Let a later observation of a subagent file replace its baseline

apply kept the first baseline recorded for a pending subagent file. A scan reports a file only on new subagent evidence after its scan position, so a later observation means the subagent wrote the file again (a build appending to a log, a second Edit after a turn boundary), and the stale baseline counted those lines as user work. The later baseline now wins; a user edit made between two of the subagent's writes to the same file counts as the subagent's.