refactor(proxy): extract take_sse_block helper with CRLF delimiter support

Replace inline `buffer.find("\n\n")` SSE splitting logic across streaming,
streaming_responses, response_handler, and response_processor with a shared
`take_sse_block` function that handles both `\n\n` and `\r\n\r\n` delimiters.

src-tauri/src/proxy/providers/streaming.rs

@@ -2,7 +2,7 @@
 //!
 //! 实现 OpenAI SSE → Anthropic SSE 格式转换
 
-use crate::proxy::sse::strip_sse_field;
+use crate::proxy::sse::{strip_sse_field, take_sse_block};
 use bytes::Bytes;
 use futures::stream::{Stream, StreamExt};
 use serde::{Deserialize, Serialize};
@@ -110,10 +110,7 @@ pub fn create_anthropic_sse_stream<E: std::error::Error + Send + 'static>(
                     let text = String::from_utf8_lossy(&bytes);
                     buffer.push_str(&text);
 
-                    while let Some(pos) = buffer.find("\n\n") {
-                        let line = buffer[..pos].to_string();
-                        buffer = buffer[pos + 2..].to_string();
-
+                    while let Some(line) = take_sse_block(&mut buffer) {
                         if line.trim().is_empty() {
                             continue;
                         }

src-tauri/src/proxy/providers/streaming_responses.rs

@@ -9,7 +9,7 @@
 //! 与 Chat Completions 的 delta chunk 模型完全不同，需要独立的状态机处理。
 
 use super::transform_responses::{build_anthropic_usage_from_responses, map_responses_stop_reason};
-use crate::proxy::sse::strip_sse_field;
+use crate::proxy::sse::{strip_sse_field, take_sse_block};
 use bytes::Bytes;
 use futures::stream::{Stream, StreamExt};
 use serde_json::{json, Value};
@@ -122,10 +122,7 @@ pub fn create_anthropic_sse_stream_from_responses<E: std::error::Error + Send +
                     buffer.push_str(&text);
 
                     // SSE 事件由 \n\n 分隔
-                    while let Some(pos) = buffer.find("\n\n") {
-                        let block = buffer[..pos].to_string();
-                        buffer = buffer[pos + 2..].to_string();
-
+                    while let Some(block) = take_sse_block(&mut buffer) {
                         if block.trim().is_empty() {
                             continue;
                         }

src-tauri/src/proxy/response_handler.rs

@@ -5,7 +5,7 @@
 use super::session::ProxySession;
 use super::usage::parser::TokenUsage;
 use super::ProxyError;
-use crate::proxy::sse::strip_sse_field;
+use crate::proxy::sse::{strip_sse_field, take_sse_block};
 use bytes::Bytes;
 use futures::stream::{Stream, StreamExt};
 use serde_json::Value;
@@ -86,10 +86,7 @@ impl StreamHandler {
                         buffer.push_str(&text);
 
                         // 提取完整事件
-                        while let Some(pos) = buffer.find("\n\n") {
-                            let event_text = buffer[..pos].to_string();
-                            buffer = buffer[pos + 2..].to_string();
-
+                        while let Some(event_text) = take_sse_block(&mut buffer) {
                             for line in event_text.lines() {
                                 if let Some(data) = strip_sse_field(line, "data") {
                                     if data.trim() != "[DONE]" {

src-tauri/src/proxy/response_processor.rs

@@ -7,7 +7,7 @@ use super::{
     handler_context::{RequestContext, StreamingTimeoutConfig},
     hyper_client::ProxyResponse,
     server::ProxyState,
-    sse::strip_sse_field,
+    sse::{strip_sse_field, take_sse_block},
     usage::parser::TokenUsage,
     ProxyError,
 };
@@ -623,10 +623,7 @@ pub fn create_logged_passthrough_stream(
                     buffer.push_str(&text);
 
                     // 尝试解析并记录完整的 SSE 事件
-                    while let Some(pos) = buffer.find("\n\n") {
-                        let event_text = buffer[..pos].to_string();
-                        buffer = buffer[pos + 2..].to_string();
-
+                    while let Some(event_text) = take_sse_block(&mut buffer) {
                         if !event_text.trim().is_empty() {
                             // 提取 data 部分并尝试解析为 JSON
                             for line in event_text.lines() {

src-tauri/src/proxy/sse.rs

@@ -4,9 +4,27 @@ pub(crate) fn strip_sse_field<'a>(line: &'a str, field: &str) -> Option<&'a str>
         .or_else(|| line.strip_prefix(&format!("{field}:")))
 }
 
+#[inline]
+pub(crate) fn take_sse_block(buffer: &mut String) -> Option<String> {
+    let mut best: Option<(usize, usize)> = None;
+
+    for (delimiter, len) in [("\r\n\r\n", 4usize), ("\n\n", 2usize)] {
+        if let Some(pos) = buffer.find(delimiter) {
+            if best.is_none_or(|(best_pos, _)| pos < best_pos) {
+                best = Some((pos, len));
+            }
+        }
+    }
+
+    let (pos, len) = best?;
+    let block = buffer[..pos].to_string();
+    buffer.drain(..pos + len);
+    Some(block)
+}
+
 #[cfg(test)]
 mod tests {
-    use super::strip_sse_field;
+    use super::{strip_sse_field, take_sse_block};
 
     #[test]
     fn strip_sse_field_accepts_optional_space() {
@@ -28,4 +46,26 @@ mod tests {
         );
         assert_eq!(strip_sse_field("id:1", "data"), None);
     }
+
+    #[test]
+    fn take_sse_block_supports_lf_delimiters() {
+        let mut buffer = "data: {\"ok\":true}\n\nrest".to_string();
+
+        assert_eq!(
+            take_sse_block(&mut buffer),
+            Some("data: {\"ok\":true}".to_string())
+        );
+        assert_eq!(buffer, "rest");
+    }
+
+    #[test]
+    fn take_sse_block_supports_crlf_delimiters() {
+        let mut buffer = "data: {\"ok\":true}\r\n\r\nrest".to_string();
+
+        assert_eq!(
+            take_sse_block(&mut buffer),
+            Some("data: {\"ok\":true}".to_string())
+        );
+        assert_eq!(buffer, "rest");
+    }
 }