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, 2 insertions, 47 deletions

diff --git a/spec/test_models.lua b/spec/test_models.lua
index ae01396..56d0877 100644
--- a/spec/test_models.lua
+++ b/spec/test_models.lua
@@ -1,4 +1,4 @@
--- subagents/models.lua: the four catalog query forms and the profile join.
+-- subagents/models.lua: the three catalog query forms.
 --
 -- The fake host answers by query shape, so each case checks both what the tool
 -- asked the host for (`handle.models_queries`) and how it rendered the answer.
@@ -42,25 +42,9 @@ local function catalog(query)
     }
 end
 
-local function profile_set()
-    local reviewer = {
-        name = "reviewer",
-        description = "Reviews changes",
-        model = "anthropic:sonnet",
-        reasoning = "high",
-        body = "b",
-    }
-    local scout = { name = "scout", description = "", body = "b" }
-    return {
-        list = { reviewer, scout },
-        by_name = { reviewer = reviewer, scout = scout },
-        warnings = {},
-    }
-end
-
 local function with_host(fn)
     local handle = fake.install({ models_response = catalog })
-    local ok, err = pcall(fn, handle, profile_set())
+    local ok, err = pcall(fn, handle)
     handle.restore()
     if not ok then
         error(err, 0)
@@ -119,35 +103,6 @@ return {
         end)
     end },
 
-    { "an agent with a model reports that model", function()
-        with_host(function(handle, profiles)
-            local text = models.handle({ agent = "reviewer" }, profiles)
-            has(text, "agent: reviewer")
-            has(text, "description: Reviews changes")
-            has(text, "wire model: claude-sonnet-4-6")
-            has(text, "profile reasoning: high")
-            assert(handle.models_queries[1].model == "anthropic:sonnet", "the profile model is looked up")
-        end)
-    end },
-
-    { "an agent without a model says it inherits", function()
-        with_host(function(handle, profiles)
-            local text = models.handle({ agent = "scout" }, profiles)
-            has(text, "agent: scout")
-            has(text, "model: inherits the primary model")
-            has(text, "inherited model: anthropic:sonnet")
-            assert(next(handle.models_queries[1]) == nil, "the inherited case asks for the overview")
-        end)
-    end },
-
-    { "an unknown agent names the known profiles", function()
-        with_host(function(handle, profiles)
-            local text = models.handle({ agent = "ghost" }, profiles)
-            has(text, "Error: unknown agent 'ghost'")
-            has(text, "reviewer, scout")
-        end)
-    end },
-
     { "a non-string field is refused", function()
         with_host(function(handle, profiles)
             has(models.handle({ query = 12 }, profiles), "Error: `query` must be a non-empty string")