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, 31 insertions, 11 deletions

diff --git a/spec/test_run.lua b/spec/test_run.lua
index 57c6e47..b2c5783 100644
--- a/spec/test_run.lua
+++ b/spec/test_run.lua
@@ -75,11 +75,15 @@ return {
         end)
     end },
 
-    { "both agent and id is refused", function()
+    { "multiple selectors are refused", function()
         with_host(function(handle, profiles)
             local text = run.handle({ agent = "reviewer", id = "0198-x", prompt = "go" }, profiles)
             has(text, "Error:")
-            has(text, "not both")
+            has(text, "exactly one of `agent`")
+            assert(#handle.spawns == 0)
+
+            text = run.handle({ agent = "reviewer", system_prompt = "Be concise.", prompt = "go" }, profiles)
+            has(text, "exactly one of `agent`")
             assert(#handle.spawns == 0)
         end)
     end },
@@ -124,6 +128,21 @@ return {
         end)
     end },
 
+    { "an inline system prompt starts a child without a profile", function()
+        with_host(function(handle, profiles)
+            local text = run.handle({ system_prompt = "Be a focused investigator.", prompt = "Find the cause." }, profiles)
+            assert(#handle.spawns == 1)
+            local messages = handle.spawns[1].system_messages
+            assert(#messages == 2, "expected role and inline prompt")
+            assert(messages[1].text == spawn.CHILD_ROLE)
+            assert(messages[2].text == "Be a focused investigator.")
+            local manifest = messages[2].metadata.subagents
+            assert(manifest.agent == "subagent", tostring(manifest.agent))
+            assert(manifest.inline == true, "inline prompts must remain identifiable on replay")
+            has(text, "agent: subagent")
+        end)
+    end },
+
     { "subagents.run presents its child prompt only when expanded", function()
         with_host(function(handle, profiles)
             handle.queue_for("reviewer", { events = {
@@ -171,22 +190,23 @@ return {
         end)
     end },
 
-    { "the primary's system context comes first, then the role, then the profile", function()
+    { "the primary's system context and dialogue are not copied", function()
         with_host(function(handle, profiles)
             run.handle({ agent = "reviewer", prompt = "go" }, profiles)
             local messages = handle.spawns[1].system_messages
-            assert(#messages == 4, "expected two copied messages plus role and profile, saw " .. #messages)
-            assert(messages[1].text == "Project context.", tostring(messages[1].text))
-            assert(messages[2].text == "House style.", tostring(messages[2].text))
-            assert(messages[3].text == spawn.CHILD_ROLE, "the child role follows the primary's context")
-            assert(messages[4].text == "You are a reviewer.\n", "the profile body is last")
-            assert(messages[1].metadata == nil, "copied context carries no manifest")
+            assert(#messages == 2, "expected only role and profile messages, saw " .. #messages)
+            assert(messages[1].text == spawn.CHILD_ROLE, "the child role is first")
+            assert(messages[2].text == "You are a reviewer.\n", "the profile defines the child context")
+            for _, message in ipairs(messages) do
+                assert(message.text ~= "Primary core prompt.", "the primary system prompt must not reach the child")
+                assert(message.text ~= "Project context.", "primary system additions must not be copied")
+            end
         end, {
             primary_messages = {
-                { role = "system", text = "Project context." },
+                { role = "system", text = "Primary core prompt." },
                 { role = "user", text = "the parent dialogue is never copied" },
                 { role = "assistant", text = "nor this" },
-                { role = "system", text = "House style." },
+                { role = "system", text = "Project context." },
             },
         })
     end },