Emdash source with visual editor image upload fix

Fixes:
1. media.ts: wrap placeholder generation in try-catch
2. toolbar.ts: check r.ok, display error message in popover

packages/core/tests/fields/portable-text.test.ts

@@ -0,0 +1,45 @@
+import { describe, it, expect } from "vitest";
+
+import { portableText } from "../../src/fields/portable-text.js";
+
+describe("portableText field", () => {
+	it("should create field definition", () => {
+		const field = portableText();
+
+		expect(field.type).toBe("portableText");
+		expect(field.schema).toBeDefined();
+		expect(field.ui?.widget).toBe("portableText");
+	});
+
+	it("should accept valid Portable Text", () => {
+		const field = portableText();
+		const valid = [
+			{
+				_type: "block",
+				_key: "abc123",
+				style: "normal",
+				children: [{ _type: "span", text: "Hello World" }],
+			},
+		];
+
+		expect(() => field.schema.parse(valid)).not.toThrow();
+	});
+
+	it("should reject invalid Portable Text", () => {
+		const field = portableText();
+
+		expect(() => field.schema.parse("not an array")).toThrow();
+		expect(() => field.schema.parse([{ missing: "_type" }])).toThrow();
+	});
+
+	it("should support required option", () => {
+		const required = portableText({ required: true });
+		const optional = portableText({ required: false });
+
+		// Required should reject undefined
+		expect(() => required.schema.parse(undefined)).toThrow();
+
+		// Optional should accept undefined
+		expect(() => optional.schema.parse(undefined)).not.toThrow();
+	});
+});