[echarles]

A foreignDockerfile could not COPY from a build context. This takes one inline, in build.dockerfile.context, the way dependencyFile already keeps its file in the spec.

• Bounded at 1 MiB: it is stored with the version. Its bytes are in the spec's digest, so a version names exactly what it built.
• Each file goes through validate_build_context: no absolute path, no .., no symlink (a file here has no way to be one). Paths the build itself writes are reserved.
• write_build_context checks each target again against the folder, because that is the step that writes.
• COPY is allowed only for what the context holds. With none, it is refused as before.
• context is left out of the dump when unset, so no existing spec's digest moves. dockerfile sources refuse it.

Tested: unit tests, and a real build copying and running a context file, with DATALAYER_ENVIRONMENT_DOCKER_TESTS=1. A local image stood in for the approved base.

[Copilot]

🟡 Changes recommended

Context validation bypasses allow generated Dockerfiles and resolved locks to be overwritten, while valid JSON-form and wildcard COPY sources are incorrectly rejected.

4 open issues

• Write Dockerfile context only for foreign Dockerfile specs · New
• Normalize context paths before checking reserved build files · New
• Match COPY and ADD wildcard sources against context paths · New
• Parse JSON-form COPY sources separately from shell syntax · New

What changed in this PR

Adds inline build-context files for foreignDockerfile environments, enabling Dockerfile COPY instructions to use files stored with the environment version and covered by its spec digest.

Changes:

• Adds context-file models, validation, and a 1 MiB decoded-content limit while preserving digests when context is unset.
• Adds context-aware source checks and writes supplied files into the Datalayer build directory.
• Updates the schema, documentation, unit tests, and Docker integration coverage.

File	Description
tests/​test_environment_foreign_contract_layer.py	Tests context validation, digests, file writing, and image copying.
schemas/​environment-v1alpha1.json	Defines inline context files and the optional context field.
docs/​docs/​environments/​specification.mdx	Documents inline context support and its size limit.
code_sandboxes/​environments/​spec.py	Models and validates context files; omits unset context from serialization.
code_sandboxes/​environments/​contract.py	Adds context limits, reserved paths, and source-membership checks.
code_sandboxes/​environments/​adapters/​datalayer.py	Writes context files and permissions before building.

_{Review effort: Balanced}