fix(template): expose params as top-level view local

Closes expose-params-in-views-2.

Adds a test confirming that `params` is correctly extracted from the
thread-local `req` and injected as a top-level `params` key in the
render data, matching the ergonomics of `req`.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: Olivier Bonnaure

src/interpreter/builtins/template.rs

@@ -1815,6 +1815,39 @@ mod tests {
         clear_current_controller();
     }
 
+    #[test]
+    fn inject_request_context_exposes_params_as_top_level_local() {
+        let mut params_map = HashPairs::default();
+        params_map.insert(
+            HashKey::String("q".to_string()),
+            Value::String("search".into()),
+        );
+        set_current_request(make_request(&[(
+            "params",
+            Value::Hash(Rc::new(RefCell::new(params_map))),
+        )]));
+        let data = empty_data();
+        inject_request_context(&data);
+        let Value::Hash(h) = &data else {
+            unreachable!()
+        };
+        let h = h.borrow();
+        assert!(
+            h.contains_key(&HashKey::String("params".to_string())),
+            "params should be injected as top-level view local"
+        );
+        let params = h.get(&HashKey::String("params".to_string())).unwrap();
+        let Value::Hash(params_hash) = params else {
+            unreachable!("params should be a Hash")
+        };
+        let params = params_hash.borrow();
+        assert_eq!(
+            params.get(&HashKey::String("q".to_string())),
+            Some(&Value::String("search".into()))
+        );
+        clear_current_request();
+    }
+
     #[test]
     fn explicit_render_data_wins_over_instance_field() {
         set_current_controller(make_instance(&[(