fix: use original title from webhook payload instead of fetched title (#793)

* fix: use original title from webhook payload instead of fetched title

- Add extractOriginalTitle() helper to extract title from webhook payload
- Add originalTitle parameter to fetchGitHubData()
- Update tag mode to pass original title from webhook context
- Add tests for extractOriginalTitle and originalTitle parameter

This ensures the title used in prompts is the one that existed when the
trigger event occurred, rather than a potentially modified title fetched
later via GraphQL.

* fix: add title sanitization and explicit TOCTOU test

- Apply sanitizeContent() to titles in formatContext() for defense-in-depth
- Add explicit test documenting TOCTOU prevention for title handling

src/github/data/fetcher.ts

@@ -3,6 +3,8 @@ import type { Octokits } from "../api/client";
 import { ISSUE_QUERY, PR_QUERY, USER_QUERY } from "../api/queries/github";
 import {
   isIssueCommentEvent,
+  isIssuesEvent,
+  isPullRequestEvent,
   isPullRequestReviewEvent,
   isPullRequestReviewCommentEvent,
   type ParsedGitHubContext,
@@ -40,6 +42,31 @@ export function extractTriggerTimestamp(
   return undefined;
 }
 
+/**
+ * Extracts the original title from the GitHub webhook payload.
+ * This is the title as it existed when the trigger event occurred.
+ *
+ * @param context - Parsed GitHub context from webhook
+ * @returns The original title string or undefined if not available
+ */
+export function extractOriginalTitle(
+  context: ParsedGitHubContext,
+): string | undefined {
+  if (isIssueCommentEvent(context)) {
+    return context.payload.issue?.title;
+  } else if (isPullRequestEvent(context)) {
+    return context.payload.pull_request?.title;
+  } else if (isPullRequestReviewEvent(context)) {
+    return context.payload.pull_request?.title;
+  } else if (isPullRequestReviewCommentEvent(context)) {
+    return context.payload.pull_request?.title;
+  } else if (isIssuesEvent(context)) {
+    return context.payload.issue?.title;
+  }
+
+  return undefined;
+}
+
 /**
  * Filters comments to only include those that existed in their final state before the trigger time.
  * This prevents malicious actors from editing comments after the trigger to inject harmful content.
@@ -146,6 +173,7 @@ type FetchDataParams = {
   isPR: boolean;
   triggerUsername?: string;
   triggerTime?: string;
+  originalTitle?: string;
 };
 
 export type GitHubFileWithSHA = GitHubFile & {
@@ -169,6 +197,7 @@ export async function fetchGitHubData({
   isPR,
   triggerUsername,
   triggerTime,
+  originalTitle,
 }: FetchDataParams): Promise<FetchDataResult> {
   const [owner, repo] = repository.split("/");
   if (!owner || !repo) {
@@ -354,6 +383,11 @@ export async function fetchGitHubData({
     triggerDisplayName = await fetchUserDisplayName(octokits, triggerUsername);
   }
 
+  // Use the original title from the webhook payload if provided
+  if (originalTitle !== undefined) {
+    contextData.title = originalTitle;
+  }
+
   return {
     contextData,
     comments,

src/github/data/formatter.ts

@@ -14,7 +14,8 @@ export function formatContext(
 ): string {
   if (isPR) {
     const prData = contextData as GitHubPullRequest;
-    return `PR Title: ${prData.title}
+    const sanitizedTitle = sanitizeContent(prData.title);
+    return `PR Title: ${sanitizedTitle}
 PR Author: ${prData.author.login}
 PR Branch: ${prData.headRefName} -> ${prData.baseRefName}
 PR State: ${prData.state}
@@ -24,7 +25,8 @@ Total Commits: ${prData.commits.totalCount}
 Changed Files: ${prData.files.nodes.length} files`;
   } else {
     const issueData = contextData as GitHubIssue;
-    return `Issue Title: ${issueData.title}
+    const sanitizedTitle = sanitizeContent(issueData.title);
+    return `Issue Title: ${sanitizedTitle}
 Issue Author: ${issueData.author.login}
 Issue State: ${issueData.state}`;
   }

src/modes/tag/index.ts

@@ -12,6 +12,7 @@ import { prepareMcpConfig } from "../../mcp/install-mcp-server";
 import {
   fetchGitHubData,
   extractTriggerTimestamp,
+  extractOriginalTitle,
 } from "../../github/data/fetcher";
 import { createPrompt, generateDefaultPrompt } from "../../create-prompt";
 import { isEntityContext } from "../../github/context";
@@ -78,6 +79,7 @@ export const tagMode: Mode = {
     const commentId = commentData.id;
 
     const triggerTime = extractTriggerTimestamp(context);
+    const originalTitle = extractOriginalTitle(context);
 
     const githubData = await fetchGitHubData({
       octokits: octokit,
@@ -86,6 +88,7 @@ export const tagMode: Mode = {
       isPR: context.isPR,
       triggerUsername: context.actor,
       triggerTime,
+      originalTitle,
     });
 
     // Setup branch