feat(app): 优化图片加载、状态管理与搜索交互体验

- 拆分 load_image 为 _load_image_raw 与 load_image，隔离索引构建与 UI 错误提示
  - 移除 build_index 中的进度条，避免副作用
  - 使用 session_state 管理 query_url 与 query_image_bytes，修复切换输入方式时状态丢失
  - 示例图片选择后增加 st.rerun()，确保 UI 即时刷新
  - 搜索前增加空值校验，给出更友好的提示信息

app.py

@@ -373,18 +373,24 @@ def get_embedder() -> CLIPEmbedder:
 
 
 # ─── Utilities ───────────────────────────────────────────────────────────────
-def load_image(source: str | io.BytesIO) -> Image.Image | None:
+def _load_image_raw(source: str | io.BytesIO) -> Image.Image | None:
     try:
         if isinstance(source, str):
             resp = requests.get(source, timeout=30)
             resp.raise_for_status()
             return Image.open(io.BytesIO(resp.content)).convert("RGB")
         return Image.open(source).convert("RGB")
-    except Exception as e:
-        st.error(f"图片加载失败: {e}")
+    except Exception:
         return None
 
 
+def load_image(source: str | io.BytesIO) -> Image.Image | None:
+    img = _load_image_raw(source)
+    if img is None:
+        st.error("图片加载失败，请检查链接是否可访问或文件是否损坏")
+    return img
+
+
 def cosine_similarity(a: np.ndarray, b: np.ndarray) -> float:
     return float(np.dot(a, b))
 
@@ -393,13 +399,10 @@ def cosine_similarity(a: np.ndarray, b: np.ndarray) -> float:
 def build_index() -> tuple[list[dict], list[str], list[str]]:
     embedder = get_embedder()
     items, succeeded, failed = [], [], []
-    progress = st.progress(0, text="正在构建病虫害图片索引...")
-    total = len(PEST_KNOWLEDGE)
-    for i, pest in enumerate(PEST_KNOWLEDGE):
-        img = load_image(pest.url)
+    for pest in PEST_KNOWLEDGE:
+        img = _load_image_raw(pest.url)
         if img is None:
             failed.append(pest.name)
-            progress.progress((i + 1) / total, text=f"索引构建中 ({i + 1}/{total})...")
             continue
         try:
             embedding = embedder.embed(img)
@@ -415,8 +418,6 @@ def build_index() -> tuple[list[dict], list[str], list[str]]:
             succeeded.append(pest.name)
         except Exception:
             failed.append(pest.name)
-        progress.progress((i + 1) / total, text=f"索引构建中 ({i + 1}/{total})...")
-    progress.empty()
     return items, succeeded, failed
 
 
@@ -429,16 +430,26 @@ with st.sidebar:
     st.markdown('<div class="section-header" style="margin-top:0">🖼️ 输入方式</div>', unsafe_allow_html=True)
     input_mode = st.radio("", ["上传本地图片", "输入图片 URL", "选择示例图片"], label_visibility="collapsed")
 
+    # 初始化 session_state
+    if "query_url" not in st.session_state:
+        st.session_state.query_url = ""
+    if "query_image_bytes" not in st.session_state:
+        st.session_state.query_image_bytes = None
+
     query_source = None
     query_url = ""
 
     if input_mode == "上传本地图片":
         uploaded = st.file_uploader("选择图片", type=["jpg", "jpeg", "png", "webp"])
         if uploaded is not None:
-            query_source = io.BytesIO(uploaded.getvalue())
-            query_url = ""
+            st.session_state.query_image_bytes = uploaded.getvalue()
+            st.session_state.query_url = ""
+        if st.session_state.query_image_bytes is not None:
+            query_source = io.BytesIO(st.session_state.query_image_bytes)
     elif input_mode == "输入图片 URL":
-        query_url = st.text_input("图片 URL", placeholder="https://example.com/image.jpg")
+        query_url = st.text_input("图片 URL", value=st.session_state.query_url, placeholder="https://example.com/image.jpg")
+        st.session_state.query_url = query_url
+        st.session_state.query_image_bytes = None
         if query_url.strip():
             query_source = query_url.strip()
     else:
@@ -448,7 +459,9 @@ with st.sidebar:
             with cols[idx % 2]:
                 if st.button(name, key=f"ex_{name}"):
                     st.session_state.query_url = url
-        if "query_url" in st.session_state:
+                    st.session_state.query_image_bytes = None
+                    st.rerun()
+        if st.session_state.query_url:
             query_url = st.session_state.query_url
             query_source = query_url
             st.image(query_url, use_container_width=True)
@@ -493,7 +506,12 @@ if badges:
 st.markdown("<br>", unsafe_allow_html=True)
 
 # ─── Search Logic ────────────────────────────────────────────────────────────
-if search_clicked and query_source is not None and index_items:
+if search_clicked:
+    if query_source is None:
+        st.warning("请先上传图片、输入图片 URL 或选择示例图片后再点击搜索")
+    elif not index_items:
+        st.warning("知识库索引为空，请检查网络连接后刷新页面重试。")
+    else:
         query_img = load_image(query_source)
         if query_img is not None:
             col_query, col_preview = st.columns([1, 3])
@@ -587,9 +605,6 @@ if search_clicked and query_source is not None and index_items:
                 </div>
                 """, unsafe_allow_html=True)
 
-elif search_clicked and not index_items:
-    st.warning("知识库索引为空，请检查网络连接后刷新页面重试。")
-
 # ─── Footer ───────────────────────────────────────────────────────────────────
 st.markdown("<br>", unsafe_allow_html=True)
 st.markdown("""