replay: original-remaining=1; wrapper-remaining=3; reads=ABC; raw-never-rewound
order: unread(A),unread(B) -> BA; unread([A,B]) -> AB
default-capacity=1; extra-byte=rejected; two-byte-array=rejected; capacity-reusable=true
EOF misuse: read=-1; unread(-1); next-read=255; guarded-peek=-1
letters: token=name; delimiter='='; tail=42
byte-values=256; prefix-lengths=9; mark/reset=unsupported; closed-read/unread=rejected
PASS 294 checks; byte-array sources only, no file or network I/O
