Use case

When reviewing PR with more that 300 changed files agent is unable to perform review.

Issue location

Underlying github-service.ts (https://github.com/augmentcode/augment-agent/blob/main/src/services/github-service.ts#L132) uses the GitHub pulls.get endpoint with diff media type. GitHub's API returns a 422 too_large error for this endpoint when the diff exceeds 300 files. This is a hard GitHub API limitation — no amount of configuration can work around it.
The irony is that getPullRequestFiles already uses the paginated listFiles endpoint correctly. But the diff content is fetched via the non-paginated route.

quoting from logs

Error: [...] [Augment Agent] Sorry, the diff exceeded the maximum number of files (300). Consider using 'List pull requests files' API or locally cloning the repository instead.: {"resource":"PullRequest","field":"diff","code":"too_large"} - https://github.com/proxy/docs.github.com/rest/pulls/pulls#list-pull-requests-files | Data: {
  "error": "undefined"
}

Possible fix

Generate the diff locally from the checked-out repo (which is already checked out in the action) using git diff
Use listFiles with the patch field per file instead of fetching the monolithic diff