Search results category is reset on every input change

[janbrasna]

Describe the bug
Fine–tuning wording in instant search keeps reseting the product category to what was the original value when instant search was launched.

Preconditions
Start e.g. from a desktop article/forum, and look for a topic relevant to e.g. other OS or device.

Steps to reproduce

1. Search for one common term
2. Click on product/category filter in sidebar
3. See relevant results
4. Amend the wording in search input

Expected behavior
The same filter is applied.

Actual behavior
Product is reset back to the initial one.

Screenshots/Screencasts

Screen.Recording.2026-08-11.at.13.53.22.mov

Additional context
This is most visible when you hit an article for a wrong product from "all", as after you end up there, all subsequent searches are scoped for it, so trying to get results for any other product will reset the filter back to the unwanted product after every search input edit, for puzzling results.

Desktop (please complete the following information):

• macOS 15, FXDE

[emilghittasv]

The kb article "stamps" the product into every search (https://github.com/mozilla/kitsune/blob/main/kitsune/wiki/jinja2/wiki/base.html#L6). Clicking on the product filter only changes the in memory param (https://github.com/mozilla/kitsune/blob/main/kitsune/sumo/static/sumo/tpl/search-results.njk#L11).

When a new term is amended it rebuilds params from the form (https://github.com/mozilla/kitsune/blob/2816620a8591670f562e2c212068cb8b5ad39d5b/kitsune/sumo/static/sumo/js/instant_search.js#L256)

I have always treated this as an expected outcome but I also agree with changing this and respect the chosen product filter.