spawn_session and spawn_subsession now forward the dispatching session's
current thinking level to the new session, clamped by pi to the spawned
model's capabilities, instead of falling back to the configured default.
spawn_session and spawn_subsession accept an optional model parameter as
an exact provider/model-id (strict matching; unknown specs fail listing
available models; omitting it keeps the inherited model). The chat
composer opens a model completion menu on # and inserts a
#provider/model-id reference into the draft, which agents forward as
the model parameter.
Add a project-scoped spawn_session tool so agents can dispatch new,
independent sessions (ralph loops, long-plan chaining). Spawned sessions
are constrained to a workspace/worktree of the same registered project,
appear in the session list immediately via a new session.created event,
and the capability is on by default with a Settings -> Session daemon
toggle (spawnSessions / PI_WEB_SPAWN_SESSIONS).
Note: adds a session daemon code path, so pi-web-sessiond.service must be
restarted manually for the server side to take effect.