Policies

Product guide: what the capability brings, for whom, its limits and the version that delivered it - no configuration syntax.

What it does	Enriches a flow without touching the upstream: set, remove or rename headers, rewrite a path, filter a response's fields, mask personal data, translate an upstream's non-standard status, ask a third-party service before relaying. Policies attach at four levels (global, host, routes, operation), the most precise wins, under CEL conditions compiled at load
Why it matters	What elsewhere takes a plugin each team maintains becomes a declaration reviewed in Git. An effective chain is simulated before it is deployed: you know which policy applies to which request, without calling the upstream
Use cases	Serve only a closed list of fields to a partner; mask an IBAN in a response; turn a legacy system's 200 {"error":...} into a real 404; ask a risk service whether it accepts an order
Limits	No embedded code: WebAssembly modules are a 2.0.0 candidate; an external call always declares its timeout and its failure behaviour, never defaulted; no negotiated compression before 1.8.0
Since	0.1.0 (policy engine), 1.0.0 (simulation), 1.2.0 (response body and status, external call)
Configure	Enriching a flow, Reshaping a response, Delegating a decision to a service