Coordinator relays to a Remote Control session arrive inside tool results when the session is mid-task
Setup
A Claude Code session on a Windows 11 PC (Claude desktop app, Code tab), started over Remote Control from a Claude Project conversation. The project's cloud session sends it <relay from="coordinator"> notes to coordinate work.
Versions on the PC: Claude Code 2.1.295 (bundled with the desktop app, entrypoint claude-desktop); Claude desktop app 2.31226.1; Agent SDK 0.3.295.
What happens
- When a coordinator relay arrives while the PC session is idle, it is delivered as a turn of its own. The session acts on it.
- When a relay arrives while the PC session is mid-task (running tools), it is appended to the end of the next tool result (seen on PowerShell output and on ToolSearch output), wrapped in a
<system-reminder>block that says "SYSTEM NOTIFICATION - NOT USER INPUT".
In one session on 2026-10-13 this happened five times mid-task, against four relays delivered correctly while idle.
Why it matters
Text at the end of a tool result is where a prompt injection would appear, and nothing ties the embedded relay to the coordinator channel except its own text. The session therefore treated five genuine relays as untrusted and did not act on them. It carried on with work the cloud session had already taken over, which duplicated work and needed the user to step in and confirm the relays were real.
By contrast, a user message sent mid-task is also surfaced alongside a tool result, but with an explicit note from the harness saying it is a user message. The relays had no equivalent.
Expected
A relay that arrives mid-task should be delivered in a form the model can tell apart from tool output: either held until it can be its own turn, or surfaced with the same kind of harness-level framing a mid-task user message gets.
Reproduce
- Start a Remote Control session on a PC from a Project conversation.
- Give the PC session a task that runs several tool calls.
- While it is running, have the project's cloud session send it a relay.
- The relay appears inside the next tool result, not as its own turn.