From e0e0a1f41476b6ae1918599e90936ed8b12dd209 Mon Sep 17 00:00:00 2001
From: theBGuy <60308670+theBGuy@users.noreply.github.com>
Date: Thu, 21 May 2026 20:39:30 +0000
Subject: [PATCH 1/2] fix(async-retryer): preserve message and cause for
 non-Error throws

---
 packages/pacer/src/async-retryer.ts        | 12 +++++++++++-
 packages/pacer/tests/async-retryer.test.ts | 18 ++++++++++++++++++
 2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/packages/pacer/src/async-retryer.ts b/packages/pacer/src/async-retryer.ts
index 4bbce86d2..8e1f7f443 100644
--- a/packages/pacer/src/async-retryer.ts
+++ b/packages/pacer/src/async-retryer.ts
@@ -538,7 +538,17 @@ export class AsyncRetryer<TFn extends AnyAsyncFunction> {
         ) {
           return undefined
         }
-        lastError = error instanceof Error ? error : new Error(String(error))
+        lastError =
+          error instanceof Error
+            ? error
+            : new Error(
+                typeof error === 'object' &&
+                  error !== null &&
+                  typeof (error as any).message === 'string'
+                  ? (error as any).message
+                  : String(error),
+                { cause: error },
+              )
         this.#setState({ lastError })
 
         // Call onError for every error (including during retries)
diff --git a/packages/pacer/tests/async-retryer.test.ts b/packages/pacer/tests/async-retryer.test.ts
index 448ea9194..1b75d8aa4 100644
--- a/packages/pacer/tests/async-retryer.test.ts
+++ b/packages/pacer/tests/async-retryer.test.ts
@@ -387,6 +387,24 @@ describe('AsyncRetryer', () => {
       expect(onLastError).toHaveBeenCalledTimes(1)
       expect(onLastError).toHaveBeenCalledWith(error, retryer)
     })
+
+    it('should preserve plain object error message and cause', async () => {
+      const originalError = { message: 'readable error', code: 'E001' }
+      const mockFn = vi.fn().mockRejectedValue(originalError)
+      const retryer = new AsyncRetryer(mockFn, {
+        maxAttempts: 1,
+        throwOnError: true,
+      })
+
+      try {
+        await retryer.execute()
+        expect.unreachable('Expected execute to throw')
+      } catch (error) {
+        expect(error).toBeInstanceOf(Error)
+        expect((error as Error).message).toBe('readable error')
+        expect((error as Error & { cause?: unknown }).cause).toBe(originalError)
+      }
+    })
   })
 
   describe('State Management', () => {

From 4a83cc6429d10055f9141c76611409085f70b928 Mon Sep 17 00:00:00 2001
From: theBGuy <60308670+theBGuy@users.noreply.github.com>
Date: Thu, 21 May 2026 20:43:41 +0000
Subject: [PATCH 2/2] chore: add changeset for async-retryer error
 normalization fix

---
 .changeset/big-bikes-wash.md | 5 +++++
 1 file changed, 5 insertions(+)
 create mode 100644 .changeset/big-bikes-wash.md

diff --git a/.changeset/big-bikes-wash.md b/.changeset/big-bikes-wash.md
new file mode 100644
index 000000000..cb824bf7d
--- /dev/null
+++ b/.changeset/big-bikes-wash.md
@@ -0,0 +1,5 @@
+---
+'@tanstack/pacer': patch
+---
+
+Fix AsyncRetryer error normalization to preserve plain-object message values and attach the original thrown value as cause.