[DOCS] Agent definition schemas missing `background: true` option for always-background execution

Documentation Type

Missing documentation (feature not documented)

Documentation Location

https://code.claude.com/docs/en/sub-agents

Section/Topic

Subagent frontmatter schema and --agents JSON schema docs.

Current Documentation

The documented subagent/frontmatter schema includes fields like:

name, description, tools, disallowedTools, model, permissionMode, maxTurns, skills, mcpServers, hooks, memory

The CLI --agents format also documents field options, but not background.

What's Wrong or Missing?

Claude Code v2.1.49 adds support for background: true in agent definitions to always run as background tasks.

Current docs omit this option in both schema references, making the feature undiscoverable.

Suggested Improvement

Document background in both places:

1. sub-agents supported frontmatter fields table,
2. cli-reference --agents field table.

Include a small example and clarify interaction with permission prompts and MCP tool availability.

Impact

Medium - Makes feature difficult to understand

Additional Context

Affected Pages:

| Page | Line(s) | Context |
|------|---------|---------|
| https://code.claude.com/docs/en/sub-agents | 203-220 | Supported frontmatter fields omit background |
| https://code.claude.com/docs/en/cli-reference | 85-97 | --agents field list omits background |

Total scope: 2 pages affected