fix(toolsets): merge MCP tools when alias collides with static toolset

If an MCP server registers itself under the same name as a built-in
toolset (e.g. an MCP "homeassistant" running alongside the built-in
`homeassistant` toolset), `get_toolset()` returned the static definition
early and the MCP tools were silently shadowed — they got registered
into `mcp-homeassistant` but never surfaced when the agent looked up
`homeassistant`.

Detect the collision via the registry alias (`alias_target` starting
with `mcp-`) and merge the two tool lists. The description is annotated
so the source is visible in `/toolsets info`.

tests/test_toolsets.py

@@ -56,6 +56,24 @@ class TestGetToolset:
         assert set(ts["tools"]) == {"web_search", "web_extract", "web_search_plus"}
 
 
+    def test_static_and_mcp_alias_with_same_name_are_merged(self, monkeypatch):
+        # An MCP server named like a built-in toolset registers a bare alias to its
+        # `mcp-<name>` toolset; the static entry must union those tools in (and keep
+        # its own includes) instead of shadowing the server.
+        TOOLSETS["_mergetest"] = {"description": "static", "tools": ["builtin_tool_a"], "includes": ["web"]}
+        try:
+            reg = ToolRegistry()
+            reg.register(name="mcp__mergetest_call", toolset="mcp-_mergetest",
+                         schema=_make_schema("mcp__mergetest_call", "Call"), handler=_dummy_handler)
+            reg.register_toolset_alias("_mergetest", "mcp-_mergetest")
+            monkeypatch.setattr("tools.registry.registry", reg)
+
+            ts = get_toolset("_mergetest")
+            assert {"builtin_tool_a", "mcp__mergetest_call"} <= set(ts["tools"])
+            assert ts["includes"] == ["web"]
+        finally:
+            del TOOLSETS["_mergetest"]
+
 
 class TestResolveToolset:
     def test_leaf_toolset(self):

toolsets.py

@@ -281,8 +281,14 @@ def get_toolset(name: str, *, include_registry: bool = True) -> Optional[Dict[st
         return toolset if toolset else None
 
     if toolset:
-        merged_tools = sorted(set(toolset.get("tools", [])) | set(registry.get_tool_names_for_toolset(name)))
-        return {**toolset, "tools": merged_tools}
+        merged_tools = set(toolset.get("tools", [])) | set(registry.get_tool_names_for_toolset(name))
+        # An MCP server named like a built-in toolset ("homeassistant", "browser") registers a bare
+        # alias to its `mcp-<name>` toolset; without this union the static entry shadows it and the
+        # server's tools never reach the model even though discovery registered them.
+        alias_target = registry.get_toolset_alias_target(name)
+        if alias_target and alias_target != name:
+            merged_tools |= set(registry.get_tool_names_for_toolset(alias_target))
+        return {**toolset, "tools": sorted(merged_tools)}
 
     if name in _get_plugin_toolset_names():
         # Plugin toolset; shown as its MCP server alias when one exists.