selfhost: port append + spread — N_SPREAD parser + rt_ensure builtin

test/wcc/990_selfhost.c

@@ -345,6 +345,35 @@ probe_ww_compile(const char *bin)
 		  "  dec(&c); dec(&c); dec(&c);\n"
 		  "  return c.x;\n"
 		  "};", 2 },
+		/* append(s, v, ...) builtin — Hare's rt::ensure model.
+		 * Each value: PUSHQ AX, ADDQ $1 to s.len, LEAQ s/MOVQ esz
+		 * args for rt_ensure, then write into the freshly-grown
+		 * slot. Returns s.len = 3 after appending three u8s. */
+		{ "use os;\n"
+		  "fn main() i32 = {\n"
+		  "  let s: []u8;\n"
+		  "  s.ptr = nil; s.len = 0; s.cap = 0;\n"
+		  "  append(s, 65u8, 66u8, 67u8);\n"
+		  "  return s.len: i32;\n"
+		  "};", 3 },
+		/* append(s, items...) spread variant — wraps the per-value
+		 * body in a counted loop over items.len. Combined with
+		 * single-value appends in the same fn. dst ends up with
+		 * [1, 10, 20, 30] — sum = 61. */
+		{ "use os;\n"
+		  "fn main() i32 = {\n"
+		  "  let src: []i64;\n"
+		  "  src.ptr = nil; src.len = 0; src.cap = 0;\n"
+		  "  append(src, 10i64, 20i64, 30i64);\n"
+		  "  let dst: []i64;\n"
+		  "  dst.ptr = nil; dst.len = 0; dst.cap = 0;\n"
+		  "  append(dst, 1i64);\n"
+		  "  append(dst, src...);\n"
+		  "  let total: i64 = 0i64;\n"
+		  "  let i: i32 = 0;\n"
+		  "  for (i < dst.len) { total += dst[i]; i += 1; };\n"
+		  "  return total: i32;\n"
+		  "};", 61 },
 		/* switch with multi-expr cases + default. Lowers to a chain
 		 * of CMPQ + JE; the scrutinee lands in a fresh 8B local slot
 		 * (".sw_N") so case bodies can spill SP without losing it.

test/wcc/994_w6c_ww.c

@@ -159,6 +159,25 @@ main(void)
 		  "  return -1;\n"
 		  "};\n"
 		  "fn main() i32 = { return classify(2); };" },
+		{ "append",
+		  "use os;\n"
+		  "fn main() i32 = {\n"
+		  "  let s: []u8;\n"
+		  "  s.ptr = nil; s.len = 0; s.cap = 0;\n"
+		  "  append(s, 65u8, 66u8, 67u8);\n"
+		  "  return s.len: i32;\n"
+		  "};" },
+		{ "append_spread",
+		  "use os;\n"
+		  "fn main() i32 = {\n"
+		  "  let src: []i64;\n"
+		  "  src.ptr = nil; src.len = 0; src.cap = 0;\n"
+		  "  append(src, 10i64, 20i64);\n"
+		  "  let dst: []i64;\n"
+		  "  dst.ptr = nil; dst.len = 0; dst.cap = 0;\n"
+		  "  append(dst, src...);\n"
+		  "  return dst.len: i32;\n"
+		  "};" },
 		{ NULL, NULL },
 	};