fix(cursor): stabilize tool result handoff for Cursor tool calls (#275)

- Stop double-translation in Cursor executor path (preserved tool_results)
- Normalize OpenAI+Anthropic tool flows into Cursor-compatible shapes
- escapeXml() prevents tag injection in tool_result blocks
- Set-based finalizedIds for O(1) deduplication (replaces O(n) .find)
- Byte guard (0x7b) before payload.toString on non-JSON frames
- Convert console.log noise to debugLog() (prod clean)

Fixes #274. Reviewed-by: Antigravity

open-sse/executors/cursor.ts

@@ -29,7 +29,6 @@ import {
 } from "../utils/cursorProtobuf.ts";
 import { estimateUsage } from "../utils/usageTracking.ts";
 import { FORMATS } from "../translator/formats.ts";
-import { buildCursorRequest } from "../translator/request/openai-to-cursor.ts";
 import crypto from "crypto";
 import { v5 as uuidv5 } from "uuid";
 import zlib from "zlib";
@@ -59,13 +58,18 @@ const COMPRESS_FLAG = {
   GZIP_BOTH: 0x03,
 };
 
+const CURSOR_STREAM_DEBUG = process.env.CURSOR_STREAM_DEBUG === "1";
+const debugLog = (...args: unknown[]) => {
+  if (CURSOR_STREAM_DEBUG) console.log(...args);
+};
+
 function decompressPayload(payload, flags) {
   // Check if payload is JSON error (starts with {"error")
   if (payload.length > 10 && payload[0] === 0x7b && payload[1] === 0x22) {
     try {
       const text = payload.toString("utf-8");
       if (text.startsWith('{"error"')) {
-        console.log(`[DECOMPRESS] Detected JSON error, skipping decompression`);
+        debugLog(`[DECOMPRESS] Detected JSON error, skipping decompression`);
         return payload;
       }
     } catch {}
@@ -89,14 +93,14 @@ function decompressPayload(payload, flags) {
         try {
           return zlib.inflateRawSync(payload);
         } catch (rawErr) {
-          console.log(
+          debugLog(
             `[DECOMPRESS ERROR] flags=${flags}, payloadSize=${payload.length}, gzip=${gzipErr.message}, deflate=${deflateErr.message}, raw=${rawErr.message}`
           );
-          console.log(
+          debugLog(
             `[DECOMPRESS ERROR] First 50 bytes (hex):`,
             payload.slice(0, 50).toString("hex")
           );
-          console.log(
+          debugLog(
             `[DECOMPRESS ERROR] First 50 bytes (utf8):`,
             payload
               .slice(0, 50)
@@ -136,6 +140,41 @@ function createErrorResponse(jsonError) {
   );
 }
 
+function parseCursorJsonErrorFrame(text: string) {
+  try {
+    return JSON.parse(text);
+  } catch {
+    return null;
+  }
+}
+
+function isToolBoundaryAbort(jsonError: any, toolCallCount: number) {
+  if (!jsonError || toolCallCount <= 0) return false;
+  const code = jsonError?.error?.code || "";
+  const debugError = jsonError?.error?.details?.[0]?.debug?.error || "";
+  const title = jsonError?.error?.details?.[0]?.debug?.details?.title || "";
+  const detail = jsonError?.error?.details?.[0]?.debug?.details?.detail || "";
+  const message = `${title} ${detail}`.toLowerCase();
+  const isAbortedCode = code === "aborted" || debugError === "ERROR_USER_ABORTED_REQUEST";
+  return isAbortedCode && message.includes("tool call ended before result was received");
+}
+
+function mergeToolCallDelta(existing, incoming) {
+  const mergedName = incoming?.function?.name || existing?.function?.name || "";
+  const existingArgs = existing?.function?.arguments || "";
+  const deltaArgs = incoming?.function?.arguments || "";
+  return {
+    id: incoming.id || existing.id,
+    type: "function",
+    function: {
+      name: mergedName,
+      arguments: `${existingArgs}${deltaArgs}`,
+    },
+    isLast: Boolean(existing?.isLast || incoming?.isLast),
+    index: existing?.index ?? incoming?.index ?? 0,
+  };
+}
+
 type CursorHttpResponse = {
   status: number;
   headers: Record<string, unknown>;
@@ -230,10 +269,10 @@ export class CursorExecutor extends BaseExecutor {
   }
 
   transformRequest(model, body, stream, credentials) {
-    // Call translator to convert OpenAI format to Cursor format
-    const translatedBody = buildCursorRequest(model, body, stream, credentials);
-    const messages = translatedBody.messages || [];
-    const tools = translatedBody.tools || body.tools || [];
+    // Messages are already translated by chatCore (claude→openai→cursor)
+    // Do NOT call buildCursorRequest again — double-translation drops tool_results
+    const messages = body.messages || [];
+    const tools = body.tools || [];
     const reasoningEffort = body.reasoning_effort || null;
     return generateCursorBody(messages, model, tools, reasoningEffort);
   }
@@ -379,13 +418,14 @@ export class CursorExecutor extends BaseExecutor {
     let totalContent = "";
     const toolCalls = [];
     const toolCallsMap = new Map(); // Track streaming tool calls by ID
+    const finalizedIds = new Set<string>();
     let frameCount = 0;
 
-    console.log(`[CURSOR BUFFER] Total length: ${buffer.length} bytes`);
+    debugLog(`[CURSOR BUFFER] Total length: ${buffer.length} bytes`);
 
     while (offset < buffer.length) {
       if (offset + 5 > buffer.length) {
-        console.log(
+        debugLog(
           `[CURSOR BUFFER] Reached end, offset=${offset}, remaining=${buffer.length - offset}`
         );
         break;
@@ -394,12 +434,12 @@ export class CursorExecutor extends BaseExecutor {
       const flags = buffer[offset];
       const length = buffer.readUInt32BE(offset + 1);
 
-      console.log(
+      debugLog(
         `[CURSOR BUFFER] Frame ${frameCount + 1}: flags=0x${flags.toString(16).padStart(2, "0")}, length=${length}`
       );
 
       if (offset + 5 + length > buffer.length) {
-        console.log(
+        debugLog(
           `[CURSOR BUFFER] Incomplete frame, offset=${offset}, length=${length}, buffer.length=${buffer.length}`
         );
         break;
@@ -411,21 +451,37 @@ export class CursorExecutor extends BaseExecutor {
 
       payload = decompressPayload(payload, flags);
       if (!payload) {
-        console.log(`[CURSOR BUFFER] Frame ${frameCount}: decompression failed, skipping`);
+        debugLog(`[CURSOR BUFFER] Frame ${frameCount}: decompression failed, skipping`);
         continue;
       }
 
-      try {
-        const text = payload.toString("utf-8");
-        if (text.startsWith("{") && text.includes('"error"')) {
-          return createErrorResponse(JSON.parse(text));
-        }
-      } catch {}
+      // Check for JSON error frames (byte guard: skip toString on non-JSON frames)
+      if (payload.length > 0 && payload[0] === 0x7b) {
+        try {
+          const text = payload.toString("utf-8");
+          if (text.includes('"error"')) {
+            const hasContent = totalContent || toolCallsMap.size > 0;
+            debugLog(
+              `[CURSOR BUFFER] Error frame (hasContent=${hasContent}): ${text.slice(0, 500)}`
+            );
+            if (hasContent) {
+              break;
+            }
+            return createErrorResponse(JSON.parse(text));
+          }
+        } catch {}
+      }
 
       const result = extractTextFromResponse(new Uint8Array(payload));
-      console.log(`[CURSOR DECODED] Frame ${frameCount}:`, result);
+      debugLog(`[CURSOR DECODED] Frame ${frameCount}:`, result);
 
       if (result.error) {
+        const hasContent = totalContent || toolCallsMap.size > 0;
+        debugLog(`[CURSOR BUFFER] Decoded error (hasContent=${hasContent}): ${result.error}`);
+        // If we already have content, treat error as stream termination
+        if (hasContent) {
+          break;
+        }
         return new Response(
           JSON.stringify({
             error: {
@@ -457,6 +513,7 @@ export class CursorExecutor extends BaseExecutor {
         // Push to final array when isLast is true
         if (tc.isLast) {
           const finalToolCall = toolCallsMap.get(tc.id);
+          finalizedIds.add(tc.id);
           toolCalls.push({
             id: finalToolCall.id,
             type: finalToolCall.type,
@@ -471,15 +528,15 @@ export class CursorExecutor extends BaseExecutor {
       if (result.text) totalContent += result.text;
     }
 
-    console.log(
+    debugLog(
       `[CURSOR BUFFER] Parsed ${frameCount} frames, toolCallsMap size: ${toolCallsMap.size}, finalized toolCalls: ${toolCalls.length}`
     );
 
     // Finalize all remaining tool calls in map (in case stream ended without isLast=true)
     for (const [id, tc] of toolCallsMap.entries()) {
       // Check if already in final array
-      if (!toolCalls.find((t) => t.id === id)) {
-        console.log(`[CURSOR BUFFER] Finalizing incomplete tool call: ${id}, isLast=${tc.isLast}`);
+      if (!finalizedIds.has(id)) {
+        debugLog(`[CURSOR BUFFER] Finalizing incomplete tool call: ${id}, isLast=${tc.isLast}`);
         toolCalls.push({
           id: tc.id,
           type: tc.type,
@@ -491,7 +548,7 @@ export class CursorExecutor extends BaseExecutor {
       }
     }
 
-    console.log(`[CURSOR BUFFER] Final toolCalls count: ${toolCalls.length}`);
+    debugLog(`[CURSOR BUFFER] Final toolCalls count: ${toolCalls.length}`);
 
     const message: Record<string, unknown> = {
       role: "assistant",
@@ -534,13 +591,15 @@ export class CursorExecutor extends BaseExecutor {
     let totalContent = "";
     const toolCalls = [];
     const toolCallsMap = new Map(); // Track streaming tool calls by ID
+    const finalizedIds = new Set<string>();
+    const emittedToolCallIds = new Set<string>();
     let frameCount = 0;
 
-    console.log(`[CURSOR BUFFER SSE] Total length: ${buffer.length} bytes`);
+    debugLog(`[CURSOR BUFFER SSE] Total length: ${buffer.length} bytes`);
 
     while (offset < buffer.length) {
       if (offset + 5 > buffer.length) {
-        console.log(
+        debugLog(
           `[CURSOR BUFFER SSE] Reached end, offset=${offset}, remaining=${buffer.length - offset}`
         );
         break;
@@ -549,12 +608,12 @@ export class CursorExecutor extends BaseExecutor {
       const flags = buffer[offset];
       const length = buffer.readUInt32BE(offset + 1);
 
-      console.log(
+      debugLog(
         `[CURSOR BUFFER SSE] Frame ${frameCount + 1}: flags=0x${flags.toString(16).padStart(2, "0")}, length=${length}`
       );
 
       if (offset + 5 + length > buffer.length) {
-        console.log(
+        debugLog(
           `[CURSOR BUFFER SSE] Incomplete frame, offset=${offset}, length=${length}, buffer.length=${buffer.length}`
         );
         break;
@@ -566,21 +625,37 @@ export class CursorExecutor extends BaseExecutor {
 
       payload = decompressPayload(payload, flags);
       if (!payload) {
-        console.log(`[CURSOR BUFFER SSE] Frame ${frameCount}: decompression failed, skipping`);
+        debugLog(`[CURSOR BUFFER SSE] Frame ${frameCount}: decompression failed, skipping`);
         continue;
       }
 
-      try {
-        const text = payload.toString("utf-8");
-        if (text.startsWith("{") && text.includes('"error"')) {
-          return createErrorResponse(JSON.parse(text));
-        }
-      } catch {}
+      // Check for JSON error frames (byte-guard: only decode if starts with '{')
+      if (payload[0] === 0x7b) {
+        try {
+          const text = payload.toString("utf-8");
+          if (text.includes('"error"')) {
+            const hasContent = chunks.length > 0 || totalContent || toolCallsMap.size > 0;
+            debugLog(
+              `[CURSOR BUFFER SSE] Error frame (hasContent=${hasContent}): ${text.slice(0, 500)}`
+            );
+            if (hasContent) {
+              break;
+            }
+            return createErrorResponse(JSON.parse(text));
+          }
+        } catch {}
+      }
 
       const result = extractTextFromResponse(new Uint8Array(payload));
-      console.log(`[CURSOR DECODED SSE] Frame ${frameCount}:`, result);
+      debugLog(`[CURSOR DECODED SSE] Frame ${frameCount}:`, result);
 
       if (result.error) {
+        const hasContent = chunks.length > 0 || totalContent || toolCallsMap.size > 0;
+        debugLog(`[CURSOR BUFFER SSE] Decoded error (hasContent=${hasContent}): ${result.error}`);
+        // If we already have content, treat error as stream termination
+        if (hasContent) {
+          break;
+        }
         return new Response(
           JSON.stringify({
             error: {
@@ -626,6 +701,7 @@ export class CursorExecutor extends BaseExecutor {
 
           // Stream the delta arguments
           if (tc.function.arguments) {
+            emittedToolCallIds.add(tc.id);
             chunks.push(
               `data: ${JSON.stringify({
                 id: responseId,
@@ -657,10 +733,12 @@ export class CursorExecutor extends BaseExecutor {
         } else {
           // New tool call - assign index and add to map
           const toolCallIndex = toolCalls.length;
+          finalizedIds.add(tc.id);
           toolCalls.push({ ...tc, index: toolCallIndex });
           toolCallsMap.set(tc.id, { ...tc, index: toolCallIndex });
 
           // Stream initial tool call with name
+          emittedToolCallIds.add(tc.id);
           chunks.push(
             `data: ${JSON.stringify({
               id: responseId,
@@ -714,10 +792,58 @@ export class CursorExecutor extends BaseExecutor {
       }
     }
 
-    console.log(
+    debugLog(
       `[CURSOR BUFFER SSE] Parsed ${frameCount} frames, toolCallsMap size: ${toolCallsMap.size}, toolCalls array: ${toolCalls.length}`
     );
 
+    // Finalize all remaining tool calls in map (stream may have ended without isLast=true)
+    for (const [id, tc] of toolCallsMap.entries()) {
+      if (!finalizedIds.has(id)) {
+        debugLog(`[CURSOR BUFFER SSE] Finalizing incomplete tool call: ${id}, isLast=${tc.isLast}`);
+        const toolCallIndex = toolCalls.length;
+        toolCalls.push({
+          id: tc.id,
+          type: tc.type,
+          index: toolCallIndex,
+          function: {
+            name: tc.function.name,
+            arguments: tc.function.arguments,
+          },
+        });
+
+        // Emit SSE chunk for the finalized tool call if not already emitted
+        if (!emittedToolCallIds.has(tc.id)) {
+          chunks.push(
+            `data: ${JSON.stringify({
+              id: responseId,
+              object: "chat.completion.chunk",
+              created,
+              model,
+              choices: [
+                {
+                  index: 0,
+                  delta: {
+                    tool_calls: [
+                      {
+                        index: toolCallIndex,
+                        id: tc.id,
+                        type: "function",
+                        function: {
+                          name: tc.function.name,
+                          arguments: tc.function.arguments,
+                        },
+                      },
+                    ],
+                  },
+                  finish_reason: null,
+                },
+              ],
+            })}\n\n`
+          );
+        }
+      }
+    }
+
     if (chunks.length === 0 && toolCalls.length === 0) {
       chunks.push(
         `data: ${JSON.stringify({

open-sse/translator/request/openai-to-cursor.ts

@@ -1,19 +1,84 @@
 /**
  * OpenAI to Cursor Request Translator
- * Converts OpenAI messages to Cursor simple format
+ * Converts OpenAI messages to Cursor ask/agent format.
+ *
+ * Important: Cursor can loop when tool outputs are sent via protobuf tool_results
+ * with partial schema mismatches. For stability, tool outputs are represented as
+ * structured text blocks in user messages.
  */
 import { register } from "../registry.ts";
 import { FORMATS } from "../formats.ts";
 
-/**
- * Convert OpenAI messages to Cursor format with native tool_results support
- * - system → user with [System Instructions] prefix
- * - tool → accumulate into tool_results array for next user/assistant message
- * - assistant with tool_calls → keep tool_calls structure (Cursor supports it natively)
- */
+type TextPart = { type?: string; text?: string };
+type ToolUsePart = { type?: string; id?: string; name?: string; input?: unknown };
+type ToolResultPart = { type?: string; tool_use_id?: string; content?: unknown };
+
+function normalizeToolCallId(id: unknown): string {
+  return typeof id === "string" ? id.split("\n")[0] : "";
+}
+
+function extractContent(content: unknown): string {
+  if (typeof content === "string") return content;
+  if (Array.isArray(content)) {
+    return content
+      .filter((part): part is TextPart => {
+        if (!part || typeof part !== "object") return false;
+        const maybe = part as TextPart;
+        return maybe.type === "text" && typeof maybe.text === "string";
+      })
+      .map((part) => part.text as string)
+      .join("");
+  }
+  return "";
+}
+
+function sanitizeToolResultText(text: string): string {
+  // Strip non-printable control chars that can produce backend request errors.
+  return text.replace(/[\u0000-\u0008\u000B\u000C\u000E-\u001F\u007F]/g, "");
+}
+
+function escapeXml(text: string): string {
+  return text.replace(/&/g, "&amp;").replace(/</g, "&lt;").replace(/>/g, "&gt;");
+}
+
+function buildToolResultBlock(toolName: string, toolCallId: string, resultText: string): string {
+  const cleanResult = sanitizeToolResultText(resultText || "");
+  return [
+    "<tool_result>",
+    `<tool_name>${escapeXml(toolName || "tool")}</tool_name>`,
+    `<tool_call_id>${escapeXml(toolCallId || "")}</tool_call_id>`,
+    `<result>${escapeXml(cleanResult)}</result>`,
+    "</tool_result>",
+  ].join("\n");
+}
+
 function convertMessages(messages) {
   const result = [];
-  let pendingToolResults = [];
+  // Build a map of tool_call_id -> tool name from assistant tool calls.
+  const toolCallMetaMap = new Map();
+  const rememberToolMeta = (toolCallId: string, toolName: string) => {
+    if (!toolCallId) return;
+    const name = toolName || "tool";
+    toolCallMetaMap.set(toolCallId, { name });
+    const normalized = normalizeToolCallId(toolCallId);
+    if (normalized && normalized !== toolCallId) {
+      toolCallMetaMap.set(normalized, { name });
+    }
+  };
+
+  for (const msg of messages) {
+    if (msg.role === "assistant" && msg.tool_calls) {
+      for (const tc of msg.tool_calls) {
+        rememberToolMeta(tc.id || "", tc.function?.name || "tool");
+      }
+    }
+    if (msg.role === "assistant" && Array.isArray(msg.content)) {
+      for (const part of msg.content as ToolUsePart[]) {
+        if (part?.type !== "tool_use") continue;
+        rememberToolMeta(part.id || "", part.name || "tool");
+      }
+    }
+  }
 
   for (let i = 0; i < messages.length; i++) {
     const msg = messages[i];
@@ -21,83 +86,89 @@ function convertMessages(messages) {
     if (msg.role === "system") {
       result.push({
         role: "user",
-        content: `[System Instructions]\n${msg.content}`,
+        content: `[System Instructions]\n${extractContent(msg.content)}`,
       });
       continue;
     }
 
     if (msg.role === "tool") {
-      let toolContent = "";
-      if (typeof msg.content === "string") {
-        toolContent = msg.content;
-      } else if (Array.isArray(msg.content)) {
-        for (const part of msg.content) {
-          if (part.type === "text") {
-            toolContent += part.text;
-          }
-        }
-      }
-
-      const toolName = msg.name || "tool";
+      const toolContent = extractContent(msg.content);
       const toolCallId = msg.tool_call_id || "";
-
-      // Accumulate tool result
-      pendingToolResults.push({
-        tool_call_id: toolCallId,
-        name: toolName,
-        index: pendingToolResults.length,
-        raw_args: toolContent,
+      const toolMeta = toolCallMetaMap.get(toolCallId) || {};
+      const toolName = msg.name || toolMeta.name || "tool";
+      result.push({
+        role: "user",
+        content: buildToolResultBlock(toolName, toolCallId, toolContent),
       });
       continue;
     }
 
     if (msg.role === "user" || msg.role === "assistant") {
-      let content = "";
-
-      if (typeof msg.content === "string") {
-        content = msg.content;
-      } else if (Array.isArray(msg.content)) {
-        for (const part of msg.content) {
-          if (part.type === "text") {
-            content += part.text;
+      if (msg.role === "user" && Array.isArray(msg.content)) {
+        const parts: string[] = [];
+        for (const block of msg.content as Array<TextPart | ToolResultPart>) {
+          if (!block || typeof block !== "object") continue;
+          if (block.type === "text") {
+            if (typeof (block as TextPart).text === "string") {
+              parts.push((block as TextPart).text || "");
+            }
+            continue;
+          }
+          if (block.type === "tool_result") {
+            const tr = block as ToolResultPart;
+            const toolCallId = tr.tool_use_id || "";
+            const toolMeta =
+              toolCallMetaMap.get(toolCallId) ||
+              toolCallMetaMap.get(normalizeToolCallId(toolCallId));
+            const toolName = toolMeta?.name || "tool";
+            const toolContent = extractContent(tr.content);
+            parts.push(buildToolResultBlock(toolName, toolCallId, toolContent));
           }
         }
+        const joined = parts.filter(Boolean).join("\n");
+        if (joined) result.push({ role: "user", content: joined });
+        continue;
       }
 
-      // Keep tool_calls structure for assistant messages
+      const content = extractContent(msg.content);
+
       if (msg.role === "assistant" && msg.tool_calls && msg.tool_calls.length > 0) {
         const assistantMsg: {
           role: string;
           content?: string;
           tool_calls?: unknown;
-          tool_results?: Array<Record<string, unknown>>;
-        } = { role: "assistant" };
-        if (content) {
-          assistantMsg.content = content;
-        }
-        assistantMsg.tool_calls = msg.tool_calls;
-
-        // Attach pending tool results to assistant message with tool_calls
-        if (pendingToolResults.length > 0) {
-          assistantMsg.tool_results = pendingToolResults;
-          pendingToolResults = [];
-        }
-
+        } = { role: "assistant", content: content || "" };
+        assistantMsg.tool_calls = msg.tool_calls.map((tc) => {
+          const { index, ...rest } = tc || {};
+          return rest;
+        });
         result.push(assistantMsg);
-      } else if (content || pendingToolResults.length > 0) {
-        const msgObj: {
-          role: string;
-          content: string;
-          tool_results?: Array<Record<string, unknown>>;
-        } = { role: msg.role, content: content || "" };
+      } else if (msg.role === "assistant" && Array.isArray(msg.content)) {
+        const extractedToolCalls = (msg.content as ToolUsePart[])
+          .filter((b) => b?.type === "tool_use")
+          .map((b) => ({
+            id: b.id || "",
+            type: "function",
+            function: {
+              name: b.name || "tool",
+              arguments: JSON.stringify(b.input || {}),
+            },
+          }))
+          .filter((tc) => tc.id);
 
-        // Attach pending tool results to this message
-        if (pendingToolResults.length > 0) {
-          msgObj.tool_results = pendingToolResults;
-          pendingToolResults = [];
+        if (extractedToolCalls.length > 0) {
+          result.push({
+            role: "assistant",
+            content: content || "",
+            tool_calls: extractedToolCalls,
+          });
+        } else if (content) {
+          result.push({ role: "assistant", content });
+        }
+      } else {
+        if (content) {
+          result.push({ role: msg.role, content });
         }
-
-        result.push(msgObj);
       }
     }
   }

open-sse/utils/cursorProtobuf.ts

@@ -10,8 +10,9 @@
 import { v4 as uuidv4 } from "uuid";
 import zlib from "zlib";
 
-const DEBUG = true;
+const DEBUG = process.env.CURSOR_PROTOBUF_DEBUG === "1";
 const log = (tag, ...args) => DEBUG && console.log(`[PROTOBUF:${tag}]`, ...args);
+const textDecoder = new TextDecoder();
 
 /**
  * Schema version — bump when updating field definitions.
@@ -28,6 +29,7 @@ const ROLE = { USER: 1, ASSISTANT: 2 };
 const UNIFIED_MODE = { CHAT: 1, AGENT: 2 };
 
 const THINKING_LEVEL = { UNSPECIFIED: 0, MEDIUM: 1, HIGH: 2 };
+const CLIENT_SIDE_TOOL_V2 = { MCP: 19 };
 
 const FIELD = {
   // StreamUnifiedChatRequestWithTools (top level)
@@ -74,6 +76,28 @@ const FIELD = {
   TOOL_RESULT_INDEX: 3,
   TOOL_RESULT_RAW_ARGS: 5,
   TOOL_RESULT_RESULT: 8,
+  TOOL_RESULT_TOOL_CALL: 11,
+  TOOL_RESULT_MODEL_CALL_ID: 12,
+
+  // ClientSideToolV2Result (nested inside ToolResult.result)
+  CLIENT_RESULT_TOOL: 1,
+  CLIENT_RESULT_MCP_RESULT: 28,
+  CLIENT_RESULT_TOOL_CALL_ID: 35,
+  CLIENT_RESULT_MODEL_CALL_ID: 48,
+  CLIENT_RESULT_TOOL_INDEX: 49,
+
+  // MCPResult (nested inside ClientSideToolV2Result.mcp_result)
+  MCP_RESULT_SELECTED_TOOL: 1,
+  MCP_RESULT_RESULT: 2,
+
+  // ClientSideToolV2Call (nested inside ToolResult.tool_call)
+  CLIENT_CALL_TOOL: 1,
+  CLIENT_CALL_MCP_PARAMS: 27,
+  CLIENT_CALL_TOOL_CALL_ID: 3,
+  CLIENT_CALL_NAME: 9,
+  CLIENT_CALL_RAW_ARGS: 10,
+  CLIENT_CALL_TOOL_INDEX: 48,
+  CLIENT_CALL_MODEL_CALL_ID: 49,
 
   // Model
   MODEL_NAME: 1,
@@ -120,6 +144,7 @@ const FIELD = {
   TOOL_NAME: 9,
   TOOL_RAW_ARGS: 10,
   TOOL_IS_LAST: 11,
+  TOOL_IS_LAST_ALT: 15,
   TOOL_MCP_PARAMS: 27,
 
   // MCPParams
@@ -202,16 +227,149 @@ function concatArrays(...arrays) {
 // ==================== MESSAGE ENCODING ====================
 
 export function encodeToolResult(toolResult) {
-  const toolCallId = toolResult.tool_call_id || "";
-  const toolName = toolResult.name || "";
-  const toolIndex = toolResult.index || 0;
+  const { toolCallId, modelCallId } = parseToolCallId(toolResult.tool_call_id || "");
+  const rawToolName = toolResult.name || "";
+  const toolName = formatCursorToolName(rawToolName);
+  const { selectedTool, serverName } = parseCursorToolName(toolName);
+  const toolIndex = toolResult.index > 0 ? toolResult.index : 1;
   const rawArgs = toolResult.raw_args || "{}";
+  const resultContent = toolResult.result || "";
+  const encodedResultMessage = encodeClientSideToolResult(
+    toolCallId,
+    modelCallId,
+    selectedTool,
+    toolIndex,
+    resultContent
+  );
+  const encodedToolCallMessage = encodeClientSideToolCall(
+    toolCallId,
+    modelCallId,
+    toolName,
+    selectedTool,
+    serverName,
+    rawArgs,
+    toolIndex
+  );
 
   return concatArrays(
     encodeField(FIELD.TOOL_RESULT_CALL_ID, WIRE_TYPE.LEN, toolCallId),
     encodeField(FIELD.TOOL_RESULT_NAME, WIRE_TYPE.LEN, toolName),
     encodeField(FIELD.TOOL_RESULT_INDEX, WIRE_TYPE.VARINT, toolIndex),
-    encodeField(FIELD.TOOL_RESULT_RAW_ARGS, WIRE_TYPE.LEN, rawArgs)
+    ...(modelCallId
+      ? [encodeField(FIELD.TOOL_RESULT_MODEL_CALL_ID, WIRE_TYPE.LEN, modelCallId)]
+      : []),
+    encodeField(FIELD.TOOL_RESULT_RAW_ARGS, WIRE_TYPE.LEN, rawArgs),
+    ...(encodedResultMessage
+      ? [encodeField(FIELD.TOOL_RESULT_RESULT, WIRE_TYPE.LEN, encodedResultMessage)]
+      : []),
+    encodeField(FIELD.TOOL_RESULT_TOOL_CALL, WIRE_TYPE.LEN, encodedToolCallMessage)
+  );
+}
+
+function parseToolCallId(toolCallIdRaw) {
+  if (typeof toolCallIdRaw !== "string" || toolCallIdRaw.length === 0) {
+    return { toolCallId: "", modelCallId: null };
+  }
+  const delimiter = "\nmc_";
+  const idx = toolCallIdRaw.indexOf(delimiter);
+  if (idx >= 0) {
+    return {
+      toolCallId: toolCallIdRaw.slice(0, idx),
+      modelCallId: toolCallIdRaw.slice(idx + delimiter.length),
+    };
+  }
+  return { toolCallId: toolCallIdRaw, modelCallId: null };
+}
+
+function formatCursorToolName(rawName) {
+  const base = typeof rawName === "string" && rawName.length > 0 ? rawName : "tool";
+
+  if (base.startsWith("mcp__")) {
+    const rest = base.slice("mcp__".length);
+    const splitIdx = rest.indexOf("__");
+    if (splitIdx >= 0) {
+      const server = rest.slice(0, splitIdx) || "custom";
+      const name = rest.slice(splitIdx + 2) || "tool";
+      return `mcp_${server}_${name}`;
+    }
+    return `mcp_custom_${rest || "tool"}`;
+  }
+
+  if (base.startsWith("mcp_")) return base;
+  return `mcp_custom_${base}`;
+}
+
+function parseCursorToolName(formattedName) {
+  if (typeof formattedName !== "string" || !formattedName.startsWith("mcp_")) {
+    return { serverName: "custom", selectedTool: formattedName || "tool" };
+  }
+
+  const tail = formattedName.slice("mcp_".length);
+  const splitIdx = tail.indexOf("_");
+  if (splitIdx < 0) {
+    return { serverName: "custom", selectedTool: tail || "tool" };
+  }
+
+  return {
+    serverName: tail.slice(0, splitIdx) || "custom",
+    selectedTool: tail.slice(splitIdx + 1) || "tool",
+  };
+}
+
+function encodeClientSideToolResult(toolCallId, modelCallId, toolName, toolIndex, resultContent) {
+  const outputText = typeof resultContent === "string" ? resultContent : "";
+  const selectedTool = typeof toolName === "string" && toolName.length > 0 ? toolName : "tool";
+
+  const mcpResult = concatArrays(
+    encodeField(FIELD.MCP_RESULT_SELECTED_TOOL, WIRE_TYPE.LEN, selectedTool),
+    encodeField(FIELD.MCP_RESULT_RESULT, WIRE_TYPE.LEN, outputText)
+  );
+
+  return concatArrays(
+    encodeField(FIELD.CLIENT_RESULT_TOOL, WIRE_TYPE.VARINT, CLIENT_SIDE_TOOL_V2.MCP),
+    encodeField(FIELD.CLIENT_RESULT_MCP_RESULT, WIRE_TYPE.LEN, mcpResult),
+    ...(toolCallId
+      ? [encodeField(FIELD.CLIENT_RESULT_TOOL_CALL_ID, WIRE_TYPE.LEN, toolCallId)]
+      : []),
+    ...(modelCallId
+      ? [encodeField(FIELD.CLIENT_RESULT_MODEL_CALL_ID, WIRE_TYPE.LEN, modelCallId)]
+      : []),
+    encodeField(FIELD.CLIENT_RESULT_TOOL_INDEX, WIRE_TYPE.VARINT, toolIndex)
+  );
+}
+
+function encodeMcpParamsForCall(toolName, rawArgs, serverName) {
+  const tool = concatArrays(
+    encodeField(FIELD.MCP_TOOL_NAME, WIRE_TYPE.LEN, toolName || "tool"),
+    encodeField(FIELD.MCP_TOOL_PARAMS, WIRE_TYPE.LEN, rawArgs || "{}"),
+    encodeField(FIELD.MCP_TOOL_SERVER, WIRE_TYPE.LEN, serverName || "custom")
+  );
+  return encodeField(FIELD.MCP_TOOLS_LIST, WIRE_TYPE.LEN, tool);
+}
+
+function encodeClientSideToolCall(
+  toolCallId,
+  modelCallId,
+  toolName,
+  selectedTool,
+  serverName,
+  rawArgs,
+  toolIndex
+) {
+  return concatArrays(
+    encodeField(FIELD.CLIENT_CALL_TOOL, WIRE_TYPE.VARINT, CLIENT_SIDE_TOOL_V2.MCP),
+    encodeField(
+      FIELD.CLIENT_CALL_MCP_PARAMS,
+      WIRE_TYPE.LEN,
+      encodeMcpParamsForCall(selectedTool, rawArgs, serverName)
+    ),
+    ...(toolCallId ? [encodeField(FIELD.CLIENT_CALL_TOOL_CALL_ID, WIRE_TYPE.LEN, toolCallId)] : []),
+    encodeField(FIELD.CLIENT_CALL_NAME, WIRE_TYPE.LEN, toolName || "tool"),
+    encodeField(FIELD.CLIENT_CALL_RAW_ARGS, WIRE_TYPE.LEN, rawArgs || "{}"),
+    encodeField(FIELD.CLIENT_CALL_TOOL_INDEX, WIRE_TYPE.VARINT, toolIndex > 0 ? toolIndex : 1),
+    ...(modelCallId
+      ? [encodeField(FIELD.CLIENT_CALL_MODEL_CALL_ID, WIRE_TYPE.LEN, modelCallId)]
+      : [])
   );
 }
 
@@ -311,13 +469,70 @@ export function encodeRequest(messages, modelName, tools = [], reasoningEffort =
   const isAgentic = hasTools;
   const formattedMessages = [];
   const messageIds = [];
+  const normalizedMessages = [];
 
-  // Prepare messages
+  // Guardrail: split mixed assistant payload into separate assistant messages.
   for (let i = 0; i < messages.length; i++) {
     const msg = messages[i];
+    const hasToolCalls = Array.isArray(msg?.tool_calls) && msg.tool_calls.length > 0;
+    const hasToolResults = Array.isArray(msg?.tool_results) && msg.tool_results.length > 0;
+
+    if (msg?.role === "assistant" && hasToolCalls && hasToolResults) {
+      log(
+        "ENCODE",
+        `normalizing mixed assistant tool payload at msg[${i}] (calls=${msg.tool_calls.length}, results=${msg.tool_results.length})`
+      );
+
+      // Keep assistant tool call message without embedded results
+      normalizedMessages.push({
+        ...msg,
+        tool_results: [],
+      });
+
+      // Avoid inserting duplicate assistant tool-result message if next one already matches
+      const nextMsg = messages[i + 1];
+      const nextHasToolResults =
+        nextMsg?.role === "assistant" &&
+        Array.isArray(nextMsg?.tool_results) &&
+        nextMsg.tool_results.length > 0;
+      const currentIds = new Set(
+        msg.tool_results.map((tr) => tr?.tool_call_id).filter((id) => typeof id === "string")
+      );
+      const nextIds = new Set(
+        (nextMsg?.tool_results || [])
+          .map((tr) => tr?.tool_call_id)
+          .filter((id) => typeof id === "string")
+      );
+      let sameIds = currentIds.size > 0 && currentIds.size === nextIds.size;
+      if (sameIds) {
+        for (const id of currentIds) {
+          if (!nextIds.has(id)) {
+            sameIds = false;
+            break;
+          }
+        }
+      }
+
+      if (!(nextHasToolResults && sameIds)) {
+        normalizedMessages.push({
+          role: "assistant",
+          content: "",
+          tool_results: msg.tool_results,
+        });
+      }
+
+      continue;
+    }
+
+    normalizedMessages.push(msg);
+  }
+
+  // Prepare messages
+  for (let i = 0; i < normalizedMessages.length; i++) {
+    const msg = normalizedMessages[i];
     const role = msg.role === "user" ? ROLE.USER : ROLE.ASSISTANT;
     const msgId = uuidv4();
-    const isLast = i === messages.length - 1;
+    const isLast = i === normalizedMessages.length - 1;
 
     formattedMessages.push({
       content: msg.content,
@@ -535,18 +750,19 @@ function extractToolCall(toolCallData) {
 
   // Extract tool call ID
   if (toolCall.has(FIELD.TOOL_ID)) {
-    const fullId = new TextDecoder().decode(toolCall.get(FIELD.TOOL_ID)[0].value);
-    toolCallId = fullId.split("\n")[0]; // Cursor returns multi-line ID, take first line
+    toolCallId = textDecoder.decode(toolCall.get(FIELD.TOOL_ID)[0].value);
   }
 
   // Extract tool name
   if (toolCall.has(FIELD.TOOL_NAME)) {
-    toolName = new TextDecoder().decode(toolCall.get(FIELD.TOOL_NAME)[0].value);
+    toolName = textDecoder.decode(toolCall.get(FIELD.TOOL_NAME)[0].value);
   }
 
   // Extract is_last flag
   if (toolCall.has(FIELD.TOOL_IS_LAST)) {
     isLast = toolCall.get(FIELD.TOOL_IS_LAST)[0].value !== 0;
+  } else if (toolCall.has(FIELD.TOOL_IS_LAST_ALT)) {
+    isLast = toolCall.get(FIELD.TOOL_IS_LAST_ALT)[0].value !== 0;
   }
 
   // Extract MCP params - nested real tool info
@@ -558,11 +774,11 @@ function extractToolCall(toolCallData) {
         const tool = decodeMessage(mcpParams.get(FIELD.MCP_TOOLS_LIST)[0].value);
 
         if (tool.has(FIELD.MCP_NESTED_NAME)) {
-          toolName = new TextDecoder().decode(tool.get(FIELD.MCP_NESTED_NAME)[0].value);
+          toolName = textDecoder.decode(tool.get(FIELD.MCP_NESTED_NAME)[0].value);
         }
 
         if (tool.has(FIELD.MCP_NESTED_PARAMS)) {
-          rawArgs = new TextDecoder().decode(tool.get(FIELD.MCP_NESTED_PARAMS)[0].value);
+          rawArgs = textDecoder.decode(tool.get(FIELD.MCP_NESTED_PARAMS)[0].value);
         }
       }
     } catch (err) {
@@ -572,7 +788,7 @@ function extractToolCall(toolCallData) {
 
   // Fallback to raw_args
   if (!rawArgs && toolCall.has(FIELD.TOOL_RAW_ARGS)) {
-    rawArgs = new TextDecoder().decode(toolCall.get(FIELD.TOOL_RAW_ARGS)[0].value);
+    rawArgs = textDecoder.decode(toolCall.get(FIELD.TOOL_RAW_ARGS)[0].value);
   }
 
   if (toolCallId && toolName) {
@@ -597,7 +813,7 @@ function extractTextAndThinking(responseData) {
 
   // Extract text
   if (nested.has(FIELD.RESPONSE_TEXT)) {
-    text = new TextDecoder().decode(nested.get(FIELD.RESPONSE_TEXT)[0].value);
+    text = textDecoder.decode(nested.get(FIELD.RESPONSE_TEXT)[0].value);
   }
 
   // Extract thinking
@@ -605,7 +821,7 @@ function extractTextAndThinking(responseData) {
     try {
       const thinkingMsg = decodeMessage(nested.get(FIELD.THINKING)[0].value);
       if (thinkingMsg.has(FIELD.THINKING_TEXT)) {
-        thinking = new TextDecoder().decode(thinkingMsg.get(FIELD.THINKING_TEXT)[0].value);
+        thinking = textDecoder.decode(thinkingMsg.get(FIELD.THINKING_TEXT)[0].value);
       }
     } catch (err) {
       log("EXTRACT", `Thinking parse error: ${err.message}`);