diff --git a/go/compose/fromruntime/fromruntime.go b/go/compose/fromruntime/fromruntime.go
index a2a98e0..ae0f323 100644
--- a/go/compose/fromruntime/fromruntime.go
+++ b/go/compose/fromruntime/fromruntime.go
@@ -28,9 +28,30 @@ func (States) Get(state, key string) ([]byte, bool, error) {
 // Keys are a state's keys.
 func (States) Keys(state string) ([]string, error) { return stdio.State(state).Keys() }
 
-// Reader is frombus's Reader over this bundle's read states, fetching archives over HTTP.
+// Reader is frombus's Reader over this bundle's read states key by key, fetching archives over HTTP. A holder that
+// composes again and again reads through Watched instead (novox/hq ADR 0580).
 func Reader() frombus.Reader { return frombus.StatesReader(States{}, HTTPFetch) }
 
+// Watched is frombus's States over a watched copy (novox/hq ADR 0580 clause 1): the states a composition reads whole
+// (placement, haves, modules, resolved values) from the copy, a build by key when asked, a manifest once per digest.
+type Watched struct{ *stdio.WatchedStates }
+
+// Get is a key's value: a build read now, a manifest kept once read, any other state's from the copy.
+func (w Watched) Get(state, key string) ([]byte, bool, error) {
+	switch state {
+	case frombus.BuildsRead:
+		return w.Direct(state, key)
+	case frombus.ManifestsRead:
+		return w.Once(state, key)
+	}
+	return w.WatchedStates.Get(state, key)
+}
+
+// WatchedReader is frombus's Reader over w, fetching archives over HTTP.
+func WatchedReader(w *stdio.WatchedStates) frombus.Reader {
+	return frombus.StatesReader(Watched{w}, HTTPFetch)
+}
+
 // HTTPFetch reads an archive over HTTP, at most 256 MiB.
 func HTTPFetch(ctx context.Context, url string) ([]byte, error) {
 	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
diff --git a/go/state_test.go b/go/state_test.go
index cac843b..bef4cbd 100644
--- a/go/state_test.go
+++ b/go/state_test.go
@@ -230,4 +230,45 @@ func TestABundleKeepsAndWatchesStateThroughTheRuntime(t *testing.T) {
 		t.Fatalf("the get answered %v", r)
 	}
 	_ = inW.Close()
+
+	// ADR 0580 clause 1: the watched copy answers keys and values after the watch's current values, a later put or delete
+	// changes its answer, a follower's then sees the copy that took its change, each state is watched once, and a
+	// value kept once is read by key once.
+	handles, watches, gets := map[string]func(StateChange) error{}, map[string]int{}, 0
+	w := WatchedStatesOver(func(state string, handle func(StateChange) error) error {
+		watches[state]++
+		handles[state] = handle
+		return handle(StateChange{State: state, Key: "a", Op: OpPut, Value: []byte("1"), Current: true})
+	}, func(state, key string) ([]byte, bool, error) { gets++; return []byte(key), key != "missing", nil })
+	var thenSaw []string
+	w.Follow("placement", func(c StateChange) error {
+		v, found, _ := w.Get("placement", c.Key)
+		thenSaw = append(thenSaw, fmt.Sprintf("%s %s %s %v", c.Op, c.Key, v, found))
+		return nil
+	})
+	if keys, err := w.Keys("placement"); err != nil || fmt.Sprint(keys) != "[a]" {
+		t.Fatalf("the copy's keys are %v (%v)", keys, err)
+	}
+	_ = handles["placement"](StateChange{Key: "b", Op: OpPut, Value: []byte("2")})
+	_ = handles["placement"](StateChange{Key: "a", Op: OpDelete})
+	vals, _ := w.Values("placement")
+	if v, found, _ := w.Get("placement", "a"); found || string(vals["b"]) != "2" || len(vals) != 1 || v != nil {
+		t.Fatalf("after a put and a delete the copy is %v", vals)
+	}
+	if fmt.Sprint(thenSaw) != "[put a 1 true put b 2 true delete a  false]" {
+		t.Fatalf("then saw %v", thenSaw)
+	}
+	_, _ = w.Keys("placement")
+	if watches["placement"] != 1 {
+		t.Fatalf("the state was watched %d times", watches["placement"])
+	}
+	for range 2 {
+		if v, found, _ := w.Once("manifests", "d1"); !found || string(v) != "d1" {
+			t.Fatalf("once read %q %v", v, found)
+		}
+		_, _, _ = w.Once("manifests", "missing")
+	}
+	if gets != 3 {
+		t.Fatalf("a kept value was read by key %d times, want once, and the missing one twice", gets)
+	}
 }
diff --git a/go/watched.go b/go/watched.go
new file mode 100644
index 0000000..1cb7578
--- /dev/null
+++ b/go/watched.go
@@ -0,0 +1,216 @@
+package stdio
+
+import (
+	"fmt"
+	"sort"
+	"sync"
+	"time"
+)
+
+// WatchedStates is a copy of the states a module reads, each filled by its own watch and kept by its changes (novox/hq
+// ADR 0580 clause 1): a read of a whole state is one watch's current values, never a get per key, which took a
+// composition past 30 seconds and a compare past its call bound. A state is watched on its first read, or on Follow,
+// and the watch hands every current value over before the read is answered, so the copy is complete from the first
+// answer. A key whose value never changes once written (a manifest, by its digest) is read once with Once and kept.
+// A state helper, no rule: what a module reads is its own.
+type WatchedStates struct {
+	watch func(state string, handle func(StateChange) error) error
+	get   func(state, key string) ([]byte, bool, error)
+
+	mu     sync.Mutex
+	states map[string]*watchedState
+	once   map[string][]byte
+}
+
+type watchedState struct {
+	ready chan struct{} // closed once the watch's current values are all in the copy, or it was refused
+	err   error
+
+	mu      sync.Mutex
+	values  map[string][]byte
+	then    []func(StateChange) error
+	started bool          // the current values are in, so a change runs then at once
+	pending []StateChange // the current values, run through then once all are in
+	thenMu  sync.Mutex    // then runs one change at a time
+}
+
+// NewWatchedStates is the copy over this bundle's runtime: each state by KeptState.Watch, Once by KeptState.Get.
+func NewWatchedStates() *WatchedStates {
+	return WatchedStatesOver(
+		func(state string, handle func(StateChange) error) error { return State(state).Watch("", handle) },
+		func(state, key string) ([]byte, bool, error) {
+			e, err := State(state).Get(key)
+			if err != nil || e == nil {
+				return nil, false, err
+			}
+			return e.Value, true, nil
+		})
+}
+
+// WatchedStatesOver is the copy over a watch and a get of one's own (a process's bus, a test's): watch hands handle
+// every current value and returns once they are handled, then hands every change; get reads one key.
+func WatchedStatesOver(watch func(state string, handle func(StateChange) error) error,
+	get func(state, key string) ([]byte, bool, error)) *WatchedStates {
+	return &WatchedStates{watch: watch, get: get, states: map[string]*watchedState{}, once: map[string][]byte{}}
+}
+
+// watched is the state's copy, its watch started now when it has none, the caller waiting until its current values
+// are in. then, when given, runs after the copy took each change: the current values once they are all in (a then
+// that reads the copy reads it whole), each later change as it comes. No lock is held while the watch starts, so a
+// then may read any state of the copy.
+func (w *WatchedStates) watched(state string, then func(StateChange) error) (*watchedState, error) {
+	w.mu.Lock()
+	s, ok := w.states[state]
+	if ok {
+		w.mu.Unlock()
+		<-s.ready
+		if s.err != nil {
+			return nil, s.err
+		}
+		if then != nil {
+			s.mu.Lock()
+			s.then = append(s.then, then)
+			s.mu.Unlock()
+		}
+		return s, nil
+	}
+	s = &watchedState{ready: make(chan struct{}), values: map[string][]byte{}}
+	if then != nil {
+		s.then = []func(StateChange) error{then}
+	}
+	w.states[state] = s
+	w.mu.Unlock()
+	err := w.watch(state, func(c StateChange) error {
+		s.mu.Lock()
+		if c.Op == OpPut {
+			s.values[c.Key] = append([]byte(nil), c.Value...)
+		} else {
+			delete(s.values, c.Key)
+		}
+		if !s.started {
+			s.pending = append(s.pending, c)
+			s.mu.Unlock()
+			return nil
+		}
+		s.mu.Unlock()
+		return s.run(state, c)
+	})
+	if err != nil {
+		s.err = fmt.Errorf("the state %s is not watched: %w", state, err)
+		w.mu.Lock()
+		delete(w.states, state) // asked again on the next read
+		w.mu.Unlock()
+		close(s.ready)
+		return nil, s.err
+	}
+	s.mu.Lock()
+	s.started = true
+	pending := s.pending
+	s.pending = nil
+	s.mu.Unlock()
+	close(s.ready)
+	for _, c := range pending {
+		if err := s.run(state, c); err != nil {
+			sayf("%v", err)
+		}
+	}
+	return s, nil
+}
+
+// run hands one change, already in the copy, to every then.
+func (s *watchedState) run(state string, c StateChange) error {
+	s.thenMu.Lock()
+	defer s.thenMu.Unlock()
+	s.mu.Lock()
+	then := append([]func(StateChange) error(nil), s.then...)
+	s.mu.Unlock()
+	var errs []error
+	for _, f := range then {
+		if err := f(c); err != nil {
+			errs = append(errs, err)
+		}
+	}
+	if len(errs) > 0 {
+		return fmt.Errorf("%s %s: %v", state, c.Key, errs)
+	}
+	return nil
+}
+
+// Follow watches the state into the copy and runs then on each change after the copy took it, so a reader then wakes
+// never reads a copy older than its change; it asks again until the watch is taken (2 s, doubled to a minute), as
+// KeptState.Follow does. On a state already watched then hears the changes from now on.
+func (w *WatchedStates) Follow(state string, then func(StateChange) error) {
+	for wait := 2 * time.Second; ; wait = min(wait*2, time.Minute) {
+		if _, err := w.watched(state, then); err == nil {
+			return
+		} else {
+			sayf("%v; asking again in %s", err, wait)
+		}
+		time.Sleep(wait)
+	}
+}
+
+// Get is a key's value in the copy, false when it has none.
+func (w *WatchedStates) Get(state, key string) ([]byte, bool, error) {
+	s, err := w.watched(state, nil)
+	if err != nil {
+		return nil, false, err
+	}
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	v, ok := s.values[key]
+	return v, ok, nil
+}
+
+// Keys are the state's keys in the copy, sorted.
+func (w *WatchedStates) Keys(state string) ([]string, error) {
+	s, err := w.watched(state, nil)
+	if err != nil {
+		return nil, err
+	}
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	keys := make([]string, 0, len(s.values))
+	for k := range s.values {
+		keys = append(keys, k)
+	}
+	sort.Strings(keys)
+	return keys, nil
+}
+
+// Values is every key's value in the copy.
+func (w *WatchedStates) Values(state string) (map[string][]byte, error) {
+	s, err := w.watched(state, nil)
+	if err != nil {
+		return nil, err
+	}
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	out := make(map[string][]byte, len(s.values))
+	for k, v := range s.values {
+		out[k] = v
+	}
+	return out, nil
+}
+
+// Once is a key whose value never changes once written, read by key the first time it is found and kept after: a
+// manifest by its digest. A key not found is not kept, so it is read again on the next ask.
+func (w *WatchedStates) Once(state, key string) ([]byte, bool, error) {
+	w.mu.Lock()
+	v, ok := w.once[state+" "+key]
+	w.mu.Unlock()
+	if ok {
+		return v, true, nil
+	}
+	v, found, err := w.get(state, key)
+	if err != nil || !found {
+		return nil, false, err
+	}
+	w.mu.Lock()
+	w.once[state+" "+key] = v
+	w.mu.Unlock()
+	return v, true, nil
+}
+
+// Direct is a key read by key now, not from the copy: a value that changes and is read one at a time (a build).
+func (w *WatchedStates) Direct(state, key string) ([]byte, bool, error) { return w.get(state, key) }