The cheapest way to try a CI cost gate: run it in warn mode for a week
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The #1 objection to gating agent cost in CI is "I won't add a check that fails my builds." The fix is report-only mode — three properties to look for in any cost gate before you let it block.

If you run LLM/agent workflows, a prompt tweak or a model swap can quietly multiply per-run token cost, and you usually find out on the invoice. The pattern that’s worked for us: a CI check that measures token cost per run and flags a regression against a baseline — but gated in warn mode first (annotate the PR, never fail the build) so the team trusts the numbers before you turn on blocking.

Write-up covers what to measure, why warn-mode-first, and the failure modes.

Disclosure: I maintain the OSS tooling behind it (a CI cost-guardrail Action + tokenscope, Apache-2.0). Sharing mostly the warn-mode-first rollout pattern, which applies whatever tool you use — happy to answer setup questions.