v0.1.15

Added

• Changelog with automated release notes.

Changed

• Agent state is serialized as JSON automatically; chains no longer need an
  explicit .use(agent.jsonState()). Existing chains that still include it
  keep working, and the wire format is unchanged.

Fixed

• Tool-result messages (message.new with role: "tool") now carry the tool
  name instead of null, so consumers reading only the message stream (e.g.
  reconstructing a transcript from session events) no longer have to correlate
  tool_call_id back to the originating tool call to recover the name.