bake computing incorrect context path in the presence of nested include directives

Contributing guidelines

• I've read the contributing guidelines and wholeheartedly agree

I've found a bug and checked that ...

• ... the documentation does not mention anything about my problem
• ... there are no open or closed issues that are related to my problem

Description

When using the include directory to include into a.yml file b.yml and then to include into b.yml file c.yml, the context for c.yml is not calculated relative to c.yml directory but to b.yml creating a non-existing path.

$ ls a.yml b/b.yml c/c.yml
a.yml   b/b.yml c/c.yml

$ cat a.yml
include:
  - path:
      - ./b/b.yml

services:
  a:
    build:
      context: .
      dockerfile_inline: FROM scratch

$ cat b/b.yml
include:
  - path:
      - ../c/c.yml

services:
  b:
    build:
      context: .
      dockerfile_inline: FROM scratch

$ cat c/c.yml
services:
  c:
    build:
      context: .
      dockerfile_inline: FROM scratch

Expected behaviour

Trying to build with bake should work.

Actual behaviour

docker buildx bake -f a.yml
[+] Building 0.2s (1/1) FINISHED                                               docker:desktop-linux
 => [internal] load local bake definitions                                                     0.0s
 => => reading a.yml 119B / 119B                                                               0.0s
ERROR: unable to prepare context: path "b/c" not found

The error is clear, context for service "c" is being computed as "b/c", which is a non-existent path. It should be "c" instead.

docker buildx bake -f a.yml --print
[+] Building 0.0s (1/1) FINISHED
 => [internal] load local bake definitions                                                     0.0s
 => => reading a.yml 119B / 119B                                                               0.0s
{
  "group": {
    "default": {
      "targets": [
        "a",
        "b",
        "c"
      ]
    }
  },
  "target": {
    "a": {
      "context": ".",
      "dockerfile": "Dockerfile",
      "dockerfile-inline": "FROM scratch"
    },
    "b": {
      "context": "b",
      "dockerfile": "Dockerfile",
      "dockerfile-inline": "FROM scratch"
    },
    "c": {
      "context": "b/c",
      "dockerfile": "Dockerfile",
      "dockerfile-inline": "FROM scratch"
    }
  }
}```

### Buildx version

github.com/docker/buildx v0.22.0-desktop.1 b45d7a53aa26a5e76aae051acdb15775c0e178da

### Docker info

```text
Client: Docker Engine - Community
 Version:    28.0.1
 Context:    desktop-linux
 Debug Mode: false
 Plugins:
  ai: Docker AI Agent - Ask Gordon (Docker Inc.)
    Version:  v1.1.3
    Path:     /Users/davi/.docker/cli-plugins/docker-ai
  buildx: Docker Buildx (Docker Inc.)
    Version:  v0.22.0-desktop.1
    Path:     /Users/davi/.docker/cli-plugins/docker-buildx
  cloud: Docker Cloud (Docker Inc.)
    Version:  0.2.20
    Path:     /Users/davi/.docker/cli-plugins/docker-cloud
  compose: Docker Compose (Docker Inc.)
    Version:  v2.34.0-desktop.1
    Path:     /Users/davi/.docker/cli-plugins/docker-compose
  debug: Get a shell into any image or container (Docker Inc.)
    Version:  0.0.38
    Path:     /Users/davi/.docker/cli-plugins/docker-debug
  desktop: Docker Desktop commands (Beta) (Docker Inc.)
    Version:  v0.1.6
    Path:     /Users/davi/.docker/cli-plugins/docker-desktop
  dev: Docker Dev Environments (Docker Inc.)
    Version:  v0.1.2
    Path:     /Users/davi/.docker/cli-plugins/docker-dev
  extension: Manages Docker extensions (Docker Inc.)
    Version:  v0.2.27
    Path:     /Users/davi/.docker/cli-plugins/docker-extension
  init: Creates Docker-related starter files for your project (Docker Inc.)
    Version:  v1.4.0
    Path:     /Users/davi/.docker/cli-plugins/docker-init
  model: Docker Model Runner (Docker Inc.)
    Version:  v0.1.4
    Path:     /Users/davi/.docker/cli-plugins/docker-model
  sbom: View the packaged-based Software Bill Of Materials (SBOM) for an image (Anchore Inc.)
    Version:  0.6.0
    Path:     /Users/davi/.docker/cli-plugins/docker-sbom
  scout: Docker Scout (Docker Inc.)
    Version:  v1.17.0
    Path:     /Users/davi/.docker/cli-plugins/docker-scout

Server:
 Containers: 0
  Running: 0
  Paused: 0
  Stopped: 0
 Images: 5
 Server Version: 28.0.4
 Storage Driver: overlay2
  Backing Filesystem: extfs
  Supports d_type: true
  Using metacopy: false
  Native Overlay Diff: true
  userxattr: false
 Logging Driver: json-file
 Cgroup Driver: cgroupfs
 Cgroup Version: 2
 Plugins:
  Volume: local
  Network: bridge host ipvlan macvlan null overlay
  Log: awslogs fluentd gcplogs gelf journald json-file local splunk syslog
 CDI spec directories:
  /etc/cdi
  /var/run/cdi
 Swarm: inactive
 Runtimes: io.containerd.runc.v2 runc
 Default Runtime: runc
 Init Binary: docker-init
 containerd version: 753481ec61c7c8955a23d6ff7bc8e4daed455734
 runc version: v1.2.5-0-g59923ef
 init version: de40ad0
 Security Options:
  seccomp
   Profile: unconfined
  cgroupns
 Kernel Version: 6.10.14-linuxkit
 Operating System: Docker Desktop
 OSType: linux
 Architecture: aarch64
 CPUs: 8
 Total Memory: 7.654GiB
 Name: docker-desktop
 ID: 92deabd9-1aab-4e3d-88e7-3c4757a4b0aa
 Docker Root Dir: /var/lib/docker
 Debug Mode: false
 HTTP Proxy: http.docker.internal:3128
 HTTPS Proxy: http.docker.internal:3128
 No Proxy: hubproxy.docker.internal
 Labels:
  com.docker.desktop.address=unix:///Users/davi/Library/Containers/com.docker.docker/Data/docker-cli.sock
 Experimental: false
 Insecure Registries:
  hubproxy.docker.internal:5555
  ::1/128
  127.0.0.0/8
 Live Restore Enabled: false

Builders list

NAME/NODE           DRIVER/ENDPOINT     STATUS    BUILDKIT   PLATFORMS
default             docker
 \_ default          \_ default         running   v0.20.2    linux/amd64 (+2), linux/arm64, linux/arm (+2), linux/ppc64le, (3 more)
desktop-linux*      docker
 \_ desktop-linux    \_ desktop-linux   running   v0.20.2    linux/amd64 (+2), linux/arm64, linux/arm (+2), linux/ppc64le, (3 more)

Configuration

See the fields above with full reproduction.

Build logs

See logs on the fields above.

Additional info

No response

Start with the nested a.yml, b/b.yml, and c/c.yml reproduction, then run docker buildx bake -f a.yml --print to inspect the computed contexts. Trace the bake include handling from this entry point and verify that the c service resolves its context as c rather than b/c; the original build command should then succeed.