Agents naturally expect `gt handoff -s "Subject" -m "Message"` to work
like `gt mail send`. Now it does:
- Added --subject/-s and --message/-m flags to gt handoff
- Added --self flag to gt mail send for sending to self
- Handoff auto-sends mail to self before respawning pane
This makes agent-initiated handoff more ergonomic - they can include
context in a single command instead of two separate steps.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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