Description

Due to #14249 loading default_env.nu before the user's env.nu, variables that were defined there were overriding:

• Inherited values
• Some values that were set in the Rust code, such as the NU_LIB_PATH when set using --include-path.

This change checks to see if a variable already exists, uses its value if so, and sets the default value otherwise.

Note: ENV_CONVERSIONS is still "forced" to a default value regardless, as it needs to run reliably. There's probably not much reason to inherit it, but I'm open to the idea if there's a use-case.

User-Facing Changes

• Before: Variables that were set in default_env.nu always overrode those that were inherited from the parent process or set internally
• After: Inherited and internal environment variables will take priority.

Tests + Formatting

• 🟢 toolkit fmt
• 🟢 toolkit clippy
• 🟢 toolkit test
• 🟢 toolkit test stdlib

After Submitting

Will try to find a good place to mention this behavior in the Config chapter updates