## Stack Context
This stack makes AI Gateway data and budgets the source of truth for AI
spend controls.
1. Re-back the per-chat cost endpoint with AI Gateway data (#27328,
merged).
2. **This PR:** remove native chat usage limits.
3. Remove native chat cost tracking and its dedicated admin UI (#27330).
## Summary
Removes the native usage-limit API, SDK types, SQL, and chat enforcement
for deployment, user, and group chat limits. Compact AI Gateway budget
indicators remain in the Agents sidebar, user menu, and group settings.
Gateway budget rejections and provider quota failures continue to
classify as usage-limit errors, including a 409 response for synchronous
title generation.
Budget-period labels now use the API's UTC boundaries, so users see the
same dates in every browser timezone. The documentation explains the AI
Gateway replacement, its licensing requirements, and the differences
from native limits.
No schema is dropped in this release. The usage-limit table, index, user
and group columns, constraints, audit mappings, and generated scan
fields remain for mixed-version rolling upgrades. #27600 tracks their
removal after the compatibility window.
## Breaking change
Native day, week, and month chat spend limits are removed and are not
migrated. AI Gateway budgets are month-based, group-scoped with per-user
overrides, and require the AI Gateway entitlement. Deployments without
that entitlement no longer have chat spend enforcement.
> Mux prepared this PR on Mike's behalf.
Michael Suchacz
f0e6ac64b3