diff --git a/crates/workshop-rs/src/parser.rs b/crates/workshop-rs/src/parser.rs
index ab83ced..fbc3471 100644
--- a/crates/workshop-rs/src/parser.rs
+++ b/crates/workshop-rs/src/parser.rs
@@ -1431,7 +1431,7 @@ impl Parser<'_> {
         if !is_event_player {
             // Object/member assignments use the same value grammar as member
             // reads (`receiver.member` and `receiver.member[index]`). Keep
-            // this source-level form distinct from catalog actions: the
+            // this native member-assignment form distinct from catalog actions: the
             // receiver and member are dynamic Workshop values, not a builtin
             // identity. Global and Event Player assignments are handled by
             // their dedicated variable paths above and below.
diff --git a/crates/workshop-rs/src/validate.rs b/crates/workshop-rs/src/validate.rs
index db862cf..1ccdfc4 100644
--- a/crates/workshop-rs/src/validate.rs
+++ b/crates/workshop-rs/src/validate.rs
@@ -140,7 +140,18 @@ fn validate_action(
             validate_value(program, catalog, *player, errors);
             validate_value(program, catalog, *value, errors);
         }
-        wir::Action::AssignMember { target, value, .. } => {
+        wir::Action::AssignMember {
+            target,
+            value,
+            span,
+            ..
+        } => {
+            if !is_member_assignment_target(program, *target) {
+                errors.push(WorkshopError::Malformed {
+                    message: "AssignMember target must be a memberAccess value".to_string(),
+                    span: *span,
+                });
+            }
             validate_value(program, catalog, *target, errors);
             validate_value(program, catalog, *value, errors);
         }
@@ -203,6 +214,16 @@ fn validate_action(
     }
 }
 
+fn is_member_assignment_target(program: &wir::Program, target: wir::ValueId) -> bool {
+    match program.values.get(target) {
+        Some(wir::ValueNode {
+            value: wir::Value::Call { name, args },
+            ..
+        }) if name == "memberAccess" => (2..=3).contains(&args.len()),
+        _ => false,
+    }
+}
+
 fn validate_value(
     program: &wir::Program,
     catalog: &Catalog,
diff --git a/crates/workshop-rs/src/wir/mod.rs b/crates/workshop-rs/src/wir/mod.rs
index 7520cde..1f93d12 100644
--- a/crates/workshop-rs/src/wir/mod.rs
+++ b/crates/workshop-rs/src/wir/mod.rs
@@ -351,9 +351,9 @@ pub enum Action {
         /// The exact span of the modified variable identifier.
         target_span: Option<Span>,
     },
-    /// Assignment to a dynamic Workshop object member, optionally through an
-    /// indexed `memberAccess` value. This is source semantics, not a builtin
-    /// catalog action; the emitter preserves the member-assignment syntax.
+    /// Assignment to a canonical Workshop member-access target, optionally
+    /// indexed. This is not a builtin catalog action; the emitter preserves
+    /// the native member-assignment syntax.
     AssignMember {
         target: ValueId,
         op: Option<ModifyOp>,
diff --git a/crates/workshop-rs/tests/parser.rs b/crates/workshop-rs/tests/parser.rs
index 9bd5885..419ed4c 100644
--- a/crates/workshop-rs/tests/parser.rs
+++ b/crates/workshop-rs/tests/parser.rs
@@ -249,7 +249,7 @@ fn every_corpus_workshop_text_parses_to_valid_wir() {
 }
 
 #[test]
-fn member_assignment_lowers_to_source_semantic_wir() {
+fn member_assignment_lowers_to_canonical_wir() {
     let text = r#"rule ("member") { event { Ongoing - Global; } actions {
         All Players(All Teams).abilityHUD[17] = True;
         Global.botOrisaChild.botDoesUniqueBehaviour = False;
diff --git a/crates/workshop-rs/tests/wir_expansion.rs b/crates/workshop-rs/tests/wir_expansion.rs
index 8c9cdcc..e02e927 100644
--- a/crates/workshop-rs/tests/wir_expansion.rs
+++ b/crates/workshop-rs/tests/wir_expansion.rs
@@ -50,6 +50,163 @@ fn member_access_has_a_canonical_shape_contract() {
     );
 }
 
+#[test]
+fn indexed_members_and_native_break_controls_have_one_canonical_contract() {
+    let catalog = catalog();
+    let locale = Locale::new("en-US");
+    let source = r#"
+        variables { global: 0: values }
+        rule ("interop primitives") {
+            event { Ongoing - Global; }
+            actions {
+                Global.values[1] = 2;
+                Event Player.values[0] = 3;
+                If(True);
+                    Event Player.payload.member[0] = 4;
+                    Skip If(True, 1);
+                    While(True);
+                        Break;
+                        Continue;
+                    End;
+                Else;
+                    Skip(2);
+                End;
+            }
+        }
+    "#;
+    let program = workshop_rs::parser::parse_with_context(source, &catalog, &locale, &catalog)
+        .expect("native indexed/member and control-flow forms parse");
+    program
+        .validate()
+        .expect("canonical WIR is structurally valid");
+    validate::validate_canonical_ids(&program, &catalog).expect("catalog ids resolve");
+
+    let rule = program.rules.iter().next().expect("rule");
+    assert!(matches!(
+        program.actions.get(rule.actions[0]),
+        Some(Action::Call { name, args, .. })
+            if name == "setGlobalVariableAtIndex"
+                && args.len() == 3
+                && matches!(program.values.get(args[0]).map(|node| &node.value), Some(Value::GlobalVariable(_)))
+    ));
+    assert!(matches!(
+        program.actions.get(rule.actions[1]),
+        Some(Action::Call { name, args, .. })
+            if name == "setPlayerVariableAtIndex"
+                && args.len() == 3
+                && matches!(program.values.get(args[0]).map(|node| &node.value), Some(Value::PlayerVariable { .. }))
+    ));
+
+    let Action::If {
+        branches,
+        else_body: Some(else_body),
+        ..
+    } = program.actions.get(rule.actions[2]).expect("if action")
+    else {
+        panic!("expected an if with an else branch");
+    };
+    let member_action = program
+        .actions
+        .get(branches[0].body[0])
+        .expect("member assignment");
+    let Action::AssignMember { target, .. } = member_action else {
+        panic!("expected canonical member assignment");
+    };
+    assert!(matches!(
+        program.values.get(*target).map(|node| &node.value),
+        Some(Value::Call { name, args })
+            if name == "memberAccess"
+                && args.len() == 3
+                && matches!(program.values.get(args[1]).map(|node| &node.value), Some(Value::String(member)) if member == "member")
+    ));
+    assert!(matches!(
+        program.actions.get(branches[0].body[1]),
+        Some(Action::Call { name, args, .. }) if name == "skipIf" && args.len() == 2
+    ));
+    let Action::While { body, .. } = program.actions.get(branches[0].body[2]).expect("while")
+    else {
+        panic!("expected nested while");
+    };
+    assert!(matches!(
+        program.actions.get(body[0]),
+        Some(Action::Call { name, args, .. }) if name == "break" && args.is_empty()
+    ));
+    assert!(matches!(
+        program.actions.get(body[1]),
+        Some(Action::Call { name, args, .. }) if name == "continue" && args.is_empty()
+    ));
+    assert!(matches!(
+        program.actions.get(else_body[0]),
+        Some(Action::Call { name, args, .. }) if name == "skip" && args.len() == 1
+    ));
+
+    let emitted = workshop_rs::emitter::emit(&program, &catalog, &locale).expect("emits");
+    let reparsed = workshop_rs::parser::parse_with_context(&emitted, &catalog, &locale, &catalog)
+        .expect("emitted native controls reparse");
+    assert!(workshop_rs::roundtrip::equivalent(&program, &reparsed));
+    assert_eq!(
+        emitted,
+        workshop_rs::emitter::emit(&reparsed, &catalog, &locale).expect("re-emits")
+    );
+}
+
+#[test]
+fn assign_member_rejects_non_lvalue_member_access_targets() {
+    let catalog = catalog();
+    let mut program = wir::Program::default();
+    let receiver = program
+        .values
+        .push(ValueNode::new(Value::EventPlayer, None));
+    let member = program
+        .values
+        .push(ValueNode::new(Value::String("payload".into()), None));
+    let member_access = program.values.push(ValueNode::new(
+        Value::Call {
+            name: "memberAccess".into(),
+            args: vec![receiver, member],
+        },
+        None,
+    ));
+    let index = program.values.push(ValueNode::new(
+        Value::Number {
+            value: 1.0,
+            text: "1".into(),
+        },
+        None,
+    ));
+    let target = program.values.push(ValueNode::new(
+        Value::Call {
+            name: "valueInArray".into(),
+            args: vec![member_access, index],
+        },
+        None,
+    ));
+    let value = program.values.push(ValueNode::new(Value::Bool(true), None));
+    let action = program.actions.push(Action::AssignMember {
+        target,
+        op: None,
+        value,
+        span: None,
+    });
+    program.rules.push(wir::Rule {
+        name: "invalid member target".into(),
+        span: None,
+        name_span: None,
+        disabled: false,
+        event: Event::Global,
+        conditions: vec![],
+        actions: vec![action],
+    });
+
+    let error = validate::validate_canonical_ids(&program, &catalog)
+        .expect_err("AssignMember must require a memberAccess target");
+    assert!(
+        error
+            .to_string()
+            .contains("AssignMember target must be a memberAccess value")
+    );
+}
+
 fn span(file: workshop_rs::ids::Id<SourceFile>, line: u32, col: u32, end_col: u32) -> Span {
     Span::new(file, Position::new(line, col), Position::new(line, end_col))
 }
diff --git a/docs/implementation-role.md b/docs/implementation-role.md
index 4fdf028..994aef3 100644
--- a/docs/implementation-role.md
+++ b/docs/implementation-role.md
@@ -54,3 +54,33 @@ implementation.
 
 This keeps the shared Workshop contract useful without turning it into a union
 of every frontend/compiler's internal model.
+
+## Indexed members and control-flow lowering contract
+
+The canonical WIR contract for the interoperability surface in
+`wrightkit/workshop-rs#123` is deliberately composed from native Workshop
+identities:
+
+- indexing a declared global or player variable uses the catalog-backed
+  `set*VariableAtIndex` and `modify*VariableAtIndex` action calls;
+- a member read is the `memberAccess(receiver, "member"[, index])` value call,
+  and `AssignMember` accepts only that canonical member-access value as its
+  assignment target without assigning it dictionary, object, or container type
+  semantics;
+- native `Break`, `Continue`, `Skip`, and `Skip If` actions remain generic
+  catalog action calls and can occur inside the existing structured `If`,
+  `While`, and `For` actions.
+
+There are no `Dictionary`, `Switch`, or `Break` WIR nodes. OPY dictionary and
+switch lowering remains an `opy-rs` concern: a source form is consumable only
+after it is lowered to the native indexed/member or control-flow calls above.
+If no lossless lowering exists, `opy-rs` must report its explicit integration
+boundary rather than extending this Workshop contract with source-language
+carriers.
+
+This classifies the remaining interoperability probes without using OPY syntax
+as Workshop evidence: the dictionary-literal probe is an OPY-owned lowering
+gap unless it folds to one of the native indexed/member forms, while the
+nested and multiple switch-break probes have the required native `Break`,
+`Skip`, and `Skip If` primitives but still require `opy-rs` to prove a lossless
+source-to-Workshop lowering for their control-flow shape.