search: fuzzy matching via edit distance + 18 tests

editDist as an O(m*n) row-based Levenshtein DP (naive recursion is exponential
and times out under load); fuzzyTerms/fuzzyDocs/fuzzyRankTfIdf expand a term to
indexed terms within a max edit distance. 166/166.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/search/tests/fuzzy.sx

@@ -0,0 +1,74 @@
+;; Extension — fuzzy matching via Levenshtein edit distance.
+;; Corpus: 1 "color flavor"  2 "colour kitten"  3 "colored"
+;; allTerms: color colored colour flavor kitten
+
+(define
+  fuzzy-setup
+  "idx = indexDoc 3 \"colored\" (indexDoc 2 \"colour kitten\" (indexDoc 1 \"color flavor\" emptyIndex))\n")
+
+(define
+  fuzzy-cases
+  (list
+    (list
+      "editDist substitution"
+      "[editDist \"kitten\" \"sitten\"]"
+      (list 1))
+    (list "editDist equal" "[editDist \"abc\" \"abc\"]" (list 0))
+    (list "editDist deletion" "[editDist \"abc\" \"ab\"]" (list 1))
+    (list "editDist insertion" "[editDist \"ab\" \"abc\"]" (list 1))
+    (list "editDist from empty" "[editDist \"\" \"abc\"]" (list 3))
+    (list "editDist both empty" "[editDist \"\" \"\"]" (list 0))
+    (list
+      "editDist classic"
+      "[editDist \"kitten\" \"sitting\"]"
+      (list 3))
+    (list
+      "editDist color colour"
+      "[editDist \"color\" \"colour\"]"
+      (list 1))
+    (list
+      "editDist color colored"
+      "[editDist \"color\" \"colored\"]"
+      (list 2))
+    (list
+      "fuzzy terms dist 1"
+      "fuzzyTerms 1 \"color\" idx"
+      (list "color" "colour"))
+    (list
+      "fuzzy terms dist 2"
+      "fuzzyTerms 2 \"color\" idx"
+      (list "color" "colored" "colour"))
+    (list "fuzzy terms exact" "fuzzyTerms 0 \"color\" idx" (list "color"))
+    (list
+      "fuzzy terms other word"
+      "fuzzyTerms 1 \"flavour\" idx"
+      (list "flavor"))
+    (list
+      "fuzzy docs dist 1"
+      "fuzzyDocs 1 \"color\" idx"
+      (list 1 2))
+    (list
+      "fuzzy docs dist 2"
+      "fuzzyDocs 2 \"color\" idx"
+      (list 1 2 3))
+    (list "fuzzy docs none" "fuzzyDocs 1 \"zzzzz\" idx" (list))
+    (list
+      "fuzzy rank dist 1"
+      "fuzzyRankTfIdf 1 \"color\" idx"
+      (list 1 2))
+    (list
+      "fuzzy rank dist 2"
+      "fuzzyRankTfIdf 2 \"color\" idx"
+      (list 1 2 3))))
+
+(define
+  fuzzy-results
+  (search-batch fuzzy-setup (map (fn (c) (nth c 1)) fuzzy-cases)))
+
+(map-indexed
+  (fn
+    (i c)
+    (hk-test (nth c 0) (nth fuzzy-results i) (nth c 2)))
+  fuzzy-cases)
+
+{:fail hk-test-fail :pass hk-test-pass :fails hk-test-fails}