Validation-pass fixes; DESIGN.md describes the shipped seam

jobs: a child whose wake pipe cannot be armed is refused up front instead of
started into a state nothing can wake (the luv-less drain loop survives only
for hosts without a loop); a closing child keeps its concurrency slot and
its id's exclusivity until the pump actually exits, so teardown can no
longer over-admit new children or let two turns share one session file.
Resume-metadata reads honor the plain-error contract on a malformed store.

workflow: the built-in schema subset validator is the only validator — the
jsonschema probe made behavior depend on an undeclared rock (see rockspec:
that dependency is deliberately rejected); dead exports and the unreachable
half of the structured-output guard are gone, keeping the empty-arguments
provider case.

DESIGN.md's seam sections now describe the shipped division: binding-level
async jobs and tool control, host-level resolve_model/ExtHost/turn events/
component handles, rock-level policy; protocol bodies run to completion on
the loop thread and cannot yield, cancellation is scoped to the stream that
opened it, and a child's compaction leaves protocol sessions alone.

1 files changed, 47 insertions, 0 deletions

diff --git a/spec/test_workflow.lua b/spec/test_workflow.lua
index c5ba06c..5d58c01 100644
--- a/spec/test_workflow.lua
+++ b/spec/test_workflow.lua
@@ -231,6 +231,53 @@ return {
         end)
     end },
 
+    -- One validator, always the built-in one: a schema must not be judged by
+    -- whether an undeclared rock happens to be installed on this machine.
+    { "validation never consults the jsonschema rock", function()
+        if not json_available() then
+            return "skip", "dkjson is not installed"
+        end
+        local restore = package.loaded.jsonschema
+        package.loaded.jsonschema = {
+            generate_validator = function()
+                return function()
+                    return false, "the rock must not be consulted"
+                end
+            end,
+        }
+        local ok, err = pcall(with_host, function(handle, profiles)
+            handle.queue_for("alpha", { structured_json = '{"items":["x"]}' })
+            local result = workflow.execute(workflow.workflow(function(ctx)
+                return ctx:agent({
+                    agent = "alpha",
+                    prompt = "split it",
+                    output = { schema = ITEMS_SCHEMA },
+                }):await()
+            end), "input", { profiles = profiles })
+            assert(result.status == "completed", tostring(result.error))
+            assert(result.output.items[1] == "x", "the built-in validator accepted it")
+        end)
+        package.loaded.jsonschema = restore
+        if not ok then
+            error(err, 0)
+        end
+    end },
+
+    { "a structured worker whose output tool carried no arguments fails as missing", function()
+        with_host(function(handle, profiles)
+            handle.queue_for("alpha", { structured_json = "" })
+            local result = workflow.execute(workflow.workflow(function(ctx)
+                return ctx:agent({
+                    agent = "alpha",
+                    prompt = "split it",
+                    output = { schema = ITEMS_SCHEMA },
+                }):await()
+            end), "input", { profiles = profiles })
+            assert(result.status == "failed", tostring(result.status))
+            has(result.error, "structured output missing")
+        end)
+    end },
+
     { "a structured worker that answers in prose fails", function()
         with_host(function(handle, profiles)
             handle.queue_for("alpha", { output = "prose, not a tool call" })