cua-driver >= 0.17 splits the semantic_v2 snapshot payload: action-bearing
refs live in the `refs` array while `content_refs` carries every node
with EMPTY action lists. _ref_map only absorbed content_refs, so every
click/pointer/type ref was registered with no declared actions and all
typed-browser mutations failed with browser_ref_stale.
Merge refs + content_refs + snapshot.refs with set union so action info
is never dropped by an empty content entry. Verified against the 0.17
split format, the legacy refs-only format, the transitional dict format,
and the snapshot.refs fallback.
weisiwu
bbd3462e25