Make sure AI-Completion exceptions don't crash the REPL

[waf]

e.g. network errors and HTTP errors should be caught and surfaced as REPL feedback -- not crash the REPL.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.3%. Comparing base (0100808) to head (7641a39).

Additional details and impacted files

@@           Coverage Diff           @@
##            main    #501     +/-   ##
=======================================
+ Coverage   80.1%   80.3%   +0.1%     
=======================================
  Files        126     126             
  Lines       9339    9362     +23     
  Branches    1398    1399      +1     
=======================================
+ Hits        7488    7519     +31     
+ Misses      1363    1355      -8     
  Partials     488     488             

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