feat(api): stream attachments with Content-Length

gitsheets 2.9 gives every BlobHandle a size and a real stream()
(gitsheets#306), so a 200 no longer buffers the whole blob.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011Q2tgjZEUrtvVk6k8SpdXJ

Author: themightychris

apps/api/src/routes/attachments.ts

@@ -11,7 +11,7 @@
  * (gitsheets auto-refresh) and after a hot reload (`store.public.refresh()`).
  *
  * The blob hash is the `ETag`, so a revalidation is answered with 304 without
- * reading the blob at all.
+ * reading the blob at all; a 200 streams the blob with its `Content-Length`.
  */
 import type { FastifyInstance, FastifyRequest } from 'fastify';
 
@@ -120,7 +120,12 @@ export async function attachmentRoutes(fastify: FastifyInstance): Promise<void>
         return reply.code(304).send();
       }
 
-      return reply.type(inferContentType(key)).send(await blob.read());
+      // Stream rather than buffer: gitsheets serves small blobs from one
+      // in-core read and pipes larger ones from git.
+      return reply
+        .type(inferContentType(key))
+        .header('Content-Length', blob.size)
+        .send(blob.stream());
     },
   );
 }

apps/api/tests/attachments.test.ts

@@ -186,4 +186,17 @@ describe('GET /api/attachments/*', () => {
     const res = await app.inject({ method: 'GET', url: '/api/attachments/not-a-sheet/x/y.png' });
     expect(res.statusCode).toBe(404);
   });
+
+  it('streams a blob larger than 1 MiB intact, with Content-Length', async () => {
+    const big = Buffer.alloc(3 * 1024 * 1024 + 17);
+    for (let i = 0; i < big.length; i++) big[i] = (i * 31 + 7) & 0xff;
+    await seedRawBlob(dataRepo.path, 'people/big/scan.pdf', big, 'seed a large attachment');
+    app = await bootApp();
+
+    const res = await app.inject({ method: 'GET', url: '/api/attachments/people/big/scan.pdf' });
+    expect(res.statusCode).toBe(200);
+    expect(res.headers['content-length']).toBe(String(big.length));
+    expect(res.rawPayload.equals(big)).toBe(true);
+  });
 });
+