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, 23 insertions, 18 deletions

diff --git a/spec/test_workflow.lua b/spec/test_workflow.lua
index 5d58c01..2e66448 100644
--- a/spec/test_workflow.lua
+++ b/spec/test_workflow.lua
@@ -35,7 +35,7 @@ end
 local function three_children(ctx)
     local handles = {}
     for index, name in ipairs({ "alpha", "beta", "gamma" }) do
-        handles[index] = ctx:agent({ agent = name, prompt = "work on " .. name })
+        handles[index] = ctx:agent({ name = name, agent = name, prompt = "work on " .. name })
     end
     return handles
 end
@@ -100,27 +100,27 @@ return {
         with_host(function(handle, profiles)
             handle.queue_for("alpha", { output = "just me" })
             local result = workflow.execute(workflow.workflow(function(ctx)
-                return ctx:agent({ agent = "alpha", prompt = "go" }):await()
+                return ctx:agent({ name = "only", agent = "alpha", prompt = "go" }):await()
             end), "input", { profiles = profiles })
             assert(result.status == "completed", tostring(result.status))
             assert(result.output == "just me", tostring(result.output))
         end)
     end },
 
-    { "the gate keeps four children in flight and queues the rest", function()
+    { "the gate keeps five children in flight and queues the rest", function()
         with_host(function(handle, profiles)
             local results = workflow.execute(workflow.workflow(function(ctx)
                 local handles = {}
-                for index = 1, 5 do
-                    handles[index] = ctx:agent({ agent = "alpha", prompt = "task " .. index })
+                for index = 1, 6 do
+                    handles[index] = ctx:agent({ name = "job-" .. index, agent = "alpha", prompt = "task " .. index })
                 end
-                assert(#handle.runs == 4, "four turns run at once, saw " .. #handle.runs)
+                assert(#handle.runs == 5, "five turns run at once, saw " .. #handle.runs)
                 return ctx:await(handles, "all")
             end), "input", { profiles = profiles })
 
-            assert(#results == 5, "every child reports")
-            assert(#handle.runs == 5, "the queued child starts once a slot frees up")
-            assert(handle.max_live == 4, "never more than four at once, peaked at " .. handle.max_live)
+            assert(#results == 6, "every child reports")
+            assert(#handle.runs == 6, "the queued child starts once a slot frees up")
+            assert(handle.max_live == 5, "never more than five at once, peaked at " .. handle.max_live)
         end)
     end },
 
@@ -129,8 +129,8 @@ return {
             handle.queue_for("beta", { output = "B" })
 
             local results = workflow.execute(workflow.workflow(function(ctx)
-                local first = ctx:agent({ agent = "alpha", model = "openai:ghost", prompt = "a" })
-                local second = ctx:agent({ agent = "beta", prompt = "b" })
+                local first = ctx:agent({ name = "first", agent = "alpha", model = "openai:ghost", prompt = "a" })
+                local second = ctx:agent({ name = "second", agent = "beta", prompt = "b" })
                 return ctx:await({ first, second }, "all")
             end), "input", { profiles = profiles })
 
@@ -146,7 +146,7 @@ return {
         with_host(function(handle, profiles)
             handle.queue_for("alpha", { status = "failed", error = "provider refused", resumable = false })
             local result = workflow.execute(workflow.workflow(function(ctx)
-                return ctx:agent({ agent = "alpha", prompt = "a" }):await()
+                return ctx:agent({ name = "failed", agent = "alpha", prompt = "a" }):await()
             end), "input", { profiles = profiles })
             assert(result.status == "failed")
             assert(result.error == "provider refused", tostring(result.error))
@@ -162,8 +162,8 @@ return {
             handle.queue({ output = "the first turn wins" })
 
             local results = workflow.execute(workflow.workflow(function(ctx)
-                local first = ctx:agent({ id = "0198-child", prompt = "a" })
-                local second = ctx:agent({ id = "0198-child", prompt = "b" })
+                local first = ctx:agent({ name = "first", id = "0198-child", prompt = "a" })
+                local second = ctx:agent({ name = "second", id = "0198-child", prompt = "b" })
                 return ctx:await({ first, second }, "all")
             end), "input", { profiles = profiles })
 
@@ -182,6 +182,7 @@ return {
             handle.queue_for("alpha", { structured_json = '{"items":["x","y"]}' })
             local result = workflow.execute(workflow.workflow(function(ctx)
                 return ctx:agent({
+                    name = "worker",
                     agent = "alpha",
                     prompt = "split it",
                     output = { description = "Return the work items.", schema = ITEMS_SCHEMA },
@@ -219,6 +220,7 @@ return {
             handle.queue_for("alpha", { structured_json = '{"nope":1}' })
             local result = workflow.execute(workflow.workflow(function(ctx)
                 return ctx:agent({
+                    name = "worker",
                     agent = "alpha",
                     prompt = "split it",
                     output = { schema = ITEMS_SCHEMA },
@@ -249,6 +251,7 @@ return {
             handle.queue_for("alpha", { structured_json = '{"items":["x"]}' })
             local result = workflow.execute(workflow.workflow(function(ctx)
                 return ctx:agent({
+                    name = "worker",
                     agent = "alpha",
                     prompt = "split it",
                     output = { schema = ITEMS_SCHEMA },
@@ -268,6 +271,7 @@ return {
             handle.queue_for("alpha", { structured_json = "" })
             local result = workflow.execute(workflow.workflow(function(ctx)
                 return ctx:agent({
+                    name = "worker",
                     agent = "alpha",
                     prompt = "split it",
                     output = { schema = ITEMS_SCHEMA },
@@ -283,6 +287,7 @@ return {
             handle.queue_for("alpha", { output = "prose, not a tool call" })
             local result = workflow.execute(workflow.workflow(function(ctx)
                 return ctx:agent({
+                    name = "worker",
                     agent = "alpha",
                     prompt = "split it",
                     output = { schema = ITEMS_SCHEMA },
@@ -299,8 +304,8 @@ return {
             handle.queue_for("gamma", { output = "C" })
 
             local first_status = workflow.execute(workflow.workflow(function(ctx)
-                local rejected = ctx:agent({ agent = "alpha", model = "openai:ghost", prompt = "a" })
-                local live = { rejected, ctx:agent({ agent = "beta", prompt = "b" }) }
+                local rejected = ctx:agent({ name = "rejected", agent = "alpha", model = "openai:ghost", prompt = "a" })
+                local live = { rejected, ctx:agent({ name = "live", agent = "beta", prompt = "b" }) }
                 local result, remaining = ctx:await(live, "first")
                 assert(#remaining == 1, "the pending sibling stays outstanding")
                 assert(handle.polls == 0, "a cached result must not reach the job machinery")
@@ -326,7 +331,7 @@ return {
     { "handles the callback never awaited are settled before returning", function()
         with_host(function(handle, profiles)
             workflow.execute(workflow.workflow(function(ctx)
-                ctx:agent({ agent = "alpha", prompt = "orphan" })
+                ctx:agent({ name = "orphan", agent = "alpha", prompt = "orphan" })
                 return "done"
             end), "input", { profiles = profiles })
             assert(#handle.jobs == 1, "one child ran")
@@ -337,7 +342,7 @@ return {
     { "an unknown agent inside a workflow is a workflow error", function()
         with_host(function(handle, profiles)
             local ok, err = pcall(workflow.execute, workflow.workflow(function(ctx)
-                ctx:agent({ agent = "ghost", prompt = "go" })
+                ctx:agent({ name = "ghost", agent = "ghost", prompt = "go" })
             end), "input", { profiles = profiles })
             assert(not ok, "an unknown profile is a programmer error, not a child failure")
             has(tostring(err), "unknown agent 'ghost'")