wcc: chained-dot str leaf loads the cap word, both stages

A str field reached through a chained dot (o.i.s) emitted two loads
(ptr, len) and stored a stale CX as the cap — both stages, at any
non-zero chain depth. Emit the full header at the chained-dot leaf.
Review item #29.

Both stages move in one commit: one emission contract; splitting
would leave the byte-id gates red between the halves.

test/wcc/949_f6_header_run.c

@@ -139,6 +139,36 @@ static const struct row rows[] = {
 	  "	if (ys.len == 6) { return 0; };\n"
 	  "	return 1;\n"
 	  "};\n", 0, K_RUN, NULL },
+	/* #29 (#263 both-stages): chained-dot str leaf `o.i.s` (depth-2)
+	 * dropped the cap word — a junk strlit before the chain left CX
+	 * stale, so t.cap read 2 (the junk's cap) instead of 5. Now the
+	 * str leaf loads all three header words like the slice arm. */
+	{ "chained_str_cap",
+	  "package main;\n"
+	  "type inner = struct { s: str, x: i64 };\n"
+	  "type outer = struct { i: inner, y: i64 };\n"
+	  "export fn main() i32 = {\n"
+	  "	let iv: inner = inner { s = \"hello\", x = 0 };\n"
+	  "	let o: outer = outer { i = iv, y = 0 };\n"
+	  "	let junk: str = \"ab\";\n"
+	  "	let t: str = o.i.s;\n"
+	  "	return t.cap: i32;\n"
+	  "};\n", 5, K_RUN, NULL },
+	/* #29 sibling: the str leaf sits at a NON-ZERO field offset within the
+	 * inner struct (a leading i64 pad pushes `s` to +8, so totaloff != 0).
+	 * Exercises the chained-leaf offset arithmetic the offset-0 row leaves
+	 * untested. Junk strlit before the chain; cap == len == 7. */
+	{ "chained_str_cap_offset",
+	  "package main;\n"
+	  "type inner = struct { pad: i64, s: str };\n"
+	  "type outer = struct { i: inner, y: i64 };\n"
+	  "export fn main() i32 = {\n"
+	  "	let iv: inner = inner { pad = 0, s = \"worldly\" };\n"
+	  "	let o: outer = outer { i = iv, y = 0 };\n"
+	  "	let junk: str = \"ab\";\n"
+	  "	let t: str = o.i.s;\n"
+	  "	return t.cap: i32;\n"
+	  "};\n", 7, K_RUN, NULL },
 };
 
 static int