GitHub fetch_pr and fetch_commit return invalid unified diffs without file headers

Problem

The GitHub connector advertises a unified diff string from fetch_pr and fetch_commit. For a four-file change, both return concatenated hunks without diff --git, ---, or +++ file headers. The resulting string cannot be parsed as a unified patch and does not identify which file owns each hunk.

Reproduction

Use public repository openai/codex, merged PR #43126 and commit 008bbd5884122dc95aaece19ecfe0fc6a59dcf36. In Code Mode, call:

const pr = await tools.mcp__codex_apps__github_fetch_pr({
  repo_full_name: "openai/codex", pr_number: 43126
});
const commit = await tools.mcp__codex_apps__github_fetch_commit({
  repo_full_name: "openai/codex",
  commit_sha: "008bbd5884122dc95aaece19ecfe0fc6a59dcf36"
});
const complete = await tools.mcp__codex_apps__github_get_pr_diff({
  repo_full_name: "openai/codex", pr_number: 43126, format: "diff"
});

Inspect each returned structuredContent.diff (accommodate the separate wrapper mismatch in #43132 if necessary).

Both incomplete strings begin with:

@@ -27,6 +27,7 @@ single_version_override(

Save the strings as text files and run git apply --stat FILE (this parses the patch without applying it). The fetch_pr output fails with exit 128 and patch fragment without header. The get_pr_diff output succeeds with exit 0 and reports four files, 169 insertions and two deletions.

Expected behavior

A field advertised as a unified diff should retain file boundaries and names. Return a complete unified diff, or expose explicitly documented per-file patches with filenames. Cover multi-file commits and PRs with a parser-based regression test.

Environment and scope

Observed September 6, 2026 on macOS 26.6.2, installed Codex CLI 0.153.4, GitHub plugin package 0.1.12-5f7cd798dc99. Refreshing the marketplace package returned the same version and byte-identical files. The package contains connector metadata and assets; the hosted backend version is unknown.

An independent parent agent reproduced the test agent's result. The calls succeeded without tool errors; the defect is in the advertised diff's contents. get_pr_diff supplies a working PR alternative. Root cause and ownership within the hosted connector/result transformation are not established.

Duplicate check

On September 6, 2026, searches across open and closed openai/codex issues found no exact duplicate: "fetch_pr" "diff", "fetch_commit" "diff", and "patch fragment without header" each returned zero issues. Broader header/filename searches did not identify the same defect.

Public source fixture: https://github.com/openai/codex/pull/43126

Start by comparing the structuredContent.diff from fetch_pr and fetch_commit with get_pr_diff using the openai/codex PR #43126 and commit 008bbd5884122dc95aaece19ecfe0fc6a59dcf36. Run git apply --stat on saved outputs and add a parser-based regression test covering multi-file PRs and commits. Done means returned diffs retain file headers, filenames, and parse successfully.