test-output.txt

$ cargo test -p bill_payments --test test_recurring_lifecycle -- --nocapture

running 17 tests
test test_create_bill_due_date_far_past_rejected ... ok
test test_create_bill_due_date_future_accepted ... ok
test test_create_bill_due_date_exactly_now_accepted ... ok
test test_create_bill_due_date_one_second_past_rejected ... ok
test test_create_bill_due_date_zero_rejected ... ok
test test_create_bill_frequency_max_accepted ... ok
test test_create_bill_frequency_over_max_rejected ... ok
test test_create_bill_frequency_zero_non_recurring_accepted ... ok
test test_create_bill_frequency_zero_rejected ... ok
test test_recurring_bill_lifecycle ... ok
test test_recurring_child_catchup_when_paid_extremely_late ... ok
test test_recurring_child_due_date_formula_on_time_payment ... ok
test test_recurring_child_due_date_independent_of_paid_at ... ok
test test_recurring_early_payment_does_not_shift_child_due_date ... ok
test test_recurring_frequency_max_child_due_date ... ok
test test_recurring_frequency_one_day_child_due_date ... ok
test test_recurring_multi_cycle_due_dates_chain_correctly ... ok

test result: ok. 17 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.07s

--- Coverage (cargo llvm-cov, test_recurring_lifecycle only) ---
Function          Segments covered   %
create_bill       130 / 142          92%
pay_bill          123 / 137          90%

Uncovered segments are exclusively in paths unrelated to this issue:
  create_bill: pause guard, InvalidAmount, OwnerBillCapExceeded, external_ref claim
  pay_bill:    pause guard, BillNotFound, Unauthorized, non-recurring unpaid-total adjust

All InvalidDueDate boundary lines and all recurring child-formula lines are 100% covered.