test(managed_agents): guard rail — proxy must not import claude_agent_sdk

Phase 2 architecture (LIT-2879): the agent runtime runs on the
per-Session VM, not in the proxy. Add a pytest that scans
litellm/proxy/ and fails if any source file imports claude_agent_sdk.

Currently passes (zero offenders). The test enforces that the boundary
stays intact going forward.

Tracks LIT-2879.

tests/test_litellm/managed_agents/test_proxy_no_claude_agent_sdk.py

@@ -0,0 +1,55 @@
+"""Architecture guard: the proxy never imports ``claude_agent_sdk``.
+
+Phase 2 boundary (LIT-2879): the agent runtime runs ON the per-Session
+VM (in ``litellm/managed_agents/daemon/runtime/``), not inside the
+proxy process. Any import of ``claude_agent_sdk`` from
+``litellm/proxy/`` would mean someone reintroduced the in-proxy runtime
+shape that Phase 1 had to roll back.
+
+This test scans every ``.py`` file under ``litellm/proxy/`` and fails if
+``claude_agent_sdk`` appears in an ``import`` or ``from ... import``
+statement.
+
+If this test fails:
+
+* Move the import into ``litellm/managed_agents/daemon/runtime/`` —
+  that is the only place ``claude_agent_sdk`` is allowed to live.
+* The proxy talks to the daemon over the
+  ``/v1/internal/sessions/{sid}/...`` control-plane endpoints; it
+  never instantiates the SDK directly.
+"""
+
+import pathlib
+import re
+
+import pytest
+
+# tests/test_litellm/managed_agents/ → repo root is parents[3]
+REPO_ROOT = pathlib.Path(__file__).resolve().parents[3]
+PROXY_DIR = REPO_ROOT / "litellm" / "proxy"
+
+# Match either `import claude_agent_sdk` or `from claude_agent_sdk ...`.
+_IMPORT_RE = re.compile(
+    r"^\s*(?:import\s+claude_agent_sdk|from\s+claude_agent_sdk(?:\s|\.))",
+    re.MULTILINE,
+)
+
+
+def _iter_proxy_python_files() -> list[pathlib.Path]:
+    return [p for p in PROXY_DIR.rglob("*.py") if p.is_file()]
+
+
+def test_proxy_does_not_import_claude_agent_sdk() -> None:
+    offenders: list[str] = []
+    for path in _iter_proxy_python_files():
+        text = path.read_text(encoding="utf-8", errors="replace")
+        if _IMPORT_RE.search(text):
+            offenders.append(str(path.relative_to(REPO_ROOT)))
+
+    if offenders:
+        pretty = "\n  ".join(offenders)
+        pytest.fail(
+            "claude_agent_sdk must not be imported from litellm/proxy/.\n"
+            "Move the import into litellm/managed_agents/daemon/runtime/.\n"
+            f"Offending files:\n  {pretty}"
+        )