Feature request: allow Claude Code cloud sessions to communicate with each other via SendMessage (like local/RC sessions)

Summary

Locally (CLI) and in Remote Control (RC) sessions, Claude Code sessions can use the SendMessage tool to communicate with each other — e.g. a parent session coordinating with sibling sessions, or steering an in-progress session.

Cloud sessions (claude.ai/code, and sessions run via the Claude Code Remote / claude-code-remote MCP server in cloud/managed environments) currently lack this capability. There's no equivalent of SendMessage that lets one cloud session talk to another cloud session directly.

Why this matters

This makes it harder to orchestrate multi-session workflows in the cloud — e.g. fan-out task delegation, one session monitoring/steering another, or cross-session coordination — that already work (at least in principle) locally or via RC.

Existing partial tooling

The cloud/managed environment already exposes some session-management tools for reference, but nothing that lets one running session push a message directly into another running session:

• create_session
• list_sessions
• send_later
• interrupt_session

None of these provide a direct session-to-session SendMessage equivalent for cloud sessions.

Request

Add SendMessage (or an equivalent) support for cloud sessions so they can communicate with each other the same way local and RC sessions do.

Related issues

There's a large body of existing issues about cross-session SendMessage reliability for local/RC/desktop sessions (e.g. #87261, #85160, #76437), but they're about fixing or extending messaging that already exists for those surfaces. This request is specifically about the absence of any session-to-session messaging primitive for cloud sessions.

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