Development record

`.abcd/development/brief/04-surfaces/11-history.md:55-58` describes capture as idempotent on the content hash, session id and source labels together: identical content is a no-op and a different session writes a new record. Capture also supersedes (`resolveSupersession`, `internal/core/history/history.go:391`). A body that extends a stored record of the same session, agent and labels deletes that record and the result carries a `superseded` field, and a body that is a prefix of a stored one is a no-op despite its different hash. Neither the chapter nor `commands/history.md` says this, or that a capture can remove a stored record.