Per Greptile's review on #5717: the previous
`if result.get('messages') is not None` guard created an asymmetric
condition where the silent-failure classifier could miss the injected
fallback when the agent result had `messages: None` (which never
actually happens in practice since `finalize_turn` always returns a
list, but the asymmetry read as code smell). Drop the guard; the
writeback is now unconditional on `isinstance(result, dict)`.
Per the maintainer's review on #5717: there may be a
`finalize_turn` invariant on the agent branch this WebUI ships
against that already appends the fallback as an assistant row, in
which case the live bug is gone and this PR becomes a regression
guard. Reframe the test docstrings as dual-purpose pins of the user-
visible closure-text contract so they read correctly under both
interpretations.
Co-authored-by: b3nw <b3nw@users.noreply.github.com>
