feat(example): start DSH's folder picker on the persisted workspace (#36)

The directory picker has no start-path setting: it lists $HOME whenever it
opens. With the image default HOME=/home/node the folder explorer started on
a throwaway directory, so point HOME at the PVC-backed /workspace in both
sandbox templates. `~` and $HOME-relative tool caches/config follow; DSH_HOME
stays /home/node/.dsh, so sessions, config and credentials are unaffected.

Document the trade-off in the image contract and both examples, add
troubleshooting for sandboxes whose pod env was stamped before the change,
and assert HOME/~ in the e2e walkthrough.

Co-authored-by: SREDevOpsAgents <agents@sredevops.org>

.dsh/skills/dsh-agent-sandbox-platform/references/platform-runbook.md

@@ -125,6 +125,15 @@ kubectl -n "$NS" patch sandboxwarmpool "$POOL" --type merge -p '{"spec":{"replic
   throwaway pod, patch the policy, then resume.
 - Agent files live at `/workspace`, the same PVC mounted with
   `subPath: workspace`; it survives suspend/resume and dies with the PVC.
+- The templates set `HOME=/workspace` (the image default is `/home/node`). DSH's
+  directory picker lists `$HOME` when it opens and has no start-path setting, so
+  this is what makes the folder explorer start on the persisted workspace; `~`
+  and `$HOME`-relative tool caches/config also resolve there. `DSH_HOME` remains
+  `/home/node/.dsh`, so state and credentials stay out of the workspace. Pod env
+  is stamped at sandbox creation: a sandbox created before the override keeps
+  the old `HOME` until it is recreated (or its `podTemplate` is patched and the
+  sandbox resumed). Verify with
+  `kubectl -n "$NS" exec "$POD" -- printenv HOME`.
 - DSH confines bash with its own file sandbox (`bubblewrap`, else Landlock) and
   fails closed with `SANDBOX_UNAVAILABLE` when neither works. The image ships
   `bubblewrap`, but it is unsetuid and needs an unprivileged user namespace that