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, 16 insertions, 0 deletions

diff --git a/spec/test_profiles.lua b/spec/test_profiles.lua
index 3a052b9..f2a54a2 100644
--- a/spec/test_profiles.lua
+++ b/spec/test_profiles.lua
@@ -124,6 +124,22 @@ return {
             table.concat(found.warnings, " | "))
     end },
 
+    { "config roots follow every host layer, in host order", function()
+        local fake = require("spec.fake_ext")
+        local paths = require("subagents.paths")
+        local handle = fake.install()
+        local ok, err = pcall(function()
+            local roots = paths.config_roots("workflows")
+            assert(#roots == 4, "expected one root per layer, saw " .. #roots)
+            assert(roots[1] == "/data/panto/agent/workflows", roots[1])
+            assert(roots[2] == "/home/u/.config/panto/workflows", roots[2])
+            assert(roots[3] == "/proj/.panto/workflows", roots[3])
+            assert(roots[4] == "/proj/.panto/local/workflows", roots[4])
+        end)
+        handle.restore()
+        if not ok then error(err, 0) end
+    end },
+
     { "the list is sorted by name", function()
         local found, reason = fixture_or_skip()
         if not found then