Work handed to a second model, which may not ask

subagent_run gives a self-contained piece of work to a helper carrying the
parent's connection, directory, model and effort, and hands its answer back as
the tool result. The mechanism is the one scheduled runs already use -- a hidden
chat, one turn, wake_chat, and a poll -- so tools, rounds, budgets, metrics and
steps all work with no second implementation. The two alternatives were
rejected where they had already been rejected once: a nested Generation is two
replies writing one transcript, and a one-shot complete() has no tools, which
schedule/runner.py records as useless for exactly this case.

Every restriction is a property of the child's row, applied by resolve_tools
after the gates, because a rule that lives in a system message is one a page the
model just read can argue with. No questions, no recursion, nothing that writes
unless the call asked for it and the parent's own mode would not have stopped
first, and commands only from a fixed read-only list -- in every mode including
Auto, because the task text can have come from a page.

Withdrawing ask_user turned out to be half of "nobody is watching". An approval
still built a card nobody could see and parked the reply until approval_timeout,
which from every screen is the feature not working. Chat.unattended is the
question now, and not the kind: _authorise answers with a refusal instead. A
scheduled task's chat had the same hole and is covered by the same flag.

Three bounds, counted where each is knowable: per reply on the parent's
Generation, instance-wide in a set a restart clears, and per helper in settings
of its own so one runs out of room long before the reply that asked. Past the
clock the helper is stopped rather than abandoned, so a partial answer comes
back with a sentence saying so.

Also: four gates had shipped into the scope menu with no name, taking the first
tool's label instead -- the canvas switch read "Canvas written". There is a test
that refuses a family without one.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/lembas/db/models/chat.py

@@ -257,6 +257,21 @@ class Chat(UUIDPrimaryKey, Timestamps, Base):
     image_workflow_id: Mapped[str | None] = mapped_column(String(32))
     image_checkpoint: Mapped[str] = mapped_column(String(300), default="")
 
+    # --- Subagents -----------------------------------------------------------
+    # The chat whose reply spawned this one, when a model delegated a piece of
+    # work. A plain id and not a ForeignKey, for the reason the three above
+    # give, and validated on read. Its presence is what makes a chat a
+    # subagent's: `agent/session.py` sizes it smaller, `services/subagent.py`
+    # refuses to spawn from one, and the sweep finds it.
+    parent_chat_id: Mapped[str | None] = mapped_column(String(32))
+    # Nobody is at the keyboard for this conversation, and nothing in it may
+    # stop to ask. Not the same question as `kind`: a scheduled task's chat is
+    # unattended because of what started it, a subagent's because of what it is,
+    # and a future third thing will be unattended for a third reason. Reading
+    # the flag rather than the kind is what stops each of those needing its own
+    # branch in `resolve_tools` and in `_authorise`.
+    unattended: Mapped[bool] = mapped_column(Boolean, default=False, nullable=False)
+
     # Which files are open in the canvas panel, and which of them is in front.
     # {"tabs": [{"key": "agent:/srv/app/main.py", "title": …, "source": …}],
     #  "active": "agent:/srv/app/main.py"}