File-Upload: Attachments-Tabelle, Base64-Speicherung, Frontend mit Drag&Drop/Paste/Preview, Error-Handling Fix

Services/DatabaseService.cs

@@ -97,6 +97,21 @@ public class DatabaseService
             CREATE INDEX IF NOT EXISTS idx_messages_chain ON messages(chain_id);
         ");
 
+        conn.Execute(@"
+            CREATE TABLE IF NOT EXISTS attachments (
+                id            INTEGER PRIMARY KEY AUTOINCREMENT,
+                message_id    INTEGER NOT NULL,
+                type          TEXT NOT NULL,
+                media_type    TEXT NOT NULL,
+                file_name     TEXT,
+                data          TEXT NOT NULL,
+                created_at    TEXT NOT NULL,
+                FOREIGN KEY (message_id) REFERENCES messages(id)
+            );
+
+            CREATE INDEX IF NOT EXISTS idx_attachments_message ON attachments(message_id);
+        ");
+
         // Migrations
         TryAddColumn(conn, "sessions", "agent_id", "TEXT");
         TryAddColumn(conn, "sessions", "description", "TEXT");
@@ -105,6 +120,7 @@ public class DatabaseService
         TryAddColumn(conn, "sessions", "context", "TEXT");
         TryAddColumn(conn, "sessions", "is_deleted", "INTEGER NOT NULL DEFAULT 0");
         TryAddColumn(conn, "chains", "agent_id", "TEXT");
+        TryAddColumn(conn, "messages", "attachment_count", "INTEGER NOT NULL DEFAULT 0");
     }
 
     private void TryAddColumn(SqliteConnection conn, string table, string column, string type)
@@ -338,12 +354,40 @@ public class DatabaseService
         using var conn = CreateConnection();
         record.CreatedAt = DateTime.UtcNow.ToString("o");
         return await conn.ExecuteScalarAsync<long>(@"
-            INSERT INTO messages (chain_id, role, type, content, tool_name, tool_call_id, is_error, iteration, created_at)
-            VALUES (@ChainId, @Role, @Type, @Content, @ToolName, @ToolCallId, @IsError, @Iteration, @CreatedAt);
+            INSERT INTO messages (chain_id, role, type, content, tool_name, tool_call_id, is_error, iteration, attachment_count, created_at)
+            VALUES (@ChainId, @Role, @Type, @Content, @ToolName, @ToolCallId, @IsError, @Iteration, @AttachmentCount, @CreatedAt);
             SELECT last_insert_rowid();
         ", record);
     }
 
+    // ── Attachments ──
+
+    public async Task SaveAttachment(AttachmentRecord attachment)
+    {
+        using var conn = CreateConnection();
+        attachment.CreatedAt = DateTime.UtcNow.ToString("o");
+        await conn.ExecuteAsync(@"
+            INSERT INTO attachments (message_id, type, media_type, file_name, data, created_at)
+            VALUES (@MessageId, @Type, @MediaType, @FileName, @Data, @CreatedAt)
+        ", attachment);
+    }
+
+    public async Task<IEnumerable<AttachmentRecord>> GetAttachments(long messageId)
+    {
+        using var conn = CreateConnection();
+        return await conn.QueryAsync<AttachmentRecord>(
+            "SELECT * FROM attachments WHERE message_id = @messageId ORDER BY id",
+            new { messageId });
+    }
+
+    public async Task<IEnumerable<AttachmentRecord>> GetAttachmentsForMessages(IEnumerable<long> messageIds)
+    {
+        using var conn = CreateConnection();
+        return await conn.QueryAsync<AttachmentRecord>(
+            "SELECT * FROM attachments WHERE message_id IN @messageIds ORDER BY id",
+            new { messageIds });
+    }
+
     public async Task<IEnumerable<MessageRecord>> GetChainMessages(string chainId)
     {
         using var conn = CreateConnection();