merge: integrate messaging R2 polling producer

# Conflicts:
#	docs/superpowers/specs/2026-07-28-messaging-production-capability-design.md
#	src/app-bootstrap/gradle.lockfile
#	src/app-bootstrap/src/test/java/dev/caskeleton/bootstrap/architecture/ArchitectureViolationFixtureTest.java
#	src/build.gradle

src/shared-contract/CLAUDE.md

@@ -25,6 +25,9 @@ envelope shape, metric cardinality bounds, tracing seam, domain-context propagat
   `tracing/SpanErrorRecorder`) — W3C `traceparent` value type, baggage allowlist,
   and the span-error-recording seam (feature-distributed-tracing-contract; the OTel
   tracer runtime is a fork-activated seam, so these stay Java-stdlib-only).
+- Generic messaging envelope schema resources under `contracts/messaging/envelope/`.
+  They own transport-neutral envelope metadata only; feature payload schemas remain in their
+  feature-owner modules. Resource presence is not runtime discovery or registration.
 
 ## Allowed
 - Java standard library ONLY. No Spring, no Jackson, no JPA imports.
@@ -32,6 +35,8 @@ envelope shape, metric cardinality bounds, tracing seam, domain-context propagat
 ## Forbidden
 - business/domain concept (domain error codes belong in the consuming module).
 - framework imports (HTTP status is expressed as transport-neutral `int`; the web module maps it).
+- claiming Draft 2020-12 validator compatibility before the messaging adapter's Task 6 validator
+  qualification exists.
 
 ## Test
 ```bash