docker: the container runtime as a module, with its tools in Go

Claims node-container-runtime (ADR 0207). Owns the packages, the socket and a weekly prune of dangling images and unused build cache. Serves 18 tools over every container, marking the mesh's. daemon.json, docker.service and the docker group are left to a proposed change: dnsmasq and zsh declare them today, and the controller refuses a second declaration (README).
2026-10-04 12:37:44 +02:00
parent 83a51832d7
commit d4a6008bd6
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@@ -0,0 +1,166 @@
+# docker
+
+The container runtime as a module (novox/hq to-be 42 phase 1, item 8; research 027/01–02; ADR 0166,
+ADR 0207). It claims the node seat `node-container-runtime`. That seat carries no verbs yet: its verbs,
+and the host creating containers through its holder, wait on ADR 0166's acceptance. Until then the
+tools below are the module's own.
+
+## What it declares
+
+| resource | what | the host's rule |
+|---|---|---|
+| `package` | `docker` | installed if absent; never uninstalled when the module goes |
+| `buildx` | `docker-buildx` | the same. Only the build machine has it today; `docker build` needs it for BuildKit everywhere |
+| `socket` | `docker.socket` running, enabled at boot | given back as found when the module goes (ADR 0118) |
+| `prune-service`, `prune-timer` | `/etc/systemd/system/docker-prune.{service,timer}`, written whole | removed with the module |
+| `prune` | `docker-prune.timer` running, enabled at boot; restarted when either file changes | stopped and disabled with the module (the mesh made the unit) |
+
+The weekly prune takes **dangling images and build cache unused for a week, and nothing else**. It
+takes no volume, no container and no image a container uses, so it never touches a container the mesh
+holds. It runs at idle priority, at a random point in the hour after the weekly mark. A run missed
+while the machine was off happens at the next boot.
+
+**Capabilities:** `package-manager`, `service-manager`, `privileged`. It does not declare
+`container-runtime`: under ADR 0165, which is still proposed, that word means a running daemon, and
+the module that installs the daemon cannot require it.
+
+## What it does not declare yet, and why
+
+Three things this module should own are already declared by other modules on every machine. The
+controller refuses two modules on one node that declare the same `path`, `unit`, `name` or `package`
+(`checkResources`, mesh-controller `internal/catalogue/resolve.go`). Declaring any of them here would
+make the module unassignable everywhere. The refusals were checked against the controller's own
+check:
+
+```
+zsh and docker both declare the name "${machine:account}"
+dnsmasq and docker both declare the path "/etc/docker/daemon.json"
+dnsmasq and docker both declare the unit "docker.service"
+```
+
+### 1. `/etc/docker/daemon.json` and `docker.service` (issue 190)
+
+Today the file has three writers. Each writes into it (`into: json`, ADR 0102) and reloads the
+service:
+
+- **`dnsmasq`** writes `dns` and `live-restore`, through `dnsmasq.runtime-dns` and `dnsmasq.runtime`.
+- **The private network**, generated by the controller (`internal/overlay/generator.go`), writes
+  `insecure-registries`. The collision check does not see generated resources.
+- **Nobody** writes log rotation. One machine has `log-driver` and `log-opts` by hand.
+
+**The change proposed, in one merge:**
+
+1. `dnsmasq` drops its `runtime-dns` and `runtime` resources.
+2. `docker` adds the two resources below:
+
+   ```json
+   {"id": "daemon", "type": "file", "path": "/etc/docker/daemon.json", "mode": "0644", "into": "json",
+    "content": "{\"dns\": [\"${machine:address}\"], \"live-restore\": true, \"log-driver\": \"json-file\", \"log-opts\": {\"max-size\": \"100m\", \"max-file\": \"5\"}}\n"},
+   {"id": "runtime", "type": "service", "unit": "docker.service", "state": "running", "boot": "enabled", "reload-on": ["daemon"]}
+   ```
+
+   The service is **reloaded, never restarted**: a restart stops every container. The daemon reads
+   `live-restore` on a reload. It reads `dns`, `log-driver` and `log-opts` only at its next start, so
+   they apply then (to containers created afterwards, for the log keys). With `live-restore` on, that
+   start keeps every container running.
+
+**Why one merge, and only after this module is on every machine:**
+
+- In one apply, the host first gives back the resources that are no longer declared, then applies
+  the new ones (mesh-host `apply.go`).
+- `dnsmasq` gives back `dns` and `live-restore` to what they held before it, and `docker` sets them
+  again in the same apply. The daemon is reloaded once, after both steps.
+- A machine pushed the new `dnsmasq` *without* this module would keep its pre-mesh values for both
+  keys. On one machine that is `live-restore: false`, and the next daemon restart there would stop
+  every container.
+
+**Later:** the controller hands the registry to this module as a value, and the overlay stops
+generating its two resources (issue 190, steps 2 and 5). Until then the overlay keeps writing its one
+key beside this module's. The host merges disjoint keys correctly; the mesh-host `into.go` record is
+per resource.
+
+### 2. The operator account's membership of the `docker` group
+
+The right shape is the host's `user` shape. Its `groups` are additive: the host runs
+`usermod --append` and never takes a group away.
+
+```json
+{"id": "group", "type": "user", "name": "${machine:account}", "groups": ["docker"]}
+```
+
+`zsh` already declares a `user` resource for the same account (its login shell). The controller
+compares `name` across modules, so the two collide.
+
+**The change proposed (mesh-controller, `checkResources`):** judge a `user` resource by the fields it
+sets, not by its name:
+
+- `shell` and `home` stay single-owner;
+- `groups` may be declared by any number of modules, because the host only adds them.
+
+Then this module declares the resource above, and no module has to carry another's group.
+
+Today the operator account is in the group on every machine, by hand. Nothing is lost while it waits.
+
+## The bootstrap's runtime
+
+On the machine the mesh was first installed on, the foundation bundle declared `package docker`
+(`container-runtime`) and `docker.service` running and enabled (`container-runtime-running`). ADR 0207
+§5 exempts them.
+
+- The host records them under their bare ids, with origin *carried*. A mesh declaration's orphan pass
+  never sees them (mesh-host `store.go`).
+- So `docker.package` here is a **second record of the same package**. The apply says "already
+  installed", and neither record ever uninstalls it.
+- This module does not declare `docker.service` today, so nothing overlaps there. The proposed step
+  1 would add a second record of that unit. Its found state is *running*, because genesis started
+  it, so undeclaring this module would leave the daemon running.
+
+## Tools
+
+The tools run as the operator account. If the daemon's socket refuses that account, a call is asked
+again through `sudo -n` (a process keeps the groups it started with). Every call has a 20 s bound.
+A failure is an error naming how it failed, never an empty answer.
+
+**Every container on the machine is in scope.** A container the mesh holds carries the host's label
+`mesh-host.id` (its value names the assignment), and every answer says `mesh_held`.
+
+| tool | | what |
+|---|---|---|
+| `docker_list` | r | every container: image, state, health, restarts, ports, mounts, compose project, `mesh_held`; filter by owner, state or name |
+| `docker_inspect` | r | one container whole, **environment values left out** (names kept) |
+| `docker_logs` | r | the last lines of both streams, merged in order, with timestamps (default 200, at most 2000) |
+| `docker_stats` | r | CPU, memory, I/O and process count per running container, heaviest first |
+| `docker_start` / `docker_stop` / `docker_restart` | a | one container. On a mesh-held one, the answer says the host restores its declared state at its next apply |
+| `docker_top` | r | the processes inside one container |
+| `docker_images` | r | images, largest first, with the containers using each; `dangling`, `unused` or `used` |
+| `docker_prune` | a | dangling images and build cache, and stopped containers the mesh does not hold if `containers` is true. **A dry run unless `dry_run` is false. Never a volume** |
+| `docker_disk_usage` | r | `docker system df -v`: total, active and reclaimable per kind, with the largest of each |
+| `docker_networks` | r | networks, subnets, and the containers on each |
+| `docker_volumes` | r | volumes, who mounts each, whether the mesh holds one of them, anonymous or not, and sizes if asked |
+| `docker_events` | r | the runtime's events over a window ending now (default 60 min, at most 24 h), without exec noise |
+| `docker_daemon_config` | r | `daemon.json` as on disk, `docker info`'s essentials, and keys the daemon has not taken yet |
+| `docker_unlabelled` | r | the containers the mesh does not hold: the cleanup list |
+| `docker_problems` | r | unhealthy, restarting, dead, killed for memory, failed, or restarted five times or more |
+| `docker_ports` | r | every published port, and the containers on the host's network |
+
+## Tests
+
+```
+go test ./...
+```
+
+The tests run against a fake runner and cover:
+
+- escalation through `sudo -n` on a refused socket, and never as root;
+- each failure named by its cause;
+- a name or id never read as an option;
+- mesh-held marking;
+- the environment left out of `inspect`;
+- the restore note on a mesh-held act;
+- prune being a dry run by default and never reaching a volume, a mesh container or `--volumes`;
+- the log merge;
+- size parsing;
+- what the daemon has not yet taken;
+- event filtering;
+- volume ownership;
+- that the tools served are exactly the manifest's `tools`.
@@ -0,0 +1,360 @@
+package main
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"io/fs"
+	"os"
+	"reflect"
+	"strings"
+	"testing"
+	"time"
+)
+
+type call struct {
+	name string
+	args []string
+}
+
+// fake answers each command by the first rule whose prefix matches "name arg arg…".
+type fake struct {
+	rules []rule
+	calls []call
+}
+
+type rule struct {
+	prefix string
+	ran    Ran
+}
+
+func (f *fake) on(prefix string, r Ran) *fake { f.rules = append(f.rules, rule{prefix, r}); return f }
+
+func (f *fake) run(_ context.Context, name string, args ...string) Ran {
+	f.calls = append(f.calls, call{name, args})
+	line := strings.Join(append([]string{name}, args...), " ")
+	for _, r := range f.rules {
+		if strings.HasPrefix(line, r.prefix) {
+			return r.ran
+		}
+	}
+	return Ran{Status: 1, Stderr: "unexpected: " + line}
+}
+
+func (f *fake) ran(prefix string) bool {
+	for _, c := range f.calls {
+		if strings.HasPrefix(strings.Join(append([]string{c.name}, c.args...), " "), prefix) {
+			return true
+		}
+	}
+	return false
+}
+
+func client(f *fake, uid int) *Client {
+	return &Client{Run: f.run, UID: uid, ReadFile: func(string) ([]byte, error) { return nil, fs.ErrNotExist },
+		Now: func() time.Time { return time.Date(2026, 10, 4, 12, 0, 0, 0, time.UTC) }}
+}
+
+const held = `{"Id":"aaaaaaaaaaaaaaaa","Name":"/mesh-web","Created":"2026-10-01T00:00:00Z","Image":"sha256:img1",
+ "Config":{"Image":"web:1","Labels":{"mesh-host.id":"hello-web.server","mesh-host.spec":"x"},"Env":["PASSWORD=hunter2","PATH=/bin"]},
+ "State":{"Status":"running","Running":true,"StartedAt":"2026-10-01T00:00:01Z","FinishedAt":"0001-01-01T00:00:00Z","Health":{"Status":"healthy"}},
+ "HostConfig":{"RestartPolicy":{"Name":"unless-stopped"},"NetworkMode":"bridge"},
+ "NetworkSettings":{"Ports":{"80/tcp":[{"HostIp":"0.0.0.0","HostPort":"8080"}]}},
+ "Mounts":[{"Type":"volume","Name":"webdata","Destination":"/data","RW":true}]}`
+
+const stray = `{"Id":"bbbbbbbbbbbbbbbb","Name":"/dev-db","Created":"2026-09-01T00:00:00Z","Image":"sha256:img2",
+ "Config":{"Image":"postgres:16","Labels":{"com.docker.compose.project":"dev","com.docker.compose.project.working_dir":"/home/op/dev"}},
+ "State":{"Status":"exited","ExitCode":1,"FinishedAt":"2026-09-02T00:00:00Z"},
+ "HostConfig":{"RestartPolicy":{"Name":"no"}},"NetworkSettings":{"Ports":{}},
+ "Mounts":[{"Type":"volume","Name":"dbdata","Destination":"/var/lib/postgresql/data","RW":true}]}`
+
+func machine() *fake {
+	return (&fake{}).
+		on("docker ps --all --quiet --no-trunc", Ran{Stdout: "aaaaaaaaaaaaaaaa\nbbbbbbbbbbbbbbbb\n"}).
+		on("docker container inspect aaaaaaaaaaaaaaaa bbbbbbbbbbbbbbbb", Ran{Stdout: "[" + held + "," + stray + "]"}).
+		on("docker container inspect mesh-web", Ran{Stdout: "[" + held + "]"}).
+		on("docker container inspect dev-db", Ran{Stdout: "[" + stray + "]"})
+}
+
+func TestARefusedSocketIsAskedAgainThroughSudoWithoutAPromptUnlessThisIsRoot(t *testing.T) {
+	denied := Ran{Status: 1, Stderr: "permission denied while trying to connect to the Docker daemon socket at unix:///var/run/docker.sock: Get ...: dial unix /var/run/docker.sock: connect: permission denied\n"}
+	f := (&fake{}).on("docker ", denied).on("sudo -n docker info", Ran{Stdout: "{}"})
+	if _, err := client(f, 1000).docker(context.Background(), "info", "--format", "{{json .}}"); err != nil {
+		t.Fatal(err)
+	}
+	if !f.ran("sudo -n docker info --format") {
+		t.Fatalf("not escalated: %+v", f.calls)
+	}
+	f = (&fake{}).on("docker ", denied)
+	if _, err := client(f, 0).docker(context.Background(), "info"); err == nil || f.ran("sudo") {
+		t.Fatalf("root escalated or answered: %v %+v", err, f.calls)
+	}
+}
+
+func TestFailuresAreNamedByHowTheyFailed(t *testing.T) {
+	denied := Ran{Status: 1, Stderr: "permission denied while trying to connect to the Docker daemon socket at unix:///var/run/docker.sock\n"}
+	cases := map[string]*fake{
+		"may not escalate without a prompt": (&fake{}).on("docker ", denied).on("sudo ", Ran{Status: 1, Stderr: "sudo: a password is required\n"}),
+		"sudo is not installed":             (&fake{}).on("docker ", denied).on("sudo ", Ran{Status: 127, Err: "ENOENT"}),
+		"docker is not installed":           (&fake{}).on("docker ", Ran{Status: 127, Err: "ENOENT"}),
+		"daemon is not answering":           (&fake{}).on("docker ", Ran{Status: 1, Stderr: "Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?\n"}),
+		"did not answer: no answer within":  (&fake{}).on("docker ", Ran{Status: 124, Err: "no answer within 20 s"}),
+		"docker info failed (3): boom":      (&fake{}).on("docker ", Ran{Status: 3, Stderr: "boom\n"}),
+	}
+	for want, f := range cases {
+		_, err := client(f, 1000).docker(context.Background(), "info")
+		if err == nil || !strings.Contains(err.Error(), want) {
+			t.Errorf("want %q, got %v", want, err)
+		}
+	}
+}
+
+func TestANameIsNeverAnOption(t *testing.T) {
+	for _, bad := range []string{"--help", "-v", "", "a b", "x;y"} {
+		if _, err := Ref(bad); err == nil {
+			t.Errorf("%q accepted", bad)
+		}
+	}
+	for _, good := range []string{"mesh-web", "aaaaaaaaaaaa", "registry.mesh.internal:5100/x@sha256:abc", "dev_db.1"} {
+		if _, err := Ref(good); err != nil {
+			t.Errorf("%q refused: %v", good, err)
+		}
+	}
+	f := machine()
+	for _, verb := range []string{"start", "stop", "restart"} {
+		if _, err := client(f, 1000).Act(context.Background(), verb, "--rm"); err == nil {
+			t.Errorf("%s took an option", verb)
+		}
+	}
+	if len(f.calls) != 0 {
+		t.Fatalf("docker was called: %+v", f.calls)
+	}
+}
+
+func TestEveryContainerIsListedAndTheMeshsAreMarked(t *testing.T) {
+	c := client(machine(), 1000)
+	all, err := c.Containers(context.Background(), "", "", "")
+	if err != nil || len(all) != 2 {
+		t.Fatalf("%v %+v", err, all)
+	}
+	web, db := all[1], all[0]
+	if !web.MeshHeld || web.HeldBy != "hello-web.server" || web.Module != "hello-web" || web.Health != "healthy" {
+		t.Errorf("held: %+v", web)
+	}
+	if !reflect.DeepEqual(web.Ports, []string{"0.0.0.0:8080->80/tcp"}) || web.Mounts[0].Name != "webdata" {
+		t.Errorf("ports/mounts: %+v", web)
+	}
+	if db.MeshHeld || db.Compose != "dev" || db.ComposeDir != "/home/op/dev" || db.FinishedAt == "" {
+		t.Errorf("stray: %+v", db)
+	}
+	mesh, _ := c.Containers(context.Background(), "mesh", "", "")
+	other, _ := c.Containers(context.Background(), "other", "", "")
+	if len(mesh) != 1 || mesh[0].Name != "mesh-web" || len(other) != 1 || other[0].Name != "dev-db" {
+		t.Errorf("held filter: %+v / %+v", mesh, other)
+	}
+	if _, err := c.Containers(context.Background(), "mine", "", ""); err == nil {
+		t.Error("an unknown held filter was accepted")
+	}
+}
+
+func TestNoContainersIsAnEmptyListAndAFailureIsAnError(t *testing.T) {
+	got, err := client((&fake{}).on("docker ps", Ran{}), 1000).Containers(context.Background(), "", "", "")
+	if err != nil || got == nil || len(got) != 0 {
+		t.Fatalf("%v %v", got, err)
+	}
+	if _, err := client((&fake{}).on("docker ps", Ran{Status: 1, Stderr: "Cannot connect to the Docker daemon\n"}), 1000).Containers(context.Background(), "", "", ""); err == nil {
+		t.Fatal("a daemon that does not answer read as no containers")
+	}
+}
+
+func TestInspectLeavesTheEnvironmentsValuesOut(t *testing.T) {
+	got, err := client(machine(), 1000).Inspect(context.Background(), "mesh-web")
+	if err != nil {
+		t.Fatal(err)
+	}
+	b, _ := json.Marshal(got)
+	if strings.Contains(string(b), "hunter2") || !strings.Contains(string(b), `"PASSWORD"`) || got["mesh_held"] != true {
+		t.Fatalf("%s", b)
+	}
+}
+
+func TestActingOnAMeshContainerSaysTheHostRestoresIt(t *testing.T) {
+	f := machine().on("docker stop", Ran{}).on("docker start", Ran{})
+	got, err := client(f, 1000).Act(context.Background(), "stop", "mesh-web")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !f.ran("docker stop --time 10 mesh-web") || got["mesh_held"] != true || !strings.Contains(got["note"].(string), "host restores") {
+		t.Fatalf("%v %+v", got, f.calls)
+	}
+	got, _ = client(f, 1000).Act(context.Background(), "start", "dev-db")
+	if _, noted := got["note"]; noted || got["mesh_held"] != false {
+		t.Fatalf("a stray was noted: %v", got)
+	}
+}
+
+func TestPruneIsADryRunByDefaultAndNeverTouchesAVolumeOrAMeshContainer(t *testing.T) {
+	f := machine().
+		on("docker image ls --no-trunc --filter dangling=true", Ran{Stdout: `{"ID":"sha256:dead","Size":"1.5GB"}` + "\n"}).
+		on("docker system df --format", Ran{Stdout: `{"Type":"Build Cache","TotalCount":"3","Size":"2GB","Reclaimable":"1GB"}` + "\n"}).
+		on("docker image prune", Ran{Stdout: "Deleted Images:\nx\n\nTotal reclaimed space: 1.5GB\n"}).
+		on("docker builder prune", Ran{Stdout: "Total:\t1GB\n"}).
+		on("docker container rm", Ran{})
+	c := client(f, 1000)
+	got, err := c.Prune(context.Background(), PruneAsk{Images: true, BuildCache: true, Containers: true, DryRun: true})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if f.ran("docker image prune") || f.ran("docker builder prune") || f.ran("docker container rm") {
+		t.Fatalf("a dry run removed something: %+v", f.calls)
+	}
+	if got["images"].(map[string]any)["dangling"] != 1 || !reflect.DeepEqual(got["containers"].(map[string]any)["stopped_not_held"], []string{"dev-db"}) {
+		t.Fatalf("%v", got)
+	}
+	got, err = c.Prune(context.Background(), PruneAsk{Images: true, BuildCache: true, Containers: true, OlderThanH: 24})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !f.ran("docker image prune --force --filter until=24h") || !f.ran("docker builder prune --force --filter until=24h") || !f.ran("docker container rm dev-db") {
+		t.Fatalf("not pruned: %+v", f.calls)
+	}
+	for _, c := range f.calls {
+		line := strings.Join(c.args, " ")
+		if strings.Contains(line, "volume") || strings.Contains(line, "mesh-web") && c.args[0] != "container" || strings.Contains(line, "--volumes") || strings.Contains(line, "--all") && c.args[0] != "ps" {
+			t.Errorf("prune reached too far: %s", line)
+		}
+	}
+	if got["images"].(map[string]any)["reclaimed"] != "1.5GB" || got["build_cache"].(map[string]any)["reclaimed"] != "1GB" {
+		t.Errorf("reclaimed: %v", got)
+	}
+}
+
+func TestLogsMergeBothStreamsInOrderAndKeepTheTail(t *testing.T) {
+	f := (&fake{}).on("docker logs", Ran{Stdout: "2026-10-04T10:00:01Z out one\n2026-10-04T10:00:03Z out two\n", Stderr: "2026-10-04T10:00:02Z err one\n"})
+	got, err := client(f, 1000).Logs(context.Background(), "web", 2, "30m")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !reflect.DeepEqual(got["lines"], []string{"2026-10-04T10:00:02Z err one", "2026-10-04T10:00:03Z out two"}) {
+		t.Fatalf("%v", got["lines"])
+	}
+	if !f.ran("docker logs --timestamps --tail 2 --since 30m web") {
+		t.Fatalf("%+v", f.calls)
+	}
+	if _, err := client(f, 1000).Logs(context.Background(), "web", 2, "--follow"); err == nil {
+		t.Fatal("since took an option")
+	}
+	f = (&fake{}).on("docker logs", Ran{Status: 1, Stderr: "Error response from daemon: No such container: nope\n"})
+	if _, err := client(f, 1000).Logs(context.Background(), "nope", 2, ""); err == nil {
+		t.Fatal("a missing container read as no lines")
+	}
+}
+
+func TestSizesAreReadAsDockerPrintsThem(t *testing.T) {
+	for in, want := range map[string]int64{"0B": 0, "55.63GB": 55630000000, "33.2MiB": 34812723, "1.5kB": 1500, "12MB (34%)": 12000000, "N/A": -1} {
+		if got := Bytes(in); got != want {
+			t.Errorf("%s: %d, want %d", in, got, want)
+		}
+	}
+}
+
+func TestDaemonConfigSaysWhatTheDaemonHasNotTakenYet(t *testing.T) {
+	f := (&fake{}).on("docker info", Ran{Stdout: `{"ServerVersion":"29.8.2","LiveRestoreEnabled":false,"LoggingDriver":"json-file","RegistryConfig":{"IndexConfigs":{"docker.io":{"Secure":true},"registry.mesh.internal:5100":{"Secure":false}}}}`})
+	c := client(f, 1000)
+	c.ReadFile = func(string) ([]byte, error) {
+		return []byte(`{"live-restore": true, "dns": ["10.0.0.1"], "log-driver": "local"}`), nil
+	}
+	got, err := c.DaemonConfig(context.Background())
+	if err != nil {
+		t.Fatal(err)
+	}
+	pending := strings.Join(got["pending"].([]string), "\n")
+	if !strings.Contains(pending, "live-restore is true in the file and false") || !strings.Contains(pending, "log-driver is local") {
+		t.Errorf("pending: %s", pending)
+	}
+	if !reflect.DeepEqual(got["daemon"].(map[string]any)["InsecureRegistries"], []string{"registry.mesh.internal:5100"}) {
+		t.Errorf("registries: %v", got["daemon"])
+	}
+	if !reflect.DeepEqual(got["read_only_at_start"], []string{"dns", "log-driver"}) {
+		t.Errorf("start-only: %v", got["read_only_at_start"])
+	}
+	c.ReadFile = func(string) ([]byte, error) { return nil, os.ErrNotExist }
+	got, _ = c.DaemonConfig(context.Background())
+	if !strings.HasPrefix(got["file_state"].(string), "absent") {
+		t.Errorf("absent: %v", got["file_state"])
+	}
+	c.ReadFile = func(string) ([]byte, error) { return nil, errors.New("permission denied") }
+	got, _ = c.DaemonConfig(context.Background())
+	if !strings.HasPrefix(got["file_state"].(string), "unreadable") {
+		t.Errorf("unreadable: %v", got["file_state"])
+	}
+}
+
+func TestEventsAreABoundedWindowWithoutExecNoise(t *testing.T) {
+	out := `{"Type":"container","Action":"exec_start: pg_isready","Actor":{"ID":"aaaaaaaaaaaaaaaa","Attributes":{"name":"db"}},"timeNano":1}
+{"Type":"container","Action":"die","Actor":{"ID":"aaaaaaaaaaaaaaaa","Attributes":{"name":"web","mesh-host.id":"hello-web.server","exitCode":"137"}},"timeNano":2}
+`
+	f := (&fake{}).on("docker events", Ran{Stdout: out})
+	got, err := client(f, 1000).Events(context.Background(), 30, "container", 10, false)
+	if err != nil {
+		t.Fatal(err)
+	}
+	evs := got["events"].([]map[string]any)
+	if len(evs) != 1 || evs[0]["action"] != "die" || evs[0]["mesh_held"] != true || evs[0]["exit_code"] != "137" {
+		t.Fatalf("%v", evs)
+	}
+	if !f.ran("docker events --since 30m --until 0s --format {{json .}} --filter type=container") {
+		t.Fatalf("%+v", f.calls)
+	}
+	if _, err := client(f, 1000).Events(context.Background(), 30, "secret", 10, false); err == nil {
+		t.Fatal("an unknown type was accepted")
+	}
+}
+
+func TestVolumesSayWhoMountsThemAndWhetherTheMeshDoes(t *testing.T) {
+	f := machine().
+		on("docker volume ls --quiet", Ran{Stdout: "webdata\ndbdata\nloose\n"}).
+		on("docker volume inspect", Ran{Stdout: `[{"Name":"webdata","Driver":"local"},{"Name":"dbdata","Driver":"local"},{"Name":"loose","Driver":"local","Labels":{"com.docker.volume.anonymous":""}}]`})
+	got, err := client(f, 1000).Volumes(context.Background(), false, false)
+	if err != nil {
+		t.Fatal(err)
+	}
+	vols := got["volumes"].([]map[string]any)
+	if vols[0]["mesh_held"] != true || vols[1]["mesh_held"] != false || len(vols[2]["mounted_by"].([]map[string]any)) != 0 || vols[2]["anonymous"] != true {
+		t.Fatalf("%v", vols)
+	}
+	got, _ = client(f, 1000).Volumes(context.Background(), true, false)
+	if got["count"] != 1 {
+		t.Fatalf("unmounted: %v", got)
+	}
+}
+
+func TestImagesNameTheirUsers(t *testing.T) {
+	f := machine().on("docker image ls", Ran{Stdout: `{"ID":"sha256:img1","Repository":"web","Tag":"1","Size":"100MB"}
+{"ID":"sha256:img3","Repository":"<none>","Tag":"<none>","Size":"2GB"}
+`})
+	got, err := client(f, 1000).Images(context.Background(), "", "", 10)
+	if err != nil {
+		t.Fatal(err)
+	}
+	imgs := got["images"].([]Image)
+	if imgs[0].ID != "sha256:img3" || !imgs[0].Dangling || imgs[1].UsedBy[0] != "mesh-web" || !imgs[1].MeshUsed {
+		t.Fatalf("%+v", imgs)
+	}
+	got, _ = client(f, 1000).Images(context.Background(), "unused", "", 10)
+	if got["count"] != 1 {
+		t.Fatalf("unused: %v", got)
+	}
+}
+
+func TestProblemsNameWhyAndUnlabelledIsTheCleanupList(t *testing.T) {
+	c := client(machine(), 1000)
+	p, err := c.Problems(context.Background())
+	if err != nil || len(p) != 1 || p[0]["name"] != "dev-db" || p[0]["why"].([]string)[0] != "exited 1" {
+		t.Fatalf("%v %v", p, err)
+	}
+	u, err := c.Unlabelled(context.Background())
+	if err != nil || u["count"] != 1 {
+		t.Fatalf("%v %v", u, err)
+	}
+}
@@ -0,0 +1,279 @@
+// docker's Go tools bundle (novox/hq ADR 0188, ADR 0193): a process the node's tool runtime launches
+// and speaks MCP over stdio to, through the Go SDK. It answers for every container on this machine —
+// the mesh's and every other — and for the runtime's images, networks, volumes, events and
+// configuration. It runs as the operator account (ADR 0175 §4); docker.go says how it reaches the
+// daemon's socket. The host applies the module's resources; these tools answer about the runtime.
+package main
+
+import (
+	"context"
+	"fmt"
+	"math"
+	"os"
+	"strings"
+
+	stdio "git.novox.be/novox/mesh-sdk/go"
+)
+
+func main() {
+	// An empty name serves as the module the runtime names (MESH_SERVED_MODULE): docker.
+	if err := stdio.Serve("", tools(NewClient())); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+}
+
+var containerArg = map[string]any{"type": "string", "description": "the container's name or id"}
+
+func tools(c *Client) []stdio.Tool {
+	ctx := context.Background()
+	act := func(verb, description string) stdio.Tool {
+		return stdio.Tool{
+			Name: "docker_" + verb, Description: description,
+			Input: map[string]any{"container": containerArg},
+			Run: func(args map[string]any) (any, error) {
+				ref, err := text(args, "container")
+				if err != nil {
+					return nil, err
+				}
+				return c.Act(ctx, verb, ref)
+			},
+		}
+	}
+	return []stdio.Tool{
+		{
+			Name: "docker_list",
+			Description: "Every container on this machine — the mesh's and every other — with its image, state, health, restarts, " +
+				"published ports, mounts, compose project, and mesh_held/held_by (the assignment that holds it).",
+			Input: map[string]any{
+				"held":  map[string]any{"type": "string", "enum": []string{"all", "mesh", "other"}, "description": "whose: all (default), the mesh's, or the others"},
+				"state": map[string]any{"type": "string", "description": "only containers in this state (running, exited, created, restarting, paused, dead)"},
+				"match": map[string]any{"type": "string", "description": "only containers whose name or image contains this"},
+			},
+			Run: func(args map[string]any) (any, error) {
+				list, err := c.Containers(ctx, optional(args, "held"), optional(args, "state"), optional(args, "match"))
+				if err != nil {
+					return nil, err
+				}
+				return map[string]any{"count": len(list), "containers": list}, nil
+			},
+		},
+		{
+			Name:        "docker_inspect",
+			Description: "One container whole, as docker inspects it, with mesh_held; its environment's values are left out (names kept), because that is where a container's secrets are.",
+			Input:       map[string]any{"container": containerArg},
+			Run: func(args map[string]any) (any, error) {
+				ref, err := text(args, "container")
+				if err != nil {
+					return nil, err
+				}
+				return c.Inspect(ctx, ref)
+			},
+		},
+		{
+			Name:        "docker_logs",
+			Description: "The last lines one container wrote, both streams merged in order, each with its timestamp (default 200, at most 2000 lines; a line is cut at 4 KiB).",
+			Input: map[string]any{
+				"container": containerArg,
+				"lines":     map[string]any{"type": "integer", "description": "how many lines from the end (default 200, at most 2000)"},
+				"since":     map[string]any{"type": "string", "description": "only lines since then: a duration such as 30m or 2h, or a time"},
+			},
+			Run: func(args map[string]any) (any, error) {
+				ref, err := text(args, "container")
+				if err != nil {
+					return nil, err
+				}
+				n, err := bounded(args, "lines", 200, 2000)
+				if err != nil {
+					return nil, err
+				}
+				return c.Logs(ctx, ref, n, optional(args, "since"))
+			},
+		},
+		{
+			Name:        "docker_stats",
+			Description: "What the running containers use now — CPU, memory, network and disk I/O, processes — the heaviest by memory first; or one container's.",
+			Input:       map[string]any{"container": map[string]any{"type": "string", "description": "one container (optional)"}},
+			Run: func(args map[string]any) (any, error) {
+				stats, err := c.Stats(ctx, optional(args, "container"))
+				if err != nil {
+					return nil, err
+				}
+				return map[string]any{"count": len(stats), "containers": stats}, nil
+			},
+		},
+		act("start", "Start one container. A container the mesh holds is started too, and the answer says the host restores what its declaration says at its next apply."),
+		act("stop", "Stop one container (ten seconds, then killed). For a container the mesh holds, the answer says the host will start it again at its next apply if its declaration says running."),
+		act("restart", "Restart one container (ten seconds to stop, then killed); the answer says whether the mesh holds it."),
+		{
+			Name:        "docker_top",
+			Description: "The processes running inside one container: pid, user, elapsed time, CPU, resident memory and command.",
+			Input:       map[string]any{"container": containerArg},
+			Run: func(args map[string]any) (any, error) {
+				ref, err := text(args, "container")
+				if err != nil {
+					return nil, err
+				}
+				return c.Top(ctx, ref)
+			},
+		},
+		{
+			Name: "docker_images",
+			Description: "The images on this machine, the largest first, each with its size and the containers using it (and whether one of them is the mesh's). " +
+				"filter: all, dangling, unused or used.",
+			Input: map[string]any{
+				"filter": map[string]any{"type": "string", "enum": []string{"all", "dangling", "unused", "used"}, "description": "which images (default all)"},
+				"match":  map[string]any{"type": "string", "description": "only images whose repository:tag contains this"},
+				"limit":  map[string]any{"type": "integer", "description": "how many to show (default 100, at most 1000); count says how many matched"},
+			},
+			Run: func(args map[string]any) (any, error) {
+				n, err := bounded(args, "limit", 100, 1000)
+				if err != nil {
+					return nil, err
+				}
+				return c.Images(ctx, optional(args, "filter"), optional(args, "match"), n)
+			},
+		},
+		{
+			Name: "docker_prune",
+			Description: "Reclaim space: dangling images and unused build cache, and — only when containers is true — stopped containers the mesh does not hold. " +
+				"Never a volume, never a container the mesh holds, never an image a container uses. A dry run by default: it lists what would go; dry_run false removes it.",
+			Input: map[string]any{
+				"dry_run":          map[string]any{"type": "boolean", "description": "list only (default true)"},
+				"images":           map[string]any{"type": "boolean", "description": "dangling images (default true)"},
+				"build_cache":      map[string]any{"type": "boolean", "description": "build cache nothing refers to (default true)"},
+				"containers":       map[string]any{"type": "boolean", "description": "stopped containers the mesh does not hold (default false); what they mounted is kept"},
+				"older_than_hours": map[string]any{"type": "integer", "description": "only what is older than this many hours (default 0: any age)"},
+			},
+			Run: func(args map[string]any) (any, error) {
+				older := 0
+				if v, ok := args["older_than_hours"]; ok && v != nil && v != float64(0) {
+					n, err := bounded(args, "older_than_hours", 0, 24*365)
+					if err != nil {
+						return nil, err
+					}
+					older = n
+				}
+				return c.Prune(ctx, PruneAsk{
+					DryRun: flag(args, "dry_run", true), Images: flag(args, "images", true), BuildCache: flag(args, "build_cache", true),
+					Containers: flag(args, "containers", false), OlderThanH: older,
+				})
+			},
+		},
+		{
+			Name:        "docker_disk_usage",
+			Description: "What the runtime takes on disk (docker system df -v): per kind — images, containers, volumes, build cache — the total, the active and the reclaimable, and the largest of each.",
+			Input:       map[string]any{"top": map[string]any{"type": "integer", "description": "how many of the largest per kind (default 10, at most 100)"}},
+			Run: func(args map[string]any) (any, error) {
+				n, err := bounded(args, "top", 10, 100)
+				if err != nil {
+					return nil, err
+				}
+				return c.DiskUsage(ctx, n)
+			},
+		},
+		{
+			Name:        "docker_networks",
+			Description: "Every network the runtime has: driver, scope, subnets and gateway, and the running containers on it with their addresses and whether the mesh holds them.",
+			Run:         func(map[string]any) (any, error) { return c.Networks(ctx) },
+		},
+		{
+			Name:        "docker_volumes",
+			Description: "Every volume with the containers mounting it, whether the mesh holds any of them, whether it is anonymous, its compose project, and — when sizes is true (slower) — its size.",
+			Input: map[string]any{
+				"unmounted": map[string]any{"type": "boolean", "description": "only volumes no container mounts (default false)"},
+				"sizes":     map[string]any{"type": "boolean", "description": "measure each volume (default false: it walks every volume)"},
+			},
+			Run: func(args map[string]any) (any, error) {
+				return c.Volumes(ctx, flag(args, "unmounted", false), flag(args, "sizes", false))
+			},
+		},
+		{
+			Name:        "docker_events",
+			Description: "What the runtime did in a window ending now (default the last 60 minutes, at most 24 hours): containers created, started, died, health changes, images pulled — with mesh_held. Exec events are left out unless asked.",
+			Input: map[string]any{
+				"minutes": map[string]any{"type": "integer", "description": "how far back (default 60, at most 1440)"},
+				"type":    map[string]any{"type": "string", "description": "only one kind: container, image, network, volume, daemon, plugin or builder"},
+				"limit":   map[string]any{"type": "integer", "description": "the latest this many (default 200, at most 2000)"},
+				"execs":   map[string]any{"type": "boolean", "description": "include exec_* events (default false: health checks make many)"},
+			},
+			Run: func(args map[string]any) (any, error) {
+				minutes, err := bounded(args, "minutes", 60, 1440)
+				if err != nil {
+					return nil, err
+				}
+				limit, err := bounded(args, "limit", 200, 2000)
+				if err != nil {
+					return nil, err
+				}
+				return c.Events(ctx, minutes, optional(args, "type"), limit, flag(args, "execs", false))
+			},
+		},
+		{
+			Name: "docker_daemon_config",
+			Description: "The runtime's configuration: /etc/docker/daemon.json as it is on disk, the daemon's essentials as it runs now (docker info: version, storage and logging drivers, " +
+				"live restore, root directory, insecure registries, warnings), and where the two differ — keys a reload or only a restart would take.",
+			Run: func(map[string]any) (any, error) { return c.DaemonConfig(ctx) },
+		},
+		{
+			Name:        "docker_unlabelled",
+			Description: "The containers the mesh does not hold — the cleanup list — each with its image, state, compose project and directory, ports and mounts.",
+			Run:         func(map[string]any) (any, error) { return c.Unlabelled(ctx) },
+		},
+		{
+			Name:        "docker_problems",
+			Description: "Every container that is not well: unhealthy, restarting, dead, killed for memory, exited with a failure, or restarted five times or more — with whether the mesh holds it.",
+			Run: func(map[string]any) (any, error) {
+				p, err := c.Problems(ctx)
+				if err != nil {
+					return nil, err
+				}
+				return map[string]any{"count": len(p), "containers": p}, nil
+			},
+		},
+		{
+			Name:        "docker_ports",
+			Description: "Every port the containers publish on this machine (address:port -> container port), and the containers on the host's network, which publish whatever they listen on.",
+			Run: func(map[string]any) (any, error) {
+				p, err := c.Ports(ctx)
+				if err != nil {
+					return nil, err
+				}
+				return map[string]any{"count": len(p), "ports": p}, nil
+			},
+		},
+	}
+}
+
+func text(args map[string]any, key string) (string, error) {
+	s, _ := args[key].(string)
+	if s = strings.TrimSpace(s); s == "" {
+		return "", fmt.Errorf("%s is required", key)
+	}
+	return s, nil
+}
+
+func optional(args map[string]any, key string) string {
+	s, _ := args[key].(string)
+	return strings.TrimSpace(s)
+}
+
+func flag(args map[string]any, key string, def bool) bool {
+	if b, ok := args[key].(bool); ok {
+		return b
+	}
+	return def
+}
+
+// bounded is a whole number argument, defaulted when absent and held to a ceiling.
+func bounded(args map[string]any, key string, def, most int) (int, error) {
+	v, ok := args[key]
+	if !ok || v == nil {
+		return def, nil
+	}
+	f, ok := v.(float64)
+	if !ok || f != math.Trunc(f) || f < 1 {
+		return 0, fmt.Errorf("%s must be a whole number of at least 1", key)
+	}
+	return int(math.Min(f, float64(most))), nil
+}
@@ -0,0 +1,59 @@
+package main
+
+import (
+	"bytes"
+	"context"
+	"errors"
+	"fmt"
+	"os/exec"
+	"strings"
+	"time"
+)
+
+// Ran is what a command did: its output, its exit status, and why it never ran to an answer.
+type Ran struct {
+	Stdout string
+	Stderr string
+	Status int
+	// Err is "ENOENT" when the program is not installed, or says it was ended for taking too long.
+	Err string
+}
+
+// Runner runs one command, so every tool can be tested without a daemon.
+type Runner func(ctx context.Context, name string, args ...string) Ran
+
+// CallTimeout is how long one docker command may take: below the runtime's thirty-second call
+// limit, so a daemon that hangs is answered as such rather than as a call the runtime gave up on.
+const CallTimeout = 20 * time.Second
+
+// ExecRunner runs a command on this machine, bounded by CallTimeout.
+func ExecRunner(ctx context.Context, name string, args ...string) Ran {
+	ctx, cancel := context.WithTimeout(ctx, CallTimeout)
+	defer cancel()
+	cmd := exec.CommandContext(ctx, name, args...)
+	var out, errb bytes.Buffer
+	cmd.Stdout, cmd.Stderr = &out, &errb
+	err := cmd.Run()
+	r := Ran{Stdout: out.String(), Stderr: errb.String()}
+	var exitErr *exec.ExitError
+	switch {
+	case errors.Is(ctx.Err(), context.DeadlineExceeded):
+		r.Status, r.Err = 124, fmt.Sprintf("no answer within %d s", int(CallTimeout/time.Second))
+	case errors.Is(err, exec.ErrNotFound):
+		r.Status, r.Err = 127, "ENOENT"
+	case errors.As(err, &exitErr):
+		r.Status = exitErr.ExitCode()
+	case err != nil:
+		r.Status, r.Err = 1, err.Error()
+	}
+	return r
+}
+
+func firstLine(s string) string {
+	for _, l := range strings.Split(s, "\n") {
+		if l = strings.TrimSpace(l); l != "" {
+			return l
+		}
+	}
+	return ""
+}
@@ -0,0 +1,60 @@
+package main
+
+import (
+	"encoding/json"
+	"os"
+	"reflect"
+	"sort"
+	"strings"
+	"testing"
+)
+
+func TestTheToolsServedAreTheToolsTheManifestNames(t *testing.T) {
+	raw, err := os.ReadFile("../../module.json")
+	if err != nil {
+		t.Fatal(err)
+	}
+	var m struct {
+		Tools []string `json:"tools"`
+	}
+	if err := json.Unmarshal(raw, &m); err != nil {
+		t.Fatal(err)
+	}
+	served := []string{}
+	for _, tool := range tools(client(&fake{}, 1000)) {
+		if !strings.HasPrefix(tool.Name, "docker_") || tool.Description == "" || tool.Run == nil {
+			t.Errorf("tool %q", tool.Name)
+		}
+		served = append(served, tool.Name)
+	}
+	sort.Strings(served)
+	listed := append([]string{}, m.Tools...)
+	sort.Strings(listed)
+	if !reflect.DeepEqual(served, listed) {
+		t.Fatalf("served %v, manifest %v", served, listed)
+	}
+}
+
+func TestNumbersAreDefaultedAndBounded(t *testing.T) {
+	if n, _ := bounded(map[string]any{}, "lines", 200, 2000); n != 200 {
+		t.Error(n)
+	}
+	if n, _ := bounded(map[string]any{"lines": float64(99999)}, "lines", 200, 2000); n != 2000 {
+		t.Error(n)
+	}
+	for _, bad := range []any{float64(0), float64(-1), float64(1.5), "10"} {
+		if _, err := bounded(map[string]any{"lines": bad}, "lines", 200, 2000); err == nil {
+			t.Errorf("%v accepted", bad)
+		}
+	}
+}
+
+func TestAStopFromTheToolNeedsAContainer(t *testing.T) {
+	for _, tool := range tools(client(&fake{}, 1000)) {
+		if tool.Name == "docker_stop" {
+			if _, err := tool.Run(map[string]any{}); err == nil {
+				t.Fatal("a stop without a container was accepted")
+			}
+		}
+	}
+}
@@ -0,0 +1,5 @@
+module docker
+
+go 1.22
+
+require git.novox.be/novox/mesh-sdk/go v0.1.6
@@ -0,0 +1,2 @@
+git.novox.be/novox/mesh-sdk/go v0.1.6 h1:9qzdYONYbJdWcu6sxQcq9v1LI0JxcfkiKYkMUzJSkVQ=
+git.novox.be/novox/mesh-sdk/go v0.1.6/go.mod h1:GFuZUElBZ9A++mxgIKo97aXXo+kV0uJ/UkbhQPPIbrY=
@@ -0,0 +1,94 @@
+{
+  "module": "docker",
+  "version": "1",
+  "capabilities": [
+    "package-manager",
+    "service-manager",
+    "privileged"
+  ],
+  "claims": [
+    {
+      "name": "node-container-runtime",
+      "scope": "node"
+    }
+  ],
+  "tools": [
+    "docker_list",
+    "docker_inspect",
+    "docker_logs",
+    "docker_stats",
+    "docker_start",
+    "docker_stop",
+    "docker_restart",
+    "docker_top",
+    "docker_images",
+    "docker_prune",
+    "docker_disk_usage",
+    "docker_networks",
+    "docker_volumes",
+    "docker_events",
+    "docker_daemon_config",
+    "docker_unlabelled",
+    "docker_problems",
+    "docker_ports"
+  ],
+  "resources": [
+    {
+      "id": "package",
+      "type": "package",
+      "package": "docker"
+    },
+    {
+      "id": "buildx",
+      "type": "package",
+      "package": "docker-buildx"
+    },
+    {
+      "id": "socket",
+      "type": "service",
+      "unit": "docker.socket",
+      "state": "running",
+      "boot": "enabled"
+    },
+    {
+      "id": "prune-service",
+      "type": "file",
+      "path": "/etc/systemd/system/docker-prune.service",
+      "mode": "0644",
+      "content": "# Generated by the mesh. Do not edit — module docker writes this file and replaces it at every push.\n[Unit]\nDescription=Prune dangling images and unused build cache (the mesh's docker module)\n# Never volumes, never a container, never an image a container uses: dangling\n# images and build cache nothing refers to, unused for a week. What a person\n# prunes beyond that is docker_prune's, by hand.\nAfter=docker.service\nConditionPathExists=/run/docker.sock\n\n[Service]\nType=oneshot\nNice=19\nIOSchedulingClass=idle\nExecStart=/usr/bin/docker image prune --force --filter until=168h\nExecStart=/usr/bin/docker builder prune --force --filter until=168h\n"
+    },
+    {
+      "id": "prune-timer",
+      "type": "file",
+      "path": "/etc/systemd/system/docker-prune.timer",
+      "mode": "0644",
+      "content": "# Generated by the mesh. Do not edit — module docker writes this file and replaces it at every push.\n[Unit]\nDescription=Weekly prune of dangling images and unused build cache (the mesh's docker module)\n\n[Timer]\nOnCalendar=weekly\nRandomizedDelaySec=1h\nPersistent=true\n\n[Install]\nWantedBy=timers.target\n"
+    },
+    {
+      "id": "prune",
+      "type": "service",
+      "unit": "docker-prune.timer",
+      "state": "running",
+      "boot": "enabled",
+      "restart-on": [
+        "prune-service",
+        "prune-timer"
+      ]
+    }
+  ],
+  "build": {
+    "artifacts": [
+      {
+        "name": "tools",
+        "kind": "bundle",
+        "language": "go",
+        "system": "arch",
+        "from": "cmd/docker-tools",
+        "binary": "docker-tools",
+        "loads": [
+          "docker-tools"
+        ]
+      }
+    ]
+  }
+}