feat: detect subscriber-only tweets via tweetInterstitial (#33)

Extract visibility metadata from TweetWithVisibilityResults wrapper
before unwrapping. Adds is_subscriber_only field to Tweet model,
with full serialization roundtrip and test coverage.

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

tests/conftest.py

@@ -38,6 +38,7 @@ def tweet_factory():
             score=overrides.pop("score", 0.0),
             article_title=overrides.pop("article_title", None),
             article_text=overrides.pop("article_text", None),
+            is_subscriber_only=overrides.pop("is_subscriber_only", False),
         )
 
     return _make_tweet

tests/fixtures/list_timeline.json

@@ -15,6 +15,10 @@
                       "tweet_results": {
                         "result": {
                           "__typename": "TweetWithVisibilityResults",
+                          "tweetInterstitial": {
+                            "__typename": "TweetInterstitial",
+                            "text": { "rtl": false, "text": "Subscribe to @lister to see this post" }
+                          },
                           "tweet": {
                             "__typename": "Tweet",
                             "rest_id": "700",

tests/test_client.py

@@ -641,6 +641,7 @@ class TestParseTweetResult:
         tweet = parse_tweet_result(wrapped)
         assert tweet is not None
         assert tweet.id == "1234567890"
+        assert tweet.is_subscriber_only is False
 
     @patch("twitter_cli.client._get_cffi_session")
     @patch("twitter_cli.client._gen_ct_headers", return_value={})

tests/test_parser_fixtures.py

@@ -74,6 +74,7 @@ def test_parse_list_timeline_fixture_with_visibility_wrapper(fixture_loader) ->
     assert cursor == "list-cursor"
     assert tweets[0].author.verified is True
     assert tweets[0].lang == "zh"
+    assert tweets[0].is_subscriber_only is True
 
 
 def test_fetch_user_list_with_fixture(monkeypatch, fixture_loader) -> None:

tests/test_serialization.py

@@ -77,3 +77,11 @@ def test_tweet_roundtrip_preserves_article_fields(tweet_factory) -> None:
 
     assert restored.article_title == "Long-form title"
     assert restored.article_text == "Intro\n\n## Details"
+
+
+def test_tweet_roundtrip_preserves_subscriber_only(tweet_factory) -> None:
+    tweet = tweet_factory("99", is_subscriber_only=True)
+    payload = tweet_to_dict(tweet)
+    assert payload["isSubscriberOnly"] is True
+    restored = tweet_from_dict(payload)
+    assert restored.is_subscriber_only is True