fix(collab): rebuild guest context after host compaction

CollabGuestLink.#applyFrame only rebuilt the guest agent message array for message entries; compaction/branch_summary entries rewrite the host history (appendCompaction + buildDisplaySessionContext + replaceMessages), so the guest kept the stale pre-compaction transcript while the host held the compacted view. Rebuild the guest message array from the ingested entries on those history-rewriting entries, mirroring the host.

Fixes #9781