Clarify that SIMD-0392 balance checking semantics apply to fee/commission distribution

proposals/0392-relax-minimum-balance-check.md

@@ -87,6 +87,11 @@ else:
 assert(acc.post_exec_balance == 0 or acc.post_exec_balance >= min_allowed_balance)
 ```
 
+The same pre/post-balance semantics MUST also be applied to fee distribution:
+transaction fee debits and subsequent fee distribution are treated as an
+additional balance-changing phase, and the invariant above MUST be enforced
+using the pre-fee and post-fee balances.
+
 The check ensures that an account's balance is always rent-exempt as of
 the last (re)allocation of its data:
 
@@ -107,7 +112,9 @@ section for more details.
 ### Implementation details
 
 - The pre-execution balance MUST be captured before any state is modified
-  (e.g. before fee collection, instruction execution, etc).
+  (e.g. before fee collection, instruction execution, etc). This same
+  `pre_exec_balance` snapshot MUST be reused when enforcing the minimum balance
+  invariant across both instruction execution and fee debiting/distribution.
 - The pre and post-execution sizes are compared to determine if upwards
   reallocation occurred.
 - The pre-execution owner MUST be captured. If the account owner changes during