Add trace_varmap() helper to track variable_map state during JoinIR merge.
Enable with NYASH_TRACE_VARMAP=1 to see variable→ValueId mappings.
Strategic trace points in Pattern 3:
- pattern3_before_merge: State before JoinIR→MIR merge
- pattern3_after_merge: State after merge (detects missing updates)
- pattern3_exit_phi_connected: State after exit PHI connection
This would have caught the 1.5hr debugging session bug instantly:
[varmap/pattern3_after_merge] sum=ValueId(5) ← still old value!
[varmap/pattern3_exit_phi_connected] sum=ValueId(0) ← fixed!
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
e01d1b8a7c