Constant GIT_DIFF_RENAME_LIMIT 

pub const GIT_DIFF_RENAME_LIMIT: u8 = _; // 2u8

Similarity rename detection was skipped: the unmatched add/delete candidate set exceeded BLIT_GIT_RENAME_LIMIT, so the response fell back to the exact-oid join. Renders as “rename detection skipped” instead of unexplained delete+add pairs.