Same principle as the enum-enumeration fix, mara caught it in review:
the description said where full output lives, but format_task's own
answer already names the exact path when output was actually
truncated — the description doesn't need to say it too.
Mirrors #4333's split on the sibling hive-subagent-mcp surface (mara's
ruling there, quoted on #4336: "dont explain all the possible states
that can be returned in the tool description. instead explain the
status when returning it").
status_explanation() carries what each TaskStatus means and what to do
about it, appended to every format_task answer. The status tool's
description shrinks to what it's for; a caller only ever sees one
state at a time and now learns what it means without cross-referencing
anything else.
