Legacy `=` mixin definitions missing from Stylus compressed output

Goal

Migrate a small application's Stylus stylesheets from legacy = mixin syntax to Stylus 1.x without service interruption while keeping compiled CSS output stable.

Constraints

Stylus 0.x and 1.x handle variable interpolation differently, and the newer --compress flag may drop mixins defined with the legacy = sign syntax. It is unclear whether existing = mixins must be rewritten as explicit extend calls before enabling compression, or whether both syntaxes can coexist during a rolling deploy.

Questions

• Does Stylus 1.x --compress silently discard mixins defined with the legacy = sign syntax?
• Can legacy = mixins and modern extend blocks coexist in the same stylesheet during migration?
• What build configuration preserves source maps when original .styl files are absent after deployment?