NO ONE VULNERABLE
A K 8 6 4
A 8 7
J 9 7 5
K 6 4 2
A Q 8 3
K 10 4
In defense, there are three messages you can give your partner.
Here is a useful rule which should help you sort out what is going on.
A suit preference signal takes a back seat to BOTH of the other signals.
If a signal can be interpreted as attitude or count, it is so interpreted.
A suit preference signal is always the last interpretation. PartnerŐs nine of spades is therefore encouraging, showing the queen.
Remember the bidding? Partner raised spades. He is not showing a doubleton. Your plan therefore is to lead your singleton diamond and then to put partner in with the queen of spades for a diamond ruff.
The key is not to lose track of the bidding. If you forgot that partner raised spades, you will realize that the nine of spades can't be a doubleton.
Following the rule above, the nine of spades can only be an encouraging card telling you he has the queen of spades.
NOTE- A suit preference card is usually defined as an unusually emphatic card. If East absolutely wants a diamond shift, he has to play the queen!
NOTE- If East has QJ5, he will play the queen, which shows the jack. The queen will be interpreted as suit preference only when West can tell that East doesn't have the jack. On this hand, the jack is in the dummy so East could play the queen and be sure of getting a diamond shift if he needed one.