fix: set AGENT_TOOLSDIRECTORY for self-hosted mode to prevent permission errors on macOS

[xingzihai]

Summary

Fixes permission errors when using self-hosted mode on macOS with actions that rely on AGENT_TOOLSDIRECTORY (e.g., actions/setup-python).

Problem

When running act in self-hosted mode on macOS:

1. The host system may have AGENT_TOOLSDIRECTORY set from a GitHub Actions runner installation (e.g., /Users/runner/hostedtoolcache)
2. This environment variable is passed through to action scripts via os.Environ()
3. Actions like setup-python check for AGENT_TOOLSDIRECTORY and use it if set
4. The script tries to create /Users/runner/hostedtoolcache/Python, but:
   • /Users/runner doesn't exist
   • The user lacks permission to create it
   • The action fails with a permission error

Root Cause

In startHostEnvironment, the AGENT_TOOLSDIRECTORY from the host system's environment overrides the RUNNER_TOOL_CACHE value that act sets.

Solution

Explicitly set AGENT_TOOLSDIRECTORY to match RUNNER_TOOL_CACHE before the os.Environ() loop:

// Set AGENT_TOOLSDIRECTORY to match RUNNER_TOOL_CACHE for self-hosted mode
// This ensures that actions like setup-python use the correct tool cache path
// instead of potentially using a host system's AGENT_TOOLSDIRECTORY value
rc.Env["AGENT_TOOLSDIRECTORY"] = toolCache

This ensures:

• AGENT_TOOLSDIRECTORY uses the act-defined path
• Host system's AGENT_TOOLSDIRECTORY is ignored
• Actions use the correct local cache path

Changes

• pkg/runner/run_context.go (+4 lines)

Fixes #5974