PLAN-COMPILER-VM: record non-negotiable end state — ONE evaluator, legacy deleted

Dual-path + emit-time legacy fallback are transitional scaffolding only; the VM
must reach parity at BOTH comptime sites (emit time AND lowering time), after
which the -Dcomptime-flat flag, the fallback, and interp.zig are all removed.
We do not ship both evaluators permanently.

current/PLAN-COMPILER-VM.md

@@ -41,6 +41,14 @@ fast.
   field-by-field marshaling — gone.
 - `declare`/`define`/`type_info` and `#compiler`/`BuildOptions` ride this one
   mechanism; the bespoke interp arms are deleted.
+- **ONE evaluator at the end — non-negotiable.** The legacy tagged-`Value` interpreter
+  (`interp.zig`) is **DELETED**. We do NOT ship both permanently. "Dual-path"
+  (a compiler-API fn with both a legacy `compiler_lib` handler AND a VM-native impl) and
+  the emit-time legacy fallback are **transitional only** — scaffolding while the VM
+  reaches parity at BOTH comptime sites (emit time AND lowering time). The flag
+  `-Dcomptime-flat` is the swap mechanism; once the VM runs everywhere with parity, the
+  flag, the fallback, and `interp.zig` all go. Any "VM-only at emit, legacy at lowering"
+  split is a waypoint, never the destination.
 
 ## Principles (hold at every step)