FIX: adding kit_system_id info to forward solution

doc/changes/dev/13520.bugfix.rst

@@ -0,0 +1 @@
+Preserve ``kit_system_id`` in forward-solution ``Info``, by :newcontrib: 'Melih Yayli'

doc/changes/names.inc

@@ -210,6 +210,7 @@
 .. _Matti Hämäläinen: https://research.aalto.fi/en/persons/matti-h%C3%A4m%C3%A4l%C3%A4inen/
 .. _Matti Toivonen: https://github.com/mattitoi
 .. _Mauricio Cespedes Tenorio: https://github.com/mcespedes99
+.. _Melih Yayli: https://github.com/yaylim
 .. _Michael Straube: https://github.com/mistraube
 .. _Michal Žák: https://github.com/michalrzak
 .. _Michiru Kaneda: https://github.com/rcmdnk

mne/forward/_make_forward.py

@@ -496,7 +496,7 @@ def _prepare_for_forward(
     mri_id = dict(machid=np.zeros(2, np.int32), version=0, secs=0, usecs=0)
 
     info_trans = str(trans) if isinstance(trans, Path) else trans
-    info = Info(
+    kwargs_fwd_info = dict(
         chs=info["chs"],
         comps=info["comps"],
         # The forward-writing code always wants a dev_head_t, so give an identity one
@@ -510,6 +510,11 @@ def _prepare_for_forward(
         bads=info["bads"],
         mri_head_t=mri_head_t,
     )
+
+    if "kit_system_id" in info:
+        kwargs_fwd_info["kit_system_id"] = info["kit_system_id"]
+
+    info = Info(**kwargs_fwd_info)
     info._update_redundant()
     info._check_consistency()
     logger.info("")

mne/forward/tests/test_make_forward.py

@@ -270,6 +270,9 @@ def test_make_forward_solution_kit(tmp_path, fname_src_small):
     )
     _compare_forwards(fwd, fwd_py, 157, n_src_small, meg_rtol=1e-3, meg_atol=1e-7)
 
+    # NEW TEST: ensure kit_system_id survives the forward-info rewrite
+    assert "kit_system_id" in fwd_py["info"]
+
 
 @requires_mne
 def test_make_forward_solution_bti(fname_src_small):