* fix(executor): strip orphan reasoning ids when store is disabled
Codex backend requires store=false and treats reasoning items with an
id but no usable encrypted_content as store lookups, which 404 with
"Item with id not found". Drop those orphan ids after removing invalid
encrypted_content (and when encrypted_content is already missing),
while preserving ids when store=true.
* fix(executor): skip id delete when reasoning item has no id
Avoid sjson.Delete on encrypted_content drops that never carried an id,
matching the orphan-id path's Exists() guard.
