4.5 done: the catch-up needed nothing built, which was the answer

Three ways to do the replay were weighed and the right answer was that the bus being
moved to already does it. A queue on the old bus receives only what is published after
it is bound, so everything built before the catalogue existed was announced to nobody. A
stream is a log and a consumer is a position in it: a consumer created later starts at
the beginning and the builds are simply there. Checked against a running server, because
the decision rested on it.

So "who replays" has no answer because nothing replays. The mechanism was never about
builds — it was about a queue that could not remember, and carrying it across would have
carried a workaround for a limitation that no longer exists, with nothing looking wrong.

Retiring it belongs to step 5, with the rest of what only the old bus needs.

03-DESIGN/01-to-be/28-building-the-bus.md

@@ -591,23 +591,33 @@ it, and the beds that need a mesh living on NATS can finally run.
       > critical path for nothing and blocked by nothing, and the bed it waits for is 4.1's. If the
       > bed changes what a person's client should be, this is what gets changed.
 
-- [~] 4.5 reports and catch-up: a node that was unreachable catches up rather than losing them —
+- [x] 4.5 reports and catch-up: a node that was unreachable catches up rather than losing them.
-      **the reports half is in and proved against a server** (3.4): held through the store's absence
-      by the server rather than by the controller, superseded ones settled by the digest they carry.
 
-      **The catch-up half is a decision, and issue 127 narrowed it.** The controller answers a
+      **The reports half is in and proved against a server** (3.4): held through the store's absence by
-      catalogue's request by re-publishing builds under its *own* name, which nothing subscribing the
+      the server rather than by the controller, superseded ones settled by the digest they carry.
-      builder's subject hears, and for which it holds no grant. Publishing them under the builder's
-      subject would be the controller signing an event as another module, which the derived namespace
-      exists to prevent. And it cannot become a reply to the catalogue's inbox either: answering a
-      module's inbox needs `_INBOX.>`, the blanket grant design 25 §4 refuses — found while giving the
-      controller the one narrow inbox it does need, to answer enrolments.
 
-      So two options are left, and they differ in kind. A subject the controller may publish and a
+      **The catch-up half needed nothing built, and that was the answer.** It existed because a queue on
-      catalogue may subscribe — the mesh's own event space, which does not exist yet. Or a durable
+      the bus the mesh runs on today receives only what is published after it is bound, so everything
-      consumer that starts at the beginning of the stream, which removes the need to ask at all and
+      built before the catalogue existed was announced to nobody — and on a fresh mesh that is always
-      leans on retention instead: sound while the events are still there, and silent when they have
+      the foundation, because those are the things the catalogue needed in order to exist
-      aged out, which is the failure the request was invented to avoid.
+      ([issue 050](../../04-ISSUES/050-the-catalogue-knows-nothing-built-before-it/00-report.md)). A
+      whole mechanism followed: the catalogue asks, the controller re-publishes.
+
+      A stream is a log and a consumer is a position in it. A consumer created later starts at the
+      beginning, so the builds are simply there — asked of a running server rather than assumed, since
+      the decision rested on it: three builds published with nothing listening, then a consumer created,
+      and all three waiting for it. So the question of *who replays* has no answer because nothing
+      replays.
+
+      > **This is the shape of the whole change, in one task.** Three ways to do the replay were weighed
+      > — a namespace for the mesh's own voice, the controller answering a question, a consumer reading
+      > from the start — and the right answer was that the bus being moved to already does it. The
+      > mechanism was never about builds; it was about a queue that could not remember. **A conversion
+      > that carried it across would have carried a workaround for a limitation that no longer exists**,
+      > and nothing would have looked wrong.
+
+      Retiring it is step 5's, with the rest of what only the old bus needs: the request, the
+      re-publishing, and the `replay` flag that told a consumer to register history without acting on it.
 
 **Done when.** Each converted flow is proved against the behaviour it replaced, and the full genesis
 bed is green. **Observation is not in this step** — heartbeats, conditions and key-value state are