docs: align mechanical handoff wording

BUILDER.md

@@ -339,10 +339,11 @@ item to its flow in the same comment ([LABELS.md](LABELS.md)).
 
 When the round passes — every panel verdict approves the **current head**,
 and no `blocker:*` stands (conflicts rebased, CI green, drill recorded if
-this is a release PR) — hand it to the human, in order:
+this is a release PR) — the engine performs these mechanical steps on the
+builder's behalf, in order:
 
 1. request the human's review;
-2. set `state:needs-human` yourself;
+2. set `state:needs-human`;
 3. post the engine-rendered handoff comment: approvals at the current head,
    the head SHA, and a pointer to the PR body's **Round log**.
 

CONTRIBUTING.md

@@ -68,9 +68,11 @@ already proven:
    feedback. ([REVIEWER.md](REVIEWER.md) for why a comment-only review stalls
    the machine.)
 5. **Handoff**: when the round passes — every panel verdict is an approval of
-   the current head and no `blocker:*` label stands — the author posts the
-   round summary, requests the human's review, and sets `state:needs-human`.
-   The label write is optimistic; the reconciler validates it within seconds.
+   the current head and no `blocker:*` label stands — the engine requests the
+   human's review, sets `state:needs-human`, and posts the handoff facts
+   (approvals at the current head, head SHA, and Round-log pointer) on the
+   author's behalf. The label write is optimistic; the reconciler validates
+   it within seconds.
 6. **A human merges.** Nothing else merges.
 
 ### Roster