[gateway] Add the Gateway runtime, common HTTP layer, lifecycle, and test infrastructure

.github/workflows/gateway-ci.yml

@@ -15,10 +15,8 @@
 # specific language governing permissions and limitations
 # under the License.
 
-# CI gates for the fluss-gateway module. The gateway is its own Cargo workspace,
-# so it gets its own workflow: triggering on gateway changes never builds the
-# fluss-rust workspace, and fluss-rust changes never build the gateway. `uses:`
-# step inputs stay relative to the repository root.
+# Gateway-only CI: gateway changes never build the fluss-rust workspace and vice versa.
+# `uses:` step inputs are relative to the repository root.
 name: Gateway CI
 
 on:
@@ -71,10 +69,18 @@ jobs:
           RUST_LOG: DEBUG
           RUST_BACKTRACE: full
 
+      - name: OpenAPI drift check
+        run: |
+          cargo test --lib protocol::rest::openapi::tests::export_checked_in_document -- --ignored --exact
+          git diff --exit-code openapi.yaml
+
+      - name: OpenAPI external validation
+        run: npx --yes @redocly/cli@1 lint openapi.yaml
+
   msrv:
     name: "Gateway MSRV (1.88)"
-    # The rust-toolchain.toml floats to stable, so a plain build never catches use of features newer
-    # than the declared rust-version. Pin the MSRV explicitly here; `+toolchain` overrides the file.
+    # rust-toolchain.toml floats to stable, so a plain build never catches features newer
+    # than the declared rust-version; `+toolchain` overrides the file here.
     timeout-minutes: 60
     runs-on: ubuntu-latest
     steps: