Added

• $ARGUMENTS syntax for custom slash commands as alternative to $@ for all arguments joined. Aligns with patterns used by Claude, Codex, and OpenCode. Both syntaxes remain fully supported. (#418 by @skuridin)

Changed

• Slash commands and hook commands now work during streaming: Previously, using a slash command or hook command while the agent was streaming would crash with "Agent is already processing". Now:
  • Hook commands execute immediately (they manage their own LLM interaction via pi.sendMessage())
  • File-based slash commands are expanded and queued via steer/followUp
  • steer() and followUp() now expand file-based slash commands and error on hook commands (hook commands cannot be queued)
  • prompt() accepts new streamingBehavior option ("steer" or "followUp") to specify queueing behavior during streaming
  • RPC prompt command now accepts optional streamingBehavior field (#420)

Fixed

• Slash command argument substitution now processes positional arguments ($1, $2, etc.) before all-arguments ($@, $ARGUMENTS) to prevent recursive substitution when argument values contain dollar-digit patterns like $100. (#418 by @skuridin)