Avoid (or help explain) `chrs ls` errors on feed that errored out

Image a feed that has terminated in an error/exception - so the terminal node "exists" but is "invalid".

Now, in `chrs`:

```
chrs cd feed/452
```

puts us "in" that feed. Doing

```
chrs ls
Error:
0: Path not found: rudolphpienaar/feed_452/pl-dircopy_3975/pl-spleendatads_4034/pl-monai_spleenseg_4040
```

can be confusing, esp the error message.

## Suggestion:

* If a "context" is an invalid node, place the context into the parent which by definition must be valid
* Alternatively, print an error message such that a user can recover. For instance "The context is invalid, usually because the terminal node is probably invalid due to a run exception. Please cd to another location in this feed"

Start by reproducing the behavior with `chrs cd feed/452` followed by `chrs ls`, then trace the CLI handling for invalid terminal-node context and the resulting path-not-found error. Done means an invalid context either moves to its valid parent or reports a clear recovery-oriented message, with the behavior verified for this feed scenario.

Written by the indexing model from the issue text.