cdp: make Network.enable idempotent

[Ppsoft1991]

Summary

• make Network.enable idempotent per browser context
• clean up partially registered network listeners if enabling fails
• reset the registration state when Network.disable runs
• add a regression test that verifies a response body is captured exactly once after two enable calls

Root cause

Notification.register appends a listener on every call. Calling Network.enable twice therefore registers the same http_response_data callback twice, and onHttpResponseData appends every chunk twice to captured_responses.

This is independent of #3037, which covers Network event payload completeness and worker request propagation.

Reproduction

Without this fix, the new test receives:

<p>1</p> <p>2</p>
<p>1</p> <p>2</p>

instead of the fixture body once.

Testing

• regression test: 1/1 passed after failing on unpatched main
• TEST_FILTER='cdp.Network' ... zig build ... test: 9/9 passed
• full test suite: 1062/1062 passed
• tracked Zig files: zig fmt --check
• git diff --check

[karlseguin]

I think I'd rather dedupe in notification. We currently have no case where a receiver should add multiple listeners to an event (and I can't imagine ever needing it):

pub fn register(self: *Notification, comptime event: EventType, receiver: anytype, func: EventFunc(event)) !void {
    const allocator = self.allocator;
    const gop = try self.listeners.getOrPut(allocator, @intFromPtr(receiver));
    if (gop.found_existing) {
        for (gop.value_ptr.items) |existing| {
            if (existing.event == event) {
                lp.assert(@as(*const anyopaque, @ptrCast(func)) == existing.func, "different notification callbacks per receiver", .{.event = event});
                return;
            }
        }
    } else {
        gop.value_ptr.* = .empty;
    }

    var list = &@field(self.event_listeners, @tagName(event));
    var listener = try self.mem_pool.create();
    errdefer self.mem_pool.destroy(listener);

    listener.* = .{
        .node = .{},
        .list = list,
        .receiver = receiver,
        .event = event,
        .func = @ptrCast(func),
        .struct_name = @typeName(@typeInfo(@TypeOf(receiver)).pointer.child),
    };
    try gop.value_ptr.append(allocator, listener);

    // we don't add this until we've successfully added the entry to
    // self.listeners
    list.append(&listener.node);
}

(would be nice to add a test for this too).

Can remove the existing download_events_registered.

If you agree and prefer, you can close this and I'll make the change.

[Ppsoft1991]

I agree with your approach. Deduplicating in Notification.register is cleaner and more appropriate. Please feel free to make the change; I’ll close this PR.