How to deploy monorepo Dockerfile to Digital Ocean App Platform

I'm attempting to configure a two-component (frontend + backend) monorepo deployment using Digital Ocean's App Platform. I'm starting with the backend. The monorepo looks like:

client/  <-- NextJS project
server/  <-- NestJS project

The Dockerfile (server/Dockerfile) is simple:

FROM node:24-alpine
COPY . .
RUN npm install && npm run build && npm prune --production
CMD ["npm", "run", "start:prod"]

And the service portion of Digital Ocean app spec looks like:

services:
- dockerfile_path: server/Dockerfile
  gitlab:
    branch: main
    deploy_on_push: true
    repo: craigotis/myproject
  http_port: 8080
  instance_count: 1
  instance_size_slug: apps-s-1vcpu-0.5gb
  internal_ports:
  - 4000
  name: myproject-server
  source_dir: server

The deployment logs start out fine:

Nov 01 17:40:00  ╭──────────── git repo clone ───────────╼
Nov 01 17:40:00   › fetching app source code
Nov 01 17:40:00   => Selecting branch "main"
Nov 01 17:40:21   => Checking out commit "...."
Nov 01 17:40:25
Nov 01 17:40:25   ✔ cloned repo to /.app_platform_workspace
Nov 01 17:40:25  ╰────────────────────────────────────────╼
Nov 01 17:40:25
Nov 01 17:40:25   › applying source directory server
Nov 01 17:40:25   ✔ using workspace root /.app_platform_workspace/server
Nov 01 17:40:25
Nov 01 17:40:25  ╭──────────── dockerfile build ───────────╼
Nov 01 17:40:25   › using dockerfile /.app_platform_workspace/server/Dockerfile
Nov 01 17:40:25   › using build context /.app_platform_workspace/server
Nov 01 17:40:25
Nov 01 17:40:25  INFO[0000] Retrieving image manifest node:24-alpine
Nov 01 17:40:25  INFO[0000] Retrieving image library/node:24-alpine from registry mirror <registry-uri-0>
Nov 01 17:40:25  INFO[0000] Retrieving image manifest node:24-alpine
Nov 01 17:40:25  INFO[0000] Returning cached image manifest
Nov 01 17:40:25  INFO[0000] Built cross stage deps: map[]
Nov 01 17:40:25  INFO[0000] Retrieving image manifest node:24-alpine
Nov 01 17:40:25  INFO[0000] Returning cached image manifest
Nov 01 17:40:25  INFO[0000] Retrieving image manifest node:24-alpine
Nov 01 17:40:25  INFO[0000] Returning cached image manifest
Nov 01 17:40:25  INFO[0000] Executing 0 build triggers
Nov 01 17:40:25  INFO[0000] Building stage 'node:24-alpine' [idx: '0', base-idx: '-1']
Nov 01 17:40:25  INFO[0000] Checking for cached layer <registry-uri-1>
Nov 01 17:40:25  INFO[0000] No cached layer found for cmd RUN npm install && npm run build && npm prune --production
Nov 01 17:40:25  INFO[0000] Unpacking rootfs as cmd COPY . . requires it.
Nov 01 17:40:28  INFO[0002] Initializing snapshotter ...
Nov 01 17:40:28  INFO[0002] Taking snapshot of full filesystem...
Nov 01 17:40:32  INFO[0007] COPY . .
Nov 01 17:40:32  INFO[0007] Taking snapshot of files...
Nov 01 17:40:32  INFO[0007] RUN npm install && npm run build && npm prune --production
Nov 01 17:40:33  INFO[0007] Cmd: /bin/sh
Nov 01 17:40:33  INFO[0007] Args: [-c npm install && npm run build && npm prune --production]
Nov 01 17:40:33  INFO[0007] Running: [/bin/sh -c npm install && npm run build && npm prune --production]

But the build process fails because it seems the COPY . . command pulled in the entire contents of the repo - not just the subdirectory. As a result, there are failures like:

Nov 01 17:41:05  proc/1/cwd/client/app/page.tsx:32:9 - error TS17004: Cannot use JSX unless the '--jsx' flag is provided.
Nov 01 17:41:05
Nov 01 17:41:05  32         <AnalyticsPortal state={state} />
Nov 01 17:41:05              ~~~~~~~~~~~~~~~~~~~~~~~~~

Note that client and server both have been pulled into the Dockerfile. Is there a way to deploy individual components using the Dockerfile strategy from a monorepo on Digital Ocean?