Scope Brazil2026ElectionFilter to viewers in Brazil

[keithadler]

Brazil2026ElectionFilter never reads the viewer's country, so as written it applies to every For You request in every country rather than to the viewers the Electoral Court order covers.

Evidence

should_remove takes only the candidate and the viewer's follow list (filter L1363), and the filter is added to the pre-scoring chain unconditionally (pipeline L368).

Both mechanisms needed to scope it already exist and are unused:

• ScoredPostsQuery carries country_code (query.rs L46)
• Filter::enable(&self, query) gates a filter per request (filter.rs L21) and is honoured by the pipeline (candidate_pipeline.rs L352)

Eight other filters in the same chain already use enable() for exactly this: VideoFilter, TopicIdsFilter, NewUserMinEngagementFilter, InventoryHoldoutFilter and others.

There is also a layering signal. Every other jurisdiction-scoped rule in the repo lives in visibility-filtering and checks viewer country. No filter in home-mixer/filters/ reads viewer country at all, so this is the only geo-scoped rule in a service with no geo-scoping convention.

Change

Adds an enable() override gating the filter on country_code == "br", case-insensitively.

Unknown or empty country codes leave the filter disabled, which matches the existing convention for legal withholding: viewer_in_withheld_country in visibility-filtering/rules/tes_rules.rs returns false when the viewer country is not known. Happy to invert that to fail-closed if you would rather over-apply than under-apply on unknown geo.

Adds four tests. Existing tests call filter() directly and are unaffected.

If this is intentional

Applying globally does guarantee compliance regardless of geolocation accuracy, which matters with VPNs and travel. If that is the reasoning, please close this, though a comment recording the decision might be worth adding, since the surrounding conventions read the other way.

Caveat

home-mixer ships no Cargo.toml, so I could not compile or run the tests. The file is rustfmt --check clean under edition 2021. Verification of the change is on you.

[ByteJoseph]

Hi.
I think their goal in open-sourcing this algorithm was just transparency, not open-source collaboration

[TolstoyDotCom]

Per AI: "The fundamental premise of Brazilian electoral law is that a recommendation engine is an active publisher, not a passive host. When an algorithm selects a political post and injects it into a user’s "For You" or "Home" feed, it is a deliberate act of algorithmic promotion. Therefore, the TSE mandates that any platform utilizing a recommendation system must remove reported candidate profiles and their organic content from algorithmic distribution altogether."

From Twitter's POV, being an "active publisher" might make it easier to sue for libel and so on.

From everyone else's view, it's too bad Twitter can't just ditch their highly-flawed recommendation engine & let tweets stand on their own.