Are the ESC override rules documented anywhere?

[jkodroff]

Problem description

I can't find out what the rules are for precedence of ESC Environment values versus:

1. Explicit config values (either stored in the stack config or passed via the CLI)
2. Local environment variables

This came up as a question in the Community Slack: https://pulumi-community.slack.com/archives/C0602S4P4T1/p1739811249207619

Obviously, it's a bummer to have to write and run code myself to figure out the behavior (and not having any way to know whether the intended behavior is what's being exhibited), so I think we need to document this.

[kujenga]

This would be quite useful to know! From Slack, we are now using this to override values from the environment (e.g. versions) locally when running "preview" in CI, so that we can check what it will look like before actually updating the environment ahead of "up". That trick was non-obvious without the context on config overriding the envs.

[thoward]

Note that we do cover precedence rules for multiple ESC environments (eg. that are composed/inherited): https://www.pulumi.com/docs/esc/environments/working-with-environments/#precedence-rules ... but it doesn't cover the cases you're describing here. That might be a good place to add this info. Alternatively, this might be a natural place to add that: https://www.pulumi.com/docs/esc/integrations/infrastructure/pulumi-iac/ or here https://www.pulumi.com/docs/esc/environments/working-with-environments/#using-environments-with-pulumi-iac