Catch up on merges the bus announced and never handed over (hq issue 266)

The controller acted only on what its events consumer handed it, so a merge
the bus skipped left modules behind with nothing said. The stream is now read
back every five minutes on a single-filter consumer, and any merge that would
still move a module after ten minutes is said and acted on.

cmd/mesh-controller/missed_merges.go

@@ -0,0 +1,131 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"time"
+
+	"github.com/novox/mesh-controller/internal/inventory"
+	"github.com/novox/mesh-controller/internal/link"
+)
+
+// **A merge the bus announced and the controller never acted on is caught up** (novox/hq issue 266).
+//
+// The forge's poll announces every merge on the events stream, and the controller acts on what its
+// consumer there hands it. On 2026-10-06 one merge was on the stream and never handed over: the bus
+// server moved the consumer past it — a fault of consumers with several filters in the server the
+// mesh ran — and the controller, which only acts on what it is handed, said nothing. The modules
+// built from that repository stayed behind and were built by hand.
+//
+// So the stream is read back on a timer, on a consumer of its own filtered on merges alone, and every
+// announcement older than mergeGrace is judged as SourceMoved would judge it. **No record of what
+// was handled is kept, because none is needed**: acting on a merge marks every module it moved as
+// looked at since, so an announcement already acted on reads as history and moves nothing. One that
+// would still move something was never acted on — it is said, and acted on now.
+const (
+	// mergeGrace is how long an announcement is left to the controller's own consumer before it is
+	// judged missed. That consumer hands over one event at a time, and a merge waits behind a build
+	// outcome that is being acted on; acting on a merge itself asks builds and does not wait for them.
+	mergeGrace = 10 * time.Minute
+	// mergeLookBack is how far back a pass reads. A merge missed longer ago than this was missed by a
+	// controller that was not running this, and is the operator's to look at, not a surprise rebuild.
+	mergeLookBack = 24 * time.Hour
+	// mergeCatchUpEvery is how often the stream is read back.
+	mergeCatchUpEvery = 5 * time.Minute
+)
+
+// merges is what reads back the forge's announcements; the link server, or a test's list.
+type merges interface {
+	AnnouncedMerges(ctx context.Context, since time.Time) ([]link.AnnouncedMerge, error)
+}
+
+// catchingUpOnMerges reads back the forge's announcements on a timer, until the context ends.
+func catchingUpOnMerges(ctx context.Context, open *stores, announced merges) {
+	f := following{open}
+	catalogued := func(ctx context.Context) ([]inventory.Entry, map[string][]inventory.ReadRepository, error) {
+		entries, err := open.inventory.Catalogued(ctx)
+		if err != nil {
+			return nil, nil, err
+		}
+		read, err := open.inventory.ReadRepositories(ctx)
+		return entries, read, err
+	}
+	failing := ""
+	tick := time.NewTicker(mergeCatchUpEvery)
+	defer tick.Stop()
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		case <-tick.C:
+		}
+		err := catchUpOnMerges(ctx, time.Now(), announced, catalogued, f.SourceMoved, func(format string, args ...any) {
+			fmt.Printf(format+"\n", args...)
+		})
+		// A pass that cannot read says so once, not every five minutes, and says when it reads again.
+		why := ""
+		if err != nil {
+			why = err.Error()
+		}
+		if why != failing {
+			if why != "" {
+				fmt.Printf("merges the bus may not have handed over cannot be looked for: %s\n", why)
+			} else {
+				fmt.Println("merges the bus may not have handed over are looked for again")
+			}
+			failing = why
+		}
+	}
+}
+
+// catchUpOnMerges is one pass: every announcement older than mergeGrace that acting on would still
+// move something is said and acted on, oldest first.
+//
+// Judged twice: once against the catalogue as the pass found it, and again just before acting,
+// because acting on an earlier missed merge of the same repository may have moved what a later one
+// would have.
+func catchUpOnMerges(ctx context.Context, now time.Time, announced merges,
+	catalogued func(context.Context) ([]inventory.Entry, map[string][]inventory.ReadRepository, error),
+	act func(context.Context, link.SourceMoved) error, say func(string, ...any)) error {
+
+	all, err := announced.AnnouncedMerges(ctx, now.Add(-mergeLookBack))
+	if err != nil {
+		return err
+	}
+	entries, read, err := catalogued(ctx)
+	if err != nil {
+		return err
+	}
+	for _, a := range all {
+		if now.Sub(a.At) < mergeGrace {
+			continue
+		}
+		if len(wouldMove(a.SourceMoved, entries, read)) == 0 {
+			continue
+		}
+		if entries, read, err = catalogued(ctx); err != nil {
+			return err
+		}
+		moves := wouldMove(a.SourceMoved, entries, read)
+		if len(moves) == 0 {
+			continue
+		}
+		var names []string
+		for _, e := range moves {
+			names = append(names, e.Manifest.Module)
+		}
+		say("%s/%s merged into %s (%.8s), announced %s ago, and the controller never acted on it: the bus "+
+			"did not hand the announcement over (novox/hq issue 266). %s %s behind it; acting on it now",
+			a.Owner, a.Repo, a.Base, a.Commit, now.Sub(a.At).Round(time.Minute), readableList(names),
+			isAre(len(names)))
+		if err := act(ctx, a.SourceMoved); err != nil {
+			say("%s/%s moved to %.8s and the mesh could not act on it: %v; the next pass tries again",
+				a.Owner, a.Repo, a.Commit, err)
+			continue
+		}
+		if entries, read, err = catalogued(ctx); err != nil {
+			return err
+		}
+	}
+	return nil
+}