FIX: preserve calendar view when navigating months

[elRicharde]

Problem

After the category route fix in #166, navigating between months in the
calendar view incorrectly switches the view to the list template, even
when the user stays within a calendar-enabled category.

Steps to reproduce:

1. Open a calendar-enabled category (e.g. /c/events/20)
2. Verify calendar view is rendered
3. Click the "next month" or "previous month" arrow
4. URL changes to /c/events/20?start=...&end=... (note the missing /l/calendar)
5. View flips to list - expected: calendar for the new month

The same issue affects the global calendar route (/calendar).

Root cause

transitionToMonth() in events-calendar.js called:

router.transitionTo({ queryParams: { start, end } });

Without an explicit route name, Ember resolved the transition to the
category's base route (discovery.category) instead of the calendar
filter route - the /l/calendar segment was dropped from the URL.

The afterModel hook in route:discovery.category (modified in #166
to prevent calendar template leaking into non-calendar categories) then
sees model.filterType !== "calendar" and executes:

} else if (this.templateName === "discovery/calendar") {
  this.templateName = "discovery/list";
}

resetting the template to list. Topics for the new month are loaded
correctly, but rendered in the wrong view.

This bug existed before #166 but was masked by the earlier template
leak - #166 correctly fixed that leak, which surfaced this pre-existing
issue in transitionToMonth.

Fix

Transition explicitly to the correct calendar route so the filter is
preserved in the URL:

• discovery.calendarCategory with category_slug_path_with_id as
  positional parameter when a category context exists
• discovery.calendar for the global calendar route (no dynamic segments)

The routes xxxCategory are dynamically generated by Discourse core's
app-route-map.js
from Site.currentProp("filters"), with a single *category_slug_path_with_id
glob segment in the format <slug>/<id>. This matches how Discourse core
itself transitions, e.g. in build-category-route.js:

this.router.replaceWith(
  "discovery.categoryNone",
  params.category_slug_path_with_id
);

The const category = this.get("category") lookup is hoisted to the top
of the function since it is now needed both for route selection and in
the existing .then() callback (minor deduplication).

Testing

Tested manually on Discourse Version: 2026.4.0-latest ( 480a052a10 )

• ✅ Category calendar: next month stays in calendar view
• ✅ Category calendar: previous month stays in calendar view
• ✅ Category calendar: "Today" button returns to current month in calendar view
• ✅ Global calendar (/calendar): month navigation stays in calendar view
• ✅ Topics for the new month are loaded correctly
• ✅ Navigating from calendar category to non-calendar category still
  correctly shows list view (regression check for Fix calendar view leaking to non-calendar categories during SPA navigation - Update discourse-events.js #166)

Related

• Relates to Fix calendar view leaking to non-calendar categories during SPA navigation - Update discourse-events.js #166

[elRicharde]

Note: the Metadata check fails because the plugin version hasn't been bumped. I left this to the maintainer @angusmcleod as with my previous PR (#166) - happy to bump it myself if preferred.

All tested and ok from my side, let me know if there is something more to do here. Thanks and BR Richard

[elRicharde]

@angusmcleod - can i support here anyhow to get this PR accepted and merged?
BR Richard

[elRicharde]

Just wondering if this is the right place here @angusmcleod , but last time merge was quick and easy here..
Any update would be nice. Thx

[angusmcleod]

Thanks 👍