[knight22-21]

Summary

• Support live model overrides in \MultiModelRouter\ so interactive model switches (/model, /fast) take immediate precedence during agent loops.
• Improve session history token estimation and context fitting with \it_request_context\ to retain system prompts and newest messages within model context budgets.
• Add /history\ REPL command and session resume prompt when running interactively.
• Replace \�iosqlite\ with standard \sqlite3\ in \core/storage.py\ and ensure thread-safe CodePrism background loop initialization.
• Lower default compression threshold from 0.6 to 0.45.

Tests

• 
  uff check devagent/ tests/\ passes.
• Unit tests in \ est_budget.py, \ est_phase5.py, and \ est_phase8.py\ pass.