Container env vars not updated by features while setting up

[Benjamin-Etheredge]

What happened?
When using base devcontainers and features to install additional tooling, the environment variables set by the features are not correctly set for other features and commands. If a feature defines a new containerEnv, it will work. But if it extends an existing environment variable, it is not updated.
I suspect this breaks a TON of features if one depends on another.

What did you expect to happen instead?
Environment variable adjustment from features to work for other features and commands

How can we reproduce the bug? (as minimally and precisely as possible)

My devcontainer.json:

{
	"image": "mcr.microsoft.com/devcontainers/base:noble",
	"features": {
		"ghcr.io/devcontainers/features/python:1": {},
		"ghcr.io/devcontainers/features/rust:1": {}
	},
	"postStartCommand": "env"
}

The following will show PYTHON_PATH and other variables set by the feature show up correctly, but PATH is not updated to the correct version for subsequent features or commands. At the start of features, it shows the correct values, but in the features, the path is incorrect as shown by the rust feature printing out PATH during setup.

Local Environment:

• DevPod Version: v0.5.21
• Operating System: windows
• ARCH of the OS: AMD64

DevPod Provider:

• Local/remote provider: docker

Anything else we need to know?
The variables are set correctly in the terminal after starting the devcontainer. The issue is only present during feature setup and commands like postCreateCommand.