站点 Logo 展示：优先显示图片，无 URL 或加载失败时回退为站点名称首字母。

src/composables/useSiteLogo.ts

@@ -0,0 +1,30 @@
+import { computed, ref, watch } from 'vue'
+import { useSiteStore } from '@/stores/site'
+
+/**
+ * 站点 Logo：图片加载失败时回退为站点名称首字母
+ */
+export function useSiteLogo(src?: () => string | undefined) {
+  const siteStore = useSiteStore()
+  const siteName = computed(() => siteStore.siteName || 'MES系统')
+  const siteLogo = computed(() => src?.() ?? siteStore.siteLogo)
+  const logoLoadFailed = ref(false)
+  const showSiteLogoImg = computed(() => !!siteLogo.value && !logoLoadFailed.value)
+  const fallbackLetter = computed(() => siteName.value.charAt(0) || 'M')
+
+  watch(siteLogo, () => {
+    logoLoadFailed.value = false
+  })
+
+  function handleLogoError() {
+    logoLoadFailed.value = true
+  }
+
+  return {
+    siteName,
+    siteLogo,
+    showSiteLogoImg,
+    fallbackLetter,
+    handleLogoError,
+  }
+}