fix(rest): the shipped objectQLProvider absorbs only the branded never-registered rejection

.changeset/objectql-provider-three-state.md

@@ -0,0 +1,41 @@
+---
+"@objectstack/rest": minor
+---
+
+fix(rest): the shipped `objectQLProvider` stops collapsing "the engine is wired and broke" into "no engine is wired" (#13904)
+
+Runtime behaviour change on a public REST door, shipped as `minor` under the
+repo's launch-window convention — the same convention the #13476 family's
+changeset (`engine-unresolvable-fails-loud.md`, PR #13910) and #13279's name
+for the identical class of change on this same door. This change additionally
+moves one row refused → served (a factory-registered engine now resolves and
+serves), so it sits strictly inside the class that convention governs.
+
+`rest-api-plugin.ts` handed `RestServer` an engine provider shaped
+`try { return ctx.getService('objectql'); } catch { return undefined; }`. The
+sync accessor throws for three distinguishable registry facts — never
+registered (the supported no-data-plane embedder), registered as a factory
+(wrong accessor for it), and a registration that failed to build — and the
+catch-all answered all three with the `undefined` the seam contract reads as
+"no engine is wired". So the #13476 transport repair (`wiredEngineOrLoud`,
+which turns a provider REJECTION into the loud 503 outage) never fired on the
+shipped single-kernel wiring: the provider absorbed one layer before the seam
+could see the fact.
+
+The provider now resolves through `kernel.getServiceAsync` →
+`PluginLoader.getService` and absorbs ONLY the branded "never registered"
+rejection (`isServiceNotRegisteredError`, #13905) — the registry's own
+classification, never message text, closed set, loud default. Observable
+changes, all in the wired-single-kernel deployment:
+
+- an embedder that never wired a data plane keeps its quiet answer, unchanged
+  and pinned (403 at the package door, as before);
+- an engine registered as a service FACTORY now actually resolves and serves
+  (previously the sync accessor could only throw `is async - use await`, read
+  as "no engine": the door refused a wired, constructible engine);
+- an engine whose registration FAILS TO BUILD now rejects loudly, so the door
+  answers 503 `SERVICE_UNAVAILABLE` instead of telling an authenticated
+  administrator they lack a capability.
+
+A KernelBase-shaped host (`LiteKernel`, no async accessor, no factories) keeps
+both of its answers byte-identically through the sync fallback leg.