Messages sent from a linked environment show "Agent" instead of the sending thread #34708

What happened

When an agent's t3_thread_send targets a thread in a linked environment, the receiving thread's folded row says "Agent" instead of the sender's title and has no "Open thread" button. Same-environment sends show both.

Diagnosis

The sender is lost on the way. PeerForwarding.forward forwards the arguments and mode limits but not the calling thread. The receiving side runs the send as the link's client session, which has no thread, so OrchestratorMcpService.sendToThread records no senderThreadId. The message also has no field for the sender's environment, so clients could not find the sender even with an id. Remote delegate_task already solves this with delegatedFrom: { environmentId, threadId, title }.

Steps to reproduce

1. Link environment A to B (Labs → Linked environments).
2. From an agent thread on A, t3_thread_send to a thread on B.
3. Open the thread on B: the row reads "Agent", with no "Open thread".

Version

0.1.10-nightly.20261111.4544; code unchanged on main at 7462f23.

Environment

macOS arm64, desktop app, two linked Macs.

Evidence

The forwarded messages (ids contain thread-send:fwd:) are stored with createdBy: agent, creationSource: mcp and no senderThreadId.

Related issues

#23135 (folded agent rows), #18194 (senderThreadId in t3_thread_read).

Filed by

claude (claude-opus-5-5) via t3 triage