fix(streaming): align finish_reason logic with non-streaming path

The streaming path (ChatCompletionsStreamingAdapter) now correctly maps
TOOL_SUSPENDED and MAX_ITERATIONS to finish_reason, matching the behavior
of the non-streaming path (ChatCompletionsResponseBuilder).

Previously, the streaming path only checked for ToolUseBlock presence,
which could lead to inconsistent behavior:
- TOOL_SUSPENDED was typically unaffected (ToolUseBlock always present)
- MAX_ITERATIONS would incorrectly return 'stop' instead of 'length'

Changes:
- Check event.getMessage().getGenerateReason() in isLast branch
- Map TOOL_SUSPENDED -> 'tool_calls'
- Map MAX_ITERATIONS -> 'length'
- Fall back to ToolUseBlock check for other cases

This ensures consistent finish_reason behavior between streaming and
non-streaming responses.

Resolves review comment from LearningGp.

Author: Alexxigang

agentscope-extensions/agentscope-extensions-chat-completions-web/src/main/java/io/agentscope/core/chat/completions/streaming/ChatCompletionsStreamingAdapter.java

@@ -24,6 +24,7 @@
 import io.agentscope.core.chat.completions.model.ChatCompletionsChunk;
 import io.agentscope.core.chat.completions.model.ToolCall;
 import io.agentscope.core.message.ContentBlock;
+import io.agentscope.core.message.GenerateReason;
 import io.agentscope.core.message.Msg;
 import io.agentscope.core.message.TextBlock;
 import io.agentscope.core.message.ToolResultBlock;
@@ -250,9 +251,23 @@ private Flux<ChatCompletionsChunk> convertEventToChunksInternal(
 
         // Add finish chunk if this is the last event
         if (event.isLast()) {
-            boolean hasToolCalls =
-                    contentBlocks.stream().anyMatch(block -> block instanceof ToolUseBlock);
-            String finishReason = hasToolCalls ? "tool_calls" : "stop";
+            // Determine finish reason based on GenerateReason or tool calls
+            // This mirrors the logic in ChatCompletionsResponseBuilder
+            String finishReason;
+            GenerateReason generateReason =
+                    event.getMessage() != null ? event.getMessage().getGenerateReason() : null;
+
+            if (generateReason == GenerateReason.TOOL_SUSPENDED) {
+                finishReason = "tool_calls";
+            } else if (generateReason == GenerateReason.MAX_ITERATIONS) {
+                finishReason = "length";
+            } else {
+                // Fall back to checking for tool calls in content
+                boolean hasToolCalls =
+                        contentBlocks.stream().anyMatch(block -> block instanceof ToolUseBlock);
+                finishReason = hasToolCalls ? "tool_calls" : "stop";
+            }
+
             chunks.add(ChatCompletionsChunk.finishChunk(requestId, model, finishReason));
         }