PCL/NilPy — Windows tk compatibility (opt-in emulate/wrap)

• Type: feature (Track M — MSWindows campaign; file-owned by Track B, lib/pcl). Gate = make lib-test green on Linux (Linux path unchanged); Windows tk = Wine-smoke best-effort.
• Status: backlog. Implements the resolution of [[decide-nilpy-gui-tk-vs-pcl]]. Blocked-by [[feature-port-windows-pe]] (needs a Windows binary to run at all).
• Owner: —
• Opened: 2026-07-21.

What

NilPy import 'tk.pas' as tk must "just work" on Windows too. (Spelling note, 2026-08-19: a bare import tk no longer reaches the Pascal unit — [[decide-nilpy-imports-that-collide-with-a-pascal-rtl-unit]]. tk is deliberately NOT on the Python-serving list; lib/pcl/tkinter.pas is the unit written to BE the Python module, tk.pas is the layer under it. Nothing about this ticket changes — only how the examples spell the import.) The decision ([[decide-nilpy-gui-tk-vs-pcl]]) is a compile-time platform switch inside lib/pcl/tk.pas — Linux keeps the real Tcl/Tk embed (works, cheap system dep); Windows gets an opt-in emulate/wrap in one isolated include, so the Tcl/Tk DLL-swarm never touches the zero-dep Windows binary.

{$ifdef WINDOWS}
  {$include windows-tk-compat.inc}   // this ticket — stub now, fill later
{$else}
  // existing real Tcl/Tk embed, untouched
{$endif}

Shape (deliberately incremental)

• Now: land the {$ifdef WINDOWS} split + a windows-tk-compat.inc stub that compiles and gives a clear "tk-on-Windows not yet implemented" at the tk-call boundary. Zero Linux impact (the else-branch is today's code verbatim).
• Later: fill the include — most cheaply as a thin tk-shaped veneer over the Win32 widgetset ([[feature-pcl-win32-widgetset]]), so NilPy tk on Windows rides the same zero-dep user32/gdi32 path as Pascal GUI. (Alternative: bundle libtcl/libtk — rejected, that's the swarm.)

Explicitly NOT

• Not a Linux change — the real Tcl/Tk embed stays exactly as-is.
• Not gated on real-Windows parity (no Windows box; Wine-smoke only, best-effort).

Acceptance

• Linux: tk.pas builds and the NilPy IDE / examples/tk/*.npy run byte-unchanged (else-branch = today's embed). make lib-test green.
• Windows stub: --target=x86_64-windows compiles tk.pas (takes the ifdef branch) and fails gracefully with a clear message at first tk use — no silent breakage, no libtcl dependency pulled into the PE.