Improved StackAssertionError error logging

.claude/CLAUDE-KNOWLEDGE.md

@@ -403,3 +403,6 @@ A: `packages/template/vitest.config.ts` installs a Vite transform plugin for Vit
 
 ## Q: How does the Mintlify apps sidebar filter stay in sync with theme changes?
 A: `docs-mintlify/apps-sidebar-filter.js` injects the Apps filter with inline styles, so the MutationObserver must reapply `applySidebarAppsFilterTheme` when an existing input is found. Theme detection should handle both `html.dark` and `data-theme="dark"` signals.
+
+## Q: How should `StackAssertionError` preserve an underlying thrown error?
+A: Pass the underlying error as the `cause` property in the second argument. The `StackAssertionError` constructor only forwards `cause` into `ErrorOptions`, so storing a caught error under an `error` property captures it as ordinary metadata instead of preserving the error cause chain.

apps/backend/src/app/api/latest/connected-accounts/access-token-helpers.tsx

@@ -26,7 +26,6 @@ function captureOAuthAccessTokenRefreshIssue(options: {
       attempts: options.refreshError.attempts,
       retryCount: options.refreshError.retryCount,
       sawAmbiguousRefreshAttempt: options.refreshError.sawAmbiguousRefreshAttempt,
-      error: options.refreshError.cause,
       causes: options.refreshError.causes,
     },
   ));
@@ -197,7 +196,7 @@ export async function retrieveOrRefreshAccessToken(options: {
             refreshError: tokenSetResult.error,
           });
           const assertionError = new StackAssertionError('Unexpected error refreshing access token — this may indicate a bug or misconfiguration', {
-            error: tokenSetResult.error.cause,
+            cause: tokenSetResult.error.cause,
             providerClass: providerInstance.constructor.name,
             refreshErrorType: tokenSetResult.error.type,
             attempts: tokenSetResult.error.attempts,
@@ -210,7 +209,7 @@ export async function retrieveOrRefreshAccessToken(options: {
         }
         default: {
           const _: never = tokenSetResult.error;
-          throw new StackAssertionError("Unhandled OAuth access token refresh error", { error: _ });
+          throw new StackAssertionError("Unhandled OAuth access token refresh error", { cause: _ });
         }
       }
     }

apps/backend/src/app/api/latest/users/crud.tsx

@@ -882,7 +882,7 @@ export const usersCrudHandlers = createLazyProxy(() => createCrudHandlers(usersC
               }
             });
             throw new StackAssertionError("Failed to update team member", {
-              error: e,
+              cause: e,
               tenancy_id: auth.tenancy.id,
               user_id: params.user_id,
               team_id: data.selected_team_id,

apps/backend/src/lib/email-rendering.tsx

@@ -154,7 +154,7 @@ export async function renderEmailWithTemplate(
         // This can happen with complex or invalid JSX
         captureError("email-transpilation-template-error", new StackAssertionError(
           "Failed to transpile template for editable markers",
-          { error: e instanceof Error ? e.message : String(e) }
+          { cause: e }
         ));
       }
     }
@@ -169,7 +169,7 @@ export async function renderEmailWithTemplate(
         // If transpilation fails, fall back to original source
         captureError("email-transpilation-theme-error", new StackAssertionError(
           "Failed to transpile theme for editable markers",
-          { error: e instanceof Error ? e.message : String(e) }
+          { cause: e }
         ));
       }
     }

apps/backend/src/lib/events.tsx

@@ -247,7 +247,7 @@ export async function logEvent<T extends EventType[]>(
       data = await eventType.dataSchema.validate(data, { strict: true, stripUnknown: false });
     } catch (error) {
       if (error instanceof yup.ValidationError) {
-        throw new StackAssertionError(`Invalid event data for event type: ${eventType.id}`, { eventType, data, error, originalData, originalEventTypes: eventTypes, cause: error });
+        throw new StackAssertionError(`Invalid event data for event type: ${eventType.id}`, { eventType, data, originalData, originalEventTypes: eventTypes, cause: error });
       }
       throw error;
     }

apps/backend/src/lib/js-execution.tsx

@@ -236,7 +236,7 @@ async function runWithFallback(code: string, options: ExecuteJavascriptOptions):
 
   captureError(`js-execution-freestyle-failed`, new StackAssertionError(
     `JS execution freestyle engine failed, falling back to vercel sandbox engine`,
-    { error: retryResult.error, innerCode: code, innerOptions: options }
+    { cause: retryResult.error, innerCode: code, innerOptions: options }
   ));
 
   try {
@@ -245,7 +245,7 @@ async function runWithFallback(code: string, options: ExecuteJavascriptOptions):
   } catch (error){
       captureError(`js-execution-vercel-sandbox-failed`, new StackAssertionError(
         `JS execution vercel sandbox engine failed after fallback from freestyle engine`,
-        { error: error, innerCode: code, innerOptions: options }
+        { cause: error, innerCode: code, innerOptions: options }
       ));
       throw new StackAssertionError("Vercel Sandbox service unavailable", { cause: error, innerCode: code, innerOptions: options });
   }

apps/backend/src/lib/stripe.tsx

@@ -104,7 +104,7 @@ export async function resolveProductFromStripeMetadata(options: {
           tenancyId: options.tenancyId,
           productString,
           metadata: options.metadata,
-          error,
+          cause: error,
         }
       );
     }

apps/backend/src/oauth/providers/apple.tsx

@@ -35,7 +35,7 @@ export class AppleProvider extends OAuthBaseProvider {
     try {
       payload = decodeJwt(idToken);
     } catch (error) {
-      throw new StackAssertionError("Error decoding Apple ID token", { error });
+      throw new StackAssertionError("Error decoding Apple ID token", { cause: error });
     }
 
     return validateUserInfo({

packages/stack-shared/src/interface/client-interface.ts

@@ -1562,7 +1562,7 @@ export class StackClientInterface {
           // refresh token was already invalid, just continue like nothing happened
         } else {
           // this should never happen
-          throw new StackAssertionError("Unexpected error", { error: resOrError.error });
+          throw new StackAssertionError("Unexpected error", { cause: resOrError.error });
         }
       } else {
         // user was signed out successfully, all good