Which product modules are available in a region

Answers, for the selected platform region, which product modules the platform actually offers there — so the console can hide a module it cannot deliver instead of rendering a menu item whose every request fails. A module is available IFF the region's OpenStack catalog (and, for VPN, its neutron extension list) provides everything the module needs, the control plane can drive those services, AND an operator has not switched the module off for this region. An operator may switch a module OFF as a product decision but can NEVER switch one ON that the region does not serve, so available: true always means the region really provides it. Returns an entry for EVERY module, always — never a partial map. A client must never have to read "absent" as "fine": that is exactly how a gating gap becomes a broken button. WHAT THIS DELIBERATELY DOES NOT RETURN: no OpenStack service type, no endpoint URL, no discovered version, no operator note, no provider or OpenStack region identity — and no distinction between "not sold here" and "the region cannot do it". All of that is operator information (same reasoning as .../compute/flavors/availability, which hides raw host capacity behind a boolean). reason is a token from a small server-side vocabulary — not_offered_in_region today — typed as a plain string rather than a closed enum so a token added later degrades to a generic sentence instead of failing to parse and silently dropping the gating for every module. available is NOT a reservation: the create paths enforce the same rule authoritatively, and an operator can close a module between this read and a create. Validation: region must be shape-valid and resolve to a region bound to an ENABLED provider, else 404 NOT_FOUND. Async & state: Synchronous read; no state change. Errors: 401 unauthenticated; 404 when the region is unknown, bound to nothing, or its provider is disabled — ONE answer for all three, so the response discloses nothing about which (and 404 rather than an empty list, since an empty modules array is indistinguishable from a region where nothing is on, and a client should re-read GET /regions instead of rendering a fully-greyed region); 500 read-model failure. Idempotency/Concurrency: Safe. NOT cacheable — the answer is a gate and changes the moment an operator flips an override, so the response is sent Cache-Control: no-store.