mavend: an unconfigured capability names the gap (V-479)

Netscan and the crawler both declined their own turn when the wiring was
nil, and the question fell through to the search leg. "какие устройства в
сети?" came back as a paragraph about routers in general, and a question
about his own LAN went to an upstream engine — the personal boundary
exists to stop exactly that. A URL he named came back answered as though
he had not named it.

Both now claim the turn once their own recogniser has matched, and say
which capability is missing: net_off and page_off in the query family.

TestQueryWebPassesWhenNotConfigured encoded the old decision, that
announcing a configuration status is only for a capability that exists and
failed. It is rewritten, not deleted: the gap is the answer now.

cmd/mavend/crawls_test.go

@@ -125,13 +125,17 @@ func TestQueryWebPassesWithoutAURL(t *testing.T) {
 	}
 }
 
-// A daemon where page reading was never turned on — the default — answers the
-// question the way it did before the capability existed. Claiming the turn to
-// report a configuration status is for something that exists and failed.
-func TestQueryWebPassesWhenNotConfigured(t *testing.T) {
+// A daemon where page reading was never turned on names the gap. He asked
+// about one page, nothing else on the box can read it, and the old behaviour
+// here was to answer as though the URL had not been said (Vikunja #479).
+func TestQueryWebNamesTheGapWhenNotConfigured(t *testing.T) {
 	h := buildWebHandler(nil)
-	if reply, ok := askWeb(h, "посмотри https://example.org/page"); ok {
-		t.Fatalf("an unconfigured crawler claimed the turn with %q", reply)
+	reply, ok := askWeb(h, "посмотри https://example.org/page")
+	if !ok {
+		t.Fatal("an unconfigured crawler let the page question fall through")
+	}
+	if !phraser.IsQ(phraser.QueryPageOff, nil, reply) {
+		t.Errorf("got %q, want the gap named", reply)
 	}
 }