diff --git a/.changeset/nice-socks-bow.md b/.changeset/nice-socks-bow.md
new file mode 100644
index 000000000..3c3670c32
--- /dev/null
+++ b/.changeset/nice-socks-bow.md
@@ -0,0 +1,5 @@
+---
+"@browserbasehq/stagehand": patch
+---
+
+fix: waitForDomNetworkQuiet() causing `act()` to hang indefinitely
diff --git a/packages/core/lib/v3/handlers/handlerUtils/actHandlerUtils.ts b/packages/core/lib/v3/handlers/handlerUtils/actHandlerUtils.ts
index 7a8ffb9a3..a5f2bc155 100644
--- a/packages/core/lib/v3/handlers/handlerUtils/actHandlerUtils.ts
+++ b/packages/core/lib/v3/handlers/handlerUtils/actHandlerUtils.ts
@@ -528,8 +528,12 @@ export async function waitForDomNetworkQuiet(
   frame: Frame,
   timeoutMs?: number,
 ): Promise<void> {
-  const timeout = typeof timeoutMs === "number" ? timeoutMs : 5_000;
+  const overallTimeout =
+    typeof timeoutMs === "number" && Number.isFinite(timeoutMs)
+      ? Math.max(0, timeoutMs)
+      : 5_000;
   const client = frame.session;
+  const settleStart = Date.now();
 
   // Ensure a document exists; if not, wait for DOMContentLoaded on this frame.
   let hasDoc: boolean;
@@ -539,8 +543,16 @@ export async function waitForDomNetworkQuiet(
   } catch {
     hasDoc = false;
   }
-  if (!hasDoc) {
-    await frame.waitForLoadState("domcontentloaded").catch(() => {});
+  if (!hasDoc && overallTimeout > 0) {
+    await frame
+      .waitForLoadState("domcontentloaded", overallTimeout)
+      .catch(() => {});
+  }
+
+  const elapsed = Date.now() - settleStart;
+  const remainingBudget = Math.max(0, overallTimeout - elapsed);
+  if (remainingBudget === 0) {
+    return;
   }
 
   await client.send("Network.enable").catch(() => {});
@@ -653,7 +665,7 @@ export async function waitForDomNetworkQuiet(
         });
       }
       resolveDone();
-    }, timeout);
+    }, remainingBudget);
 
     const resolveDone = () => {
       client.off("Network.requestWillBeSent", onRequest);
diff --git a/packages/core/lib/v3/understudy/frame.ts b/packages/core/lib/v3/understudy/frame.ts
index c9e26bf96..9735bf82a 100644
--- a/packages/core/lib/v3/understudy/frame.ts
+++ b/packages/core/lib/v3/understudy/frame.ts
@@ -243,16 +243,45 @@ export class Frame implements FrameManager {
   /** Wait for a lifecycle state (load/domcontentloaded/networkidle) */
   async waitForLoadState(
     state: "load" | "domcontentloaded" | "networkidle" = "load",
+    timeoutMs: number = 15_000,
   ): Promise<void> {
     await this.session.send("Page.enable");
-    await new Promise<void>((resolve) => {
+    const targetState = state.toLowerCase();
+    const timeout = Math.max(0, timeoutMs);
+    await new Promise<void>((resolve, reject) => {
+      let done = false;
+      let timer: ReturnType<typeof setTimeout> | null = null;
+      const finish = () => {
+        if (done) return;
+        done = true;
+        this.session.off("Page.lifecycleEvent", handler);
+        if (timer) {
+          clearTimeout(timer);
+          timer = null;
+        }
+        resolve();
+      };
       const handler = (evt: Protocol.Page.LifecycleEventEvent) => {
-        if (evt.frameId === this.frameId && evt.name === state) {
-          this.session.off("Page.lifecycleEvent", handler);
-          resolve();
+        const sameFrame = evt.frameId === this.frameId;
+        // need to normalize here because CDP lifecycle names look like 'DOMContentLoaded'
+        // but we accept 'domcontentloaded'
+        const lifecycleName = String(evt.name ?? "").toLowerCase();
+        if (sameFrame && lifecycleName === targetState) {
+          finish();
         }
       };
       this.session.on("Page.lifecycleEvent", handler);
+
+      timer = setTimeout(() => {
+        if (done) return;
+        done = true;
+        this.session.off("Page.lifecycleEvent", handler);
+        reject(
+          new Error(
+            `waitForLoadState(${state}) timed out after ${timeout}ms for frame ${this.frameId}`,
+          ),
+        );
+      }, timeout);
     });
   }