diff --git a/openmed/.jules/bolt.md b/openmed/.jules/bolt.md
new file mode 100644
index 0000000..8fcb703
--- /dev/null
+++ b/openmed/.jules/bolt.md
@@ -0,0 +1,3 @@
+## 2024-05-24 - Cache alias lookups for clinical section detection
+**Learning:** In `openmed/openmed/clinical/sections/detect.py`, `_alias_lookups` was repeatedly parsing section header lexicons and building dictionaries for each line of a document. For large, many-line documents, this caused significant slowdowns because the section lookup computation is deterministic based on the language. Additionally, since the return values needed caching, a regular dict couldn't be safely cached due to mutability.
+**Action:** When caching dictionaries generated from configuration or lexicons, use `@functools.lru_cache` and ensure the return type is explicitly wrapped in `types.MappingProxyType` to prevent any downstream modifications to the cached object.
diff --git a/openmed/openmed/clinical/sections/detect.py b/openmed/openmed/clinical/sections/detect.py
index 8716746..3293ed0 100644
--- a/openmed/openmed/clinical/sections/detect.py
+++ b/openmed/openmed/clinical/sections/detect.py
@@ -2,6 +2,8 @@
 
 from __future__ import annotations
 
+import functools
+import types
 from collections.abc import Iterable, Mapping
 from dataclasses import dataclass
 from typing import Any
@@ -244,6 +246,7 @@ def _is_underline(text: str) -> bool:
     return len(stripped) >= 3 and set(stripped) <= _UNDERLINE_CHARS
 
 
+@functools.lru_cache(maxsize=16)
 def _alias_lookups(language: str | None) -> tuple[tuple[str, Mapping[str, str]], ...]:
     languages = (
         tuple(dict.fromkeys((get_section_lexicon(language).language, "en")))
@@ -253,14 +256,15 @@ def _alias_lookups(language: str | None) -> tuple[tuple[str, Mapping[str, str]],
     return tuple((code, _aliases_for_language(code)) for code in languages)
 
 
-def _aliases_for_language(language: str) -> dict[str, str]:
+@functools.lru_cache(maxsize=32)
+def _aliases_for_language(language: str) -> Mapping[str, str]:
     lexicon = get_section_lexicon(language)
     aliases: dict[str, str] = {}
     for label, headers in lexicon.sections.items():
         aliases[normalize_section_header(label)] = label
         for header in headers:
             aliases[normalize_section_header(header)] = label
-    return aliases
+    return types.MappingProxyType(aliases)
 
 
 def _dedupe_hits(hits: Iterable[_HeaderHit]) -> tuple[_HeaderHit, ...]: