What a Windows editor saves, and a standard user's Windows install (from dev 9d6f66456a3d)

- CRLF line endings are read as newlines on every system (the reader used
  to delete the pair, collapsing a Notepad++ file into one line on Linux
  and macOS); a leading UTF-8 byte-order mark is ignored; a UTF-16 or
  Windows-1252 source is refused with the encoding, the place and the
  remedy named. .gitattributes pins LF in every clone.
- Windows source install: the repository path must hold no space (GNU
  Make), accented letters are fine (every linker input is relative now);
  python.org's Python is selected ahead of an MSYS2 one that poppler pulls
  in; TeX Live goes to its Windows default C:\texlive\2026.
- The Python binding needs an ASCII installation path on Windows, and its
  suite says so there.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

env/makefile.env

@@ -34,6 +34,19 @@ endif
 ifneq (,$(filter MINGW% MSYS%,$(UNAME_S)))
 PYTHON        := python
 PYTHON_PREFIX := $(shell cygpath -m "$$($(PYTHON) -c 'import sys; print(sys.base_prefix)')")
+# The interpreter "python" resolves to must be python.org's, which has an
+# import library under libs/.  MSYS2's own python (installed as a dependency
+# of poppler, through glib2) sits in /ucrt64/bin ahead of it and has none:
+# a build against it compiles nothing (no Include/Python.h) or embeds an
+# interpreter without the user's pip packages.  env/runtime.env puts
+# python.org's directory first; refuse rather than build the wrong thing.
+# (Asked of the interpreter, not $(wildcard): the prefix "C:/Program Files"
+# has a space, on which wildcard splits.)
+ifeq (,$(NOPYTHON))
+ifneq (yes,$(shell $(PYTHON) -c 'import os, sys; print("yes" if os.path.isdir(os.path.join(sys.base_prefix, "libs")) else "no")'))
+$(error "python" is $(PYTHON_PREFIX)/python, not python.org's interpreter (no libs/ there); source env/runtime.env, which puts python.org's Python first on PATH)
+endif
+endif
 PYTHON_INC    := -I"$(PYTHON_PREFIX)/Include"
 PYTHON_LIB    := -L"$(PYTHON_PREFIX)/libs" -l$(shell $(PYTHON) -c 'import sys; print("python%d%d" % sys.version_info[:2])')
 else