phase29ao(p51): unify split-scan v0/v1 value-join path

src/mir/builder/control_flow/plan/composer/coreloop_v1.rs

@@ -255,6 +255,47 @@ mod tests {
         assert!(matches!(composed, Some(crate::mir::builder::control_flow::plan::CorePlan::Loop(_))));
     }
 
+    #[test]
+    fn coreloop_v1_rejects_split_scan_without_value_join() {
+        let condition = ASTNode::Literal {
+            value: LiteralValue::Bool(true),
+            span: Span::unknown(),
+        };
+        let facts = LoopFacts {
+            condition_shape: ConditionShape::Unknown,
+            step_shape: StepShape::Unknown,
+            skeleton: SkeletonFacts {
+                kind: SkeletonKind::Loop,
+            },
+            features: LoopFeatureFacts::default(),
+            scan_with_init: None,
+            split_scan: Some(crate::mir::builder::control_flow::plan::facts::loop_facts::SplitScanFacts {
+                s_var: "s".to_string(),
+                sep_var: "sep".to_string(),
+                result_var: "result".to_string(),
+                i_var: "i".to_string(),
+                start_var: "start".to_string(),
+                shape: SplitScanShape::Minimal,
+            }),
+            pattern1_simplewhile: None,
+            pattern3_ifphi: None,
+            pattern4_continue: None,
+            pattern5_infinite_early_exit: None,
+            pattern8_bool_predicate_scan: None,
+            pattern9_accum_const_loop: None,
+            pattern2_break: None,
+            pattern2_loopbodylocal: None,
+        };
+        let canonical = canonicalize_loop_facts(facts);
+        let mut builder = MirBuilder::new();
+        builder.enter_function_for_test("coreloop_v1_split_scan_no_join".to_string());
+        let ctx =
+            LoopPatternContext::new(&condition, &[], "coreloop_v1_split_scan_no_join", false, false);
+        let composed =
+            try_compose_core_loop_v1(&mut builder, &canonical, &ctx).expect("Ok");
+        assert!(composed.is_none());
+    }
+
     #[test]
     fn coreloop_v1_rejects_split_scan_with_disallowed_exitmap() {
         let condition = ASTNode::Literal {