test(anthropic): cover the cache_control rebuild shapes and type the test helpers

Codecov flagged the 5m ttl branch and the empty-system path of the wire
builder; both now have a test. Greptile asked for full typing on the new
test helpers.

tests/test_litellm/litellm_core_utils/prompt_templates/test_litellm_core_utils_prompt_templates_factory.py

@@ -3613,3 +3613,16 @@ def test_anthropic_messages_pt_system_string_content_becomes_text_block():
 
     assert result[1] == {"role": "system", "content": [{"type": "text", "text": "Answer in one word."}]}
 
+
+def test_anthropic_messages_pt_drops_a_system_message_with_no_text():
+    """Anthropic rejects empty text blocks, so a text-less system message must
+    vanish rather than reach the wire as an empty system turn."""
+    messages = [
+        {"role": "user", "content": "First question"},
+        {"role": "system", "content": ""},
+        {"role": "assistant", "content": "Yes"},
+    ]
+
+    result = anthropic_messages_pt(messages=messages, model="claude-opus-4-8", llm_provider="anthropic")
+
+    assert [m["role"] for m in result] == ["user", "assistant"]

tests/test_litellm/llms/anthropic/chat/test_anthropic_chat_transformation.py

@@ -6237,7 +6237,7 @@ REMINDER_TEXT = "<system-reminder>Answer with exactly one word.</system-reminder
 CACHED_SYSTEM_BLOCK = {"type": "text", "text": "You are terse.", "cache_control": {"type": "ephemeral"}}
 
 
-def _chat_request(config, model, messages):
+def _chat_request(config: AnthropicConfig, model: str, messages: list[dict]) -> dict:
     return config.transform_request(
         model=model,
         messages=messages,
@@ -6247,7 +6247,7 @@ def _chat_request(config, model, messages):
     )
 
 
-def _reminder_conversation():
+def _reminder_conversation() -> list[dict]:
     """The shape Claude Code sends mid-session: cached system prompt, turns, a
     reminder right after a user turn, an assistant turn, a fresh user turn."""
     return [
@@ -6261,7 +6261,7 @@ def _reminder_conversation():
     ]
 
 
-def _texts(message):
+def _texts(message: dict) -> list[str]:
     return [block["text"] for block in message["content"] if block.get("type") == "text"]
 
 
@@ -6418,7 +6418,7 @@ def test_chat_mid_conversation_system_keeps_earlier_turns_a_prefix_of_the_next_r
     assert len(later_blocks) > len(earlier_blocks)
 
 
-def _role_block_pairs(messages):
+def _role_block_pairs(messages: list[dict]) -> list[tuple[str, object]]:
     return [
         (message["role"], block)
         for message in messages

tests/test_litellm/llms/anthropic/test_mid_conversation_system.py

@@ -5,6 +5,8 @@ Anthropic, Vertex, Azure AI and Bedrock Invoke transformation tests; these pin
 the pure placement rules on the OpenAI-format message list.
 """
 
+import pytest
+
 import litellm
 from litellm.llms.anthropic.mid_conversation_system import (
     CONVERTED_SYSTEM_NOTE,
@@ -13,11 +15,11 @@ from litellm.llms.anthropic.mid_conversation_system import (
 )
 
 
-def _roles(messages):
+def _roles(messages: object) -> list[str]:
     return [m["role"] if isinstance(m, dict) else m.role for m in messages]
 
 
-def _texts(message):
+def _texts(message: dict) -> list[str]:
     return [block["text"] for block in message["content"]]
 
 
@@ -125,19 +127,35 @@ def test_unflagged_conversion_keeps_the_client_order_when_no_tool_result_follows
     assert _texts(placed[2]) == [CONVERTED_SYSTEM_NOTE, "reminder"]
 
 
-def test_unflagged_conversion_rebuilds_cache_control_on_the_converted_block():
+@pytest.mark.parametrize(
+    "cache_control, expected",
+    [
+        ({"type": "ephemeral", "ttl": "1h"}, {"type": "ephemeral", "ttl": "1h"}),
+        ({"type": "ephemeral", "ttl": "5m"}, {"type": "ephemeral", "ttl": "5m"}),
+        ({"type": "ephemeral", "ttl": "2h"}, {"type": "ephemeral"}),
+    ],
+)
+def test_unflagged_conversion_rebuilds_cache_control_on_the_converted_block(cache_control, expected):
+    """Only the shapes Anthropic accepts survive: ephemeral with a 5m or 1h ttl, or no ttl."""
     messages = [
         {"role": "user", "content": "q1"},
-        {"role": "system", "content": "reminder", "cache_control": {"type": "ephemeral", "ttl": "1h"}},
+        {"role": "system", "content": "reminder", "cache_control": cache_control},
     ]
 
     placed = place_mid_conversation_system(messages, supports_mid_conversation_system=False)
 
-    assert placed[1]["content"][1] == {
-        "type": "text",
-        "text": "reminder",
-        "cache_control": {"type": "ephemeral", "ttl": "1h"},
-    }
+    assert placed[1]["content"][1] == {"type": "text", "text": "reminder", "cache_control": expected}
+
+
+def test_unflagged_conversion_drops_a_cache_control_that_is_not_ephemeral():
+    messages = [
+        {"role": "user", "content": "q1"},
+        {"role": "system", "content": "reminder", "cache_control": {"type": "persistent"}},
+    ]
+
+    placed = place_mid_conversation_system(messages, supports_mid_conversation_system=False)
+
+    assert placed[1]["content"][1] == {"type": "text", "text": "reminder"}
 
 
 def test_placement_is_a_no_op_without_later_system_messages():

tests/test_litellm/llms/azure_ai/claude/test_azure_anthropic_transformation.py

@@ -415,7 +415,7 @@ class TestAzureAnthropicConfig:
         assert "context-management-2025-06-27" in headers["anthropic-beta"]
 
 
-def _mid_conversation_system_conversation():
+def _mid_conversation_system_conversation() -> list[dict]:
     return [
         {"role": "system", "content": [{"type": "text", "text": "You are terse.", "cache_control": {"type": "ephemeral"}}]},
         {"role": "user", "content": "First question"},

tests/test_litellm/llms/bedrock/chat/invoke_transformations/test_bedrock_chat_invoke_transformations_anthropic_claude3_transformation.py

@@ -544,7 +544,7 @@ def test_output_format_removed_from_bedrock_invoke_request():
     ), f"output_format should be removed for Bedrock Invoke, got keys: {result.keys()}"
 
 
-def _mid_conversation_system_conversation():
+def _mid_conversation_system_conversation() -> list[dict]:
     return [
         {"role": "system", "content": [{"type": "text", "text": "You are terse.", "cache_control": {"type": "ephemeral"}}]},
         {"role": "user", "content": "First question"},

tests/test_litellm/llms/vertex_ai/vertex_ai_partner_models/anthropic/test_vertex_ai_partner_models_anthropic_transformation.py

@@ -729,7 +729,7 @@ def test_sanitize_strips_effort_for_haiku_45():
     assert data["output_config"] == {"effort": "high"}
 
 
-def _mid_conversation_system_conversation():
+def _mid_conversation_system_conversation() -> list[dict]:
     return [
         {"role": "system", "content": [{"type": "text", "text": "You are terse.", "cache_control": {"type": "ephemeral"}}]},
         {"role": "user", "content": "First question"},