fix: ship bubblewrap for DSH's command sandbox, keep agents usable without it (#35)

* fix(example): keep agents usable when DSH's inner sandbox has no backend

DSH confines bash commands itself (bubblewrap, else Landlock) and fails closed
with SANDBOX_UNAVAILABLE when no runner is usable. In this hardened pod -
non-root, capabilities dropped, seccomp RuntimeDefault - bubblewrap cannot
start (it needs CAP_SYS_ADMIN) and the pod exposes no Landlock runner, so the
shipped workspace-write default made every command fail:

  sandbox mode "workspace-write" is requested but no sandbox backend is usable

The DSH base bundle at the pinned ref documents DSH_PERMISSION_MODE as the
explicit deployment override, so set it to danger-full-access in both sandbox
templates. The per-user pod is the isolation boundary in this example (its own
pod, PVC and Service; non-root; all capabilities dropped), so a working agent
is worth more than an inner file policy that cannot be enforced. Note that
danger-full-access also turns approval prompts off.

Trade-off documented rather than hidden: an agent command can now read its own
DSH_HOME (including .credentials.yaml) and write anywhere in the container.
Hosts where a runner works should keep workspace-write or read-only.

- main-image docs: DSH_PERMISSION_MODE row plus a note on the runners and the
  fail-closed behavior
- example README: limits bullet and a troubleshooting row with the in-pod
  backend check and how to restore a confined mode
- architecture: tenant-isolation bullet extended
- skill runbook/troubleshooting: operation guidance; never grant CAP_SYS_ADMIN
  or seccompProfile: Unconfined to "fix" this without an explicit decision

Verified: make check (14 manifests), make lint, YAML assertions on both
templates, and the override expression at the pinned dsh-v0.2.1-rc.5 base
bundle (mode: !!js process.env.DSH_PERMISSION_MODE ?? 'workspace-write').

* fix(image): install bubblewrap for DSH's command sandbox

DSH's Linux sandbox runner chain is bubblewrap, then Landlock, and it fails
closed with SANDBOX_UNAVAILABLE when neither works. The image shipped neither,
so a sandboxed agent had no way to execute confined commands.

Add bubblewrap to the runtime stage. Debian ships it unsetuid (0.12.0), so it
still needs unprivileged user namespaces plus the namespace/mount syscalls: in a
hardened pod (all capabilities dropped, RuntimeDefault seccomp) it usually
cannot create one, and DSH then falls back to Landlock or, failing that, to the
DSH_PERMISSION_MODE=danger-full-access override the templates already set.
Where the host allows an unprivileged user namespace, the first-choice runner
now exists, so the confined modes can be restored.

Docs corrected to match: bubblewrap is no longer "absent"; the blocker is the
unsetuid binary's namespace requirement, not a missing CAP_SYS_ADMIN grant.

Verified: make check, make lint; the package exists in the pinned base
(node:24-trixie-slim, bubblewrap 0.12.0-1~deb13u1); a throwaway container with
the pod's flags (--user 1000 --cap-drop ALL --security-opt no-new-privileges)
still cannot create a namespace, which is why the override stays. No local image
build was run.

* ci(image): build and smoke-test the main image on PRs that touch it

The Dockerfile and the pins in versions.env could only be validated by a merge
to main or by running `make image` by hand; neither gives a PR-time signal.

Add ci-image.yaml: on pull requests that change Dockerfile, .dockerignore or
versions.env (and on manual dispatch) it builds linux/amd64 natively with the
pins sourced from versions.env - no registry login, no push - loads the image
locally and smoke-tests it:

- the packaged CLI runs and reports the pinned version
- the container is the non-root node user (1000) and owns /workspace + DSH_HOME
- the bubblewrap command-sandbox runner is present
- the OCI version label matches versions.env
- a container serves /favicon.svg (the same unauthenticated probe the shipped
  manifests use), with logs filtered so the launch token is never printed

Path-filtered like the other on-demand checks, so it is not a required status
check; the published multi-arch build stays in build-main.yaml and release.yaml.

Docs updated in the same change: AGENTS.md repository map and testing table,
docs/gitflow.md checks section, docs/main-image.md build section.

Verified: actionlint 1.7.12 and yamllint 1.38.0 (CI versions) clean over the
whole repository, plus make check and make lint.

---------

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

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

@@ -123,6 +123,16 @@ kubectl -n "$NS" patch sandboxwarmpool "$POOL" --type merge -p '{"spec":{"replic
   `0600`; the template uses `fsGroupChangePolicy: OnRootMismatch`. If a resumed
   sandbox crash-loops with a mode-660 error, suspend it, fix the file with a
   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.
+- 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
+  this hardened pod (all capabilities dropped, RuntimeDefault seccomp) does not
+  grant; that plus no Landlock runner is why the template sets
+  `DSH_PERMISSION_MODE=danger-full-access` and treats the pod as the boundary.
+  Never "fix" it by granting `CAP_SYS_ADMIN` or `seccompProfile: Unconfined`
+  without an explicit decision.
 
 ## 8. Gateway layer
 

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

@@ -18,6 +18,7 @@ events, then compare desired vs observed state. Keep output bounded. Never
 | `ImagePullBackOff` | describe events | Wrong image/tag, private GHCR package, missing pull secret; on kind, load the image under the exact manifest ref. |
 | `CrashLoopBackOff`, probe 401 | logs, `describe` | Probe path is `/`; use `/favicon.svg`. |
 | Restart with mode-660 error | logs mention `.credentials.yaml` | kubelet fsGroup widened the file; suspend, `chmod 600` from a throwaway pod, patch `fsGroupChangePolicy: OnRootMismatch`, resume. |
+| Every bash command fails with `SANDBOX_UNAVAILABLE` | DSH tool result names the requested mode and backends | DSH's own command sandbox has no usable runner: `bubblewrap` ships in the image but is unsetuid and needs an unprivileged user namespace this hardened pod does not grant, and no Landlock runner is available. The example template sets `DSH_PERMISSION_MODE=danger-full-access`; do not grant capabilities to restore it unless the operator explicitly accepts that downgrade. |
 | PVC `Pending` | `kubectl describe pvc`, StorageClass | No default provisioner, access mode, zone binding. |
 | Launch token not found | `kubectl logs <pod> --tail=2000 | grep 'dsh web:'` | Pod not ready yet, or logs rotated. Do not guess tokens; wait for readiness. |
 | Sandbox reports `Finished=True` | pod phase, `kubectl get events` | The backing Pod reached `Failed` (eviction, spot reclaim) and `failedPodPolicy` defaults to `Retain`. Delete the Pod to force a replacement, or set `Recreate` (v1.0.8+) on the Sandbox/template; the claim and PVCs survive either way. |