plan 9: an interrupted or failed undo can be finished

1 files changed, 13 insertions, 3 deletions

diff --git a/docs/design.md b/docs/design.md
index 11e859e..caa2a0f 100644
--- a/docs/design.md
+++ b/docs/design.md
@@ -618,9 +618,19 @@ not logged; declined files are.
 
 - `krino log` lists recent runs: id, time, directories, counts.
 - `krino undo` reverses the most recent run, in every directory it
-  touched; if that run is itself an undo run, it is refused. An older run
-  is undone by naming it: `krino undo RUN`. Undo runs cannot themselves be
-  undone.
+  touched. An older run is undone by naming it: `krino undo RUN`. Undo runs
+  cannot themselves be undone: naming one is refused.
+- A run is undone as far as it can be. Reversals an earlier undo of the
+  same run completed are not offered again, so an undo that stopped part
+  way (a refused or failed step, an interrupt) is finished by undoing the
+  run once more; when the most recent run is itself an undo, plain
+  `krino undo` does exactly that for the run it undid.
+- A file is identified by its directory and its path within it, so two
+  directories' files of the same name are reversed apart. A file that one
+  directory's rules move into another included directory, which sorts it
+  again in the same run, is two files to undo, reversed in the order the
+  run touched them; the first may then be refused as missing (known
+  limitation).
 - Undo builds a plan like any other, shown and approved the same way
   (`-y` and `-n` apply). Its per-file prompt has no `t` or `d`.