Models that know about each other, and have a self

Three features sharing one idea: a model here started from nothing every
conversation and had no notion that anything else existed.

THE ROSTER. `chat.roster_block` builds one line per model this *person* can
reach -- through `permissions.models_visible_to`, never the table -- and
`{{model_roster}}` carries it, gated on the `friend` family for the reason the
memories block is gated on `memory`: a list of peers a model cannot talk to is
context spent on nothing, and one checkbox is then the whole switch. New
`Model.notes` column, a column and not a `capabilities_json` key for the reason
`context_length` and `reasoning_efforts` both carry.

ASKING A FRIEND. A second entry point in `services/subagent.py` rather than a
second module, so one place still owns the bounds and the lifecycle. `_create_
child` takes the friend's (model_id, connection_id) *pair*, because Model is
unique on both and an id alone does not say which endpoint. Three things differ
from a helper: the effort is the friend's own default and never the parent's (the
1.3.0 bug by another door -- the vocabularies differ and a level a model does not
take raises inside its chat template), the chat is ordinary even when the asker's
is an agent chat, and `scope_json["role"]` marks it so `core.friend` speaks
instead of `core.subagent`. `friend` joins the unattended withdrawal set: a
friend that could ask a friend is the same unbounded fan-out in politer clothes.
Budget, concurrency and quota are shared with helpers, so one reply cannot spend
the allowance twice.

PERSONALITY. One table, two roles, `owner_id IS NULL` the discriminator: the
model's own persona, and its read of one person. Keyed on the model's *text* id
with no foreign key, because "Test & refresh" deletes a model the endpoint has
stopped listing and a personality must not be collateral. `PersonaRevision`
copies SkillRevision, and so does the argument: the safety story for a model
rewriting itself is a record and a way back, not a gate. The reflection is shown
to the person it is about, in their own settings, which is the whole of why
keeping one is acceptable. `persona` is withdrawn from any unattended chat --
a helper's task, a friend's question and a schedule's instruction are all words
nobody watched being written.

Two bugs found while reading for this, both silent:

`review_model_id` stored a `Model` primary key, so a refresh taken while an
endpoint was not listing that model unset the administrator's choice -- and
`_reviewer` then fell back to the chat's own model, so pictures were judged by
a model nobody chose. Now the text id, with the primary key still accepted.

`_messages_after` used a bare `>` on `created_at`, so a row sharing the edited
turn's microsecond survived a rewind -- and `_send` writes a user turn and its
placeholder back to back, which is exactly that tie. Deliberately NOT
`thread_tail`'s `(created_at, id)` tiebreak: ids are random UUIDs, so that
settles a tie by coin toss. A tie now reads as "later", which is the safe
direction for an operation whose purpose is to discard what follows.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/lembas/services/personas.py

@@ -0,0 +1,225 @@
+"""A model's personality, and its read of the person it is talking to.
+
+Both live in one table (`db/models/persona.py` says why) and both reach the
+model the way the memories block does: a `{{variable}}` and a fragment, never a
+second system-prompt layer.
+
+Three rules, and each is here rather than in the column so a write that breaks
+one can be trimmed with an explanation instead of failing somebody's turn -- the
+rule `memories.py` already follows:
+
+* **Capped.** Both texts are in front of the model on every single request, so
+  a personality that grows without limit is a context window that shrinks
+  without anybody noticing.
+* **Snapshotted before every change.** A model may rewrite its own persona, so
+  what stops a bad rewrite being permanent is a record and a way back. Not a
+  gate: the roadmap already states the same limit for model-written skills.
+* **A reflection belongs to the person it is about.** It is keyed on their id,
+  read only for them, and shown to them in their own settings. A model-written
+  note about somebody that they cannot see is not something this application
+  should hold.
+"""
+
+from __future__ import annotations
+
+import logging
+
+from sqlalchemy import select
+from sqlalchemy.orm import Session as DBSession
+
+from lembas.db.models import AUTHOR_MODEL, AUTHOR_USER, Persona, PersonaRevision, User
+
+log = logging.getLogger(__name__)
+
+# Who a model is. Room for a real character -- a voice, what it cares about, how
+# it argues -- and not room for a second system prompt. An administrator who
+# wants more than this wants `Model.system_prompt`, which is the layer meant for
+# instructions and is not rewritten by the model.
+MAX_PERSONA_CHARS = 1200
+
+# What one model has made of one person. Shorter on purpose: it is a standing
+# impression, not a file. Anything that needs more than this is either a memory
+# (a fact) or a note (a document).
+MAX_VIEW_CHARS = 800
+
+# How many "before" states are kept. Enough to undo a bad afternoon, bounded so
+# a model editing itself every turn cannot grow the table without limit.
+MAX_REVISIONS = 20
+
+
+def _limit(reflection: bool) -> int:
+    return MAX_VIEW_CHARS if reflection else MAX_PERSONA_CHARS
+
+
+def get(db: DBSession, model_key: str, owner: User | None) -> Persona | None:
+    """The persona for a model, or that model's read of one person.
+
+    `owner=None` asks for the model's own persona. There is no fallback between
+    the two: a reflection is not a kind of persona and must not stand in for a
+    missing one.
+    """
+    if not model_key:
+        return None
+    return db.scalars(
+        select(Persona).where(
+            Persona.model_key == model_key,
+            Persona.owner_id == (owner.id if owner is not None else None),
+        )
+    ).first()
+
+
+def reflections_for(db: DBSession, owner: User | None) -> list[Persona]:
+    """Every model's read of one person, for that person's own settings page."""
+    if owner is None:
+        return []
+    return list(
+        db.scalars(
+            select(Persona)
+            .where(Persona.owner_id == owner.id)
+            .order_by(Persona.model_key)
+        )
+    )
+
+
+def personas_for(db: DBSession, model_keys: list[str]) -> dict[str, Persona]:
+    """Every model's own persona, keyed by model id. For the admin screens."""
+    if not model_keys:
+        return {}
+    rows = db.scalars(
+        select(Persona).where(
+            Persona.model_key.in_(model_keys), Persona.owner_id.is_(None)
+        )
+    )
+    return {row.model_key: row for row in rows}
+
+
+def write(
+    db: DBSession,
+    *,
+    model_key: str,
+    owner: User | None,
+    content: str,
+    author: str = AUTHOR_MODEL,
+    note: str = "",
+) -> Persona:
+    """Set a persona or a reflection, keeping what was there.
+
+    Returns the row. Raises `ValueError` only for a write with no model to
+    attach to -- an over-long text is trimmed rather than refused, because the
+    alternative is a model losing a turn to a length it could not have known.
+    """
+    if not model_key:
+        raise ValueError("There is no model to write a personality for.")
+
+    reflection = owner is not None
+    text = (content or "").strip()[: _limit(reflection)]
+    row = get(db, model_key, owner)
+
+    if row is None:
+        row = Persona(
+            model_key=model_key,
+            owner_id=owner.id if reflection else None,
+            content=text,
+            author=author if author in (AUTHOR_USER, AUTHOR_MODEL) else AUTHOR_MODEL,
+        )
+        db.add(row)
+        db.commit()
+        return row
+
+    if row.content == text:
+        # Nothing changed, so nothing is snapshotted. Otherwise a model that
+        # rewrites itself with the same words every turn fills the history with
+        # identical revisions and pushes the real "before" out of it.
+        return row
+
+    db.add(
+        PersonaRevision(
+            persona_id=row.id,
+            content=row.content,
+            author=row.author,
+            note=(note or "").strip()[:200],
+        )
+    )
+    row.content = text
+    row.author = author if author in (AUTHOR_USER, AUTHOR_MODEL) else AUTHOR_MODEL
+    db.commit()
+    _prune(db, row)
+    return row
+
+
+def _prune(db: DBSession, row: Persona) -> None:
+    """Drop the oldest revisions past the ceiling.
+
+    Queried rather than read off `row.revisions`, and ordered with the id as a
+    tiebreak. Both matter. The session is built with `expire_on_commit=False`, so
+    the loaded collection can be a version of the list from before the write that
+    prompted this -- which is how the first draft of this deleted a row that was
+    already gone and left one that should have been. And revisions written in the
+    same microsecond order arbitrarily under `created_at` alone, so which ones
+    "the oldest" names would not be stable.
+    """
+    extra = list(
+        db.scalars(
+            select(PersonaRevision)
+            .where(PersonaRevision.persona_id == row.id)
+            .order_by(PersonaRevision.created_at.desc(), PersonaRevision.id.desc())
+            .offset(MAX_REVISIONS)
+        )
+    )
+    if not extra:
+        return
+    for revision in extra:
+        db.delete(revision)
+    db.commit()
+    # Or the caller's next read of `row.revisions` is the list that still has
+    # them in it.
+    db.expire(row, ["revisions"])
+
+
+def revert(db: DBSession, row: Persona, revision: PersonaRevision) -> Persona:
+    """Put a previous text back, as the person doing the reverting.
+
+    Goes through `write`, so the text being replaced is itself snapshotted: an
+    undo that cannot be undone is a second way to lose the same work.
+    """
+    owner = db.get(User, row.owner_id) if row.owner_id else None
+    return write(
+        db,
+        model_key=row.model_key,
+        owner=owner,
+        content=revision.content,
+        author=AUTHOR_USER,
+        note="reverted",
+    )
+
+
+def clear(db: DBSession, row: Persona) -> None:
+    db.delete(row)
+    db.commit()
+
+
+def block(db: DBSession, model_key: str, owner: User | None) -> str:
+    """The text as the prompt carries it, or "" when there is nothing to say.
+
+    Empty and disabled are the same answer on purpose: the fragments that read
+    this are gated on it with `requires`, so both make the whole section vanish
+    rather than leaving a heading above nothing.
+    """
+    row = get(db, model_key, owner)
+    if row is None or not row.enabled:
+        return ""
+    return (row.content or "").strip()
+
+
+__all__ = [
+    "MAX_PERSONA_CHARS",
+    "MAX_REVISIONS",
+    "MAX_VIEW_CHARS",
+    "block",
+    "clear",
+    "get",
+    "personas_for",
+    "reflections_for",
+    "revert",
+    "write",
+]