feat(mcp log): print mcp stderr to opencode log file (#9982)

Co-authored-by: chuxuan.liang <chuxuan.liang@bytedance.com>
Co-authored-by: Aiden Cline <63023139+rekram1-node@users.noreply.github.com>

packages/opencode/src/mcp/index.ts

@@ -409,7 +409,7 @@ export namespace MCP {
       const [cmd, ...args] = mcp.command
       const cwd = Instance.directory
       const transport = new StdioClientTransport({
-        stderr: "ignore",
+        stderr: "pipe",
         command: cmd,
         args,
         cwd,
@@ -419,6 +419,9 @@ export namespace MCP {
           ...mcp.environment,
         },
       })
+      transport.stderr?.on("data", (chunk: Buffer) => {
+        log.info(`mcp stderr: ${chunk.toString()}`, { key })
+      })
 
       const connectTimeout = mcp.timeout ?? DEFAULT_TIMEOUT
       try {