diff --git a/server/src/scenario/scenario-scheduler.service.ts b/server/src/scenario/scenario-scheduler.service.ts
index e2e0513..49c7a59 100644
--- a/server/src/scenario/scenario-scheduler.service.ts
+++ b/server/src/scenario/scenario-scheduler.service.ts
@@ -46,6 +46,7 @@ export class ScenarioSchedulerService implements OnModuleInit {
 
   private static readonly DEFAULT_SCENARIO_TIMEOUT_SEC = 600;
   private static readonly DEFAULT_STEP_TIMEOUT_SEC = 60;
+  private static readonly CONCURRENCY_LIMIT = 10;
 
   constructor(
     @InjectRepository(ScenarioRunEntity)
@@ -97,7 +98,7 @@ export class ScenarioSchedulerService implements OnModuleInit {
               ),
             ),
           ),
-        { concurrency: 10 },
+        { concurrency: ScenarioSchedulerService.CONCURRENCY_LIMIT },
       ),
     );
   }
@@ -168,38 +169,61 @@ export class ScenarioSchedulerService implements OnModuleInit {
   @Interval(1000)
   async pickUpPendingRuns(): Promise<void> {
     const pending = await this.runRepo.find({ where: { status: "pending" } });
-    for (const run of pending) {
-      if (this.activeRuns.has(run.id)) continue;
-      this.activeRuns.add(run.id);
-      run.status = "in_progress";
-      await this.runRepo.save(run);
-      this.logger.log(`Run #${run.id} → in_progress`);
-      // Pre-load credential map for the scenario
-      const credMap = await this.scenarioService
-        .buildCredentialMap(run.scenarioId)
-        .catch(() => ({}) as Record<string, unknown>);
-      this.runCredentials.set(run.id, credMap);
-      // Pre-load snippet map
-      const snippetMap = await this.snippetService
-        .buildSnippetMap()
-        .catch(() => ({}) as Record<string, string>);
-      this.runSnippets.set(run.id, snippetMap);
-      // Pre-load selected environment data
-      const environmentData = await this.environmentRepo
-        .findOneBy({ id: run.environmentId })
-        .then((env) => env?.data ?? {})
-        .catch(() => ({}) as EnvironmentData);
-      this.runEnvironments.set(run.id, environmentData);
-      // Cache scenario-level timeout for the run
-      const scenario = await this.scenarioService
-        .findOne(run.scenarioId)
-        .catch(() => null);
-      this.runScenarioTimeouts.set(run.id, scenario?.timeoutSeconds ?? null);
-      const traceId = crypto.randomUUID();
-      void traceStorage.run({ traceId }, () =>
-        this.processRunToCompletion(run.id),
-      );
-    }
+    const newRuns = pending.filter((run) => !this.activeRuns.has(run.id));
+    if (newRuns.length === 0) return;
+
+    await Effect.runPromise(
+      Effect.forEach(
+        newRuns,
+        (run) => {
+          this.activeRuns.add(run.id);
+          return Effect.tryPromise(async () => {
+            run.status = "in_progress";
+            await this.runRepo.save(run);
+            this.logger.log(`Run #${run.id} → in_progress`);
+            const credMap = await this.scenarioService
+              .buildCredentialMap(run.scenarioId)
+              .catch(() => ({}) as Record<string, unknown>);
+            this.runCredentials.set(run.id, credMap);
+            const snippetMap = await this.snippetService
+              .buildSnippetMap()
+              .catch(() => ({}) as Record<string, string>);
+            this.runSnippets.set(run.id, snippetMap);
+            const environmentData = await this.environmentRepo
+              .findOneBy({ id: run.environmentId })
+              .then((env) => env?.data ?? {})
+              .catch(() => ({}) as EnvironmentData);
+            this.runEnvironments.set(run.id, environmentData);
+            const scenario = await this.scenarioService
+              .findOne(run.scenarioId)
+              .catch(() => null);
+            this.runScenarioTimeouts.set(run.id, scenario?.timeoutSeconds ?? null);
+            const traceId = crypto.randomUUID();
+            void traceStorage.run({ traceId }, () =>
+              this.processRunToCompletion(run.id),
+            );
+          }).pipe(
+            Effect.catchAll((err) =>
+              Effect.promise(async () => {
+                this.activeRuns.delete(run.id);
+                this.runCredentials.delete(run.id);
+                this.runSnippets.delete(run.id);
+                this.runEnvironments.delete(run.id);
+                this.runScenarioTimeouts.delete(run.id);
+                this.logger.error(
+                  `Run #${run.id}: setup failed — ${String(err)}`,
+                );
+                await this.failRun(
+                  run.id,
+                  `Run setup failed: ${String(err)}`,
+                ).catch(() => {});
+              }),
+            ),
+          );
+        },
+        { concurrency: ScenarioSchedulerService.CONCURRENCY_LIMIT },
+      ),
+    );
   }
 
   private async processRunToCompletion(runId: string): Promise<void> {