docs(keycloak-session-store): import the session-storage lab as a new project

The keycloak project ended with four open questions that design could not
settle. A two-VM lab was built to answer them by measurement, and this is
that material: 26 experiments, 125 raw command outputs, 22 browser captures.

Follows the import procedure in README.md.

  source/     the originating repository verbatim — 78 documents, 28 SVGs,
              8 manifests, plus .source-revision recording the commit
  final/      the SSOT
    document.md   729 lines written from the 29 experiment documents, not
                  concatenated: what was predicted, what was measured, and
                  where the measurement itself was wrong
    evidence/raw    125 outputs, flattened to <experiment>__<file> because
                    the originals collided (01-baseline.txt appeared three
                    times) and the audit only globs the top level
    evidence/meta   one per raw file; command and exitCode are null and the
                    README says why rather than inventing them
    evidence/browser  22 captures
    assets/       three diagrams through techviz
    .techviz/     their VizSpecs

A separate project rather than an addition to keycloak: the B-layer answers
that project's four questions, but the A, C and D layers are about cluster
failure, SSO and operations, and one document.md should hold one subject.
The four question records there can point here through 관계.

Recorded rather than papered over: only three of the 28 diagrams were
remade. The repository forbids hand-drawn SVG and forbids titles inside the
canvas; all 28 originals carry both, so converting them is redrawing, not
reformatting. They stay in source/ and the gap is written into the document.

verify-pipeline.py passes. audit-records.py reports no issues.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

docs/clean-architecture-backend-template/final/evidence/raw/047a-jpa-custom-retry-policy-probe.java

@@ -0,0 +1,43 @@
+import dev.caskeleton.adapter.outbound.persistence.api.PersistenceOperationName;
+import dev.caskeleton.adapter.outbound.persistence.api.error.JpaFailureContext;
+import dev.caskeleton.adapter.outbound.persistence.api.error.SerializationFailureException;
+import dev.caskeleton.adapter.outbound.persistence.api.transaction.*;
+import dev.caskeleton.adapter.outbound.persistence.transaction.*;
+import java.time.*;
+import java.util.concurrent.atomic.AtomicInteger;
+import org.springframework.transaction.*;
+import org.springframework.transaction.support.SimpleTransactionStatus;
+
+public class JpaCustomRetryPolicyProbe {
+  public static void main(String[] args) {
+    AtomicInteger customPolicyCalls = new AtomicInteger();
+    AtomicInteger workCalls = new AtomicInteger();
+    PlatformTransactionManager tm = new PlatformTransactionManager() {
+      public TransactionStatus getTransaction(TransactionDefinition d) { return new SimpleTransactionStatus(true); }
+      public void commit(TransactionStatus s) {}
+      public void rollback(TransactionStatus s) {}
+    };
+    Clock clock = Clock.fixed(Instant.parse("2026-08-29T00:00:00Z"), ZoneOffset.UTC);
+    SpringJpaTransactionExecutor executor = new SpringJpaTransactionExecutor(tm, clock);
+    JpaRetryPolicy custom = (failure, attempt) -> {
+      customPolicyCalls.incrementAndGet();
+      return RetryDecision.fail("custom-policy-called");
+    };
+    FullTransactionRetryCoordinator coordinator = new FullTransactionRetryCoordinator(
+        executor, custom, ignored -> {}, clock, Duration.ofSeconds(30), RetryEventListener.noop());
+    RetryProfile retry = RetryProfile.boundedContention("probe.write", 2);
+    TransactionProfile profile = TransactionProfile.write("probe.write", Duration.ofSeconds(5)).withRetryProfile(retry);
+    PersistenceOperationName operation = new PersistenceOperationName("probe.write");
+    try {
+      coordinator.execute(operation, profile, () -> {
+        int call = workCalls.incrementAndGet();
+        throw new SerializationFailureException(
+            JpaFailureContext.retryable(operation, "40001", call, Duration.ZERO, null));
+      });
+    } catch (SerializationFailureException expected) {
+      System.out.println("thrown=" + expected.category());
+    }
+    System.out.println("customPolicyCalls=" + customPolicyCalls.get());
+    System.out.println("workCalls=" + workCalls.get());
+  }
+}