Context-window occupancy snapshot for the current (root) session, surfaced in
the statusline. Raw measurements only — any percentage is a presentation
concern derived at the edges, with no policy (e.g. auto-compaction) baked in.
A patch of session overrides produced by every caller (CLI, TUI, gateway,
external serve clients). None means “leave unchanged” for every field —
there is exactly one meaning, regardless of who built the value.
Partial update to a live session’s mutable state. Each field is optional so
a caller patches only what changed; absent fields are left untouched.
Catalog-dependent fields are resolved before the update takes effect.