Improve open-tab prompt fallback resiliency

Co-authored-by: Shri Sukhani <shrisukhani@users.noreply.github.com>

Author: cursoragent

currentState.md

@@ -158,6 +158,7 @@ HyperAgent exposes a TypeScript SDK for browser automation with three primary pa
   - `getCDPClientForPage` now always clears pending init promises (including failed init paths) and tolerates trap-prone `page.once` close-listener attachment with sanitized warnings.
 - Removed stale inline TODO/commented dead code in markdown conversion utility to keep cleanup pass consistent.
 - Replaced remaining TODO-style OOPIF note in a11y DOM extraction with an accurate non-actionable implementation constraint note; `src/` now has no lingering TODO/FIXME/HACK markers.
+- Hardened prompt open-tab summary fallback behavior: when context/tab enumeration is unavailable or trap-prone, prompts now fall back to the current tab line rather than opaque "Open tabs unavailable" text.
 - Hardened A11y DOM option ingestion (`useCache`, `onFrameChunk`, `filterAdTrackingFrames`) with trap-safe reads, so malformed option objects no longer break extraction setup.
 - Hardened A11y DOM debug-option lookup (`getDebugOptions`) with trap-safe fallback defaults and sanitized warning diagnostics.
 - Hardened OpenAI/Anthropic structured-schema debug-option reads so trap-prone debug-option access no longer interrupts structured invocation paths.

src/agent/messages/builder.test.ts

@@ -451,7 +451,7 @@ describe("buildAgentStepMessages", () => {
     expect(joined.length).toBeLessThan(6000);
   });
 
-  it("falls back to placeholder text when open tabs cannot be listed", async () => {
+  it("falls back to current-tab line when open tabs cannot be listed", async () => {
     const page = {
       url: () => "https://example.com/current",
       context: () => {
@@ -481,7 +481,46 @@ describe("buildAgentStepMessages", () => {
       .join("\n");
 
     expect(joined).toContain("=== Open Tabs ===");
-    expect(joined).toContain("Open tabs unavailable");
+    expect(joined).toContain("[0] https://example.com/current (current)");
+    expect(joined).not.toContain("Open tabs unavailable");
+  });
+
+  it("falls back to current-tab line when context pages method getter traps", async () => {
+    const context = {};
+    Object.defineProperty(context, "pages", {
+      get: () => {
+        throw new Error("pages getter trap");
+      },
+      configurable: true,
+    });
+    const page = {
+      url: () => "https://example.com/current",
+      context: () => context as ReturnType<Page["context"]>,
+    } as unknown as Page;
+
+    const messages = await buildAgentStepMessages(
+      [{ role: "system", content: "system" }],
+      [],
+      "task",
+      page,
+      {
+        elements: new Map(),
+        domState: "dom",
+        xpathMap: {},
+        backendNodeMap: {},
+      },
+      undefined,
+      []
+    );
+
+    const joined = messages
+      .map((message) =>
+        typeof message.content === "string" ? message.content : ""
+      )
+      .join("\n");
+
+    expect(joined).toContain("[0] https://example.com/current (current)");
+    expect(joined).not.toContain("Open tabs unavailable");
   });
 
   it("falls back to placeholder text when current URL cannot be read", async () => {

src/agent/messages/builder.ts

@@ -410,11 +410,28 @@ function normalizeScrollInfo(value: unknown): [number, number] {
 }
 
 function getOpenTabsSummary(page: Page): string {
+  const currentTabFallback = (() => {
+    try {
+      return `[0] ${truncateTabUrl(page.url() || "about:blank")} (current)`;
+    } catch {
+      return "[0] about:blank (url unavailable) (current)";
+    }
+  })();
   try {
-    const pages = page.context().pages();
+    const context = page.context();
+    if (!context || typeof context !== "object") {
+      return currentTabFallback;
+    }
+    const pagesMethod = (context as { pages?: unknown }).pages;
+    if (typeof pagesMethod !== "function") {
+      return currentTabFallback;
+    }
+    const pages = pagesMethod.call(context) as ReturnType<
+      ReturnType<Page["context"]>["pages"]
+    >;
     const pageEntries = materializeSafePages(pages);
     if (pageEntries.length === 0) {
-      return `[0] ${truncateTabUrl(page.url() || "about:blank")} (current)`;
+      return currentTabFallback;
     }
     let visibleEntries = pageEntries.slice(0, MAX_OPEN_TAB_ENTRIES);
     const currentEntry = pageEntries.find((entry) => entry.openPage === page);
@@ -447,7 +464,7 @@ function getOpenTabsSummary(page: Page): string {
     }
     return tabLines.join("\n");
   } catch {
-    return "Open tabs unavailable";
+    return currentTabFallback;
   }
 }