X (Twitter) API cost controls — per-workspace X posting limits

What problem does this solve?
Mixpost Enterprise SaaS operators share a single X developer API account across all customer workspaces. Since X moved to pay-per-use pricing in February 2026 ($0.015 per post, $0.20 per post with a URL), a single heavy user posting exclusively to X with URLs can generate unexpected and significant API costs for the operator — costs the operator has no way to predict, cap, or control within the platform.

Describe the solution
Add X-specific posting limits as a configurable feature limit within subscription plans — similar to how scheduled post limits and channel limits are already enforced.
Specifically:

Maximum X posts per month per workspace
Maximum X posts containing URLs per month per workspace

These limits would appear in the plan configuration alongside existing limits and be enforced natively by the platform before the post is sent to the X API.

Alternatives considered

• Fair use policy in Terms of Service — places the burden on the operator to monitor and enforce manually, not scalable
• Removing X from the platform entirely — loses a key platform for customers
• Charging extra for X access — unusual in the market and would put customers off
• Monitoring via a separate admin tool — reactive, not preventive, still exposes the operator to cost spikes