Investigate transaction metrics when a shard acts as a subrouter and recruits additional participants. Verify whether the originating internal/external classification is propagated; currently, recruited participants may be misclassified as external.

Acceptance criteria:

• Add a subrouter jstest eg. covering $lookup/$graphLookup within a transaction
• If misclassification is confirmed, add regression-covered handling; otherwise, document the expected metric skew and rationale