fix: preserve Dockerfile-specific .dockerignore files

[lawrence3699]

Fixes #969

Summary

• copy the source Dockerfile's sibling .dockerignore file next to the generated Dockerfile-with-features
• apply the same fix to both compose-backed builds and direct Dockerfile builds, since both paths rewrite Dockerfiles into a temp folder before building
• add focused regression coverage for a compose build that uses a non-standard Dockerfile name

Why this is correct

When the CLI rewrites a Dockerfile into a temp folder, Docker stops seeing the original <Dockerfile>.dockerignore file because it only looks for Dockerfile-specific ignore files next to the Dockerfile it is actually building. Copying that sibling file alongside the generated Dockerfile preserves Docker's existing lookup and precedence rules.

Validation

• focused ts-node repro around buildAndExtendDockerCompose: before the patch the generated temp Dockerfile had no sibling .dockerignore; after the patch it does, with the original contents preserved
• ./node_modules/.bin/tsc -b
• ./node_modules/.bin/eslint src/spec-node/dockerCompose.ts src/spec-node/singleContainer.ts src/spec-node/dockerignoreUtils.ts src/test/dockerignore.test.ts

I could not run the Docker-backed CLI test suite in this environment because Docker is not installed here.

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[Copilot]

Pull request overview

This PR fixes devcontainer builds so Dockerfile-specific ignore files (e.g. dev.Dockerfile.dockerignore) continue to apply when the CLI rewrites the Dockerfile into a temp folder (e.g. Dockerfile-with-features), aligning behavior with Docker’s documented .dockerignore lookup rules.

Changes:

• Copy <source Dockerfile>.dockerignore alongside the generated Dockerfile-with-features for direct Dockerfile builds.
• Apply the same .dockerignore preservation for compose-backed builds when generating the compose build override Dockerfile.
• Add a regression test covering a compose build that uses a non-standard Dockerfile name.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
src/spec-node/dockerignoreUtils.ts	Adds helper to copy Dockerfile-specific .dockerignore to the generated Dockerfile location.
src/spec-node/singleContainer.ts	Calls the helper when generating Dockerfile-with-features for direct Dockerfile builds.
src/spec-node/dockerCompose.ts	Calls the helper for compose builds after writing Dockerfile-with-features.
src/test/dockerignore.test.ts	Adds regression coverage ensuring the generated compose Dockerfile has the sibling .dockerignore.

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[Copilot]

This test creates a fake docker executable as a #!/bin/sh script and relies on chmod + shebang execution. That approach will fail on Windows when running tests via Node’s child_process.spawn (even under Git Bash), because Windows cannot directly execute shebang scripts without an explicit interpreter. Consider generating a cross-platform fake (e.g. a small Node.js .js script invoked via node, or a .cmd wrapper on win32), or skipping this test on process.platform === 'win32'.

[Copilot]

sourceDockerfilePath is resolved using Node's path.resolve(...) even though the rest of the compose path handling uses cliHost.path (which can be posix/win32 depending on the host). This can produce incorrect paths when the CLI host path semantics differ from the local Node process (e.g. WSL/remote scenarios), and would prevent reading/copying the Dockerfile-specific .dockerignore. Use cliHost.path.resolve(context, dockerfilePath) (and avoid mixing path and cliHost.path) to keep resolution consistent.

Suggested change

	sourceDockerfilePath = cliHost.path.isAbsolute(dockerfilePath) ? dockerfilePath : path.resolve(context, dockerfilePath);
	sourceDockerfilePath = cliHost.path.isAbsolute(dockerfilePath) ? dockerfilePath : cliHost.path.resolve(context, dockerfilePath);