docs: readme + smoke test recipe

README.md

@@ -1,2 +1,100 @@
 # plugin-platform-router
-Velocity plugin: watches Agones GameServers and registers them as forced-host backends. Phase 3.1a sub-project of grounds-platform.
+
+Velocity plugin that watches Agones `GameServer` CRDs in Kubernetes and exposes
+them as Velocity backends with virtual-host-driven routing. Sub-project of
+[grounds-platform](https://github.com/groundsgg/grounds-platform) Phase 3.1a.
+
+The same plugin runs in two modes:
+
+| Mode       | Watch scope                                  | Hostname format                                |
+| ---------- | -------------------------------------------- | ---------------------------------------------- |
+| `platform` | one namespace inside a per-dev vCluster      | `{fleet}.{cluster}.platform.mc.grnds.io`       |
+| `staging`  | all `preview-*` namespaces in shared staging | `{namespace-suffix}.preview.mc.grnds.io`       |
+
+Mode is selected via the bundled `config.toml` (mounted by the Helm chart
+in production).
+
+## How it works
+
+1. On `ProxyInitializeEvent`, the plugin loads its config, builds an in-cluster
+   `KubernetesClient`, and starts a fabric8 `SharedIndexInformer` against
+   `gameservers.agones.dev/v1`.
+2. Every Agones `GameServer` reaching `Ready` (or `Allocated`) is registered
+   with Velocity via `proxy.registerServer(ServerInfo)`. The forced-host
+   hostname is computed from the GS's namespace + fleet label.
+3. A `PlayerChooseInitialServerEvent` listener (PostOrder.LATE) inspects the
+   connecting player's virtual host, looks up the matching fleet, and picks a
+   ready backend round-robin.
+4. State changes (Unhealthy / Reserved / Shutdown) deregister the backend.
+   When the last ready backend in a fleet goes away, the hostname is removed
+   and any further connection to it is rejected with "no available servers".
+
+## Configuration
+
+```toml
+# Mode selector. "platform" or "staging".
+routerMode = "platform"
+
+# Cluster identifier — populated from GROUNDS_CLUSTER_NAME env by the chart.
+# Required in platform mode. Ignored (warned) in staging mode.
+clusterName = "${GROUNDS_CLUSTER_NAME}"
+
+# Namespace watch scope.
+# Platform: a single namespace name.
+# Staging: a glob (currently honoured client-side as a "preview-" prefix).
+namespaceSelector = "default"
+
+# DNS suffix appended after {fleet}.{cluster} (platform) or
+# {namespace-suffix} (staging).
+hostnameSuffix = "platform.mc.grnds.io"
+
+# Re-sync interval for the informer. Accepts 30s / 5m / 1h.
+resyncInterval = "30s"
+```
+
+`${ENV_VAR}` interpolation is supported. `clusterName` is the typical
+hand-off point with the chart.
+
+## RBAC
+
+The plugin needs `get`, `list`, `watch` on `gameservers.agones.dev`:
+
+- Platform mode: scoped to the configured namespace via `Role` + `RoleBinding`.
+- Staging mode: cluster-wide via `ClusterRole` + `ClusterRoleBinding` (the
+  `preview-*` filter happens client-side).
+
+The Helm chart [grounds-platform-template](https://github.com/groundsgg/grounds-platform-template)
+provisions both.
+
+## Build
+
+```sh
+./gradlew build      # compiles, runs tests, produces the shadow JAR
+./gradlew shadowJar  # just the artifact at build/libs/plugin-platform-router-<version>-all.jar
+./gradlew spotlessApply # auto-format Kotlin sources
+```
+
+JDK 25 toolchain, JVM 24 target. Velocity API 3.5.0-SNAPSHOT.
+
+## Local smoke (kind + Agones)
+
+End-to-end smoke:
+
+1. `kind create cluster`
+2. Install Agones via Helm (`helm install agones agones/agones --namespace agones-system --create-namespace`).
+3. Apply a sample Fleet (e.g. the `simple-game-server` fleet from Agones examples).
+4. `docker run --rm -v $PWD/build/libs:/plugins -v $HOME/.kube/config:/root/.kube/config:ro itzg/mc-proxy ...`
+   (or run Velocity locally with `KUBECONFIG` pointed at kind).
+5. Connect a Minecraft client to `<fleet>.<cluster>.platform.mc.grnds.io`
+   (resolve via `/etc/hosts` for local testing) and verify the connection
+   reaches the GS.
+
+## Status
+
+| Phase | What | State |
+| --- | --- | --- |
+| 3.1a sub-project 1 | plugin-platform-router | In progress (this repo) |
+
+## License
+
+Apache-2.0.