Document Agent Host session handoff restrictions

[ntrogh]

Product change

• Source: chat: hide delegation from agent host sessions vscode#334089
• Merged: 2026-09-02T20:19:06Z

Local sessions can initiate a handoff to another harness. Local and remote Agent Host sessions cannot initiate handoff and therefore do not show the session target picker, but they remain valid handoff destinations.

Why the docs need an update

The handoff instructions in docs/agents/run/agent-harnesses.md imply that every ongoing session can select a target. They do not distinguish supported handoff sources from destinations.

Suggested documentation

• docs/agents/run/agent-harnesses.md: State that only Local sessions can initiate handoff and clarify that Agent Host sessions remain available as destinations.

Details to verify

• Local and remote Agent Host sessions set supportsDelegation to false.
• The restriction applies to the handoff source, not the destination.

Acceptance criteria

• The handoff instructions accurately distinguish supported source sessions from target sessions.
• Readers understand why the session target picker is unavailable in Agent Host sessions.