haskell: Phase 10 — fromIntegral verified as prelude identity (+4 tests, 14/14)

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

plans/haskell-completeness.md

@@ -148,9 +148,10 @@ No OCaml changes are needed. The view type is fully representable as an SX dict.
   note limit in a comment if there is one. _Verified; documented practical
   limit of 2^53 (≈ 9e15) due to Haskell tokenizer parsing larger int literals
   as floats. Raw SX is exact to ±2^62. See header comment in `numerics.sx`._
-- [ ] `fromIntegral :: (Integral a, Num b) => a -> b` — identity in our runtime
+- [x] `fromIntegral :: (Integral a, Num b) => a -> b` — identity in our runtime
   (all numbers share one SX type); register as a builtin no-op with the correct
-  typeclass signature.
+  typeclass signature. _Already in `hk-prelude-src` as `fromIntegral x = x`;
+  verified with new tests in `numerics.sx`._
 - [ ] `toInteger`, `fromInteger` — same treatment.
 - [ ] Float/Double literals round-trip through `hk-show-val`:
   `show 3.14 = "3.14"`, `show 1.0e10 = "1.0e10"`.
@@ -295,6 +296,13 @@ No OCaml changes are needed. The view type is fully representable as an SX dict.
 
 _Newest first._
 
+**2026-05-07** — Phase 10 `fromIntegral` verified (already an identity in prelude):
+- Pre-existing `fromIntegral x = x` line in `hk-prelude-src` was already
+  correct — all numbers share one SX type, so the identity implementation is
+  exactly what the plan asked for. Added 4 tests in `numerics.sx` covering:
+  positive int, negative int, mixed-arithmetic, and `map fromIntegral [1,2,3]`.
+  Suite is now 14/14.
+
 **2026-05-07** — Phase 10 large-integer audit (numerics.sx 10/10):
 - Investigated SX number behavior in Haskell context. Findings:
     • Raw SX `*`, `+`, etc. on two ints stay exact up to ±2^62 (~4.6e18).