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/unit/request-context.test.ts

@@ -0,0 +1,79 @@
+import { describe, expect, it } from "vitest";
+
+import { getRequestContext, runWithContext } from "../../src/request-context.js";
+
+describe("request context", () => {
+	it("returns undefined outside any context", () => {
+		expect(getRequestContext()).toBeUndefined();
+	});
+
+	it("returns context inside runWithContext", () => {
+		const ctx = { editMode: true };
+		runWithContext(ctx, () => {
+			expect(getRequestContext()).toBe(ctx);
+		});
+	});
+
+	it("returns undefined after runWithContext completes", () => {
+		runWithContext({ editMode: true }, () => {});
+		expect(getRequestContext()).toBeUndefined();
+	});
+
+	it("propagates through async boundaries", async () => {
+		const ctx = { editMode: true, preview: { collection: "posts", id: "1" } };
+		await runWithContext(ctx, async () => {
+			await new Promise((resolve) => setTimeout(resolve, 1));
+			expect(getRequestContext()).toBe(ctx);
+		});
+	});
+
+	it("isolates concurrent contexts", async () => {
+		const results: boolean[] = [];
+		await Promise.all([
+			runWithContext({ editMode: true }, async () => {
+				await new Promise((resolve) => setTimeout(resolve, 10));
+				results.push(getRequestContext()!.editMode);
+			}),
+			runWithContext({ editMode: false }, async () => {
+				await new Promise((resolve) => setTimeout(resolve, 5));
+				results.push(getRequestContext()!.editMode);
+			}),
+		]);
+		// Second resolves first (5ms < 10ms), so false appears before true
+		expect(results).toContain(true);
+		expect(results).toContain(false);
+		expect(results).toHaveLength(2);
+	});
+
+	it("includes preview info when set", () => {
+		const ctx = {
+			editMode: false,
+			preview: { collection: "posts", id: "abc-123" },
+		};
+		runWithContext(ctx, () => {
+			const result = getRequestContext();
+			expect(result?.preview).toEqual({ collection: "posts", id: "abc-123" });
+			expect(result?.editMode).toBe(false);
+		});
+	});
+
+	it("includes db override when set", () => {
+		const fakeDb = { isKysely: true } as never;
+		const ctx = {
+			editMode: false,
+			db: fakeDb,
+		};
+		runWithContext(ctx, () => {
+			const result = getRequestContext();
+			expect(result?.db).toBe(fakeDb);
+		});
+	});
+
+	it("db override is undefined when not set", () => {
+		const ctx = { editMode: false };
+		runWithContext(ctx, () => {
+			const result = getRequestContext();
+			expect(result?.db).toBeUndefined();
+		});
+	});
+});