display_caveat

Return what a successful file operation could not show, if anything.

Every case here leaves the caveat as the user's only account of a change the transcript cannot render, so each has to name what is missing. Silence would read as a complete report.

Covers all of DiffOutcome rather than the subset that mounts a diff: a delete whose pre-image was lost produces no diff at all, so a caveat routed only through the diff would leave destroying a 5,000-line file rendering exactly like destroying an empty one.

Lives here rather than on any one surface because three need it: the tool row, the DiffMessage that may replace it, and non_interactive's printed output. A caveat produced in only one place is a caveat that goes missing on whichever surface the user happens to be using — which is how -p came to print an unqualified path for a change it could not verify.

Keyed on the outcome rather than on a FileOperationRecord so a widget holding only the outcome produces the identical sentence, and the wording cannot drift between surfaces. That holds for every outcome whose text is self-contained; unreadable_after is the exception, degrading to a generic reason without after_read_error. No current caller reaches it — that path leaves record.diff unset, so no DiffMessage mounts — but a future one passing only the outcome would render a weaker sentence than the tool row.