This lets the environment name vary within a request by the context a
component, log or error being executed in.
A potentially different API would be something like
`setEnvironmentName()` but we'd have to extend the `ReadableStream` or
something to do that like we do for `.allReady`. As a function though it
has some expansion possibilities, e.g. we could potentially also pass
some information to it for context about what is being asked for.
If it changes before completing a task, we also emit the change so that
we have the debug info for what the environment was before entering a
component and what it was after completing it.
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