Implement Apex Agent MVP scaffold

tests/test_executor.py

@@ -0,0 +1,26 @@
+from __future__ import annotations
+
+from runtime.executor import Executor, ExecutorConfig
+from runtime.planner import PlannedStep
+
+
+def test_executor_retries_until_transient_tool_succeeds() -> None:
+    calls = {"count": 0}
+
+    def flaky_tool() -> dict[str, bool]:
+        calls["count"] += 1
+        if calls["count"] < 3:
+            raise RuntimeError("transient")
+        return {"ok": True}
+
+    executor = Executor(
+        tools={"flaky": flaky_tool},
+        config=ExecutorConfig(max_retries=3, backoff_seconds=0),
+    )
+
+    result = executor.execute(PlannedStep(action="flaky", description="retry"))
+
+    assert result.success is True
+    assert result.attempts == 3
+    assert result.result == {"ok": True}
+