The code-tour skill mentioned the CodeTour 'ref' field only in an example,
with no explanation of its behavior. CodeTour resolves each step's file
content from the git revision named by 'ref' (not the working tree) whenever
ref differs from HEAD, so any file that does not exist at that revision fails
to open with 'The editor could not be opened because the file was not found'
- even though the file is present on disk.
This bit a generated PR tour where ref was set to the base branch (develop):
every file ADDED by the PR is absent on the base, so all new-file steps 404'd
while the tour tree and comments still rendered, making the cause non-obvious.
Adds a 'The ref Field' section explaining the resolution behavior and the
rule that PR tours must pin ref to the branch head (never the base), plus a
validation step to confirm every referenced file exists at the chosen ref.
