mesh-tools/node-tools/internal/runtime/runtime.go

// Package runtime is the node's tool runtime (novox/hq ADR 0175, ADR 0193), the Go port of
// node-tools' runtime.ts in its launch-only form: it launches every assigned module's bundle,
// serves each module's tools on that module's subjects and each held seat's verbs on the seat's,
// and answers for every module the verb that says what it serves. It imports nothing and knows no
// language.
package runtime

import (
	"encoding/json"
	"errors"
	"fmt"
	"os"
	"path/filepath"
	"sort"
	"strings"
	"sync"

	"github.com/novox/mesh-tools/node-tools/internal/announce"
	"github.com/novox/mesh-tools/node-tools/internal/bus"
	"github.com/novox/mesh-tools/node-tools/internal/launch"
)

// ToolsVerb is the verb every module's runtime answers for it (ADR 0152): its tools, from the code
// that answers them.
const ToolsVerb = "tools"

// Words the mesh sets for the runtime (ADR 0175, ADR 0192).
const (
	ToolModules     = "MESH_TOOL_MODULES"
	ToolEnv         = "MESH_TOOL_ENV"
	OperatorAccount = "MESH_OPERATOR_ACCOUNT"
	OperatorHome    = "MESH_OPERATOR_HOME"
)

// Served is one module this runtime serves and its entrypoints.
type Served struct {
	Module      string
	Entrypoints []string
}

// ToolsAnswer is what `tools` answers for one module.
type ToolsAnswer struct {
	Module string       `json:"module"`
	Tools  []ListedTool `json:"tools"`
	Failed string       `json:"failed,omitempty"`
}

// ListedTool is one tool as a module's `tools` answer lists it.
type ListedTool struct {
	Name        string          `json:"name"`
	Description string          `json:"description"`
	Input       json.RawMessage `json:"input"`
	Subjects    []string        `json:"subjects,omitempty"`
}

// NodeRuntimeModule is the module that is a machine's runtime, serving every module on it.
const NodeRuntimeModule = "node-tools"

// runtimeOnly are the words of the runtime's own environment no bundle is given.
var runtimeOnly = map[string]bool{ToolEnv: true, ToolModules: true, "MESH_BROKER_FILE": true,
	"MESH_BROKER_URL": true, "MESH_CONSOLE_LISTEN": true}

// ServedModulesFrom reads MESH_TOOL_MODULES: `<module>=<entrypoint>` entries, comma-separated, several
// per module. The one-module form — a bare path, or the runtime's own module — is the per-module
// containers' (to-be 38 WP4c) and refused here: the node's runtime imports nothing.
func ServedModulesFrom(spec, own string) ([]Served, error) {
	order := []string{}
	by := map[string][]string{}
	for _, raw := range strings.Split(spec, ",") {
		entry := strings.TrimSpace(raw)
		if entry == "" {
			continue
		}
		module, path, ok := strings.Cut(entry, "=")
		module, path = strings.TrimSpace(module), strings.TrimSpace(path)
		if !ok || module == "" || path == "" {
			return nil, fmt.Errorf("%s: %q is not <module>=<entrypoint>; the runtime launches the bundles it "+
				"is given and imports nothing (novox/hq ADR 0193)", ToolModules, entry)
		}
		// The node's runtime serves the machine's modules and never itself. **A runtime on a module's own
		// account serves that module and nothing else** (novox/hq ADR 0259 §8): the router and a channel that
		// proves its sender reach the bus on an account of their own, never the machine's runtime.
		switch {
		case own == NodeRuntimeModule && module == own:
			return nil, fmt.Errorf("%s: %q is the runtime itself; it launches the bundles it is given and "+
				"imports nothing (novox/hq ADR 0193)", ToolModules, entry)
		case own != NodeRuntimeModule && module != own:
			return nil, fmt.Errorf("%s: %q is another module's; a runtime on %s's own account serves %s alone "+
				"(novox/hq ADR 0259)", ToolModules, entry, own, own)
		}
		if _, seen := by[module]; !seen {
			order = append(order, module)
		}
		by[module] = append(by[module], path)
	}
	out := make([]Served, 0, len(order))
	for _, m := range order {
		out = append(out, Served{Module: m, Entrypoints: by[m]})
	}
	return out, nil
}

// TakeToolEnvs reads the composed environments (ADR 0192) and removes them from the process's, so no
// bundle finds another's there.
func TakeToolEnvs() (map[string]map[string]string, error) {
	raw := os.Getenv(ToolEnv)
	os.Unsetenv(ToolEnv)
	out := map[string]map[string]string{}
	if raw == "" {
		return out, nil
	}
	var parsed map[string]map[string]any
	if err := json.Unmarshal([]byte(raw), &parsed); err != nil {
		return nil, fmt.Errorf(`%s is not JSON of the shape {"<module>": {"<word>": "<value>"}}: %w`, ToolEnv, err)
	}
	for module, words := range parsed {
		own := map[string]string{}
		for k, v := range words {
			if s, ok := v.(string); ok {
				own[k] = s
			} else {
				b, _ := json.Marshal(v)
				own[k] = string(b)
			}
		}
		out[module] = own
	}
	return out, nil
}

type registration struct {
	module string // the module's own name, or a seat's
	owner  string // the module whose bundle made it
	tools  []launch.Tool
}

// Run launches, binds and serves. It answers a stop function.
func Run(conn *bus.Conn, served []Served, envs map[string]map[string]string, logf func(string, ...any)) (func(), error) {
	if account := os.Getenv(OperatorAccount); account != "" {
		home := ""
		if h := os.Getenv(OperatorHome); h != "" {
			home = " (home " + h + ")"
		}
		logf("[mesh-tools] the operator's account here is %s%s", account, home)
	}
	modules := make([]string, 0, len(served))
	isServed := map[string]bool{}
	for _, s := range served {
		modules = append(modules, s.Module)
		isServed[s.Module] = true
		conn.Follow(s.Module)
	}
	node := conn.Node()

	base := os.Environ()
	envFor := func(module string) []string { return BundleEnv(base, envs[module], module, node) }

	// The module's events, for every child of it that subscribes (ADR 0198): one consumer per module,
	// bound the first time any of its children subscribes, each event handed to every child that did.
	events := &consumers{conn: conn, logf: logf, of: map[string]*moduleEvents{}}

	failed := map[string]string{}
	var registrations []registration
	var stops []func()
	for _, s := range served {
		for _, entry := range s.Entrypoints {
			path, _ := filepath.Abs(entry)
			module := s.Module
			fail := func(why string) {
				failed[module] = why
				logf("[mesh-tools] %s's bundle %s failed to load: %s; its tools are not served here", module, entry, why)
			}
			if !launch.Executable(path) {
				fail(path + " is not executable; a bundle the runtime serves is started, never imported, and its build makes it executable (novox/hq ADR 0193)")
				continue
			}
			child, err := launch.Start(module, path, envFor(module), events.forModule(module), logf)
			if err != nil {
				fail(err.Error())
				continue
			}
			stops = append(stops, child.Stop)
			for _, r := range child.Registrations {
				registrations = append(registrations, registration{module: r.Module, owner: module, tools: r.Tools})
			}
		}
	}

	claimed := map[string]bool{}
	for _, m := range modules {
		if mem := conn.Membership(m); mem != nil {
			for _, s := range mem.Seats {
				claimed[s.Seat] = true
			}
		}
	}
	var own []registration
	for _, r := range registrations {
		switch {
		case isServed[r.module]:
			own = append(own, r)
		case claimed[r.module]:
		default:
			logf(`[mesh-tools] %s registers tools under "%s", which is neither a module served here nor a seat one of them claims; not served until the mesh issues the claim`, r.owner, r.module)
		}
	}
	stopAll := func() {
		events.stopAll()
		for i := len(stops) - 1; i >= 0; i-- {
			stops[i]()
		}
	}
	for _, r := range own {
		seen := map[string]bool{}
		for _, t := range r.tools {
			if t.Name == ToolsVerb {
				stopAll()
				return nil, fmt.Errorf(`%s names a tool "%s", which is the verb the runtime answers for every module with what it serves (novox/hq ADR 0152) — refused, rename it`, r.module, ToolsVerb)
			}
			if seen[t.Name] {
				stopAll()
				return nil, fmt.Errorf("%s exposes two tools named %s — refused", r.module, t.Name)
			}
			seen[t.Name] = true
		}
	}

	var names []string
	byModule := map[string][]launch.Tool{}
	for _, r := range own {
		for _, t := range r.tools {
			t := t
			stop, err := conn.Handle(r.module+"."+t.Name, func(body json.RawMessage) (any, error) {
				return t.Run(argsOf(body))
			})
			if err != nil {
				logf("[mesh-tools] cannot serve %s.%s: %v", r.module, t.Name, err)
				continue
			}
			names = append(names, r.module+"."+t.Name)
			stops = append(stops, stop)
		}
		byModule[r.module] = append(byModule[r.module], r.tools...)
	}
	for _, module := range modules {
		module := module
		tools := byModule[module]
		why := failed[module]
		if len(tools) == 0 && why == "" {
			continue // a pure-events module: silent, as it always was
		}
		stop, err := conn.Handle(module+"."+ToolsVerb, func(json.RawMessage) (any, error) {
			answer := ToolsAnswer{Module: module, Tools: []ListedTool{}, Failed: why}
			for _, t := range tools {
				answer.Tools = append(answer.Tools, ListedTool{Name: t.Name, Description: t.Description,
					Input: t.Input, Subjects: subjectsOf(conn, module, t.Name)})
			}
			return answer, nil
		})
		if err == nil {
			stops = append(stops, stop)
		}
	}

	failedNames := make([]string, 0, len(failed))
	for _, m := range modules {
		if _, f := failed[m]; f {
			failedNames = append(failedNames, m)
		}
	}
	line := fmt.Sprintf("[mesh-tools] serving %d tool(s) for %d module(s): %s", len(names), len(modules), orNone(names))
	if len(failedNames) > 0 {
		line += fmt.Sprintf("; not serving %s, whose bundle(s) failed to load", strings.Join(failedNames, ", "))
	}
	logf("%s", line)
	stops = append(stops, serveSeats(conn, modules, registrations, logf))

	// **What it serves, it announces** (novox/hq ADR 0197): the NATS services protocol's discovery,
	// answered with what is served at the moment it is asked — re-served memberships included.
	announced, err := announce.Serve(conn, announce.Service{
		Name: conn.Module(), ID: instanceOf(conn),
		Description: "the mesh's tool runtime on " + node + ": every assigned module's tools and the seats they hold",
		Metadata:    map[string]string{"node": node},
	}, func() []announce.Endpoint { return endpointsOf(conn, own, registrations, modules) })
	if err != nil {
		logf("[mesh-tools] cannot announce what it serves: %v", err)
	} else {
		stops = append(stops, announced)
	}
	conn.Flush()
	return stopAll, nil
}

// instanceOf is this runtime's instance on the bus: its machine, which is what tells two instances of
// one service apart; the connection's module where it has no machine.
func instanceOf(conn *bus.Conn) string {
	if n := conn.Node(); n != "" {
		return n
	}
	return conn.Module()
}

// endpointsOf is everything this runtime serves now: each served module's tools on every subject the
// mesh issued for them, and each held seat's verbs on the seat's subject (ADR 0197).
func endpointsOf(conn *bus.Conn, own []registration, registrations []registration, modules []string) []announce.Endpoint {
	node := conn.Node()
	var out []announce.Endpoint
	for _, r := range own {
		for _, t := range r.tools {
			served := conn.ServedOn(r.module, t.Name)
			interchangeable := false
			for _, s := range served {
				interchangeable = interchangeable || s.Subject == "mesh.mod."+r.module+".tool."+t.Name
			}
			for _, s := range served {
				out = append(out, announce.Endpoint{Kind: announce.KindTool, Module: r.module, Tool: t.Name,
					Node: node, Description: t.Description, Schema: t.Input, Interchangeable: interchangeable,
					Subject: s.Subject, Queue: s.Queue})
			}
		}
	}
	impl := map[string]map[string]launch.Tool{}
	for _, r := range registrations {
		if impl[r.module] == nil {
			impl[r.module] = map[string]launch.Tool{}
		}
		for _, t := range r.tools {
			impl[r.module][t.Name] = t
		}
	}
	have := map[string]bool{}
	for _, module := range modules {
		m := conn.Membership(module)
		if m == nil {
			continue
		}
		for _, v := range m.Seats {
			t, ok := impl[v.Seat][v.Verb]
			if !ok || have[v.Subject] {
				continue
			}
			have[v.Subject] = true
			scope := "mesh"
			if node != "" && strings.HasSuffix(v.Subject, "."+node) {
				scope = "node"
			}
			out = append(out, announce.Endpoint{Kind: announce.KindSeat, Module: module, Tool: v.Verb, Seat: v.Seat,
				Scope: scope, Node: node, Description: t.Description, Schema: t.Input, Subject: v.Subject})
		}
	}
	return out
}

func orNone(names []string) string {
	if len(names) == 0 {
		return "(none)"
	}
	return strings.Join(names, ", ")
}

// argsOf is a call's arguments as the tool receives them: an object, `{}` for none.
func argsOf(body json.RawMessage) json.RawMessage {
	trimmed := strings.TrimSpace(string(body))
	if trimmed == "" || trimmed == "null" {
		return json.RawMessage("{}")
	}
	return body
}

// subjectsOf is where a tool is answered as the mesh issued it: the plain subject first, then this
// machine's; nothing before a membership is issued.
func subjectsOf(conn *bus.Conn, module, tool string) []string {
	m := conn.Membership(module)
	if m == nil {
		return nil
	}
	var plain, mine []string
	for _, s := range m.Serves {
		subject := strings.ReplaceAll(s.Subject, "{tool}", tool)
		if s.Queue != "" {
			plain = append(plain, subject)
		} else {
			mine = append(mine, subject)
		}
	}
	return append(plain, mine...)
}

// serveSeats serves every verb of every seat a served module holds, where the mesh issued it, by
// the tool of the same name registered under the seat's name (ADR 0159, 0160) — and serves again
// whenever a membership changes. Whether this machine holds the seat is the bus's to decide.
func serveSeats(conn *bus.Conn, modules []string, registrations []registration, logf func(string, ...any)) func() {
	impl := map[string]map[string]launch.Tool{}
	for _, r := range registrations {
		if impl[r.module] == nil {
			impl[r.module] = map[string]launch.Tool{}
		}
		for _, t := range r.tools {
			impl[r.module][t.Name] = t
		}
	}
	var mu sync.Mutex
	var stops []func()
	serve := func() {
		mu.Lock()
		defer mu.Unlock()
		for _, s := range stops {
			s()
		}
		stops = nil
		have := map[string]bool{}
		for _, module := range modules {
			m := conn.Membership(module)
			if m == nil {
				continue
			}
			for _, v := range m.Seats {
				if have[v.Subject] {
					continue
				}
				have[v.Subject] = true
				t, ok := impl[v.Seat][v.Verb]
				if !ok {
					logf("[mesh-tools] %s claims %s and implements no %s, which that seat promises; not served", module, v.Seat, v.Verb)
					continue
				}
				stop, err := conn.HandleSubject(v.Subject, func(body json.RawMessage) (any, error) {
					return t.Run(argsOf(body))
				})
				if err != nil {
					logf("[mesh-tools] cannot serve %s's %s on %s: %v", v.Seat, v.Verb, v.Subject, err)
					continue
				}
				stops = append(stops, stop)
				logf("[mesh-tools] serving %s's %s on %s, admitted where %s holds the seat", v.Seat, v.Verb, v.Subject, module)
			}
		}
	}
	serve()
	conn.OnMembership(func(bus.Membership) { go func() { serve(); conn.Flush() }() })
	return func() {
		mu.Lock()
		defer mu.Unlock()
		for _, s := range stops {
			s()
		}
		stops = nil
	}
}

// consumers holds, per module the runtime serves, the one durable consumer its events arrive on and
// the children its events are handed to (novox/hq ADR 0198).
type consumers struct {
	conn *bus.Conn
	logf func(string, ...any)
	mu   sync.Mutex
	of   map[string]*moduleEvents
	// seatBound is each module's seat traffic bound once: a worker taken, a proof subject answered.
	seatBound map[string]func()
}

type moduleEvents struct {
	stop     func()
	delivers []*func(json.RawMessage) error
}

// stopAll unbinds every module's consumer.
func (c *consumers) stopAll() {
	c.mu.Lock()
	defer c.mu.Unlock()
	for _, m := range c.of {
		if m.stop != nil {
			m.stop()
		}
	}
	c.of = map[string]*moduleEvents{}
	for _, stop := range c.seatBound {
		stop()
	}
	c.seatBound = map[string]func(){}
}

// forModule is the bus one launched bundle of a module reaches the mesh through.
func (c *consumers) forModule(module string) launch.Bus {
	return &moduleBus{all: c, module: module}
}

type moduleBus struct {
	all     *consumers
	module  string
	mu      sync.Mutex
	deliver *func(json.RawMessage) error
}

// Publish emits an event as the module (ADR 0193).
func (b *moduleBus) Publish(params json.RawMessage) error {
	var env bus.Envelope
	if err := json.Unmarshal(params, &env); err != nil {
		return fmt.Errorf("not an event envelope: %w", err)
	}
	return b.all.conn.PublishAs(b.module, env)
}

// Ask calls a tool as the module: `{key, body}`, answered with the tool's result (ADR 0198).
func (b *moduleBus) Ask(params json.RawMessage) (json.RawMessage, error) {
	var asked struct {
		Key  string          `json:"key"`
		Body json.RawMessage `json:"body"`
	}
	if err := json.Unmarshal(params, &asked); err != nil || asked.Key == "" {
		return nil, fmt.Errorf("mesh/ask names no tool: {key, body}")
	}
	body := any(asked.Body)
	if len(asked.Body) == 0 {
		body = map[string]any{}
	}
	answered, err := b.all.conn.AskAs(b.module, asked.Key, body)
	if err != nil {
		return nil, err
	}
	if len(answered.Result) == 0 {
		return json.RawMessage("null"), nil
	}
	return answered.Result, nil
}

// Subscribe hands this bundle the module's events. The consumer is bound once per module; each of
// the module's children that subscribed is handed every event, and the event is acknowledged only
// when all of them took it — one consumer split between two readers would give each half.
func (b *moduleBus) Subscribe(deliver func(json.RawMessage) error) error {
	b.mu.Lock()
	if b.deliver == nil {
		d := deliver
		b.deliver = &d
	} else {
		*b.deliver = deliver
	}
	mine := b.deliver
	b.mu.Unlock()

	c := b.all
	c.mu.Lock()
	defer c.mu.Unlock()
	m := c.of[b.module]
	if m == nil {
		m = &moduleEvents{}
		c.of[b.module] = m
	}
	listed := false
	for _, d := range m.delivers {
		if d == mine {
			listed = true
		}
	}
	if !listed {
		m.delivers = append(m.delivers, mine)
	}
	if m.stop != nil {
		return nil
	}
	module := b.module
	stop, err := c.conn.ConsumeAs(module, func(env bus.Envelope) error {
		raw, err := json.Marshal(env)
		if err != nil {
			return err
		}
		c.mu.Lock()
		targets := append([]*func(json.RawMessage) error(nil), c.of[module].delivers...)
		c.mu.Unlock()
		for _, d := range targets {
			if err := (*d)(raw); err != nil {
				c.logf("[mesh-tools] %s did not take %s%s: %s; offered again in %s", module, env.Key,
					eventRef(env), whyNotTaken(err), bus.NakDelay)
				return err
			}
		}
		return nil
	})
	if err != nil {
		return err
	}
	m.stop = stop
	c.logf("[mesh-tools] %s's events arrive on its consumer %s", module, bus.ConsumerOf(c.conn.Node(), module))
	return nil
}

// whyNotTaken says why a bundle did not take an event, so the line names who failed: the module's
// handler, in its own words — an error it answered — or the runtime not reaching it. A bundle's
// handler error read bare ("Unexpected end of JSON input") looked like the runtime's (issue 276).
func whyNotTaken(err error) string {
	var refused *launch.Refused
	if errors.As(err, &refused) {
		return fmt.Sprintf("its handler answered an error, in its own words: %q (an event is taken by any answer that is not an error)", refused.Message)
	}
	return err.Error()
}

// eventRef names the event a line is about by its id, when it has one, so its offers can be told
// apart from another event's.
func eventRef(env bus.Envelope) string {
	if id := env.Headers["x-event-id"]; id != "" {
		return " (event " + id + ")"
	}
	return ""
}

// stateAsked is what a bundle names when it reaches its state (ADR 0201): the state by the name its
// module uses, a key, and for a put the value.
type stateAsked struct {
	State    string          `json:"state"`
	Key      string          `json:"key"`
	Value    json.RawMessage `json:"value"`
	Revision uint64          `json:"revision"`
}

// State answers a bundle's `get`, `put`, `delete` and `keys` on its module's state (ADR 0201). The
// runtime refuses, with the reason, a state the module was not issued and a write to one it only reads.
func (b *moduleBus) State(verb string, params json.RawMessage) (json.RawMessage, error) {
	var asked stateAsked
	if err := json.Unmarshal(params, &asked); err != nil || asked.State == "" {
		return nil, fmt.Errorf("mesh/state.%s names no state: {state, key, value}", verb)
	}
	conn := b.all.conn
	var answer any
	switch verb {
	case "get":
		entry, err := conn.StateGet(b.module, asked.State, asked.Key)
		if err != nil {
			return nil, err
		}
		if entry == nil {
			return json.RawMessage("null"), nil
		}
		answer = entry
	case "put":
		revision, err := conn.StatePut(b.module, asked.State, asked.Key, asked.Value)
		if err != nil {
			return nil, err
		}
		answer = map[string]any{"revision": revision}
	case "delete":
		if err := conn.StateDelete(b.module, asked.State, asked.Key); err != nil {
			return nil, err
		}
		answer = map[string]any{}
	case "keys":
		keys, err := conn.StateKeys(b.module, asked.State)
		if err != nil {
			return nil, err
		}
		answer = keys
	case "create":
		// Only when the key has no value: of two writers making it, one wins (novox/hq ADR 0259).
		revision, err := conn.StateCreate(b.module, asked.State, asked.Key, asked.Value)
		if err != nil {
			return nil, err
		}
		answer = map[string]any{"revision": revision}
	case "update":
		// Only when the key is still at the revision read: a second answer to one ask loses (ADR 0259).
		revision, err := conn.StateUpdate(b.module, asked.State, asked.Key, asked.Value, asked.Revision)
		if err != nil {
			return nil, err
		}
		answer = map[string]any{"revision": revision}
	default:
		return nil, fmt.Errorf("the runtime answers no mesh/state.%s", verb)
	}
	return json.Marshal(answer)
}

// Watch hands a bundle its module's state as it is and as it changes (ADR 0201): `{state, key}`, the
// key a pattern with `*` and `**`, empty for every key.
func (b *moduleBus) Watch(params json.RawMessage, deliver func(json.RawMessage) error) (func(), error) {
	var asked stateAsked
	if err := json.Unmarshal(params, &asked); err != nil || asked.State == "" {
		return nil, fmt.Errorf("mesh/state.watch names no state: {state, key}")
	}
	return b.all.conn.StateWatch(b.module, asked.State, asked.Key, func(change bus.StateChange) error {
		raw, err := json.Marshal(change)
		if err != nil {
			return err
		}
		return deliver(raw)
	})
}

// seatAsked is what a bundle names for its seat traffic (novox/hq ADR 0259 §3).
type seatAsked struct {
	Subject string          `json:"subject"`
	Body    json.RawMessage `json:"body"`
	ID      string          `json:"id"`
	Worker  string          `json:"worker"`
	Bucket  string          `json:"bucket"`
	Key     string          `json:"key"`
}

// Seat answers a bundle's seat traffic, each as the module and only as far as its membership lists:
// `publish` an accept or an event, `prove` (ask a proof), `record` (read a record kept for it), `take` a
// worker's work and `answer` a proof subject — the last two bound once per module and subject, each
// message or proof handed to the module's child that asked last (novox/hq ADR 0259 §3).
func (b *moduleBus) Seat(verb string, params json.RawMessage, handOn func(string, any) (json.RawMessage, error)) (json.RawMessage, error) {
	var asked seatAsked
	if err := json.Unmarshal(params, &asked); err != nil {
		return nil, fmt.Errorf("mesh/seat.%s: %w", verb, err)
	}
	conn := b.all.conn
	switch verb {
	case "publish":
		seq, duplicate, err := conn.SeatPublishSaid(b.module, asked.Subject, asked.Body, asked.ID)
		if err != nil {
			return nil, err
		}
		return json.Marshal(map[string]any{"sequence": seq, "duplicate": duplicate})
	case "prove":
		return conn.SeatProve(b.module, asked.Subject, asked.Body)
	case "kinds":
		kinds, err := conn.SeatKinds(b.module)
		if err != nil {
			return nil, err
		}
		return json.Marshal(kinds)
	case "record":
		entry, err := conn.SeatRecord(b.module, asked.Bucket, asked.Key)
		if err != nil || entry == nil {
			return json.RawMessage("null"), err
		}
		return json.Marshal(entry)
	case "take":
		key := "take " + asked.Worker
		if b.bound(key) {
			return json.RawMessage(`{}`), nil
		}
		stop, err := conn.SeatTake(b.module, asked.Worker, func(w bus.Work) error {
			_, err := handOn("mesh/work", map[string]any{"work": w})
			return err
		})
		if err != nil {
			return nil, err
		}
		b.bind(key, stop)
		b.all.logf("[mesh-tools] %s takes its work from %s", b.module, asked.Worker)
		return json.RawMessage(`{}`), nil
	case "answer":
		key := "answer " + asked.Subject
		if b.bound(key) {
			return json.RawMessage(`{}`), nil
		}
		stop, err := conn.SeatAnswer(b.module, asked.Subject, func(subject string, body json.RawMessage) (json.RawMessage, error) {
			return handOn("mesh/proof", map[string]any{"subject": subject, "body": body})
		})
		if err != nil {
			return nil, err
		}
		b.bind(key, stop)
		b.all.logf("[mesh-tools] %s answers the proofs on %s", b.module, asked.Subject)
		return json.RawMessage(`{}`), nil
	}
	return nil, fmt.Errorf("the runtime answers no mesh/seat.%s", verb)
}

// bound and bind keep, per module, what its seat traffic is bound to, so a child that starts again and
// asks again is handed what is already bound instead of a second reader of it.
func (b *moduleBus) bound(key string) bool {
	b.all.mu.Lock()
	defer b.all.mu.Unlock()
	_, ok := b.all.seatBound[b.module+" "+key]
	return ok
}

func (b *moduleBus) bind(key string, stop func()) {
	b.all.mu.Lock()
	defer b.all.mu.Unlock()
	if b.all.seatBound == nil {
		b.all.seatBound = map[string]func(){}
	}
	b.all.seatBound[b.module+" "+key] = stop
}

// BundleEnv is what one module's bundle is started with: the runtime's environment without its own words,
// the module's composed words over it, and the module's and machine's names. **No bus word reaches a
// bundle** (security review of 2026-10-08): the credential and the bus's address are the runtime's, and a
// bundle reaches the bus only through the runtime.
func BundleEnv(base []string, given map[string]string, module, node string) []string {
	words := map[string]string{}
	for _, kv := range base {
		if k, v, ok := strings.Cut(kv, "="); ok && !runtimeOnly[k] {
			words[k] = v
		}
	}
	for k, v := range given {
		if !runtimeOnly[k] {
			words[k] = v
		}
	}
	words["MESH_SERVED_MODULE"] = module
	words["MESH_MODULE"] = module
	if node != "" {
		words["MESH_NODE"] = node
	}
	out := make([]string, 0, len(words))
	for k, v := range words {
		out = append(out, k+"="+v)
	}
	sort.Strings(out)
	return out
}