First properly working state.

src/index.ts

@@ -7,15 +7,12 @@ import {
 } from '@jupyterlab/notebook';
 
 import {
-	CodeCell
+	Cell, CodeCell
 } from '@jupyterlab/cells';
 
 
 import './codemirror-finesse';
 
-/**
- * The plugin registration information.
- */
 const plugin: JupyterFrontEndPlugin<void> = {
 	activate,
 	id: 'finesse-syntax-jupyter',
@@ -27,8 +24,7 @@ function activate(app: JupyterFrontEnd, tracker: INotebookTracker) {
 	tracker.widgetAdded.connect(activate_finesse)
 };
 
-
-function check_syntax(sender: Notebook): void {
+function check_all(sender: Notebook): void {
 	sender.widgets.forEach(cell => {
 		if (cell instanceof CodeCell && cell.model.mimeType != "text/x-finesse-python") {
 			cell.model.mimeType = "text/x-finesse-python";
@@ -36,11 +32,19 @@ function check_syntax(sender: Notebook): void {
 	});
 };
 
+function check_cell(sender: Notebook, cell: Cell): void {
+	if (cell instanceof CodeCell) {
+		cell.model.mimeType = "text/x-finesse-python";
+	}
+}
+
 function activate_finesse(sender: INotebookTracker, panel: NotebookPanel): void {
-	panel.content.modelContentChanged.connect(check_syntax);
+	panel.content.activeCellChanged.connect(check_cell);
+
+	// I ain't proud of this, but it's the sanest way I could find to get
+	// the syntax highlighting to change on startup without selecting a
+	// different cell
+	setTimeout(() => {check_all(panel.content)}, 1000);
 };
 
-/**
- * Export the plugin as default.
- */
 export default plugin;