Steve, please see my updated diagram
I decided to use a separate interface on SRX for this: ge-0/0/4
Assigned B.B.B.B.x/24 on SRX for ge-0/0/4.0 - zone trust
I connected LAN port on Router X into the port on SRX ge-0/0/4
On Router X I added static route with destination to B.B.B.B.x/24 on SRX (ge-0/0/4.0)
Added policy from trust to trust to match source-address any, destination-address any, application any and permit
I ssh into SRX and I can ping Laptop B connected to Router X LAN interface:
ping b.b.b.x/24 interface ge-0/0/4.0
From Laptop B I can ping IP B.B.B.B.x/24 assigned to ge-0/0/4.0 on SRX
But I can't communicate with Workstation A connected to SRX on VLAN123 A.A.A.A/24 (zone trust) from Laptop B
And Workstation A can't see Laptop B
Did I miss to add anything on SRX?