diff --git a/src/data/operation.ts b/src/data/operation.ts
index 2de0e46..d2a62ca 100644
--- a/src/data/operation.ts
+++ b/src/data/operation.ts
@@ -101,6 +101,8 @@ export function runOperation<T>(
     let settled = false;
     let cleanup: Cleanup;
     const unsubscribers: Array<() => void> = [];
+    let finishStart!: () => void;
+    const startFinished = new Promise<void>((resolve) => { finishStart = resolve; });
 
     const finish = (error: TradingViewError | undefined, value?: T) => {
       if (settled) return;
@@ -108,12 +110,15 @@ export function runOperation<T>(
       clearTimeout(timer);
       signal?.removeEventListener('abort', onAbort);
       for (const off of unsubscribers) off();
-      try {
-        cleanup?.();
-      } catch {
-        // Cleanup must never hide the result.
-      }
-      connection.release().catch(() => {}).then(() => {
+      // `start` may resolve synchronously, before it has returned its cleanup.
+      startFinished.then(() => {
+        try {
+          cleanup?.();
+        } catch {
+          // Cleanup must never hide the result.
+        }
+        return connection.release().catch(() => {});
+      }).then(() => {
         if (error) reject(error);
         else resolve(value as T);
       });
@@ -138,6 +143,8 @@ export function runOperation<T>(
       });
     } catch (error) {
       finish(toTradingViewError(error, 'INVALID_ARGUMENT'));
+    } finally {
+      finishStart();
     }
   });
 }
@@ -195,6 +202,8 @@ export function startWatcher<W extends Watcher>(
   let active = true;
   let started = false;
   let cleanup: Cleanup;
+  let finishStart!: () => void;
+  const startFinished = new Promise<void>((resolve) => { finishStart = resolve; });
   let stopPromise: Promise<void> | undefined;
   let resolveClosed!: () => void;
   const closed = new Promise<void>((resolve) => { resolveClosed = resolve; });
@@ -220,12 +229,15 @@ export function startWatcher<W extends Watcher>(
     clearTimeout(timer);
     signal?.removeEventListener('abort', onAbort);
     for (const off of unsubscribers) off();
-    try {
-      cleanup?.();
-    } catch {
-      // Ignore cleanup failures.
-    }
-    stopPromise = connection.release().catch(() => {}).then(() => resolveClosed());
+    // A synchronous ready/fail can stop before `start` returns its cleanup.
+    stopPromise = startFinished.then(() => {
+      try {
+        cleanup?.();
+      } catch {
+        // Ignore cleanup failures.
+      }
+      return connection.release().catch(() => {});
+    }).then(() => resolveClosed());
     return stopPromise;
   };
 
@@ -273,6 +285,8 @@ export function startWatcher<W extends Watcher>(
     });
   } catch (error) {
     fail(error);
+  } finally {
+    finishStart();
   }
 
   return startPromise;
diff --git a/tests/unit/operation.test.ts b/tests/unit/operation.test.ts
new file mode 100644
index 0000000..5cad215
--- /dev/null
+++ b/tests/unit/operation.test.ts
@@ -0,0 +1,59 @@
+import { describe, expect, it, vi } from 'vitest';
+import { TradingViewClient } from '../../src/client/client.js';
+import { runOperation, startWatcher } from '../../src/data/operation.js';
+import { FakeServer } from '../helpers/fake-server.js';
+
+function sharedClient() {
+  const server = new FakeServer();
+  return new TradingViewClient({ transport: server.transport });
+}
+
+describe('synchronous operation lifecycle', () => {
+  it('runs cleanup before resolving a one-shot operation', async () => {
+    const client = sharedClient();
+    const cleanup = vi.fn();
+    try {
+      const value = await runOperation({ client }, 'immediate', ({ resolve }) => {
+        resolve(42);
+        return cleanup;
+      });
+      expect(value).toBe(42);
+      expect(cleanup).toHaveBeenCalledOnce();
+      expect(client.isClosed).toBe(false);
+    } finally {
+      await client.close();
+    }
+  });
+
+  it('runs cleanup after a watcher becomes ready synchronously', async () => {
+    const client = sharedClient();
+    const cleanup = vi.fn();
+    try {
+      const watcher = await startWatcher({ client }, 'immediate', {}, ({ ready }) => {
+        ready();
+        return cleanup;
+      }, (base) => base);
+      await watcher.stop();
+      await watcher.closed;
+      expect(cleanup).toHaveBeenCalledOnce();
+      expect(client.isClosed).toBe(false);
+    } finally {
+      await client.close();
+    }
+  });
+
+  it('runs cleanup after a watcher fails synchronously', async () => {
+    const client = sharedClient();
+    const cleanup = vi.fn();
+    try {
+      await expect(startWatcher({ client }, 'immediate', {}, ({ fail }) => {
+        fail(new Error('startup failed'));
+        return cleanup;
+      }, (base) => base)).rejects.toThrow('startup failed');
+      expect(cleanup).toHaveBeenCalledOnce();
+      expect(client.isClosed).toBe(false);
+    } finally {
+      await client.close();
+    }
+  });
+});