MAIN 6575ce32508bd7908444241f3719aa33aaf77f90, real web Commit dialog, feature.txt selected, unrelated.txt excluded
HEAD=85064a7bb232bec86beb318765a5a88b3fa95c06
parents=132a9adf3d8646f720a5e4e917655c0f6ee27ade
subject=Verify selected merge commit
MERGE_HEAD=missing
?? unrelated.txt

PR d3f224ec0c85880a534b1bc42eceb7bcc4cce555 selected-file commit rejected in web UI
Error: Cannot commit selected files during a merge. Commit all files to finish the merge.
HEAD, index, MERGE_HEAD, MERGE_MSG, MERGE_MODE, ORIG_HEAD, and four working files: byte/hash identical
{
  "head": "132a9adf3d8646f720a5e4e917655c0f6ee27ade",
  "metadata": {
    "index": "3d1815f27aed6f5a44cef3b819f12da6f21f1f827cc1d7f40fb32487dc5a4a38",
    "MERGE_HEAD": "04d47e9702159527b4db170ab5811b4a673ecffe88915786d2d9c3f3329ecca6",
    "MERGE_MSG": "ffca8acc3497b61231a69ab772e6293f0926e05e25177f4806ddcf6009eb5fcf",
    "MERGE_MODE": "5940fba849655f7fd20878b451607d8f40866326bde6753ac71ebc855b646a55",
    "ORIG_HEAD": "502b5b72f7a164f1066e88ecab13c9774bc3bfa65b32a76c6130c322dc273c37"
  },
  "files": {
    "README.md": "base\n",
    "feature.txt": "feature\n",
    "main.txt": "main\n",
    "unrelated.txt": "unrelated\n"
  }
}

PR all-file commit through same web dialog:
HEAD=2e5ab94ada9f82ff0ac623624c5e90585a94669d
parents=132a9adf3d8646f720a5e4e917655c0f6ee27ade c1ec6c40b1037af09626794cdc470c7c280fb923
subject=Finish merge with both parents
MERGE_HEAD=missing

PR ordinary selected-file commit, branch AND tag named MERGE_HEAD, no merge metadata:
HEAD=e19146d63cdba87e3c87ef2ebc535700cee58417
parents=2e5ab94ada9f82ff0ac623624c5e90585a94669d
subject=Verify ordinary selected commit with named refs
selected.txt
?? remaining.txt
2e5ab94ada9f82ff0ac623624c5e90585a94669d refs/heads/MERGE_HEAD
c1ec6c40b1037af09626794cdc470c7c280fb923 refs/heads/feature
e19146d63cdba87e3c87ef2ebc535700cee58417 refs/heads/main
2e5ab94ada9f82ff0ac623624c5e90585a94669d refs/tags/MERGE_HEAD
MERGE_HEAD_metadata=absent