[bug] Review Agent fails on private GitHub repositories when fetching PR diff

[hql287]

Describe the bug

The Review Agent fails to review pull requests in a private GitHub repository because it cannot fetch the PR diff.

The webhook is received successfully, the review agent starts processing, and GitHub API access works, but the review fails when github-pr-parser attempts to fetch the .diff URL from GitHub.

To reproduce

Configure Review Agent according to documentation.
Install GitHub App on a private GitHub repository.
Open a PR.
Comment:
/review
Observe Review Agent logs.

Expected Behavior

The Review Agent should fetch the PR diff and generate a review.

Actual Behavior

The Review Agent fails while fetching the diff.

Logs:

[review-agent] Received a pull request event for #525
[github-pr-parser] Error fetching diff: Not Found
GET https://github.com/MyOrg/myrepo/pull/525.diff
404 Not Found

Sourcebot deployment information

Sourcebot: v5.0.1
Deployment: Docker Compose
GitHub App configured
Private GitHub repository
Review Agent enabled
DeepSeek configured as model provider
Self-hosted deployment

Additional information

The GitHub token can successfully access the PR through the GitHub API:

curl \
  -H "Authorization: token <TOKEN>" \
  https://api.github.com/repos/MyOrg/myrepo/pulls/525

This returns the PR JSON successfully.

The PR API returns:

{
  "diff_url": "https://github.com/MyOrg/myrepo/pull/525.diff"
}

However, fetching that URL directly returns 404:

curl -I -L \
  -H "Authorization: token <TOKEN>" \
  https://github.com/MyOrg/myrepo/pull/525.diff

Response:

HTTP/2 404

This appears to be the step where the Review Agent fails.

Question

Is the Review Agent expected to support private GitHub repositories?

[hql287]

I also tested fetching the diff through the GitHub API using the Accept: application/vnd.github.diff header:

curl \
  -H "Authorization: token <TOKEN>" \
  -H "Accept: application/vnd.github.diff" \
  https://api.github.com/repos/Fordeer/monorepo/pulls/525 | head -20 

and This successfully returns the PR diff:

diff --git a/apps/story_video/ui/src/apis/client-hook.ts b/apps/story_video/ui/src/apis/client-hook.ts
index 0458c35c3..ce09f14ed 100644
--- a/apps/story_video/ui/src/apis/client-hook.ts
+++ b/apps/story_video/ui/src/apis/client-hook.ts
@@ -75,9 +75,6 @@ export const useSafeApi = (): SafeApi => {

So i guess the token can access the private PR and the diff is available through the GitHub API.
The failure only happens when fetching the github.com/.../pull/.diff URL directly.