Skill tool not available after upgrading to 2.1.38, skills execute via sub-agents instead

Environment

• Claude Code version: 2.1.38 (also reproduced on 2.1.32 after downgrade)
• OS: Windows 10
• Terminal: Windows Terminal
• Model: GLM (non-Anthropic model)

Description

After upgrading to v2.1.38, the Skill tool is no longer available in the tool set. Skills defined in .claude/skills/ are still listed in the system prompt as "available for use with the Skill tool", but the actual Skill tool does not exist in the available tools.

As a result, when skills are invoked, they execute inside sub-agents (via the Task tool) instead of running in the main conversation context. This causes:

1. Loss of conversation context - sub-agents don't have full conversation history
2. Information loss during communication between main context and sub-agents
3. Additional latency from spawning new agents

Steps to Reproduce

1. Upgrade to Claude Code 2.1.38
2. Define skills in .claude/skills/ directory (minimal frontmatter with only name and description)
3. Start a conversation and check available tools - no Skill tool present
4. Invoke a skill - it executes via Task tool (sub-agent) instead of inline

Expected Behavior

The Skill tool should be available, and skills should execute in the main conversation context as they did in earlier versions.

Actual Behavior

• No Skill tool in the tool set
• Skills are forced to execute via sub-agents (Task tool)
• Downgrading to 2.1.32 does not restore the Skill tool

Additional Context

Skill frontmatter contains only name and description fields - no context: fork or agent-related settings. The sub-agent execution appears to be a platform-level change, not a skill configuration issue.