diff --git a/headroom/compression/handlers/code_handler.py b/headroom/compression/handlers/code_handler.py
index 309876316..3de5a20cb 100644
--- a/headroom/compression/handlers/code_handler.py
+++ b/headroom/compression/handlers/code_handler.py
@@ -20,7 +20,6 @@ import logging
 import re
 import threading
 from dataclasses import dataclass
-from enum import Enum
 from typing import Any
 
 from headroom.compression.handlers.base import BaseStructureHandler, HandlerResult
@@ -107,19 +106,6 @@ def _ts_children(node: Any) -> list[Any]:
     return [node.child(i) for i in range(node.child_count())]
 
 
-class CodeLanguage(Enum):
-    """Supported programming languages."""
-
-    PYTHON = "python"
-    JAVASCRIPT = "javascript"
-    TYPESCRIPT = "typescript"
-    GO = "go"
-    RUST = "rust"
-    JAVA = "java"
-    C = "c"
-    CPP = "cpp"
-
-
 @dataclass
 class CodeSpan:
     """A span of code with its structural role."""
@@ -236,6 +222,16 @@ _CONTAINER_BODY_TYPES: frozenset[str] = frozenset(
     }
 )
 
+# Language-detection markers for _detect_language
+_LANGUAGE_MARKERS: dict[str, list[str]] = {
+    "python": ["def ", "import ", "from ", "class ", "async def"],
+    "javascript": ["function ", "const ", "let ", "var ", "=>"],
+    "typescript": ["interface ", "type ", ": string", ": number"],
+    "go": ["func ", "package ", "import (", "type "],
+    "rust": ["fn ", "let mut", "impl ", "pub fn", "use "],
+    "java": ["public class", "private ", "protected ", "void "],
+}
+
 # Import patterns for fallback
 _IMPORT_PATTERNS: dict[str, re.Pattern[str]] = {
     "python": re.compile(r"^\s*(import\s+\w+|from\s+\w+\s+import)", re.MULTILINE),
@@ -608,8 +604,10 @@ class CodeStructureHandler(BaseStructureHandler):
 
         for span in spans:
             if span.is_structural:
-                for i in range(span.start, min(span.end, length)):
-                    mask[i] = True
+                start = min(span.start, length)
+                end = min(span.end, length)
+                if start < end:
+                    mask[start:end] = [True] * (end - start)
 
         return mask
 
@@ -622,18 +620,8 @@ class CodeStructureHandler(BaseStructureHandler):
         Returns:
             Language name (lowercase).
         """
-        # Check for language-specific markers
-        markers = {
-            "python": ["def ", "import ", "from ", "class ", "async def"],
-            "javascript": ["function ", "const ", "let ", "var ", "=>"],
-            "typescript": ["interface ", "type ", ": string", ": number"],
-            "go": ["func ", "package ", "import (", "type "],
-            "rust": ["fn ", "let mut", "impl ", "pub fn", "use "],
-            "java": ["public class", "private ", "protected ", "void "],
-        }
-
         scores: dict[str, int] = {}
-        for lang, patterns in markers.items():
+        for lang, patterns in _LANGUAGE_MARKERS.items():
             scores[lang] = sum(1 for p in patterns if p in content)
 
         if not scores or max(scores.values()) == 0:
diff --git a/headroom/compression/handlers/json_handler.py b/headroom/compression/handlers/json_handler.py
index 80d4f7ec5..9c54908ba 100644
--- a/headroom/compression/handlers/json_handler.py
+++ b/headroom/compression/handlers/json_handler.py
@@ -183,11 +183,8 @@ class JSONStructureHandler(BaseStructureHandler):
                 for i in range(token.start, min(token.end, len(mask))):
                     mask[i] = True
 
-        # Convert to character tokens if needed
-        char_tokens = list(content) if tokens == list(content) else tokens
-
         return HandlerResult(
-            mask=StructureMask(tokens=char_tokens, mask=mask),
+            mask=StructureMask(tokens=tokens, mask=mask),
             handler_name=self.name,
             confidence=1.0,
             metadata={
@@ -326,7 +323,9 @@ class JSONStructureHandler(BaseStructureHandler):
                 i += 1
                 while i < n and content[i] != '"':
                     if content[i] == "\\":
-                        i += 2  # Skip escaped character
+                        # Clamp: a trailing backslash at EOF must not
+                        # step past the buffer.
+                        i = min(i + 2, n)
                     else:
                         i += 1
                 i += 1  # Include closing quote