fix(webfetch): avoid rewriting successful redirect content

src/hooks/webfetch-redirect-guard/hook.ts

@@ -56,6 +56,10 @@ function isRedirectLoopError(output: string): boolean {
   return WEBFETCH_REDIRECT_ERROR_PATTERNS.some((pattern) => pattern.test(output))
 }
 
+function isToolErrorOutput(output: string): boolean {
+  return output.trimStart().toLowerCase().startsWith("error:")
+}
+
 function buildRedirectLimitMessage(url?: string): string {
   const suffix = url ? ` for ${url}` : ""
   return `Error: WebFetch failed: exceeded maximum redirects (${MAX_WEBFETCH_REDIRECTS})${suffix}`
@@ -111,7 +115,7 @@ export function createWebFetchRedirectGuardHook(_ctx: PluginInput) {
         return
       }
 
-      if (isRedirectLoopError(output.output)) {
+      if (isToolErrorOutput(output.output) && isRedirectLoopError(output.output)) {
         output.output = buildRedirectLimitMessage()
       }
     },

src/hooks/webfetch-redirect-guard/index.test.ts

@@ -49,7 +49,7 @@ function createFetchMock(
   implementation: (input: RequestInfo | URL, init?: RequestInit) => Promise<Response>,
 ): typeof fetch {
   return Object.assign(implementation, {
-    preconnect: originalFetch.preconnect,
+    preconnect: Reflect.get(originalFetch, "preconnect"),
   })
 }
 
@@ -152,6 +152,20 @@ describe("createWebFetchRedirectGuardHook", () => {
         )
       })
     })
+
+    describe("#when successful fetched content mentions redirect loops", () => {
+      it("#then should keep the content unchanged", async () => {
+        const hook = createWebFetchRedirectGuardHook({} as never)
+        const input = createInput()
+        const output = createAfterOutput("This page explains why browsers hit too many redirects in some setups.")
+
+        await hook["tool.execute.after"](input, output)
+
+        expect(output.output).toBe(
+          "This page explains why browsers hit too many redirects in some setups.",
+        )
+      })
+    })
   })
 
   describe("#given a non-webfetch tool", () => {