Deliver a merge whose walk said its modules matched what runs, instead of stopping it as stranded (hq issue 611)

A walk that moved nothing because every module's recorded build source held none of the changed files now
says so per module (delivery.unchanged). Such a merge moves nothing (ADR 0270 §1): it is delivered, naming
the modules, not stopped 20 minutes later with the operator asked about a change already on every machine.
A module the walk neither built nor said unchanged still stops it (issue 474).

modules/mesh-delivery/cmd/mesh-delivery/issue611_test.go

@@ -0,0 +1,150 @@
+package main
+
+import (
+	"sort"
+	"strings"
+	"testing"
+	"time"
+)
+
+// novox/hq issue 611: mesh-controller #293 changed one test file. Its check's plan, made while another walk built
+// build-agent and route-proxy, read them whole and named them; at the cut their recorded build sources held none of
+// its files, so its walk was done with no tier, "moved nothing the mesh holds: nothing to walk". The stranded rule
+// (issue 474) read that as "ended without building build-agent, route-proxy", stopped it, and the operator was asked
+// about a change already on every machine. The controller now says per module that the build matched what runs
+// (the walk's delivery.unchanged), and such a delivery is delivered: its merge moves nothing (ADR 0270 §1). A walk
+// that says neither — not built, not unchanged — still stops it.
+
+const (
+	head293  = "94c928b4c7e1d2aa"
+	merge293 = "8f1aec0f2b9d6e11"
+	walk293  = "plan-1791867648768608552"
+)
+
+var at293 = time.Date(2026, 10, 13, 5, 10, 0, 0, time.UTC)
+
+// matched is the why the controller gives a module it says unchanged.
+const matched = "its build source in novox/mesh-controller holds none of the 1 changed file(s) " +
+	"(e.g. internal/builder/replay363_test.go): the build the mesh holds is its build"
+
+// replay293 is #293 checked moving build-agent and route-proxy, merged, and its walk done with no tier, saying the
+// modules named unchanged.
+func replay293(t *testing.T, unchanged map[string]string) *world {
+	t.Helper()
+	w := newWorldOver(t, newMemStore(), newFakeController(), newFakeForge(), at293.Add(-time.Minute))
+	p := pr(ctl474, 293, head293, "fix/363-replay", "internal/builder/replay363_test.go")
+	w.h.PullUpdated(p)
+	w.h.Checked(verdictMoving(ctl474, 293, head293, "build-agent", "route-proxy"))
+	w.later(time.Minute)
+	w.h.PullMerged(mergedAt(p, merge293, at293))
+	w.later(90 * time.Second)
+	note := nothingNote
+	if len(unchanged) > 0 {
+		note += "; unchanged, the build the mesh holds is theirs: " + strings.Join(sortedKeys(unchanged), ", ")
+	}
+	w.h.WalkMoved(w.ctl.put(Walk{ID: walk293, Repository: ctl474, Branch: "main", Commit: merge293, Created: w.now,
+		Updated: w.now, State: walkDone, Tiers: [][]string{}, Modules: map[string]*WalkModule{}, Note: note,
+		Delivery: &WalkDelivery{Awaits: "mesh-delivery", Merges: []WalkMerge{{Repository: ctl474, Commit: merge293}},
+			Unchanged: unchanged}}))
+	w.settleAll()
+	return w
+}
+
+// The live case: every module its plan named, the walk said matched what runs. Delivered at once, naming them, a
+// success on the pull request, and nothing listed by stalled or asked of the operator, then or past the grace.
+func TestAMergeWhoseModulesMatchWhatRunsIsDelivered(t *testing.T) {
+	w := replay293(t, map[string]string{"build-agent": matched, "route-proxy": matched})
+	id := IDOf(ctl474, head293)
+	d := w.delivery(id)
+	if d.State != Delivered {
+		t.Fatalf("#293, its modules said unchanged by its walk, is %s, waiting for %q", d.State, w.h.waitsFor(d))
+	}
+	why := d.Transitions[len(d.Transitions)-1].Why
+	for _, want := range []string{walk293, "build-agent, route-proxy", "matched what runs"} {
+		if !strings.Contains(why, want) {
+			t.Fatalf("delivered as %q, not saying %q", why, want)
+		}
+	}
+	if d.Stranded != "" {
+		t.Fatalf("it was read as stranded: %q", d.Stranded)
+	}
+	status := w.forge.statuses["novox/mesh-controller@"+head293+" mesh/delivery"]
+	if !strings.HasPrefix(status, "success ") {
+		t.Fatalf("mesh/delivery says %q", status)
+	}
+	w.later(strandedAfter + time.Minute)
+	w.settleAll()
+	if s := w.state(id); s != Delivered {
+		t.Fatalf("past the grace it is %s", s)
+	}
+	if lines := w.h.Stalled(); len(lines) != 0 {
+		t.Fatalf("stalled lists %+v", lines)
+	}
+}
+
+// A walk that said only one of its modules unchanged left the other unbuilt: it is still stopped past the grace,
+// naming only the module nothing delivered.
+func TestAMergeWithAModuleNeitherBuiltNorUnchangedIsStillStopped(t *testing.T) {
+	w := replay293(t, map[string]string{"build-agent": matched})
+	id := IDOf(ctl474, head293)
+	if s := w.state(id); s != Published {
+		t.Fatalf("within the grace it is %s", s)
+	}
+	w.later(strandedAfter + time.Minute)
+	w.settleAll()
+	d := w.delivery(id)
+	if d.State != Stopped {
+		t.Fatalf("route-proxy neither built nor unchanged, it is %s", d.State)
+	}
+	why := d.Transitions[len(d.Transitions)-1].Why
+	if !strings.Contains(why, "without building route-proxy (") {
+		t.Fatalf("its stop says %q", why)
+	}
+}
+
+// A walk that says nothing unchanged — a controller from before, or one that built nothing at all — stops it as
+// before (issue 474).
+func TestAMergeWhoseWalkSaysNothingUnchangedIsStillStopped(t *testing.T) {
+	w := replay293(t, nil)
+	w.later(strandedAfter + time.Minute)
+	w.settleAll()
+	if d := w.delivery(IDOf(ctl474, head293)); d.State != Stopped ||
+		!strings.Contains(d.Stranded, "without building build-agent, route-proxy") {
+		t.Fatalf("it is %s: %q", d.State, d.Stranded)
+	}
+}
+
+// Batched behind a later merge of its branch (issue 474's shape), a merge whose module the walk said unchanged moves
+// nothing at either commit: delivered, not covered by a later merge that delivered nothing for it.
+func TestABatchedMergeWhoseModuleMatchesWhatRunsIsDelivered(t *testing.T) {
+	w := newWorldOver(t, newMemStore(), newFakeController(), newFakeForge(), at215.Add(-time.Minute))
+	p215 := pr(ctl474, 215, head215, "fix/431-make-check-runs-what-the-gate-runs", "Makefile")
+	p217 := pr(ctl474, 217, head217, "fix/432-a-test-reads-what-it-carries", "cmd/mesh-controller/check_test.go")
+	w.h.PullUpdated(p215)
+	w.h.PullUpdated(p217)
+	w.h.Checked(verdictMoving(ctl474, 215, head215, "build-agent"))
+	w.h.Checked(verdictMoving(ctl474, 217, head217))
+	w.later(time.Minute)
+	w.h.PullMerged(mergedAt(p215, merge215, at215))
+	w.later(time.Minute)
+	w.h.PullMerged(mergedAt(p217, merge217, at215.Add(56*time.Second)))
+	w.later(90 * time.Second)
+	w.h.WalkMoved(w.ctl.put(Walk{ID: batchWalk, Repository: ctl474, Branch: "main", Commit: merge217, Created: w.now,
+		Updated: w.now, State: walkDone, Tiers: [][]string{}, Modules: map[string]*WalkModule{}, Note: nothingNote,
+		Delivery: &WalkDelivery{Awaits: "mesh-delivery", Merges: []WalkMerge{
+			{Repository: ctl474, Commit: merge215, Carried: merge217}, {Repository: ctl474, Commit: merge217}},
+			Unchanged: map[string]string{"build-agent": "its build source holds none of the 2 changed file(s)"}}}))
+	w.settleAll()
+	if d := w.delivery(IDOf(ctl474, head215)); d.State != Delivered {
+		t.Fatalf("#215, build-agent said unchanged by its batch's walk, is %s, waiting for %q", d.State, w.h.waitsFor(d))
+	}
+}
+
+func sortedKeys(m map[string]string) []string {
+	var out []string
+	for k := range m {
+		out = append(out, k)
+	}
+	sort.Strings(out)
+	return out
+}

modules/mesh-delivery/cmd/mesh-delivery/model.go

@@ -3,6 +3,7 @@ package main
 import (
 	"encoding/json"
 	"fmt"
+	"maps"
 	"regexp"
 	"sort"
 	"strings"
@@ -460,6 +461,11 @@ type WalkDelivery struct {
 	// cut, is the walk under the same id: its next record is `building`. A merge this owner reads in a batch is
 	// not held as unwalked while the batch is heard of.
 	Batch *WalkBatch `json:"batch,omitempty"`
+	// Unchanged are the modules the walk did not build because their build source holds none of the files its
+	// merges changed, each with why (novox/hq issue 611, ADR 0267 §5): the build the mesh holds is theirs. A delivery
+	// plan that read them whole names them; this says they matched what runs, not that the walk left them unbuilt.
+	// Absent from a controller that does not say it.
+	Unchanged map[string]string `json:"unchanged,omitempty"`
 }
 
 // WalkMerge is one merge a walk answers.
@@ -583,6 +589,9 @@ type WalkSeen struct {
 	// from them.
 	Moved     []string `json:"moved,omitempty"`
 	MovedSaid bool     `json:"moved_said,omitempty"`
+	// Unchanged are the modules the walk said matched what runs, with why (novox/hq issue 611): not built, and
+	// nothing for it to deliver.
+	Unchanged map[string]string `json:"unchanged,omitempty"`
 }
 
 // Seen is a walk as a delivery keeps it.
@@ -594,6 +603,9 @@ func (w Walk) Seen() *WalkSeen {
 		s.Waits = d.Awaits != "" && d.Go == nil
 		s.GoBy = d.By
 		s.StoppedBy, s.StoppedWhy = d.Stopped, d.StoppedWhy
+		if len(d.Unchanged) > 0 {
+			s.Unchanged = maps.Clone(d.Unchanged)
+		}
 	}
 	s.Branch = w.Branch
 	s.Created = w.Created
@@ -644,9 +656,10 @@ func (d *Delivery) stoppedWords() string {
 	return s
 }
 
-// walkMovedItsModules is whether the walk it follows built every module its plan moves, and whether that is known:
-// from the modules the walk's record names, or, for a record kept before they were, from a walk of no tier, which
-// moved nothing. Unknown when its plan is not known.
+// walkMovedItsModules is whether the walk it follows answered every module its plan moves, and whether that is
+// known: each built, or said unchanged — its build source holds none of the files the walk's merges changed, so the
+// build the mesh holds is its build (novox/hq issue 611) — from the modules the walk's record names, or, for a
+// record kept before they were, from a walk of no tier, which moved nothing. Unknown when its plan is not known.
 func (d *Delivery) walkMovedItsModules() (moved, known bool) {
 	if d.Walk == nil || d.Plan == nil {
 		return false, false
@@ -654,28 +667,46 @@ func (d *Delivery) walkMovedItsModules() (moved, known bool) {
 	if !d.Walk.MovedSaid && d.Walk.Tiers > 0 {
 		return false, false
 	}
-	for _, m := range d.Plan.Moved {
-		if !containsString(d.Walk.Moved, m) {
-			return false, true
-		}
-	}
-	return true, true
+	return len(d.notMovedBy()) == 0, true
 }
 
-// notMovedBy is the modules its plan moves that the walk it follows did not build.
+// notMovedBy is the modules its plan moves that the walk it follows neither built nor said unchanged: what a walk
+// that ended without building them left undelivered.
 func (d *Delivery) notMovedBy() []string {
 	var out []string
 	if d.Walk == nil || d.Plan == nil {
 		return nil
 	}
 	for _, m := range d.Plan.Moved {
-		if !containsString(d.Walk.Moved, m) {
+		if _, unchanged := d.Walk.Unchanged[m]; !containsString(d.Walk.Moved, m) && !unchanged {
 			out = append(out, m)
 		}
 	}
 	return out
 }
 
+// unchangedOfIts is the modules its plan moves that the walk it follows said matched what runs, sorted (novox/hq
+// issue 611).
+func (d *Delivery) unchangedOfIts() []string {
+	var out []string
+	if d.Walk == nil || d.Plan == nil {
+		return nil
+	}
+	for _, m := range d.Plan.Moved {
+		if _, unchanged := d.Walk.Unchanged[m]; unchanged && !containsString(d.Walk.Moved, m) {
+			out = append(out, m)
+		}
+	}
+	sort.Strings(out)
+	return out
+}
+
+// builtNoneOfIts is whether the walk it follows built none of the modules its plan moves and said each unchanged:
+// its merge moves nothing, whichever commit the walk carried (ADR 0270 §1).
+func (d *Delivery) builtNoneOfIts() bool {
+	return d.Plan != nil && len(d.Plan.Moved) > 0 && len(d.unchangedOfIts()) == len(d.Plan.Moved)
+}
+
 // Started is whether the walk is past its wait: it waited for nobody, or was let go — whatever came of it
 // since. A walk superseded or stopped while it waited never started.
 func (s *WalkSeen) Started() bool { return s != nil && !s.Waits && (s.WaitedFor == "" || s.GoBy != "") }

modules/mesh-delivery/cmd/mesh-delivery/table.go

@@ -249,19 +249,31 @@ var Table = []Row{
 		}},
 	{From: []State{Published}, Event: EvDone, To: Delivered,
 		Guard: "nothing for a walk to move; or its walk, carrying its own commit, ended done before its word having built " +
-			"every module it moves (novox/hq issue 474)",
+			"every module it moves or said it unchanged (novox/hq issue 474); or its walk said every module it moves " +
+			"unchanged, its build source holding none of the files changed, so it moves nothing (novox/hq issue 611, " +
+			"ADR 0270 §1)",
 		Holds: func(d *Delivery, f Facts) error {
 			if d.Walk == nil && d.MovesNothing() {
 				return nil
 			}
 			moved, _ := d.walkMovedItsModules()
-			return unless(d.endedUnstarted() && !d.carriedLater() && moved, "a walk moves it")
+			return unless(d.endedUnstarted() && moved && (!d.carriedLater() || d.builtNoneOfIts()), "a walk moves it")
 		},
 		Says: func(d *Delivery) string {
 			if d.Walk == nil {
 				return "nothing for a walk to move"
 			}
-			return fmt.Sprintf("its walk %s ended done before its word, having built every module it moves", d.Walk.ID)
+			unchanged := d.unchangedOfIts()
+			switch {
+			case len(unchanged) == 0:
+				return fmt.Sprintf("its walk %s ended done before its word, having built every module it moves", d.Walk.ID)
+			case d.builtNoneOfIts():
+				return fmt.Sprintf("its walk %s moved nothing: %s matched what runs, its build source holding none of "+
+					"the files changed, so the build the mesh holds is its build (novox/hq issue 611)", d.Walk.ID,
+					strings.Join(unchanged, ", "))
+			}
+			return fmt.Sprintf("its walk %s ended done before its word, having built every module it moves but %s, "+
+				"which matched what runs (novox/hq issue 611)", d.Walk.ID, strings.Join(unchanged, ", "))
 		}},
 	{From: []State{Published, Ready}, Event: EvHold, To: Held,
 		Guard: "something holds it for a person: its group's composed check did not pass for the heads that merged, " +