Readability vectors: a store followed by one stray byte is refused by every runtime

The manifest held only three-byte and whole-store trailers, so a Rust reader that
tolerated a single trailing byte passed every suite while C#, TypeScript and Python
refused the file.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

tests/vectors/document-variants-c2a/readability/generate.py

@@ -31,6 +31,7 @@ vectors = {
     "scalar": b"\x01",
     "map": b"\x80",
     "truncated": whole[:-1],
+    "trailing-byte": whole + b"\x01",
     "trailing-bytes": whole + b"\x01\x02\x03",
     "trailing-store": whole + whole,
     # A header and a body of the wrong shape, for both readable headers.

tests/vectors/document-variants-c2a/readability/manifest.txt

@@ -16,6 +16,7 @@ bin-header-v9.bin   refuses  refuses  refuses  refuses
 scalar.bin          refuses  refuses  refuses  refuses
 map.bin             refuses  refuses  refuses  refuses
 truncated.bin       refuses  refuses  refuses  refuses
+trailing-byte.bin   refuses  refuses  refuses  refuses
 trailing-bytes.bin  refuses  refuses  refuses  refuses
 trailing-store.bin  refuses  refuses  refuses  refuses
 bad-body-v1.bin     refuses  refuses  refuses  refuses

tests/vectors/document-variants-c2a/readability/trailing-byte.bin

@@ -0,0 +1 @@
+“²cultcache.store.v3‘—¬vectors.item¬vectors.item¯vectors.item.v1¬vectors.itemÙL{"schemaName":"vectors.item","schemaVersion":"vectors.item.v1","members":[]}‘¬vectors.item<65>’”¥alpha¬vectors.item¹2026-09-29T00:00:00+00:00Ä’¥alpha
”¤beta¬vectors.item¹2026-09-29T00:00:01+00:00Ä’¤beta