Take no rebuild into a waiting walk, and ask what a tier left unasked (hq issue 754)

A rebuild that landed while a walk waited for mesh-delivery's word was taken as
the walk's build of that module; once let go, the walk asked a tier only when
every module of it was unasked, so it never asked the rest and stood still.

A walk now takes only the outcomes of builds it asked, and none while it waits;
a rebuild does not join a waiting walk and says it runs beside it; and a tier
asked in part is asked the rest, including a module held built that the walk
never asked for, which is somebody else's build and not sent as the walk's.

cmd/mesh-controller/release_plan.go

@@ -259,10 +259,11 @@ func applied(module string, builtAt time.Time, running []string, reports []inven
 	return len(waiting) == 0, waiting
 }
 
-// askTier asks the build machine for every module of the tier, and marks each asked. A module
+// askTier asks the build machine for the named modules of the plan's tier — all of it, or what of it is still
+// unasked (novox/hq issue 754) — and marks each asked. A module
 // the catalogue no longer holds, or whose ask could not be made, is a failure of the plan: a tier
 // half asked is a tier that will never complete.
-func askTier(ctx context.Context, inv *inventory.Inventory, p *inventory.Plan) error {
+func askTier(ctx context.Context, inv *inventory.Inventory, p *inventory.Plan, names []string) error {
 	entries, err := inv.Catalogued(ctx)
 	if err != nil {
 		return err
@@ -271,12 +272,62 @@ func askTier(ctx context.Context, inv *inventory.Inventory, p *inventory.Plan) e
 	for _, e := range entries {
 		byName[e.Manifest.Module] = e
 	}
-	for _, name := range p.Tiers[p.Tier] {
+	for _, name := range names {
 		askModule(ctx, p, name, byName)
 	}
 	return nil
 }
 
+// unaskedOf are the modules of a plan's current tier it has still to ask: those it never asked, and one it holds
+// built that it never asked for (novox/hq issue 754) — a build taken in by a controller from before a walk took
+// only its own asks, somebody else's, which the walk would otherwise send as its own (ADR 0219). A tier partly asked is asked the rest, not
+// waited on for ever: a walk that waits for every build of a tier it never asked whole never moves again.
+func unaskedOf(p inventory.Plan) []string {
+	if p.Tier >= len(p.Tiers) {
+		return nil
+	}
+	var out []string
+	for _, m := range p.Tiers[p.Tier] {
+		s := p.Modules[m]
+		switch {
+		case s == nil || s.State == "":
+			out = append(out, m)
+		case s.State == "built" && s.Build == "" && s.AskedAt == nil:
+			out = append(out, m)
+		}
+	}
+	return out
+}
+
+// askedInTier says the plan asked a module of its current tier itself: under an id, or at a time it kept.
+func askedInTier(p inventory.Plan) bool {
+	if p.Tier >= len(p.Tiers) {
+		return false
+	}
+	for _, m := range p.Tiers[p.Tier] {
+		if s := p.Modules[m]; s != nil && (s.Build != "" || s.AskedAt != nil) {
+			return true
+		}
+	}
+	return false
+}
+
+// takesOutcome says whether a build's outcome is the plan's for a module of its current tier (novox/hq ADR 0219,
+// issues 219 and 754). **A walk that waits for its delivery's word asks nothing, and so is answered by nothing**
+// (ADR 0239): a rebuild that lands in the wait is somebody else's build. **Nor is a module the plan never asked
+// answered**: taken, the plan held a module built that it never asked, and waited for the rest of the tier for
+// ever. Asked under an id, the plan takes that id's outcome and no other; asked before ids were kept, a build
+// asked at or after the plan's ask.
+func takesOutcome(p inventory.Plan, state *inventory.PlanModule, asked time.Time, id string) bool {
+	if p.Waiting() || state == nil || (state.Build == "" && state.AskedAt == nil) {
+		return false
+	}
+	if state.Build != "" {
+		return state.Build == id
+	}
+	return !askedBefore(asked, state.AskedAt)
+}
+
 // askABuild is how a plan asks for one build, not waited for, and learns the id it asked under. A
 // variable so a test of what a plan does around an ask needs no build machine.
 //
@@ -526,22 +577,15 @@ func planBuiltSaying(ctx context.Context, open *stores, module, commit, failed s
 		if !inTier {
 			continue
 		}
-		state := p.Modules[module]
-		if state == nil {
-			state = &inventory.PlanModule{}
-			p.Modules[module] = state
-		}
 		// **The plan's own ask is its outcome, by id** (novox/hq ADR 0219); another build of the module
 		// is, as before, when it was asked at or after the plan's ask (issue 219).
 		// **A module asked under an id is answered by that id's outcome and no other** (novox/hq ADR
 		// 0219): a replay, a rebuild beside the plan, or an older ask finishing late is somebody else's
 		// build, made from other source, and settling the plan with it would send that. A plan from
-		// before ids were kept is matched as it was: by when the build was asked (issue 219).
-		if state.Build != "" {
-			if state.Build != id {
-				continue
-			}
-		} else if askedBefore(asked, state.AskedAt) {
+		// before ids were kept is matched as it was: by when the build was asked (issue 219). A walk
+		// waiting for its word, or a module it never asked, takes no outcome at all (issue 754).
+		state := p.Modules[module]
+		if !takesOutcome(*p, state, asked, id) {
 			continue
 		}
 		if failed != "" && deletedAtSource(failed) {
@@ -747,17 +791,11 @@ func advanceOnce(ctx context.Context, open *stores, p *inventory.Plan,
 		return true, nil
 	}
 	tier := p.Tiers[p.Tier]
-	// Not yet asked: ask.
-	unasked := 0
-	for _, m := range tier {
-		if s := p.Modules[m]; s == nil || s.State == "" {
-			unasked++
-		}
-	}
-	if unasked == len(tier) {
+	// Not yet asked: ask — the whole tier, or what of it is still unasked (novox/hq issue 754).
+	if unasked := unaskedOf(*p); len(unasked) > 0 {
 		// **One walk at a time** (novox/hq ADR 0276): a walk about to ask its first tier while another started
 		// walk is open waits for that one to end, let go or not, and says so.
-		if p.Tier == 0 {
+		if p.Tier == 0 && !askedInTier(*p) {
 			if behind, err := startedBeside(ctx, inv, p.ID, p.Created); err != nil {
 				return false, err
 			} else if behind != "" {
@@ -767,7 +805,10 @@ func advanceOnce(ctx context.Context, open *stores, p *inventory.Plan,
 				return changed, nil
 			}
 		}
-		if err := askTier(ctx, inv, p); err != nil {
+		if len(unasked) < len(tier) {
+			fmt.Printf("%s: tier %d was asked in part; asking the rest: %s\n", p.ID, p.Tier, strings.Join(unasked, ", "))
+		}
+		if err := askTier(ctx, inv, p, unasked); err != nil {
 			return false, err
 		}
 		return true, nil