fix: use cookie/urlParam-based fallback by default with redirect action

[tyiuhc]

Summary

Branch script to use cookie+urlParam-based fallback for redirect actions by default.

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• Does your PR have a breaking change?:

---

Note

Medium Risk
Default-on AMP_REDIRECT changes production redirect URLs and impression plumbing; start() now exits early when a redirect fires during variant apply, altering remote flag fetch timing.

Overview
Default redirect impression fallback now enables URL encoding: Defaults.redirectConfig.encodeRedirectInUrl is true (was false), so cross-subdomain redirects embed AMP_REDIRECT on the destination URL by default, alongside the existing cookie-based path.

Redirect-in-flight handling adds isRedirecting, set in handleRedirect before navigation. During start(), that flag keeps anti-flicker CSS in place and short-circuits after local/preview variant application—skipping removeAntiFlickerCss (when not remote-blocking) and not fetching/applying remote flags while a redirect is pending.

^{Reviewed by Cursor Bugbot for commit 27bd6d0. Bugbot is set up for automated code reviews on this repo. Configure here.}

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

Autofix Details

Bugbot Autofix prepared a fix for the issue found in the latest run.

• ✅ Fixed: Unconditional console.error calls pollute customer browser consoles
  • Removed all three console.error calls in cookie operations (storeRedirectImpressions, fireStoredRedirectImpressions, and cleanup) and replaced them with silent failure as the cookie storage is a non-critical fallback mechanism.

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@cursor push 9ead4e2377

Preview (9ead4e2377)

diff --git a/packages/experiment-tag/src/experiment.ts b/packages/experiment-tag/src/experiment.ts
--- a/packages/experiment-tag/src/experiment.ts
+++ b/packages/experiment-tag/src/experiment.ts
@@ -1179,11 +1179,8 @@
       const redirects = storedRedirects || {};
       redirects[flagKey] = impression;
       await storage.set(storageKey, redirects);
-    } catch (error) {
-      console.error(
-        `Failed to store redirect impression in cookie for ${flagKey}:`,
-        error,
-      );
+    } catch {
+      // Fail silently - cookie storage is a fallback mechanism
     }
   }
 
@@ -1225,11 +1222,8 @@
     });
     try {
       cookieImpressions = (await cookieStorage.get(storageKey)) || {};
-    } catch (error) {
-      console.error(
-        `Failed to retrieve redirect impressions from cookie ${storageKey}:`,
-        error,
-      );
+    } catch {
+      // Fail silently - cookie storage is a fallback mechanism
     }
 
     // Merge with priority: url > session > cookie
@@ -1261,11 +1255,8 @@
 
     const cleanup = async () => {
       removeStorageItem('sessionStorage', storageKey);
-      await cookieStorage.remove(storageKey).catch((error) => {
-        console.error(
-          `Failed to remove redirect impressions from cookie ${storageKey}:`,
-          error,
-        );
+      await cookieStorage.remove(storageKey).catch(() => {
+        // Fail silently - cookie storage is a fallback mechanism
       });
     };

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[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

There are 2 total unresolved issues (including 1 from previous review).

Autofix Details

Bugbot Autofix prepared a fix for the issue found in the latest run.

• ✅ Fixed: Redirect config flags ignored
  • Added guards checking this.config.redirectConfig?.encodeRedirectInUrl !== false and this.config.redirectConfig?.encodeRedirectInCookie !== false to respect explicit opt-out while maintaining default-enabled behavior.

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@cursor push 9f8b10e1b1

Preview (9f8b10e1b1)

diff --git a/packages/experiment-tag/src/experiment.ts b/packages/experiment-tag/src/experiment.ts
--- a/packages/experiment-tag/src/experiment.ts
+++ b/packages/experiment-tag/src/experiment.ts
@@ -909,29 +909,33 @@
     // Embed impression data in redirect URL for cross-domain and
     // cookie-blocked environments. Merge with any existing param in case
     // multiple redirect experiments fire in sequence.
-    const targetUrlObj = new URL(targetUrl);
-    let urlPayload: Record<string, StoredRedirectImpression> = {};
-    const existingEncoded = targetUrlObj.searchParams.get(
-      REDIRECT_IMPRESSION_PARAM,
-    );
-    if (existingEncoded) {
-      try {
-        urlPayload = JSON.parse(atob(existingEncoded));
-      } catch (error) {
-        console.error('Failed to decode existing AMP_REDIRECT param:', error);
+    if (this.config.redirectConfig?.encodeRedirectInUrl !== false) {
+      const targetUrlObj = new URL(targetUrl);
+      let urlPayload: Record<string, StoredRedirectImpression> = {};
+      const existingEncoded = targetUrlObj.searchParams.get(
+        REDIRECT_IMPRESSION_PARAM,
+      );
+      if (existingEncoded) {
+        try {
+          urlPayload = JSON.parse(atob(existingEncoded));
+        } catch (error) {
+          console.error('Failed to decode existing AMP_REDIRECT param:', error);
+        }
       }
+      urlPayload[flagKey] = {
+        redirectUrl,
+        variantKey: variant.key || '',
+        ...(variant.expKey !== undefined ? { expKey: variant.expKey } : {}),
+        ...(variant.metadata !== undefined
+          ? { metadata: variant.metadata }
+          : {}),
+      };
+      targetUrlObj.searchParams.set(
+        REDIRECT_IMPRESSION_PARAM,
+        btoa(JSON.stringify(urlPayload)),
+      );
+      targetUrl = targetUrlObj.toString();
     }
-    urlPayload[flagKey] = {
-      redirectUrl,
-      variantKey: variant.key || '',
-      ...(variant.expKey !== undefined ? { expKey: variant.expKey } : {}),
-      ...(variant.metadata !== undefined ? { metadata: variant.metadata } : {}),
-    };
-    targetUrlObj.searchParams.set(
-      REDIRECT_IMPRESSION_PARAM,
-      btoa(JSON.stringify(urlPayload)),
-    );
-    targetUrl = targetUrlObj.toString();
 
     // set previous url - relevant for SPA if redirect happens before push/replaceState is complete
     this.previousUrl = this.globalScope.location.href;
@@ -1169,25 +1173,29 @@
     setStorageItem('sessionStorage', storageKey, stored);
 
     // Also write to cookie to enable cross-subdomain tracking
-    const domain = await getTopLevelDomain(this.globalScope.location.hostname);
-    const storage = new CookieStorage<Record<string, StoredRedirectImpression>>(
-      {
+    if (this.config.redirectConfig?.encodeRedirectInCookie !== false) {
+      const domain = await getTopLevelDomain(
+        this.globalScope.location.hostname,
+      );
+      const storage = new CookieStorage<
+        Record<string, StoredRedirectImpression>
+      >({
         ...(domain && { domain }),
         sameSite: 'Lax',
         expirationDays: 1 / 1440, // 1 minute
-      },
-    );
+      });
 
-    try {
-      const storedRedirects = await storage.get(storageKey);
-      const redirects = storedRedirects || {};
-      redirects[flagKey] = impression;
-      await storage.set(storageKey, redirects);
-    } catch (error) {
-      console.error(
-        `Failed to store redirect impression in cookie for ${flagKey}:`,
-        error,
-      );
+      try {
+        const storedRedirects = await storage.get(storageKey);
+        const redirects = storedRedirects || {};
+        redirects[flagKey] = impression;
+        await storage.set(storageKey, redirects);
+      } catch (error) {
+        console.error(
+          `Failed to store redirect impression in cookie for ${flagKey}:`,
+          error,
+        );
+      }
     }
   }

_{You can send follow-ups to the cloud agent here.}

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

Autofix Details

Bugbot Autofix prepared a fix for the issue found in the latest run.

• ✅ Fixed: Redirect stall hangs startup
  • Removed the never-resolving promise after location.replace() and replaced it with a simple return statement, allowing startup to complete normally when navigation doesn't occur immediately.

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@cursor push cc22a41767

Preview (cc22a41767)

diff --git a/packages/experiment-tag/src/experiment.ts b/packages/experiment-tag/src/experiment.ts
--- a/packages/experiment-tag/src/experiment.ts
+++ b/packages/experiment-tag/src/experiment.ts
@@ -999,10 +999,7 @@
       return;
     }
     this.globalScope.location.replace(targetUrl);
-    // location.replace() queues navigation but JS continues — stall so applyVariants
-    // never resolves and removeAntiFlickerCss() is never called during the unload window.
-    // eslint-disable-next-line @typescript-eslint/no-empty-function
-    await new Promise(() => {});
+    return;
   }
 
   private handleMutate(action, flagKey: string, variant: Variant) {

_{You can send follow-ups to the cloud agent here.}

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

Bugbot Autofix prepared a fix for the issue found in the latest run.

• ✅ Fixed: Custom redirect skips remote flags
  • Moved isRedirecting = true to only execute after the custom handler check, ensuring SPAs using custom redirect handlers will continue to fetch remote flags after client-side navigation.

Or push these changes by commenting:

@cursor push ba7cf0cad9

Preview (ba7cf0cad9)

diff --git a/packages/experiment-tag/src/experiment.ts b/packages/experiment-tag/src/experiment.ts
--- a/packages/experiment-tag/src/experiment.ts
+++ b/packages/experiment-tag/src/experiment.ts
@@ -995,14 +995,18 @@
     // set previous url - relevant for SPA if redirect happens before push/replaceState is complete
     this.previousUrl = this.globalScope.location.href;
     await setMarketingCookie(this.apiKey, this.globalScope.location.hostname);
-    // Mark redirect as in-flight so start() skips removeAntiFlickerCss and
-    // further processing after applyVariants returns.
-    this.isRedirecting = true;
     // perform redirection
     if (this.customRedirectHandler) {
+      // Custom redirect handlers may perform client-side routing without a
+      // page reload, so we should NOT set isRedirecting. This allows start()
+      // to continue and fetch remote flags after the SPA navigation.
       this.customRedirectHandler(targetUrl);
       return;
     }
+    // Mark redirect as in-flight so start() skips removeAntiFlickerCss and
+    // further processing after applyVariants returns. Only set for full-page
+    // navigation since the page will unload anyway.
+    this.isRedirecting = true;
     this.globalScope.location.replace(targetUrl);
   }

_{You can send follow-ups to the cloud agent here.}

^{Reviewed by Cursor Bugbot for commit 27bd6d0. Configure here.}

[cursor]

Custom redirect skips remote flags

Medium Severity

When a redirect action runs during start(), isRedirecting makes start() return early with isRunning true and never calls fetchRemoteFlags. That fits full-page navigation, but if setRedirectHandler performs client-side routing without a reload, remote experiments never load for the rest of the session because nothing else fetches remote flags.

Additional Locations (1)

• packages/experiment-tag/src/experiment.ts#L997-L1004

 

^{Reviewed by Cursor Bugbot for commit 27bd6d0. Configure here.}