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/reference.test.ts

@@ -0,0 +1,40 @@
+import { describe, it, expect } from "vitest";
+
+import { reference } from "../../src/fields/reference.js";
+
+describe("reference field", () => {
+	it("should create field definition", () => {
+		const field = reference("posts");
+
+		expect(field.type).toBe("reference");
+		expect(field.schema).toBeDefined();
+		expect(field.ui?.widget).toBe("reference");
+		expect(field.options?.collection).toBe("posts");
+	});
+
+	it("should accept valid reference ID", () => {
+		const field = reference("posts");
+
+		expect(() => field.schema.parse("post-123")).not.toThrow();
+		expect(() => field.schema.parse("abc-def-ghi")).not.toThrow();
+	});
+
+	it("should reject invalid reference", () => {
+		const field = reference("posts");
+
+		expect(() => field.schema.parse(123)).toThrow();
+		expect(() => field.schema.parse({})).toThrow();
+		expect(() => field.schema.parse(null)).toThrow();
+	});
+
+	it("should support required option", () => {
+		const required = reference("posts", { required: true });
+		const optional = reference("posts", { required: false });
+
+		// Required should reject undefined
+		expect(() => required.schema.parse(undefined)).toThrow();
+
+		// Optional should accept undefined
+		expect(() => optional.schema.parse(undefined)).not.toThrow();
+	});
+});