fix: omit skills from initialize request when 'all'

'all' and omitted both mean 'no filter' at the wire level, so only send
the field when it is an explicit list. Keeps the CLI control schema as a
plain string[] (which the zod-to-proto pipeline can represent) while the
'all' sentinel remains at the Python API surface for ergonomics.

Author: jsham042

src/claude_agent_sdk/_internal/query.py

@@ -164,7 +164,9 @@ async def initialize(self) -> dict[str, Any] | None:
             request["agents"] = self._agents
         if self._exclude_dynamic_sections is not None:
             request["excludeDynamicSections"] = self._exclude_dynamic_sections
-        if self._skills is not None:
+        # 'all' and omitted are equivalent at the wire level (no filter), so
+        # only send the field when it's an explicit list.
+        if isinstance(self._skills, list):
             request["skills"] = self._skills
 
         # Use longer timeout for initialize since MCP servers may take time to start

tests/test_query.py

@@ -59,22 +59,20 @@ def test_initialize_omits_exclude_dynamic_sections_when_unset():
     assert "excludeDynamicSections" not in sent
 
 
-def test_initialize_sends_skills_when_set():
-    """Query.initialize() includes skills (list, 'all', or empty) in the control request."""
+def test_initialize_sends_skills_list():
+    """Query.initialize() includes skills only when it is a list."""
     sent = _capture_initialize_request(skills=["pdf", "docx"])
     assert sent["skills"] == ["pdf", "docx"]
 
-    sent_all = _capture_initialize_request(skills="all")
-    assert sent_all["skills"] == "all"
-
     sent_empty = _capture_initialize_request(skills=[])
     assert sent_empty["skills"] == []
 
 
-def test_initialize_omits_skills_when_unset():
-    """skills is absent from initialize when not configured."""
-    sent = _capture_initialize_request()
-    assert "skills" not in sent
+def test_initialize_omits_skills_for_none_and_all():
+    """'all' and None both omit skills from initialize (no filter at wire level)."""
+    assert "skills" not in _capture_initialize_request()
+    assert "skills" not in _capture_initialize_request(skills=None)
+    assert "skills" not in _capture_initialize_request(skills="all")
 
 
 def _make_mock_transport(messages, control_requests=None):