test(stream): move full-fallback-resend threading test to thread routing suite

The Telegram final-delivery suite is the wrong home and its delete
assertion duplicates test_stream_consumer.py. Keep only the new
behaviour: a full resend threads its first chunk to the originating
message; later chunks stay unthreaded.

tests/gateway/test_stream_consumer_thread_routing.py

@@ -172,3 +172,27 @@ class TestFeishuFallbackThreadRouting:
             f"Expected receive_id_type='thread_id', got '{receive_id_type}'"
         )
 
+
+class TestFallbackResendThreading:
+    """#103068: a full fallback resend replaces the preview, so it must land in
+    the originating thread; tail continuations keep their unthreaded delivery."""
+
+    @pytest.mark.asyncio
+    async def test_full_fallback_resend_threads_first_chunk_only(self):
+        adapter = _make_adapter(max_length=700)
+        adapter.send.side_effect = [
+            SimpleNamespace(success=True, message_id=f"full_{i}") for i in range(10)
+        ]
+        consumer = GatewayStreamConsumer(adapter, "chat_123", initial_reply_to_id="om_user_1")
+        consumer._message_id = "om_preview"
+        consumer._last_sent_text = "truncated snapshot"
+        consumer._already_sent = True
+        consumer._fallback_final_send = True
+
+        final = " ".join(["word"] * 400)  # not prefixed by the snapshot -> full resend
+        await consumer._send_fallback_final(final)
+
+        calls = adapter.send.await_args_list
+        assert len(calls) > 1
+        assert calls[0].kwargs["reply_to"] == "om_user_1"
+        assert all("reply_to" not in c.kwargs for c in calls[1:])

tests/gateway/test_telegram_final_delivery.py

@@ -149,28 +149,6 @@ async def test_complete_preview_survives_long_flood_fallback_failure(monkeypatch
     assert consumer.delivered_final_matches("Final answer") is True
 
 
-@pytest.mark.asyncio
-async def test_full_fallback_resend_threads_and_deletes_truncated_preview():
-    """When the visible prefix is not a prefix of the final (Feishu post vs
-    cleaned text), fallback resends the whole answer. Thread it to the user
-    message and delete the truncated edit bubble (#103068)."""
-    adapter = _adapter()
-    adapter.send.return_value = SendResult(success=True, message_id="full-1")
-
-    consumer = GatewayStreamConsumer(
-        adapter, "chat-1", initial_reply_to_id="user-1",
-    )
-    consumer._message_id = "preview-1"
-    consumer._last_sent_text = "truncated snapshot"
-    consumer._already_sent = True
-    consumer._fallback_final_send = True
-
-    await consumer._send_fallback_final("full completed answer that does not start with the snapshot")
-
-    assert adapter.send.await_args.kwargs["reply_to"] == "user-1"
-    adapter.delete_message.assert_awaited()
-
-
 @pytest.mark.asyncio
 async def test_telegram_long_flood_result_keeps_retry_after():
     """The real adapter contract preserves the server delay for consumers."""