test(e2e): the fixture was the invented wire format too

The e2e wrote its subos manifest in the same shape the broken reader expected,
so it kept passing while the feature did nothing against a real subos. Fixing
the reader made it fail, which is the correct outcome and the reason the fix
is trustworthy.

The comment now says the structure is a wire format rather than a convenience,
because the invented shape is the tidier-looking of the two and someone will
want to "simplify" it back.

Author: speak-agent

tests/e2e/200_subos_env_reaches_program.sh

@@ -14,6 +14,12 @@
 # know what any of these variables mean -- it carries whatever the subos
 # declares -- and a test naming LIBGL_DRIVERS_PATH would quietly suggest
 # otherwise.
+#
+# The JSON below is xlings's REAL shape: `envs` is an object keyed by binding,
+# whose values are arrays of declarations. The first version of this test wrote
+# an array of {binding, decls} -- a shape xlings never produces -- and it
+# passed, because the reader had been written from the same misunderstanding.
+# Do not "simplify" this structure; it is a wire format, not a convenience.
 set -euo pipefail
 
 TMP=$(mktemp -d)
@@ -28,9 +34,9 @@ mkdir -p "$subos/usr/lib/dri"
 cat > "$subos/.xlings.json" <<'EOF'
 { "workspace": {},
   "subos_info": { "schema_version": 1, "runtime": "glibc@2.39",
-    "envs": [ { "binding": "probe@1", "decls": [
+    "envs": { "probe@1": [
       { "var": "MCPP_E2E_PROBE", "op": "prepend",
-        "value": "${subosdir}/usr/lib/dri" } ] } ] } }
+        "value": "${subosdir}/usr/lib/dri" } ] } } }
 EOF
 
 cd "$TMP"