fix(search): recover adjacent transposition typos in fuzzy ranking

packages/shared/src/searchRanking.test.ts

@@ -33,6 +33,19 @@ describe("scoreQueryMatch", () => {
   });
 });
 
+describe("scoreQueryMatch typo tolerance", () => {
+  const match = (value: string, query: string) =>
+    scoreQueryMatch({ value, query, exactBase: 0, prefixBase: 10, fuzzyBase: 50 });
+
+  it("recovers a single adjacent transposition without accepting arbitrary edits", () => {
+    expect(match("search", "serach")).toBe(51);
+    expect(match("search", "search")).toBe(0);
+    expect(match("search", "searxh")).toBeNull();
+    expect(match("cat", "cta")).toBeNull();
+    expect(match("search", "serahc")).toBeNull();
+  });
+});
+
 describe("scoreSubsequenceMatch", () => {
   it("scores tighter subsequences ahead of looser ones", () => {
     const compact = scoreSubsequenceMatch("ghfixci", "gfc");

packages/shared/src/searchRanking.ts

@@ -58,6 +58,16 @@ export function scoreSubsequenceMatch(
   return null;
 }
 
+/** A single adjacent-key ordering mistake, without broad edit-distance matches. */
+function isAdjacentTransposition(value: string, query: string): boolean {
+  if (query.length < 4 || value.length !== query.length) return false;
+  let first = 0;
+  while (first < query.length && value[first] === query[first]) first += 1;
+  if (first >= query.length - 1) return false;
+  if (value[first] !== query[first + 1] || value[first + 1] !== query[first]) return false;
+  return value.slice(first + 2) === query.slice(first + 2);
+}
+
 function lengthPenalty(value: string, query: string): number {
   return Math.min(64, Math.max(0, value.length - query.length));
 }
@@ -135,6 +145,9 @@ export function scoreQueryMatch(input: {
     if (fuzzyScore !== null) {
       return input.fuzzyBase + fuzzyScore;
     }
+    if (isAdjacentTransposition(value, query)) {
+      return input.fuzzyBase + 1;
+    }
   }
 
   return null;