data_group_settings(db: DBSession, user: User) -> dict:
     """What the Data tab on /settings shows: which group each connection reads.
 
@@ -251,6 +289,68 @@ def _data_group_settings(db: DBSession, user: User) -> dict:
     }
 
 
+def describe_verdict(verdict) -> str:
+    """Why a model is not offered, in the reader's language.
+
+    `talk.Verdict` carries a code so this can be said here with `t()`, while a
+    model refused a friend is told the same thing in English.
+    """
+    from lembas.services import talk
+
+    rule = verdict.rule
+    if verdict.why in (talk.WHY_INSTANCE_RULE, talk.WHY_YOUR_RULE) and rule is not None:
+        frm = i18n.t("any model") if rule.from_model == "*" else rule.from_model
+        to = i18n.t("any model") if rule.to_model == "*" else rule.to_model
+        if verdict.why == talk.WHY_INSTANCE_RULE:
+            if rule.effect == "allow":
+                return i18n.t("The instance's rule %(a)s → %(b)s allows it.", a=frm, b=to)
+            return i18n.t("The instance's rule %(a)s → %(b)s forbids it.", a=frm, b=to)
+        if rule.effect == "allow":
+            return i18n.t("Your rule %(a)s → %(b)s allows it.", a=frm, b=to)
+        return i18n.t("Your rule %(a)s → %(b)s forbids it.", a=frm, b=to)
+    return {
+        talk.WHY_GROUP: i18n.t("It is in another data group."),
+        talk.WHY_INSTANCE_CLOSED: i18n.t("The instance lets no model talk to another."),
+        talk.WHY_YOUR_CLOSED: i18n.t("Your setting lets no model talk to another."),
+    }.get(verdict.why, "")
+
+
+def _helper_context(db: DBSession, user: User, chat: Chat | None, own: str) -> dict:
+    """The helpers picker: models designated for this chat's model, to add by hand.
+
+    Only when helpers are on and this person may send one, and only when
+    something is designated -- with nothing designated the model is its own
+    helper and there is nothing to choose. On the new-chat screen the choice
+    rides along with the first message, exactly as the crowd's does.
+    """
+    from lembas.services import helpers as helpers_service
+
+    empty = {"helper_choices": [], "helper_member_ids": []}
+    if not settings_store.subagents(db).get("enabled"):
+        return empty
+    if not permissions.has(db, user, "tools.subagent"):
+        return empty
+    main = chat if chat is not None else own
+    if not main:
+        return empty
+    choices = helpers_service.picker(db, main, user)
+    return {
+        "helper_choices": choices,
+        "helper_reasons": {
+            choice.model.model_id: (
+                # One literal, not two adjacent ones: the catalogue extractor
+                # reads the first string of a `t()` call only, so a sentence split
+                # across two would be looked up under a key that exists nowhere.
+                i18n.t("It cannot run beside this model's reply: one of them serves one request at a time, or their connection holds one model at a time.")  # noqa: E501
+                if choice.capacity
+                else (describe_verdict(choice.verdict) if not choice.addable else "")
+            )
+            for choice in choices
+        },
+        "helper_member_ids": [row.model_id for row in chat.helpers] if chat else [],
+    }
+
+
 def _crowd_context(
     db: DBSession, user: User, chat: Chat | None, models: list, default_model_id: str = ""
 ) -> dict:
@@ -271,24 +371,39 @@ def _crowd_context(
 
     settings = settings_store.crowd(db)
     if not settings["enabled"]:
-        return {"crowd_available": [], "crowd_member_ids": [], "crowd_skipped": []}
+        return {
+            "crowd_available": [],
+            "crowd_held_back": [],
+            "crowd_member_ids": [],
+            "crowd_skipped": [],
+        }
 
     # On the new-chat screen the "own" model is whichever one the picker is
     # showing, so the list excludes it for the same reason it does in a chat:
     # adding it would have it answer twice in a row.
     own = chat.model_id if chat is not None else default_model_id
-    # Only the main model's data group: a member is sent the whole conversation.
-    # On the new-chat screen that is the group of the model the picker shows,
-    # which is the one the chat will be pinned to.
+    # The talk rules, evaluated from the main model -- on the new-chat screen the
+    # one the picker shows, whose data group the chat will be pinned to. Offered
+    # models are the main list; the rest are named below it with the reason, and
+    # may still be ticked by hand where the rules let this person do that.
+    from lembas.services import talk
+
     group = (
         data_groups.for_chat(db, chat)
         if chat is not None
         else (data_groups.for_pair(db, user, own) if own else None)
     )
-    if group is not None:
-        allowed = {m.id for m in chat_service.available_models(db, user, group)}
-        models = [model for model in models if model.id in allowed]
-    others = [model for model in models if model.model_id != own]
+    if own and group is not None:
+        pairs = talk.candidates(db, user, own, group)
+    else:
+        pairs = [(model, talk.Verdict(offered=True, addable=True)) for model in models]
+    pairs = [(model, verdict) for model, verdict in pairs if model.model_id != own]
+    others = [model for model, verdict in pairs if verdict.offered]
+    held_back = [
+        {"model": model, "addable": verdict.addable, "reason": describe_verdict(verdict)}
+        for model, verdict in pairs
+        if not verdict.offered
+    ]
     members = (
         [
             row.model_id
@@ -297,16 +412,17 @@ def _crowd_context(
         if chat is not None
         else []
     )
-    reachable = {model.model_id for model in others}
+    reachable = {model.model_id for model, verdict in pairs if verdict.addable}
     speakers = 1 + len([model_id for model_id in members if model_id in reachable])
     rounds = int(settings["max_rounds"])
     return {
         "crowd_available": others,
+        "crowd_held_back": held_back,
         "crowd_member_ids": [model_id for model_id in members if model_id in reachable],
         "crowd_skipped": (
             crowd_service.unreachable_members(db, chat, user) if chat is not None else []
         ),
-        # One round is out and back: everybody answers, everybody but the last is
+    # One round is out and back: everybody answers, everybody but the last is
         # asked whether they disagree, and the main model closes.
         "crowd_replies": max(1, speakers * 2 - 1),
         "crowd_rounds": rounds,
@@ -839,6 +955,9 @@ async def chat_index(
                 context["models"],
                 preselected.model_id if preselected is not None else "",
             ),
+            **_helper_context(
+                db, user, None, preselected.model_id if preselected is not None else ""
+            ),
             "starting_temporary": temporary,
             "temporary_toggle_url": new_chat_url(temporary="" if temporary else "1"),
             "model_navigate_url": without_model + ("&" if "?" in without_model else "?") + "model=",
@@ -1034,6 +1153,7 @@ async def settings_page(
             # template shows the two apart rather than printing the raw key.
             "split_key": personas_service.split_key,
             **_data_group_settings(db, user),
+            **_talk_settings(db, user),
             # Sorted rather than left in set order, because a list of six
             # hundred zones that is not alphabetical is one nobody can use.
             "languages": i18n.LANGUAGES,

src/lembas/api/preferences.py

@@ -371,3 +371,93 @@ async def delete_personal_group(db: Db, user: RequiredUser, group_id: str) -> Re
     except ValueError as exc:
         return RedirectResponse(f"/settings?error={quote(str(exc))}", status_code=303)
     return RedirectResponse("/settings?saved=Data+group+deleted.", status_code=303)
+
+
+# --- Talk rules ----------------------------------------------------------------
+# A person's own layer of who may talk to whom. Anybody may keep one: without
+# `rules.override` it can only narrow what the instance allows, which is theirs
+# to decide; with it, it wins. See services/talk.py.
+@router.post("/talk-mode")
+async def set_talk_mode(db: Db, user: RequiredUser, mode: str = Form("")) -> Response:
+    from lembas.services import talk
+
+    settings_map = {**(user.settings_json or {})}
+    if mode in talk.MODES:
+        settings_map[talk.SETTING_KEY] = mode
+    else:
+        settings_map.pop(talk.SETTING_KEY, None)
+    user.settings_json = settings_map
+    db.commit()
+    return RedirectResponse("/settings?saved=Model+rules+updated.", status_code=303)
+
+
+@router.post("/talk-rules")
+async def add_talk_rule(
+    db: Db,
+    user: RequiredUser,
+    from_model: str = Form("*"),
+    to_model: str = Form("*"),
+    effect: str = Form("deny"),
+    both: bool = Form(False),
+) -> Response:
+    from lembas.services import talk
+
+    talk.set_rule(db, user, from_model, to_model, effect, both=both)
+    return RedirectResponse("/settings?saved=Model+rules+updated.", status_code=303)
+
+
+@router.post("/talk-rules/{rule_id}/delete")
+async def delete_talk_rule(db: Db, user: RequiredUser, rule_id: str) -> Response:
+    from lembas.services import talk
+
+    talk.delete_rule(db, user, rule_id)
+    return RedirectResponse("/settings?saved=Model+rules+updated.", status_code=303)
+
+
+# --- Helper models -------------------------------------------------------------
+# A person's own designations: for each of their models, others it may send
+# helpers to. Added to the instance's, for them alone. Needs `helpers.designate`.
+def _refuse_without_designate(db, user) -> Response | None:
+    from lembas.services import helpers
+
+    if helpers.may_designate(db, user):
+        return None
+    return RedirectResponse(
+        "/settings?error=You+may+not+choose+your+own+helper+models.", status_code=303
+    )
+
+
+@router.post("/helpers")
+async def add_own_helper(
+    db: Db,
+    user: RequiredUser,
+    main_model: str = Form(""),
+    helper_model: str = Form(""),
+    offer: bool = Form(False),
+) -> Response:
+    from lembas.security import permissions
+    from lembas.services import helpers
+
+    refused = _refuse_without_designate(db, user)
+    if refused is not None:
+        return refused
+    # Only models this person can reach, on both sides: a designation naming one
+    # they cannot use would never be offered and would sit there unexplained.
+    if main_model == helper_model or not (
+        permissions.can_use_model(db, user, main_model)
+        and permissions.can_use_model(db, user, helper_model)
+    ):
+        return RedirectResponse("/settings?error=Choose+two+different+models.", status_code=303)
+    helpers.set_designation(db, user, main_model, helper_model, offer=offer)
+    return RedirectResponse("/settings?saved=Helper+models+updated.", status_code=303)
+
+
+@router.post("/helpers/{designation_id}/delete")
+async def delete_own_helper(db: Db, user: RequiredUser, designation_id: str) -> Response:
+    from lembas.services import helpers
+
+    refused = _refuse_without_designate(db, user)
+    if refused is not None:
+        return refused
+    helpers.delete_designation(db, user, designation_id)
+    return RedirectResponse("/settings?saved=Helper+models+updated.", status_code=303)

src/lembas/db/models/__init__.py

@@ -31,12 +31,14 @@ from lembas.db.models.chat import (
     ROLE_TOOL,
     ROLE_USER,
     Chat,
+    ChatHelper,
     CrowdMember,
     Folder,
     Message,
 )
 from lembas.db.models.connection import Connection, Model, model_groups
 from lembas.db.models.data_group import DEFAULT_GROUP, DataGroup, InDataGroup
+from lembas.db.models.helper import HelperDesignation
 from lembas.db.models.image import ImageWorkflow
 from lembas.db.models.library import (
     AUTHOR_MODEL,
@@ -84,6 +86,7 @@ from lembas.db.models.schedule import (
 )
 from lembas.db.models.setting import Setting
 from lembas.db.models.suggestion import Suggestion
+from lembas.db.models.talk import ANY_MODEL, EFFECT_ALLOW, EFFECT_DENY, EFFECTS, TalkRule
 from lembas.db.models.tool import (
     RESPONSE_JSON,
     RESPONSE_MODES,
@@ -165,11 +168,18 @@ __all__ = [
     "Report",
     "Schedule",
     "Chat",
+    "ChatHelper",
     "CrowdMember",
+    "HelperDesignation",
     "Job",
     "Connection",
     "DEFAULT_GROUP",
     "DataGroup",
+    "ANY_MODEL",
+    "EFFECT_ALLOW",
+    "EFFECT_DENY",
+    "EFFECTS",
+    "TalkRule",
     "InDataGroup",
     "CustomTool",
     "CHUNK_DOCUMENT",

src/lembas/db/models/chat.py

@@ -325,6 +325,12 @@ class Chat(UUIDPrimaryKey, Timestamps, InDataGroup, Base):
         cascade="all, delete-orphan",
         order_by="CrowdMember.position",
     )
+    # Helper models somebody added to this chat by hand. See `ChatHelper`.
+    helpers: Mapped[list[ChatHelper]] = relationship(
+        back_populates="chat",
+        cascade="all, delete-orphan",
+        order_by="ChatHelper.position",
+    )
 
     def __repr__(self) -> str:
         return f"<Chat {self.title!r}>"
@@ -372,6 +378,30 @@ class CrowdMember(UUIDPrimaryKey, Timestamps, Base):
         return f"<CrowdMember {self.model_id} at {self.position}>"
 
 
+class ChatHelper(UUIDPrimaryKey, Timestamps, Base):
+    """A model added to this chat by hand, for its model to send helpers to.
+
+    `CrowdMember`'s shape and `CrowdMember`'s reasoning: the model is text with
+    no foreign key, so a "Test & refresh" cannot silently empty the list. A
+    helper that no longer resolves is simply not offered.
+    """
+
+    __tablename__ = "chat_helpers"
+    __table_args__ = (UniqueConstraint("chat_id", "model_id"),)
+
+    chat_id: Mapped[str] = mapped_column(
+        String(32), ForeignKey("chats.id", ondelete="CASCADE"), nullable=False, index=True
+    )
+    model_id: Mapped[str] = mapped_column(String(300), nullable=False)
+    connection_id: Mapped[str | None] = mapped_column(String(32), nullable=True)
+    position: Mapped[int] = mapped_column(Integer, default=0, nullable=False)
+
+    chat: Mapped[Chat] = relationship(back_populates="helpers")
+
+    def __repr__(self) -> str:
+        return f"<ChatHelper {self.model_id} at {self.position}>"
+
+
 class Message(UUIDPrimaryKey, Timestamps, Base):
     __tablename__ = "messages"
 

src/lembas/db/models/connection.py

@@ -71,6 +71,14 @@ class Connection(UUIDPrimaryKey, Timestamps, InDataGroup, Base):
     unload_url: Mapped[str] = mapped_column(String(500), default="")
     unload_method: Mapped[str] = mapped_column(String(8), default="POST")
 
+    # Whether this endpoint holds one model at a time -- llama-swap in front of
+    # one GPU, which swaps the model out to serve another. A model here may then
+    # be its own helper, never another model from this connection: the helper
+    # would evict the model whose reply is waiting on it. Named for the
+    # *restrictive* state on purpose: `sync_schema` backfills a NOT NULL boolean
+    # with False, so False has to mean "as before" (any number of models at once).
+    one_model_at_a_time: Mapped[bool] = mapped_column(Boolean, default=False, nullable=False)
+
     # Result of the most recent "Test & refresh", surfaced in the admin list.
     last_checked_at: Mapped[datetime | None] = mapped_column(DateTime(timezone=True))
     last_error: Mapped[str] = mapped_column(Text, default="")
@@ -119,6 +127,12 @@ class Model(UUIDPrimaryKey, Timestamps, Base):
     position: Mapped[int] = mapped_column(Integer, default=0, nullable=False)
     # Pinned models are offered first, before the full list.
     pinned: Mapped[bool] = mapped_column(Boolean, default=False, nullable=False)
+    # Whether this model serves one request at a time, so it cannot be its own
+    # helper: the helper's request would queue behind the reply that is waiting
+    # for it. The restrictive state, for the backfill reason on
+    # `Connection.one_model_at_a_time`. A column and not a `capabilities_json`
+    # key, because that dict is rebuilt from the checkboxes on every save.
+    single_session: Mapped[bool] = mapped_column(Boolean, default=False, nullable=False)
 
     # Public models are usable by anyone; otherwise access comes from `groups`.
     public: Mapped[bool] = mapped_column(Boolean, default=True, nullable=False)

src/lembas/db/models/helper.py

@@ -0,0 +1,37 @@
+"""Which models a main model may send helpers to, besides itself.
+
+Designated **per main model**, on the owner's word: gpt-oss may use qwen35,
+bonsai may use deepseek-flash, and neither says anything about the other. The
+instance designates (`owner_id` NULL); a person holding `helpers.designate` may
+add their own, and theirs are added to the instance's -- a row of theirs for the
+same pair wins, which is how they change whether it is offered.
+
+`offer` says whether the main model may choose the helper itself. Off, it can be
+added to a chat only by hand, and is then the chat's.
+
+Text model ids and no foreign key, for the reason every such reference here has:
+"Test & refresh" recreates `Model` rows.
+"""
+
+from __future__ import annotations
+
+from sqlalchemy import Boolean, ForeignKey, String, UniqueConstraint
+from sqlalchemy.orm import Mapped, mapped_column
+
+from lembas.db.base import Base, Timestamps, UUIDPrimaryKey
+
+
+class HelperDesignation(UUIDPrimaryKey, Timestamps, Base):
+    __tablename__ = "helper_designations"
+    __table_args__ = (UniqueConstraint("owner_id", "main_model", "helper_model"),)
+
+    owner_id: Mapped[str | None] = mapped_column(
+        String(32), ForeignKey("users.id", ondelete="CASCADE"), nullable=True, index=True
+    )
+    main_model: Mapped[str] = mapped_column(String(300), nullable=False)
+    helper_model: Mapped[str] = mapped_column(String(300), nullable=False)
+    helper_connection_id: Mapped[str] = mapped_column(String(32), default="")
+    offer: Mapped[bool] = mapped_column(Boolean, default=True, nullable=False)
+
+    def __repr__(self) -> str:
+        return f"<HelperDesignation {self.main_model} -> {self.helper_model}>"

src/lembas/db/models/talk.py

@@ -0,0 +1,43 @@
+"""Talk rules: which model may talk to which.
+
+A rule names a *main* model -- the one a chat belongs to -- and a *target*, and
+says allow or deny. It governs who a main model is offered as a crowd member, as
+a friend to ask, and on its roster of peers. Keyed on the models' text ids, never
+a `Model` primary key, for the reason every such reference here is: "Test &
+refresh" recreates the row, and a rule that silently stopped applying after a
+refresh is the worst kind of rule.
+
+`owner_id` NULL is an instance rule, written by an administrator. Set, it is one
+person's own. `*` on either side means any model. See services/talk.py for how
+the two layers and the instance's mode are combined.
+"""
+
+from __future__ import annotations
+
+from sqlalchemy import ForeignKey, String, UniqueConstraint
+from sqlalchemy.orm import Mapped, mapped_column
+
+from lembas.db.base import Base, Timestamps, UUIDPrimaryKey
+
+ANY_MODEL = "*"
+EFFECT_ALLOW = "allow"
+EFFECT_DENY = "deny"
+EFFECTS = (EFFECT_ALLOW, EFFECT_DENY)
+
+
+class TalkRule(UUIDPrimaryKey, Timestamps, Base):
+    """One rule: may `from_model` talk to `to_model`, for everybody or one person."""
+
+    __tablename__ = "talk_rules"
+    __table_args__ = (UniqueConstraint("owner_id", "from_model", "to_model"),)
+
+    owner_id: Mapped[str | None] = mapped_column(
+        String(32), ForeignKey("users.id", ondelete="CASCADE"), nullable=True, index=True
+    )
+    from_model: Mapped[str] = mapped_column(String(300), nullable=False)
+    to_model: Mapped[str] = mapped_column(String(300), nullable=False)
+    effect: Mapped[str] = mapped_column(String(8), nullable=False, default=EFFECT_DENY)
+
+    def __repr__(self) -> str:
+        whose = self.owner_id or "instance"
+        return f"<TalkRule {whose} {self.from_model} -> {self.to_model} {self.effect}>"

src/lembas/main.py

@@ -23,6 +23,7 @@ from lembas.api import (
     admin_images,
     admin_models,
     admin_prompts,
+    admin_rules,
     admin_schedules,
     admin_search,
     admin_suggestions,
@@ -231,6 +232,7 @@ def create_app() -> FastAPI:
     app.include_router(admin_agents.router)
     app.include_router(admin_crowd.router)
     app.include_router(admin_data_groups.router)
+    app.include_router(admin_rules.router)
     app.include_router(push.router)
     app.include_router(branding.router)
 

src/lembas/security/permissions.py

@@ -334,6 +334,31 @@ PERMISSION_DEFS: tuple[PermissionDef, ...] = (
     # themselves, and move their own records between groups. Off by default,
     # because it moves what a provider can read -- and an instance that never
     # looks should keep the arrangement its administrator made.
+    # Talk rules: which model may bring which into a conversation. The
+    # instance's rules apply to everybody; a person may always narrow them for
+    # themselves, and with this they may also widen them -- their own rules and
+    # mode then win, and they may add any model to a crowd by hand. Off by
+    # default, because an instance rule is usually there for a reason.
+    PermissionDef(
+        "rules.override",
+        "Override the model rules for themselves",
+        "Let this person's own rules about which model may talk to which win over "
+        "the instance's, and let them add any model to a crowd by hand.",
+        False,
+        "Chat",
+    ),
+    # Helpers on another model. The instance designates which models each main
+    # model may send helpers to; this lets a person add their own designations
+    # for themselves. Off by default: a designation decides where a person's
+    # tasks -- and whatever context a model writes into them -- are sent.
+    PermissionDef(
+        "helpers.designate",
+        "Choose their own helper models",
+        "Let this person designate, for each model, other models it may send "
+        "helpers to -- added to the instance's designations, for them alone.",
+        False,
+        "Chat",
+    ),
     PermissionDef(
         "data.manage",
         "Manage their own data groups",

src/lembas/services/chat.py

@@ -906,7 +906,14 @@ def roster_models(
     would be both a leak and a dead end, since asking it anything is refused by
     the same check.
     """
-    return [model for model in available_models(db, user, group) if model.model_id != exclude]
+    if group is not None:
+        # Who the main model may talk to, by the talk rules -- a different data
+        # group counting as a deny that only an explicit rule opens. `exclude`
+        # is the main model at every call site that passes a group.
+        from lembas.services import talk
+
+        return talk.offered(db, user, exclude, group)
+    return [model for model in available_models(db, user) if model.model_id != exclude]
 
 
 def roster_block(

src/lembas/services/crowd.py

@@ -273,17 +273,18 @@ def member_speakers(db: DBSession, chat: Chat, user=None) -> list:
     Deduplicated against the main model: adding the chat's own model to the crowd
     would have it answer twice in a row, which is not what anybody meant by it.
 
-    And narrowed to the chat's data group: a member from another group would be
-    handed this conversation, which is exactly what groups exist to prevent.
+    And narrowed by the talk rules, evaluated from the main model -- which is
+    also where a different data group counts as a deny that only a rule opens.
     """
     from lembas.services import chat as chat_service
-    from lembas.services import data_groups
+    from lembas.services import data_groups, talk
 
+    # `addable`, not `offered`: a member somebody added by hand is exactly one the
+    # rules would not have offered, and skipping it when the round runs would
+    # quietly undo their choice.
     reachable = {
         model.model_id: model
-        for model in chat_service.roster_models(
-            db, user, exclude="", group=data_groups.for_chat(db, chat)
-        )
+        for model in talk.addable(db, user, chat.model_id, data_groups.for_chat(db, chat))
     }
     speakers = [chat_service.Speaker(chat.model_id, chat.connection_id)]
     seen = {chat.model_id}
@@ -297,14 +298,11 @@ def member_speakers(db: DBSession, chat: Chat, user=None) -> list:
 
 def unreachable_members(db: DBSession, chat: Chat, user=None) -> list[str]:
     """Members that will be skipped, so a screen can say so rather than lie."""
-    from lembas.services import chat as chat_service
-    from lembas.services import data_groups
+    from lembas.services import data_groups, talk
 
     reachable = {
         model.model_id
-        for model in chat_service.roster_models(
-            db, user, exclude="", group=data_groups.for_chat(db, chat)
-        )
+        for model in talk.addable(db, user, chat.model_id, data_groups.for_chat(db, chat))
     }
     return [
         member.model_id

src/lembas/services/harness.py

@@ -292,6 +292,9 @@ def context_variables(
         # opinion. One fragment covering all three would say nothing useful to
         # any of them.
         "friend": "",
+        # Where a helper may run, when that is more than the answering model.
+        # Filled below, from the same candidates the tool's enum was built from.
+        "helper_models": "",
         # Who else is here. Filled below, where the chat's own model is known --
         # a model does not need telling that it exists.
         "model_roster": "",
@@ -364,6 +367,9 @@ def context_variables(
                 db, user, exclude=speaking.model_id, group=group
             )
 
+        if "subagent" in families and speaking.model_id == chat.model_id:
+            values["helper_models"] = _helper_models(db, chat, user)
+
         if "persona" in families:
             # This person's own personality for this model, falling back to the
             # administrator's default until the model has written one with them;
@@ -376,6 +382,37 @@ def context_variables(
     return values
 
 
+def _helper_models(db: DBSession, chat, user) -> str:
+    """One line per model a helper may run on, or "" when it is only this one.
+
+    The same candidates `tools._subagent_defs` built the `model` enum from, so
+    the list the model reads and the values the call accepts cannot disagree.
+    Roster-shaped and capped the same way.
+    """
+    from lembas.services import chat as chat_service
+    from lembas.services import helpers as helpers_service
+
+    found = helpers_service.candidates(db, chat, user)
+    if len(found) < 2:
+        return ""
+    lines: list[str] = []
+    budget = chat_service.MAX_ROSTER_CHARS
+    for candidate in found[: chat_service.MAX_ROSTER_MODELS]:
+        model = candidate.model
+        parts = ((model.description or "").strip(), (model.notes or "").strip())
+        about = " ".join(" ".join(p for p in parts if p).split())[: chat_service.MAX_ROSTER_ENTRY]
+        line = f"- {model.label} ({model.model_id})"
+        if candidate.source == helpers_service.SOURCE_SELF:
+            line += " — you"
+        elif about:
+            line += f" — {about}"
+        if len(line) > budget:
+            break
+        budget -= len(line)
+        lines.append(line)
+    return "\n".join(lines)
+
+
 def _schedule_values(db: DBSession, chat, user) -> dict[str, str]:
     """What a scheduled task's chat is for, and how often it comes round.
 

src/lembas/services/helpers.py

@@ -0,0 +1,363 @@
+"""Which model a helper runs on: the main model itself, or one designated for it.
+
+`subagent_run` used to have one answer -- the parent's own model. It has three
+sources now, in this order, and they are decided here by logic, never by the
+model:
+
+1. **The main model itself**, unless it cannot run two requests at once.
+2. **Helpers somebody added to this chat by hand** (`ChatHelper`).
+3. **Helpers designated for the main model with `offer` on** -- by the instance,
+   or by a person holding `helpers.designate` -- which the model may choose.
+
+Each candidate passes two checks before it is offered:
+
+* **Capacity.** A model marked *serves one request at a time* cannot be its own
+  helper: the helper's request would queue behind the very reply waiting for it.
+  A connection marked *holds one model at a time* (llama-swap in front of one
+  GPU) cannot serve a helper on another of its models: loading it evicts the
+  model whose reply is waiting. The main model may still help itself there.
+  Both flags default off, so an instance that never sets them behaves exactly as
+  before -- the main model is its own helper.
+* **The talk rules**, read from the main model: a chat's hand-added helpers need
+  to be `addable`, a designation the model chooses itself needs to be `offered`.
+  A different data group is the deny a rule has to open, exactly as for a crowd.
+
+`ask_friend` and the crowd do not take the capacity check, on the owner's word:
+both are sequential, and waiting for a model to load is accepted there.
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+
+from sqlalchemy import select
+from sqlalchemy.orm import Session as DBSession
+
+from lembas.db.models import Chat, ChatHelper, HelperDesignation, Model, User
+
+PERMISSION = "helpers.designate"
+
+SOURCE_SELF = "self"
+SOURCE_CHAT = "chat"
+SOURCE_OFFERED = "offered"
+
+
+@dataclass(frozen=True)
+class Candidate:
+    """A model a helper may run on, and why it is on the list."""
+
+    model: Model
+    source: str
+
+
+@dataclass(frozen=True)
+class Choice:
+    """One designation as the helpers picker shows it.
+
+    `reason` is in English, for a model; `capacity` and `verdict` are what a
+    screen needs to say the same thing in the reader's language.
+    """
+
+    model: Model
+    offer: bool
+    addable: bool
+    reason: str
+    capacity: bool = False
+    verdict: object = None
+
+
+def may_designate(db: DBSession, user: User | None) -> bool:
+    from lembas.security import permissions
+
+    return user is not None and permissions.has(db, user, PERMISSION)
+
+
+def main_row(db: DBSession, chat: Chat) -> Model | None:
+    """The chat's own model as a row, on the connection it is reached through."""
+    from lembas.services import chat as chat_service
+
+    return chat_service.model_row(db, chat_service.speaker_for(db, chat))
+
+
+def capacity_refusal(main: Model | None, helper: Model) -> str:
+    """Why this helper cannot run beside the main model's waiting reply, or ""."""
+    if main is None:
+        return ""
+    if helper.model_id == main.model_id and helper.connection_id == main.connection_id:
+        if helper.single_session:
+            return (
+                f"{helper.label} serves one request at a time, so it cannot be its own "
+                f"helper: the helper would wait behind the reply that is waiting for it."
+            )
+        return ""
+    if helper.connection_id == main.connection_id:
+        connection = helper.connection
+        if connection is not None and connection.one_model_at_a_time:
+            return (
+                f"{connection.name} holds one model at a time, so a helper on "
+                f"{helper.label} would unload {main.label} while its reply waits."
+            )
+    return ""
+
+
+def designations(db: DBSession, user: User | None, main_model: str) -> list[HelperDesignation]:
+    """The helpers designated for one main model: the instance's, then the person's.
+
+    A person's own row for the same helper replaces the instance's -- that is
+    how they change whether it is offered -- and theirs count only while they
+    hold `helpers.designate`.
+    """
+    rows = list(
+        db.scalars(
+            select(HelperDesignation)
+            .where(
+                HelperDesignation.owner_id.is_(None),
+                HelperDesignation.main_model == main_model,
+            )
+            .order_by(HelperDesignation.helper_model)
+        )
+    )
+    if user is not None and may_designate(db, user):
+        own = list(
+            db.scalars(
+                select(HelperDesignation)
+                .where(
+                    HelperDesignation.owner_id == user.id,
+                    HelperDesignation.main_model == main_model,
+                )
+                .order_by(HelperDesignation.helper_model)
+            )
+        )
+        replaced = {row.helper_model for row in own}
+        rows = [row for row in rows if row.helper_model not in replaced] + own
+    return rows
+
+
+def _reachable(db: DBSession, user: User | None, model_id: str, connection_id: str | None):
+    """The row this person can reach for a model id, preferring a named connection."""
+    from lembas.services import chat as chat_service
+
+    rows = [m for m in chat_service.available_models(db, user) if m.model_id == model_id]
+    rows.sort(key=lambda m: m.connection_id != (connection_id or ""))
+    return rows[0] if rows else None
+
+
+def candidates(db: DBSession, chat: Chat, user: User | None) -> list[Candidate]:
+    """Every model a helper of this chat may run on, in the order it is chosen."""
+    from lembas.services import data_groups, talk
+
+    main = main_row(db, chat)
+    group = data_groups.for_chat(db, chat)
+    judge = talk.Judge(db, user)
+    found: list[Candidate] = []
+    seen: set[str] = set()
+
+    if main is not None and not capacity_refusal(main, main):
+        found.append(Candidate(main, SOURCE_SELF))
+        seen.add(main.model_id)
+
+    for row in chat.helpers:
+        model = _reachable(db, user, row.model_id, row.connection_id)
+        if model is None or model.model_id in seen:
+            continue
+        if not judge.verdict(chat.model_id, group, model).addable:
+            continue
+        if capacity_refusal(main, model):
+            continue
+        found.append(Candidate(model, SOURCE_CHAT))
+        seen.add(model.model_id)
+
+    for row in designations(db, user, chat.model_id):
+        if not row.offer or row.helper_model in seen:
+            continue
+        model = _reachable(db, user, row.helper_model, row.helper_connection_id)
+        if model is None:
+            continue
+        if not judge.verdict(chat.model_id, group, model).offered:
+            continue
+        if capacity_refusal(main, model):
+            continue
+        found.append(Candidate(model, SOURCE_OFFERED))
+        seen.add(model.model_id)
+    return found
+
+
+def choose(
+    db: DBSession, chat: Chat, user: User | None, wanted: str
+) -> tuple[Model | None, str]:
+    """The model a helper runs on, or a refusal saying what could have been named.
+
+    `wanted` comes from a tool call, so it is matched against the candidates and
+    nothing else -- by model id, then by label. Empty means the default: the main
+    model itself, or failing that the first helper added to this chat by hand.
+    """
+    found = candidates(db, chat, user)
+    names = ", ".join(c.model.model_id for c in found)
+    wanted = (wanted or "").strip()
+    if not wanted:
+        for source in (SOURCE_SELF, SOURCE_CHAT):
+            for candidate in found:
+                if candidate.source == source:
+                    return candidate.model, ""
+        if found:
+            return None, f"Name the model to send the helper to. You may use: {names}."
+        return None, _why_none(db, chat)
+
+    lowered = wanted.lower()
+    for candidate in found:
+        if lowered in (candidate.model.model_id.lower(), candidate.model.label.lower()):
+            return candidate.model, ""
+
+    main = main_row(db, chat)
+    target = _reachable(db, user, wanted, None)
+    if target is not None and capacity_refusal(main, target):
+        reason = capacity_refusal(main, target)
+    else:
+        reason = f"{wanted!r} is not a helper you may use."
+    return None, f"{reason} You may use: {names}." if names else f"{reason} {_why_none(db, chat)}"
+
+
+def _why_none(db: DBSession, chat: Chat) -> str:
+    main = main_row(db, chat)
+    if main is not None and capacity_refusal(main, main):
+        return capacity_refusal(main, main) + " No other helper is set up for it."
+    return "No helper model is available here. Do this part yourself."
+
+
+def picker(db: DBSession, chat_or_main: Chat | str, user: User | None) -> list[Choice]:
+    """The designations for a main model, as the composer's helpers picker lists them.
+
+    Every designation, offered or not, with whether this person may add it to
+    the chat by hand and, where not, why. On the new-chat screen there is no
+    chat yet, so a main model id is passed instead.
+    """
+    from lembas.services import data_groups, talk
+
+    if isinstance(chat_or_main, Chat):
+        main_model = chat_or_main.model_id
+        main = main_row(db, chat_or_main)
+        group = data_groups.for_chat(db, chat_or_main)
+    else:
+        main_model = chat_or_main
+        main = _reachable(db, user, main_model, None)
+        group = data_groups.for_pair(db, user, main_model)
+    judge = talk.Judge(db, user)
+    shown: list[Choice] = []
+    for row in designations(db, user, main_model):
+        model = _reachable(db, user, row.helper_model, row.helper_connection_id)
+        if model is None:
+            continue
+        verdict = judge.verdict(main_model, group, model)
+        capacity = capacity_refusal(main, model)
+        reason = capacity or ("" if verdict.addable else verdict.reason)
+        shown.append(
+            Choice(
+                model,
+                row.offer,
+                bool(verdict.addable and not capacity),
+                reason,
+                capacity=bool(capacity),
+                verdict=verdict,
+            )
+        )
+    return shown
+
+
+def set_designation(
+    db: DBSession,
+    owner: User | None,
+    main_model: str,
+    helper_model: str,
+    *,
+    offer: bool,
+    connection_id: str = "",
+) -> None:
+    """Designate a helper for a main model, or change whether it is offered."""
+    main_model = (main_model or "").strip()[:300]
+    helper_model = (helper_model or "").strip()[:300]
+    if not main_model or not helper_model:
+        return
+    existing = db.scalar(
+        select(HelperDesignation).where(
+            (
+                HelperDesignation.owner_id.is_(None)
+                if owner is None
+                else HelperDesignation.owner_id == owner.id
+            ),
+            HelperDesignation.main_model == main_model,
+            HelperDesignation.helper_model == helper_model,
+        )
+    )
+    if existing is not None:
+        existing.offer = offer
+        existing.helper_connection_id = connection_id or existing.helper_connection_id
+    else:
+        db.add(
+            HelperDesignation(
+                owner_id=owner.id if owner is not None else None,
+                main_model=main_model,
+                helper_model=helper_model,
+                helper_connection_id=connection_id or "",
+                offer=offer,
+            )
+        )
+    db.commit()
+
+
+def delete_designation(db: DBSession, owner: User | None, designation_id: str) -> bool:
+    row = db.get(HelperDesignation, designation_id)
+    if row is None or row.owner_id != (owner.id if owner is not None else None):
+        return False
+    db.delete(row)
+    db.commit()
+    return True
+
+
+def own_designations(db: DBSession, owner: User | None) -> list[HelperDesignation]:
+    return list(
+        db.scalars(
+            select(HelperDesignation)
+            .where(
+                HelperDesignation.owner_id.is_(None)
+                if owner is None
+                else HelperDesignation.owner_id == owner.id
+            )
+            .order_by(HelperDesignation.main_model, HelperDesignation.helper_model)
+        )
+    )
+
+
+def apply_chat_helpers(db: DBSession, chat: Chat, user: User | None, values: list[str]) -> None:
+    """Replace a chat's hand-added helpers with the models named.
+
+    Only designations for the chat's model this person may add -- the talk rules
+    and the capacity check, the same as the picker shows -- and never the chat's
+    own model, which is its own helper already.
+    """
+    allowed = {c.model.model_id: c.model for c in picker(db, chat, user) if c.addable}
+    wanted: list[str] = []
+    for value in values:
+        value = str(value).strip()
+        if value and value in allowed and value != chat.model_id and value not in wanted:
+            wanted.append(value)
+    chat.helpers = [
+        ChatHelper(model_id=model_id, connection_id=allowed[model_id].connection_id, position=i)
+        for i, model_id in enumerate(wanted)
+    ]
+
+
+__all__ = [
+    "PERMISSION",
+    "Candidate",
+    "Choice",
+    "apply_chat_helpers",
+    "candidates",
+    "capacity_refusal",
+    "choose",
+    "delete_designation",
+    "designations",
+    "may_designate",
+    "own_designations",
+    "picker",
+    "set_designation",
+]

src/lembas/services/prompts.py

@@ -163,6 +163,14 @@ VARIABLES: tuple[Variable, ...] = (
         "page, bounded, and empty unless this model may ask one of them a "
         "question — a list of peers it cannot reach is context spent on nothing.",
     ),
+    Variable(
+        "helper_models",
+        "The models a helper may run on",
+        "One line per model subagent_run may send a helper to, the answering model "
+        "first when it may be its own helper: its name, the id to pass as model, "
+        "and what it is for. Empty when the only choice is the model itself, so the "
+        "section vanishes and the tool reads as it always did.",
+    ),
     Variable(
         "persona",
         "Its personality with this person",
@@ -1366,6 +1374,28 @@ BUILTIN: tuple[Fragment, ...] = (
             "because a helper made it."
         ),
     ),
+    Fragment(
+        key="tool.subagent_models",
+        label="Which model a helper runs on",
+        group=GROUP_TOOLS,
+        order=252,
+        families=("subagent",),
+        variables=("helper_models",),
+        requires=("helper_models",),
+        hint="Appears only when a helper may run on a model other than the one "
+        "answering -- the chat's own helpers added by hand, or ones designated for "
+        "this model and offered to it. The list is built after the capacity check "
+        "and the model rules, so every line is one the call will accept.",
+        default=(
+            "### Where a helper can run\n"
+            "\n"
+            "subagent_run takes a model. Leave it out for the first one below; name "
+            "another, by the id in brackets, when its strengths suit the piece of work "
+            "better. Only these are accepted:\n"
+            "\n"
+            "{{helper_models}}"
+        ),
+    ),
     Fragment(
         key="tool.subagent_agent",
         label="Helpers on a machine",

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.
 

src/lembas/services/subagent.py

@@ -196,6 +196,7 @@ def _create_child(
     title: str,
     write: bool,
     friend: Model | None = None,
+    helper: Model | None = None,
 ) -> Chat:
     """The hidden chat one helper or one friend runs in.
 
@@ -225,6 +226,10 @@ def _create_child(
 
     peer = friend is not None
     owner = db.get(User, parent.user_id) if parent.user_id else None
+    # A helper on another model runs on that model -- as a pair, for the reason
+    # the friend is -- and reads that model's data group, exactly as a friend
+    # does. It is still a helper: the parent's kind, machine and scope.
+    other = friend or helper
     child = Chat(
         user_id=parent.user_id,
         # An ordinary chat for a friend even when the asking one is an agent
@@ -232,14 +237,14 @@ def _create_child(
         # and a peer being asked a question is not working on one.
         kind=KIND_CHAT if peer else parent.kind,
         title=title[:200] or ("Question" if peer else "Helper"),
-        model_id=friend.model_id if peer else parent.model_id,
-        connection_id=friend.connection_id if peer else parent.connection_id,
+        model_id=other.model_id if other is not None else parent.model_id,
+        connection_id=other.connection_id if other is not None else parent.connection_id,
         # The helper is in its parent's group, doing its parent's work. A friend
         # is in its own model's, so it reads its own group's data and never the
         # asker's.
         data_group_id=(
-            data_groups.for_pair(db, owner, friend.model_id, friend.connection_id)
-            if peer
+            data_groups.for_pair(db, owner, other.model_id, other.connection_id)
+            if other is not None
             else data_groups.for_chat(db, parent)
         ),
         # Never in a listing, and swept a day later even if it is kept.
@@ -254,8 +259,11 @@ def _create_child(
         child.agent_mode = MODE_WRITING if write else MODE_READING
     if peer:
         child.scope_json = {**(child.scope_json or {}), "role": ROLE_FRIEND}
-        effort = str((friend.params_json or {}).get("reasoning_effort") or "")
-        if effort not in chat_service.efforts_for(friend):
+    if other is not None:
+        # The other model's own default, never the parent's: the vocabularies
+        # differ, and `high` handed to a Bonsai raises inside its chat template.
+        effort = str((other.params_json or {}).get("reasoning_effort") or "")
+        if effort not in chat_service.efforts_for(other):
             effort = ""
     else:
         effort = chat_service.resolved_effort(parent)
@@ -455,6 +463,7 @@ async def _run_subagent(context: ToolContext, args: dict[str, Any]) -> ToolOutco
     title = str(args.get("title") or "").strip() or task[:60]
     briefing = str(args.get("context") or "")
     want_write = bool(args.get("write"))
+    wanted_model = str(args.get("model") or "")
 
     if not task:
         return _error(
@@ -493,6 +502,15 @@ async def _run_subagent(context: ToolContext, args: dict[str, Any]) -> ToolOutco
         if owner is None:  # pragma: no cover - a chat outliving its owner
             return _error("That account no longer exists.", task=task)
 
+        # Which model the helper runs on -- decided by logic, never taken on the
+        # model's word: the name is matched against the candidates the tool was
+        # built from, which already passed the capacity check and the talk rules.
+        from lembas.services import helpers as helpers_service
+
+        helper, refusal = helpers_service.choose(db, parent, owner, wanted_model)
+        if helper is None:
+            return _error(refusal, task=task)
+
         # After the refusals above and before anything is created. The order is
         # the design: a call that could never have worked should be told *why*
         # rather than told it has run out of helpers, and the counter should
@@ -508,7 +526,13 @@ async def _run_subagent(context: ToolContext, args: dict[str, Any]) -> ToolOutco
         if refusal:
             return _error(refusal, task=task)
 
-        child = _create_child(db, parent, title=title, write=write)
+        own = (
+            helper.model_id == parent.model_id
+            and (not parent.connection_id or helper.connection_id == parent.connection_id)
+        )
+        child = _create_child(
+            db, parent, title=title, write=write, helper=None if own else helper
+        )
         child_id = child.id
 
     _LIVE.add(child_id)
@@ -812,10 +836,27 @@ def friend_tool_defs() -> list[ToolDef]:
     ]
 
 
-def tool_defs() -> list[ToolDef]:
-    """The one tool, built here so `services/tools.py` need not know the wording."""
+def tool_defs(models: list[str] | None = None) -> list[ToolDef]:
+    """The one tool, built here so `services/tools.py` need not know the wording.
+
+    `models` is who a helper may run on, from `helpers.candidates`, the main
+    model first when it is its own helper. One of them, or none given, is the
+    tool as it always was; more adds a `model` argument whose enum is exactly
+    that list, so a small model cannot type a name that was never offered.
+    """
     from lembas.services.tools import FAMILY_SUBAGENT, RISK_READ, ToolDef
 
+    properties = _subagent_properties()
+    if models and len(models) > 1:
+        properties["model"] = {
+            "type": "string",
+            "enum": list(models),
+            "description": (
+                "Which model the helper runs on. Leave it out for the default "
+                f"({models[0]}). Choose another when its strengths suit the task "
+                "better -- the list of helpers you were given says what each is."
+            ),
+        }
     return [
         ToolDef(
             name="subagent_run",
@@ -836,39 +877,7 @@ def tool_defs() -> list[ToolDef]:
             ),
             parameters={
                 "type": "object",
-                "properties": {
-                    "task": {
-                        "type": "string",
-                        "description": (
-                            "What the helper is to do, written out in full and as "
-                            "an instruction. Say what a good answer contains and "
-                            "how long it should be. It is read on its own, with "
-                            "none of this conversation around it."
-                        ),
-                    },
-                    "title": {
-                        "type": "string",
-                        "description": "A few words naming this piece of work.",
-                    },
-                    "context": {
-                        "type": "string",
-                        "description": (
-                            "Facts the helper needs that it cannot look up — what "
-                            "the reader asked for, decisions already made, names "
-                            "and paths. Not a summary of the conversation."
-                        ),
-                    },
-                    "write": {
-                        "type": "boolean",
-                        "description": (
-                            "True if the helper must change something: write a "
-                            "file, keep a note, file a report. Leave it out for "
-                            "anything that only reads, which is nearly always. A "
-                            "writing helper is refused where you would have been "
-                            "stopped for approval yourself."
-                        ),
-                    },
-                },
+                "properties": properties,
                 "required": ["task"],
             },
             run=_run_subagent,
@@ -894,3 +903,40 @@ __all__ = [
     "live_count",
     "tool_defs",
 ]
+
+
+def _subagent_properties() -> dict[str, Any]:
+    """The arguments every `subagent_run` has; `tool_defs` may add `model`."""
+    return {
+        "task": {
+            "type": "string",
+            "description": (
+                "What the helper is to do, written out in full and as "
+                "an instruction. Say what a good answer contains and "
+                "how long it should be. It is read on its own, with "
+                "none of this conversation around it."
+            ),
+        },
+        "title": {
+            "type": "string",
+            "description": "A few words naming this piece of work.",
+        },
+        "context": {
+            "type": "string",
+            "description": (
+                "Facts the helper needs that it cannot look up — what "
+                "the reader asked for, decisions already made, names "
+                "and paths. Not a summary of the conversation."
+            ),
+        },
+        "write": {
+            "type": "boolean",
+            "description": (
+                "True if the helper must change something: write a "
+                "file, keep a note, file a report. Leave it out for "
+                "anything that only reads, which is nearly always. A "
+                "writing helper is refused where you would have been "
+                "stopped for approval yourself."
+            ),
+        },
+    }

src/lembas/services/talk.py

@@ -0,0 +1,354 @@
+"""Who may talk to whom: the rules behind the crowd, `ask_friend` and the roster.
+
+Always evaluated **from the chat's main model**. If the main model may not talk
+to a target, the target is not *offered* -- not listed on its roster, not named
+as a friend it may ask, not in the crowd picker's main list. Members of a crowd
+are not checked against each other: the rule is about who a conversation's own
+model brings in, and a member loses `friend` and `subagent` anyway.
+
+Two answers, because the owner asked for two things:
+
+* **offered** -- what happens on its own: the roster, a friend a model names, the
+  picker's main list.
+* **addable** -- what a person may do by hand in the crowd picker. A rule a
+  person wrote for themselves is soft for them; an instance rule is hard, unless
+  they hold `rules.override`.
+
+`decide` is pure -- plain values in, a `Verdict` out -- so every combination is
+tested without a database, and the admin page's matrix is drawn by the same
+function that enforces the rules, which is what makes the matrix trustworthy.
+
+**A different data group is an implicit deny.** A crowd member or a friend is
+sent the conversation, so a model in another group joins only when a rule says
+so explicitly: the administrator's, or a person's own when they hold the
+override. It then reads its own group's stores, never the chat's.
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+
+from sqlalchemy import select
+from sqlalchemy.orm import Session as DBSession
+
+from lembas.db.models import (
+    ANY_MODEL,
+    EFFECT_ALLOW,
+    EFFECT_DENY,
+    EFFECTS,
+    Model,
+    TalkRule,
+    User,
+)
+
+MODE_OPEN = "open"
+MODE_CLOSED = "closed"
+MODES = (MODE_OPEN, MODE_CLOSED)
+
+# Where a person's own mode is kept in `settings_json`. Empty follows the instance.
+SETTING_KEY = "talk_mode"
+
+# Lets a person's own rules and mode win over the instance's, for them alone.
+PERMISSION = "rules.override"
+
+
+@dataclass(frozen=True)
+class Rule:
+    from_model: str
+    to_model: str
+    effect: str
+
+
+# Why something is not offered. A code rather than a sentence, so a screen can
+# say it in the reader's language (`api/admin_rules.py:describe`) while a model
+# refused a friend is told it in English (`Verdict.reason`).
+WHY_INSTANCE_RULE = "instance_rule"
+WHY_YOUR_RULE = "your_rule"
+WHY_GROUP = "group"
+WHY_INSTANCE_CLOSED = "instance_closed"
+WHY_YOUR_CLOSED = "your_closed"
+
+
+@dataclass(frozen=True)
+class Verdict:
+    offered: bool
+    addable: bool
+    why: str = ""
+    rule: Rule | None = None
+
+    @property
+    def reason(self) -> str:
+        """The reason in English, for a model -- or "" when it is offered."""
+        if self.offered or not self.why:
+            return ""
+        if self.why in (WHY_INSTANCE_RULE, WHY_YOUR_RULE) and self.rule is not None:
+            whose = "the instance's" if self.why == WHY_INSTANCE_RULE else "your"
+            return _named(self.rule, whose)
+        return {
+            WHY_GROUP: "it is in another data group",
+            WHY_INSTANCE_CLOSED: "the instance allows no model to talk to another",
+            WHY_YOUR_CLOSED: "your setting allows no model to talk to another",
+        }.get(self.why, "")
+
+
+def match(rules: list[Rule], main: str, target: str) -> Rule | None:
+    """The most specific rule for a pair: exact, then `main -> *`, `* -> target`, `* -> *`."""
+    for wanted in ((main, target), (main, ANY_MODEL), (ANY_MODEL, target), (ANY_MODEL, ANY_MODEL)):
+        for rule in rules:
+            if (rule.from_model, rule.to_model) == wanted:
+                return rule
+    return None
+
+
+def _named(rule: Rule, whose: str) -> str:
+    frm = "any model" if rule.from_model == ANY_MODEL else rule.from_model
+    to = "any model" if rule.to_model == ANY_MODEL else rule.to_model
+    verb = "allows" if rule.effect == EFFECT_ALLOW else "forbids"
+    return f"{whose} rule {frm} → {to} {verb} it"
+
+
+def decide(
+    *,
+    instance_mode: str,
+    instance_rule: Rule | None,
+    user_mode: str = "",
+    user_rule: Rule | None = None,
+    override: bool = False,
+    same_group: bool = True,
+) -> Verdict:
+    """Whether a main model may talk to a target, offered and by hand.
+
+    The instance's verdict is its most specific rule, or failing that its mode
+    -- with a different data group counting as a deny that only an explicit
+    allow opens.
+
+    Without the override a person can only narrow: their own rule or their
+    `closed` mode can take something off what is offered, and since those are
+    theirs, they may still add it by hand. With the override, their explicit
+    rule wins outright, then their mode, then the instance's verdict; and they
+    may add anything by hand, because doing so is their explicit decision.
+    """
+    if instance_rule is not None:
+        instance_ok = instance_rule.effect == EFFECT_ALLOW
+        instance_why: tuple[str, Rule | None] = (WHY_INSTANCE_RULE, instance_rule)
+    elif not same_group:
+        instance_ok, instance_why = False, (WHY_GROUP, None)
+    else:
+        instance_ok = instance_mode != MODE_CLOSED
+        instance_why = (WHY_INSTANCE_CLOSED, None)
+
+    if not override:
+        if user_rule is not None:
+            user_ok = user_rule.effect == EFFECT_ALLOW
+            user_why: tuple[str, Rule | None] = (WHY_YOUR_RULE, user_rule)
+        elif user_mode == MODE_CLOSED:
+            user_ok, user_why = False, (WHY_YOUR_CLOSED, None)
+        else:
+            user_ok, user_why = True, ("", None)
+        offered = instance_ok and user_ok
+        why, rule = ("", None) if offered else (instance_why if not instance_ok else user_why)
+        return Verdict(offered=offered, addable=instance_ok, why=why, rule=rule)
+
+    if user_rule is not None:
+        ok = user_rule.effect == EFFECT_ALLOW
+        why, rule = (WHY_YOUR_RULE, user_rule)
+    elif user_mode == MODE_CLOSED:
+        ok, (why, rule) = False, (WHY_YOUR_CLOSED, None)
+    elif user_mode == MODE_OPEN:
+        allowed = instance_rule is not None and instance_rule.effect == EFFECT_ALLOW
+        ok = same_group or allowed
+        why, rule = (WHY_GROUP, None)
+    else:
+        ok = instance_ok
+        why, rule = instance_why
+    if ok:
+        why, rule = "", None
+    return Verdict(offered=ok, addable=True, why=why, rule=rule)
+
+
+# --- Loading what `decide` needs ---------------------------------------------------
+def _rules(db: DBSession, owner_id: str | None) -> list[Rule]:
+    rows = db.scalars(
+        select(TalkRule).where(
+            TalkRule.owner_id.is_(None) if owner_id is None else TalkRule.owner_id == owner_id
+        )
+    )
+    return [Rule(r.from_model, r.to_model, r.effect) for r in rows]
+
+
+def user_mode(user: User | None) -> str:
+    if user is None:
+        return ""
+    value = str((user.settings_json or {}).get(SETTING_KEY) or "")
+    return value if value in MODES else ""
+
+
+def may_override(db: DBSession, user: User | None) -> bool:
+    from lembas.security import permissions
+
+    return user is not None and permissions.has(db, user, PERMISSION)
+
+
+class Judge:
+    """Everything `decide` needs for one person, loaded once per request.
+
+    The model lists ask about every model they show; loading the rules and the
+    connection groups per question would be a query per row of every picker.
+    `user=None` is the instance's own view, for the admin page's matrix.
+    """
+
+    def __init__(self, db: DBSession, user: User | None) -> None:
+        from lembas.services import data_groups, settings_store
+
+        self.instance_mode = settings_store.rules(db)["mode"]
+        self.instance_rules = _rules(db, None)
+        self.user_rules = _rules(db, user.id) if user is not None else []
+        self.user_mode = user_mode(user)
+        self.override = may_override(db, user)
+        self.groups = data_groups.connection_groups(db, user)
+        self.default = data_groups.DEFAULT_GROUP
+
+    def group_of(self, model: Model) -> str:
+        return self.groups.get(model.connection_id, self.default)
+
+    def verdict(self, main_model: str, main_group: str, target: Model) -> Verdict:
+        return decide(
+            instance_mode=self.instance_mode,
+            instance_rule=match(self.instance_rules, main_model, target.model_id),
+            user_mode=self.user_mode,
+            user_rule=match(self.user_rules, main_model, target.model_id),
+            override=self.override,
+            same_group=self.group_of(target) == main_group,
+        )
+
+
+def candidates(
+    db: DBSession, user: User | None, main_model: str, main_group: str
+) -> list[tuple[Model, Verdict]]:
+    """Every model this person can reach other than the main one, with its verdict."""
+    from lembas.services import chat as chat_service
+
+    judge = Judge(db, user)
+    return [
+        (model, judge.verdict(main_model, main_group, model))
+        for model in chat_service.available_models(db, user)
+        if model.model_id != main_model
+    ]
+
+
+def offered(db: DBSession, user: User | None, main_model: str, main_group: str) -> list[Model]:
+    """The models a main model is offered on its own: the roster, a friend, the picker."""
+    found = candidates(db, user, main_model, main_group)
+    return [model for model, verdict in found if verdict.offered]
+
+
+def addable(db: DBSession, user: User | None, main_model: str, main_group: str) -> list[Model]:
+    """The models a person may add to a crowd by hand."""
+    found = candidates(db, user, main_model, main_group)
+    return [model for model, verdict in found if verdict.addable]
+
+
+# --- Changing rules --------------------------------------------------------------------
+def rules_of(db: DBSession, owner: User | None) -> list[TalkRule]:
+    return list(
+        db.scalars(
+            select(TalkRule)
+            .where(
+                TalkRule.owner_id.is_(None)
+                if owner is None
+                else TalkRule.owner_id == owner.id
+            )
+            .order_by(TalkRule.from_model, TalkRule.to_model)
+        )
+    )
+
+
+def set_rule(
+    db: DBSession,
+    owner: User | None,
+    from_model: str,
+    to_model: str,
+    effect: str,
+    *,
+    both: bool = False,
+) -> None:
+    """Write one rule, or a pair in both directions. Replaces one for the same pair."""
+    from_model = (from_model or "").strip()[:300] or ANY_MODEL
+    to_model = (to_model or "").strip()[:300] or ANY_MODEL
+    if effect not in EFFECTS:
+        effect = EFFECT_DENY
+    pairs = [(from_model, to_model)]
+    if both and from_model != to_model:
+        pairs.append((to_model, from_model))
+    for frm, to in pairs:
+        existing = db.scalar(
+            select(TalkRule).where(
+                (TalkRule.owner_id.is_(None) if owner is None else TalkRule.owner_id == owner.id),
+                TalkRule.from_model == frm,
+                TalkRule.to_model == to,
+            )
+        )
+        if existing is not None:
+            existing.effect = effect
+        else:
+            db.add(
+                TalkRule(
+                    owner_id=owner.id if owner is not None else None,
+                    from_model=frm,
+                    to_model=to,
+                    effect=effect,
+                )
+            )
+    db.commit()
+
+
+def delete_rule(db: DBSession, owner: User | None, rule_id: str) -> bool:
+    """Remove one rule, only from the layer it belongs to."""
+    rule = db.get(TalkRule, rule_id)
+    if rule is None or rule.owner_id != (owner.id if owner is not None else None):
+        return False
+    db.delete(rule)
+    db.commit()
+    return True
+
+
+def matrix(db: DBSession, user: User | None, models: list[Model]) -> list[dict]:
+    """Main x target, drawn by the same `decide` that enforces the rules.
+
+    Evaluated as if the main model's chat were in the main model's own group,
+    which is what a chat started on it is.
+    """
+    judge = Judge(db, user)
+    rows = []
+    for main in models:
+        group = judge.group_of(main)
+        cells = []
+        for target in models:
+            if target.model_id == main.model_id:
+                cells.append(None)
+                continue
+            cells.append(judge.verdict(main.model_id, group, target))
+        rows.append({"main": main, "cells": cells})
+    return rows
+
+
+__all__ = [
+    "MODES",
+    "MODE_CLOSED",
+    "MODE_OPEN",
+    "PERMISSION",
+    "Judge",
+    "Rule",
+    "Verdict",
+    "addable",
+    "candidates",
+    "decide",
+    "delete_rule",
+    "match",
+    "matrix",
+    "may_override",
+    "offered",
+    "rules_of",
+    "set_rule",
+    "user_mode",
+]

src/lembas/services/tools.py

@@ -1750,13 +1750,31 @@ def _schedule_defs() -> list[ToolDef]:
     return schedule_tool.tool_defs()
 
 
-def _subagent_defs() -> list[ToolDef]:
-    """The subagent tool. Imported inside the call for the reason above."""
+def _subagent_registry_defs() -> list[ToolDef]:
     from lembas.services import subagent as subagent_service
 
     return subagent_service.tool_defs()
 
 
+def _subagent_defs(db: DBSession, chat: Chat, user: User | None) -> list[ToolDef]:
+    """The subagent tool, shaped by which models a helper may run on.
+
+    Withdrawn when there are none -- a main model that cannot help itself and
+    has no other helper set up would be offered a tool every call of which is
+    refused, and a model finds that out one wasted round at a time. With only
+    itself it is the tool it always was; with more, it gains a `model`
+    argument listing exactly those. Imported inside the call for the reason
+    above.
+    """
+    from lembas.services import helpers as helpers_service
+    from lembas.services import subagent as subagent_service
+
+    found = helpers_service.candidates(db, chat, user)
+    if not found:
+        return []
+    return subagent_service.tool_defs([c.model.model_id for c in found])
+
+
 def _friend_defs() -> list[ToolDef]:
     """The ask-a-friend tool. Same module, same reason for the late import."""
     from lembas.services import subagent as subagent_service
@@ -1824,7 +1842,9 @@ def registry(db: DBSession) -> dict[str, ToolDef]:
             # reaches the model. That omission has cost two features their
             # instructions already.
             *_schedule_defs(),
-            *_subagent_defs(),
+            # The registry wants the tool's name and family, not this chat's
+            # candidates -- so the bare definition, which needs no chat.
+            *_subagent_registry_defs(),
             *_friend_defs(),
             *_crowd_defs(),
         ]
@@ -1886,7 +1906,7 @@ def resolve_tools(
             *_agent_defs(db, chat, user),
             *(_image_defs(db, image_values) if images_ready else []),
             *(_schedule_defs() if schedules_on else []),
-            *(_subagent_defs() if subagents_on else []),
+            *(_subagent_defs(db, chat, user) if subagents_on else []),
             *(_friend_defs() if subagents_on else []),
             # Only on the closing turn, and only with a round left. Not gated on a
             # capability or a permission: a tool that exists on exactly one turn of

src/lembas/web/i18n/sk.py

@@ -1859,3 +1859,75 @@ MESSAGES.update(
         'Image review': 'Posudzovanie obrázkov',
     }
 )
+
+# --- Model rules (1.11.0) ------------------------------------------------------
+MESSAGES.update(
+    {
+        'Model rules': 'Pravidlá modelov',
+        "Which model may bring which into a conversation: as a crowd member, as a friend it asks, and on the list of other models it is told about. A rule is read from the chat's own model. A model in another data group is not offered unless a rule allows it.": 'Ktorý model môže priviesť ktorý do konverzácie: ako člena skupiny, ako priateľa, ktorého sa pýta, a na zozname ďalších modelov, o ktorých sa dozvie. Pravidlo sa číta od vlastného modelu konverzácie. Model v inej dátovej oblasti sa neponúka, kým to pravidlo nepovolí.',
+        'The starting point': 'Východisko',
+        'Any model may talk to any other, except where a rule forbids it': 'Každý model môže hovoriť s každým, okrem prípadov, keď to pravidlo zakazuje',
+        'No model may talk to another, except where a rule allows it': 'Žiadny model nesmie hovoriť s iným, okrem prípadov, keď to pravidlo povoľuje',
+        'People can always narrow this for themselves. Widening it for themselves needs the permission to override the model rules.': 'Ľudia si to pre seba môžu vždy zúžiť. Rozšíriť si to pre seba môžu len s oprávnením prekonať pravidlá modelov.',
+        'Rules': 'Pravidlá',
+        'Not offered to this model': 'Tomuto modelu sa neponúkajú',
+        'You may still add it yourself.': 'Môžete ho aj tak pridať sami.',
+        'any model': 'ľubovoľný model',
+        'may talk': 'smie hovoriť',
+        'may not talk': 'nesmie hovoriť',
+        'Delete this rule': 'Zmazať toto pravidlo',
+        'No rules yet.': 'Zatiaľ žiadne pravidlá.',
+        'This model': 'Tento model',
+        "The chat's own model.": 'Vlastný model konverzácie.',
+        'May': 'Smie',
+        'may not talk to': 'nesmie hovoriť s',
+        'may talk to': 'smie hovoriť s',
+        'That model': 'Tamten model',
+        'A crowd member, a friend it asks, a model on its roster.': 'Člen skupiny, priateľ, ktorého sa pýta, model na jeho zozname.',
+        'Both directions': 'Oboma smermi',
+        'Add rule': 'Pridať pravidlo',
+        'Who may talk to whom': 'Kto smie hovoriť s kým',
+        "Rows are the chat's own model, columns the model it would bring in. Drawn by the same rules that are enforced, so what this shows is what happens.": 'Riadky sú vlastný model konverzácie, stĺpce model, ktorý by priviedol. Kreslí to tie isté pravidlá, ktoré sa uplatňujú, takže čo tu vidíte, to sa aj stane.',
+        'itself': 'on sám',
+        'Offered': 'Ponúka sa',
+        'Who your models may talk to': 'S kým smú hovoriť vaše modely',
+        "Your rules and your setting win over the instance's, for you. You can also add any model to a crowd by hand.": 'Vaše pravidlá a vaše nastavenie majú pre vás prednosť pred pravidlami inštancie. Do skupiny môžete ručne pridať aj ľubovoľný model.',
+        "Your rules can only narrow the instance's. A model your own rule holds back can still be added to a crowd by hand; one the instance holds back cannot.": 'Vaše pravidlá môžu pravidlá inštancie len zúžiť. Model, ktorý zadrží vaše vlastné pravidlo, môžete do skupiny aj tak pridať ručne; model, ktorý zadrží inštancia, nie.',
+        'Your starting point': 'Vaše východisko',
+        'Follow the instance': 'Podľa inštancie',
+        'Any model may talk to any other': 'Každý model môže hovoriť s každým',
+        'No model may talk to another': 'Žiadny model nesmie hovoriť s iným',
+        "The instance's rule %(a)s → %(b)s allows it.": 'Pravidlo inštancie %(a)s → %(b)s to povoľuje.',
+        "The instance's rule %(a)s → %(b)s forbids it.": 'Pravidlo inštancie %(a)s → %(b)s to zakazuje.',
+        'Your rule %(a)s → %(b)s allows it.': 'Vaše pravidlo %(a)s → %(b)s to povoľuje.',
+        'Your rule %(a)s → %(b)s forbids it.': 'Vaše pravidlo %(a)s → %(b)s to zakazuje.',
+        'It is in another data group.': 'Je v inej dátovej oblasti.',
+        'The instance lets no model talk to another.': 'Inštancia nedovoľuje žiadnemu modelu hovoriť s iným.',
+        'Your setting lets no model talk to another.': 'Vaše nastavenie nedovoľuje žiadnemu modelu hovoriť s iným.',
+    }
+)
+
+# --- Helpers on another model (1.12.0) -----------------------------------------
+MESSAGES.update(
+    {
+        'Holds one model at a time': 'Drží naraz jeden model',
+        'Tick this for llama-swap in front of one GPU, or anything else that unloads one model to serve another. A model here may then be its own helper, but never send a helper to another model on this connection: loading it would unload the model whose reply is waiting.': 'Označte pri llama-swap pred jednou GPU alebo čomkoľvek, čo jeden model uvoľní, aby obslúžilo iný. Model tu potom môže byť vlastným pomocníkom, ale nikdy nepošle pomocníka inému modelu na tomto spojení: jeho načítanie by uvoľnilo model, ktorého odpoveď čaká.',
+        'Serves one request at a time': 'Obsluhuje naraz jednu požiadavku',
+        'Tick this for a model with a single slot. It then cannot be its own helper, because the helper would wait behind the reply that is waiting for it. Other models can still be its helpers.': 'Označte pri modeli s jedným slotom. Potom nemôže byť vlastným pomocníkom, lebo pomocník by čakal za odpoveďou, ktorá čaká naňho. Iné modely môžu byť jeho pomocníkmi aj tak.',
+        "Other models this one may send helpers to, for everybody. Offered ones it may choose itself; the rest can only be added to a chat by hand. It is always its own helper too, unless it serves one request at a time. The model rules and the connection's capacity are checked when a helper is sent.": 'Iné modely, ku ktorým môže tento posielať pomocníkov, pre všetkých. Ponúkané si môže vybrať sám; ostatné sa dajú do konverzácie pridať len ručne. Vždy je aj vlastným pomocníkom, pokiaľ neobsluhuje naraz jednu požiadavku. Pravidlá modelov a kapacita spojenia sa kontrolujú pri odoslaní pomocníka.',
+        'offered to the model': 'ponúkané modelu',
+        'by hand only': 'len ručne',
+        'Remove this helper': 'Odstrániť tohto pomocníka',
+        'Helper model': 'Model pomocníka',
+        'Offer it to the model': 'Ponúknuť ho modelu',
+        'Add helper': 'Pridať pomocníka',
+        'Models this one may send helpers to. Tick one to add it to this chat; one offered to the model it may choose anyway.': 'Modely, ku ktorým môže tento posielať pomocníkov. Označením ho pridáte do tejto konverzácie; ponúkaný si model môže vybrať aj tak.',
+        'Offered to the model.': 'Ponúkaný modelu.',
+        'Only when added here.': 'Len keď ho pridáte tu.',
+        'Your helper models': 'Vaše modely pomocníkov',
+        "Models each of your models may send helpers to, for you alone, on top of the instance's. Your row for the same pair replaces the instance's.": 'Modely, ku ktorým môže každý z vašich modelov posielať pomocníkov, len pre vás, navyše k tým od inštancie. Váš riadok pre tú istú dvojicu nahradí riadok inštancie.',
+        "Set by the administrator on each model's page. Adding your own needs the permission to choose your own helper models.": 'Nastavuje správca na stránke každého modelu. Na pridanie vlastných potrebujete oprávnenie vyberať si vlastné modely pomocníkov.',
+        'May send helpers to': 'Smie posielať pomocníkov k',
+        "It cannot run beside this model's reply: one of them serves one request at a time, or their connection holds one model at a time.": 'Nemôže bežať popri odpovedi tohto modelu: jeden z nich obsluhuje naraz jednu požiadavku alebo ich spojenie drží naraz jeden model.',
+    }
+)

src/lembas/web/static/css/app.css

@@ -1954,3 +1954,47 @@ body.is-resizing .canvas__body { pointer-events: none; }
 }
 a.card, .card--action { transition: transform var(--dur-2) var(--ease-out),
                                     box-shadow var(--dur-2) var(--ease-out); }
+
+/* --- Who may talk to whom --------------------------------------------------
+   The talk-rules matrix: one row per main model, one column per model it would
+   bring in. Its own scroller, because a dozen model ids across is wider than a
+   phone and the page must never scroll sideways. */
+.talk-matrix-scroll {
+  overflow-x: auto;
+  max-width: 100%;
+}
+.talk-matrix {
+  border-collapse: collapse;
+  font-size: var(--text-xs);
+}
+.talk-matrix th,
+.talk-matrix td {
+  padding: var(--sp-1) var(--sp-2);
+  border: var(--border-w) solid var(--border);
+  text-align: center;
+  white-space: nowrap;
+}
+.talk-matrix thead th { color: var(--ink-muted); font-weight: 500; }
+.talk-matrix tbody th { text-align: left; color: var(--ink-muted); font-weight: 500; }
+.talk-matrix__yes { color: var(--leaf); }
+.talk-matrix__no { color: var(--danger); }
+.talk-matrix__self { color: var(--ink-faint); }
+
+/* The add-a-rule form: three fields on a shared track so the label, the
+   control and the hint of each line up whatever the text does -- the tree's
+   subgrid rule. Stacks below a phone's width. */
+.talk-rule-form {
+  display: grid;
+  grid-template-columns: repeat(auto-fit, minmax(min(100%, 12rem), 1fr));
+  grid-template-rows: auto auto auto;
+  column-gap: var(--sp-3);
+  min-width: 0;
+  margin-top: var(--sp-4);
+}
+.talk-rule-form > .field {
+  display: grid;
+  grid-template-rows: subgrid;
+  grid-row: span 3;
+  min-width: 0;
+}
+.talk-rule-form > .btn-row { grid-column: 1 / -1; }

src/lembas/web/templates/admin/_connection_row.html

@@ -121,6 +121,15 @@
       </p>
     </div>
 
+    <div class="field">
+      <label class="checkbox">
+        <input type="checkbox" name="one_model_at_a_time" value="true"
+               {{ 'checked' if connection.one_model_at_a_time }}>
+        <span>{{ t("Holds one model at a time") }}</span>
+      </label>
+      <p class="field__hint">{{ t("Tick this for llama-swap in front of one GPU, or anything else that unloads one model to serve another. A model here may then be its own helper, but never send a helper to another model on this connection: loading it would unload the model whose reply is waiting.") }}</p>
+    </div>
+
     <div class="field">
       <label class="checkbox">
         <input type="checkbox" name="enabled" value="true"

src/lembas/web/templates/admin/_layout.html

@@ -63,6 +63,10 @@
           {{ icon("users", "icon--sm") }}
           <span class="nav-item__label">{{ t("A crowd") }}</span>
         </a>
+        <a class="nav-item {{ 'is-active' if section == 'rules' }}" href="/admin/rules">
+          {{ icon("users", "icon--sm") }}
+          <span class="nav-item__label">{{ t("Model rules") }}</span>
+        </a>
         <a class="nav-item {{ 'is-active' if section == 'audio' }}" href="/admin/audio">
           {{ icon("speaker", "icon--sm") }}
           <span class="nav-item__label">{{ t("Audio") }}</span>

src/lembas/web/templates/admin/model_detail.html

@@ -306,6 +306,15 @@
       </div>
     </div>
 
+    <div class="field">
+      <label class="checkbox">
+        <input type="checkbox" name="single_session" value="true"
+               {{ 'checked' if model.single_session }}>
+        <span>{{ t("Serves one request at a time") }}</span>
+      </label>
+      <p class="field__hint">{{ t("Tick this for a model with a single slot. It then cannot be its own helper, because the helper would wait behind the reply that is waiting for it. Other models can still be its helpers.") }}</p>
+    </div>
+
     <div class="field">
       <label class="checkbox">
         <input type="checkbox" name="public" value="true" {{ 'checked' if model.public }}>
@@ -343,6 +352,47 @@
 
 {# Outside the form above, and it has to be: two forms cannot nest, and this one
    posts somewhere else. See the note beside the Detect button. #}
+<section class="card">
+  <h2 class="card__title">{{ t("Helpers") }}</h2>
+  <p class="card__lede">{{ t("Other models this one may send helpers to, for everybody. Offered ones it may choose itself; the rest can only be added to a chat by hand. It is always its own helper too, unless it serves one request at a time. The model rules and the connection's capacity are checked when a helper is sent.") }}</p>
+  {% if designations %}
+  <ul class="model-list">
+    {% for row in designations %}
+    <li class="model-list__item">
+      <strong class="mono">{{ row.helper_model }}</strong>
+      <div class="btn-row">
+        {% if row.offer %}
+        <span class="badge badge--leaf">{{ t("offered to the model") }}</span>
+        {% else %}
+        <span class="badge">{{ t("by hand only") }}</span>
+        {% endif %}
+        <form id="remove-helper-{{ row.id }}" method="post"
+              action="/admin/models/{{ model.id }}/helpers/{{ row.id }}/delete"></form>
+        <button class="btn btn--icon btn--sm btn--danger" type="submit" form="remove-helper-{{ row.id }}"
+                aria-label="{{ t('Remove this helper') }}" title="{{ t('Remove this helper') }}">
+          {{ icon("trash", "icon--sm") }}
+        </button>
+      </div>
+    </li>
+    {% endfor %}
+  </ul>
+  {% endif %}
+  {% if helper_choices %}
+  <form method="post" action="/admin/models/{{ model.id }}/helpers" class="row"
+        style="gap: var(--sp-2); flex-wrap: wrap; margin-top: var(--sp-4)">
+    <label class="visually-hidden" for="helper-model">{{ t("Helper model") }}</label>
+    <select class="select" id="helper-model" name="helper_model" style="flex: 1; min-width: 0">
+      {% for choice in helper_choices %}<option value="{{ choice }}">{{ choice }}</option>{% endfor %}
+    </select>
+    <label class="checkbox">
+      <input type="checkbox" name="offer" value="true" checked>
+      <span>{{ t("Offer it to the model") }}</span>
+    </label>
+    <button class="btn" type="submit">{{ icon("plus", "icon--sm") }} {{ t("Add helper") }}</button>
+  </form>
+  {% endif %}
+</section>
+
 <section class="card">
   <h2 class="card__title">{{ t("Default personality") }}</h2>
   <p class="card__lede">

src/lembas/web/templates/admin/rules.html

@@ -0,0 +1,38 @@
+{% extends "admin/_layout.html" %}
+{% from "_macros.html" import icon %}
+{% set section = "rules" %}
+
+{% block title %}{{ t("Model rules") }} - {{ brand.name }}{% endblock %}
+{% block heading %}{{ t("Model rules") }}{% endblock %}
+
+{% block admin_content %}
+<p class="admin-lede">{{ t("Which model may bring which into a conversation: as a crowd member, as a friend it asks, and on the list of other models it is told about. A rule is read from the chat's own model. A model in another data group is not offered unless a rule allows it.") }}</p>
+
+{% if saved %}
+<div class="alert alert--success">{{ icon("check", "icon--sm") }} <span>{{ t("Settings saved.") }}</span></div>
+{% endif %}
+
+<section class="card">
+  <h2 class="card__title">{{ t("The starting point") }}</h2>
+  <form method="post" action="/admin/rules/mode">
+    <div class="field">
+      <label class="checkbox">
+        <input type="radio" name="mode" value="open" {{ 'checked' if mode == 'open' }}>
+        <span>{{ t("Any model may talk to any other, except where a rule forbids it") }}</span>
+      </label>
+      <label class="checkbox">
+        <input type="radio" name="mode" value="closed" {{ 'checked' if mode == 'closed' }}>
+        <span>{{ t("No model may talk to another, except where a rule allows it") }}</span>
+      </label>
+      <p class="field__hint">{{ t("People can always narrow this for themselves. Widening it for themselves needs the permission to override the model rules.") }}</p>
+    </div>
+    <div class="btn-row"><button class="btn btn--primary" type="submit">{{ t("Save") }}</button></div>
+  </form>
+</section>
+
+<section class="card">
+  <h2 class="card__title">{{ t("Rules") }}</h2>
+  {% set rules_action = "/admin/rules" %}
+  {% include "partials/_talk_rules.html" %}
+</section>
+{% endblock %}

src/lembas/web/templates/chat/_composer.html

@@ -314,7 +314,60 @@
             because a browser submits only the ticked boxes and `start_chat`
             needs to know which ones were not.
           #}
-          {% if crowd_available %}
+          {#
+            Helpers: models designated for this chat's model that it may send a
+            helper to. Ticking one adds it to this chat by hand; an offered one
+            the model may use anyway. The crowd picker's shape and its reasons:
+            a sibling empty form reached by `form=`, one hidden field always
+            sent, and the verb on the checkbox.
+          #}
+          {% if helper_choices %}
+          <div class="picker picker--up" data-picker>
+            <button class="btn btn--icon composer__btn" type="button" data-picker-toggle
+                    aria-haspopup="menu" aria-expanded="false"
+                    aria-label="{{ t('Helpers') }}" title="{{ t('Helpers') }}">
+              {{ icon("bolt") }}
+              {% if helper_member_ids %}
+              <span class="composer__count">{{ helper_member_ids|length }}</span>
+              {% endif %}
+            </button>
+            <div class="picker__menu picker__menu--scope" data-picker-menu role="menu"
+                 hidden aria-label="{{ t('Helpers') }}">
+              <p class="picker__lede">
+                {{ t("Models this one may send helpers to. Tick one to add it to this chat; one offered to the model it may choose anyway.") }}
+              </p>
+              {% if chat %}
+              <input type="hidden" name="helper_model_ids" value="" form="helpers-form">
+              {% else %}
+              <input type="hidden" name="helper_model_ids" value="">
+              {% endif %}
+              {% for choice in helper_choices %}
+              <label class="picker__option picker__option--toggle">
+                {% if chat %}
+                <input type="checkbox" name="helper_model_ids" value="{{ choice.model.model_id }}"
+                       {{ 'checked' if choice.model.model_id in helper_member_ids }}
+                       {{ 'disabled' if not choice.addable }}
+                       form="helpers-form"
+                       hx-patch="/api/chats/{{ chat.id }}" hx-swap="none">
+                {% else %}
+                <input type="checkbox" name="helper_model_ids" value="{{ choice.model.model_id }}"
+                       {{ 'disabled' if not choice.addable }}>
+                {% endif %}
+                <span class="picker__option-body">
+                  <span class="picker__option-name">{{ choice.model.label }}</span>
+                  <span class="picker__option-note">
+                    {%- if helper_reasons.get(choice.model.model_id) %}{{ helper_reasons[choice.model.model_id] }}
+                    {%- elif choice.offer %}{{ t("Offered to the model.") }}
+                    {%- else %}{{ t("Only when added here.") }}{% endif -%}
+                  </span>
+                </span>
+              </label>
+              {% endfor %}
+            </div>
+          </div>
+          {% endif %}
+
+          {% if crowd_available or crowd_held_back %}
           <div class="picker picker--up" data-picker>
             <button class="btn btn--icon composer__btn" type="button" data-picker-toggle
                     aria-haspopup="menu" aria-expanded="false"
@@ -366,6 +419,38 @@
                 </span>
               </label>
               {% endfor %}
+              {#
+                Models the talk rules do not offer to this chat's model, named
+                with the reason rather than left out. Tickable where the person
+                may still add them by hand -- their own rule, or the override --
+                and shown disabled where they may not, so the reason is visible
+                either way. Same field and same verb as the list above.
+              #}
+              {% if crowd_held_back %}
+              <p class="picker__group">{{ t("Not offered to this model") }}</p>
+              {% for row in crowd_held_back %}
+              <label class="picker__option picker__option--toggle">
+                {% if chat %}
+                <input type="checkbox" name="crowd_model_ids" value="{{ row.model.model_id }}"
+                       {{ 'checked' if row.model.model_id in crowd_member_ids }}
+                       {{ 'disabled' if not row.addable }}
+                       form="crowd-form"
+                       hx-patch="/api/chats/{{ chat.id }}" hx-swap="none">
+                {% else %}
+                <input type="checkbox" name="crowd_model_ids" value="{{ row.model.model_id }}"
+                       {{ 'checked' if row.model.model_id in crowd_member_ids }}
+                       {{ 'disabled' if not row.addable }}>
+                {% endif %}
+                <span class="picker__option-body">
+                  <span class="picker__option-name">{{ row.model.label }}</span>
+                  <span class="picker__option-note">
+                    {{ row.reason }}
+                    {% if row.addable %}{{ t("You may still add it yourself.") }}{% endif %}
+                  </span>
+                </span>
+              </label>
+              {% endfor %}
+              {% endif %}
               {% if crowd_member_ids %}
               {# One sentence and not three, with the numbers as placeholders: a
                  translation puts the parts in its own order, and two of these
@@ -593,7 +678,10 @@
        hx-patch and not hx-post: there is no POST for a chat, only PATCH, and
        htmx shows nothing when a request 405s -- which is how these controls
        spent the first half of their lives doing nothing. #}
-    {% if chat and crowd_available %}
+    {% if chat and helper_choices %}
+    <form id="helpers-form"></form>
+    {% endif %}
+    {% if chat and (crowd_available or crowd_held_back) %}
     {# Empty, and a sibling of the composer's form rather than inside it. See the
        crowd checkboxes above, and `#agent-mode-form` below, for why both halves
        of that sentence matter. #}

src/lembas/web/templates/partials/_talk_rules.html

@@ -0,0 +1,104 @@
+{#
+  The rules list, the add form and the matrix, shared by the admin page and a
+  person's own settings. The caller sets `rules_action` (where the add form and
+  the deletes post), and passes `rules`, `model_ids`, `matrix`, `matrix_models`,
+  `any_model`, `allow` and `deny`.
+
+  The delete buttons reach one empty form each by `form=`, declared outside the
+  add form, so no form is ever nested inside another -- a nested <form>
+  truncates its parent, the 1.3.0 bug.
+#}
+{% from "_macros.html" import icon %}
+
+{% if rules %}
+<ul class="model-list">
+  {% for rule in rules %}
+  <li class="model-list__item">
+    <div style="min-width: 0">
+      <strong class="mono">{{ t("any model") if rule.from_model == any_model else rule.from_model }}</strong>
+      →
+      <strong class="mono">{{ t("any model") if rule.to_model == any_model else rule.to_model }}</strong>
+    </div>
+    <div class="btn-row">
+      {% if rule.effect == allow %}
+      <span class="badge badge--leaf">{{ t("may talk") }}</span>
+      {% else %}
+      <span class="badge badge--danger">{{ t("may not talk") }}</span>
+      {% endif %}
+      <form id="delete-rule-{{ rule.id }}" method="post" action="{{ rules_action }}/{{ rule.id }}/delete"></form>
+      <button class="btn btn--icon btn--sm btn--danger" type="submit" form="delete-rule-{{ rule.id }}"
+              aria-label="{{ t('Delete this rule') }}" title="{{ t('Delete this rule') }}">
+        {{ icon("trash", "icon--sm") }}
+      </button>
+    </div>
+  </li>
+  {% endfor %}
+</ul>
+{% else %}
+<p class="field__hint">{{ t("No rules yet.") }}</p>
+{% endif %}
+
+<form method="post" action="{{ rules_action }}" class="talk-rule-form">
+  <div class="field">
+    <label class="field__label" for="rule-from">{{ t("This model") }}</label>
+    <select class="select" id="rule-from" name="from_model">
+      <option value="{{ any_model }}">{{ t("any model") }}</option>
+      {% for model_id in model_ids %}<option value="{{ model_id }}">{{ model_id }}</option>{% endfor %}
+    </select>
+    <p class="field__hint">{{ t("The chat's own model.") }}</p>
+  </div>
+  <div class="field">
+    <label class="field__label" for="rule-effect">{{ t("May") }}</label>
+    <select class="select" id="rule-effect" name="effect">
+      <option value="{{ deny }}">{{ t("may not talk to") }}</option>
+      <option value="{{ allow }}">{{ t("may talk to") }}</option>
+    </select>
+    <p class="field__hint"></p>
+  </div>
+  <div class="field">
+    <label class="field__label" for="rule-to">{{ t("That model") }}</label>
+    <select class="select" id="rule-to" name="to_model">
+      <option value="{{ any_model }}">{{ t("any model") }}</option>
+      {% for model_id in model_ids %}<option value="{{ model_id }}">{{ model_id }}</option>{% endfor %}
+    </select>
+    <p class="field__hint">{{ t("A crowd member, a friend it asks, a model on its roster.") }}</p>
+  </div>
+  <div class="btn-row">
+    <label class="checkbox">
+      <input type="checkbox" name="both" value="true">
+      <span>{{ t("Both directions") }}</span>
+    </label>
+    <button class="btn btn--primary" type="submit">{{ icon("plus", "icon--sm") }} {{ t("Add rule") }}</button>
+  </div>
+</form>
+
+{% if matrix_models|length > 1 %}
+<h3 class="card__title" style="margin-top: var(--sp-6)">{{ t("Who may talk to whom") }}</h3>
+<p class="field__hint">{{ t("Rows are the chat's own model, columns the model it would bring in. Drawn by the same rules that are enforced, so what this shows is what happens.") }}</p>
+<div class="talk-matrix-scroll">
+  <table class="talk-matrix">
+    <thead>
+      <tr>
+        <th scope="col"></th>
+        {% for model in matrix_models %}<th scope="col" class="mono">{{ model.model_id }}</th>{% endfor %}
+      </tr>
+    </thead>
+    <tbody>
+      {% for row in matrix %}
+      <tr>
+        <th scope="row" class="mono">{{ row.main.model_id }}</th>
+        {% for cell in row.cells %}
+        {% if cell is none %}
+        <td class="talk-matrix__self" aria-label="{{ t('itself') }}">·</td>
+        {% elif cell.offered %}
+        <td class="talk-matrix__yes" title="{{ t('Offered') }}">✓</td>
+        {% else %}
+        <td class="talk-matrix__no" title="{{ describe_verdict(cell) }}">✗</td>
+        {% endif %}
+        {% endfor %}
+      </tr>
+      {% endfor %}
+    </tbody>
+  </table>
+</div>
+{% endif %}

src/lembas/web/templates/settings.html

@@ -185,6 +185,100 @@
               </ul>
             </div>
             {% endif %}
+            {#
+              Who your models may talk to. Anybody may narrow the instance's rules
+              for themselves; widening them takes `rules.override`, and the text
+              below says which of the two this person has, so a rule that does
+              nothing is not a mystery.
+            #}
+            <div class="card">
+              <h2 class="card__title">{{ t("Who your models may talk to") }}</h2>
+              <p class="card__lede">
+                {% if talk_override %}
+                {{ t("Your rules and your setting win over the instance's, for you. You can also add any model to a crowd by hand.") }}
+                {% else %}
+                {{ t("Your rules can only narrow the instance's. A model your own rule holds back can still be added to a crowd by hand; one the instance holds back cannot.") }}
+                {% endif %}
+              </p>
+              <form method="post" action="/api/preferences/talk-mode" class="row"
+                    style="gap: var(--sp-2); margin-bottom: var(--sp-4)">
+                <label class="visually-hidden" for="talk-mode">{{ t("Your starting point") }}</label>
+                <select class="select" id="talk-mode" name="mode" style="flex: 1; min-width: 0">
+                  <option value="" {{ 'selected' if not talk_mode }}>{{ t("Follow the instance") }}</option>
+                  <option value="open" {{ 'selected' if talk_mode == 'open' }}>{{ t("Any model may talk to any other") }}</option>
+                  <option value="closed" {{ 'selected' if talk_mode == 'closed' }}>{{ t("No model may talk to another") }}</option>
+                </select>
+                <button class="btn" type="submit">{{ t("Save") }}</button>
+              </form>
+              {% set rules_action = "/api/preferences/talk-rules" %}
+              {% set rules = talk_rules %}
+              {% set matrix = talk_matrix %}
+              {% set matrix_models = talk_matrix_models %}
+              {% include "partials/_talk_rules.html" %}
+            </div>
+
+            {#
+              A person's own helper designations. Shown to everybody who could
+              send a helper, so the instance's arrangement is visible; editable
+              only with `helpers.designate`, because a designation decides where
+              a person's tasks are sent.
+            #}
+            {% if helper_settings_shown %}
+            <div class="card">
+              <h2 class="card__title">{{ t("Your helper models") }}</h2>
+              <p class="card__lede">
+                {% if may_designate %}
+                {{ t("Models each of your models may send helpers to, for you alone, on top of the instance's. Your row for the same pair replaces the instance's.") }}
+                {% else %}
+                {{ t("Set by the administrator on each model's page. Adding your own needs the permission to choose your own helper models.") }}
+                {% endif %}
+              </p>
+              {% if own_designations %}
+              <ul class="model-list">
+                {% for row in own_designations %}
+                <li class="model-list__item">
+                  <div style="min-width: 0">
+                    <strong class="mono">{{ row.main_model }}</strong> → <strong class="mono">{{ row.helper_model }}</strong>
+                  </div>
+                  <div class="btn-row">
+                    <span class="badge {{ 'badge--leaf' if row.offer }}">{{ t("offered to the model") if row.offer else t("by hand only") }}</span>
+                    <form id="del-helper-{{ row.id }}" method="post" action="/api/preferences/helpers/{{ row.id }}/delete"></form>
+                    <button class="btn btn--icon btn--sm btn--danger" type="submit" form="del-helper-{{ row.id }}"
+                            aria-label="{{ t('Remove this helper') }}" title="{{ t('Remove this helper') }}">
+                      {{ icon("trash", "icon--sm") }}
+                    </button>
+                  </div>
+                </li>
+                {% endfor %}
+              </ul>
+              {% endif %}
+              {% if may_designate %}
+              <form method="post" action="/api/preferences/helpers" class="talk-rule-form">
+                <div class="field">
+                  <label class="field__label" for="helper-main">{{ t("This model") }}</label>
+                  <select class="select" id="helper-main" name="main_model">
+                    {% for model_id in model_ids %}<option value="{{ model_id }}">{{ model_id }}</option>{% endfor %}
+                  </select>
+                  <p class="field__hint">{{ t("The chat's own model.") }}</p>
+                </div>
+                <div class="field">
+                  <label class="field__label" for="helper-model">{{ t("May send helpers to") }}</label>
+                  <select class="select" id="helper-model" name="helper_model">
+                    {% for model_id in model_ids %}<option value="{{ model_id }}">{{ model_id }}</option>{% endfor %}
+                  </select>
+                  <p class="field__hint"></p>
+                </div>
+                <div class="btn-row">
+                  <label class="checkbox">
+                    <input type="checkbox" name="offer" value="true" checked>
+                    <span>{{ t("Offer it to the model") }}</span>
+                  </label>
+                  <button class="btn btn--primary" type="submit">{{ icon("plus", "icon--sm") }} {{ t("Add helper") }}</button>
+                </div>
+              </form>
+              {% endif %}
+            </div>
+            {% endif %}
           </section>
 
           {# --- Appearance --- #}

tests/test_data_group_chat_pin.py

@@ -144,7 +144,11 @@ def test_a_chat_whose_model_moved_is_refused_rather_than_sent(db, owner, setup):
 
 # --- Other models reaching the conversation ------------------------------------------
 def test_a_crowd_member_from_another_group_is_refused(client, db, owner, setup):
+    """For somebody without `rules.override`: a different group is a deny only a
+    rule opens. (An administrator holds every permission, so the owner is demoted.)"""
     settings_store.update(db, {"enabled": True}, key=settings_store.CROWD)
+    owner.role = "user"
+    db.commit()
     local, _ = setup
     chat = _chat(db, owner, connection=local)
     client.patch(f"/api/chats/{chat.id}", data={"crowd_model_ids": ["local-b", "cloud-model"]})
@@ -153,6 +157,8 @@ def test_a_crowd_member_from_another_group_is_refused(client, db, owner, setup):
 
 
 def test_a_crowd_member_that_left_the_group_does_not_speak(db, owner, setup):
+    owner.role = "user"
+    db.commit()
     local, cloud = setup
     chat = _chat(db, owner, connection=local)
     db.add(CrowdMember(chat_id=chat.id, model_id="cloud-model", connection_id=cloud.id))

tests/test_helpers.py

@@ -0,0 +1,342 @@
+"""Helpers on another model: capacity, designations, the choice, and the screens.
+
+`test_subagent.py` covers what a helper is *not* given; this covers which model
+it runs on. The generation loop is stubbed the way that file stubs it, and the
+tool is always reached through `resolve_tools`, because what may be run is what
+was offered.
+"""
+
+from __future__ import annotations
+
+import json
+
+import pytest
+from sqlalchemy import select
+
+from lembas.db.models import (
+    Chat,
+    ChatHelper,
+    Connection,
+    DataGroup,
+    HelperDesignation,
+    Model,
+    User,
+)
+from lembas.services import helpers, settings_store, talk
+from lembas.services import subagent as subagent_service
+from lembas.services import tools as tools_service
+from lembas.services.crypto import encrypt
+
+
+@pytest.fixture(autouse=True)
+def setup(db, registered):
+    """Helpers on, three models on one local connection and one hosted model."""
+    settings_store.update(db, {"enabled": True}, key=settings_store.SUBAGENTS)
+    settings_store.update(db, {"default_permissions": {"tools.subagent": True}})
+    local = Connection(name="Local", base_url="http://127.0.0.1:1", api_key_encrypted=encrypt(""))
+    cloud = Connection(name="Cloud", base_url="http://127.0.0.1:2", api_key_encrypted=encrypt(""))
+    db.add_all([local, cloud])
+    db.flush()
+    tools = {"tools": True}
+    db.add_all(
+        [
+            Model(connection_id=local.id, model_id="gpt-oss", capabilities_json=tools,
+                  position=0, params_json={"reasoning_effort": "high"}),
+            Model(connection_id=local.id, model_id="qwen35", capabilities_json=tools,
+                  position=1),
+            Model(connection_id=local.id, model_id="bonsai", capabilities_json=tools,
+                  position=2, params_json={"reasoning_effort": "xhigh"},
+                  reasoning_efforts=["low", "medium", "xhigh"]),
+            Model(connection_id=cloud.id, model_id="deepseek", capabilities_json=tools,
+                  position=3),
+        ]
+    )
+    db.commit()
+    subagent_service.clear()
+    yield {"local": local, "cloud": cloud}
+    subagent_service.clear()
+
+
+def _user(db) -> User:
+    return db.scalars(select(User).order_by(User.created_at)).first()
+
+
+def _chat(db, model_id="gpt-oss", connection=None) -> Chat:
+    connection_id = connection.id if connection else db.scalar(
+        select(Model.connection_id).where(Model.model_id == model_id)
+    )
+    chat = Chat(user_id=_user(db).id, title="t", model_id=model_id, connection_id=connection_id)
+    db.add(chat)
+    db.commit()
+    return chat
+
+
+def _row(db, model_id) -> Model:
+    return db.scalar(select(Model).where(Model.model_id == model_id))
+
+
+def _ids(found) -> list[str]:
+    return [c.model.model_id for c in found]
+
+
+def _spawn(monkeypatch):
+    from lembas.db.models import ROLE_ASSISTANT, ROLE_USER
+    from lembas.db.session import session_scope
+    from lembas.services import chat as chat_service
+
+    seen: dict[str, str] = {}
+
+    async def fake_wake(chat_id: str, content: str, *, model_id: str = "") -> str:
+        seen["chat_id"] = chat_id
+        with session_scope() as db:
+            child = db.get(Chat, chat_id)
+            chat_service.create_message(db, child, ROLE_USER, content)
+            reply = chat_service.create_message(db, child, ROLE_ASSISTANT, "Done.")
+        return reply.id
+
+    monkeypatch.setattr("lembas.services.wake.wake_chat", fake_wake)
+    monkeypatch.setattr("lembas.services.generation.running_for", lambda chat_id: None)
+    return seen
+
+
+async def _run(db, chat: Chat, args: dict):
+    from lembas.services import generation as generation_service
+
+    class _Fake:
+        subagents = 0
+
+    user = _user(db)
+    resolved = tools_service.resolve_tools(db, chat, user)
+    context = tools_service.context_for(db, user, chat, tools=resolved)
+    original = generation_service.running_for
+    generation_service.running_for = (
+        lambda chat_id: _Fake() if chat_id == chat.id else original(chat_id)
+    )
+    try:
+        return await tools_service.run_tool(context, "subagent_run", json.dumps(args))
+    finally:
+        generation_service.running_for = original
+
+
+def _schema(db, chat):
+    resolved = tools_service.resolve_tools(db, chat, _user(db))
+    tool = resolved.by_name.get("subagent_run")
+    return tool.parameters["properties"] if tool else None
+
+
+# --- Capacity ---------------------------------------------------------------------------
+def test_by_default_a_model_is_its_own_helper_and_the_tool_is_unchanged(db):
+    """Both switches off, nothing designated: exactly the 1.11 behaviour."""
+    chat = _chat(db)
+    assert _ids(helpers.candidates(db, chat, _user(db))) == ["gpt-oss"]
+    assert "model" not in _schema(db, chat)
+
+
+def test_a_single_session_model_cannot_help_itself(db):
+    _row(db, "gpt-oss").single_session = True
+    db.commit()
+    chat = _chat(db)
+    assert helpers.candidates(db, chat, _user(db)) == []
+    # Nothing to send a helper to, so the tool is not offered at all.
+    assert _schema(db, chat) is None
+
+
+def test_one_model_at_a_time_forbids_another_model_on_that_connection(db, setup):
+    main, other = _row(db, "gpt-oss"), _row(db, "qwen35")
+    assert helpers.capacity_refusal(main, other) == ""
+    setup["local"].one_model_at_a_time = True
+    db.commit()
+    assert "holds one model at a time" in helpers.capacity_refusal(main, other)
+    # ...but itself, and a model on another connection, are fine.
+    assert helpers.capacity_refusal(main, main) == ""
+    assert helpers.capacity_refusal(main, _row(db, "deepseek")) == ""
+
+
+# --- Designations ------------------------------------------------------------------------
+def test_an_offered_designation_joins_the_candidates_and_the_enum(db):
+    helpers.set_designation(db, None, "gpt-oss", "qwen35", offer=True)
+    chat = _chat(db)
+    assert _ids(helpers.candidates(db, chat, _user(db))) == ["gpt-oss", "qwen35"]
+    assert _schema(db, chat)["model"]["enum"] == ["gpt-oss", "qwen35"]
+
+
+def test_a_by_hand_designation_is_used_only_once_added_to_the_chat(db):
+    helpers.set_designation(db, None, "gpt-oss", "qwen35", offer=False)
+    chat = _chat(db)
+    assert _ids(helpers.candidates(db, chat, _user(db))) == ["gpt-oss"]
+    helpers.apply_chat_helpers(db, chat, _user(db), ["qwen35"])
+    db.commit()
+    assert _ids(helpers.candidates(db, chat, _user(db))) == ["gpt-oss", "qwen35"]
+
+
+def test_designations_are_per_main_model(db):
+    helpers.set_designation(db, None, "bonsai", "qwen35", offer=True)
+    assert _ids(helpers.candidates(db, _chat(db), _user(db))) == ["gpt-oss"]
+
+
+def test_a_persons_designations_need_the_permission_and_replace_the_instances(db):
+    user = _user(db)
+    user.role = "user"
+    db.commit()
+    helpers.set_designation(db, None, "gpt-oss", "qwen35", offer=True)
+    helpers.set_designation(db, user, "gpt-oss", "qwen35", offer=False)
+    assert [d.owner_id for d in helpers.designations(db, user, "gpt-oss")] == [None]
+    settings_store.update(
+        db, {"default_permissions": {"tools.subagent": True, helpers.PERMISSION: True}}
+    )
+    rows = helpers.designations(db, user, "gpt-oss")
+    assert [(d.owner_id, d.offer) for d in rows] == [(user.id, False)]
+
+
+def test_the_talk_rules_filter_designations(db):
+    user = _user(db)
+    user.role = "user"
+    db.commit()
+    helpers.set_designation(db, None, "gpt-oss", "qwen35", offer=True)
+    talk.set_rule(db, None, "gpt-oss", "qwen35", "deny")
+    assert _ids(helpers.candidates(db, _chat(db), user)) == ["gpt-oss"]
+
+
+def test_another_data_group_needs_a_rule(db, setup):
+    user = _user(db)
+    user.role = "user"
+    db.add(DataGroup(id="hosted", name="Hosted"))
+    setup["cloud"].data_group_id = "hosted"
+    db.commit()
+    helpers.set_designation(db, None, "gpt-oss", "deepseek", offer=True)
+    assert "deepseek" not in _ids(helpers.candidates(db, _chat(db), user))
+    talk.set_rule(db, None, "gpt-oss", "deepseek", "allow")
+    assert "deepseek" in _ids(helpers.candidates(db, _chat(db), user))
+
+
+# --- The choice, at call time -------------------------------------------------------------
+async def test_a_named_helper_runs_on_that_model_with_its_own_effort(db, monkeypatch):
+    helpers.set_designation(db, None, "gpt-oss", "bonsai", offer=True)
+    chat = _chat(db)
+    chat.params_json = {"reasoning_effort": "high"}
+    db.commit()
+    seen = _spawn(monkeypatch)
+    settings_store.update(db, {"keep_transcript": True}, key=settings_store.SUBAGENTS)
+
+    outcome = await _run(db, chat, {"task": "Check it.", "model": "bonsai"})
+
+    assert outcome.event["status"] == "ok"
+    child = db.get(Chat, seen["chat_id"])
+    assert child.model_id == "bonsai"
+    # Bonsai's own default, never the parent's `high`, which it would refuse.
+    assert child.params_json["reasoning_effort"] == "xhigh"
+    assert child.parent_chat_id == chat.id
+
+
+async def test_no_model_named_is_the_main_model_itself(db, monkeypatch):
+    helpers.set_designation(db, None, "gpt-oss", "bonsai", offer=True)
+    seen = _spawn(monkeypatch)
+    settings_store.update(db, {"keep_transcript": True}, key=settings_store.SUBAGENTS)
+    await _run(db, _chat(db), {"task": "Check it."})
+    assert db.get(Chat, seen["chat_id"]).model_id == "gpt-oss"
+
+
+async def test_a_model_that_is_not_a_candidate_is_refused_with_the_list(db, monkeypatch):
+    helpers.set_designation(db, None, "gpt-oss", "bonsai", offer=True)
+    _spawn(monkeypatch)
+    outcome = await _run(db, _chat(db), {"task": "Check it.", "model": "deepseek"})
+    assert outcome.event["status"] == "error"
+    assert "bonsai" in outcome.content
+
+
+def test_without_itself_the_default_is_the_first_hand_added_helper(db):
+    _row(db, "gpt-oss").single_session = True
+    helpers.set_designation(db, None, "gpt-oss", "qwen35", offer=False)
+    db.commit()
+    chat = _chat(db)
+    helpers.apply_chat_helpers(db, chat, _user(db), ["qwen35"])
+    db.commit()
+    model, refusal = helpers.choose(db, chat, _user(db), "")
+    assert model.model_id == "qwen35" and refusal == ""
+
+
+def test_the_harness_lists_where_a_helper_can_run(db):
+    from lembas.services import harness
+
+    helpers.set_designation(db, None, "gpt-oss", "qwen35", offer=True)
+    chat = _chat(db)
+    resolved = tools_service.resolve_tools(db, chat, _user(db))
+    text = harness.compose(db, _user(db), resolved.schemas, chat=chat)
+    assert "Where a helper can run" in text
+    assert "qwen35 (qwen35)" in text
+
+
+# --- The screens -----------------------------------------------------------------------------
+def test_the_model_page_designates_a_helper(client, db):
+    model = _row(db, "gpt-oss")
+    client.post(f"/admin/models/{model.id}/helpers", data={"helper_model": "qwen35",
+                                                            "offer": "true"})
+    row = db.scalar(select(HelperDesignation))
+    assert (row.main_model, row.helper_model, row.offer) == ("gpt-oss", "qwen35", True)
+    assert "offered to the model" in client.get(f"/admin/models/{model.id}/edit").text
+
+
+def test_the_model_page_saves_single_session(client, db):
+    model = _row(db, "gpt-oss")
+    page = client.get(f"/admin/models/{model.id}/edit").text
+    assert 'name="single_session"' in page
+    client.post(f"/admin/models/{model.id}", data={"display_name": "", "enabled": "true",
+                                                    "public": "true", "single_session": "true"})
+    db.expire_all()
+    assert _row(db, "gpt-oss").single_session is True
+
+
+def test_the_connection_form_saves_one_model_at_a_time(client, db, setup):
+    local = setup["local"]
+    client.post(f"/admin/connections/{local.id}", data={"name": "Local",
+                "base_url": local.base_url, "one_model_at_a_time": "true"})
+    db.expire_all()
+    assert db.get(Connection, local.id).one_model_at_a_time is True
+
+
+def test_the_composer_picker_adds_a_helper_by_hand(client, db):
+    helpers.set_designation(db, None, "gpt-oss", "qwen35", offer=False)
+    chat = _chat(db)
+    page = client.get(f"/chat/{chat.id}").text
+    assert 'name="helper_model_ids"' in page and 'id="helpers-form"' in page
+    client.patch(f"/api/chats/{chat.id}", data={"helper_model_ids": ["qwen35"]})
+    assert [h.model_id for h in db.scalars(select(ChatHelper))] == ["qwen35"]
+    client.patch(f"/api/chats/{chat.id}", data={"helper_model_ids": [""]})
+    db.expire_all()
+    assert list(db.scalars(select(ChatHelper))) == []
+
+
+def test_a_person_adds_their_own_designation_with_the_permission(client, db):
+    user = _user(db)
+    user.role = "user"
+    db.commit()
+    data = {"main_model": "gpt-oss", "helper_model": "qwen35", "offer": "true"}
+    client.post("/api/preferences/helpers", data=data)
+    assert list(db.scalars(select(HelperDesignation))) == []
+    settings_store.update(
+        db, {"default_permissions": {"tools.subagent": True, helpers.PERMISSION: True}}
+    )
+    client.post("/api/preferences/helpers", data=data)
+    assert db.scalar(select(HelperDesignation)).owner_id == user.id
+
+
+# --- Upgrading ---------------------------------------------------------------------------------
+def test_an_upgraded_database_reads_both_switches_as_off(db, setup):
+    """Both are NOT NULL booleans, which `sync_schema` backfills with False -- which
+    is why they name the restrictive state: False has to mean "as before"."""
+    from sqlalchemy import text
+
+    from lembas.db.migrations import sync_schema
+    from lembas.db.session import get_engine
+
+    engine = get_engine()
+    db.close()
+    with engine.begin() as connection:
+        connection.execute(text("DROP TABLE IF EXISTS chat_helpers"))
+        connection.execute(text("DROP TABLE IF EXISTS helper_designations"))
+        connection.execute(text("ALTER TABLE models DROP COLUMN single_session"))
+        connection.execute(text("ALTER TABLE connections DROP COLUMN one_model_at_a_time"))
+    sync_schema(engine)
+    assert _row(db, "gpt-oss").single_session is False
+    assert db.get(Connection, setup["local"].id).one_model_at_a_time is False
+    assert _ids(helpers.candidates(db, _chat(db), _user(db))) == ["gpt-oss"]

tests/test_talk_decide.py

@@ -0,0 +1,121 @@
+"""`talk.decide`, the one function behind every talk rule, as a table.
+
+Pure -- plain values in, a verdict out -- so every combination is asserted here
+with no database, and the admin matrix, which calls the same function, cannot
+disagree with what is enforced.
+"""
+
+from __future__ import annotations
+
+import pytest
+
+from lembas.services import talk
+from lembas.services.talk import Rule, decide, match
+
+ALLOW = Rule("main", "target", "allow")
+DENY = Rule("main", "target", "deny")
+
+
+def _v(**kwargs):
+    kwargs.setdefault("instance_mode", talk.MODE_OPEN)
+    kwargs.setdefault("instance_rule", None)
+    return decide(**kwargs)
+
+
+# --- The instance's layer ------------------------------------------------------------
+@pytest.mark.parametrize(
+    ("mode", "rule", "offered"),
+    [
+        (talk.MODE_OPEN, None, True),
+        (talk.MODE_OPEN, DENY, False),
+        (talk.MODE_OPEN, ALLOW, True),
+        (talk.MODE_CLOSED, None, False),
+        (talk.MODE_CLOSED, ALLOW, True),
+        (talk.MODE_CLOSED, DENY, False),
+    ],
+)
+def test_the_instance_mode_and_its_rules(mode, rule, offered):
+    verdict = _v(instance_mode=mode, instance_rule=rule)
+    assert verdict.offered is offered
+    assert verdict.addable is offered
+
+
+def test_another_data_group_is_a_deny_only_an_explicit_allow_opens():
+    assert _v(same_group=False).offered is False
+    assert _v(same_group=False).why == talk.WHY_GROUP
+    assert _v(same_group=False, instance_rule=ALLOW).offered is True
+    # An open mode is not an explicit allow.
+    assert _v(same_group=False, instance_mode=talk.MODE_OPEN).offered is False
+
+
+# --- A person without the override can only narrow ---------------------------------
+def test_a_persons_own_deny_takes_it_off_what_is_offered_but_not_off_what_is_addable():
+    verdict = _v(user_rule=DENY)
+    assert verdict.offered is False
+    assert verdict.addable is True
+    assert verdict.why == talk.WHY_YOUR_RULE
+
+
+def test_a_persons_closed_mode_narrows_too():
+    verdict = _v(user_mode=talk.MODE_CLOSED)
+    assert (verdict.offered, verdict.addable, verdict.why) == (False, True, talk.WHY_YOUR_CLOSED)
+
+
+def test_without_the_override_a_persons_allow_cannot_widen():
+    verdict = _v(instance_rule=DENY, user_rule=ALLOW)
+    assert (verdict.offered, verdict.addable) == (False, False)
+    assert verdict.why == talk.WHY_INSTANCE_RULE
+
+
+def test_without_the_override_open_mode_cannot_widen_a_closed_instance():
+    verdict = _v(instance_mode=talk.MODE_CLOSED, user_mode=talk.MODE_OPEN)
+    assert (verdict.offered, verdict.addable) == (False, False)
+
+
+# --- With the override, the person's layer wins ---------------------------------------
+def test_with_the_override_a_persons_allow_beats_the_instances_deny():
+    verdict = _v(instance_rule=DENY, user_rule=ALLOW, override=True)
+    assert (verdict.offered, verdict.addable) == (True, True)
+
+
+def test_with_the_override_a_persons_rule_opens_another_group():
+    assert _v(same_group=False, user_rule=ALLOW, override=True).offered is True
+
+
+def test_with_the_override_open_mode_widens_a_closed_instance_but_not_across_groups():
+    assert _v(instance_mode=talk.MODE_CLOSED, user_mode=talk.MODE_OPEN, override=True).offered
+    across = _v(same_group=False, user_mode=talk.MODE_OPEN, override=True)
+    assert across.offered is False and across.why == talk.WHY_GROUP
+    # ...unless some rule explicitly allows it.
+    assert _v(
+        same_group=False, user_mode=talk.MODE_OPEN, override=True, instance_rule=ALLOW
+    ).offered
+
+
+def test_with_the_override_and_no_layer_of_their_own_the_instance_decides():
+    assert _v(instance_rule=DENY, override=True).offered is False
+
+
+def test_with_the_override_anything_may_be_added_by_hand():
+    assert _v(instance_rule=DENY, override=True).addable is True
+    assert _v(same_group=False, override=True).addable is True
+
+
+# --- Specificity -------------------------------------------------------------------------
+def test_the_most_specific_rule_wins():
+    rules = [
+        Rule("*", "*", "deny"),
+        Rule("*", "b", "allow"),
+        Rule("a", "*", "deny"),
+        Rule("a", "b", "allow"),
+    ]
+    assert match(rules, "a", "b").effect == "allow"
+    assert match(rules, "a", "c") == Rule("a", "*", "deny")
+    assert match(rules, "x", "b") == Rule("*", "b", "allow")
+    assert match(rules, "x", "y") == Rule("*", "*", "deny")
+    assert match([], "a", "b") is None
+
+
+def test_a_verdict_says_why_in_english_for_a_model():
+    assert "forbids" in _v(instance_rule=DENY).reason
+    assert _v().reason == ""

tests/test_talk_rules.py

@@ -0,0 +1,203 @@
+"""Talk rules end to end: stored, edited, and obeyed by the roster, a friend and a crowd.
+
+The table of what `decide` answers is `test_talk_decide.py`. This file is where
+those answers reach something: the roster a model is told, the friend it may
+ask, the crowd picker's two lists, a member added by hand that must still speak,
+and a rule that lets a model from another data group in.
+"""
+
+from __future__ import annotations
+
+import pytest
+from sqlalchemy import select
+
+from lembas.db.models import (
+    DEFAULT_GROUP,
+    Chat,
+    Connection,
+    CrowdMember,
+    DataGroup,
+    Model,
+    TalkRule,
+    User,
+)
+from lembas.services import chat as chat_service
+from lembas.services import crowd, settings_store, talk
+from lembas.services import subagent as subagent_service
+from lembas.services.crypto import encrypt
+
+
+@pytest.fixture
+def owner(db, registered) -> User:
+    """The first account, demoted: an administrator holds `rules.override`."""
+    user = db.scalars(select(User).order_by(User.created_at)).first()
+    user.role = "user"
+    db.commit()
+    return user
+
+
+@pytest.fixture
+def setup(db, owner):
+    settings_store.update(db, {"enabled": True}, key=settings_store.CROWD)
+    db.add(DataGroup(id="hosted", name="Hosted"))
+    local = Connection(name="Local", base_url="http://127.0.0.1:1", api_key_encrypted=encrypt(""))
+    cloud = Connection(
+        name="Cloud",
+        base_url="http://127.0.0.1:2",
+        api_key_encrypted=encrypt(""),
+        data_group_id="hosted",
+    )
+    db.add_all([local, cloud])
+    db.flush()
+    for position, (connection, name) in enumerate(
+        [(local, "gpt-oss"), (local, "qwen38"), (local, "bonsai"), (cloud, "deepseek")]
+    ):
+        db.add(Model(connection_id=connection.id, model_id=name, position=position))
+    chat = Chat(
+        user_id=owner.id,
+        model_id="gpt-oss",
+        connection_id=local.id,
+        data_group_id=DEFAULT_GROUP,
+        title="t",
+    )
+    db.add(chat)
+    db.commit()
+    return chat
+
+
+def _ids(models) -> list[str]:
+    return [m.model_id for m in models]
+
+
+def _grant_override(db):
+    settings_store.update(db, {"default_permissions": {talk.PERMISSION: True}})
+
+
+# --- The roster and the friend ------------------------------------------------------
+def test_an_instance_deny_takes_a_model_off_the_roster(db, owner, setup):
+    talk.set_rule(db, None, "gpt-oss", "qwen38", "deny")
+    roster = chat_service.roster_block(db, owner, exclude="gpt-oss", group=DEFAULT_GROUP)
+    assert "qwen38" not in roster and "bonsai" in roster
+
+
+def test_a_friend_the_rules_forbid_is_refused_with_the_reason(db, owner, setup):
+    talk.set_rule(db, None, "gpt-oss", "qwen38", "deny")
+    friend, refusal = subagent_service._resolve_friend(
+        db, owner, "qwen38", asking="gpt-oss", group=DEFAULT_GROUP
+    )
+    assert friend is None
+    listed = refusal.split("These are the ones you can:")[-1]
+    assert "qwen38" not in listed
+
+
+def test_the_rule_is_read_from_the_main_model_only(db, owner, setup):
+    """bonsai may not talk to qwen38 -- which says nothing about gpt-oss's chats."""
+    talk.set_rule(db, None, "bonsai", "qwen38", "deny")
+    assert "qwen38" in _ids(talk.offered(db, owner, "gpt-oss", DEFAULT_GROUP))
+    assert "qwen38" not in _ids(talk.offered(db, owner, "bonsai", DEFAULT_GROUP))
+
+
+def test_a_closed_instance_offers_only_what_is_allowed(db, owner, setup):
+    settings_store.update(db, {"mode": "closed"}, key=settings_store.RULES)
+    talk.set_rule(db, None, "gpt-oss", "bonsai", "allow")
+    assert _ids(talk.offered(db, owner, "gpt-oss", DEFAULT_GROUP)) == ["bonsai"]
+
+
+# --- Other data groups -----------------------------------------------------------------
+def test_another_group_is_not_offered_until_a_rule_allows_it(db, owner, setup):
+    assert "deepseek" not in _ids(talk.offered(db, owner, "gpt-oss", DEFAULT_GROUP))
+    talk.set_rule(db, None, "gpt-oss", "deepseek", "allow")
+    assert "deepseek" in _ids(talk.offered(db, owner, "gpt-oss", DEFAULT_GROUP))
+
+
+def test_a_member_from_another_group_reads_its_own_groups_data(db, owner, setup):
+    from lembas.services import data_groups
+
+    speaker = chat_service.Speaker("deepseek", None)
+    assert data_groups.for_speaker(db, owner, setup, speaker) == "hosted"
+
+
+# --- The crowd: offered, and by hand -------------------------------------------------------
+def test_the_picker_names_what_it_holds_back_and_why(client, db, owner, setup):
+    talk.set_rule(db, None, "gpt-oss", "qwen38", "deny")
+    talk.set_rule(db, owner, "gpt-oss", "bonsai", "deny")
+    page = client.get(f"/chat/{setup.id}").text
+    held = page.split("Not offered to this model")[1]
+    assert "qwen38" in held and "bonsai" in held
+    assert "The instance's rule" in held or "The instance's rule" in held
+    assert "You may still add it yourself." in held
+
+
+def test_a_persons_own_rule_is_soft_for_them(client, db, owner, setup):
+    talk.set_rule(db, owner, "gpt-oss", "bonsai", "deny")
+    client.patch(f"/api/chats/{setup.id}", data={"crowd_model_ids": ["bonsai"]})
+    assert [m.model_id for m in db.scalars(select(CrowdMember))] == ["bonsai"]
+
+
+def test_an_instance_rule_is_hard_without_the_override(client, db, owner, setup):
+    talk.set_rule(db, None, "gpt-oss", "qwen38", "deny")
+    client.patch(f"/api/chats/{setup.id}", data={"crowd_model_ids": ["qwen38"]})
+    assert list(db.scalars(select(CrowdMember))) == []
+
+
+def test_with_the_override_an_instance_rule_can_be_passed_by_hand(client, db, owner, setup):
+    _grant_override(db)
+    talk.set_rule(db, None, "gpt-oss", "qwen38", "deny")
+    client.patch(f"/api/chats/{setup.id}", data={"crowd_model_ids": ["qwen38"]})
+    assert [m.model_id for m in db.scalars(select(CrowdMember))] == ["qwen38"]
+
+
+def test_a_member_added_by_hand_still_speaks(db, owner, setup):
+    """Send time asks `addable`, not `offered`, or the choice would be undone."""
+    talk.set_rule(db, owner, "gpt-oss", "bonsai", "deny")
+    db.add(CrowdMember(chat_id=setup.id, model_id="bonsai"))
+    db.commit()
+    assert _ids(crowd.member_speakers(db, setup, owner)) == ["gpt-oss", "bonsai"]
+
+
+def test_a_member_the_instance_later_forbids_is_skipped_and_named(db, owner, setup):
+    db.add(CrowdMember(chat_id=setup.id, model_id="qwen38"))
+    db.commit()
+    talk.set_rule(db, None, "gpt-oss", "qwen38", "deny")
+    assert _ids(crowd.member_speakers(db, setup, owner)) == ["gpt-oss"]
+    assert crowd.unreachable_members(db, setup, owner) == ["qwen38"]
+
+
+# --- Storing and editing ------------------------------------------------------------------------
+def test_both_directions_writes_two_rules_and_a_second_write_replaces(db, setup):
+    talk.set_rule(db, None, "a", "b", "deny", both=True)
+    assert {(r.from_model, r.to_model) for r in db.scalars(select(TalkRule))} == {
+        ("a", "b"),
+        ("b", "a"),
+    }
+    talk.set_rule(db, None, "a", "b", "allow")
+    assert db.scalar(select(TalkRule).where(TalkRule.from_model == "a")).effect == "allow"
+
+
+def test_a_person_cannot_delete_an_instance_rule(db, owner, setup):
+    talk.set_rule(db, None, "a", "b", "deny")
+    rule = db.scalar(select(TalkRule))
+    assert talk.delete_rule(db, owner, rule.id) is False
+    assert talk.delete_rule(db, None, rule.id) is True
+
+
+def test_the_admin_page_adds_a_rule_and_draws_the_matrix(client, db, registered, setup):
+    # The fixture demoted the first account; the page is an administrator's.
+    user = db.scalars(select(User).order_by(User.created_at)).first()
+    user.role = "admin"
+    db.commit()
+    client.post("/admin/rules", data={"from_model": "gpt-oss", "to_model": "bonsai",
+                                      "effect": "deny"})
+    page = client.get("/admin/rules").text
+    assert "Who may talk to whom" in page
+    assert page.count("talk-matrix__no") >= 1
+
+
+def test_the_settings_card_sets_a_persons_mode_and_rules(client, db, owner, setup):
+    client.post("/api/preferences/talk-mode", data={"mode": "closed"})
+    client.post("/api/preferences/talk-rules", data={"from_model": "gpt-oss",
+                                                     "to_model": "bonsai", "effect": "allow"})
+    db.expire_all()
+    user = db.get(User, owner.id)
+    assert talk.user_mode(user) == "closed"
+    assert _ids(talk.offered(db, user, "gpt-oss", DEFAULT_GROUP)) == ["bonsai"]