feat: support install.codex()

[kemingy]

try it with:

def build():
    base(image="ubuntu:24.04", dev=True)
    shell('fish')
    install.codex()

[Copilot]

Pull Request Overview

This PR adds support for installing the Codex code agent in envd environments. The implementation introduces a new code agent installation framework and provides the ability to install Codex via the install.codex() Starlark function.

• Added CodeAgent type to represent code agents with name and version
• Implemented compileAgent() method to orchestrate agent installation during the build process
• Integrated agent compilation step into the LLB compilation pipeline

Reviewed Changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
pkg/lang/ir/types.go	Defines new CodeAgent struct type with name and version fields
pkg/lang/ir/v1/types.go	Adds CodeAgents field to generalGraph struct to store configured agents
pkg/lang/ir/v1/interface.go	Exposes Codex() function to configure Codex agent from Starlark
pkg/lang/ir/v1/agent.go	Implements installAgentCodex() method to download and install Codex binary
pkg/lang/ir/v1/system.go	Adds compileAgent() method and removes nolint:unparam comment
pkg/lang/ir/v1/compile.go	Integrates agent compilation into the LLB build pipeline
pkg/lang/frontend/starlark/v1/install/install.go	Adds codex builtin function to Starlark install module
pkg/lang/frontend/starlark/v1/install/const.go	Adds ruleCodex constant for the install.codex rule

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