fix: quant selector quality-order assertion (#139)

evolution/quant_selector.py

@@ -62,16 +62,6 @@ QUANT_LEVELS = [
         min_memory_headroom_gb=3.0,
         description="3-bit TurboQuant. High quality, ~6x KV compression."
     ),
-    QuantLevel(
-        name="turbo2",
-        bits_per_channel=1.5,
-        compression_ratio=10.0,
-        quality_label="balanced",
-        layer_adaptive=3,
-        kv_type="turbo2",
-        min_memory_headroom_gb=2.0,
-        description="2-bit TurboQuant. Balanced, ~10x KV compression."
-    ),
     QuantLevel(
         name="q4_0",
         bits_per_channel=4.0,
@@ -82,6 +72,16 @@ QUANT_LEVELS = [
         min_memory_headroom_gb=1.5,
         description="Standard 4-bit quant. Fast fallback, no TurboQuant."
     ),
+    QuantLevel(
+        name="turbo2",
+        bits_per_channel=1.5,
+        compression_ratio=10.0,
+        quality_label="balanced",
+        layer_adaptive=3,
+        kv_type="turbo2",
+        min_memory_headroom_gb=2.0,
+        description="2-bit TurboQuant. Balanced, ~10x KV compression."
+    ),
 ]
 
 

tests/test_quant_selector.py

@@ -20,9 +20,17 @@ from evolution.quant_selector import (
 
 class TestQuantLevels:
     def test_levels_ordered_by_quality(self):
-        """Levels should be ordered from best quality to most aggressive."""
+        """Levels should be ordered from highest quality (most bits) to most aggressive.
+
+        The selection logic iterates QUANT_LEVELS in order and picks the first
+        level that fits in available memory. So higher bits_per_channel (better
+        quality) must come first, regardless of whether it's TurboQuant or standard.
+        """
         for i in range(len(QUANT_LEVELS) - 1):
-            assert QUANT_LEVELS[i].bits_per_channel > QUANT_LEVELS[i + 1].bits_per_channel
+            assert QUANT_LEVELS[i].bits_per_channel > QUANT_LEVELS[i + 1].bits_per_channel, (
+                f"{QUANT_LEVELS[i].name} ({QUANT_LEVELS[i].bits_per_channel}b) should come "
+                f"before {QUANT_LEVELS[i+1].name} ({QUANT_LEVELS[i+1].bits_per_channel}b)"
+            )
 
     def test_all_levels_have_required_fields(self):
         for level in QUANT_LEVELS: