feat: give the sandbox a real shell toolbelt — and make an image bump reach existing users

The per-user container shipped python+node and little else, so an agent asking
for `unzip`, `ffprobe` or even `ps` found nothing and had to `sudo apt-get
install` mid-task. That fallback works, but it re-runs on **every container
recreate**, inside the task, where it costs latency and can fail — while the
image is **one, shared by every container**, so preinstalling costs its size
once for the whole box. Anything an agent reaches for repeatedly is therefore
cheaper baked in.

Added on that rule: jq, ripgrep, zip/unzip, xz-utils, sqlite3, wget,
openssh-client, procps, less, file, tzdata, dnsutils, iputils-ping, ffmpeg
(+ffprobe), imagemagick, poppler-utils and tesseract — with the ita/fra
language packs, matching the app's supported UI locales (eng and osd arrive as
hard deps). Deliberately left out: build-essential/python3-dev (~270 MB, only
for a pip package with no wheel) and pandoc (~216 MB) are big *and*
self-recoverable, so they stay on demand. 687 MB -> 1.3 GB, ffmpeg being most
of it.

The image tag goes v2 -> v3, which alone would have equipped nobody: a
container pins the image it was created from, so `ensure()` would have rebuilt
v3 and then happily reused every existing v2 container — the new tools would
have reached only users created from here on. `reusable()` now compares
`.Config.Image` too, turning a tag bump into a recreate, safe for the same
reason the `--user`/`--init` self-heal already is: the container holds no
durable state, everything lives in the bind mounts. An unreadable inspect
answers true, so a docker hiccup never churns a working container.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

CLAUDE.md

@@ -97,7 +97,7 @@ Two rules keep the boundary real, and both are enforced by the compiler:
 | `crates/skald-core/src/chat_event_bus.rs` | Global async bus for cross-session events |
 | `crates/skald-core/src/agents.rs` | Discovers agents from `agents/*/`, loads meta + system prompt |
 | `crates/skald-core/src/tools/` | Built-in tools: `exec` (**runs inside the caller's per-user Docker container** via `docker exec`, as the non-root host uid — `sudo` for system installs — with a robust /stop that reaps the command's process-group; see `container/`; the only live path is `run_with` (needs `ToolContext`) — the context-free `Tool::execute`/`execute_async` now **error** (`HOST_PATH_ERROR`) instead of the old host `sh -c`, so nothing can run a command outside the sandbox), `list_agents`, `fs/*` (route `user-memory/`/`shared-memory/` to `memory_docs`, and every other **physical** path through `ctx.fs` to the caller's per-user host workspace — see DB tables + container), `notify`, `ast_outline`, `image_generate`, MCP tools, plugin tools, cron tools |
-| `crates/skald-core/src/container/` | `ContainerManager` (§6): per-user Docker containers (the execution sandbox). Docker is a **hard requirement** — `check_docker()` fails `Skald::new` (→ shell exits) if the daemon is unreachable. Builds our own `skald-runtime` image (python+node+**sudo**; tag is **versioned** `skald-runtime:v2` so a `Dockerfile` change forces a rebuild) once from the embedded `Dockerfile`, then `reconcile_all()` at boot ensures one running container `skald-{userid}` per active user. Each container runs as the **host `uid:gid`** (`--user`, §6 UID coherence) with `--init` (tini reaps zombies); `ensure()` **self-heals** a container whose `--user` is stale (e.g. an old root one) by recreating it, and injects a passwd/shadow entry post-create so `sudo` (NOPASSWD, in the image) resolves the arbitrary uid. `build_user_fs()` assembles a user's `UserFs` (home `{WD}/homes/{userid}` → `/root`, plus each `shared/{name}` they belong to). Shells the `docker` CLI (no client crate) |
+| `crates/skald-core/src/container/` | `ContainerManager` (§6): per-user Docker containers (the execution sandbox). Docker is a **hard requirement** — `check_docker()` fails `Skald::new` (→ shell exits) if the daemon is unreachable. Builds our own `skald-runtime` image (python+node+**sudo**, plus a shell-work toolbelt — `jq`/`ripgrep`/`unzip`/`ffmpeg`/`poppler-utils`/`tesseract`/`procps`…; tag is **versioned** `skald-runtime:v3` so a `Dockerfile` change forces a rebuild) once from the embedded `Dockerfile`, then `reconcile_all()` at boot ensures one running container `skald-{userid}` per active user. Each container runs as the **host `uid:gid`** (`--user`, §6 UID coherence) with `--init` (tini reaps zombies); `ensure()` **self-heals** a container that is stale on any of three axes — `--user` (e.g. an old root one), `--init`, or the **image tag** — by recreating it, and injects a passwd/shadow entry post-create so `sudo` (NOPASSWD, in the image) resolves the arbitrary uid. The image check is what makes a tag bump reach *existing* users: a container pins the image it was created from, so without it a rebuild would only ever equip new users. `build_user_fs()` assembles a user's `UserFs` (home `{WD}/homes/{userid}` → `/root`, plus each `shared/{name}` they belong to). Shells the `docker` CLI (no client crate) |
 | `crates/skald-core/src/tool_catalog.rs` | `ToolCatalog`: unified tool listing façade (wraps ToolRegistry + McpManager) |
 | `crates/skald-core/src/events.rs` | `ServerEvent` enum streamed over WebSocket to the frontend |
 | `crates/skald-core/src/db/` | sqlx SQLite — see below |
@@ -152,7 +152,7 @@ Schema is greenfield (no migrations, §0), but a purely **additive** column land
 
 ## Filesystem & containers (blueprint §6)
 
-Each user has one **permanent Docker container** (`skald-{userid}`, our own `skald-runtime` image with python+node), created on user creation and started at boot (`ContainerManager`, `crates/skald-core/src/container/`). Docker is **required**: a missing daemon fails `Skald::new` and the process exits. The container runs as the **host `uid:gid`** (not root) so files created in-container and by the host-side fs-tools share ownership on the bind mounts (matters on native Linux; masked on macOS Docker Desktop). Because that user isn't root, the image ships passwordless `sudo` (a passwd/shadow entry is injected at create) so an agent can still `sudo apt-get install …`; `--init` runs tini as pid 1 to reap zombies.
+Each user has one **permanent Docker container** (`skald-{userid}`, our own `skald-runtime` image with python+node and a preinstalled shell toolbelt), created on user creation and started at boot (`ContainerManager`, `crates/skald-core/src/container/`). Docker is **required**: a missing daemon fails `Skald::new` and the process exits. **What goes in the image vs. what the agent installs on demand** is a real trade, and the Dockerfile states its rule: `sudo apt-get install` works in the sandbox but re-runs on **every container recreate**, inside a task, where it costs latency and can fail — while the image is **one, shared by every container**, so preinstalling costs its size once for the whole box. Anything an agent reaches for repeatedly is therefore baked in; `build-essential`/`python3-dev` and `pandoc` are deliberately left out as big *and* self-recoverable. The container runs as the **host `uid:gid`** (not root) so files created in-container and by the host-side fs-tools share ownership on the bind mounts (matters on native Linux; masked on macOS Docker Desktop). Because that user isn't root, the image ships passwordless `sudo` (a passwd/shadow entry is injected at create) so an agent can still `sudo apt-get install …`; `--init` runs tini as pid 1 to reap zombies.
 
 The agent sees **one namespace**, routed on the first path component. The choke point is `UserFs` (`core-api/src/user_fs.rs`, a pure value type carried in `ToolContext.fs`), plus `resolve_host_path()` in `tools/fs/mod.rs`: