R-1 rest, R-12, R-13: the capability words are mesh-sdk's, the ledger's fill and removal are answered, the artifact states the words

sent-get is under sent-objects-calls; mesh/ledger.fill answers the history's fill against its cap and mesh/ledger.remove
removes an instance's operations, snapshot, state and index entries, both under ledger-upkeep-calls; the runtime artifact's
`states` is exactly the words the runner states.

Builds: design 47 G §462, §488, §545, §587, §622, §155

Claude-Session: https://claude.ai/code/session_01NcbgfGKaxw984XyAPfLm4h

node-tools/internal/bus/ledger.go

@@ -10,6 +10,7 @@ import (
 	"strings"
 	"time"
 
+	"git.novox.be/novox/mesh-sdk/go/buscalls"
 	"git.novox.be/novox/mesh-sdk/go/buscompose"
 	"git.novox.be/novox/mesh-sdk/go/membership"
 	"github.com/nats-io/nats.go"
@@ -143,6 +144,76 @@ func (h *busHistory) Read(keys string, from uint64, limit int) ([]ledger.Kept, e
 	}
 }
 
+// Purge removes every operation of one instance from the history stream, on the module's ledger connection, the one
+// granted the purge of its own ledger's streams.
+func (h *busHistory) Purge(key string) error {
+	return purgeSubject(h.read, h.write, h.stream, h.prefix+"."+key)
+}
+
+// Fill is the history stream's fill against its cap, the cap the manifest gives the ledger.
+func (h *busHistory) Fill() (buscalls.Fill, error) {
+	name := h.stream
+	if name == "" {
+		ctx, cancel := context.WithTimeout(context.Background(), StateTimeout)
+		defer cancel()
+		js, err := h.read.JetStream()
+		if err != nil {
+			return buscalls.Fill{}, err
+		}
+		if name, err = js.StreamNameBySubject(ctx, h.prefix+".>"); err != nil {
+			return buscalls.Fill{}, fmt.Errorf("no stream on the bus keeps %s: %w", h.prefix, err)
+		}
+	}
+	f, err := h.read.streamFill(name)
+	return f.Fill, err
+}
+
+// purgeSubject purges one subject's messages from the stream that keeps it: the stream named, or found on the runner's
+// own connection by its subject, purged on the ledger connection.
+func purgeSubject(read, write *Conn, stream, subject string) error {
+	if write == nil {
+		return errors.New("a ledger's streams are purged only on its module's ledger connection, and none is held")
+	}
+	ctx, cancel := context.WithTimeout(context.Background(), StateTimeout)
+	defer cancel()
+	if stream == "" {
+		js, err := read.JetStream()
+		if err != nil {
+			return err
+		}
+		if stream, err = js.StreamNameBySubject(ctx, subject); err != nil {
+			return fmt.Errorf("no stream on the bus keeps %s: %w", subject, err)
+		}
+	}
+	// The purge is asked of the stream by its name, with no read of its info first: the ledger account is granted the
+	// purge of its own ledger's two streams and nothing else (PurgeAPI).
+	body, err := json.Marshal(map[string]string{"filter": subject})
+	if err != nil {
+		return err
+	}
+	reply, err := write.nc.RequestWithContext(ctx, PurgeAPI(stream), body)
+	if err != nil {
+		return fmt.Errorf("purging %s from %s: %w", subject, stream, err)
+	}
+	var ack struct {
+		Success bool `json:"success"`
+		Error   *struct {
+			Description string `json:"description"`
+		} `json:"error"`
+	}
+	if err := json.Unmarshal(reply.Data, &ack); err != nil || !ack.Success {
+		why := string(reply.Data)
+		if ack.Error != nil {
+			why = ack.Error.Description
+		}
+		return fmt.Errorf("the bus refused the purge of %s from %s: %s", subject, stream, why)
+	}
+	return nil
+}
+
+// PurgeAPI is the bus's subject that purges a stream, the one a ledger account is granted for its own ledger's streams.
+func PurgeAPI(stream string) string { return "$JS.API.STREAM.PURGE." + stream }
+
 type busState struct {
 	c      *Conn
 	bucket string
@@ -231,6 +302,11 @@ func (s *busSnapshots) Get(key string) ([]byte, uint64, error) {
 	return lastOn(s.read, "", s.prefix+"."+key)
 }
 
+// Purge removes one instance's snapshot, on the module's ledger connection.
+func (s *busSnapshots) Purge(key string) error {
+	return purgeSubject(s.read, s.write, "", s.prefix+"."+key)
+}
+
 func (s *busSnapshots) Put(key string, value []byte, expect uint64) error {
 	if s.write == nil {
 		return errors.New("a ledger's snapshot is published only on its module's ledger connection, and none is held")