The SendMessage tool schema has been simplified from a discriminated union with type/recipient/content fields to a more intuitive to/message/summary format. Agents now use to: "<name>" for direct messages and to: "*" for broadcasts. Structured protocol messages (shutdown requests, plan approvals) are sent as objects in the message field. A backward-compatibility shim (backfillObservableInput) translates old-format calls.
Evidence
Simplified SendMessage schema (search for "Recipient: teammate name", 'to must be a bare teammate name or "*"')
Strings lifted out of the shipped bundle, so the claim above can be checked against them.