post_review_comment cannot reply in-thread to existing comments

[filosof86]

Problem

post_review_comment and post_draft_comment tools have no way to reply to an existing comment thread. Every comment is posted as a new standalone thread on the given line, even when the intent is to reply to a specific reviewer's comment.

This makes it impossible for AI agents to participate in code review conversations — replies appear as disconnected comments rather than threaded responses.

Root Cause

Two issues prevent in-thread replies:

1. No in_reply_to parameter

The Gerrit REST API supports an in_reply_to field in CommentInput that links a reply to its parent comment's UUID. Neither post_review_comment nor post_draft_comment expose this parameter.

2. Missing range matching for threaded comments

Even with in_reply_to set correctly, Gerrit UI does not render the reply in-thread unless the reply's positional metadata (range) matches the parent comment's position. This is because Gerrit identifies comment threads by (file, line, range) — not by in_reply_to alone.

When a reviewer highlights a code range and leaves a comment, the comment has a range field (e.g., {"start_line": 42, "start_character": 5, "end_line": 42, "end_character": 20}). A reply that only specifies line: 42 without the matching range creates a separate thread on the same line.

3. list_change_comments does not return comment IDs

To use in_reply_to, the caller needs the parent comment's UUID. The current list_change_comments output does not include comment IDs, so there is no way to obtain the value needed for in_reply_to.

Expected Behavior

When replying to a comment, the reply should appear inside the existing comment thread in the Gerrit UI, just as it would when using the "Reply" button in the web interface.

Proposed Fix

1. Add in_reply_to parameter to post_review_comment and post_draft_comment
2. Auto-fetch parent comment's range: When in_reply_to is provided, fetch the parent comment's metadata from /changes/{id}/comments and copy its range and line into the reply's CommentInput
3. Include comment IDs in list_change_comments output so callers can obtain the UUID needed for in_reply_to

Reproduction

# This creates a NEW thread on line 42, not a reply to comment abc123_def456
post_review_comment(
    change_id="12345",
    file_path="src/main.py",
    line_number=42,
    message="Done.",
    in_reply_to="abc123_def456"  # currently not supported
)

Environment

• Gerrit version: 3.x
• gerrit-mcp-server: master branch

[filosof86]

PR is here #14