S3: the seat-list reader asks again on a timeout (issue 1966, ADR 0668)

Closes the gap #184 left: the read is safe to repeat, so a timed-out ask is asked again.

Claude-Session: https://claude.ai/code/session_01JG73KEq4zoDfM9WtYpcQgZ

go/seatlist/seatlist.go

@@ -8,7 +8,8 @@
 // one seat (that definition, Answer); the seat's two events, whose bodies name the seat (Changed). It calls the seat,
 // never the module that holds it, and only trunk definitions are held: a pull request's are the indexer's to judge.
 // An ask that reached no one (busretry.Undelivered: the bus's "no responders", as while the seat's holder re-serves) is
-// asked again within the bus's retry bound (busretry.Bound, about 30 s, backing off; issue 774's form, issue 1966).
+// asked again within the bus's retry bound (busretry.Bound, about 30 s, backing off; issue 774's form, issue 1966), and so is one
+// that timed out: the ask is a read, safe to make again (busretry.DoRepeatable; novox/hq ADR 0668).
 // Nothing else polls or waits on a timer: a reader that could not ask says so in its Status and reads again on the
 // next event or on Reload, which the host offers as a tool (Tools).
 //
@@ -361,11 +362,12 @@ func (r *Reader) ReloadIfUnread() <-chan struct{} {
 	return done
 }
 
-// ask asks the seat's verb, and again while the ask reached no one, within the bus's retry bound: a holder that re-serves
-// for a few seconds while the reader starts leaves no list unread (issue 1966). An answer, a refusal or a timeout is never
-// asked again.
+// ask asks the seat's verb, and again while the ask reached no one or timed out, within the bus's retry bound: a holder
+// that re-serves for a few seconds while the reader starts leaves no list unread (issue 1966). The ask is a read, so it
+// is safe to make again on a timeout (busretry.DoRepeatable; novox/hq ADR 0668). An answer or a refusal is never asked
+// again.
 func (r *Reader) ask(body map[string]any, what string) (json.RawMessage, error) {
-	return busretry.Do(what, func() (json.RawMessage, error) {
+	return busretry.DoRepeatable(what, func() (json.RawMessage, error) {
 		return r.cfg.Bus.Ask(Key(), body)
 	}, nil)
 }

go/seatlist/seatlist_test.go

@@ -1,6 +1,7 @@
 package seatlist
 
 import (
+	"context"
 	"encoding/json"
 	"errors"
 	"fmt"
@@ -22,6 +23,7 @@ type fakeOwner struct {
 	table    map[string]string // seat -> definition JSON, trunk
 	down     bool
 	silent   int           // when set, so many asks first reach no one (the bus's no responders), as while the holder re-serves
+	timeouts int           // when set, so many asks first time out (a deadline passed, as a callee that restarts mid-ask)
 	gate     chan struct{} // when set, an ask waits for it to be closed
 	asked    []string      // "key seat"
 	handlers map[string]func(string, json.RawMessage) error
@@ -34,6 +36,10 @@ func (f *fakeOwner) Ask(key string, body any) (json.RawMessage, error) {
 	args, _ := body.(map[string]any)
 	seat, _ := args["seat"].(string)
 	f.asked = append(f.asked, key+" "+seat)
+	if f.timeouts > 0 {
+		f.timeouts--
+		return nil, fmt.Errorf("asking %s: %w", key, context.DeadlineExceeded)
+	}
 	if f.silent > 0 {
 		f.silent--
 		return nil, fmt.Errorf("not asked: nothing on this machine answers it (%w)", nats.ErrNoResponders)
@@ -287,6 +293,17 @@ func TestStartReturnsAtOnceAndTheReaderSaysItIsReadingUntilTheSeatAnswers(t *tes
 	if st := r.Status(); !st.Heard || st.LastError != "" || !r.Has("node-b") || len(owner.asked) != 4 {
 		t.Fatalf("after a holder that re-served: %+v, asked %q: want heard on the third ask of the list", st, owner.asked)
 	}
+
+	// Issue 1966, ADR 0668: a read of the list is safe to make again, so an ask that timed out is asked again too.
+	owner = &fakeOwner{timeouts: 1, table: map[string]string{"node-b": def("node-b", "node", "put")}}
+	r, err = Start(Config{Bus: owner, Bootstrap: Bootstrapped()})
+	if err != nil {
+		t.Fatal(err)
+	}
+	<-r.Ready()
+	if st := r.Status(); !st.Heard || st.LastError != "" || !r.Has("node-b") || len(owner.asked) != 3 {
+		t.Fatalf("after an ask that timed out: %+v, asked %q: want heard on the second ask of the list", st, owner.asked)
+	}
 }
 
 // The bootstrap and the tests' seat list are copies of the same contracts files: where a seat is in both, they are equal,