Summary

Pure algorithmic performance optimizations for merge-base computation and three-way tree merging:

1. ExGitObjectstore.Walk.merge_base/4:

   • Single-read commit caching during priority walk: parsed commit structs and timestamps are cached in-memory so no commit object is decompressed more than once.
   • Early termination: stops traversal as soon as common ancestor (:both) is identified, avoiding deep traversal down shared root history.

2. ExGitObjectstore.Merge.merge_trees/5:

   • Subtree short-circuiting: if subtree SHAs match across base == ours, base == theirs, or ours == theirs, the untouched subtree is taken immediately without opening, reading, or descending into unmodified directories.
   • Three-way linear pointer merge: traverses base_entries, ours_entries, and theirs_entries simultaneously comparing entry names without intermediate Map allocations, list flattening, deduplication, or re-sorting.
   • Speculative merge mode (write: false): checks mergeability in memory without writing merged blobs or tree objects to disk storage.