fix(codegen/deno-esm): add endsWith / stripSuffix / numToFixed2 lowering (closes #470)

Three `pub extern fn` decls in stdlib/Deno.affine had no matching entry in
codegen_deno.ml's `deno_builtins` table. The codegen emitted bare calls to
undefined JS symbols at runtime (ReferenceError).

Adds direct lowerings (per the option-1 path in the issue):
  endsWith(s, x)    -> String(s).endsWith(x)
  stripSuffix(s, x) -> ((__s,__x) => __s.endsWith(__x) ? __s.slice(0,-__x.length) : __s)(s, x)
  numToFixed2(n)    -> Number(n).toFixed(2)

Adds `tests/codegen-deno/deno_string_fmt.{affine,harness.mjs}` covering the
three names plus stripSuffix passthrough on suffix-miss. The general
extern->stdlib-body linkage question (option-2 in #470) stays open as
follow-up — option-1 is the small, ship-now fix.

374/374 dune tests + all codegen-deno harnesses green.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Signed-off-by: hyperpolymath <6759885+hyperpolymath@users.noreply.github.com>

Author: hyperpolymath

lib/codegen_deno.ml

@@ -648,6 +648,12 @@ let () =
   (* Kilobyte display string: `(n/1024).toFixed(2)` — runtime number
      formatting is an honest host primitive in every language. *)
   b "kbString"    (fun a -> Printf.sprintf "(Number(%s) / 1024).toFixed(2)" (arg 0 a));
+  (* String suffix predicates + numeric formatter (#470). Originally
+     intended to ride on stdlib bodies; without extern->stdlib linkage
+     they need explicit lowering entries. *)
+  b "endsWith"    (fun a -> Printf.sprintf "String(%s).endsWith(%s)" (arg 0 a) (arg 1 a));
+  b "stripSuffix" (fun a -> Printf.sprintf "((__s, __x) => __s.endsWith(__x) ? __s.slice(0, -__x.length) : __s)(%s, %s)" (arg 0 a) (arg 1 a));
+  b "numToFixed2" (fun a -> Printf.sprintf "Number(%s).toFixed(2)" (arg 0 a));
   (* ---- misc host ---- *)
   b "dateNow"     (fun _ -> "Date.now()");
   (* `new Date().toISOString()` — UTC ISO-8601 timestamp string. Distinct

tests/codegen-deno/deno_string_fmt.affine

@@ -0,0 +1,14 @@
+// SPDX-License-Identifier: MPL-2.0
+// #470 — Deno externs `endsWith` / `stripSuffix` / `numToFixed2` needed
+// explicit lowering entries in codegen_deno.ml. Before the fix all three
+// emitted a bare call to an undefined symbol -> runtime ReferenceError.
+
+use Deno::{ endsWith, stripSuffix, numToFixed2 };
+
+pub fn is_ts(p: String) -> Bool = endsWith(p, ".ts");
+
+pub fn drop_ts_suffix(p: String) -> String = stripSuffix(p, ".ts");
+
+pub fn drop_missing_suffix(p: String) -> String = stripSuffix(p, ".rs");
+
+pub fn fmt_pct(x: Int) -> String = numToFixed2(x);

tests/codegen-deno/deno_string_fmt.harness.mjs

@@ -0,0 +1,29 @@
+// SPDX-License-Identifier: MPL-2.0
+// #470 — verify the three previously-missing Deno externs now resolve.
+
+import assert from "node:assert/strict";
+
+const {
+  is_ts,
+  drop_ts_suffix,
+  drop_missing_suffix,
+  fmt_pct,
+} = await import("./deno_string_fmt.deno.js");
+
+// endsWith
+assert.equal(is_ts("foo.ts"),   true,  "endsWith hit");
+assert.equal(is_ts("foo.tsx"),  false, "endsWith miss");
+assert.equal(is_ts(""),         false, "endsWith empty");
+
+// stripSuffix — present
+assert.equal(drop_ts_suffix("foo.ts"), "foo",   "stripSuffix removes matching suffix");
+assert.equal(drop_ts_suffix(".ts"),    "",      "stripSuffix down to empty");
+
+// stripSuffix — absent (must return input unchanged, not throw)
+assert.equal(drop_missing_suffix("foo.ts"), "foo.ts", "stripSuffix passthrough when suffix absent");
+
+// numToFixed2
+assert.equal(fmt_pct(0),    "0.00",   "numToFixed2 of 0");
+assert.equal(fmt_pct(42),   "42.00",  "numToFixed2 of int");
+
+console.log("deno_string_fmt.harness.mjs OK");