fix(packaging): guard against missing/skewed agentex-client at ADK import

The 0.13.0 split shipped agentex-sdk and agentex-client as two distributions
sharing the agentex.* namespace, coupled only by a floor pin. A partial or
version-skewed install left agentex/lib/* present but the client surface
(agentex/types, agentex/resources) missing, crashing ADK startup with a
cryptic `cannot import name 'Event' from 'agentex.types'`.

- Verify the client surface at agentex.lib import time and raise an actionable
  ImportError naming both installed versions when it is absent.
- Bump the agentex-client floor to >=0.13.0 (the first release where it ships
  separately) so an old client cannot satisfy the dep. Kept floor-only: a
  ceiling would exclude the co-versioned slim (release-please cannot bump it).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: max-parke-scale

adk/pyproject.toml

@@ -15,7 +15,7 @@ readme = "README.md"
 dependencies = [
     # Co-released in lockstep; floor-only by design — a ceiling would
     # eventually exclude the co-versioned slim (release-please can't bump it).
-    "agentex-client>=0.12.0",
+    "agentex-client>=0.13.0",
     # CLI surface (agentex.lib.cli.*, agentex.lib.sdk.config.*)
     "typer>=0.16,<0.17",
     "questionary>=2.0.1,<3",

src/agentex/lib/__init__.py

@@ -0,0 +1,5 @@
+from agentex.lib._version_guard import verify_agentex_client_available
+
+# Validate the agentex-client sibling at ADK import time so a partial/skewed
+# install fails with an actionable message, not a cryptic ImportError.
+verify_agentex_client_available()

src/agentex/lib/_version_guard.py

@@ -0,0 +1,28 @@
+"""Guard that the agentex-client REST surface (shared agentex.* namespace) is
+importable; raise an actionable error instead of a cryptic ImportError."""
+
+from __future__ import annotations
+
+from importlib.metadata import PackageNotFoundError, version
+
+
+def _version_or_missing(package: str) -> str:
+    try:
+        return version(package)
+    except PackageNotFoundError:
+        return "not installed"
+
+
+def verify_agentex_client_available() -> None:
+    # `Event` is the canary symbol whose absence crashed ADK startup in 0.13.0.
+    try:
+        from agentex.types import Event as _Event  # noqa: F401
+    except (ImportError, AttributeError) as exc:
+        raise ImportError(
+            "agentex-sdk could not import the agentex-client REST surface it "
+            "depends on (the two ship as one `agentex.*` namespace and must be "
+            "installed together at the same version). Installed: "
+            f"agentex-sdk={_version_or_missing('agentex-sdk')}, "
+            f"agentex-client={_version_or_missing('agentex-client')}. "
+            "Reinstall both, e.g. `pip install --force-reinstall agentex-sdk`."
+        ) from exc

tests/lib/test_version_guard.py

@@ -0,0 +1,22 @@
+"""Tests for the agentex-client availability guard (0.13.0 split regression)."""
+
+from __future__ import annotations
+
+import pytest
+
+from agentex.lib._version_guard import verify_agentex_client_available
+
+
+def test_passes_when_client_surface_present() -> None:
+    verify_agentex_client_available()  # both packages installed -> no raise
+
+
+def test_raises_clear_error_when_client_surface_broken(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    import agentex.types
+
+    # Simulate a skewed/partial agentex-client where the canary symbol is absent.
+    monkeypatch.delattr(agentex.types, "Event", raising=False)
+    with pytest.raises(ImportError, match="agentex-client"):
+        verify_agentex_client_available()