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/command.cpp

@@ -121,6 +121,29 @@ parse_args(
 }
 
 
+void set_command_state(
+    Machine& machine, const std::string& frame_name, const std::string& target,
+    const std::vector<std::string>& input_filenames, const std::string& output_dir,
+    const std::string& output_basename, bool display_only)
+{
+    State& S = machine.m_state;
+    S.open_frame(frame_name);
+    S.set("K_target", target);
+    S.set("K_output_dir", output_dir);
+    S.set("K_output_basename", output_basename);
+    S.set("K_stdout_only", display_only ? "true" : "false");
+    // The list form uses the standalone-"/" separator (filenames may
+    // contain spaces); K_input_filename is the single root input file.
+    S.set("K_input_filenames", join(input_filenames, " / "));
+    S.set("K_input_filename", input_filenames.empty() ? "" : input_filenames[0]);
+    S.set("K_verbose_level", std::to_string(verbose_level));
+    if (!input_filenames.empty()) {
+        S.set("K_input_dir", absolute_pathname(file_directory(input_filenames[0])));
+    } else {
+        S.set("K_input_dir", fs::current_path().string());
+    }
+}
+
 void load_klammersets(Machine& machine, const strings_t& symbols)
 {
     // "none" is the absence of a klammerset, not the name of one, so it says