Addresses Copilot's round-16 review on #2035. Two suppressed comments, both
real, and both refinements of fixes from the previous two rounds rather than
defects in the original code.
1. Round 11 settled on "a pct-encoded triplet counts as one character", but
a multi-octet character spans several triplets -- `%C3%A9` is one `é`.
Measured on a3dd8563:
x{+v:1} v = "%C3%A9x" => "x%C3" a lone lead byte, decoding to nothing
`prefixUnits` now recognizes a well-formed pct-encoded UTF-8 sequence from
its lead byte (RFC 3629: C2-DF two octets, E0-EF three, F0-F4 four;
continuations 80-BF), longest alternative first so a four-octet sequence
is not read as a two-octet one followed by loose triplets.
A malformed sequence -- a lead byte with too few continuations, or a stray
continuation -- matches no sequence alternative and falls back to
per-triplet counting. That is the conservative direction: it counts as
MORE units, so truncation keeps less rather than emitting octets that
were never in the value.
2. Round 14's per-value ceiling only covered the read. The panel calls
`previewUriTemplate` on every keystroke, and that path expands expression
by expression, so it reached the allocation-heavy encoders with the same
oversized value -- submission refused while the UI froze on the paste
anyway. Both paths now share one exported `valueLengthError`, checked
before any encoding happens.
npm run ci passes.
Signed-off-by: cliffhall <cliff@futurescale.com>