fix: include slot scripts in server island response

.changeset/server-island-slot-scripts.md

@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Fix: include `<script>` tags from components passed as slots to `server:defer` components in the server island response

packages/astro/src/runtime/server/render/server-islands.ts

@@ -158,7 +158,20 @@ export class ServerIslandComponent {
 		for (const name in this.slots) {
 			if (name !== 'fallback') {
 				const content = await renderSlotToString(this.result, this.slots[name]);
-				renderedSlots[name] = content.toString();
+				let slotHtml = content.toString();
+				// Append script instructions so that components passed as slots
+				// to server:defer components retain their scripts in the island response.
+				// renderSlotToString returns a SlotString (typed as string) that carries
+				// render instructions stripped from the HTML content.
+				const slotContent = content as unknown as import('./slot.js').SlotString;
+				if (Array.isArray(slotContent.instructions)) {
+					for (const instruction of slotContent.instructions) {
+						if (instruction.type === 'script') {
+							slotHtml += instruction.content;
+						}
+					}
+				}
+				renderedSlots[name] = slotHtml;
 			}
 		}