04-ISSUES/050-the-catalogue-knows-nothing-built-before-it/00-report.md

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+---
+status: open
+opened: 2026-09-14
+located-in: []
+fixed-by:
+amended-design:
+---
+
+# 050 — The catalogue knows nothing that was built before it
+
+## Symptom
+
+A mesh raised from bare metal built six modules in order: the shared base, a store, the catalogue,
+the control plane, a module, and a broker. Asked afterwards what it holds, the catalogue answered
+with three — exactly the three built *after* it started running:
+
+```
+amqp-ping     built from <the catalogue repository>
+lavinmq       built from <the catalogue repository>
+mesh-control  built from <the control plane repository>
+```
+
+Missing: the shared base, the store, and the catalogue itself.
+
+The catalogue learns what exists by consuming the builder's announcement over the broker. Anything
+built before it was running was announced to nobody, and nothing goes back for it.
+
+## Why this matters
+
+**The modules it cannot see are the ones a mesh is made of.** On a fresh mesh the things built
+before the catalogue are, necessarily, the things the catalogue needed in order to exist: the base
+it was compiled against and the store it keeps its records in. So the hole is not random — it is
+always the foundation, on every mesh, at exactly the moment the graph is first populated.
+
+**It breaks the question the catalogue exists to answer.** Build edges are derived facts between
+versions, and the base is the node nearly every other module hangs off. A catalogue with no record
+of the base cannot know that moving it makes everything standing on it stale, so `catalog_stale`
+answers confidently and wrongly — the worst shape for a question about what to rebuild.
+
+**Nothing reports the gap.** The catalogue does not know what it was not told, so it does not say
+"three of six" — it says three, and a reader with no independent count believes it. This was found
+by asking it a question and comparing the answer against what the mesh had just been watched doing.
+
+**The record is not lost, only the catalogue's copy.** The control plane holds every build it
+ordered, with commit, repository, path and resolved artifacts. So this is a gap between two stores
+that should agree, rather than information nobody has.
+
+## Open questions
+
+- **Should the catalogue backfill on start** — ask the control plane for the builds it already
+  recorded and take them in? That fixes the fresh-mesh case and every case where the catalogue was
+  down while something was built, which is the same fault with a different cause.
+- **Or should announcements be durable**, so a build announced while nothing was listening is
+  delivered when something is? That treats the catalogue as one consumer among several, which it
+  already is.
+- **Or should the control plane be the record and the catalogue a projection of it?** Two stores
+  that must agree, kept in step by events, is the arrangement that produced this.
+- **How would anyone notice next time?** The catalogue cannot compare itself to a source of truth
+  it does not have. Whatever is chosen, something has to be able to say "these disagree".
+
+## How this would be checked
+
+| Rule | Checked by |
+|---|---|
+| The catalogue holds every module the mesh built | A mesh is raised from bare metal and the catalogue is asked; its list is compared against the control plane's build records, and a module in one and not the other is a failure. |
+| A change to the base makes what stands on it stale | The base is rebuilt on a fresh mesh and the catalogue names the modules that must follow — which requires it to know the base exists. |