refactor(workspace): enforce layered crate boundaries

crates/aether-gateway/execution/src/lib.rs

@@ -0,0 +1,10 @@
+//! Gateway execution request-lifecycle components.
+//!
+//! This crate starts with transport-independent stream framing and bounded
+//! execution limits. Planner, executor, and response-finalization adapters can
+//! migrate behind this boundary without making the binary their owner.
+
+mod limits;
+pub mod stream;
+
+pub use limits::{MAX_ERROR_BODY_BYTES, MAX_STREAM_PREFETCH_BYTES, MAX_STREAM_PREFETCH_FRAMES};