a duplicate test in an exclude protects like one in a rule

The scopes that drive "no rule deletes a file krino found to be a
duplicate" were collected from rules only. A directory whose duplicate
tests lived in (exclude ...) forms had no scopes at all, so the
protection never engaged: krino explain said "yes duplicate" and the
next rule permanently deleted every copy. The README's promise was
false in that shape, and the spec's wording permitted it.

What matters is what krino knows, not which form taught it. The spec
and krino.conf(5) now say so too.

1 files changed, 6 insertions, 4 deletions

diff --git a/docs/design.md b/docs/design.md
index 3037308..6299288 100644
--- a/docs/design.md
+++ b/docs/design.md
@@ -295,10 +295,12 @@ jdupes. Two rules enforce this:
 
 1. A rule whose condition contains `(duplicate)` cannot contain a `delete`
    action (§4.5).
-2. In a directory whose rules use `(duplicate)`, a file that is a duplicate
-   under any of the duplicate scopes those rules use — each distinct set of
-   DIRs, and the plain `(duplicate)`, looked up for the file whether or not
-   evaluation reached that test — gets no delete step from any rule. The
+2. In a directory that uses `(duplicate)` — in a rule or in an `(exclude
+   ...)`, since what matters is what krino knows and not which form taught
+   it — a file that is a duplicate under any of the duplicate scopes that
+   directory uses — each distinct set of DIRs, and the plain `(duplicate)`,
+   looked up for the file whether or not evaluation reached that test —
+   gets no delete step from any rule. The
    plan shows the step as "skipped: a duplicate is never deleted" and the
    rest of the chain continues from the file's current path. This covers what
    rule 1 cannot see: a later rule deleting through `(matched)` or through a