Module layout_policy 

User-facing layout policy presets and deterministic fallback contract.

This module ties together the three layout subsystems:

• super::wrap::ParagraphObjective — Knuth-Plass line-break tuning
• super::vertical_metrics::VerticalPolicy — leading, baseline grid, paragraph spacing
• super::justification::JustificationControl — stretch/shrink/spacing modulation

It provides three named quality tiers (Quality, Balanced, Fast) and a deterministic fallback contract that maps runtime capabilities to the highest achievable tier.

Fallback semantics

Given a RuntimeCapability descriptor, LayoutPolicy::resolve returns a fully-resolved ResolvedPolicy that may have been degraded from the requested tier. The degradation path is:

  Quality → Balanced → Fast

Each step disables features that require capabilities not available at runtime (e.g., proportional fonts, sub-pixel rendering, hyphenation dict).

Structs

LayoutPolicy

User-facing layout policy configuration.

ResolvedPolicy

Fully-resolved layout configuration ready for use by the layout engine.

RuntimeCapability

Descriptor of available runtime capabilities.

Enums

LayoutTier

Named quality tiers for text layout.

PolicyError

Errors from policy resolution.