feat: add inline comment MCP server for experimental review mode (#414)

* feat: add inline comment MCP server for experimental review mode

- Create standalone inline PR comments without review workflow
- Support single-line and multi-line comments
- Auto-install server when in experimental review mode
- Uses octokit.rest.pulls.createReviewComment() directly

* docs: clarify GitHub code suggestion syntax in inline comment server

Add clear documentation that suggestion blocks replace the entire selected
line range and must be syntactically complete drop-in replacements.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

---------

Co-authored-by: Claude <noreply@anthropic.com>

src/mcp/github-inline-comment-server.ts

@@ -0,0 +1,178 @@
+#!/usr/bin/env node
+import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
+import { StdioServerTransport } from "@modelcontextprotocol/sdk/server/stdio.js";
+import { z } from "zod";
+import { createOctokit } from "../github/api/client";
+
+// Get repository and PR information from environment variables
+const REPO_OWNER = process.env.REPO_OWNER;
+const REPO_NAME = process.env.REPO_NAME;
+const PR_NUMBER = process.env.PR_NUMBER;
+
+if (!REPO_OWNER || !REPO_NAME || !PR_NUMBER) {
+  console.error(
+    "Error: REPO_OWNER, REPO_NAME, and PR_NUMBER environment variables are required",
+  );
+  process.exit(1);
+}
+
+// GitHub Inline Comment MCP Server - Provides inline PR comment functionality
+// Provides an inline comment tool without exposing full PR review capabilities, so that
+// Claude can't accidentally approve a PR
+const server = new McpServer({
+  name: "GitHub Inline Comment Server",
+  version: "0.0.1",
+});
+
+server.tool(
+  "create_inline_comment",
+  "Create an inline comment on a specific line or lines in a PR file",
+  {
+    path: z
+      .string()
+      .describe("The file path to comment on (e.g., 'src/index.js')"),
+    body: z
+      .string()
+      .describe(
+        "The comment text (supports markdown and GitHub code suggestion blocks). " +
+          "For code suggestions, use: ```suggestion\\nreplacement code\\n```. " +
+          "IMPORTANT: The suggestion block will REPLACE the ENTIRE line range (single line or startLine to line). " +
+          "Ensure the replacement is syntactically complete and valid - it must work as a drop-in replacement for the selected lines.",
+      ),
+    line: z
+      .number()
+      .optional()
+      .describe(
+        "Line number for single-line comments (required if startLine is not provided)",
+      ),
+    startLine: z
+      .number()
+      .optional()
+      .describe(
+        "Start line for multi-line comments (use with line parameter for the end line)",
+      ),
+    side: z
+      .enum(["LEFT", "RIGHT"])
+      .optional()
+      .default("RIGHT")
+      .describe(
+        "Side of the diff to comment on: LEFT (old code) or RIGHT (new code)",
+      ),
+    commit_id: z
+      .string()
+      .optional()
+      .describe(
+        "Specific commit SHA to comment on (defaults to latest commit)",
+      ),
+  },
+  async ({ path, body, line, startLine, side, commit_id }) => {
+    try {
+      const githubToken = process.env.GITHUB_TOKEN;
+
+      if (!githubToken) {
+        throw new Error("GITHUB_TOKEN environment variable is required");
+      }
+
+      const owner = REPO_OWNER;
+      const repo = REPO_NAME;
+      const pull_number = parseInt(PR_NUMBER, 10);
+
+      const octokit = createOctokit(githubToken).rest;
+
+      // Validate that either line or both startLine and line are provided
+      if (!line && !startLine) {
+        throw new Error(
+          "Either 'line' for single-line comments or both 'startLine' and 'line' for multi-line comments must be provided",
+        );
+      }
+
+      // If only line is provided, it's a single-line comment
+      // If both startLine and line are provided, it's a multi-line comment
+      const isSingleLine = !startLine;
+
+      const pr = await octokit.pulls.get({
+        owner,
+        repo,
+        pull_number,
+      });
+
+      const params: Parameters<
+        typeof octokit.rest.pulls.createReviewComment
+      >[0] = {
+        owner,
+        repo,
+        pull_number,
+        body,
+        path,
+        side: side || "RIGHT",
+        commit_id: commit_id || pr.data.head.sha,
+      };
+
+      if (isSingleLine) {
+        // Single-line comment
+        params.line = line;
+      } else {
+        // Multi-line comment
+        params.start_line = startLine;
+        params.start_side = side || "RIGHT";
+        params.line = line;
+      }
+
+      const result = await octokit.rest.pulls.createReviewComment(params);
+
+      return {
+        content: [
+          {
+            type: "text",
+            text: JSON.stringify(
+              {
+                success: true,
+                comment_id: result.data.id,
+                html_url: result.data.html_url,
+                path: result.data.path,
+                line: result.data.line || result.data.original_line,
+                message: `Inline comment created successfully on ${path}${isSingleLine ? ` at line ${line}` : ` from line ${startLine} to ${line}`}`,
+              },
+              null,
+              2,
+            ),
+          },
+        ],
+      };
+    } catch (error) {
+      const errorMessage =
+        error instanceof Error ? error.message : String(error);
+
+      // Provide more helpful error messages for common issues
+      let helpMessage = "";
+      if (errorMessage.includes("Validation Failed")) {
+        helpMessage =
+          "\n\nThis usually means the line number doesn't exist in the diff or the file path is incorrect. Make sure you're commenting on lines that are part of the PR's changes.";
+      } else if (errorMessage.includes("Not Found")) {
+        helpMessage =
+          "\n\nThis usually means the PR number, repository, or file path is incorrect.";
+      }
+
+      return {
+        content: [
+          {
+            type: "text",
+            text: `Error creating inline comment: ${errorMessage}${helpMessage}`,
+          },
+        ],
+        error: errorMessage,
+        isError: true,
+      };
+    }
+  },
+);
+
+async function runServer() {
+  const transport = new StdioServerTransport();
+  await server.connect(transport);
+  process.on("exit", () => {
+    server.close();
+  });
+}
+
+runServer().catch(console.error);

src/mcp/install-mcp-server.ts

@@ -111,6 +111,24 @@ export async function prepareMcpConfig(
       };
     }
 
+    // Include inline comment server for experimental review mode
+    if (context.inputs.mode === "experimental-review" && context.isPR) {
+      baseMcpConfig.mcpServers.github_inline_comment = {
+        command: "bun",
+        args: [
+          "run",
+          `${process.env.GITHUB_ACTION_PATH}/src/mcp/github-inline-comment-server.ts`,
+        ],
+        env: {
+          GITHUB_TOKEN: githubToken,
+          REPO_OWNER: owner,
+          REPO_NAME: repo,
+          PR_NUMBER: context.entityNumber?.toString() || "",
+          GITHUB_API_URL: GITHUB_API_URL,
+        },
+      };
+    }
+
     // Only add CI server if we have actions:read permission and we're in a PR context
     const hasActionsReadPermission =
       context.inputs.additionalPermissions.get("actions") === "read";

src/modes/review/index.ts

@@ -60,20 +60,8 @@ export const reviewMode: Mode = {
 
   getAllowedTools() {
     return [
-      // Context tools - to know who the current user is
-      "mcp__github__get_me",
-      // Core review tools
-      "mcp__github__create_pending_pull_request_review",
-      "mcp__github__add_comment_to_pending_review",
-      "mcp__github__submit_pending_pull_request_review",
-      "mcp__github__delete_pending_pull_request_review",
-      "mcp__github__create_and_submit_pull_request_review",
-      // Comment tools
-      "mcp__github__add_issue_comment",
-      // PR information tools
-      "mcp__github__get_pull_request",
-      "mcp__github__get_pull_request_reviews",
-      "mcp__github__get_pull_request_status",
+      "Bash(gh issue comment:*)",
+      "mcp__github_inline_comment__create_inline_comment",
     ];
   },
 
@@ -163,17 +151,13 @@ REVIEW MODE WORKFLOW:
 
 1. First, understand the PR context:
    - You are reviewing PR #${eventData.isPR && eventData.prNumber ? eventData.prNumber : "[PR number]"} in ${context.repository}
-   - Use mcp__github__get_pull_request to get PR metadata
    - Use the Read, Grep, and Glob tools to examine the modified files directly from disk
    - This provides the full context and latest state of the code
    - Look at the changed_files section above to see which files were modified
 
-2. Create a pending review:
-   - Use mcp__github__create_pending_pull_request_review to start your review
-   - This allows you to batch comments before submitting
-
-3. Add inline comments:
-   - Use mcp__github__add_comment_to_pending_review for each issue or suggestion
+2. Add comments:
+   - use Bash(gh issue comment:*) to add top-level comments
+   - Use mcp__github_inline_comment__create_inline_comment to add inline comments (prefer this where possible)
    - Parameters:
      * path: The file path (e.g., "src/index.js")
      * line: Line number for single-line comments
@@ -182,49 +166,6 @@ REVIEW MODE WORKFLOW:
      * subjectType: "line" for line-level comments
      * body: Your comment text
    
-   - When to use multi-line comments:
-     * When replacing multiple consecutive lines
-     * When the fix requires changes across several lines
-     * Example: To replace lines 19-20, use startLine: 19, line: 20
-   
-   - For code suggestions, use this EXACT format in the body:
-     \`\`\`suggestion
-     corrected code here
-     \`\`\`
-   
-   CRITICAL: GitHub suggestion blocks must ONLY contain the replacement for the specific line(s) being commented on:
-   - For single-line comments: Replace ONLY that line
-   - For multi-line comments: Replace ONLY the lines in the range
-   - Do NOT include surrounding context or function signatures
-   - Do NOT suggest changes that span beyond the commented lines
-   
-   Example for line 19 \`var name = user.name;\`:
-   WRONG:
-   \\\`\\\`\\\`suggestion
-   function processUser(user) {
-       if (!user) throw new Error('Invalid user');
-       const name = user.name;
-   \\\`\\\`\\\`
-   
-   CORRECT:
-   \\\`\\\`\\\`suggestion
-   const name = user.name;
-   \\\`\\\`\\\`
-   
-   For validation suggestions, comment on the function declaration line or create separate comments for each concern.
-
-4. Submit your review:
-   - Use mcp__github__submit_pending_pull_request_review
-   - Parameters:
-     * event: "COMMENT" (general feedback), "REQUEST_CHANGES" (issues found), or "APPROVE" (if appropriate)
-     * body: Write a comprehensive review summary that includes:
-       - Overview of what was reviewed (files, scope, focus areas)
-       - Summary of all issues found (with counts by severity if applicable)
-       - Key recommendations and action items
-       - Highlights of good practices observed
-       - Overall assessment and recommendation
-   - The body should be detailed and informative since it's the main review content
-   - Structure the body with clear sections using markdown headers
 
 REVIEW GUIDELINES: