fix: store IndexReader once; sanitize all tantivy query specials

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/lexical.rs

@@ -7,6 +7,7 @@ use tantivy::{doc, Index, TantivyDocument};
 
 pub struct LexicalIndex {
     index: Index,
+    reader: tantivy::IndexReader,
     text_field: tantivy::schema::Field,
     idx_field: tantivy::schema::Field,
 }
@@ -31,8 +32,12 @@ impl LexicalIndex {
         }
         w.commit()
             .map_err(|e| AppError::Io(format!("tantivy commit: {e}")))?;
+        let reader = index
+            .reader()
+            .map_err(|e| AppError::Io(format!("tantivy reader: {e}")))?;
         Ok(Self {
             index,
+            reader,
             text_field,
             idx_field,
         })
@@ -40,21 +45,23 @@ impl LexicalIndex {
 
     /// Returns (entry_index, bm25_score) descending.
     pub fn search(&self, query: &str, k: usize) -> Result<Vec<(usize, f32)>, AppError> {
-        let reader = self
-            .index
-            .reader()
-            .map_err(|e| AppError::Io(format!("tantivy reader: {e}")))?;
-        let searcher = reader.searcher();
+        let searcher = self.reader.searcher();
         let norm = normalize(query);
-        let sanitized = norm.replace(['(', ')', '"', ':'], " ");
+        // Strip all tantivy grammar specials (-, +, ~, *, etc.) — medical text
+        // never intends them as operators; leaving them silently corrupts recall
+        // (e.g. "C50.-" triggers NOT, "hüft-tep" loses the second token).
+        let sanitized = norm.replace(
+            ['(', ')', '"', ':', '-', '+', '[', ']', '{', '}', '~', '!', '^', '*', '\\', '?'],
+            " ",
+        );
         // Use OR semantics (default) for recall-favoring behaviour; fall back to
-        // the raw normalised query on parse error.
+        // conjunction semantics on parse error — both attempts use the sanitized string.
         let parsed = QueryParser::for_index(&self.index, vec![self.text_field])
             .parse_query(&sanitized)
             .or_else(|_| {
                 let mut qp = QueryParser::for_index(&self.index, vec![self.text_field]);
                 qp.set_conjunction_by_default();
-                qp.parse_query(&norm)
+                qp.parse_query(&sanitized)
             })
             .map_err(|e| AppError::Parse(format!("query: {e}")))?;
         let top = searcher