Args::parse kept any unrecognised `--option` as a valueless flag nobody
read, so `exec comp.new --bogus` ran with defaults and exit 0, and a
misspelt valued option left its value behind as a positional:
`--saveas z.ecproj` opened z.ecproj as the project and failed with an
unrelated "cannot read" error.
Options are now checked against the declared lists (VALUED and the new
FLAGS) before anything runs; unknown ones are a usage error naming them
(exit 2), and `--flag=value` on a flag says it takes no value.
render-frame's `--transparent` (the MCP render_frame option) was one of
the silently ignored options; it now keeps the frame's alpha.
Tests: unknown_options_are_refused, every_option_read_is_declared (every
option the code reads is declared, so none is refused),
unknown_options_are_usage_errors (exit 2, nothing runs or renders, and
--transparent renders alpha).
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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