Drop buffered inline comment when it is posted live (#1405) (#1412)

When classify_inline_comments is enabled, create_inline_comment buffers calls
without confirmed=true. The model frequently re-issues the call with confirmed=true
after reading the buffered reply, which posts the comment live but leaves the
original buffered entry behind. The post-session replay step then posts it again,
so every inline comment lands twice.

Reconcile the buffer on a live post: after a confirmed comment is created, remove
any buffered entry matching the same path, line, startLine and body so it cannot be
replayed. Extracts the reconciliation into src/mcp/inline-comment-buffer.ts (the MCP
server module starts a server on import) and adds unit tests.

Co-authored-by: archievi <13202986+archievi@users.noreply.github.com>

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

@@ -5,6 +5,7 @@ import { appendFileSync } from "fs";
 import { z } from "zod";
 import { createOctokit } from "../github/api/client";
 import { sanitizeContent } from "../github/utils/sanitizer";
+import { removeBufferedComment } from "./inline-comment-buffer";
 
 // Get repository and PR information from environment variables
 const REPO_OWNER = process.env.REPO_OWNER;
@@ -180,6 +181,16 @@ server.tool(
 
       const result = await octokit.rest.pulls.createReviewComment(params);
 
+      // The comment is now live. Drop any buffered copy of it so the
+      // post-session replay step cannot post it a second time (the model often
+      // re-issues a buffered call with confirmed=true after the buffer reply).
+      if (CLASSIFY_ENABLED) {
+        removeBufferedComment(
+          { path, line, startLine, body: sanitizedBody },
+          BUFFER_PATH,
+        );
+      }
+
       return {
         content: [
           {

src/mcp/inline-comment-buffer.ts

@@ -0,0 +1,54 @@
+import { existsSync, readFileSync, writeFileSync } from "fs";
+
+export type BufferedCommentMatch = {
+  path: string;
+  line?: number;
+  startLine?: number;
+  body: string;
+};
+
+/**
+ * Remove any buffered inline comment that matches an already-posted comment.
+ *
+ * When a comment is posted live (confirmed=true), an earlier buffered copy of
+ * the same comment must be dropped so the post-session replay step does not
+ * post it a second time. The model frequently re-issues a buffered call with
+ * confirmed=true after reading the "Set confirmed=true to post immediately"
+ * reply; previously the original buffered entry was left behind and replayed,
+ * producing duplicate inline comments.
+ *
+ * Entries are matched on path, line, startLine and body. Lines that cannot be
+ * parsed are kept untouched.
+ */
+export function removeBufferedComment(
+  match: BufferedCommentMatch,
+  bufferPath: string,
+): void {
+  if (!existsSync(bufferPath)) {
+    return;
+  }
+
+  const remaining = readFileSync(bufferPath, "utf8")
+    .split("\n")
+    .filter((line) => line.trim() !== "")
+    .filter((line) => {
+      let entry: BufferedCommentMatch;
+      try {
+        entry = JSON.parse(line);
+      } catch {
+        // Keep anything we cannot parse rather than silently dropping it.
+        return true;
+      }
+      const isSameComment =
+        entry.path === match.path &&
+        entry.line === match.line &&
+        entry.startLine === match.startLine &&
+        entry.body === match.body;
+      return !isSameComment;
+    });
+
+  writeFileSync(
+    bufferPath,
+    remaining.length > 0 ? remaining.join("\n") + "\n" : "",
+  );
+}