{#-
  FR-003 link composition: every inter-view href goes through url() so the
  selected store rides it (store_key non-empty). store_key is a render
  context variable — importing templates must
  `{% import "_links.html" as links with context %}` for it to resolve
  (a plain import renders as if no store were selected, and a direct
  render with no context at all is unchanged: undefined is falsy).
  Empty store_key emits no store param, byte-identical to the pre-seam
  hrefs. params values that are None are dropped; the store param is
  always appended last.
-#}
{% macro url(base, params={}) -%}
{%- set parts = [] -%}
{%- for key, val in params.items() if val is not none -%}
{%- set _ = parts.append(key ~ "=" ~ (val | urlencode)) -%}
{%- endfor -%}
{%- if store_key -%}
{%- set _ = parts.append("store=" ~ (store_key | urlencode)) -%}
{%- endif -%}
{{ base }}{% if parts %}?{{ parts | join("&") }}{% endif %}
{%- endmacro %}

{% macro store_field() -%}
{#- Forms drop the action URL's query string on submit (GET forms) or never
    carry one (POST actions), so the selected store rides the form body as a
    hidden input. Empty selection renders nothing — bare pages stay
    byte-identical. -#}
{%- if store_key -%}<input type="hidden" name="store" value="{{ store_key }}">{%- endif -%}
{%- endmacro %}

{% macro view_link(view, param, value, window='') -%}
{% set q = {param: value} %}
{%- if window and window != 'all' %}{% set _ = q.update({'window': window}) %}{% endif -%}
<a href="{{ url('/' ~ view, q) }}">{{ value }}</a>
{%- endmacro %}