Keep rollouts and the merges they answer in the rollouts bucket (issue 1092)

Once chain_moved records the kind, a plan is a key of the rollouts bucket under its id and the open batch is the same key in state assembling. A save refuses a copy another save moved since (the plan's own Revision, kept in its value, counts saves) and keeps the merges the record holds, so a copy read before a merge moved cannot lay it back. The merges a batch or walk answers are the record's held field, with the columns the table had; a merge no plan answers stays, flagged, in the record that held it last, or in the record kept for those. A merge moved to a plan is written to the receiving record first and then taken from the giving one; one found in both is read from the one it entered last and repaired at the next cut. Plans and merges are read from a view kept by one watch of the bucket. A bus that does not answer, a lease lost and a key moved are now not-now like the store being away, so a merge whose plan could not be written is held and handed over again, never acknowledged. The start moves release_plan and batched_merge into the bucket, one kind, counted against both tables.

internal/inventory/reachable.go

@@ -1,11 +1,16 @@
 package inventory
 
 import (
+	"context"
 	"errors"
 	"io"
 	"net"
 
 	"github.com/jackc/pgx/v5/pgconn"
+	"github.com/nats-io/nats.go"
+	"github.com/nats-io/nats.go/jetstream"
+
+	"github.com/novox/mesh-controller/internal/chain"
 )
 
 // Unreachable says whether an error means the store could not be asked right now, rather than
@@ -29,6 +34,13 @@ func Unreachable(err error) bool {
 	if err == nil {
 		return false
 	}
+	// The chain on the bus (novox/hq ADR 0408): a bus that does not answer, a lease this controller no longer holds, a key
+	// somebody else wrote first — each is "not now", as the store being away is.
+	if errors.Is(err, chain.ErrNotHeld) || errors.Is(err, chain.ErrMoved) || errors.Is(err, context.DeadlineExceeded) ||
+		errors.Is(err, nats.ErrTimeout) || errors.Is(err, nats.ErrNoResponders) || errors.Is(err, nats.ErrConnectionClosed) ||
+		errors.Is(err, nats.ErrDisconnected) || errors.Is(err, nats.ErrNoServers) || errors.Is(err, jetstream.ErrNoStreamResponse) {
+		return true
+	}
 	var pg *pgconn.PgError
 	if errors.As(err, &pg) {
 		switch pg.Code {