When adding a shield to a character on foot, AB correctly improves the armour save by +1/+2 to indicate that a model with hand weapon and shield gets +1 against ranged attacks and +2 against melee attacks.
However, if the model is equiped with a magic/runic weapon it does not get the bonus +1 for hand weapon and shield. Refer to the FAQ (warhammer_v7_FAQ.pdf quoted below)
"Q. Does a character benefit from the "Fighting with hand
weapon and shield (infantry)" rule found on page 56, if
armed with a mundane hand weapon and a magical
shield?
A. Yes. However it will not if armed with a magical
weapon and a mundane or magical shield, because the
magical weapon loses the normal rules of hand weapons."
Also p121 of the rule book states "A character that has a magic close combat weapon cannot use any other close combat weapon".
As such a Dwarf thane with gromil armour, shield and runic weapon, or an Empire Captain on foot with plate armour, shield and magic weapon, should have an armour save of 3+ not 3+/2+.
However, if the model is equiped with a magic/runic weapon it does not get the bonus +1 for hand weapon and shield. Refer to the FAQ (warhammer_v7_FAQ.pdf quoted below)
"Q. Does a character benefit from the "Fighting with hand
weapon and shield (infantry)" rule found on page 56, if
armed with a mundane hand weapon and a magical
shield?
A. Yes. However it will not if armed with a magical
weapon and a mundane or magical shield, because the
magical weapon loses the normal rules of hand weapons."
Also p121 of the rule book states "A character that has a magic close combat weapon cannot use any other close combat weapon".
As such a Dwarf thane with gromil armour, shield and runic weapon, or an Empire Captain on foot with plate armour, shield and magic weapon, should have an armour save of 3+ not 3+/2+.