Say why assign finds no module, and keep an assignment pending on its build

A merge asks for a new module's build, and assign answered "no module of that
name" until the build registered it, which read as a module nobody registered
(hq issue 325). Keep every build request, tell a build in flight, a module
known and not built, and an unknown name apart, and make an assignment made
while the build runs when the build registers the module.

cmd/mesh-controller/build.go

@@ -462,6 +462,17 @@ func buildOneAsked(ctx context.Context, source buildSource, path, ref string, wa
 	}
 	defer ask.Close()
 	fmt.Printf("  of %s\n", seat)
+	// Kept before it is asked, so `assign` knows a module is coming while its build runs (novox/hq issue 325).
+	// A dry run registers nothing, and is not kept.
+	if !dryRun {
+		if open, err := openStores(ctx); err == nil {
+			recordBuildRequest(ctx, open.inventory, inventory.BuildRequest{ID: request.ID,
+				Repository: source.Repository, Seat: source.Seat, Path: path, Ref: ref, For: "build"})
+			open.Close()
+		} else {
+			fmt.Fprintf(os.Stderr, "build %s is asked and not kept as a build request: %v\n", request.ID, err)
+		}
+	}
 
 	if wait == 0 {
 		// Asked and not waited for (novox/hq issue 176): the outcome is the role's event, and the
@@ -492,6 +503,10 @@ func buildOneAsked(ctx context.Context, source buildSource, path, ref string, wa
 	}
 	defer open.Close()
 	manifest, kept, err := takeIn(ctx, open.inventory, result)
+	// The assignments pending on this build, made or ended (novox/hq issue 325).
+	for _, line := range settlePendingOnBuild(ctx, open, result, manifest.Module, err) {
+		fmt.Printf("  %s\n", line)
+	}
 	if err != nil {
 		return request.ID, err
 	}
@@ -771,6 +786,11 @@ type answers struct {
 	// handed to the operator; healsUnread why it could not be read.
 	heals       *healsCount
 	healsUnread string
+	// pending is every assignment waiting for its module's build, and every one ended in the last day
+	// (novox/hq issue 325); pendingUnread why they could not be read. One waiting, or one ended other than
+	// applied, is not well: an assignment somebody made is not made yet, or will not be.
+	pending       []inventory.PendingAssignment
+	pendingUnread string
 }
 
 // heldBy is every artifact this mesh has built, for a build that may need one as its base.