diagrams not working

[level20peon]

I just checked out a completely fresh copy of the current Huginn master and also installed/compiled everything (gems/assets) from scratch (using rvm to install ruby 3.2.2). Unfortunately, diagrams aren't currently rendering on this system:

I am using unicorn, and the logs indicate that it actually rendered the diagram, so I am not sure where the 404 is coming from:

I, [2024-04-26T11:33:29.850370 #2232350]  INFO -- : [8094cff4-d94a-4464-8c13-bc33c276cc7c] Started GET "/scenarios/42/diagram" for x.x.x.x at 2024-04-26 11:33:29 +0200
I, [2024-04-26T11:33:29.851895 #2232350]  INFO -- : [8094cff4-d94a-4464-8c13-bc33c276cc7c] Processing by DiagramsController#show as HTML
I, [2024-04-26T11:33:29.852036 #2232350]  INFO -- : [8094cff4-d94a-4464-8c13-bc33c276cc7c]   Parameters: {"scenario_id"=>"42"}
I, [2024-04-26T11:33:30.283115 #2232350]  INFO -- : [8094cff4-d94a-4464-8c13-bc33c276cc7c]   Rendered diagrams/show.html.erb within layouts/application (Duration: 419.9ms | Allocations: 32237)
I, [2024-04-26T11:33:30.295020 #2232350]  INFO -- : [8094cff4-d94a-4464-8c13-bc33c276cc7c]   Rendered layout layouts/application.html.erb (Duration: 431.8ms | Allocations: 51930)
I, [2024-04-26T11:33:30.295243 #2232350]  INFO -- : [8094cff4-d94a-4464-8c13-bc33c276cc7c] Completed 200 OK in 443ms (Views: 424.4ms | ActiveRecord: 11.4ms | Allocations: 53240)
x.x.x.x - - [26/Apr/2024:11:33:30 +0200] "GET /scenarios/42/diagram HTTP/1.1" 200 - 0.4490

Any pointers?

PS: bare metal, debian bookworm, anything else?