The indexer takes the engine's want as its build only while the apply is in progress (issue 1921)

Claude-Session: https://claude.ai/code/session_01NcbgfFSnn24M3GcqttoU7i

modules/mesh-delivery-indexer/cmd/mesh-delivery-indexer/named_test.go

@@ -74,6 +74,9 @@ func TestTheTrunkIsTheDirectoriesTheForgeListsTrees(t *testing.T) { // 1900/AC3
 	for _, row := range []struct{ name, answer, want string }{
 		{"replacing: runs old, want new and self", `{"runs":{"fp":"src2:old"},"want":{"fp":"src2:new","self":true}}`, "src2:new"},
 		{"a want the node does not compose", `{"runs":{"fp":"src2:old"},"want":{"fp":"src2:new"}}`, "src2:old"},
+		{"replacing: the apply of the want failed or is held", `{"runs":{"fp":"src2:old"},"want":{"fp":"src2:new","self":true},"attempt":{"fp":"src2:new","held":true}}`, "src2:old"},
+		{"replacing: an attempt of another build", `{"runs":{"fp":"src2:old"},"want":{"fp":"src2:new","self":true},"attempt":{"fp":"src2:older"}}`, "src2:new"},
+		{"the want already runs", `{"runs":{"fp":"src2:new"},"want":{"fp":"src2:new","self":true}}`, "src2:new"},
 		{"a removed want", `{"runs":{"fp":"src2:old"},"want":{"fp":"src2:new","self":true,"removed":true}}`, "src2:old"},
 		{"no build runs yet, want self", `{"want":{"fp":"src2:new","self":true}}`, "src2:new"},
 	} {

modules/mesh-delivery-indexer/cmd/mesh-delivery-indexer/ownbuild.go

@@ -30,15 +30,26 @@ func ownBuildVia(call toolCaller, node string) func(ctx context.Context) (string
 				Self    bool   `json:"self"`
 				Removed bool   `json:"removed"`
 			} `json:"want"`
+			// Attempt is the engine's last apply that did not end running (failed, or held), with the build it was of.
+			Attempt *struct {
+				FP string `json:"fp"`
+			} `json:"attempt"`
 		}
 		if err := json.Unmarshal(raw, &a); err != nil {
 			return "", fmt.Errorf("the answer of %s is not a composition: %w", compositionVerb, err)
 		}
-		// While the engine replaces the indexer, this process is the successor: what runs still names the old build, and the want,
-		// composed by the node itself (self), names this one. The start fixes that build (quick fix, ADR 0639 §7: nothing is learnt
-		// later and nothing waits on a timer); a process of the old build that is started again in that window would take it too.
-		if a.Want != nil && a.Want.Self && !a.Want.Removed && a.Want.FP != "" {
-			return a.Want.FP, nil
+		// While the engine's apply of the want is in progress (what runs still names the old build, the want names another, and no
+		// attempt names that want as failed or held), this process is the successor and fixes the want's build. self is the node's
+		// standing way of composing the module, not a mark of this process, so it is not enough alone: an old process started again
+		// while the want names a successor that does not run (its apply failed or is held) takes what runs. The start fixes the
+		// build once (quick fix, ADR 0639 §7: nothing is learnt later, nothing waits on a timer); the thorough form is the
+		// engine passing each process the fingerprint it starts it with.
+		running := ""
+		if a.Runs != nil {
+			running = a.Runs.FP
+		}
+		if w := a.Want; w != nil && w.Self && !w.Removed && w.FP != "" && w.FP != running && (a.Attempt == nil || a.Attempt.FP != w.FP) {
+			return w.FP, nil
 		}
 		if a.Runs == nil || a.Runs.FP == "" {
 			return "", errors.New("the engine says no fingerprint of the indexer runs")