[P0] Function signatures remain typed returns while bodies are lowered to `(ptr,len)` return protocol

[ngmachado]

Problem

ConvertFuncOp intends to rewrite non-void function result types to (sir.ptr<1>, sir.u256), but in final conversion target func.func is legal and signatures remain as old scalar returns (i8, i256) while bodies emit sir.return ptr,len/sir.iret conventions.

Expected

Function type signatures and return op conventions must be consistent.

Actual

Mixed calling conventions coexist in emitted IR.

Evidence

• Conversion logic: src/mlir/ora/lowering/OraToSIR/patterns/ControlFlow.cpp:378
• Conversion logic: src/mlir/ora/lowering/OraToSIR/patterns/ControlFlow.cpp:387
• Phase 4 legality keeps func op legal: src/mlir/ora/lowering/OraToSIR/OraToSIR.cpp:1333
• Repro shows function signature -> i8 with memory-return body.

Impact

ABI/call lowering fragility and pass-order sensitivity.

Acceptance Criteria

• For non-void lowered functions, signatures are consistently rewritten to the return convention used in bodies.
• sir.icall result typing and callee signatures match without legalizer repair hacks.