Always emit a tool title, derived from name when unset (#4694)

* Always emit a tool title, derived from name when unset

Some MCP clients (e.g. ChatGPT) drop tools with no `title` instead of
falling back to `name` for display as the spec allows. Deriving a
default title in Tool.to_mcp_tool() fixes this for every tool built on
top of it, including the search-transform, code-mode, and session
proxy tools that never set one explicitly.

Fixes #4414

* Derive fallback title from the overridden name, document it

Addresses Codex review on #4694.

* Resolve title precedence from effective overrides

* Normalize mapping annotations before deriving the title

tests/server/transforms/test_search.py

@@ -137,6 +137,28 @@ class TestBaseTransformBehavior:
         assert await mcp.get_tool("find_tools") is not None
         assert await mcp.get_tool("run_tool") is not None
 
+    @pytest.mark.parametrize(
+        "transform_cls", [RegexSearchTransform, BM25SearchTransform]
+    )
+    async def test_synthetic_tools_have_titles(self, transform_cls):
+        """Synthetic search/call tools must carry a title.
+
+        Some MCP clients (e.g. ChatGPT) drop tools with no `title` field,
+        which breaks tool-search discovery entirely. See #4414.
+        """
+        mcp = _make_server_with_tools()
+        mcp.add_transform(
+            transform_cls(
+                search_tool_name="find_tools", call_tool_name="call_read_tool"
+            )
+        )
+        tools = await mcp.list_tools()
+        titles = {t.name: t.to_mcp_tool().title for t in tools}
+        assert titles == {
+            "find_tools": "Find Tools",
+            "call_read_tool": "Call Read Tool",
+        }
+
     async def test_search_respects_visibility_filtering(self):
         """Tools disabled via Visibility transform should not appear in search."""
         mcp = _make_server_with_tools()