Watch folders & custom Dockerfile

Question

I have a prometheus service in a mono repo, basically laid out like this:

```
Dockerfile
[main project files]
prometheus/
   Dockerfile
   prometheus.yml
```

I've successfuly set Railway to look at `prometheus/Dockerfile` for this service, but it seems to fail because it can't find the `prometheus.yml` adjacent to the Dockerfile it's using:

```
Dockerfile:8

-------------------

6 |

7 |     # Copy the prometheus configuration

8 | >>> COPY prometheus.yml /etc/prometheus/prometheus.yml

9 |

10 |     # Create auth directory and files

-------------------

ERROR: failed to build: failed to solve: failed to compute cache key: failed to calculate checksum of ref 8zznmm2qp77p10scanhloon7m::ovp8q7o3dgjpkk4k9vynvv76c: "/prometheus.yml": not found
```

This hints that Railway may not be setting the context correctly, or I don't understand how context works in Dockerfiles.