fix(stream): use io.EOF instead of errors.New("EOF") in SSEReader

errors.New("EOF") creates a distinct error instance that doesn't match
io.EOF, causing processRawHTTPStream to silently ignore normal stream
termination without sending a done response.

- SSEReader: return io.EOF instead of errors.New("EOF")
- processRawHTTPStream: handle io.EOF as normal completion, send done
  response with usage/toolCalls (aligned with processStream behavior)

Fixes #860

Author: voidkey

internal/models/chat/remote_api.go

@@ -546,7 +546,20 @@ func (c *RemoteAPIChat) processRawHTTPStream(ctx context.Context, resp *http.Res
 	for {
 		event, err := reader.ReadEvent()
 		if err != nil {
-			if err != io.EOF {
+			if err == io.EOF {
+				// 部分模型不发送 [DONE] 标记，直接关闭连接，视为正常结束
+				if state.usage != nil {
+					logger.Infof(ctx, "[LLM Usage] model=%s, prompt_tokens=%d, completion_tokens=%d, total_tokens=%d",
+						c.modelName, state.usage.PromptTokens, state.usage.CompletionTokens, state.usage.TotalTokens)
+				}
+				streamChan <- types.StreamResponse{
+					ResponseType: types.ResponseTypeAnswer,
+					Content:      "",
+					Done:         true,
+					ToolCalls:    state.buildOrderedToolCalls(),
+					Usage:        state.usage,
+				}
+			} else {
 				logger.Errorf(ctx, "Stream read error: %v", err)
 				streamChan <- types.StreamResponse{
 					ResponseType: types.ResponseTypeError,

internal/models/chat/sse_reader.go

@@ -2,7 +2,6 @@ package chat
 
 import (
 	"bufio"
-	"errors"
 	"io"
 	"strings"
 )
@@ -55,5 +54,5 @@ func (r *SSEReader) ReadEvent() (*SSEEvent, error) {
 		return nil, err
 	}
 
-	return nil, errors.New("EOF")
+	return nil, io.EOF
 }