fork: resolve Gitea branch refs via the branches endpoint

Gitea's /repos/{o}/{r}/commits/{ref} only resolves 40-hex SHAs —
a branch name like "main" returns 404 even when the branch exists.
GitHub's API is more lenient and resolves branch names server-side.
resolveGiteaPinnedRef was calling /commits/{ref} and 404ing on
branch refs, so the entire import path failed before it could
read the tree. updateStatus already used the branches endpoint
correctly; this aligns resolveGiteaPinnedRef with it.

resolveGiteaCommitSha is now a SHA-only helper that refuses to
make the API call for non-SHA refs (matches Gitea's contract).
Test mocks updated to return the branch response shape.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

server/src/__tests__/gitea-skills.test.ts

@@ -186,12 +186,12 @@ describe("resolveGiteaPinnedRef", () => {
     expect(result).toEqual({ pinnedRef: sha, trackingRef: sha });
   });
 
-  it("resolves a branch ref to its commit SHA via the commits endpoint", async () => {
+  it("resolves a branch ref to its commit SHA via the branches endpoint", async () => {
     const branchSha = "fedcba9876543210fedcba9876543210fedcba98";
     const fetchMock = vi
       .fn()
       .mockResolvedValueOnce(jsonResponse({ default_branch: "main" }))
-      .mockResolvedValueOnce(jsonResponse({ sha: branchSha }));
+      .mockResolvedValueOnce(jsonResponse({ name: "main", commit: { id: branchSha } }));
     vi.stubGlobal("fetch", fetchMock);
     const result = await resolveGiteaPinnedRef(
       parseGiteaSourceUrl("https://git.example.com/acme/skills"),
@@ -202,13 +202,23 @@ describe("resolveGiteaPinnedRef", () => {
 });
 
 describe("resolveGiteaCommitSha", () => {
-  it("returns the sha from a commit response", async () => {
+  it("returns the sha from a commit response when given a 40-hex ref", async () => {
+    const sha = "abc123abc123abc123abc123abc123abc123abcd";
     vi.stubGlobal(
       "fetch",
-      vi.fn().mockResolvedValue(jsonResponse({ sha: "abc123abc123abc123abc123abc123abc123abcd" })),
+      vi.fn().mockResolvedValue(jsonResponse({ sha })),
     );
-    const sha = await resolveGiteaCommitSha("acme", "skills", "main", giteaApiBase("git.example.com"));
-    expect(sha).toBe("abc123abc123abc123abc123abc123abc123abcd");
+    const result = await resolveGiteaCommitSha("acme", "skills", sha, giteaApiBase("git.example.com"));
+    expect(result).toBe(sha);
+  });
+
+  it("refuses to call the API for a non-SHA ref", async () => {
+    const fetchMock = vi.fn();
+    vi.stubGlobal("fetch", fetchMock);
+    await expect(
+      resolveGiteaCommitSha("acme", "skills", "main", giteaApiBase("git.example.com")),
+    ).rejects.toMatchObject({ status: 422 });
+    expect(fetchMock).not.toHaveBeenCalled();
   });
 });
 

server/src/services/gitea-skills.ts

@@ -162,6 +162,11 @@ export async function resolveGiteaCommitSha(
   ref: string,
   apiBase: string,
 ): Promise<string> {
+  if (!/^[0-9a-f]{40}$/i.test(ref.trim())) {
+    throw unprocessable(
+      `Gitea /commits endpoint only resolves SHAs; got "${ref}". Use fetchGiteaBranch for branch names.`,
+    );
+  }
   const response = await fetchGiteaJson<GiteaCommitResponse>(
     `${apiBase}/repos/${owner}/${repo}/commits/${encodeURIComponent(ref)}`,
   );
@@ -191,7 +196,13 @@ export async function resolveGiteaPinnedRef(parsed: GiteaSourceUrl): Promise<{
   const trackingRef = parsed.explicitRef
     ? parsed.ref
     : await resolveGiteaDefaultBranch(parsed.owner, parsed.repo, apiBase);
-  const pinnedRef = await resolveGiteaCommitSha(parsed.owner, parsed.repo, trackingRef, apiBase);
+  // Gitea's /repos/{o}/{r}/commits/{ref} endpoint only resolves SHAs — a branch
+  // name returns 404. The branches endpoint accepts both branch names and tags.
+  const branch = await fetchGiteaBranch(apiBase, parsed.owner, parsed.repo, trackingRef);
+  const pinnedRef = asString(branch.commit?.id);
+  if (!pinnedRef) {
+    throw unprocessable(`Failed to resolve Gitea ref ${trackingRef}`);
+  }
   return { pinnedRef, trackingRef };
 }