fix: Handle builtin out-parameter calls in RVM compiler

- Teach the hoister/destructuring planner to respect parent scope when building binding plans for extra arguments, so already-bound vars yield equality checks.
- Update the compiler’s function-call path to drop the trailing out-argument, run its binding plan after the call, and share call-target resolution logic.
- Add regression suites for builtin and user-defined out-parameter scenarios plus align the CLI example output when RVM returns undefined.

Signed-off-by: Anand Krishnamoorthi <anakrish@microsoft.com>

tests/rvm/rego/cases/builtins_out_params.yaml

@@ -0,0 +1,83 @@
+# Copyright (c) Microsoft Corporation.
+# Licensed under the MIT License.
+
+# Builtin Out-Parameter Test Suite
+# Verifies the compiler handles builtin return-argument syntax consistently
+# across variable bindings, equality checks, scheduler ordering, and literals.
+
+cases:
+  - note: builtin_out_param_simple_binding
+    data: {}
+    modules:
+      - |
+        package test
+
+        rule1 if {
+            floor(1.001, x)
+            x == 1
+        }
+    query: data.test.rule1
+    want_result: true
+
+  - note: builtin_out_param_scheduler_reordering
+    data: {}
+    modules:
+      - |
+        package test
+
+        rule2 if {
+            x == 1
+            floor(1.001, x)
+        }
+    query: data.test.rule2
+    want_result: true
+
+  - note: builtin_out_param_existing_binding_equality
+    data: {}
+    modules:
+      - |
+        package test
+
+        rule3 if {
+            x := 1
+            floor(1.001, x)
+        }
+    query: data.test.rule3
+    want_result: true
+
+  - note: builtin_out_param_existing_binding_mismatch
+    data: {}
+    modules:
+      - |
+        package test
+
+        rule31 if {
+            x := 2
+            floor(1.001, x)
+        }
+    query: data.test.rule31
+    want_result: "#undefined"
+
+  - note: builtin_out_param_literal_success
+    data: {}
+    modules:
+      - |
+        package test
+
+        rule4 if {
+            floor(1.001, 1)
+        }
+    query: data.test.rule4
+    want_result: true
+
+  - note: builtin_out_param_literal_failure
+    data: {}
+    modules:
+      - |
+        package test
+
+        rule5 if {
+            floor(1.001, 2)
+        }
+    query: data.test.rule5
+    want_result: "#undefined"

tests/rvm/rego/cases/user_fcn_out_params.yaml

@@ -0,0 +1,107 @@
+# Copyright (c) Microsoft Corporation.
+# Licensed under the MIT License.
+
+# User-Defined Out-Parameter Test Suite
+# Mirrors builtin coverage but routes through the my_floor helper rule
+# to ensure planner handling stays correct for user-defined function rules.
+
+cases:
+  - note: user_fcn_out_param_simple_binding
+    data: {}
+    modules:
+      - |
+        package test
+
+        my_floor(x) := y if {
+            floor(x, y)
+        }
+
+        rule1 if {
+            my_floor(1.001, x)
+            x == 1
+        }
+    query: data.test.rule1
+    want_result: true
+
+  - note: user_fcn_out_param_scheduler_reordering
+    data: {}
+    modules:
+      - |
+        package test
+
+        my_floor(x) := y if {
+            floor(x, y)
+        }
+
+        rule2 if {
+            x == 1
+            my_floor(1.001, x)
+        }
+    query: data.test.rule2
+    want_result: true
+
+  - note: user_fcn_out_param_existing_binding_equality
+    data: {}
+    modules:
+      - |
+        package test
+
+        my_floor(x) := y if {
+            floor(x, y)
+        }
+
+        rule3 if {
+            x := 1
+            my_floor(1.001, x)
+        }
+    query: data.test.rule3
+    want_result: true
+
+  - note: user_fcn_out_param_existing_binding_mismatch
+    data: {}
+    modules:
+      - |
+        package test
+
+        my_floor(x) := y if {
+            floor(x, y)
+        }
+
+        rule31 if {
+            x := 2
+            my_floor(1.001, x)
+        }
+    query: data.test.rule31
+    want_result: "#undefined"
+
+  - note: user_fcn_out_param_literal_success
+    data: {}
+    modules:
+      - |
+        package test
+
+        my_floor(x) := y if {
+            floor(x, y)
+        }
+
+        rule4 if {
+            my_floor(1.001, 1)
+        }
+    query: data.test.rule4
+    want_result: true
+
+  - note: user_fcn_out_param_literal_failure
+    data: {}
+    modules:
+      - |
+        package test
+
+        my_floor(x) := y if {
+            floor(x, y)
+        }
+
+        rule5 if {
+            my_floor(1.001, 2)
+        }
+    query: data.test.rule5
+    want_result: "#undefined"