User-submitted message that was never sent appeared in the conversation

What happened

During an active coding session, a message I never typed or sent appeared in the conversation as a user message. The injected text was an unrelated consumer question (a shopping/product question) — completely off-topic from the technical session I was in. It appeared immediately followed by an interrupt marker, and the assistant then responded to it as if it were my real input.

I have confirmed I did not type, paste, dictate, or send that message from my client.

Why this is concerning

This looks like a client- or server-side message routing / session-isolation issue rather than a model reasoning error — the off-topic text entered my input stream as a genuine user turn. If messages from another context can leak into a session, that is a potential session-isolation / privacy problem worth investigating.

Expected behavior

Only messages I actually submit should appear as my user turns.

Environment

• Claude Code — VSCode extension
• Model: Opus 4.8 (claude-opus-4-8[1m])
• OS: macOS (darwin 23.3.0)

Reproduction

Not reproducible on demand — occurred once, unprompted, mid-session. /bug was not available in this environment, hence filing here.