test: migrate 24 residual carriers into the fixture corpus

Audit-driven migrate-and-retire wave (one read-only auditor per
carrier batch, verdicts row-checked through the full corpus gate):
every retired carrier's assertions are now owned by declarative
fixtures or an existing owner. 238 new fixtures land (corpus 1,239 ->
1,477; cells 2,954), covering enum/str/slice/tagged array elements,
inferred-length arrays, global slice/str zero-init and literals,
global array/pointer field reads and stores, struct-literal slice
fields, struct returns, float arithmetic, size/int limits, sort and
log-vstream behavior, place-addressed stores, and append places.
Rejection rows STRENGTHEN the old nonzero-exit checks to required
diagnostic fragments; all byte-id claims fold into the blanket
test-data-byteid sweep (now 1,142 compared, 0 pinned-divergent).
Four carriers were fully redundant with existing fixtures/lang tests
(749, 722, 765, and 771's byteid rows) and retire without new rows.
Native carriers 171 -> 147 (residual 135 -> 111).

test/wcc/data/r806ap_idxfield_struct/case.ww

@@ -0,0 +1,24 @@
+//ww:run-exit 74
+package main;
+type capture = struct { content: str, start: size,
+	start_bytesize: size, end: size, end_bytesize: size };
+type thread = struct { pc: size, root_capture: capture,
+	matched: bool };
+export fn main() i32 = {
+	let threads: []thread = [];
+	append(threads, thread { pc = 7, ... });
+	append(threads, thread { pc = 1, root_capture = capture {
+		content = "bcd", start = 1, start_bytesize = 2,
+		end = 4, end_bytesize = 5 }, ... });
+	let res: []capture = [];
+	let i: size = 1;
+	append(res, threads[i].root_capture);
+	if (len(res) != 1) { return 1; };
+	if (res[0].start != 1) { return 2; };
+	if (res[0].start_bytesize != 2) { return 3; };
+	if (res[0].end != 4) { return 4; };
+	if (res[0].end_bytesize != 5) { return 5; };
+	if (res[0].content.len != 3) { return 6; };
+	if (threads[1].root_capture.end != 4) { return 7; };
+	return 74;
+};