Turn-guard builders for a session loop's between-turn hook (RMA's turn_guard: option; 0.5.0+, hook shape unchanged through 0.10). Plain data in, plain verdict out — no RMA types.

for_grant/3 prices the session's accumulated usage with Mimir.Pricing and halts once the grant budget is spent — the control-plane soft half of enforcement, for runtimes where the gateway cannot sit in the data plane. caps/1 is the mimir-less form: plain cost/token/turn caps, no minted key.

A cost cap (the grant budget, or caps/1's :max_cost_microdollars) prices cache tokens too — cache_read_input_tokens and cache_creation_input_tokens are part of the usage map Guard prices through Mimir.Pricing, the same as input/output, because cost is cost. :max_total_tokens stays input + output only.

Guards never raise mid-run, but the two cost-check failures aren't the same outcome: a pricing-table miss (no rate anywhere for the model) degrades to :cont, leaving whatever caps remain to decide, and emits a [:mimir, :guard, :pricing_miss] telemetry warning once per process per model. A misconfigured pricing entry — Mimir.Pricing raising Mimir.Pricing.InvalidConfigError for an invalid rate or an unknown key — halts instead, with {:invalid_pricing, %{model:, usage:, message:}}, rather than letting the raise propagate: a bad config entry is a real problem the caller should stop and look at, not one the guard can shrug off the way it does a merely-unpriced model.