- Replace assert statements with explicit RuntimeError guards in
  _install_thread_local_streams() to prevent silent failure under
  Python -O optimized builds (fail-fast principle)
- Fix _ThreadLocalStream.encoding return type to str | None to match
  io.TextIOBase.encoding signature, removing type: ignore[override]
- Replace threading.RLock with threading.Lock since no recursive
  acquisition occurs, communicating intent more clearly
- Simplify _real_sleep pattern in test steps to plain time.sleep()
- Add CHANGELOG.md entry for #7623 fix

ISSUES CLOSED: #7623

@@ -0,0 +1,106 @@
+"""Shared mock executor for validation pipeline step definitions."""

@@ -0,0 +86,4 @@
+            raise self._exception_names[validation_name]
+
+        if validation_name in self._non_dict_names:
+            return "not-a-dict"  # type: ignore[return-value]

@@ -0,0 +1,163 @@
+"""Step definitions for concurrent validation pipeline scenarios.

@@ -233,3 +233,12 @@ Feature: Validation pipeline
     And the vp executor returns passed for "dur-check"

@@ -236,0 +236,4 @@
+
+  # ── Concurrent pipeline stdout/stderr restoration ─────────────────
+
+  Scenario: Concurrent pipelines restore global streams after execution

@@ -97,0 +146,4 @@
+            _STREAM_ORIGINAL_STDERR = base_stderr
+            _STREAM_STDOUT_WRAPPER = _ThreadLocalStream(base_stdout)
+            _STREAM_STDERR_WRAPPER = _ThreadLocalStream(base_stderr)
+            if _STREAM_STDOUT_WRAPPER is None or _STREAM_STDERR_WRAPPER is None:

@@ -0,0 +1,106 @@
+"""Shared mock executor for validation pipeline step definitions."""

@@ -0,0 +86,4 @@
+            raise self._exception_names[validation_name]
+
+        if validation_name in self._non_dict_names:
+            return "not-a-dict"  # type: ignore[return-value]

@@ -0,0 +1,163 @@
+"""Step definitions for concurrent validation pipeline scenarios.

@@ -236,0 +236,4 @@
+
+  # ── Concurrent pipeline stdout/stderr restoration ─────────────────
+
+  Scenario: Concurrent pipelines restore global streams after execution

@@ -97,0 +146,4 @@
+            _STREAM_ORIGINAL_STDERR = base_stderr
+            _STREAM_STDOUT_WRAPPER = _ThreadLocalStream(base_stdout)
+            _STREAM_STDERR_WRAPPER = _ThreadLocalStream(base_stderr)
+            if _STREAM_STDOUT_WRAPPER is None or _STREAM_STDERR_WRAPPER is None:

@@ -116,3 +21,1 @@
-            return {"passed": True, "message": f"{validation_name} passed (default)"}
-
-        return {"passed": False, "message": f"{validation_name}: no result configured"}
+from features.mocks.validation_pipeline_mock import MockValidationExecutor