Report NAND move destination conflicts correctly

runtime/src/hle/storage/nand_api.cpp

@@ -384,6 +384,10 @@ extern "C" int32_t NANDMove_HLE(uint32_t srcPathPtr, uint32_t dstPathPtr) {
         return NAND_RESULT_OK;
     }
 
+    if (ec == std::errc::file_exists) {
+        return NAND_RESULT_EXISTS;
+    }
+
     LogNandError("NANDMove", "FAILED error=%d message='%s'", ec.value(), ec.message().c_str());
     return NAND_RESULT_UNKNOWN;
 }

runtime/src/hle/storage/nand_file_ops.h

@@ -6,5 +6,7 @@
 // Move without replacing an existing entry. Cross-filesystem regular files are
 // staged at the destination before removing the source. On failure the source
 // remains; a failed source removal can leave both complete copies.
+// The caller must keep the source stable for the duration of the move; NAND HLE
+// calls run synchronously on the cooperative guest thread without yielding.
 void NandMove(const std::filesystem::path& source, const std::filesystem::path& destination,
               std::error_code& ec);