Sub-agents receive the auto-memory index and skill listing, contrary to the docs — custom agent definitions included

Environment: Claude Code 2.1.263, macOS 15 (Darwin 25.5), Claude Max, model claude-fable-5-1 for the probe (also seen on 2.1.261 and 2.1.258 with claude-opus-5).

Expected

The sub-agents docs ("What loads at startup") and the memory docs say:

The main conversation's auto memory isn't loaded into subagents; the exception is a fork.

Subagents don't receive a pre-populated listing [of skills and MCP tools]. They can discover and invoke unlisted project, user, and plugin skills through the Skill tool during execution.

Actual

A do-nothing sub-agent's first request carries both, as attachments recorded in the transcript:

• an instructions attachment containing the project's MEMORY.md in full (19,850 chars here), alongside the CLAUDE.md files (which are documented as loading);
• a skill_listing attachment with one description line per skill (24–26k chars, ~49 skills here).

This is the case for the built-in general-purpose agent and for custom agent definitions (.claude/agents/*.md). A custom definition does replace the Claude Code system prompt as documented, and a tools: allowlist does trim the schemas — but memory index, skill listing and CLAUDE.md files arrive unchanged in all three cases:

| Sub-agent | First-request tokens (cold cache) |
|---|---|
| built-in general-purpose | 45,907 |
| custom definition, no tools: | 33,244 |
| custom definition, 8-tool allowlist | 27,832 |

The ~24k that remains in the last row is memory index + skill listing + CLAUDE.md files (+ ~3k of tool names/session context).

Steps to reproduce

1. In a project with a populated ~/.claude/projects/<project>/memory/MEMORY.md and a dozen or more skills installed, create .claude/agents/probe.md:

``
---
name: probe
description: measurement probe
---
You are a measurement probe. Do exactly what the prompt says and nothing else.
``

1. Start a new session (agent definitions load at session start) and dispatch:

Agent(subagent_type="probe", prompt="Reply with exactly the single word DONE. Do not call any tool.")

1. Open the sub-agent transcript under ~/.claude/projects/<project>/<session-id>/subagents/agent-*.jsonl. The attachment records before the first assistant turn include instructions (with the MEMORY.md path and content) and skill_listing; the first assistant usage.cache_creation_input_tokens is the figure above.

Why it matters

In sub-agent-heavy workflows this block is re-read on every call. In ours (batch runs of ~70-call sub-agents, ~250k mean context) the memory index and skill listing together are ~17k tokens, about 7% of all cache-read tokens per run — and unlike the system prompt, there is no per-agent way to leave them out: the memory frontmatter field adds a separate memory directory rather than suppressing the main index, and skills: preloads skill bodies rather than shrinking the listing. claudeMdExcludes and CLAUDE_CODE_DISABLE_AUTO_MEMORY are session-wide, so they also strip the parent conversation.

Ask

Either of:

• make the behaviour match the docs (or add a per-agent switch — e.g. a frontmatter field to opt a custom agent out of the memory index and skill listing); or
• correct the docs to describe what sub-agents actually receive, so people sizing sub-agent context can plan on it.