fix(antigravity): preserve Claude tool delta index (#2223)

Gemini response translation wrote OpenAI-shaped bookkeeping into the
shared state.toolCalls map, which the downstream openai-to-claude
translator uses for Claude block metadata. That pre-population skipped
blockIndex creation, so Anthropic input_json_delta events lost index.

Track Gemini function calls via state.geminiToolCallCount instead,
leaving state.toolCalls clean for the Claude translator.

Closes #2218

Co-authored-by: Cursor <cursoragent@cursor.com>

open-sse/translator/response/gemini-to-openai.js

@@ -25,7 +25,10 @@ function emitFunctionCall(functionCall, state) {
     type: OPENAI_BLOCK.FUNCTION,
     function: { name: fcName, arguments: JSON.stringify(fcArgs) },
   };
-  state.toolCalls.set(toolCallIndex, toolCall);
+  // Keep Gemini bookkeeping separate from the shared translator state.toolCalls map.
+  // The downstream OpenAI→Claude translator uses state.toolCalls for Claude block
+  // metadata; pre-populating it here makes Anthropic tool deltas lose index.
+  state.geminiToolCallCount = (state.geminiToolCallCount || 0) + 1;
   return buildChunk(chunkMeta(state), { tool_calls: [toolCall] }, null);
 }
 
@@ -46,6 +49,7 @@ export function geminiToOpenAIResponse(chunk, state) {
     state.messageId = response.responseId || `msg_${Date.now()}`;
     state.model = response.modelVersion || "gemini";
     state.functionIndex = 0;
+    state.geminiToolCallCount = 0;
     results.push(buildChunk(chunkMeta(state), { role: ROLE.ASSISTANT }, null));
   }
 
@@ -117,7 +121,7 @@ export function geminiToOpenAIResponse(chunk, state) {
   // Finish reason - include usage in final chunk
   if (candidate.finishReason) {
     let finishReason = toOpenAIFinish(candidate.finishReason, "gemini");
-    if (finishReason === OPENAI_FINISH.STOP && state.toolCalls.size > 0) {
+    if (finishReason === OPENAI_FINISH.STOP && state.geminiToolCallCount > 0) {
       finishReason = OPENAI_FINISH.TOOL_CALLS;
     }