From dbaa4fceaa9d3435098bedbd487b577d0d56b409 Mon Sep 17 00:00:00 2001
From: rory <rory@expensify.com>
Date: Fri, 21 Aug 2026 17:46:01 -0700
Subject: [PATCH 1/2] fix(storage): serialize Error.cause when degrading

Avoid interpolating a raw cause object into the fallback-to-cache
alert so logs stay readable.
---
 lib/storage/index.ts | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/lib/storage/index.ts b/lib/storage/index.ts
index b4e80e74c..0b15ca663 100644
--- a/lib/storage/index.ts
+++ b/lib/storage/index.ts
@@ -20,7 +20,8 @@ type Storage = {
  * Degrade performance by removing the storage provider and only using cache
  */
 function degradePerformance(error: Error) {
-    Logger.logHmmm(`Error while using ${provider.name}. Falling back to only using cache and dropping storage.\n Error: ${error.message}\n Stack: ${error.stack}\n Cause: ${error.cause}`);
+    const causeMessage = error.cause instanceof Error ? error.cause.message : typeof error.cause === 'string' ? error.cause : '';
+    Logger.logHmmm(`Error while using ${provider.name}. Falling back to only using cache and dropping storage.\n Error: ${error.message}\n Stack: ${error.stack}\n Cause: ${causeMessage}`);
     console.error(error);
     provider = MemoryOnlyProvider;
 }

From 698a3d963afb89ca411840f4a7633487f0ba886e Mon Sep 17 00:00:00 2001
From: rory <rory@expensify.com>
Date: Fri, 21 Aug 2026 22:01:38 -0700
Subject: [PATCH 2/2] fix: flatten cause serialization and cover it

Avoid a nested ternary in degradePerformance and assert the
Cause field is a readable string, not [object Object].
---
 lib/storage/index.ts                           |  7 ++++++-
 .../storage/tryOrDegradePerformanceTest.ts     | 18 ++++++++++++++++++
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/lib/storage/index.ts b/lib/storage/index.ts
index 0b15ca663..5c6313fff 100644
--- a/lib/storage/index.ts
+++ b/lib/storage/index.ts
@@ -20,7 +20,12 @@ type Storage = {
  * Degrade performance by removing the storage provider and only using cache
  */
 function degradePerformance(error: Error) {
-    const causeMessage = error.cause instanceof Error ? error.cause.message : typeof error.cause === 'string' ? error.cause : '';
+    let causeMessage = '';
+    if (error.cause instanceof Error) {
+        causeMessage = error.cause.message;
+    } else if (typeof error.cause === 'string') {
+        causeMessage = error.cause;
+    }
     Logger.logHmmm(`Error while using ${provider.name}. Falling back to only using cache and dropping storage.\n Error: ${error.message}\n Stack: ${error.stack}\n Cause: ${causeMessage}`);
     console.error(error);
     provider = MemoryOnlyProvider;
diff --git a/tests/unit/storage/tryOrDegradePerformanceTest.ts b/tests/unit/storage/tryOrDegradePerformanceTest.ts
index b160b5903..de6f8c5a3 100644
--- a/tests/unit/storage/tryOrDegradePerformanceTest.ts
+++ b/tests/unit/storage/tryOrDegradePerformanceTest.ts
@@ -69,6 +69,24 @@ describe('storage/tryOrDegradePerformance', () => {
         expect(storage.getStorageProvider().name).toBe('MemoryOnlyProvider');
     });
 
+    it('serializes Error.cause as a readable string in the degrade log', async () => {
+        const {storage, Logger} = loadIsolatedStorage();
+        const capturedLogs: CapturedLog[] = [];
+        Logger.registerLogger((data: LogData) => capturedLogs.push({level: data.level, message: data.message}));
+
+        storage.init();
+
+        const originalProvider = storage.getStorageProvider();
+        const targetError = new Error('IDBKeyVal store could not be created', {cause: new Error('underlying disk is full')});
+        originalProvider.getAllKeys = jest.fn().mockReturnValue(Promise.reject(targetError));
+
+        await expect(storage.getAllKeys()).rejects.toBe(targetError);
+
+        const degradeLog = capturedLogs.find((log) => log.level === 'hmmm' && log.message.includes('Falling back to only using cache'));
+        expect(degradeLog?.message).toContain('Cause: underlying disk is full');
+        expect(degradeLog?.message).not.toContain('[object Object]');
+    });
+
     it('propagates async rejections with unrelated messages without falling back', async () => {
         const {storage, Logger} = loadIsolatedStorage();
         const capturedLogs: CapturedLog[] = [];