Browser: cap AI snapshots to avoid context overflow

src/agents/tools/browser-tool.ts

@@ -117,6 +117,7 @@ const BrowserToolSchema = Type.Object({
   targetUrl: Type.Optional(Type.String()),
   targetId: Type.Optional(Type.String()),
   limit: Type.Optional(Type.Number()),
+  maxChars: Type.Optional(Type.Number()),
   format: Type.Optional(Type.Union([Type.Literal("aria"), Type.Literal("ai")])),
   fullPage: Type.Optional(Type.Boolean()),
   ref: Type.Optional(Type.String()),
@@ -323,10 +324,16 @@ export function createBrowserTool(opts?: {
             typeof params.limit === "number" && Number.isFinite(params.limit)
               ? params.limit
               : undefined;
+          const maxChars =
+            typeof params.maxChars === "number" &&
+            Number.isFinite(params.maxChars)
+              ? params.maxChars
+              : undefined;
           const snapshot = await browserSnapshot(baseUrl, {
             format,
             targetId,
             limit,
+            maxChars,
             profile,
           });
           if (snapshot.format === "ai") {

src/browser/client.ts

@@ -71,6 +71,7 @@ export type SnapshotResult =
       targetId: string;
       url: string;
       snapshot: string;
+      truncated?: boolean;
     };
 
 export function resolveBrowserControlUrl(overrideUrl?: string) {
@@ -248,6 +249,7 @@ export async function browserSnapshot(
     format: "aria" | "ai";
     targetId?: string;
     limit?: number;
+    maxChars?: number;
     profile?: string;
   },
 ): Promise<SnapshotResult> {
@@ -255,6 +257,9 @@ export async function browserSnapshot(
   q.set("format", opts.format);
   if (opts.targetId) q.set("targetId", opts.targetId);
   if (typeof opts.limit === "number") q.set("limit", String(opts.limit));
+  if (typeof opts.maxChars === "number" && Number.isFinite(opts.maxChars)) {
+    q.set("maxChars", String(opts.maxChars));
+  }
   if (opts.profile) q.set("profile", opts.profile);
   return await fetchBrowserJson<SnapshotResult>(
     `${baseUrl}/snapshot?${q.toString()}`,

src/browser/pw-ai.test.ts

@@ -92,6 +92,28 @@ describe("pw-ai", () => {
     expect(p2.session.detach).toHaveBeenCalledTimes(1);
   });
 
+  it("truncates oversized snapshots", async () => {
+    const { chromium } = await import("playwright-core");
+    const longSnapshot = "A".repeat(20);
+    const p1 = createPage({ targetId: "T1", snapshotFull: longSnapshot });
+    const browser = createBrowser([p1.page]);
+
+    (
+      chromium.connectOverCDP as unknown as ReturnType<typeof vi.fn>
+    ).mockResolvedValue(browser);
+
+    const mod = await importModule();
+    const res = await mod.snapshotAiViaPlaywright({
+      cdpUrl: "http://127.0.0.1:18792",
+      targetId: "T1",
+      maxChars: 10,
+    });
+
+    expect(res.truncated).toBe(true);
+    expect(res.snapshot.startsWith("AAAAAAAAAA")).toBe(true);
+    expect(res.snapshot).toContain("TRUNCATED");
+  });
+
   it("clicks a ref using aria-ref locator", async () => {
     const { chromium } = await import("playwright-core");
     const p1 = createPage({ targetId: "T1" });

src/browser/pw-tools-core.ts

@@ -10,6 +10,8 @@ import {
 let nextUploadArmId = 0;
 let nextDialogArmId = 0;
 
+const MAX_SNAPSHOT_CHARS = 80_000;
+
 function requireRef(value: unknown): string {
   const ref = typeof value === "string" ? value.trim() : "";
   if (!ref) throw new Error("ref is required");
@@ -20,7 +22,8 @@ export async function snapshotAiViaPlaywright(opts: {
   cdpUrl: string;
   targetId?: string;
   timeoutMs?: number;
-}): Promise<{ snapshot: string }> {
+  maxChars?: number;
+}): Promise<{ snapshot: string; truncated?: boolean }> {
   const page = await getPageForTargetId({
     cdpUrl: opts.cdpUrl,
     targetId: opts.targetId,
@@ -41,7 +44,18 @@ export async function snapshotAiViaPlaywright(opts: {
     ),
     track: "response",
   });
-  return { snapshot: String(result?.full ?? "") };
+  const maxChars = opts.maxChars;
+  const limit =
+    typeof maxChars === "number" && Number.isFinite(maxChars) && maxChars > 0
+      ? Math.floor(maxChars)
+      : MAX_SNAPSHOT_CHARS;
+  let snapshot = String(result?.full ?? "");
+  let truncated = false;
+  if (snapshot.length > limit) {
+    snapshot = `${snapshot.slice(0, limit)}\n\n[...TRUNCATED - page too large]`;
+    truncated = true;
+  }
+  return truncated ? { snapshot, truncated } : { snapshot };
 }
 
 export async function clickViaPlaywright(opts: {

src/browser/routes/agent.ts

@@ -560,17 +560,30 @@ export function registerBrowserAgentRoutes(
           : (await getPwAiModule())
             ? "ai"
             : "aria";
-    const limit =
+    const limitRaw =
       typeof req.query.limit === "string" ? Number(req.query.limit) : undefined;
+    const maxCharsRaw =
+      typeof req.query.maxChars === "string"
+        ? Number(req.query.maxChars)
+        : undefined;
+    const limit = Number.isFinite(limitRaw) ? limitRaw : undefined;
+    const maxChars = Number.isFinite(maxCharsRaw) ? maxCharsRaw : undefined;
 
     try {
       const tab = await profileCtx.ensureTabAvailable(targetId || undefined);
       if (format === "ai") {
         const pw = await requirePwAi(res, "ai snapshot");
         if (!pw) return;
+        const resolvedMaxChars =
+          typeof maxChars === "number" && maxChars > 0
+            ? maxChars
+            : typeof limit === "number" && limit > 0
+              ? limit
+              : undefined;
         const snap = await pw.snapshotAiViaPlaywright({
           cdpUrl: profileCtx.profile.cdpUrl,
           targetId: tab.targetId,
+          ...(resolvedMaxChars ? { maxChars: resolvedMaxChars } : {}),
         });
         return res.json({
           ok: true,