Fall back to diff3 conflict markers in resolve-conflicts

[haacked]

The resolve-conflicts skill decides how to resolve a hunk by reading its base section. Its stacked-PR duplicate detection keys off whether the base is empty, and its decision table has a Base column. Git writes that section only when merge.conflictStyle is diff3 or zdiff3. This repo's git/gitconfig.symlink sets it, but the skill is bundled for use on other hosts, where it usually isn't set and git writes two-way markers instead.

Step 2b now runs scripts/ensure-diff3-markers.sh, which re-creates the markers of each conflicted file with git checkout --conflict=diff3 when the host leaves the setting unset. It runs before the mergiraf pass, since mergiraf solve also resolves more of a file when it can see the base.

Two behaviors worth knowing about, both now documented in the skill:

The script skips a conflicted path with no markers. That path holds a binary or delete/modify conflict, or a resolution rerere already replayed, and a rewrite would destroy the resolution. It cannot detect a half-finished hand edit, so the skill tells the agent to ask first if the user was already editing.

A merge driver named by a gitattributes merge= rule re-runs on the checkout and its output wins, so the rewrite does not always produce a base section. The script reports only the files that ended up with one. On a host with mergiraf wired globally the driver already emits base sections, so the script skips everything, which is the intended no-op.

The re-merge also relabels the markers ours and theirs, so a rebase conflict loses the sha and subject of the commit being replayed. The AI-analysis step notes that.

Test plan

scripts/test-ensure-diff3-markers.sh covers the unset and merge styles rewriting, diff3 and zdiff3 leaving the file byte-identical, a rerere-style pre-resolved working tree surviving, an already-diff3 file being skipped, an add/add conflict with an empty base, a merge driver whose output has no base section going unreported, a filename with a space, and running outside a repository. It isolates from the host gitconfig with GIT_CONFIG_GLOBAL=/dev/null, otherwise this machine's own diff3 setting hides every rewrite case.

That suite and the two existing resolve-conflicts suites, which were not wired into CI before, are now in .github/workflows/test.yml. All 15 steps of that job pass locally, and shellcheck is clean on the new scripts.

[Copilot]

🟡 Changes recommended

Unresolved moderate issues remain in marker detection, path handling, merge-driver reporting, and test coverage.

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Pull request overview

Adds a portable fallback for recreating diff3 conflict markers, documents the workflow, adds tests, and wires them into CI.

Changes:

• Adds marker reconstruction with safeguards for resolved and merge-driver-managed files.
• Updates conflict-resolution guidance.
• Adds focused tests and CI coverage.

File summaries

File	Summary
ai/skills/resolve-conflicts/SKILL.md	Documents diff3 marker preparation and edge cases.
ai/skills/resolve-conflicts/scripts/test-ensure-diff3-markers.sh	Tests marker rewriting behavior.
ai/skills/resolve-conflicts/scripts/ensure-diff3-markers.sh	Recreates diff3 markers for eligible conflicts.
.github/workflows/test.yml	Runs the resolve-conflicts test suites in CI.

Review findings: the documentation examples and markerless-path guidance need clarification (nits). The script needs flexible marker-size detection, safe handling of dash-prefixed filenames, and post-checking after failed merge-driver execution (moderate). The diff3/zdiff3 tests should configure the style before merging and use byte-preserving comparisons (moderate).

Review details

Suppressed comments (8)

ai/skills/resolve-conflicts/SKILL.md:141

• Step 2b can also skip a path with no conflict markers (the rerere/binary/delete-modify cases described above), so it is not true that every skipped file carries standard two-way markers. Distinguish markerless, already-resolved paths from unresolved two-way conflicts here so the agent does not analyze an already-resolved file as a hunk.

For conflicts that remain after mergiraf (or for `other` category files), read the file and analyze each conflict hunk. Step 2b gives most files diff3-style markers. A file it skipped still carries standard two-way markers, so handle both:

ai/skills/resolve-conflicts/scripts/ensure-diff3-markers.sh:34

• These checks assume Git always emits seven-character markers. Git supports merge.conflictMarkerSize values below seven, in which case a valid conflict begins with fewer than seven </| characters and this script skips it without adding a base section. Match the marker grammar (at least three characters) instead of a fixed width.

    if ! grep -qI '^<<<<<<<' "$file" 2>/dev/null; then
        continue
    fi
    if grep -qI '^|||||||' "$file" 2>/dev/null; then
        continue
    fi

ai/skills/resolve-conflicts/scripts/ensure-diff3-markers.sh:29

• $file is passed as a positional argument without --, so a conflicted path beginning with - is parsed as a grep option rather than a filename. That can make grep read the filename stream as stdin or fail, causing this conflict to be skipped; terminate grep options before the path.

    if ! grep -qI '^<<<<<<<' "$file" 2>/dev/null; then

ai/skills/resolve-conflicts/scripts/ensure-diff3-markers.sh:32

• This grep has the same option-parsing problem for conflicted paths whose names begin with -: the path can be treated as an option instead of a file, so an existing base section may not be detected. Add -- before the path.

    if grep -qI '^|||||||' "$file" 2>/dev/null; then

ai/skills/resolve-conflicts/scripts/ensure-diff3-markers.sh:43

• The final base-section check also treats a filename beginning with - as grep options, so a successfully rewritten conflict can be omitted from the reported output for such paths. Terminate grep options before $file.

    if grep -qI '^|||||||' "$file" 2>/dev/null; then

ai/skills/resolve-conflicts/scripts/ensure-diff3-markers.sh:39

• An unresolved custom merge driver conventionally exits nonzero even when it writes a valid diff3 conflict containing a base section. This continue skips the post-check in that case, so the script fails to report a file that did gain a base section, contrary to the documented output contract; keep the warning but let the base-section check run after a failed checkout.

    if ! git checkout --conflict=diff3 -- "$file" 2>/dev/null; then
        echo "Warning: could not rewrite conflict markers in $file" >&2
        continue
    fi

ai/skills/resolve-conflicts/scripts/test-ensure-diff3-markers.sh:104

• setup_repo performs the merge at line 45 while the style is unset, and this test sets merge.conflictStyle only afterward. As a result, the file is still two-way, so the diff3/zdiff3 cases verify only the early exit and do not cover leaving an actual diff3 file byte-identical. Configure the style before the merge (or parameterize setup_repo) and compare the resulting file.

    repo=$(setup_repo)
    git -C "$repo" config merge.conflictStyle "$style"
    local before
    before=$(cat "$repo/conflict.txt")
    local output
    output=$(cd "$repo" && bash "$SCRIPT")
    assert_output "$style style prints nothing" "" "$output"
    assert_output "$style style leaves the file untouched" "$before" "$(cat "$repo/conflict.txt")"

ai/skills/resolve-conflicts/scripts/test-ensure-diff3-markers.sh:104

• The cat command substitutions strip trailing newlines, so this assertion does not actually verify the claimed byte-identical behavior for the diff3/zdiff3 cases. Hash the working-tree file (or compare it with cmp) before and after instead.

    before=$(cat "$repo/conflict.txt")
    local output
    output=$(cd "$repo" && bash "$SCRIPT")
    assert_output "$style style prints nothing" "" "$output"
    assert_output "$style style leaves the file untouched" "$before" "$(cat "$repo/conflict.txt")"

• Files reviewed: 4/4 changed files
• Comments generated: 1
• Review effort level: Lite

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