fix: harden workspace activation and snapshot retention

docs/install/server-workspace-registry.md

@@ -114,7 +114,7 @@ THT_WS_PSD_CLINICAL_EMBEDDING_BASE_URL=https://embeddings.internal.example
 ```
 
 ```dotenv
-# SSH tunnel requires explicit host-key verification and TLS target identity.
+# SSH tunnel diagnostic only; runtime sessions are fail-closed in this release.
 THT_WS_PSD_CLINICAL_DWH_TRANSPORT=ssh_tunnel
 THT_WS_PSD_CLINICAL_DWH_USER=thoth_reader
 THT_WS_PSD_CLINICAL_DWH_PASSWORD_FILE=/run/secrets/psd-dwh-reader
@@ -132,6 +132,10 @@ rather than disable verification; use runtime-trusted HTTPS or verified direct/S
 the [diagnostic protocol](../workspace-diagnostic-protocol.md) for its read-only checks and optional
 reversible writer probe.
 
+An SSH connector can be tested with strict host-key and target verification, but it intentionally
+returns `workspace_not_activatable`; configure direct or REST transport before starting sessions.
+The Git registry itself may still use SSH normally.
+
 ## Same-origin reverse proxy, bootstrap, and health
 
 Copy [the server Compose example](examples/server-compose.workspace-registry.yaml) plus exactly one