fix: normalize finish_reason to 'tool_calls' when tool calls are present (#379)

Some upstream providers (e.g. Antigravity) return non-standard finish_reason
values like 'other' instead of the OpenAI-standard 'tool_calls' when the
model invokes tools. This causes downstream consumers (e.g. OpenClaw) to
fail to execute tool calls, breaking agentic sub-agent workflows.

Changes:
- nonStreamingHandler: post-translation guard that normalizes finish_reason
  to 'tool_calls' when message.tool_calls is present
- sseToJsonHandler: accumulate tool_calls from streaming deltas in
  parseSSEToOpenAIResponse; extract function_call items from Responses API
  output in handleForcedSSEToJson
- openai-responses translator: use toolCallIndex to choose between
  'tool_calls' and 'stop' in flush and response.completed events

Tested: 7 scenarios (non-stream text, single/multiple tool calls, stream
text/tool calls, multi-turn tool conversation, tools present but unused)

open-sse/handlers/chatCore/nonStreamingHandler.js

@@ -161,6 +161,16 @@ export async function handleNonStreamingResponse({ providerResponse, provider, m
     ? translateNonStreamingResponse(responseBody, targetFormat, sourceFormat)
     : responseBody;
 
+  // Fix finish_reason for tool_calls: some providers return non-standard values (e.g. "other")
+  if (translatedResponse?.choices?.[0]) {
+    const choice = translatedResponse.choices[0];
+    const msg = choice.message;
+    const hasToolCalls = Array.isArray(msg?.tool_calls) && msg.tool_calls.length > 0;
+    if (hasToolCalls && choice.finish_reason !== "tool_calls") {
+      choice.finish_reason = "tool_calls";
+    }
+  }
+
   // Ensure OpenAI-required fields
   if (!translatedResponse.object) translatedResponse.object = "chat.completion";
   if (!translatedResponse.created) translatedResponse.created = Math.floor(Date.now() / 1000);