Assurance of Absorption After 6 Months
It is on record that the principal employer would absorb the candidate after 6 months. In which case, are you willing to give, in turn, the same assurance to the candidate while appointing them on your roll? This particular clause regarding the absorption after 6 months, subject to the candidate being found to be 'satisfactorily completing' the initial 6 months, likely to be on probation, should be worded appropriately depending on what assurance the principal employer would pass on to you.
What If the Principal Employer Doesn't Honor the Commitment?
On the contrary, what if the principal employer doesn't honor this commitment after this period? It is advisable to issue the appointment order as temporary, initially for 6 months, and to state that it can likely be continued/extended or appointed thereafter depending on the candidate's performance for the initial 6 months, which will be considered as the probation period.
Common Practice for Project-Based Appointments
This type of appointment is common where candidates are considered for appointment for a specific project mentioning the tenure. In this case, there is an option on either side to retain or close the contract with some compensation at the discretion of the employer.