cdp: avoid creating duplicate isolated worlds

If a driver asks to create an isolated world that already exists, don't create
it, return the existing one.

src/cdp/CDP.zig

@@ -714,6 +714,18 @@ pub const BrowserContext = struct {
     }
 
     pub fn createIsolatedWorld(self: *BrowserContext, world_name: []const u8, grant_universal_access: bool) !*IsolatedWorld {
+        // The name is the world's identity (matching Chrome). Clients re-issue
+        // this call after every navigation; appending a duplicate each time
+        // would grow the per-page context count without bound.
+        for (self.isolated_worlds.items) |world| {
+            if (std.mem.eql(u8, world.name, world_name)) {
+                if (world.grant_universal_access != grant_universal_access) {
+                    log.warn(.cdp, "isolated world mismatch", .{ .name = world_name, .gua = grant_universal_access });
+                }
+                return world;
+            }
+        }
+
         const browser = &self.cdp.browser;
         const arena = try browser.arena_pool.acquire(.small, "IsolatedWorld");
         errdefer arena.release();

src/cdp/domains/page.zig

@@ -244,6 +244,17 @@ fn createIsolatedWorld(cmd: *CDP.Command) !void {
     const bc = cmd.browser_context orelse return error.BrowserContextNotLoaded;
 
     const world = try bc.createIsolatedWorld(params.worldName, params.grantUniveralAccess);
+
+    // An existing world already has a live, inspector-registered context for
+    // the current document: return its id without re-registering.
+    if (world.context) |js_context| {
+        var ls: js.Local.Scope = undefined;
+        js_context.localScope(&ls);
+        defer ls.deinit();
+        const context_id = bc.inspector_session.inspector.getContextId(&ls.local);
+        return cmd.sendResult(.{ .executionContextId = context_id }, .{});
+    }
+
     const frame = bc.mainFrame() orelse return error.FrameNotLoaded;
 
     const js_context = try world.createContext(frame);
@@ -1127,6 +1138,36 @@ test "cdp.frame: getFrameTree" {
     }
 }
 
+test "cdp.frame: createIsolatedWorld is idempotent per name" {
+    var ctx = try testing.context();
+    defer ctx.deinit();
+
+    const bc = try ctx.loadBrowserContext(.{ .id = "BID-9", .url = "hi.html", .target_id = "FID-000000000X".* });
+
+    try ctx.processMessage(.{ .id = 20, .method = "Page.createIsolatedWorld", .params = .{
+        .frameId = "FID-000000000X",
+        .worldName = "utility",
+        .grantUniveralAccess = true,
+    } });
+    try testing.expectEqual(1, bc.isolated_worlds.items.len);
+    const world_context = bc.isolated_worlds.items[0].context.?;
+
+    try ctx.processMessage(.{ .id = 21, .method = "Page.createIsolatedWorld", .params = .{
+        .frameId = "FID-000000000X",
+        .worldName = "utility",
+        .grantUniveralAccess = true,
+    } });
+    try testing.expectEqual(1, bc.isolated_worlds.items.len);
+    try testing.expectEqual(world_context, bc.isolated_worlds.items[0].context.?);
+
+    try ctx.processMessage(.{ .id = 22, .method = "Page.createIsolatedWorld", .params = .{
+        .frameId = "FID-000000000X",
+        .worldName = "other",
+        .grantUniveralAccess = true,
+    } });
+    try testing.expectEqual(2, bc.isolated_worlds.items.len);
+}
+
 test "cdp.frame: child frame metadata" {
     var ctx = try testing.context();
     defer ctx.deinit();