Refactor phase 2c: split passes.clj into fold/inline/types behind a façade

passes.clj was a 1486-line grab-bag mixing three weakly-coupled concerns. Split
along the clusters the review mapped (only run-passes + the dirty flag were
shared):

  jolt.passes.fold    const-fold + the shared scalar-const? predicate (base)
  jolt.passes.inline  inline + flatten-lets + scalar-replace
  jolt.passes.types   collection-type inference + success checker + driver API
  jolt.passes         façade: run-passes + :refer re-exports of the driver fns
                      the back end looks up by name

scalar-const? was used by both the inline pass and the inference walk, so it
moves to fold (the base layer) and both refer it. The check-mode state stays
private to jolt.passes.types behind a new run-inference fn; run-passes calls it.

build-compiler! loads the three in dependency order before the façade, mirroring
the existing jolt.ir -> jolt.analyzer bootstrap. No behavior change. Also fixed
the stale ns docstring that listed four passes and omitted the type system.

Gate green: conformance 355x3, clojure-test-suite 4718 pass (>= 4695 baseline),
full jpm test exit 0.

jolt-core/jolt/passes/fold.clj

@@ -0,0 +1,103 @@
+(ns jolt.passes.fold
+  "Constant folding (always-on IR pass) plus the shared const-shape predicate.
+  Bottom-up numeric folding + dead-branch removal, total over node :ops (unknown
+  ops pass through with folded children). Portable Clojure: kernel-tier fns +
+  seed primitives only — it loads with the compiler namespaces, before the later
+  core tiers.")
+
+;; Folding computes with THE ACTUAL jolt fns, so a folded result matches what
+;; the unfolded code would produce at runtime by construction. Conservative:
+;; numbers only, the op table only names pure numeric fns, and any throw
+;; during folding (e.g. (mod x 0)) leaves the node alone for runtime.
+(def ^:private foldable
+  ;; SEED fns only: this ns loads with the compiler, BEFORE the later core
+  ;; tiers — a name from 20-coll (min/max/abs) wouldn't resolve yet.
+  {"+" + "-" - "*" * "/" /
+   "<" < ">" > "<=" <= ">=" >= "=" =
+   "inc" inc "dec" dec
+   "mod" mod "rem" rem "quot" quot
+   ;; the __bit-* seams: the PUBLIC bit fns are 20-coll variadic shells now,
+   ;; which don't exist yet when this ns loads. Folding stays 2-arg (a 3+-arg
+   ;; constant call throws arity inside the fold and is left for runtime).
+   "bit-and" __bit-and "bit-or" __bit-or "bit-xor" __bit-xor})
+
+(defn- const? [n] (= :const (get n :op)))
+(defn- const-num? [n] (and (const? n) (number? (get n :val))))
+
+(defn- fold-fn [fnode]
+  (let [op (get fnode :op)]
+    (when (or (and (= op :var) (= "clojure.core" (get fnode :ns)))
+              (= op :host))
+      (get foldable (get fnode :name)))))
+
+(defn const-fold
+  "Bottom-up constant folding: a call of a foldable numeric fn whose args are
+  all constant numbers becomes a constant; an if with a constant test becomes
+  the taken branch."
+  [node]
+  (let [op (get node :op)]
+    (cond
+      (= op :invoke)
+      (let [f (const-fold (get node :fn))
+            args (mapv const-fold (get node :args))
+            ff (fold-fn f)
+            folded (when (and ff (pos? (count args)) (every? const-num? args))
+                     (try
+                       {:op :const :val (apply ff (mapv (fn [a] (get a :val)) args))}
+                       (catch Exception e nil)))]
+        (or folded (assoc node :fn f :args args)))
+
+      (= op :if)
+      (let [t (const-fold (get node :test))]
+        (if (const? t)
+          ;; jolt truthiness = Clojure's: nil/false take else
+          (if (or (nil? (get t :val)) (= false (get t :val)))
+            (const-fold (get node :else))
+            (const-fold (get node :then)))
+          (assoc node
+                 :test t
+                 :then (const-fold (get node :then))
+                 :else (const-fold (get node :else)))))
+
+      (= op :do)
+      (assoc node
+             :statements (mapv const-fold (get node :statements))
+             :ret (const-fold (get node :ret)))
+
+      ;; let/loop bindings are [name-string init-ir] PAIRS (see
+      ;; analyzer/analyze-bindings), not maps.
+      (= op :let)
+      (assoc node
+             :bindings (mapv (fn [b] [(nth b 0) (const-fold (nth b 1))])
+                             (get node :bindings))
+             :body (const-fold (get node :body)))
+
+      (= op :loop)
+      (assoc node
+             :bindings (mapv (fn [b] [(nth b 0) (const-fold (nth b 1))])
+                             (get node :bindings))
+             :body (const-fold (get node :body)))
+
+      (= op :recur)
+      (assoc node :args (mapv const-fold (get node :args)))
+
+      (= op :fn)
+      (assoc node
+             :arities (mapv (fn [a] (assoc a :body (const-fold (get a :body))))
+                            (get node :arities)))
+
+      (= op :def)    (assoc node :init (const-fold (get node :init)))
+      (= op :throw)  (assoc node :expr (const-fold (get node :expr)))
+      (= op :vector) (assoc node :items (mapv const-fold (get node :items)))
+      (= op :set)    (assoc node :items (mapv const-fold (get node :items)))
+      (= op :map)    (assoc node :pairs (mapv (fn [pr] (mapv const-fold pr)) (get node :pairs)))
+
+      ;; leaves and anything this pass doesn't know: unchanged
+      :else node)))
+
+;; A const node whose value is a scalar literal (kw/str/num/bool). Shared by the
+;; scalar-replace pass (jolt.passes.inline) and the collection-type inference
+;; (jolt.passes.types), which both reason about const-keyed maps.
+(defn scalar-const? [n]
+  (and (= :const (get n :op))
+       (let [v (get n :val)] (or (keyword? v) (string? v) (number? v) (boolean? v)))))