[DPE-7316] Stereo mode unified charm

actions.yaml

@@ -97,3 +97,20 @@ restore:
     restore-to-time:
       type: string
       description: Point-in-time-recovery target in PSQL format.
+get-cluster-status:
+  description: Display cluster topology, PostgreSQL units health status, and Raft cluster state.
+    Only available when role=watcher.
+  params:
+    cluster-name:
+      type: string
+      description: |
+        The name of the cluster to filter the output by.
+        Useful in async-replication (Disaster Recovery) setups where multiple clusters are related.
+    standby-clusters:
+      type: boolean
+      default: false
+      description: |
+        Show status information including linked standby clusters (async replication).
+trigger-health-check:
+  description: Manually trigger health checks on PostgreSQL endpoints and return results.
+    Only available when role=watcher.

config.yaml

@@ -2,6 +2,14 @@
 # See LICENSE file for licensing details.
 
 options:
+  role:
+    description: |
+      Deployment role for this application. Set at deploy time and cannot be changed afterwards.
+      "postgresql" (default) runs the full PostgreSQL database server with Patroni.
+      "watcher" runs a lightweight Raft witness for stereo mode (2-node clusters),
+      providing quorum without running PostgreSQL.
+    type: string
+    default: "postgresql"
   synchronous-node-count:
     description: |
       Sets the number of synchronous nodes to be maintained in the cluster. Should be

metadata.yaml

@@ -45,8 +45,14 @@ provides:
     interface: cos_agent
     limit: 1
     optional: true
+  watcher-offer:
+    interface: postgresql_watcher
+    limit: 1
 
 requires:
+  watcher:
+    interface: postgresql_watcher
+    optional: true
   replication:
     interface: postgresql_async
     limit: 1