fix(review-agent): fetch private GitHub PR diffs via API

CHANGELOG.md

@@ -13,6 +13,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Fixed GitLab topic filters being incorrectly case-sensitive. [#1393](https://github.com/sourcebot-dev/sourcebot/pull/1393)
 - Fixed a crash when searching with `context:` referencing a search context that does not exist; it now returns a graceful error. [#1362](https://github.com/sourcebot-dev/sourcebot/pull/1362)
 - Fixed search queries failing to parse when negating a bare term that contains a colon (e.g. `-foo:bar`, `-http://example.com`). [#1301](https://github.com/sourcebot-dev/sourcebot/pull/1301)
+- Fixed the Review Agent failing to fetch pull request diffs for private GitHub repositories. [#1352](https://github.com/sourcebot-dev/sourcebot/pull/1352)
 
 ## [5.1.5] - 2026-07-31
 

packages/web/src/features/agents/review-agent/nodes/githubPrParser.test.ts

@@ -79,15 +79,30 @@ describe('githubPrParser', () => {
         expect(result.description).toBe('');
     });
 
-    test('fetches diff using the pull request diff_url', async () => {
-        const mockRequest = vi.fn().mockResolvedValue({ data: '' });
-        const octokit = { request: mockRequest } as unknown as Octokit;
-        const pr = makePullRequest({ diff_url: 'https://github.com/my-org/my-repo/pull/7.diff' });
+test('fetches diff using the GitHub pulls API with diff accept header', async () => {
+    const mockRequest = vi.fn().mockResolvedValue({ data: '' });
+    const octokit = { request: mockRequest } as unknown as Octokit;
+    const pr = makePullRequest({
+        owner: 'my-org',
+        repo: 'my-repo',
+        number: 7,
+        diff_url: 'https://github.com/my-org/my-repo/pull/7.diff',
+    });
 
-        await githubPrParser(octokit, pr);
+    await githubPrParser(octokit, pr);
 
-        expect(mockRequest).toHaveBeenCalledWith('https://github.com/my-org/my-repo/pull/7.diff');
-    });
+    expect(mockRequest).toHaveBeenCalledWith(
+        'GET /repos/{owner}/{repo}/pulls/{pull_number}',
+        {
+            owner: 'my-org',
+            repo: 'my-repo',
+            pull_number: 7,
+            headers: {
+                accept: 'application/vnd.github.diff',
+            },
+        }
+    );
+});
 
     test('returns empty file_diffs for an empty diff', async () => {
         const octokit = makeMockOctokit('');

packages/web/src/features/agents/review-agent/nodes/githubPrParser.ts

@@ -11,12 +11,23 @@ export const githubPrParser = async (octokit: Octokit, pullRequest: GitHubPullRe
 
     let parsedDiff: parse.File[] = [];  
     try {
-        const diff = await octokit.request(pullRequest.diff_url);
-        parsedDiff = parse(diff.data);
-    } catch (error) {
-        logger.error("Error fetching diff: ", error);
-        throw error;
-    }
+    const { owner, name: repo } = pullRequest.base.repo;
+    const pullNumber = pullRequest.number;
+
+    const diff = await octokit.request("GET /repos/{owner}/{repo}/pulls/{pull_number}", {
+        owner: owner.login,
+        repo,
+        pull_number: pullNumber,
+        headers: {
+            accept: "application/vnd.github.diff",
+        },
+    });
+
+    parsedDiff = parse(diff.data as unknown as string);
+} catch (error) {
+    logger.error("Error fetching diff: ", error);
+    throw error;
+}
 
     const sourcebotFileDiffs: (sourcebot_file_diff | null)[] = parsedDiff.map((file) => {
         if (!file.from || !file.to) {
@@ -64,4 +75,4 @@ export const githubPrParser = async (octokit: Octokit, pullRequest: GitHubPullRe
         number: pullRequest.number,
         head_sha: pullRequest.head.sha
     }
-}
+}