The Python binding (kpy/): klammertext.Machine from a script

Assembled from klammertext-dev ed13dfaa5b7a.  kpy/klammertext.cpp is a
CPython extension module giving a Python script an instance of the
Machine class -- ktext in-process, set up through the same functions the
command uses.  Errors map one-to-one to Python exceptions under the C++
names; an @eval's Python exception is chained as __cause__.  Built by
make -C mac, found through PYTHONPATH (env/runtime.env sets it), tested
by tst/kpy_test.sh.  Three engine changes came with it: Error::message(),
set_command_state(), and the @eval error report carrying its traceback.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Uv7KWxafinDPraswEf4GsC

mac/eval_python.h

@@ -17,6 +17,17 @@ public:
     std::vector<std::string> parse_modules(std::string code);
     void import_module(const std::string& module_name, bool verify = true);
     std::string get_result(PyObject* result_object);
+    // The Python exception currently raised (there must be one): clear it,
+    // return the formatted traceback, and keep the exception object in the
+    // slot below.  ktext puts the text into the Error it throws; the Python
+    // binding (kpy/) additionally chains the object as the Error's __cause__,
+    // so a script sees the ZeroDivisionError its @eval raised, with its
+    // traceback, and not only a description of it.
+    std::string fetch_python_exception();
+    // Take ownership of the exception kept by the last fetch (nullptr if
+    // none); the slot is cleared.  ktext never calls this: it terminates on
+    // the Error, and the interpreter is torn down with the process.
+    static PyObject* take_last_exception();
     std::string eval_expression(const std::string& expression, bool import_modules = true);
     std::string eval_statements(const std::string& script);
     std::string eval(std::string code);
@@ -29,4 +40,5 @@ public:
     Locator m_loc;
     PyObject* m_globals;
     PyObject* m_locals;
+    static PyObject* s_last_exception;
 };