[BUG] Cross-session send_message no longer reaches a busy recipient's turn (regression 2.1.227 → 2.1.229)

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?

Summary

A message sent from one running Claude Code session to another via cross-session send_message
surfaces in the recipient's UI but is no longer injected into the recipient's active turn or written
to its transcript while that recipient is busy. The recipient never reads or acknowledges the message
during its current turn, and a long-running/idle turn can leave it unsurfaced indefinitely. In 2.1.227
and earlier the same message was pulled into the recipient's working context and acknowledged mid-task.

Environment

• OS: Windows 11
• Claude Desktop (MSIX shell): 1.30096.5
• claude-code engine: 2.1.229 (regressed from 2.1.227; not bisected between 228/229)
• Two concurrent local sessions on one machine
• Recipient has crossSessionInbound: "accept" in ~/.claude/settings.json

Steps to reproduce

1. Run sessions A and B; B is mid-turn (actively running tools).
2. From A, call cross-session send_message targeting B.
3. Tool returns: "Message queued … it will be processed after the in-flight turn finishes."
4. Observe B.

Expected (≤ 2.1.227)

The message is injected into B's working context/transcript and B notices/acknowledges it, even mid-task.

What Should Happen?

Actual (2.1.229)

• Message appears in B's UI (auto-accepted; no accept prompt — crossSessionInbound: "accept" honored).
• Never written into B's transcript while B is busy — full-text transcript search for the message body

returns 0 hits in B.

• B does not read or act on it during its current turn.

Evidence

• Transcript search for the sent message's distinctive text → 0 hits in the recipient.
• Historical transcripts (≤ 2.1.227) show prior nudges were injected and acknowledged mid-work

(a recipient's turn reasoning "I'm noticing a cross-session message from [other session] …"; another
recipient tracking an inbound nudge to completion).

• The send_message tool result itself now states delivery is deferred until "after the in-flight turn

finishes" — it no longer injects mid-turn.

Impact

Breaks multi-session coordination that relies on a nudge reaching a peer that is currently working.
crossSessionInbound: "accept" no longer restores mid-turn delivery; it only removes the accept prompt
for the now-inert surfaced item.

Error Messages/Logs

Steps to Reproduce

Steps to reproduce

1. Run sessions A and B; B is mid-turn (actively running tools).
2. From A, call cross-session send_message targeting B.
3. Tool returns: "Message queued … it will be processed after the in-flight turn finishes."
4. Observe B.

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

2.1.226

Claude Code Version

2.1.229

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Windows Terminal

Additional Information

_No response_