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, 4 insertions, 6 deletions

diff --git a/subagents/progress.lua b/subagents/progress.lua
index 274e2a8..087a3c3 100644
--- a/subagents/progress.lua
+++ b/subagents/progress.lua
@@ -193,12 +193,10 @@ end
 -- `tool_call_complete` for one of our tools: claim that entry's component so
 -- the cards the handler is about to raise have somewhere to render.
 function M.claim(event)
-    -- The event is host userdata; a host that predates any of these fields
-    -- answers nil, and one that predates the whole object cannot be indexed.
-    local ok, name = pcall(function()
-        return event.tool_name
-    end)
-    if not ok or type(name) ~= "string" or name:sub(1, #TOOL_PREFIX) ~= TOOL_PREFIX then
+    -- The event is host userdata; an unknown field answers nil rather than
+    -- raising, and activation already refused a host too old to have these.
+    local name = event.tool_name
+    if type(name) ~= "string" or name:sub(1, #TOOL_PREFIX) ~= TOOL_PREFIX then
         return
     end
     if type(event.set_component) ~= "function" then