feat: Add tool for discussion comment write operations

[RossTarrant]

Summary

Adds a discussion_comment_write tool to the discussions toolset, enabling AI agents to add, reply to, update, delete, and mark/unmark comments as the answer on GitHub Discussions. Also enhances get_discussion_comments with an optional includeReplies parameter.

Why

Closes #1908

The discussions toolset previously only supported read operations. AI agents could read discussions but couldn't participate - posting comments, replying, or marking answers - because Discussions use GraphQL mutations, not the REST Issues API. This change brings write operations to GitHub Discussions, enabling AI agents to fully participate in discussion threads.

What changed

• New discussion_comment_write tool in pkg/github/discussions.go consolidating 6 write operations (add, reply, update, delete, mark_answer, unmark_answer) into a single method-dispatching tool
• Added includeReplies optional param to get_discussion_comments, returning nested replies (up to GitHub's 100-reply API limit per comment)
• New MinimalDiscussionComment type in pkg/github/minimal_types.go with reply support
• Updated README.md via script/generate-docs
• Added tests related to changes in pkg/github/discussions_test.go

MCP impact

• New tool added — discussion_comment_write
• Tool schema or behavior changed — get_discussion_comments gains optional includeReplies parameter;

Prompts tested (tool changes only)

• "Add a comment to discussion #XXX in the github-mcp-server repo saying 'Thanks for the update!'"
• "Reply to comment node ID DC_xxx on discussion #XXX with 'Great point!'"
• "Mark comment DC_xxx as the answer to discussion #XXX
• "Delete my comment DC_xxx on discussion #XXX"
• "Get all comments on discussion #XXX including replies"

Security / limits

• Auth / permissions considered — write operations require a token with appropriate Discussion write scopes; the tool is not marked ReadOnlyHint
• Data exposure, filtering, or token/size limits considered — includeReplies fetches up to 100 replies per comment (GitHub API maximum), documented in the parameter description

Tool renaming

• I am not renaming tools as part of this PR

Lint & tests

• Linted locally with ./script/lint
• Tested locally with ./script/test

Docs

• Updated (README via script/generate-docs)

[Copilot]

Pull request overview

This PR expands the Discussions toolset so the MCP server can write discussion comments, edit/delete them, mark answers, and optionally return nested replies from get_discussion_comments.

Changes:

• Added four new discussion comment write tools and registered them in the global tool inventory.
• Extended discussion comment responses with IDs, answer state, and optional nested replies.
• Updated tests, toolsnaps, and generated README documentation to reflect the new Discussions API surface.

Show a summary per file

File	Description
README.md	Documents the new discussion comment tools and includeReplies option.
pkg/github/tools.go	Registers the new Discussions tools in AllTools.
pkg/github/minimal_types.go	Adds the minimal response type for discussion comments.
pkg/github/discussions.go	Implements new discussion comment mutations and reply-aware comment fetching.
pkg/github/discussions_test.go	Adds/updates unit tests for the new discussion comment behavior.
pkg/github/__toolsnaps__/add_discussion_comment.snap	Snapshot for the add-comment tool schema.
pkg/github/__toolsnaps__/delete_discussion_comment.snap	Snapshot for the delete-comment tool schema.
pkg/github/__toolsnaps__/get_discussion_comments.snap	Snapshot update for the new includeReplies input.
pkg/github/__toolsnaps__/set_discussion_comment_answer.snap	Snapshot for the answer-toggle tool schema.
pkg/github/__toolsnaps__/update_discussion_comment.snap	Snapshot for the update-comment tool schema.

Copilot's findings

Comments suppressed due to low confidence (2)

pkg/github/discussions.go:752

• This handler never validates its required fields after weak-decoding, so an omitted or empty commentNodeID/body is passed straight through to the mutation. That produces confusing GraphQL failures instead of the normal local missing required parameter error path used by the repo's other write tools.

			var params struct {
				CommentNodeID string
				Body          string
			}
			if err := mapstructure.WeakDecode(args, &params); err != nil {

pkg/github/discussions.go:820

• This has the same required-parameter hole as the other new discussion write tools: commentNodeID is only weak-decoded, so missing or blank values are sent to GitHub instead of being rejected up front with a missing required parameter tool error.

			var params struct {
				CommentNodeID string
			}
			if err := mapstructure.WeakDecode(args, &params); err != nil {
				return utils.NewToolResultError(err.Error()), nil, nil

• Files reviewed: 10/10 changed files
• Comments generated: 6

[Copilot]

Copilot's findings

Comments suppressed due to low confidence (3)

pkg/github/discussions.go:873

• commentNodeID isn’t trimmed/validated for whitespace here, so a value like " " passes RequiredParam and produces a confusing backend GraphQL error. Consider applying the same strings.TrimSpace blank check used in replyToDiscussionComment.

func deleteDiscussionComment(ctx context.Context, client *githubv4.Client, args map[string]any) (*mcp.CallToolResult, any, error) {
	commentNodeID, err := RequiredParam[string](args, "commentNodeID")
	if err != nil {
		return utils.NewToolResultError(err.Error()), nil, nil
	}

pkg/github/discussions.go:908

• As with the other methods, commentNodeID is only checked for empty string. A whitespace-only value will pass and then fail at the GitHub API. Consider rejecting strings.TrimSpace(commentNodeID) == "" to give callers a consistent tool-level error.

func markDiscussionCommentAsAnswer(ctx context.Context, client *githubv4.Client, args map[string]any) (*mcp.CallToolResult, any, error) {
	commentNodeID, err := RequiredParam[string](args, "commentNodeID")
	if err != nil {
		return utils.NewToolResultError(err.Error()), nil, nil
	}

pkg/github/discussions.go:943

• commentNodeID should probably be validated for whitespace-only input (not just "") the same way it is for the reply method, otherwise callers can get opaque GraphQL errors for what is effectively a missing ID.

func unmarkDiscussionCommentAsAnswer(ctx context.Context, client *githubv4.Client, args map[string]any) (*mcp.CallToolResult, any, error) {
	commentNodeID, err := RequiredParam[string](args, "commentNodeID")
	if err != nil {
		return utils.NewToolResultError(err.Error()), nil, nil
	}

• Files reviewed: 7/7 changed files
• Comments generated: 3

[kerobbi]

Looks good to me overall! Just a couple of comments 🙂