spec: numeric tower primitives — integer?/float? predicates, contagion docs

Add integer? and float? to spec/primitives.sx predicates section.
Update number? doc and body (or-guard for integer? type).
Update / :returns to "float" (always inexact).
Update floor/ceil/truncate :returns to "integer", improve docs.
Update round doc (returns integer at ndigits=0).
Update exact?/inexact?/exact->inexact/inexact->exact docs and returns.
Update +/-/* docs to document float contagion rule.
Fix double-paren :params on truncate/exact?/inexact?/exact->inexact/inexact->exact.
4874 passed, 394 failed (baseline unchanged).

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

spec/primitives.sx

@@ -43,35 +43,35 @@
   "+"
   :params (&rest (args :as number))
   :returns "number"
-  :doc "Sum all arguments."
+  :doc "Sum all arguments. Returns integer iff all args are exact integers (float contagion)."
   :body (reduce (fn (a b) (native-add a b)) 0 args))
 
 (define-primitive
   "-"
   :params ((a :as number) &rest (b :as number))
   :returns "number"
-  :doc "Subtract. Unary: negate. Binary: a - b."
+  :doc "Subtract. Unary: negate. Binary: a - b. Float contagion: returns integer iff all args are integers."
   :body (if (empty? b) (native-neg a) (native-sub a (first b))))
 
 (define-primitive
   "*"
   :params (&rest (args :as number))
   :returns "number"
-  :doc "Multiply all arguments."
+  :doc "Multiply all arguments. Float contagion: integer result iff all args are exact integers."
   :body (reduce (fn (a b) (native-mul a b)) 1 args))
 
 (define-primitive
   "/"
   :params ((a :as number) (b :as number))
-  :returns "number"
-  :doc "Divide a by b."
+  :returns "float"
+  :doc "Divide a by b. Always returns inexact float."
   :body (native-div a b))
 
 (define-primitive
   "mod"
   :params ((a :as number) (b :as number))
   :returns "number"
-  :doc "Modulo a % b."
+  :doc "Modulo a % b. Returns integer iff both args are integers."
   :body (native-mod a b))
 
 (define-primitive
@@ -108,26 +108,26 @@
 (define-primitive
   "floor"
   :params ((x :as number))
-  :returns "number"
-  :doc "Floor to integer.")
+  :returns "integer"
+  :doc "Floor toward negative infinity — returns exact integer.")
 
 (define-primitive
   "ceil"
   :params ((x :as number))
-  :returns "number"
-  :doc "Ceiling to integer.")
+  :returns "integer"
+  :doc "Ceiling toward positive infinity — returns exact integer.")
 
 (define-primitive
   "round"
   :params ((x :as number) &rest (ndigits :as number))
   :returns "number"
-  :doc "Round to ndigits decimal places (default 0).")
+  :doc "Round to ndigits decimal places (default 0). Returns integer when ndigits is 0.")
 
 (define-primitive
   "truncate"
-  :params (((x :as number)))
-  :returns "number"
-  :doc "Truncate toward zero.")
+  :params ((x :as number))
+  :returns "integer"
+  :doc "Truncate toward zero — returns exact integer.")
 
 (define-primitive
   "remainder"
@@ -143,30 +143,30 @@
 
 (define-primitive
   "exact?"
-  :params (((x :as number)))
+  :params ((x :as number))
   :returns "boolean"
-  :doc "True if x is exact (integer-valued).")
+  :doc "True if x is an exact integer (not an inexact float).")
 
 (define-primitive
   "inexact?"
-  :params (((x :as number)))
+  :params ((x :as number))
   :returns "boolean"
-  :doc "True if x is inexact (non-integer).")
+  :doc "True if x is an inexact float (not an exact integer).")
 
 ;; --------------------------------------------------------------------------
 ;; Core — Comparison
 ;; --------------------------------------------------------------------------
 (define-primitive
   "exact->inexact"
-  :params (((x :as number)))
-  :returns "number"
-  :doc "Convert exact to inexact (identity for float tower).")
+  :params ((x :as number))
+  :returns "float"
+  :doc "Convert exact integer to inexact float. Floats pass through unchanged.")
 
 (define-primitive
   "inexact->exact"
-  :params (((x :as number)))
-  :returns "number"
-  :doc "Convert inexact to nearest exact integer.")
+  :params ((x :as number))
+  :returns "integer"
+  :doc "Convert inexact float to nearest exact integer (truncates). Integers pass through unchanged.")
 
 (define-primitive
   "make-vector"
@@ -374,8 +374,20 @@
   "number?"
   :params (x)
   :returns "boolean"
-  :doc "True if x is a number (int or float)."
-  :body (= (type-of x) "number"))
+  :doc "True if x is any number — exact integer or inexact float."
+  :body (or (= (type-of x) "number") (integer? x)))
+
+(define-primitive
+  "integer?"
+  :params (x)
+  :returns "boolean"
+  :doc "True if x is an exact integer, or a float with no fractional part (e.g. 1.0).")
+
+(define-primitive
+  "float?"
+  :params (x)
+  :returns "boolean"
+  :doc "True if x is an inexact float (Number type). Does not match exact integers.")
 
 (define-primitive
   "string?"