Add environment variable overrides for engine CLI versions

[Copilot]

Enables runtime version overrides for Copilot, Claude, and Codex CLI installations via environment variables, allowing version testing without code changes or releases.

Changes

Constants & Configuration

• Added GH_AW_COPILOT_VERSION, GH_AW_CLAUDE_VERSION, GH_AW_CODEX_VERSION constants
• Extended EngineInstallConfig with optional EnvVarName field

Engine Installation

• Copilot: Modified GenerateCopilotInstallerSteps() to inject env var with fallback
• Claude/Codex: Added GenerateNpmInstallStepsWithEnvOverride() for npm-based engines
• Updated GetBaseInstallationSteps() to conditionally apply env var pattern

Runtime Metadata (aw_info.json)

• Updated agent_version field to use environment variable pattern when no explicit version is configured
• Maintains consistency between installation steps and runtime metadata
• For Copilot: agent_version: process.env.GH_AW_COPILOT_VERSION || "0.0.395"
• For Claude: agent_version: process.env.GH_AW_CLAUDE_VERSION || "2.1.20"
• For Codex: agent_version: process.env.GH_AW_CODEX_VERSION || "0.92.0"

Version Resolution Priority

1. Workflow config (explicit engine.version)
2. Environment variable (runtime override)
3. Default constant (fallback)

Example

Setting GH_AW_COPILOT_VERSION=0.0.400 in repository variables generates:

# Installation step
- name: Install GitHub Copilot CLI
  env:
    COPILOT_VERSION: ${{ env.GH_AW_COPILOT_VERSION || '0.0.395' }}
  run: /opt/gh-aw/actions/install_copilot_cli.sh "${COPILOT_VERSION}"

// aw_info.json metadata
{
  engine_id: "copilot",
  agent_version: process.env.GH_AW_COPILOT_VERSION || "0.0.395",
  // ... other fields
}

Without the variable set, defaults to 0.0.395.

Original prompt

Allow override the default agentic engine environmen through an environment variabl.e

See a env var on the agent job that takes a environment version or the one baked into the release.

AGENT_CLI_VERSION: ${{ env.GH_AW_COPILOT_VERSION || "version" }}

then later use it when invoking the agent cli.

Add support for Claude (GH_AW_CLAUDE_VERSION) and codex (GH_AW_CODEX_VERSION)

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[pelikhan]

@copilot make sure aw_info.json is also updated

[Copilot]

@copilot make sure aw_info.json is also updated

Updated in commit 84bc564. The aw_info.json now includes environment variable support for agent_version:

• Copilot: agent_version: process.env.GH_AW_COPILOT_VERSION || "0.0.395"
• Claude: agent_version: process.env.GH_AW_CLAUDE_VERSION || "2.1.20"
• Codex: agent_version: process.env.GH_AW_CODEX_VERSION || "0.92.0"

This matches the installation behavior - when environment variables are set, both the installation steps and the metadata in aw_info.json will use the overridden versions.