diff --git a/test/wcc/928_str_abi_run.c b/test/wcc/928_str_abi_run.c
index f28e7059..b68a1fb1 100644
--- a/test/wcc/928_str_abi_run.c
+++ b/test/wcc/928_str_abi_run.c
@@ -13,7 +13,10 @@
  * AX/BX/CX value / AX:DX:CX:R8 tagged+tuple register layout: str
  * literal (cap=len), str arg, str return, str struct field, the
  * (i64,str) and (str,i64) tuple return shapes, deref-store `*p = s`,
- * and []str index write+read.
+ * and []str index write+read. Phase 2 collapse folds (str IS []u8):
+ * str byte-index read `s[i]` (element stride via the type table,
+ * commit a5ca21d) and str widened into a tagged-union variant (the
+ * payload store folded onto the common slice arm, commit b416e71).
  *
  * Deliberately NOT covered here (known, separately-tracked gaps found
  * during Commit #1 review — both byte-identical across stages, so the
@@ -142,6 +145,52 @@ static const struct row rows[] = {
 	  "    return 0;\n"
 	  "};\n",
 	  0 },
+	/* str byte index read: `s[i]` strides by the u8 element size (1),
+	 * routed through the type table post-collapse (a5ca21d). Guards
+	 * the N_INDEX str-element stride against a slice-width (24B)
+	 * miscompute now that str shares the slice path. */
+	{ "str_index_read",
+	  "export fn main() i32 = {\n"
+	  "    let s: str = \"hello\";\n"
+	  "    if (s[0]: i32 != 104) { return 1; };\n"
+	  "    if (s[1]: i32 != 101) { return 2; };\n"
+	  "    if (s[4]: i32 != 111) { return 3; };\n"
+	  "    return 0;\n"
+	  "};\n",
+	  0 },
+	/* str widened into a tagged-union variant: the payload store
+	 * folds onto the common slice arm (3-word ptr/len/cap @
+	 * slot+8/+16/+24 + tag, b416e71). Exercises literal, str-variable
+	 * and a str returned from a fn into `(str | i64)`, plus the i64
+	 * arm so the variant-tag selection is checked both ways. */
+	{ "tagged_union_str_store",
+	  "type sv = (str | i64);\n"
+	  "fn wrap(s: str) sv = { return s; };\n"
+	  "export fn main() i32 = {\n"
+	  "    let x: sv = \"hello\";\n"
+	  "    match (x) {\n"
+	  "    case let s: str => { if (s.len: i32 != 5) { return 1; }; };\n"
+	  "    case let n: i64 => { return 2; };\n"
+	  "    };\n"
+	  "    let a: str = \"world\";\n"
+	  "    let y: sv = a;\n"
+	  "    match (y) {\n"
+	  "    case let s: str => { if (s.len: i32 != 5) { return 3; }; };\n"
+	  "    case let n: i64 => { return 4; };\n"
+	  "    };\n"
+	  "    let z: sv = wrap(\"abcd\");\n"
+	  "    match (z) {\n"
+	  "    case let s: str => { if (s.len: i32 != 4) { return 5; }; };\n"
+	  "    case let n: i64 => { return 6; };\n"
+	  "    };\n"
+	  "    let w: sv = 42i64;\n"
+	  "    match (w) {\n"
+	  "    case let s: str => { return 7; };\n"
+	  "    case let n: i64 => { if (n: i32 != 42) { return 8; }; };\n"
+	  "    };\n"
+	  "    return 0;\n"
+	  "};\n",
+	  0 },
 };
 
 static int