test(patreon): fix self-contradictory attachment/postfile dedup assertion

The fixture gives the attachment and post_file the same filehash, so they
correctly collapse to one item; the test asserted both survival and collapse.
Rewrite to verify the cross-kind dedup (postfile kind covered by video test).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/test_patreon_client.py

@@ -68,24 +68,20 @@ def test_extract_gallery_dedups_image_large(client, response):
     assert all(m.post_id == "1001" for m in items)
 
 
-def test_extract_attachment_and_postfile(client, response):
+def test_extract_attachment_postfile_same_file_collapses(client, response):
     index = client._transform(response)
     post = _post_by_id(response, "1002")
     items = client.extract_media(post, index)
 
-    by_kind = {m.kind: m for m in items}
-    # attachments_media → "attachments", plus the post_file → "postfile".
-    assert set(by_kind) == {"attachments", "postfile"}
-    assert by_kind["attachments"].filename == "bonus-pack.zip"
-    assert by_kind["attachments"].filehash == "c" * 32
-    assert by_kind["postfile"].filename == "bonus-pack.zip"
-    # postfile URL also carries the same hash, but they're different kinds in
-    # different relationships; both are kept because dedup is by filehash and
-    # the attachment is encountered first... assert the post_file collapsed.
-    # (attachments resolved before postfile, same hash → postfile dropped.)
-    # So only ONE survives with that hash:
-    surviving_c = [m for m in items if m.filehash == "c" * 32]
-    assert len(surviving_c) == 1
+    # The attachment (attachments_media 9003) and the post_file are the SAME
+    # zip — both carry filehash c…. attachments resolve before postfile, so the
+    # postfile collapses into the attachment by filehash → exactly one survives.
+    # (postfile-as-a-kind is exercised separately by the video post test.)
+    assert len(items) == 1
+    item = items[0]
+    assert item.kind == "attachments"
+    assert item.filename == "bonus-pack.zip"
+    assert item.filehash == "c" * 32
 
 
 def test_extract_inline_content_img(client, response):