just path/to/recipe and (cd path/to; just recipe) should be equivalent

These are not equivalent in the context of `set fallback := true`

In parent directory, create following justfile:
```
set fallback := false

@test:
echo {{invocation_directory()}}
```
Create two sub-directories, `with` and `without`. In `with`, create the following justfile:
```
set fallback := true
```
In the parent, the following three commands all generate the same output:
```
just test
just with/test
just without/test
```
The last two differ from
```
( cd with; just test )
( cd without; just test )
```

(This makes it difficult to write generic recipes that can be inherited, since {{invocation_directory()}} is only reliable when invoked from the actual directory.)

Start by reproducing the three parent-directory commands and the two subshell commands with `set fallback` and `invocation_directory()`. Trace how path-based recipe invocation resolves fallback justfiles and compare it with execution from the target directory; done means both forms produce equivalent output without breaking fallback behavior.

Written by the indexing model from the issue text.