test(render): #30 этап 3 ревью — залочен over-fetch fork (RSS limit*2 vs HTML limit)

Развилка history_limit=limit*2 (RSS) vs limit (HTML) невидима голдену (golden-фейк
игнорирует аргумент limit и всегда отдаёт полный корпус → оба пути тримятся до
GOLDEN_LIMIT одинаково). test_rss_overfetches_history_html_does_not спаит
tg_cache.cached_get_chat_history, гоняет оба форматтера с N=7 и ассертит:
RSS форвардит limit=2*N, HTML форвардит limit=N. Мутационно проверено — красит
при унификации в любую сторону. Полный сюит 366 passed, golden не менялся.

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

tests/test_stage3_enrich.py

@@ -180,6 +180,36 @@ async def test_rss_feed_does_not_enrich_replies(monkeypatch):
     assert client.calls == [], "RSS must NOT call get_messages (enrich_replies=False)"
 
 
+# --------------------------------------------------------------------------- #
+# History over-fetch fork: RSS over-fetches limit*2 (headroom for grouping/trim),
+# HTML fetches exactly limit. This is a REAL behavioral fork that the golden oracle
+# CANNOT see (its fake_get_chat_history ignores the limit kwarg and returns the whole
+# corpus, so both paths trim to GOLDEN_LIMIT identically). A refactor that accidentally
+# unified the two would pass every golden test — so lock the forwarded limit here.
+# --------------------------------------------------------------------------- #
+@pytest.mark.asyncio
+async def test_rss_overfetches_history_html_does_not(monkeypatch):
+    N = 7
+    seen = {}
+
+    async def fake_get_chat(client, channel):
+        return SimpleNamespace(title="Test", username="testchan", id=-1001234567890)
+
+    async def spy_get_history(client, channel, limit=20):
+        seen.setdefault("limits", []).append(limit)
+        return []
+
+    monkeypatch.setattr("tg_cache.cached_get_chat", fake_get_chat, raising=False)
+    monkeypatch.setattr("tg_cache.cached_get_chat_history", spy_get_history, raising=False)
+
+    await generate_channel_rss("testchan", client=SimpleNamespace(), limit=N)
+    assert seen["limits"] == [2 * N], f"RSS must over-fetch history limit*2, got {seen['limits']}"
+
+    seen["limits"] = []
+    await generate_channel_html("testchan", client=SimpleNamespace(), limit=N)
+    assert seen["limits"] == [N], f"HTML must fetch history limit (no over-fetch), got {seen['limits']}"
+
+
 # --------------------------------------------------------------------------- #
 # Shared error handling in _prepare_feed_posts, verified through BOTH formatters.
 # The golden oracle cannot see these paths (§3.9/§3.10 are error branches), so they