sim-lib-expr-tree-server

sim-lib-expr-tree-server is the authoritative server backend for live SIM expression trees. It exports site/sim-lib-expr-tree-server as a loadable placement site and implements both the standard EvalSite frame boundary and the kernel EvalFabric realization boundary.

The server owns a bounded registry of opaque session ids and live TreeHandles. Every request runs through the caller's Cx, so the existing expr-tree/* capability checks remain authoritative. The server also accepts the operations produced by ExpressionTreeSurfaceCodec and the generic web-session/* request maps used by server-backed surfaces. It does not add a tree-specific transport or evaluator.

Each session provides:

• optimistic snapshot revisions and one-time bounded continuation tokens;
• explicit session, idle-tick, page, depth, watch, and queue limits;
• independent bounded watches with lifetime overflow evidence;
• cancellation for watches and whole sessions;
• structured remote errors that keep a connected client live;
• mandatory monotone logical ticks on changes; and
• optional injected WallClock observations used only as human evidence.

Wall time is never compared for freshness, optimistic concurrency, or idle expiry. Source, policy, calculation, receipts, and live authority remain in the server-owned expression-tree runtime. Browser and transport adapters carry only bounded snapshots, Intents, operations, and change records.

ExpressionTreeWebSurfaceFactory is the product composition point for the generic SIM browser shell. It gives each opaque browser id a fresh caller context, negotiated RemoteTransport, codec registry, and reversible session, while mapping the browser alias to exactly one authoritative tree resource. The shell keeps ownership of HTTP lifecycle, session expiry, PWA policy, and the generic Scene interpreter.

Run the focused conformance specimen with:

cargo test -p sim-lib-expr-tree-server
cargo run -p xtask -- check-recipes