One watched copy of the states a module reads, and the composer's reader over it

A whole state read key by key took the provisioner's composition of one node past 30 s and the assigner's compare past
its call bound (ADR 0580 clause 1): each state is now one watch's current values, kept by its changes; a build is read
by key and a manifest once per digest.

Claude-Session: https://claude.ai/code/session_01NcbgfJ9Gum47zkFKWRaovL

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)