diff --git a/packages/core/sdk/src/executor-cache.test.ts b/packages/core/sdk/src/executor-cache.test.ts
new file mode 100644
index 000000000..839e9c5cf
--- /dev/null
+++ b/packages/core/sdk/src/executor-cache.test.ts
@@ -0,0 +1,93 @@
+import { describe, expect, it } from "@effect/vitest";
+import { Effect } from "effect";
+
+import { createExecutor, type Executor } from "./executor";
+import { Tenant } from "./ids";
+
+// Keep in sync with the unexported fallback cache defaults in executor.ts.
+const MEMORY_CACHE_CAPACITY = 2_048;
+const MEMORY_CACHE_TTL_MS = 10 * 60 * 1000;
+
+const makeExecutor = Effect.acquireRelease(
+  createExecutor({
+    tenant: Tenant.make("test-tenant"),
+    onElicitation: "accept-all",
+  }),
+  (executor) => executor.close().pipe(Effect.ignore),
+);
+
+const withFakeNow = <A, E, R>(
+  initialNow: number,
+  run: (clock: { readonly advance: (ms: number) => void }) => Effect.Effect<A, E, R>,
+): Effect.Effect<A, E, R> =>
+  Effect.acquireUseRelease(
+    Effect.sync(() => {
+      const originalNow = Date.now;
+      let now = initialNow;
+      Date.now = () => now;
+      return {
+        advance: (ms: number) => {
+          now += ms;
+        },
+        restore: () => {
+          Date.now = originalNow;
+        },
+      };
+    }),
+    (clock) => run({ advance: clock.advance }),
+    (clock) => Effect.sync(clock.restore),
+  );
+
+describe("executor cache", () => {
+  it.effect("uses an in-memory fallback when no cache is configured", () =>
+    Effect.scoped(
+      Effect.gen(function* () {
+        const executor = yield* makeExecutor;
+
+        yield* executor.cache.set("a", "value");
+        expect(yield* executor.cache.get("a")).toBe("value");
+
+        yield* executor.cache.remove("a");
+        expect(yield* executor.cache.get("a")).toBeUndefined();
+      }),
+    ),
+  );
+
+  it.effect("expires fallback entries by TTL on get and size", () =>
+    withFakeNow(1_000, ({ advance }) =>
+      Effect.scoped(
+        Effect.gen(function* () {
+          const executor = yield* makeExecutor;
+
+          yield* executor.cache.set("a", "value");
+          expect(yield* executor.cache.size).toBe(1);
+
+          advance(MEMORY_CACHE_TTL_MS);
+
+          expect(yield* executor.cache.get("a")).toBeUndefined();
+          expect(yield* executor.cache.size).toBe(0);
+        }),
+      ),
+    ),
+  );
+
+  it.effect("refreshes fallback LRU position when an existing key is written", () =>
+    Effect.scoped(
+      Effect.gen(function* () {
+        const executor: Executor = yield* makeExecutor;
+
+        yield* executor.cache.set("a", "old");
+        for (let index = 0; index < MEMORY_CACHE_CAPACITY - 1; index += 1) {
+          yield* executor.cache.set(`key-${index}`, String(index));
+        }
+
+        yield* executor.cache.set("a", "new");
+        yield* executor.cache.set("overflow", "value");
+
+        expect(yield* executor.cache.get("a")).toBe("new");
+        expect(yield* executor.cache.get("key-0")).toBeUndefined();
+        expect(yield* executor.cache.get("key-1")).toBe("1");
+      }),
+    ),
+  );
+});
diff --git a/packages/core/sdk/src/executor.ts b/packages/core/sdk/src/executor.ts
index 3ab3757dc..d60cb70e6 100644
--- a/packages/core/sdk/src/executor.ts
+++ b/packages/core/sdk/src/executor.ts
@@ -511,6 +511,7 @@ const makeMemoryCacheStore = (): KeyValueStore.KeyValueStore => {
       Effect.sync(() => {
         const now = Date.now();
         evictExpired(now);
+        rows.delete(key);
         rows.set(key, { value, expiresAt: now + MEMORY_CACHE_TTL_MS });
         evictCapacity();
       }),