Expose actionable asset download and filesystem failure details

src/lib/services/furni-import.ts

@@ -731,13 +731,19 @@ export async function importSingleFurni(params: {
 
 	// Download icon + SWF concurrently (independent assets). Each tries its
 	// candidate URLs in order until one succeeds.
+	let iconFailure = "",
+		swfFailure = "";
 	const [iconOkResult, swfOk] = await Promise.all([
 		preservingExisting && existsSync(iconPath)
 			? Promise.resolve(true)
-			: tryDownloadCandidates(iconUrls, iconPath, "png"),
+			: tryDownloadCandidates(iconUrls, iconPath, "png", (detail) => {
+					iconFailure = detail;
+				}),
 		preservingExisting && existsSync(swfPath)
 			? Promise.resolve(true)
-			: tryDownloadCandidates(swfUrls, swfPath, "swf"),
+			: tryDownloadCandidates(swfUrls, swfPath, "swf", (detail) => {
+					swfFailure = detail;
+				}),
 	]);
 	let iconOk = iconOkResult;
 
@@ -772,10 +778,13 @@ export async function importSingleFurni(params: {
 			warnings.push("Icon download failed and SWF icon extraction also failed");
 		}
 	} else if (!iconOk) {
-		warnings.push("Icon image download failed");
+		warnings.push(
+			`Icon image download failed: ${iconFailure || "unknown cause"}`,
+		);
 	}
 
-	if (!swfOk && !nitroDownloadOk) warnings.push("SWF download failed");
+	if (!swfOk && !nitroDownloadOk)
+		warnings.push(`SWF download failed: ${swfFailure || "unknown cause"}`);
 
 	// ── Convert SWF to Nitro ──────────────────────────────────────────
 	onProgress?.("converting");
@@ -841,12 +850,10 @@ export async function importSingleFurni(params: {
 		return {
 			ok: false,
 			warnings,
-			error: isUpdate
-				? "No .nitro file could be created; existing furniture was preserved"
-				: `Import rolled back: no .nitro file could be created. ${warnings
-						.filter((warning) => /conversion|download|SWF/.test(warning))
-						.slice(-3)
-						.join(". ")}`,
+			error: `${isUpdate ? "No .nitro file could be created; existing furniture was preserved" : "Import rolled back: no .nitro file could be created"} (${classname}, revision ${rev}). ${warnings
+				.filter((warning) => /conversion|download|SWF/.test(warning))
+				.slice(-3)
+				.join(". ")}`,
 		};
 	}