fix(browser): tighten 429 detection and unify rate limit messages

- Remove errMsg.includes("429") fallback from retry-skip logic in
  pw-session.ts; the "rate limit" check alone is sufficient and avoids
  false positives from unrelated errors containing "429" (e.g. timeouts,
  port numbers, API paths)
- Export BROWSER_RATE_LIMIT_MESSAGE from client-fetch.ts and use it in
  cdp.helpers.ts instead of hand-rolled message for consistent wording

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/browser/cdp.helpers.ts

@@ -3,6 +3,7 @@ import { isLoopbackHost } from "../gateway/net.js";
 import { rawDataToString } from "../infra/ws.js";
 import { getDirectAgentForCdp, withNoProxyForCdpUrl } from "./cdp-proxy-bypass.js";
 import { CDP_HTTP_REQUEST_TIMEOUT_MS, CDP_WS_HANDSHAKE_TIMEOUT_MS } from "./cdp-timeouts.js";
+import { BROWSER_RATE_LIMIT_MESSAGE } from "./client-fetch.js";
 import { getChromeExtensionRelayAuthHeaders } from "./extension-relay.js";
 
 export { isLoopbackHost };
@@ -176,8 +177,7 @@ export async function fetchCdpChecked(
         const text = await res.text().catch(() => "");
         const detail = text ? ` (${text.slice(0, 200)})` : "";
         throw new Error(
-          `Browserbase rate limit reached (max concurrent sessions).${detail} ` +
-            `Do NOT retry - wait for the current session to complete, or upgrade your plan.`,
+          `${BROWSER_RATE_LIMIT_MESSAGE}${detail} Do NOT retry - wait for the current session to complete, or upgrade your plan.`,
         );
       }
       throw new Error(`HTTP ${res.status}`);

src/browser/client-fetch.ts

@@ -102,7 +102,7 @@ const BROWSER_TOOL_MODEL_HINT =
   "Do NOT retry the browser tool — it will keep failing. " +
   "Use an alternative approach or inform the user that the browser is currently unavailable.";
 
-const BROWSER_RATE_LIMIT_MESSAGE =
+export const BROWSER_RATE_LIMIT_MESSAGE =
   "Browserbase rate limit reached (max concurrent sessions). " +
   "Wait for the current session to complete, or upgrade your plan.";
 

src/browser/pw-session.ts

@@ -367,7 +367,7 @@ async function connectBrowser(cdpUrl: string): Promise<ConnectedBrowser> {
         lastErr = err;
         // Don't retry rate-limit errors; retrying worsens the 429.
         const errMsg = err instanceof Error ? err.message : String(err);
-        if (errMsg.includes("rate limit") || errMsg.includes("429")) {
+        if (errMsg.includes("rate limit")) {
           break;
         }
         const delay = 250 + attempt * 250;