fix(cache): stabilize tool ordering and cache markers for MCP

tests/providers/test_prompt_cache_markers.py

@@ -0,0 +1,87 @@
+from __future__ import annotations
+
+from typing import Any
+
+from nanobot.providers.anthropic_provider import AnthropicProvider
+from nanobot.providers.openai_compat_provider import OpenAICompatProvider
+
+
+def _openai_tools(*names: str) -> list[dict[str, Any]]:
+    return [
+        {
+            "type": "function",
+            "function": {
+                "name": name,
+                "description": f"{name} tool",
+                "parameters": {"type": "object", "properties": {}},
+            },
+        }
+        for name in names
+    ]
+
+
+def _anthropic_tools(*names: str) -> list[dict[str, Any]]:
+    return [
+        {
+            "name": name,
+            "description": f"{name} tool",
+            "input_schema": {"type": "object", "properties": {}},
+        }
+        for name in names
+    ]
+
+
+def _marked_openai_tool_names(tools: list[dict[str, Any]] | None) -> list[str]:
+    if not tools:
+        return []
+    marked: list[str] = []
+    for tool in tools:
+        if "cache_control" in tool:
+            marked.append((tool.get("function") or {}).get("name", ""))
+    return marked
+
+
+def _marked_anthropic_tool_names(tools: list[dict[str, Any]] | None) -> list[str]:
+    if not tools:
+        return []
+    return [tool.get("name", "") for tool in tools if "cache_control" in tool]
+
+
+def test_openai_compat_marks_builtin_boundary_and_tail_tool() -> None:
+    messages = [
+        {"role": "system", "content": "system"},
+        {"role": "assistant", "content": "assistant"},
+        {"role": "user", "content": "user"},
+    ]
+    _, marked_tools = OpenAICompatProvider._apply_cache_control(
+        messages,
+        _openai_tools("read_file", "write_file", "mcp_fs_ls", "mcp_git_status"),
+    )
+    assert _marked_openai_tool_names(marked_tools) == ["write_file", "mcp_git_status"]
+
+
+def test_anthropic_marks_builtin_boundary_and_tail_tool() -> None:
+    messages = [
+        {"role": "user", "content": "u1"},
+        {"role": "assistant", "content": "a1"},
+        {"role": "user", "content": "u2"},
+    ]
+    _, _, marked_tools = AnthropicProvider._apply_cache_control(
+        "system",
+        messages,
+        _anthropic_tools("read_file", "write_file", "mcp_fs_ls", "mcp_git_status"),
+    )
+    assert _marked_anthropic_tool_names(marked_tools) == ["write_file", "mcp_git_status"]
+
+
+def test_openai_compat_marks_only_tail_without_mcp() -> None:
+    messages = [
+        {"role": "system", "content": "system"},
+        {"role": "assistant", "content": "assistant"},
+        {"role": "user", "content": "user"},
+    ]
+    _, marked_tools = OpenAICompatProvider._apply_cache_control(
+        messages,
+        _openai_tools("read_file", "write_file"),
+    )
+    assert _marked_openai_tool_names(marked_tools) == ["write_file"]