fix(run-ops split): make passthrough assertEnvExists a no-op in single-DB

The passthrough resolver runs single-DB, so a run and its environment share
one database and there is no cross-seam FK to replace (matches main, which
dropped the TaskRun env FK). Skip the always-on hot-path findFirst; the
split-aware resolver still enforces env existence when the split makes a
DB-level FK impossible.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: d-cs

internal-packages/run-engine/src/engine/controlPlaneResolver.ts

@@ -180,15 +180,9 @@ export class PassthroughControlPlaneResolver implements ControlPlaneResolver {
     };
   }
 
-  async assertEnvExists(environmentId: string): Promise<void> {
-    const env = await this.#prisma.runtimeEnvironment.findFirst({
-      where: { id: environmentId },
-      select: { id: true },
-    });
-
-    if (!env) {
-      throw new Error(`Environment not found: ${environmentId}`);
-    }
+  async assertEnvExists(_environmentId: string): Promise<void> {
+    // No-op: passthrough is single-DB, so run and env share one database and there is
+    // no cross-seam FK to replace (matches main, which dropped the TaskRun env FK).
   }
 
   async resolveWorkerVersion(args: {

internal-packages/run-engine/src/engine/tests/controlPlaneResolverInjectability.test.ts

@@ -97,13 +97,14 @@ describe("RunEngine controlPlaneResolver injectability", () => {
           "deployment" in setup ? setup.deployment.id : undefined
         );
 
-        // assertEnvExists resolves for a present env and rejects for a missing one.
+        // The default passthrough resolver is single-DB, so assertEnvExists is a no-op:
+        // it resolves for both a present and a missing env (nothing to assert).
         await expect(
           engine.controlPlaneResolver.assertEnvExists(environment.id)
         ).resolves.toBeUndefined();
         await expect(
           engine.controlPlaneResolver.assertEnvExists("env_does_not_exist")
-        ).rejects.toThrow();
+        ).resolves.toBeUndefined();
       } finally {
         await engine.quit();
       }