Decision: Remove legacy declarative build fields from template.yaml

Status: implemented Implemented: 2026-09-29

Problem

template.yaml contained declarative build fields (python_packages, system_packages, node_packages, commands, base, copy_files) and a to_dockerfile() method that were never used in the actual CLI build flow. The real build pipeline always uses a Dockerfile directly. These fields:

• Misled contributors into thinking declarative builds were supported.
• Added dead code and model complexity to the TemplateConfig model.
• Contradicted the industry standard of Dockerfile + language-native dependency files (requirements.txt, package.json, etc.).

Decision

Remove all legacy declarative build fields and the to_dockerfile() method:

• Delete fields: python_packages, system_packages, node_packages, commands, base, copy_files from the TemplateConfig Pydantic model.
• Delete the to_dockerfile() method entirely.
• The build pipeline continues to use Dockerfile as the single source of truth for image construction.

API Design

N/A — this decision removes unused internal fields. No public API changes.

Alternatives considered

• Keep fields but mark as deprecated — adds warnings without removing dead code; users would still be confused by their presence. Rejected.
• Implement declarative builds — duplicates Dockerfile functionality with inferior flexibility; goes against industry convention. Rejected.

Dependencies

• src/agent_sandbox/models/template.py — TemplateConfig model

Test Strategy

• Verify existing template YAML files parse without the removed fields.
• Ensure abx template deploy still works with Dockerfile-based builds.

Files changed

• src/agent_sandbox/models/template.py — removed legacy fields and to_dockerfile()

Acceptance criteria

• ✅ TemplateConfig no longer accepts python_packages, system_packages, node_packages, commands, base, or copy_files
• ✅ to_dockerfile() method removed
• ✅ All existing template.yaml files load without errors
• ✅ Build pipeline unchanged (still uses Dockerfile)