ADR-005: Require callers to supply price rates

• Status: Accepted
• Date: 2026-05-22

Context

ExecutionKit records token counts. Provider prices change by model, account, region, cache behavior, and batch mode.

Decision

estimate_cost() performs arithmetic with caller-supplied per-token input and output rates. The package does not contain a price table or infer a currency.

Consequences

• Cost estimates do not become stale because of a bundled table.
• The caller must load current rates and account for provider-specific billing.
• TokenUsage remains the stable accounting value.
• estimate_cost() does not validate whether rates match the selected model.

Rejected alternatives

A built-in table would be convenient but could silently produce incorrect estimates after a price or model change.