dashboard: a subscribed node's message written out, read from it when shown

A subscribed node's messages come without being written out (their stream leaves the
text out: up to 8 KiB each, 500 at a time), so the figures box said only when, both
ends, type and size of one. Now the node answers for one message by its number,
`GET /admin/dashboard/messages/own/{seq}` (`{"text": …}`, `404` once it isn't kept),
which pages of other origins may call as they do its streams (`cors::open`), and the
page reads it when the message is shown, with its narrow token, and keeps it on the
message. Where it can't be read, the box says why.

1 files changed, 3 insertions, 2 deletions

diff --git a/docs/dashboard.md b/docs/dashboard.md
index 5eee5c9..590f72f 100644
--- a/docs/dashboard.md
+++ b/docs/dashboard.md
@@ -399,8 +399,9 @@ A subscribed node's messages with its peers are listed too, as they come from it
 named by both ends, the receiver first (`b ← a`), each once, as on the map (those
 with this node only from this node, between two subscribed nodes from the sender); its
 tooltip names the node that logged it. Shown in the figures box, it says when, both
-ends, its type and size: the message itself is written out only on the node that
-logged it.
+ends, its type, size and address, and the message written out, read from the node that
+logged it as it is shown (`/admin/dashboard/messages/own/{seq}` there, with the page's
+token), while that node still keeps it (its latest 1000).
 
 A click on a message shows it in the figures box: when, with whom, its type and size,
 and the message written out (its bytes as sizes). A click on it again, or on anything on