Accept single snippet photos and derive post IDs from titles

photo-upload/tests/test_upload.py

@@ -266,6 +266,25 @@ def test_snippet_intake_validation_and_literal_text(service):
     assert client.post("/api/snippets", headers=AUTH, data={"photos": (io.BytesIO(b"bad"), "bad.jpg")}).status_code == 400
 
 
+def test_snippet_single_photo_alias(service):
+    _, client, data = service
+    raw = photo()
+    response = client.post("/api/snippets", headers=AUTH, data={
+        "photo": (io.BytesIO(raw), "photo.jpg"), "text": "A note",
+    })
+    assert response.status_code == 202, response.json
+    assert response.json["count"] == 1
+    assert (data / "submissions" / response.json["id"] / "originals/0").read_bytes() == raw
+    duplicate = client.post("/api/snippets", headers=AUTH, data={
+        "photos": (io.BytesIO(raw), "photo.jpg"), "text": "A note",
+    })
+    assert duplicate.json["id"] == response.json["id"]
+    assert duplicate.status_code == 200
+    assert client.post("/api/snippets", headers=AUTH, data={
+        "photo": [(io.BytesIO(raw), "one.jpg"), (io.BytesIO(raw), "two.jpg")],
+    }).status_code == 400
+
+
 def test_snippet_prepend_images_recovery_and_receipt(publisher, service, monkeypatch, tmp_path):
     run, remote, client = publisher
     _, _, data = service