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/plugins/marketplace-test/src/sandbox-entry.ts

@@ -0,0 +1,55 @@
+/**
+ * Sandbox Entry Point
+ *
+ * Canonical plugin implementation using the standard format.
+ * Runs in both trusted (in-process) and sandboxed (isolate) modes.
+ */
+
+import { definePlugin } from "emdash";
+import type { PluginContext } from "emdash";
+
+interface HookEvent {
+	content?: Record<string, unknown>;
+	collection?: string;
+	isNew?: boolean;
+}
+
+export default definePlugin({
+	hooks: {
+		"content:beforeSave": {
+			handler: async (event: HookEvent, ctx: PluginContext) => {
+				ctx.log.info("[marketplace-test] beforeSave fired", {
+					collection: event.collection,
+					isNew: event.isNew,
+				});
+
+				// Record execution in storage
+				await ctx.storage.events.put(`hook-${Date.now()}`, {
+					timestamp: new Date().toISOString(),
+					type: "content:beforeSave",
+					collection: event.collection,
+					isNew: event.isNew,
+				});
+
+				return event.content;
+			},
+		},
+	},
+
+	routes: {
+		ping: {
+			handler: async (_ctx: { input: unknown; request: unknown }, pluginCtx: PluginContext) => ({
+				pong: true,
+				pluginId: pluginCtx.plugin.id,
+				timestamp: Date.now(),
+			}),
+		},
+
+		events: {
+			handler: async (_ctx: { input: unknown; request: unknown }, pluginCtx: PluginContext) => {
+				const result = await pluginCtx.storage.events.query({ limit: 10 });
+				return { count: result.items.length, items: result.items };
+			},
+		},
+	},
+});