gh-144316: Fix missing exception in _remote_debugging with debug=False

Misc/NEWS.d/next/Library/2026-02-03-19-57-41.gh-issue-144316.wop870.rst

@@ -0,0 +1 @@
+Fix missing exception handling in :mod:`_remote_debugging` when ``debug=False``. The ``set_exception_cause`` macro now always sets an exception to satisfy the C API contract, fixing intermittent assertion failures. Exception chaining with ``debug=True`` is preserved. Patch by Taegyun Kim.

Modules/_remote_debugging/_remote_debugging.h

@@ -29,6 +29,7 @@ extern "C" {
 #include "internal/pycore_interpframe.h"    // FRAME_OWNED_BY_INTERPRETER
 #include "internal/pycore_llist.h"          // struct llist_node
 #include "internal/pycore_long.h"           // _PyLong_GetZero
+#include "internal/pycore_pyerrors.h"       // _PyErr_FormatFromCause
 #include "internal/pycore_stackref.h"       // Py_TAG_BITS
 #include "../../Python/remote_debug.h"
 
@@ -174,9 +175,15 @@ typedef enum _WIN32_THREADSTATE {
 
 /* Exception cause macro */
 #define set_exception_cause(unwinder, exc_type, message) \
-    if (unwinder->debug) { \
-        _set_debug_exception_cause(exc_type, message); \
-    }
+    do { \
+        if (!PyErr_ExceptionMatches(PyExc_PermissionError)) { \
+            if (!PyErr_Occurred()) { \
+                PyErr_SetString(exc_type, message); \
+            } else if (unwinder->debug) { \
+                _PyErr_FormatFromCause(exc_type, "%s", message); \
+            } \
+        } \
+    } while (0)
 
 /* ============================================================================
  * TYPE DEFINITIONS