1. 1. Summary

Allows SBE to use a covering wildcard index on the foreign side of a $lookup instead of forcing the entire join to the classic engine, using the existing Dynamic Indexed Loop Join (DILJ) strategy. Wildcard indexes are sparse-like (they omit documents missing the indexed path), so per local document at runtime, scalar keys seek the wildcard index while null/missing/array/object keys fall back to a collection scan. Only single-path, non-partial wildcard indexes are eligible for pushdown; compound and partial wildcard indexes still force the classic engine.

• Added wildcard-index eligibility to the SBE pushdown gate in `planner_analysis.cpp`, and narrowed the "force classic" path to only compound/partial wildcard indexes; wildcard indexes are also treated as sparse for INLJ/DILJ index selection ordering.
• When a wildcard index is chosen, expands the placeholder `IndexEntry` (e.g. ` {"$**": 1}

  `) into a concrete `

  {foreignField: 1}

  ` entry via `wildcard_planning::expandWildcardIndexEntry` so downstream code treats it like any other index.

• In `query_planner.cpp`, rewrites the SBE index scan's key pattern and `multikeyPaths` to insert the wildcard index's virtual `$_path` component ahead of the foreign field, and binds it via a constant IET interval, so seeks match the real on-disk key shape.
• Extended the DILJ runtime branch in `gen_lookup.cpp` with an array/object type guard alongside the existing collation and sparse guards, since a wildcard index stores one key per sub-field and can't answer array/object local keys with a point seek.