feat(ext/sw): GitHubHost.putBlob with Git Data API fallback

Blobs ≤ BLOB_THRESHOLD_BYTES (900 KB) take the Contents API path
(same as writeFile). Larger blobs use the Git Data API: POST blob,
GET ref + commit, POST tree (with base_tree), POST commit, PATCH ref.
Tests cover both paths plus error propagation.

getBlob/deleteBlob are thin wrappers over readFile/deleteFile.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

extension/src/service-worker/__tests__/git-host.test.ts

@@ -0,0 +1,71 @@
+import { beforeEach, describe, expect, it, vi } from 'vitest';
+import { GitHubHost } from '../github';
+import { BLOB_THRESHOLD_BYTES } from '../git-host';
+
+const REPO = 'alee/test-vault';
+const TOKEN = 'ghp_TEST';
+
+function setupFetch(): ReturnType<typeof vi.fn> {
+  const fetchMock = vi.fn();
+  vi.stubGlobal('fetch', fetchMock);
+  return fetchMock;
+}
+
+describe('GitHubHost.putBlob', () => {
+  beforeEach(() => {
+    vi.unstubAllGlobals();
+  });
+
+  it('uses Contents API when content is at threshold', async () => {
+    const fetchMock = setupFetch();
+    // First fetch: GET existing file → 404 (create path)
+    fetchMock.mockResolvedValueOnce({ ok: false, status: 404, statusText: 'Not Found' } as Response);
+    // Second fetch: PUT contents → 201 created
+    fetchMock.mockResolvedValueOnce({ ok: true, status: 201, json: async () => ({}) } as Response);
+
+    const host = new GitHubHost(REPO, TOKEN);
+    const small = new Uint8Array(BLOB_THRESHOLD_BYTES);  // exactly threshold
+    await host.putBlob('attachments/abc.bin', small, 'add abc');
+
+    expect(fetchMock).toHaveBeenCalledTimes(2);
+    const lastCall = fetchMock.mock.calls[1];
+    expect(lastCall[0]).toContain('/contents/');  // Contents API
+    expect(lastCall[1]?.method).toBe('PUT');
+  });
+
+  it('uses Git Data API fallback when content exceeds threshold', async () => {
+    const fetchMock = setupFetch();
+    // 1. POST /git/blobs → blob SHA
+    fetchMock.mockResolvedValueOnce({ ok: true, status: 201, json: async () => ({ sha: 'blobsha111' }) } as Response);
+    // 2. GET /git/refs/heads/main → ref { object: { sha: 'commitsha' } }
+    fetchMock.mockResolvedValueOnce({ ok: true, status: 200, json: async () => ({ object: { sha: 'commitsha111' } }) } as Response);
+    // 3. GET /git/commits/commitsha111 → commit { tree: { sha: 'treesha' } }
+    fetchMock.mockResolvedValueOnce({ ok: true, status: 200, json: async () => ({ tree: { sha: 'treesha111' } }) } as Response);
+    // 4. POST /git/trees → new tree { sha: 'newtreesha' }
+    fetchMock.mockResolvedValueOnce({ ok: true, status: 201, json: async () => ({ sha: 'newtreesha111' }) } as Response);
+    // 5. POST /git/commits → new commit { sha: 'newcommitsha' }
+    fetchMock.mockResolvedValueOnce({ ok: true, status: 201, json: async () => ({ sha: 'newcommitsha111' }) } as Response);
+    // 6. PATCH /git/refs/heads/main → updated
+    fetchMock.mockResolvedValueOnce({ ok: true, status: 200, json: async () => ({}) } as Response);
+
+    const host = new GitHubHost(REPO, TOKEN);
+    const big = new Uint8Array(BLOB_THRESHOLD_BYTES + 1);  // one byte over
+    await host.putBlob('attachments/big.bin', big, 'add big');
+
+    expect(fetchMock).toHaveBeenCalledTimes(6);
+    expect(fetchMock.mock.calls[0][0]).toContain('/git/blobs');
+    expect(fetchMock.mock.calls[1][0]).toContain('/git/refs/heads/');
+    expect(fetchMock.mock.calls[3][0]).toContain('/git/trees');
+    expect(fetchMock.mock.calls[4][0]).toContain('/git/commits');
+    expect(fetchMock.mock.calls[5][1]?.method).toBe('PATCH');
+  });
+
+  it('throws when blob creation fails in fallback path', async () => {
+    const fetchMock = setupFetch();
+    fetchMock.mockResolvedValueOnce({ ok: false, status: 422, statusText: 'Unprocessable', text: async () => 'too big' } as Response);
+
+    const host = new GitHubHost(REPO, TOKEN);
+    const big = new Uint8Array(BLOB_THRESHOLD_BYTES + 1);
+    await expect(host.putBlob('attachments/big.bin', big, 'add big')).rejects.toThrow(/422|too big/);
+  });
+});