Improve ImageField accessibility and upload robustness

src/layouts/AdminLayout.astro

@@ -64,7 +64,10 @@ const isActive = (href: string) =>
           canvas.width = width;
           canvas.height = height;
           const ctx = canvas.getContext("2d");
-          if (!ctx) return file;
+          if (!ctx) {
+            if (typeof bitmap.close === "function") bitmap.close();
+            return file;
+          }
           ctx.drawImage(bitmap, 0, 0, width, height);
           if (typeof bitmap.close === "function") bitmap.close();
           const blob = await new Promise<Blob | null>((resolve) =>
@@ -84,6 +87,7 @@ const isActive = (href: string) =>
         if (!input || !status) return;
 
         status.textContent = "上傳中…";
+        status.classList.remove("error");
         const blob = await toOptimised(file);
         const body = new FormData();
         body.append("file", new File([blob], file.name, { type: blob.type }));
@@ -91,9 +95,13 @@ const isActive = (href: string) =>
 
         try {
           const res = await fetch("/admin/upload", { method: "POST", body });
-          const data = (await res.json()) as { ok: boolean; url?: string; error?: string };
+          const isJson = (res.headers.get("content-type") ?? "").includes("application/json");
+          const data = isJson
+            ? ((await res.json()) as { ok: boolean; url?: string; error?: string })
+            : { ok: false, error: `上傳失敗（${res.status}）。` };
           if (!res.ok || !data.ok || !data.url) {
             status.textContent = data.error ?? "上傳失敗。";
+            status.classList.add("error");
             return;
           }
           input.value = data.url;
@@ -104,15 +112,22 @@ const isActive = (href: string) =>
           status.textContent = "✓ 已上傳";
         } catch {
           status.textContent = "上傳失敗，請檢查網絡。";
+          status.classList.add("error");
         }
       }
 
       document.querySelectorAll<HTMLElement>("[data-image-field]").forEach((field) => {
         const fileInput = field.querySelector<HTMLInputElement>("[data-image-input]");
         if (!fileInput) return;
+        let busy = false;
         fileInput.addEventListener("change", () => {
           const file = fileInput.files?.[0];
-          if (file) void upload(field, file);
+          fileInput.value = "";
+          if (!file || busy) return;
+          busy = true;
+          void upload(field, file).finally(() => {
+            busy = false;
+          });
         });
       });
     </script>
@@ -185,6 +200,7 @@ const isActive = (href: string) =>
   .image-actions { display: flex; align-items: center; gap: 10px; margin-top: 8px; flex-wrap: wrap; }
   .image-actions input[type="file"] { font: inherit; font-size: 13px; max-width: 100%; }
   .image-status { font-size: 12.5px; font-weight: 600; color: #0b8a5e; }
+  .image-status.error { color: #a32d2d; }
   .image-preview { display: block; margin-top: 10px; max-width: 220px; border-radius: 10px; }
   .image-preview[hidden] { display: none; }
   .row { display: grid; gap: 12px; grid-template-columns: 1fr; }