[MODEL] Claude Code stopped delegating to custom subagents and loading skills — regression persists in Opus 4.6

Description

Claude Code no longer delegates to custom subagents or loads skills automatically, despite having a well-defined agent harness with clear descriptions and routing rules.

Setup

• Project: Multi-agent orchestration platform (Atlas Mantle) with 8 specialist agents
• Agent definitions: .claude/agents/ with clear descriptions, capabilities, and when-to-use rules
• Skills: .claude/skills/ and backend_agent_api/skills/ with YAML frontmatter triggers
• CLAUDE.md delegation table: Explicit mapping of task types to subagent_type values
• Model: Claude Opus 4.6 (1M context)
• Version: Claude Code latest (April 2026)

Expected Behavior

When given a React/TypeScript task, Claude should:

1. Load the react-flow skill (auto-triggered by tags)
2. Delegate to frontend_coder_react subagent (matches task description)
3. The subagent generates code following its specialized prompt
4. Results return to main context

Same pattern for Python tasks → backend_coder_python, tests → backend_tester_pytest, etc.

This worked correctly in earlier versions (Jan-Feb 2026).

Actual Behavior (since ~March 2026)

Claude Code:

• Never delegates to custom subagents — writes all code directly in the main context
• Never loads skills unless explicitly asked ("please read the react-flow skill")
• Ignores the CLAUDE.md delegation table entirely
• Does not scan files before editing (pre-regression: 6.6 files, post: ~2, matching AMD's telemetry in #42796)

Impact

This breaks custom agent harnesses that rely on automatic delegation. My platform has:

• 8 specialist agents with distinct prompts, tools, and output models
• 7 skills with YAML frontmatter for auto-loading
• A workflow engine that routes through specialist agents
• Per-agent RAG memory (lessons learned)

All of this is bypassed when Claude Code handles everything in the main context.

Reproduction

1. Create a .claude/agents/frontend_coder_react.md with clear description
2. Add to CLAUDE.md: "Delegate React tasks to frontend_coder_react"
3. Ask Claude Code to build a React component
4. Observe: Claude writes the code directly instead of delegating

Related Issues

• #42796 — Claude Code is unusable for complex engineering tasks
• #8558 — Claude-code does not call subagents anymore

Environment

• OS: Windows 11 Pro
• Claude Code: Latest (April 2026)
• Model: claude-opus-4-6 (1M context)
• Subscription: Claude Max/Pro