test(pixiv): fix downloader tests — skip validation on stub bytes, no media extraction in post-record tests

The stub payload is PNG bytes regardless of target extension, so the real
validator quarantined the .jpg cases; and extracting the ugoira work hit the
API seam of a fake session with no .post. Validation/quarantine plumbing
stays covered by the Patreon downloader tests.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CDgx8bQS5YrGRK76v8HUnM

tests/test_pixiv_downloader.py

@@ -67,9 +67,24 @@ def _post_and_media(work_id):
     raise AssertionError(f"no work {work_id} in fixture")
 
 
+def _post_only(work_id):
+    """Normalized post WITHOUT media extraction — the write_post_record tests
+    don't need media, and extracting an ugoira would hit the API seam."""
+    page = json.loads(_FIXTURE.read_text())
+    for work in page["illusts"]:
+        if work["id"] == work_id:
+            return _client()._normalize(work)
+    raise AssertionError(f"no work {work_id} in fixture")
+
+
 def _downloader(tmp_path, session=None):
+    # validate=False: the stub payload is PNG bytes regardless of the target
+    # extension, so real validation would quarantine the .jpg cases. The
+    # validate/quarantine plumbing is BaseNativeDownloader's, covered by the
+    # Patreon downloader tests.
     return PixivDownloader(
-        tmp_path, session=session if session is not None else _FakeSession(),
+        tmp_path, validate=False,
+        session=session if session is not None else _FakeSession(),
     )
 
 
@@ -188,7 +203,7 @@ def test_own_session_carries_app_referer(tmp_path):
 
 
 def test_write_post_record_enriched(tmp_path):
-    post, _ = _post_and_media(111)
+    post = _post_only(111)
     dl = _downloader(tmp_path)
     outcome = dl.write_post_record(post, "artist-a")
 
@@ -219,7 +234,7 @@ def test_write_post_record_enriched(tmp_path):
 
 
 def test_write_post_record_rating_r18(tmp_path):
-    post, _ = _post_and_media(222)
+    post = _post_only(222)
     dl = _downloader(tmp_path)
     outcome = dl.write_post_record(post, "artist-a")
     data = json.loads(outcome.path.read_text())
@@ -228,7 +243,7 @@ def test_write_post_record_rating_r18(tmp_path):
 
 
 def test_write_post_record_includes_ugoira_frames(tmp_path):
-    post, _ = _post_and_media(333)
+    post = _post_only(333)
     frames = [{"file": "000000.jpg", "delay": 90}]
     post["_work"]["_ugoira_frames"] = frames
     dl = _downloader(tmp_path)