feat: wire TikZ export button through anywidget comm channel

- Add Python-side _on_custom_msg handler that receives export_tikz
  request from JS, generates .tex content, and sends it back as
  tikz_data message (avoids server-side file paths)
- Standalone mode: disable TikZ button with tooltip; SVG still works
- Jupyter mode: clicking Export TikZ triggers model.send() → Python
  generates content → JS receives blob → browser downloads .tex
- 139 passed, 5 skipped; build + twine check pass

Author: maedoc

src/tvb_phaseplane/static/widget.js

@@ -15843,10 +15843,31 @@ export function render({ model, el }) {
   editorApplyBtn.addEventListener("click", applyEditor);
   editorCopyBtn.addEventListener("click", copySpec);
   el.querySelector(".ppw-export-svg").addEventListener("click", exportToSVG);
-  el.querySelector(".ppw-export-tikz").addEventListener("click", () => {
+
+  // TikZ export requires a live Python kernel; disabled in standalone.
+  const tikzBtn = el.querySelector(".ppw-export-tikz");
+  if (isStandalone) {
+    tikzBtn.disabled = true;
+    tikzBtn.title = "TikZ export requires a Jupyter kernel";
+  }
+  tikzBtn.addEventListener("click", () => {
+    if (isStandalone) {
+      alert("TikZ export requires a Jupyter kernel. Use widget.export_tikz('file.tex') in a notebook cell instead.");
+      return;
+    }
     model.send({ type: "export_tikz" });
   });
 
+  // Listen for TikZ data coming back from the Python kernel
+  if (!isStandalone) {
+    model.on('msg:custom', (msg) => {
+      if (msg && msg.type === 'tikz_data') {
+        const blob = new Blob([msg.content], { type: 'application/x-tex' });
+        downloadBlob(blob, msg.filename || 'phase_plane.tex');
+      }
+    });
+  }
+
   // ═════════════════════════════════════════════════════════════
   //  INITIALISATION
   // ═════════════════════════════════════════════════════════════

src/tvb_phaseplane/widget.py

@@ -7,7 +7,9 @@
 """
 
 import json
+import os
 import pathlib
+import tempfile
 
 import anywidget
 import numpy as np
@@ -98,6 +100,8 @@ def __init__(self, model=None, **kwargs):
             kwargs.setdefault("model_name", model.name)
         super().__init__(**kwargs)
         self._update_model()
+        # Register handler for custom JS → Python messages (e.g. TikZ export)
+        self.on_msg(self._on_custom_msg)
 
     def _get_model(self):
         from .models import MODEL_REGISTRY
@@ -481,3 +485,24 @@ def export_tikz(self, filename: str | pathlib.Path = "phase_plane.tex"):
         )
         filename.write_text(tex, encoding="utf-8")
         return str(filename)
+
+    # ── Custom message handler (JS → Python) ──
+
+    def _on_custom_msg(self, _widget, content, buffers):
+        """Handle messages from the JS front-end."""
+        msg_type = content.get("type")
+        if msg_type == "export_tikz":
+            fd, tmppath = tempfile.mkstemp(suffix=".tex", prefix="phase_plane_")
+            os.close(fd)
+            try:
+                self.export_tikz(tmppath)
+                tex_content = pathlib.Path(tmppath).read_text(encoding="utf-8")
+                self.send(
+                    {
+                        "type": "tikz_data",
+                        "content": tex_content,
+                        "filename": "phase_plane.tex",
+                    }
+                )
+            finally:
+                os.unlink(tmppath)