from_cbor_hex only requires a valid prefix, so appending bytes to a real
transaction let sign.ts silently sign a shorter transaction than the caller
supplied and return a confident result — a signature over different bytes
than what was asked for, with nothing to reveal the discrepancy. sign.ts
calls from_cbor_hex independently of decode.ts and does not inherit that
module's consumption check (commit 5da4447) automatically; this closes the
same gap here, with the identical case-insensitive comparison and reasoning.
Also closes an untested claim: decode.ts's own suite documents but never
pins that the case-insensitive comparison tolerates legitimate uppercase-hex
input without a false positive. Pinned here for sign.ts.
Edge-case pass beyond the brief's 7 tests, all reproduced against the
unmodified implementation before any fix and mutation-verified after:
- trailing bytes silently accepted (BUG, fixed above)
- existing vkey witnesses are preserved and appended to, not replaced
(already correct; mutation-tested by dropping the copy loop)
- two different keys produce two independently-verifying witnesses,
chained or independent (already correct)
- determinism strengthened to compare raw signature bytes across a
freshly re-derived key instance, not just the memoized one (already
correct)
- auxiliary data / metadata survives signing byte-for-byte, body hash
unchanged (already correct)
- no thrown error, on any path, ever echoes the private key value
(already correct; mutation-tested by deliberately leaking it)
c9afa96571