sim-lib-view-expr-tree

sim-lib-view-expr-tree is the bounded, reversible SurfaceCodec for a Mathematica-like expression-tree outline.

The codec consumes one ordinary revisioned snapshot value and emits only standard SIM Scene nodes. Expanded cells show bounded source and result faces, freshness, revisions, optional human timestamps, inherited policy badges, receipt evidence, and actions. Expanded directories carry complete or explicitly truncated child pages. Collapsed nodes omit their body, so the snapshot source fetches no descendant or face payload until disclosure.

Desktop and phone arrangements are selected from open SurfaceCaps density metadata. There is no device enum and no expression-tree wire or view/edit protocol. Standard Intents decode through the same codec to existing expr-tree/* operations with expr-tree.read, expr-tree.write, or expr-tree.calculate requirements. Disclosure and continuation remain revision-checked surface-session operations.

use sim_kernel::{Cx, DefaultFactory, EagerPolicy, Expr};
use sim_lib_view::{SurfaceCodec, surface};
use sim_lib_view_expr_tree::{
    ExpressionTreeSnapshot, ExpressionTreeSurfaceCodec, NodeSnapshot,
};
use std::sync::Arc;

let value = ExpressionTreeSnapshot::new(
    Expr::String("tree:demo".into()),
    1,
    vec![NodeSnapshot::collapsed_dir("/", "root", 1)],
)
.to_expr();
let mut cx = Cx::new(Arc::new(EagerPolicy), Arc::new(DefaultFactory));
let scene = ExpressionTreeSurfaceCodec::new().encode(
    &mut cx,
    &value,
    &surface::preset("phone").unwrap(),
)?;
# Ok::<(), sim_kernel::Error>(())

The authoritative server adapter is responsible for producing snapshot pages from the live expression-tree session. This crate owns the stable presentation and reversible intent boundary, not storage, calculation, transport, or browser session lifetime.