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AGENTS.md

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+# AGENTS.md - horizon-operator
+
+## Project overview
+
+See [README.md](README.md) for a full project overview, configuration examples,
+and contributing guidelines.
+
+## Tech stack
+
+| Layer | Technology |
+|-------|------------|
+| Language | Go (modules; `go.work` is local-only, never commit it) |
+| Scaffolding | [Kubebuilder v4](https://book.kubebuilder.io/) + [Operator SDK](https://sdk.operatorframework.io/) |
+| CRD generation | controller-gen (DeepCopy, CRDs, RBAC, webhooks) |
+| Config management | Kustomize |
+| Packaging | OLM bundle |
+| Testing | Ginkgo/Gomega + envtest (functional), KUTTL (integration) |
+| Linting | golangci-lint (`.golangci.yaml`) |
+| CI | Zuul (`zuul.d/`), Prow (`.ci-operator.yaml`), GitHub Actions |
+
+## Custom Resources
+
+| Kind | Purpose |
+|------|---------|
+| `Horizon` | Single CR managing the Horizon dashboard deployment (httpd/WSGI). No sub-CRs. |
+
+The `Horizon` CR has defaulting and validating admission webhooks.
+
+## Directory structure
+
+**Maintenance rule:** when directories are added, removed, or renamed, or when
+their purpose changes, update this table to match.
+
+| Directory | Contents |
+|-----------|----------|
+| `api/v1beta1/` | CRD types (`horizon_types.go`), conditions, webhook markers |
+| `cmd/` | `main.go` entry point |
+| `internal/controller/` | Reconciler: `horizon_controller.go` |
+| `internal/horizon/` | Horizon resource builders (deployment, volumes, config) |
+| `internal/webhook/` | Webhook implementation |
+| `templates/` | Config files and scripts mounted into pods via `OPERATOR_TEMPLATES` env var |
+| `config/crd,rbac,manager,webhook/` | Generated Kubernetes manifests (CRDs, RBAC, deployment, webhooks) |
+| `config/samples/` | Example CRs (Kustomize overlays). `base/`, `custom-theme/`, `httpd-overrides/` for customization. |
+| `test/functional/` | envtest-based Ginkgo/Gomega tests |
+| `test/kuttl/` | KUTTL integration tests |
+| `hack/` | Helper scripts (CRD schema checker, local webhook runner) |
+
+## Build commands
+
+After modifying Go code, always run: `make generate manifests fmt vet`.
+Before sending a commit, always run: `pre-commit run --all-files`.
+
+## Code style guidelines
+
+- Follow standard openstack-k8s-operators conventions and lib-common patterns.
+- Use `lib-common` modules for conditions, endpoints, TLS, storage, and other
+  cross-cutting concerns rather than re-implementing them.
+- CRD types go in `api/v1beta1/`. Controller logic goes in
+  `internal/controller/`. Resource-building helpers go in `internal/horizon/`.
+- Config templates are plain files in `templates/` -- they are mounted at
+  runtime via the `OPERATOR_TEMPLATES` environment variable.
+- Webhook logic is split between the kubebuilder markers in `api/v1beta1/` and
+  the implementation in `internal/webhook/`.
+
+## Testing
+
+- Functional tests use the envtest framework with Ginkgo/Gomega and live in
+  `test/functional/`.
+- KUTTL integration tests live in `test/kuttl/`.
+- Run all functional tests: `make test`.
+- When adding a new field or feature, add corresponding test cases in
+  `test/functional/` and update fixture data accordingly.
+
+## Key dependencies
+
+- [lib-common](https://github.com/openstack-k8s-operators/lib-common): shared modules for conditions, endpoints, TLS, secrets, etc.
+- [infra-operator](https://github.com/openstack-k8s-operators/infra-operator): Memcached and topology APIs.
+- [keystone-operator](https://github.com/openstack-k8s-operators/keystone-operator): identity service registration.
+- [dev-docs/developer.md](https://github.com/openstack-k8s-operators/dev-docs/blob/main/developer.md): developer guide and coding conventions.