feat(libsy): advisor_gate review-gate algorithm

Cargo.toml

@@ -32,6 +32,7 @@ jsonschema = { version = "0.49.4", default-features = false }
 jsonptr = { version = "0.8.1", default-features = false, features = ["std", "json", "resolve"] }
 parking_lot = "0.12"
 rand = "0.10"
+regex = "1"
 reqwest = { version = "0.13.4", default-features = false, features = ["json", "rustls", "stream"] }
 serde = { version = "1", features = ["derive"] }
 serde_json = "1"

crates/libsy/Cargo.toml

@@ -28,6 +28,7 @@ jsonptr.workspace = true
 opentelemetry = { version = "0.32", default-features = false, features = ["metrics"] }
 parking_lot.workspace = true
 rand.workspace = true
+regex.workspace = true
 switchyard-protocol.workspace = true
 thiserror.workspace = true
 tokio.workspace = true
@@ -36,6 +37,8 @@ tracing.workspace = true
 tracing-opentelemetry.workspace = true
 
 [dev-dependencies]
+# HeaderMap construction for budget-scope tests.
+http.workspace = true
 # SDK + in-memory exporter to assert what the observability layer records.
 opentelemetry_sdk = { version = "0.32", features = ["metrics", "testing", "trace"] }
 tokio.workspace = true

crates/libsy/src/algorithms.rs

@@ -6,6 +6,7 @@
 //! Everything public here is re-exported at the crate root; reach for it by name —
 //! `use switchyard_libsy::Random`.
 
+pub mod advisor_gate;
 pub mod fall_through;
 pub mod llm_class;
 pub mod noop;