fix(rt): handle closure aggregate and non-tuple tuple-arg fallback

Add a rule for `aggregateKindClosure` to construct closures as
`Aggregate(variantIdx(0), ARGS)`, matching the existing tuple and ADT
aggregate handling.

Add an `[owise]` fallback to `#setTupleArgs` for `Value` arguments
that are not wrapped in an `Aggregate` tuple. This handles closure-call
paths where a single argument is passed directly.

Test: `closure-no-capture.rs` — a non-capturing closure passed through
a generic `FnOnce` call. Exercises the `#setTupleArgs` fallback for
unwrapped single-value arguments.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: Stevengre

kmir/src/kmir/kdist/mir-semantics/kmir.md

@@ -604,6 +604,12 @@ Therefore a heuristics is used here:
         => #setLocalValue(place(local(IDX), .ProjectionElems), #incrementRef(VAL)) ~> #setTupleArgs(IDX +Int 1, REST)
         ...
        </k>
+
+  // Fallback for closure-call paths where the argument is not wrapped as a tuple.
+  rule <k> #setTupleArgs(IDX, VAL:Value)
+        => #setLocalValue(place(local(IDX), .ProjectionElems), #incrementRef(VAL))
+        ...
+       </k> [owise]
 ```
 
 

kmir/src/kmir/kdist/mir-semantics/rt/data.md

@@ -1051,6 +1051,12 @@ Literal arrays are also built using this RValue.
         ...
        </k>
 
+  rule <k> ARGS:List ~> #mkAggregate(aggregateKindClosure(_CLOSUREDEF, _GENERICARGS))
+        =>
+            Aggregate(variantIdx(0), ARGS)
+        ...
+       </k>
+
 
   // #readOperands accumulates a list of `TypedLocal` values from operands
   syntax KItem ::= #readOperands ( Operands )

kmir/src/tests/integration/data/prove-rs/closure-no-capture.rs

@@ -0,0 +1,12 @@
+fn apply<F: FnOnce(u8) -> u8>(f: F, v: u8) -> u8 {
+    f(v)
+}
+
+fn main() {
+    let _ = repro();
+}
+
+fn repro() -> u8 {
+    let f = |x: u8| x + 1;
+    apply(f, 41u8)
+}