OpenAPI Generator dependency

Pinned upstream OpenAPI Generator CLI JAR

The Apache-2.0 OpenAPI Generator CLI is pinned to 7.26.0 from Maven Central. The self-contained JAR uses the repository Java toolchain. Its SHA-256 SRI pin is in include.MODULE.bazel; the downloaded bytes were also checked against the publisher’s .jar.sha1. The first-party wrapper is tools/openapi_generator.