cdp: add LP domain and getMarkdown method

This PR introduces a custom CDP domain 'LP' (Lightpanda) to expose browser-specific tools. The first method, 'LP.getMarkdown', allows retrieving a Markdown representation of the DOM or a specific node by its 'nodeId'. This is optimized for AI agents and LLM-based scraping tasks.

src/cdp/domains/lp.zig

@@ -0,0 +1,59 @@
+// Copyright (C) 2023-2026  Lightpanda (Selecy SAS)
+//
+// Francis Bouvier <francis@lightpanda.io>
+// Pierre Tachoire <pierre@lightpanda.io>
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as
+// published by the Free Software Foundation, either version 3 of the
+// License, or (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+const std = @import("std");
+const lp = @import("lightpanda");
+const markdown = lp.markdown;
+const Node = @import("../Node.zig");
+
+pub fn processMessage(cmd: anytype) !void {
+    const action = std.meta.stringToEnum(enum {
+        getMarkdown,
+    }, cmd.input.action) orelse return error.UnknownMethod;
+
+    switch (action) {
+        .getMarkdown => return getMarkdown(cmd),
+    }
+}
+
+fn getMarkdown(cmd: anytype) !void {
+    const Params = struct {
+        nodeId: ?Node.Id = null,
+    };
+    const params = (try cmd.params(Params)) orelse Params{};
+
+    const bc = cmd.browser_context orelse return error.NoBrowserContext;
+
+    const dom_node = if (params.nodeId) |nodeId| blk: {
+        const node = bc.node_registry.lookup_by_id.get(nodeId) orelse return error.InvalidNodeId;
+        break :blk node.dom;
+    } else blk: {
+        const page = bc.session.currentPage() orelse return error.PageNotLoaded;
+        break :blk page.window._document.asNode();
+    };
+
+    const page = bc.session.currentPage() orelse return error.PageNotLoaded;
+
+    var aw = std.Io.Writer.Allocating.init(cmd.arena);
+    defer aw.deinit();
+    try markdown.dump(dom_node, .{}, &aw.writer, page);
+
+    return cmd.sendResult(.{
+        .markdown = aw.written(),
+    }, .{});
+}