From c8200a6747122ced1aa25d82ada957d1a581f73e Mon Sep 17 00:00:00 2001
From: Gabriel Brown <gbrown@ksensetech.com>
Date: Sat, 11 Jul 2026 13:39:08 -0400
Subject: [PATCH] feat(sync): add resolveBranchHead to fetch branch tip SHA

---
 packages/backend/convex/githubClient.ts       | 10 ++++++++
 .../backend/tests/unit/github-head.test.ts    | 24 +++++++++++++++++++
 2 files changed, 34 insertions(+)
 create mode 100644 packages/backend/tests/unit/github-head.test.ts

diff --git a/packages/backend/convex/githubClient.ts b/packages/backend/convex/githubClient.ts
index cea1e0a..4fd06c8 100644
--- a/packages/backend/convex/githubClient.ts
+++ b/packages/backend/convex/githubClient.ts
@@ -88,6 +88,16 @@ export const getRepository = async (
   return result.data;
 };
 
+export const resolveBranchHead = async (
+  octokit: Octokit,
+  owner: string,
+  repo: string,
+  branch: string,
+): Promise<{ sha: string }> => {
+  const result = await octokit.rest.repos.getBranch({ owner, repo, branch });
+  return { sha: result.data.commit.sha };
+};
+
 const toMillis = (value?: string | null) =>
   value ? new Date(value).getTime() : undefined;
 
diff --git a/packages/backend/tests/unit/github-head.test.ts b/packages/backend/tests/unit/github-head.test.ts
new file mode 100644
index 0000000..9e6fd60
--- /dev/null
+++ b/packages/backend/tests/unit/github-head.test.ts
@@ -0,0 +1,24 @@
+import type { Octokit } from '@octokit/rest';
+import { describe, expect, it, vi } from 'vitest';
+
+import { resolveBranchHead } from '../../convex/githubClient';
+
+describe('resolveBranchHead', () => {
+  it('returns the branch tip sha from the branch ref', async () => {
+    const getBranch = vi.fn(async () => ({
+      data: { commit: { sha: 'deadbeef' } },
+    }));
+    const octokit = {
+      rest: { repos: { getBranch } },
+    } as unknown as Octokit;
+
+    const result = await resolveBranchHead(octokit, 'o', 'r', 'main');
+
+    expect(result.sha).toBe('deadbeef');
+    expect(getBranch).toHaveBeenCalledWith({
+      owner: 'o',
+      repo: 'r',
+      branch: 'main',
+    });
+  });
+});