session_capacity

This code is registered so the envelope contract and its docs_url anchor stay stable, but nothing emits it. The MCP server caps a workspace at 100 concurrent sessions and enforces that by evicting the oldest session rather than refusing the new one, so the caller that hits the cap gets a normal successful response — it's an older session elsewhere that is dropped. Do not write retry logic against this code.

If sessions are being evicted under you, the fix is not a retry: audit how many MCP hosts are connected to the workspace and disconnect the ones you don't need (Settings → Developer → Connected apps).