[BUG] Messages posted to a session's own inbox socket render the full peer envelope instead of the collapsed preview

What's Wrong?

Claude Code 2.1.268, macOS, Ghostty. Peer messages sent with SendMessage from another session render as the one-line preview described in the cross-session messaging docs: › Message from @probe-sender: … (ctrl+o to expand). A message posted by a script to the session's own inbox socket (CLAUDE_CODE_MESSAGING_SOCKET, with the CLAUDE_CODE_MESSAGING_TOKEN auth line, per the own-child rules) does not collapse. When the session is idle, the whole delivered turn renders inline: the "Another Claude session sent a message:" header, the body, and the full permission-laundering paragraph.

I have a local tool that posts a user's review comments from a browser page back into the session this way, so every comment shows up in the transcript wrapped in ~120 words of boilerplate.

Socket post arriving while idle:

<img width="683" height="188" alt="Image" src="https://github.com/user-attachments/assets/20710e91-f732-41ae-ba82-1ab779199a3b" />

SendMessage from a named session, same session a few minutes later:

<img width="1672" height="118" alt="Image" src="https://github.com/user-attachments/assets/6ef5e156-df12-4fc7-8e98-909deecd6b8e" />

The two kinds of message also differ in what the model receives. A SendMessage arrives wrapped in an envelope element carrying the sender:

Another Claude session sent a message:
<cross-session-message from="uds:/tmp/cc-socks/44971.sock" from-name="probe-sender" from-mode="prompting">
variant H: sent via SendMessage from a named session (probe-sender) while recipient idle
</cross-session-message>

This came from another Claude session — not typed by your user, …

A socket post arrives as bare text between the same header and footer, with no envelope and no from= address (the footer still says "reply via SendMessage to the from= address"):

Another Claude session sent a message:
variant F: plain format, delivered while the session is idle

This came from another Claude session — not typed by your user, …

So my guess is the collapse keys on the envelope or the sender name, and own-child socket posts have neither. Adding a top-level name, from, sender, or agentName field to the socket JSON changed nothing.

Timing matters too. The same socket post arriving mid-turn renders as just the body, styled like a typed prompt, with no header or footer visible. Only the idle case shows the full envelope. Since a script posting to the socket is usually reacting to something while the session waits, idle is the common case.

<img width="1666" height="484" alt="Image" src="https://github.com/user-attachments/assets/59d053dd-d8da-416b-9f6c-f8ab7c816f42" />

What Should Happen?

A socket post should render the same way a SendMessage does: a collapsed one-line preview, expandable with Ctrl+O. The header and footer are model-facing plumbing and shouldn't take up transcript space either way. Since the protocol has no sender field, a generic label like Message from inbox socket: would be fine.

Steps to Reproduce

1. Start an interactive session with cross-session messaging enabled (macOS or Linux).
2. Ask Claude to run this in the background so the message lands after the turn ends:

``sh
sleep 8; printf '%s\n%s\n' \
"{\"type\":\"auth\",\"token\":\"$CLAUDE_CODE_MESSAGING_TOKEN\"}" \
'{"type":"user","message":{"role":"user","content":"hello from socket"}}' \
| nc -w 2 -U "$CLAUDE_CODE_MESSAGING_SOCKET"
``

1. Let the turn end. The message renders as a full user turn with header and footer.
2. For comparison, from a second session: claude -p --name probe-sender --allowedTools SendMessage "Use SendMessage to send 'hello' to the session named <first session's name>". That one renders as › Message from @probe-sender: hello (ctrl+o to expand).
3. Run step 2 again without the sleep, while Claude is mid-turn. The body renders alone, without the envelope.

Is this a regression?

I don't know. Docs say peer messages collapse since 2.1.247 (changelog: "Changed cross-session peer messages to collapse by default to a one-line Message from @<sender>: <first line> preview"). I don't know whether socket posts ever collapsed.

Related: #73647 and #80625 are about the same envelope rendering in full on Remote Control and mobile for teammate messages. #86133 asks for the collapsed display back after 2.1.228. None of them cover the inbox socket path, which is the documented way for hooks and scripts to post into a session.

Version

2.1.268

Platform

macOS, Ghostty terminal