fix(main): seed keyviz routes after distribution catalog applies

Codex round-1 P1 on PR #647: seedKeyVizRoutes ran BEFORE
setupDistributionCatalog. setupDistributionCatalog calls
distribution.EnsureCatalogSnapshot which applies a catalog snapshot
back into the engine — including the durable non-zero RouteIDs from
the catalog. Seeding earlier registered the placeholder RouteID=0
entries from buildEngine; subsequent dispatches (which resolve to
post-snapshot RouteIDs) found no slot and Observe dropped every
mutation, leaving the heatmap empty even when traffic was flowing.

Move the seed call to after setupDistributionCatalog returns so the
sampler sees the catalog's authoritative IDs. Existing tests cover
the seed mechanics; the ordering bug surfaced only in the live
startup path which the unit tests don't exercise.

Author: bootjp

main.go

@@ -289,14 +289,20 @@ func run() error {
 	lockResolver := kv.NewLockResolver(shardStore, shardGroups, nil)
 	cleanup.Add(func() { lockResolver.Close() })
 	sampler := buildKeyVizSampler()
-	seedKeyVizRoutes(sampler, cfg.engine)
 	coordinate := kv.NewShardedCoordinator(cfg.engine, shardGroups, cfg.defaultGroup, clock, shardStore).
 		WithLeaseReadObserver(metricsRegistry.LeaseReadObserver()).
 		WithSampler(keyVizSamplerForCoordinator(sampler))
 	distCatalog, err := setupDistributionCatalog(ctx, runtimes, cfg.engine)
 	if err != nil {
 		return err
 	}
+	// Seed AFTER setupDistributionCatalog so the sampler picks up the
+	// catalog-assigned RouteIDs. EnsureCatalogSnapshot inside
+	// setupDistributionCatalog applies a snapshot back into the engine
+	// with durable non-zero RouteIDs; seeding earlier would register
+	// the placeholder zero IDs from buildEngine and Observe would miss
+	// every dispatched mutation.
+	seedKeyVizRoutes(sampler, cfg.engine)
 	eg, runCtx := errgroup.WithContext(ctx)
 	eg.Go(func() error {
 		return runDistributionCatalogWatcher(runCtx, distCatalog, cfg.engine)