[BUG] Cross-session messages silently dropped since 2.1.227 — sender gets success, target session never receives them

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

mcp__ccd_session_mgmt__send_message returns a success result to the sender, and the message is visible in the target session's event list / UI, but it is never appended to the target session's conversation transcript. The receiving model therefore has no knowledge of the message at all.

The failure is completely silent in both directions: the sender believes the handoff succeeded and finishes its turn, while the receiver, when later asked about it, correctly reports that the message is not in its context. Nothing errors, nothing is logged.

What Should Happen?

Expected: a message sent with send_message is appended to the target session's transcript as a <cross-session-message …> user entry, so the receiving model sees it.

Actual: the entry is never written. The message appears only in the UI/event layer. list_events for the target session shows it; the session's .jsonl transcript does not contain it.

Error Messages/Logs

Steps to Reproduce

Open two sessions, A and B, in the desktop app.
Let B finish a turn and go idle (do not close it — it stays isRunning: true).
From A, call mcp__ccd_session_mgmt__send_message targeting B.
A receives Message sent to session … ("B"), no error.
Open B and ask it about the message.
Result: B has no knowledge of the message. Its transcript never received it. The message is visible via list_events for B and rendered as a card in the UI.

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

2.1.222

Claude Code Version

2.1.227

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_