fix(sync): paginate compare and resolve real head SHA

packages/backend/convex/githubClient.ts

@@ -117,6 +117,9 @@ const normalizeCompareCommit = (
   htmlUrl: commit.html_url,
 });
 
+const COMPARE_PER_PAGE = 100;
+const COMPARE_MAX_PAGES = 30; // bound: up to 3000 commits collected
+
 export const compareAcrossForkNetwork = async (
   octokit: Octokit,
   args: {
@@ -125,24 +128,46 @@ export const compareAcrossForkNetwork = async (
     baseOwner: string;
     baseBranch: string;
     headOwner: string;
+    headRepo: string;
     headBranch: string;
   },
 ): Promise<GitHubCompareSummary> => {
   const basehead = `${args.baseOwner}:${args.baseBranch}...${args.headOwner}:${args.headBranch}`;
-  const result = await octokit.rest.repos.compareCommitsWithBasehead({
+  const first = await octokit.rest.repos.compareCommitsWithBasehead({
     owner: args.owner,
     repo: args.repo,
     basehead,
-    per_page: 100,
+    per_page: COMPARE_PER_PAGE,
+    page: 1,
   });
-  const commits = result.data.commits.map(normalizeCompareCommit);
+  const rawCommits = [...first.data.commits];
+  const totalCommits = first.data.total_commits;
+  let page = 2;
+  while (rawCommits.length < totalCommits && page <= COMPARE_MAX_PAGES) {
+    const next = await octokit.rest.repos.compareCommitsWithBasehead({
+      owner: args.owner,
+      repo: args.repo,
+      basehead,
+      per_page: COMPARE_PER_PAGE,
+      page,
+    });
+    if (next.data.commits.length === 0) break;
+    rawCommits.push(...next.data.commits);
+    page += 1;
+  }
+  const head = await resolveBranchHead(
+    octokit,
+    args.headOwner,
+    args.headRepo,
+    args.headBranch,
+  );
   return {
-    aheadBy: result.data.ahead_by,
+    aheadBy: first.data.ahead_by,
-    mergeBaseSha: result.data.merge_base_commit.sha,
+    mergeBaseSha: first.data.merge_base_commit.sha,
-    headSha: commits[commits.length - 1]?.sha,
+    headSha: head.sha,
-    baseSha: result.data.base_commit.sha,
+    baseSha: first.data.base_commit.sha,
-    htmlUrl: result.data.html_url,
+    htmlUrl: first.data.html_url,
-    commits,
+    commits: rawCommits.map(normalizeCompareCommit),
   };
 };
 

packages/backend/convex/githubSync.ts

@@ -32,8 +32,13 @@ const toStatus = (upstreamAheadBy: number, forkAheadBy: number) => {
   return 'unknown' as const;
 };
 
-const getLastCommitAt = (compare: GitHubCompareSummary) =>
+const getLastCommitAt = (compare: GitHubCompareSummary) => {
-  compare.commits[compare.commits.length - 1]?.committedAt;
+  const head = compare.commits.find((c) => c.sha === compare.headSha);
+  return (
+    head?.committedAt ??
+    compare.commits[compare.commits.length - 1]?.committedAt
+  );
+};
 
 const ensureForkMetadata = (spoon: Doc<'spoons'>) => {
   if (!spoon.forkOwner || !spoon.forkRepo) {
@@ -121,6 +126,7 @@ const refreshOwnedSpoon = async (
         baseOwner: forkOwner,
         baseBranch: resolvedForkBranch,
         headOwner: spoon.upstreamOwner,
+        headRepo: spoon.upstreamRepo,
         headBranch: upstreamBranch,
       }),
       compareAcrossForkNetwork(octokit, {
@@ -129,6 +135,7 @@ const refreshOwnedSpoon = async (
         baseOwner: spoon.upstreamOwner,
         baseBranch: upstreamBranch,
         headOwner: forkOwner,
+        headRepo: forkRepo,
         headBranch: resolvedForkBranch,
       }),
       listPullRequests(octokit, { owner: forkOwner, repo: forkRepo }),

packages/backend/tests/unit/github-head.test.ts

@@ -1,7 +1,10 @@
 import type { Octokit } from '@octokit/rest';
 import { describe, expect, it, vi } from 'vitest';
 
-import { resolveBranchHead } from '../../convex/githubClient';
+import {
+  compareAcrossForkNetwork,
+  resolveBranchHead,
+} from '../../convex/githubClient';
 
 describe('resolveBranchHead', () => {
   it('returns the branch tip sha from the branch ref', async () => {
@@ -22,3 +25,84 @@ describe('resolveBranchHead', () => {
     });
   });
 });
+
+const makeCommit = (sha: string) => ({
+  sha,
+  commit: {
+    message: `commit ${sha}`,
+    author: { name: 'Dev', email: 'dev@example.com', date: '2026-01-01T00:00:00Z' },
+    committer: { name: 'Dev', email: 'dev@example.com', date: '2026-01-01T00:00:00Z' },
+  },
+  author: { login: 'dev' },
+  html_url: `https://github.com/o/r/commit/${sha}`,
+});
+
+describe('compareAcrossForkNetwork', () => {
+  it('paginates the compare and takes headSha from the branch tip, not the last commit', async () => {
+    const page1 = Array.from({ length: 100 }, (_, i) => makeCommit(`c${i}`));
+    // Last commit in the collected list is a DIFFERENT sha than the branch tip.
+    const page2 = Array.from({ length: 50 }, (_, i) =>
+      makeCommit(i === 49 ? 'LAST_COMMIT_NOT_TIP' : `c${100 + i}`),
+    );
+
+    const compareCommitsWithBasehead = vi.fn(
+      async ({ page }: { page?: number }) => {
+        const commits = page === 2 ? page2 : page1;
+        return {
+          data: {
+            total_commits: 150,
+            ahead_by: 150,
+            merge_base_commit: { sha: 'MERGE_BASE' },
+            base_commit: { sha: 'BASE' },
+            html_url: 'https://github.com/o/r/compare/base...head',
+            commits,
+          },
+        };
+      },
+    );
+    const getBranch = vi.fn(async () => ({
+      data: { commit: { sha: 'TIP' } },
+    }));
+    const octokit = {
+      rest: { repos: { compareCommitsWithBasehead, getBranch } },
+    } as unknown as Octokit;
+
+    const result = await compareAcrossForkNetwork(octokit, {
+      owner: 'up',
+      repo: 'upstream-repo',
+      baseOwner: 'fork',
+      baseBranch: 'main',
+      headOwner: 'up',
+      headRepo: 'upstream-repo',
+      headBranch: 'main',
+    });
+
+    // Core bug: head is the branch tip, NOT the last commit in the compare list.
+    expect(result.headSha).toBe('TIP');
+    expect(result.commits[result.commits.length - 1]?.sha).toBe(
+      'LAST_COMMIT_NOT_TIP',
+    );
+    expect(result.headSha).not.toBe('LAST_COMMIT_NOT_TIP');
+
+    // ahead_by / merge base / base come from the first compare page.
+    expect(result.aheadBy).toBe(150);
+    expect(result.mergeBaseSha).toBe('MERGE_BASE');
+    expect(result.baseSha).toBe('BASE');
+
+    // All commits collected across both pages.
+    expect(result.commits).toHaveLength(150);
+
+    // Pagination is bounded and the tip is resolved via a single branch ref call.
+    expect(getBranch).toHaveBeenCalledTimes(1);
+    expect(getBranch).toHaveBeenCalledWith({
+      owner: 'up',
+      repo: 'upstream-repo',
+      branch: 'main',
+    });
+    expect(compareCommitsWithBasehead).toHaveBeenCalledTimes(2);
+    expect(compareCommitsWithBasehead.mock.calls[0]?.[0]).toMatchObject({
+      per_page: 100,
+      page: 1,
+    });
+  });
+});