fix(deploy): let the hub's sandboxes run under bubblewrap

deploy/compose.yml

@@ -42,6 +42,17 @@ services:
       retries: 30
   hub:
     <<: *hub
+    # The coder and designer run their commands under bubblewrap, which gives
+    # each one its own user, pid and mount namespaces with a fresh /proc.
+    # Docker's default seccomp profile refuses the namespaces without
+    # CAP_SYS_ADMIN, its AppArmor profile refuses the mount propagation, and
+    # its masked /proc paths refuse the fresh /proc, so the hub runs without
+    # those three and keeps its capabilities dropped. On Ubuntu 24.04 hosts
+    # the kernel must also allow it; see "Sandboxes" in docs/SELF_HOST.md.
+    security_opt:
+      - seccomp=unconfined
+      - apparmor=unconfined
+      - systempaths=unconfined
     ports:
       - "127.0.0.1:${PORT:-8000}:${PORT:-8000}"
       - "127.0.0.1:1455:1455"

docs/SELF_HOST.md

@@ -104,6 +104,25 @@ docker compose --env-file .env.hub --project-directory . -f deploy/compose.yml -
 
 `bun run docker:up` runs the same.
 
+## Sandboxes
+
+The coder and designer run every command under bubblewrap, which needs a user
+namespace with its capabilities intact, mount propagation and a fresh `/proc`.
+The hub service runs with `seccomp=unconfined`, `apparmor=unconfined` and
+`systempaths=unconfined` for that; its capabilities stay dropped. Ubuntu 24.04
+and later strip the capabilities from unprivileged user namespaces, so on such
+a host (including the Ubuntu VM that Colima runs) also turn that restriction
+off, and make it persist across reboots:
+
+```sh
+sudo sysctl -w kernel.apparmor_restrict_unprivileged_userns=0
+echo kernel.apparmor_restrict_unprivileged_userns=0 | sudo tee /etc/sysctl.d/60-builder-userns.conf
+```
+
+Without it every designer and coder tool call fails with
+`sandbox_tool_process_failed: bwrap: No permissions to create a new namespace`
+or `bwrap: setting up uid map: Permission denied`.
+
 ## Sidecars in Docker
 
 Agents run in sidecars. By default the hub starts them as processes beside