Add background Lua workflows, inline child prompts, and layered config

subagents.lua now starts a workflow on its own coroutine and returns a
session-scoped id immediately, so fan-out continues while the primary keeps
working; completion wakes the primary, and later calls read immutable records
from subagents.workflows. Every ctx:agent takes a workflow-unique name so those
records are addressable. A session_start guidance message tells the primary when
to reach for run vs lua.

Children no longer inherit the primary's system context: a child starts from the
fixed child-role instruction plus its profile, and subagents.run/ctx:agent
accept an inline system_prompt instead of a profile. The now-redundant `agent`
form of subagents.models is gone.

Concurrency defaults to five and is configurable through [subagents]
max_concurrent in any layered config.toml; turn boundaries reap only settled
jobs so background workflows survive, while interrupt and session end cancel.

Config roots come from panto.ext.dirs.layers rather than a hand-rolled XDG
lookup, which picks up the base and git-ignored local layers for both agents/
and workflows/.

TOML workflows tighten up: the subagents.workflow tool takes a discovered name
only (inline `steps` duplicated subagents.lua at less power), an optional
top-level `output` array chooses the reported steps and their order instead of
the terminal set, a step with no workflow input gets no empty input heading, and
a workflow naming an undiscovered agent is rejected at discovery rather than
part-way through a run.

1 files changed, 5 insertions, 7 deletions

diff --git a/subagents/profiles.lua b/subagents/profiles.lua
index 4ae9f91..b1acdf3 100644
--- a/subagents/profiles.lua
+++ b/subagents/profiles.lua
@@ -1,13 +1,11 @@
 -- Discover agent profiles: Markdown files with YAML frontmatter.
 --
--- Two layers are read, lowest precedence first:
+-- One `agents/**/*.md` root per host config layer, lowest precedence first:
+-- base, user, project, local (`panto.ext.dirs.layers`; see subagents/paths.lua).
 --
---   1. ${XDG_CONFIG_HOME:-$HOME/.config}/panto/agents/**/*.md   (user)
---   2. <cwd>/.panto/agents/**/*.md                              (project)
---
--- A project profile shadows a user profile with the same resolved name. Both
--- layers are walked recursively; nesting is organisational only and never part
--- of a profile's name.
+-- A later layer's profile shadows an earlier one with the same resolved name.
+-- Every layer is walked recursively; nesting is organisational only and never
+-- part of a profile's name.
 --
 -- Recognised frontmatter keys, all optional:
 --