screen: judged after the policy is gone, too

Review 3, R4: whether a batch was judged followed the receiving
document's policy now (and whether the batch writes one). After the
policy was removed, or replaced by a version the node doesn't know,
changes written under it and received late went in unjudged, while
nodes that had them earlier judged them; REFUSALS gave up likewise.

Screening now remembers that the document held a policy, known or not
(Screening::policed), and judges what it receives while it does, each
change by the policy at its dependencies; REFUSALS judges then too
(not under a policy the node doesn't know, as before). Not across a
restart, which access.md says.

1 files changed, 4 insertions, 1 deletions

diff --git a/docs/access.md b/docs/access.md
index fdcf23c..2ef94d3 100644
--- a/docs/access.md
+++ b/docs/access.md
@@ -320,7 +320,10 @@ change by the policy it was written under: a joining node judges its first sync,
 policy's own change and everything after it, as every other node does, and waits for
 the signatures of what was written under a policy requiring them. While neither
 its document nor what it receives holds a policy, it judges only that a root is the
-epoch's, and nothing costs more than applying the changes.
+epoch's, and nothing costs more than applying the changes. A policy removed, or
+replaced by one the node doesn't know, still judges what was written under it and
+comes late, as long as the node runs (after a restart, a document without a policy
+is judged as one that never had one).
 
 An epoch's root is pinned. A remake's is its epoch's ID, the hash of its snapshot. The
 first epoch's is its genesis change, which its genesis node logs (`The swarm's root`)