Self-referential subagent IDs are rejected instead of creating a new child #45356

Description

Some models echo the calling session's ID in subagent.sessionID while requesting a new subagent. The continuation path treats that ID as an existing session and rejects it because a session is not its own child.

Plugins

None

OpenCode version

V2

Steps to reproduce

1. Start a session.
2. Call subagent with a valid subagent agent, prompt, and description, but set sessionID to the calling session's ID.
3. The call fails with Session <id> is not a child of the current session instead of creating a child session.

Screenshot and/or share link

Not applicable.

Operating System

Linux

Terminal

Not applicable.