feat: 附件通过 base64 内容实现前端直接下载

- MediaItem/MediaSummary 新增 content_base64 和 file_name 字段
- 解析附件时读取文件内容并 base64 编码（限 50MB），前端 Blob 下载
- 创建 Session 后返回完整 topics 列表，前端侧边栏实时同步
- 简化话题历史加载逻辑，不再回退到 session 消息

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/bus/message.rs

@@ -24,6 +24,8 @@ pub struct MediaItem {
     pub media_type: String, // "image", "audio", "file", "video"
     pub mime_type: Option<String>,
     pub original_key: Option<String>, // Feishu file_key for download
+    pub content_base64: Option<String>, // Base64-encoded file content for web download
+    pub file_name: Option<String>,      // Display file name
 }
 
 impl MediaItem {
@@ -33,6 +35,8 @@ impl MediaItem {
             media_type: media_type.into(),
             mime_type: None,
             original_key: None,
+            content_base64: None,
+            file_name: None,
         }
     }
 }

src/command/handlers/session.rs

@@ -1,5 +1,6 @@
 use crate::command::context::CommandContext;
 use crate::command::handler::{CommandHandler, CommandMetadata};
+use crate::command::handlers::list_topics::TopicSummary;
 use crate::command::response::{CommandError, CommandResponse, MessageKind};
 use crate::command::Command;
 use crate::gateway::session::SessionManager;
@@ -94,8 +95,30 @@ async fn handle_create_session(
         }
     }
 
+    // Query the full topic list so the frontend sidebar can update
+    let topics = handler
+        .store
+        .list_topics(session_id)
+        .map_err(|e| CommandError::new("LIST_TOPICS_ERROR", e.to_string()))?;
+
+    let topic_summaries: Vec<TopicSummary> = topics
+        .into_iter()
+        .map(|t| TopicSummary {
+            topic_id: t.id,
+            session_id: t.session_id,
+            title: t.title,
+            message_count: t.message_count,
+            created_at: t.created_at,
+            last_active_at: t.last_active_at,
+        })
+        .collect();
+
+    let topics_json = serde_json::to_string(&topic_summaries)
+        .map_err(|e| CommandError::new("SERIALIZE_ERROR", e.to_string()))?;
+
     Ok(CommandResponse::success(ctx.request_id)
         .with_message(MessageKind::Notification, &topic.title)
+        .with_metadata("topics", &topics_json)
         .with_metadata("topic_id", &topic.id)
         .with_metadata("session_id", &topic.session_id)
         .with_metadata("message_count", &topic.message_count.to_string()))

src/gateway/ws.rs

@@ -418,15 +418,12 @@ fn resolve_ws_sender_id(sender_id: Option<&str>, runtime_session_id: &str) -> St
 /// 加载并发送话题历史消息
 async fn send_topic_history(
     store: &Arc<crate::storage::SessionStore>,
-    session_id: &str,
+    _session_id: &str,
     topic_id: &str,
     sender: &mpsc::Sender<WsOutbound>,
 ) -> Result<(), Box<dyn std::error::Error>> {
     // 加载话题消息
-    let mut messages = store.load_messages_for_topic(topic_id)?;
-    if messages.is_empty() {
-        messages = store.load_messages(session_id)?;
-    }
+    let messages = store.load_messages_for_topic(topic_id)?;
 
     tracing::info!(topic_id = %topic_id, message_count = messages.len(), "Sending topic history");
 

src/protocol/mod.rs

@@ -40,6 +40,10 @@ pub struct MediaSummary {
     pub media_type: String,
     #[serde(default, skip_serializing_if = "Option::is_none")]
     pub mime_type: Option<String>,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub content_base64: Option<String>,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub file_name: Option<String>,
 }
 
 #[derive(Debug, Clone, Serialize, Deserialize)]

src/protocol/ws_adapter.rs

@@ -77,6 +77,8 @@ pub(crate) fn ws_outbound_from_outbound_message(message: &OutboundMessage) -> Ve
                     path: m.path.clone(),
                     media_type: m.media_type.clone(),
                     mime_type: m.mime_type.clone(),
+                    content_base64: m.content_base64.clone(),
+                    file_name: m.file_name.clone(),
                 })
                 .collect();
             vec![WsOutbound::AssistantResponse {

src/tools/session_send.rs

@@ -1,8 +1,10 @@
+use std::io::Read;
 use std::path::Path;
 use std::sync::Arc;
 
 use anyhow::anyhow;
 use async_trait::async_trait;
+use base64::Engine;
 use serde_json::json;
 
 use crate::bus::MediaItem;
@@ -205,11 +207,27 @@ fn parse_attachments(value: &serde_json::Value) -> anyhow::Result<Vec<MediaItem>
             return Err(anyhow!("attachment file is empty: {}", raw_path));
         }
 
+        let content_base64 = (metadata.len() <= 50 * 1024 * 1024)
+            .then(|| {
+                let mut file = std::fs::File::open(&raw_path)?;
+                let mut buf = Vec::with_capacity(metadata.len() as usize);
+                file.read_to_end(&mut buf)?;
+                Ok::<_, anyhow::Error>(base64::engine::general_purpose::STANDARD.encode(&buf))
+            })
+            .transpose()?;
+
+        let file_name = Path::new(&raw_path)
+            .file_name()
+            .and_then(|n| n.to_str())
+            .map(ToOwned::to_owned);
+
         let media_type = infer_media_type(&raw_path);
         let mut item = MediaItem::new(raw_path.to_string(), media_type);
         item.mime_type = mime_guess::from_path(&raw_path)
             .first_raw()
             .map(ToOwned::to_owned);
+        item.content_base64 = content_base64;
+        item.file_name = file_name;
         attachments.push(item);
     }
 

web/src/components/Chat/MessageBubble.tsx

@@ -23,25 +23,52 @@ function getFileName(path: string): string {
 }
 
 function AttachmentCard({ attachment }: { attachment: Attachment }) {
-  const fileName = getFileName(attachment.path)
-  const downloadUrl = `/download?path=${encodeURIComponent(attachment.path)}`
+  const fileName = attachment.file_name || getFileName(attachment.path)
+
+  const handleDownload = (e: React.MouseEvent) => {
+    if (!attachment.content_base64) return
+
+    e.preventDefault()
+    const mimeType = attachment.mime_type || 'application/octet-stream'
+    const byteChars = atob(attachment.content_base64)
+    const byteNums = new Array(byteChars.length)
+    for (let i = 0; i < byteChars.length; i++) {
+      byteNums[i] = byteChars.charCodeAt(i)
+    }
+    const byteArr = new Uint8Array(byteNums)
+    const blob = new Blob([byteArr], { type: mimeType })
+    const url = URL.createObjectURL(blob)
+
+    const a = document.createElement('a')
+    a.href = url
+    a.download = fileName
+    document.body.appendChild(a)
+    a.click()
+    document.body.removeChild(a)
+    URL.revokeObjectURL(url)
+  }
+
+  const canDownload = !!attachment.content_base64
 
   return (
-    <a
-      href={downloadUrl}
-      download={fileName}
-      className="flex items-center gap-2 rounded-lg bg-white/5 border border-white/10 px-3 py-2 text-xs hover:bg-white/10 hover:border-[#00f0ff]/30 transition-colors cursor-pointer group"
-      title={`下载 ${fileName}`}
+    <div
+      onClick={canDownload ? handleDownload : undefined}
+      className={`flex items-center gap-2 rounded-lg bg-white/5 border border-white/10 px-3 py-2 text-xs transition-colors group ${
+        canDownload ? 'hover:bg-white/10 hover:border-[#00f0ff]/30 cursor-pointer' : ''
+      }`}
+      title={canDownload ? `下载 ${fileName}` : attachment.path}
     >
-      <span className="text-zinc-400 group-hover:text-[#00f0ff] transition-colors">
+      <span className={`text-zinc-400 transition-colors ${canDownload ? 'group-hover:text-[#00f0ff]' : ''}`}>
         {getAttachmentIcon(attachment.media_type)}
       </span>
-      <span className="text-zinc-300 truncate max-w-[200px] group-hover:text-white transition-colors" title={attachment.path}>
+      <span className={`text-zinc-300 truncate max-w-[200px] transition-colors ${canDownload ? 'group-hover:text-white' : ''}`} title={attachment.path}>
         {fileName}
       </span>
       <span className="text-zinc-600 ml-auto shrink-0">{attachment.media_type}</span>
+      {canDownload && (
         <Download className="h-3 w-3 text-zinc-600 group-hover:text-[#00f0ff] transition-colors" />
-    </a>
+      )}
+    </div>
   )
 }
 

web/src/types/protocol.ts

@@ -31,6 +31,8 @@ export interface Attachment {
   path: string
   media_type: string
   mime_type?: string
+  content_base64?: string
+  file_name?: string
 }
 
 export interface AssistantResponse {