--brief flag doesn't inject SendUserMessage tool

Description

claude --brief help text says: "Enable SendUserMessage tool for agent-to-user communication"

But starting a session with --brief doesn't actually add SendUserMessage to the available tools. The model streams text normally and has no awareness of the tool.

Evidence

• claude --help shows: --brief Enable SendUserMessage tool for agent-to-user communication
• The tool definition exists in the compiled binary (v2.1.76) with full metadata: name, legacy name ("Brief"), description, prompt, and system prompt guidance
• The embedded system prompt describes a detail view vs main view routing mechanism
• Starting claude --brief (interactive, no -p) does not inject the tool. The model responds normally and denies knowledge of SendUserMessage when asked directly
• claude --brief -p also doesn't use it (just outputs minimal text)

Expected behavior

--brief should inject SendUserMessage into the tool list so the model can route messages through it as described in the embedded system prompt.

Environment

• Claude Code v2.1.76
• macOS (Darwin 25.3.0)