Juniors with exactly 1 session get expected='?' (manual-review marker
from attendance.py). The fill-first allocation block summed and cast
expected values numerically without guarding against this, causing a
TypeError: unsupported operand type(s) for +: 'int' and 'str' on the
/juniors route whenever any matched payment landed on such a month.
Add _expected_amount() helper that coerces non-numeric markers to 0
(same convention the final-balance calculation at line 512 already used)
and apply it in the two failing spots plus the existing isinstance check.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
