The node composes again only when what it composes from changed, so a want, placement, module or value written again asks the vault nothing (issue 774)

Every put under want.<node>.>, every module's take-in and every placement write
made a pass, and each pass asked the vault for the node's own secrets. The
shadow's change check moves onto the composer, gains the want (by its
fingerprint, the only part composed) and serves both loops.

internal/selfcompose/shadow.go

@@ -4,7 +4,6 @@ import (
 	"bytes"
 	"context"
 	"fmt"
-	"reflect"
 	"sort"
 	"strings"
 	"sync"
@@ -231,7 +230,7 @@ func (s *Shadow) Run(ctx context.Context) error {
 			case t.in == 6:
 				changed = s.takeWant(t.u)
 			default:
-				changed = s.takeChanged(ins[t.in], t.u)
+				changed = c.takeChanged(ins[t.in], t.u)
 			}
 			if changed {
 				if t.in != 0 {
@@ -264,53 +263,6 @@ func (s *Shadow) Run(ctx context.Context) error {
 	}
 }
 
-// takeChanged takes u through in.take and says whether the entry it names changed: a placement, a module or a config
-// value written again with the value it held changes nothing composed.
-func (s *Shadow) takeChanged(in input, u agent.Update) bool {
-	before, had, known := s.entry(in.bucket, u.Key)
-	in.take(s.c, u)
-	if !known {
-		return true
-	}
-	after, has, _ := s.entry(in.bucket, u.Key)
-	return had != has || !reflect.DeepEqual(before, after)
-}
-
-// entry is what the composer holds of one key of bucket, whether it holds it, and whether the bucket is one it knows.
-func (s *Shadow) entry(bucket, key string) (v any, has, known bool) {
-	c := s.c
-	c.mu.Lock()
-	defer c.mu.Unlock()
-	switch bucket {
-	case delivery.PlacementBucket:
-		node, err := delivery.ParsePlacementKey(key)
-		if err != nil {
-			return nil, false, true
-		}
-		p, ok := c.placements[node]
-		return p, ok, true
-	case delivery.ModulesBucket:
-		name, err := delivery.ParseModulesKey(key)
-		if err != nil {
-			return nil, false, true
-		}
-		m, ok := c.modules[name]
-		return m, ok, true
-	case ResolvedBucket:
-		rest, ok := strings.CutPrefix(key, c.env.Node+".")
-		if !ok {
-			return nil, false, true
-		}
-		module, k, ok := strings.Cut(rest, ".")
-		if !ok {
-			return nil, false, true
-		}
-		val, ok := c.values[module][k]
-		return val, ok, true
-	}
-	return nil, false, false
-}
-
 // revsOf is a proposal's keys' revisions, by node, as one word.
 func revsOf(keys map[string]candidateKey) string {
 	nodes := make([]string, 0, len(keys))