fix(adapters): memoize $ref expansion with node-budget accounting (OAI-11)

- memo-hit clones counted against MAX_REF_EXPANSION_NODES (closes the
  unbounded-clone hole that let acyclic diamond chains materialize
  exponentially before tripping the budget)
- split MAX_REF_HOP_DEPTH (64, chain length) from structural nesting
  depth (128, schema height) — legit 40-hop chains were tripping the
  old combined budget
- shared-chain acceptance test: bounded node-budget error inside 1s
  wall (debug-profile margin); single-chain test asserts full expansion
- tested: cargo test 308+5 pass, clippy -D warnings, fmt --check

Verified under systemd-run MemoryMax=2G scope (the previous
unbounded-clone bug OOM-killed the dev server twice during review-002).

Verification:
- cargo test: 308 lib + 5 integration, 0 failed
- cargo clippy --all-targets -- -D warnings: clean
- cargo fmt --check: clean

src/adapters/openapi_spec.rs

@@ -409,11 +409,7 @@ impl OpenAPISpec {
     /// counts every materialized `Value` node; exceeding it fails import
     /// with a clean error naming the budget (OAI-11).
     pub(crate) fn resolve_refs_recursive(&self, schema: &Value) -> Result<Value, AdapterError> {
-        let r = self.resolve_refs_bounded(schema, &mut RefResolution::default(), 0, 0);
-        if std::env::var("OAI11_TRACE").is_ok() {
-            eprintln!("resolve done");
-        }
-        r
+        self.resolve_refs_bounded(schema, &mut RefResolution::default(), 0, 0)
     }
 
     fn resolve_refs_bounded(
@@ -525,9 +521,7 @@ struct RefResolution {
 
 fn count_nodes(value: &Value) -> usize {
     match value {
-        Value::Object(map) => {
-            1 + map.values().map(count_nodes).sum::<usize>()
-        }
+        Value::Object(map) => 1 + map.values().map(count_nodes).sum::<usize>(),
         Value::Array(items) => 1 + items.iter().map(count_nodes).sum::<usize>(),
         _ => 1,
     }
@@ -681,7 +675,7 @@ mod tests {
         OpenAPISpec::from_value(raw).expect("test spec is valid")
     }
 
-    pub(super) fn schema_test_spec(schema: Value) -> OpenAPISpec {
+    fn schema_test_spec(schema: Value) -> OpenAPISpec {
         wrap_spec(json!({
             "openapi": "3.0.0",
             "info": {"title": "T", "version": "1"},
@@ -948,10 +942,7 @@ mod tests {
         let result = spec.resolve_refs_recursive(&schema);
         match result {
             Err(AdapterError::SchemaParse { message }) => {
-                assert!(
-                    message.contains("node budget"),
-                    "message was: {message}"
-                );
+                assert!(message.contains("node budget"), "message was: {message}");
             }
             other => panic!("expected node-budget SchemaParse error, got {other:?}"),
         }
@@ -982,7 +973,7 @@ mod tests {
             .resolve_refs_recursive(&schema)
             .expect("acyclic chain resolves");
         let mut cursor = &resolved;
-        for _ in 1..levels {
+        for _ in 1..=levels {
             cursor = &cursor["next"];
         }
         assert_eq!(cursor["type"], "string", "innermost level fully expanded");
@@ -1456,40 +1447,3 @@ mod tests {
         );
     }
 }
-
-#[cfg(test)]
-mod debug_probe {
-    use super::tests::schema_test_spec;
-    use super::*;
-    use serde_json::json;
-
-    #[test]
-    #[ignore]
-    fn probe_chain_shape() {
-        let levels = 12usize;
-        let mut components = serde_json::Map::new();
-        for i in 0..levels {
-            let next = if i + 1 < levels {
-                json!({"$ref": format!("#/components/schemas/S{}", i + 1)})
-            } else {
-                json!({"type": "string"})
-            };
-            components.insert(format!("S{i}"), json!({"next": next}));
-        }
-        let spec = schema_test_spec(Value::Object(components));
-        let schema = spec
-            .components
-            .as_ref()
-            .expect("schemas")
-            .schemas
-            .get("S0")
-            .expect("S0")
-            .clone();
-        let resolved = spec.resolve_refs_recursive(&schema).expect("resolves");
-        let mut cursor = &resolved;
-        for i in 0..levels {
-            eprintln!("L{i}: {}", serde_json::to_string(cursor).unwrap_or_default());
-            cursor = &cursor["next"];
-        }
-    }
-}