search: Phase 2 query AST + boolean/phrase eval + 28 tests

Query ADT (Term|And|Or|Not|Phrase) and evalQuery over docid-sorted posting
lists: boolean ops as linear merges, Not over the allDocs universe, Phrase via
positional adjacency. Batched both test suites into one program eval each
(search-batch) so they finish under heavy CPU load. 46/46.

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

lib/search/testlib.sx

@@ -27,3 +27,24 @@
     (search-hk->sx
       (hk-deep-force
         (get (hk-eval-program (hk-core (str search/src extra))) name)))))
+
+(define
+  search-join
+  (fn
+    (sep xs)
+    (cond
+      ((empty? xs) "")
+      ((empty? (rest xs)) (first xs))
+      (:else (str (first xs) sep (search-join sep (rest xs)))))))
+
+;; Batch many haskell expressions into ONE program evaluation (amortizes the
+;; cost of parsing/binding search/src — important under heavy CPU load).
+;; `setup` is extra top-level Haskell; `exprs` is a list of expression strings
+;; whose results form a single haskell list. Returns the SX list of results.
+(define
+  search-batch
+  (fn
+    (setup exprs)
+    (search-eval
+      (str setup "\nresult = [" (search-join ", " exprs) "]\n")
+      "result")))