[Bug] MCP Server Tool Response: structuredContent Displayed While content Array Ignored

Bug Description
When an MCP server returns a tool response containing both content (array of text/data) and structuredContent (metadata), Claude Code only displays structuredContent and ignores content.

Environment Info

• Platform: darwin
• Terminal: tmux
• Version: 2.0.67
• Feedback ID: 6f82e95d-a1ab-409a-a310-e12b0b9f9a0b

Steps to Reproduce

1. Configure glab mcp serve as an MCP server (stdio transport)
2. Call any glab tool, e.g., glab_mr_list
3. Observe that only structuredContent is displayed

Expected Behavior

Display the content field (array of text items containing actual data like the MR list)

Actual Behavior

Only shows structuredContent metadata:

{"pagination":{"actual_end":1006,"actual_size":1006,"actual_start":0,"limit":50000,"offset":0,"total_size":1006,"truncated":false}}

Evidence

MCP server logs (captured via wrapper script) show both fields are sent correctly by the server:

Request:

{"method":"tools/call","params":{"name":"glab_mr_list","arguments":{}},"jsonrpc":"2.0","id":2}

Response (from glab mcp serve):

{
  "jsonrpc": "2.0",
  "id": 2,
  "result": {
    "content": [
      {
        "type": "text",
        "text": "Showing 8 open merge requests on synology/OrangeDrive. (Page 1)\n\n!1359\tsynology/OrangeDrive!1359\tfeat: support complex share paths...\n..."
      }
    ],
    "structuredContent": {
      "pagination": {
        "actual_end": 1006,
        "actual_size": 1006,
        "actual_start": 0,
        "limit": 50000,
        "offset": 0,
        "total_size": 1006,
        "truncated": false
      }
    }
  }
}

What Claude Code displays to the user:
Only the structuredContent portion - the actual MR list in content is completely ignored.

Analysis

According to the MCP specification, CallToolResult supports both:

• content: Primary response data (array of content items like text, images)
• structuredContent: Optional structured metadata

The MCP SDK schema (found in the binary) correctly defines both fields:

mF=CY.extend({content:b.array(w9B).default([]),structuredContent:b.object({}).passthrough().optional(),isError:b.optional(b.boolean())})

The issue appears to be in the response rendering/display logic that extracts data from MCP tool results - it seems to prioritize or exclusively use structuredContent when present, ignoring content.

Notes

• Issue likely introduced in v2.0.21 when structuredContent support was added (per CHANGELOG.md)
• Workaround: Use CLI commands directly via Bash tool instead of MCP tools
• The glab MCP server is working correctly - this is a Claude Code client-side parsing issue

Wrapper Script Used for Logging

#!/bin/bash
LOG_FILE="${GLAB_MCP_LOG:-/tmp/glab-mcp-$(date +%Y%m%d-%H%M%S).log}"
exec 3>&1
log_with_timestamp() {
    while IFS= read -r line; do
        echo "[$(date '+%Y-%m-%d %H:%M:%S')] $1: $line" >> "$LOG_FILE"
    done
}
echo "=== glab mcp serve started at $(date) ===" >> "$LOG_FILE"
tee >(log_with_timestamp "IN" >&2 2>/dev/null) | \
    glab mcp serve 2>> "$LOG_FILE" | \
    tee >(log_with_timestamp "OUT" >&2 2>/dev/null)