fix(kiro): 修复 Kiro thinking 流重写按字节截断导致的 UTF-8 边界 panic (#320)

- events.rs: 保留 <thinking>/</thinking> 尾部窗口时改为按 UTF-8 字符边界拆分，避免中文流式 chunk 在 String 切片时 panic
- tests.rs: 抽取 Kiro report_context 构造并补充普通文本/思维块内多字节内容回归测试

apps/aether-gateway/src/ai_pipeline/adaptation/kiro/stream/state/events.rs

@@ -11,6 +11,30 @@ use crate::GatewayError;
 use super::super::AwsEventFrame;
 use super::super::KiroClaudeStreamState;
 
+fn floor_char_boundary(text: &str, index: usize) -> usize {
+    let mut boundary = index.min(text.len());
+    while boundary > 0 && !text.is_char_boundary(boundary) {
+        boundary -= 1;
+    }
+    boundary
+}
+
+fn split_preserving_trailing_bytes(
+    buffer: &str,
+    trailing_bytes: usize,
+) -> Option<(String, String)> {
+    if buffer.len() <= trailing_bytes {
+        return None;
+    }
+
+    let split = floor_char_boundary(buffer, buffer.len() - trailing_bytes);
+    if split == 0 {
+        return None;
+    }
+
+    Some((buffer[..split].to_string(), buffer[split..].to_string()))
+}
+
 impl KiroClaudeStreamState {
     pub(super) fn process_frame(&mut self, frame: AwsEventFrame) -> Result<Vec<u8>, GatewayError> {
         let message_type = frame.headers.message_type().unwrap_or("event");
@@ -150,12 +174,12 @@ impl KiroClaudeStreamState {
                 }
 
                 let keep = "<thinking>".len();
-                if self.thinking_buffer.len() > keep {
-                    let split = self.thinking_buffer.len() - keep;
-                    let safe = self.thinking_buffer[..split].to_string();
+                if let Some((safe, remaining)) =
+                    split_preserving_trailing_bytes(&self.thinking_buffer, keep)
+                {
                     if !safe.trim().is_empty() {
                         events.extend(self.emit_text_delta(&safe));
-                        self.thinking_buffer = self.thinking_buffer[split..].to_string();
+                        self.thinking_buffer = remaining;
                     }
                 }
                 break;
@@ -185,12 +209,12 @@ impl KiroClaudeStreamState {
                 }
 
                 let keep = "</thinking>".len();
-                if self.thinking_buffer.len() > keep {
-                    let split = self.thinking_buffer.len() - keep;
-                    let safe = self.thinking_buffer[..split].to_string();
+                if let Some((safe, remaining)) =
+                    split_preserving_trailing_bytes(&self.thinking_buffer, keep)
+                {
                     if !safe.is_empty() {
                         events.extend(self.emit_thinking_delta(&safe));
-                        self.thinking_buffer = self.thinking_buffer[split..].to_string();
+                        self.thinking_buffer = remaining;
                     }
                 }
                 break;

apps/aether-gateway/src/ai_pipeline/adaptation/kiro/stream/tests.rs

@@ -37,14 +37,26 @@ fn encode_frame(headers: Vec<u8>, payload: Vec<u8>) -> Vec<u8> {
     out
 }
 
-#[test]
-fn kiro_stream_rewriter_converts_text_events_to_claude_sse() {
-    let report_context = json!({
+fn kiro_report_context(thinking_enabled: bool) -> Value {
+    let mut context = json!({
         "provider_api_format": "claude:cli",
         "client_api_format": "claude:cli",
         "envelope_name": "kiro:generateAssistantResponse",
         "mapped_model": "claude-sonnet-4.5"
     });
+    if thinking_enabled {
+        context["original_request_body"] = json!({
+            "thinking": {
+                "type": "enabled"
+            }
+        });
+    }
+    context
+}
+
+#[test]
+fn kiro_stream_rewriter_converts_text_events_to_claude_sse() {
+    let report_context = kiro_report_context(false);
     let mut rewriter = KiroToClaudeCliStreamState::new(&report_context);
     let chunk = [
         encode_event_frame(
@@ -76,12 +88,7 @@ fn kiro_stream_rewriter_converts_text_events_to_claude_sse() {
 
 #[test]
 fn kiro_stream_rewriter_converts_tool_use_to_claude_events() {
-    let report_context = json!({
-        "provider_api_format": "claude:cli",
-        "client_api_format": "claude:cli",
-        "envelope_name": "kiro:generateAssistantResponse",
-        "mapped_model": "claude-sonnet-4.5"
-    });
+    let report_context = kiro_report_context(false);
     let mut rewriter = KiroToClaudeCliStreamState::new(&report_context);
     let chunk = [
         encode_event_frame(
@@ -115,3 +122,45 @@ fn kiro_stream_rewriter_converts_tool_use_to_claude_events() {
     assert!(text.contains("\"partial_json\":\"{\\\"city\\\":\\\"SF\\\"}\""));
     assert!(text.contains("\"stop_reason\":\"tool_use\""));
 }
+
+#[test]
+fn kiro_stream_rewriter_handles_multibyte_text_without_thinking_tag() {
+    let report_context = kiro_report_context(true);
+    let mut rewriter = KiroToClaudeCliStreamState::new(&report_context);
+    let chunk = encode_event_frame(
+        "event",
+        Some("assistantResponseEvent"),
+        &json!({"content": "\n\n你好！有"}),
+    );
+
+    let first = rewriter
+        .push_chunk(&report_context, &chunk)
+        .expect("rewrite should succeed");
+    let rest = rewriter
+        .finish(&report_context)
+        .expect("finish should succeed");
+    let text = String::from_utf8([first, rest].concat()).expect("utf8 should decode");
+    assert!(text.contains("\"type\":\"text_delta\""));
+    assert!(text.contains("你好！有"));
+}
+
+#[test]
+fn kiro_stream_rewriter_handles_multibyte_text_inside_thinking_block() {
+    let report_context = kiro_report_context(true);
+    let mut rewriter = KiroToClaudeCliStreamState::new(&report_context);
+    let chunk = encode_event_frame(
+        "event",
+        Some("assistantResponseEvent"),
+        &json!({"content": "<thinking>\n\n你好！有"}),
+    );
+
+    let first = rewriter
+        .push_chunk(&report_context, &chunk)
+        .expect("rewrite should succeed");
+    let rest = rewriter
+        .finish(&report_context)
+        .expect("finish should succeed");
+    let text = String::from_utf8([first, rest].concat()).expect("utf8 should decode");
+    assert!(text.contains("\"type\":\"thinking_delta\""));
+    assert!(text.contains("你好！有"));
+}