How the transient preparation preview (#60, DD-029) is presented — what, if anything, shows WHILE the
file parses and the geometry builds. Orthogonal to quality/qualityMode (which govern the FINAL
representation): this NEVER drops extrusion segments or lowers final geometry — it only controls how
often incomplete work is drawn to the screen.
'auto' (the eventual default): the renderer chooses 'lines' vs 'hold' per build from the
render-cost/capability estimate (DD-029 §4 D1) — cheap scenes stream lines, expensive scenes take
the single-reveal 'hold' path. Until that estimate lands it resolves to 'lines'. An explicit
'lines'/'hold'/'off' always overrides.
'lines': stream the progressive line preview as it parses/builds, then replace it with the final
build. (Backward-compatible; its intermediate redraws are budget-throttled in a later phase.)
'hold': single clean reveal — keep emitting progress but reveal NOTHING incomplete: no line
preview AND no intermediate renders of the growing build; the first thing shown is the finished,
correctly-coloured build, revealed once at completion (DD-029 §4 D1).
'off': suppress the progressive preview entirely and emit no preview progress — the consumer
supplies its own loading/progress treatment until the final build is revealed.
How the transient preparation preview (#60, DD-029) is presented — what, if anything, shows WHILE the file parses and the geometry builds. Orthogonal to
quality/qualityMode(which govern the FINAL representation): this NEVER drops extrusion segments or lowers final geometry — it only controls how often incomplete work is drawn to the screen.'auto'(the eventual default): the renderer chooses'lines'vs'hold'per build from the render-cost/capability estimate (DD-029 §4 D1) — cheap scenes stream lines, expensive scenes take the single-reveal'hold'path. Until that estimate lands it resolves to'lines'. An explicit'lines'/'hold'/'off'always overrides.'lines': stream the progressive line preview as it parses/builds, then replace it with the final build. (Backward-compatible; its intermediate redraws are budget-throttled in a later phase.)'hold': single clean reveal — keep emitting progress but reveal NOTHING incomplete: no line preview AND no intermediate renders of the growing build; the first thing shown is the finished, correctly-coloured build, revealed once at completion (DD-029 §4 D1).'off': suppress the progressive preview entirely and emit no preview progress — the consumer supplies its own loading/progress treatment until the final build is revealed.