feat: rehydrate L3 metadata from event log on startup

TurboVec persists vectors via the sidecar but kept entry metadata
(sessionId/turnId/text) only in an in-memory map, so restarting with
backend=turbovec silently dropped every query hit (the id→metadata
lookup missed). Rebuild that map from the ChatTurnEvent log at startup.

- RehydratableL3MemoryStore: capability interface for stores whose
  vectors persist independently of the JVM. TurboVec implements it;
  InMemory deliberately does not (its vectors are volatile too).
- L3MetadataRehydrator replays ChatTurnEvents into the metadata map.
  No embedder: the query path never reads entry.vector, so vectors
  stay in the sidecar and metadata comes from the event log (the
  source of truth, invariant #1). Short-circuits for non-rehydratable
  backends before scanning the log.
- Wired into Main before the server accepts queries; no sidecar spawn.

Backfill of never-embedded history (needs the embedder) is a separate
follow-up. The in_memory non-durability warning already exists.

apps/server/src/main/kotlin/com/correx/apps/server/Main.kt

@@ -26,6 +26,7 @@ import com.correx.core.kernel.orchestration.OrchestratorEngines
 import com.correx.core.kernel.orchestration.OrchestratorRepositories
 import com.correx.core.kernel.retry.DefaultRetryCoordinator
 import com.correx.core.risk.DefaultRiskAssessor
+import com.correx.core.router.l3.L3MetadataRehydrator
 import com.correx.core.router.model.RouterConfig
 import com.correx.core.sessions.DefaultSessionReducer
 import com.correx.core.sessions.DefaultSessionRepository
@@ -54,6 +55,7 @@ import com.correx.infrastructure.tools.ShellConfig
 import com.correx.infrastructure.tools.ToolConfig
 import io.ktor.server.engine.embeddedServer
 import io.ktor.server.netty.Netty
+import kotlinx.coroutines.runBlocking
 import org.slf4j.LoggerFactory
 import java.nio.file.Path
 import java.nio.file.Paths
@@ -163,6 +165,10 @@ fun main() {
     val routerConfig = correxConfig.router
     val embedder = InfrastructureModule.createEmbedderFromConfig(routerConfig.embedder)
     val l3MemoryStore = InfrastructureModule.createL3MemoryStoreFromConfig(routerConfig.l3)
+    // Rebuild the L3 metadata map from the ChatTurnEvent log before serving queries:
+    // persisted vectors survive restart but the metadata map does not (no-op for
+    // non-rehydratable backends like in_memory).
+    runBlocking { L3MetadataRehydrator(eventStore).rehydrate(l3MemoryStore) }
     val routerFacade = InfrastructureModule.createRouterFacade(
         eventStore = eventStore,
         inferenceRouter = inferenceRouter,