Let a composition not run say why, the assigner not running among it, and name the indexer's words for a removed module, so a check never waits for a composition nobody makes (issue 1297, B3d)

go/delivery/checker.go

@@ -96,10 +96,16 @@ type LevelResult struct {
 
 // The states of a Composition (ADR 0484 clause 6): the composition check is the assigner's, so until it delivers a
 // verdict says CompositionNotRun, and a line never says the composition passed on that.
+//
+// A composition not run may say why in its Words: AssignerNotRunning when no instance of the assigner is online, so a
+// check never waits for a composition nobody is making (issue 1297).
 const (
 	CompositionNotRun = "not-run"
 	CompositionPass   = "pass"
 	CompositionFail   = "fail"
+
+	// AssignerNotRunning is the Words of a composition not run because no instance of the assigner is online.
+	AssignerNotRunning = "the assigner is not running"
 )
 
 // Composition is what the check of the machines' composition made of a verdict: its State (not-run, pass or fail), the
@@ -156,8 +162,8 @@ func (c *Composition) check() error {
 	}
 	switch c.State {
 	case CompositionNotRun:
-		if c.Words != "" || c.SDK != "" || len(c.Machines) > 0 {
-			return fmt.Errorf("delivery: the verdict's composition is not run and says nothing of words, the mesh-sdk commit or machines")
+		if c.SDK != "" || len(c.Machines) > 0 {
+			return fmt.Errorf("delivery: the verdict's composition is not run and names no mesh-sdk commit or machines")
 		}
 	case CompositionPass:
 		if c.SDK == "" {

go/delivery/checker_test.go

@@ -262,6 +262,16 @@ func TestVerdictCarriesSkippedCompositionAndOverBound(t *testing.T) {
 	if _, err := EncodeVerdict(notRun); err != nil {
 		t.Errorf("a composition not yet run refused: %v", err)
 	}
+	// 1297: a composition not run says why when the assigner is not running, and round-trips with its words.
+	notRunning := passVerdict()
+	notRunning.Composition = &Composition{State: CompositionNotRun, Words: AssignerNotRunning}
+	data, err = EncodeVerdict(notRunning)
+	if err != nil {
+		t.Fatalf("a composition not run because the assigner is not running refused: %v", err)
+	}
+	if back, err := DecodeVerdict(data); err != nil || back.Composition.Words != AssignerNotRunning {
+		t.Errorf("its words came back as %+v, %v", back.Composition, err)
+	}
 	failed := passVerdict()
 	failed.State, failed.Failed = VerdictFail, FailedFirst{Machine: "ace", Words: "x"}
 	failed.Composition = &Composition{State: CompositionFail, Words: "path /etc/x is owned by two modules", SDK: failed.SDK, Machines: []string{"ace"}}

go/delivery/source.go

@@ -271,6 +271,10 @@ type CandidatePull struct {
 	Fps     map[string]CandidateModule `json:"fps,omitempty"`
 }
 
+// CandidateNoneNoModule is the None2 of a candidate's module whose directory the merge preview names no manifest for:
+// the change removes the module. The indexer writes it and the assigner reads it as a removal (issue 1297).
+const CandidateNoneNoModule = "the merge preview names no manifest for the module's directory"
+
 // CandidateModule is one touched module's new-form fingerprint FP2 (`src2:` and 64 hex digits), or None2, the reason
 // it has none; exactly one of them. Manifest is the digest of the module's manifest as read at the preview.
 type CandidateModule struct {