fix: Implement /resume slash command (Issue #2869)

[ten-jampa]

Summary

Fixes Issue #2869: Session history not persisting between restarts

Problem

When Hermes was closed and reopened, showed empty and showed "Unknown command" - session history was not persisting between restarts.

Root Cause

The command was registered in the command registry but not implemented as a slash command handler - it only worked via the CLI flag when starting Hermes.

Solution

1. Add slash command handler in :

   • — Lists available saved sessions
   • — Resumes that session and loads history from the database

2. Improve command:

   • Now loads history from database if not in current session
   • Shows saved sessions when no history is available
   • Provides helpful prompt to use

3. Fix NoneType crash:

   • Handle explicitly null field in session listing to prevent error

Testing

hermes
/resume              # Lists saved sessions
/resume <session-id> # Resumes session with full history
/history             # Shows history from database

Files Changed

• — Added /resume handler, improved /history, fixed NoneType handling