From 94893851656724b259c81fbc190d97e07552a1a7 Mon Sep 17 00:00:00 2001
From: jochen <jschoubben@gmail.com>
Date: Thu, 5 Nov 2026 15:35:19 +0100
Subject: [PATCH] seat list: the bus of a process on its own credential (a verb
 called through its connection, the seat's events as handlers of the module's
 event hub), so the checker and the grants part read the list as every part
 does (B7e; issue 1966)

Claude-Session: https://claude.ai/code/session_01NcbgfFSnn24M3GcqttoU7i
---
 go/seatlist/processbus.go      | 44 ++++++++++++++++++++++++++++++++
 go/seatlist/processbus_test.go | 46 ++++++++++++++++++++++++++++++++++
 2 files changed, 90 insertions(+)
 create mode 100644 go/seatlist/processbus.go
 create mode 100644 go/seatlist/processbus_test.go

diff --git a/go/seatlist/processbus.go b/go/seatlist/processbus.go
new file mode 100644
index 0000000..b9a3e88
--- /dev/null
+++ b/go/seatlist/processbus.go
@@ -0,0 +1,44 @@
+package seatlist
+
+import (
+	"encoding/json"
+	"fmt"
+	"strings"
+
+	"github.com/nats-io/nats.go/jetstream"
+
+	"git.novox.be/novox/mesh-sdk/go/seatdef"
+)
+
+// EventHandlers is where a process registers the handler of a subject on the module's one pull of its durable consumer
+// (process.EventHub). Register every handler, then start the hub.
+type EventHandlers interface {
+	Handle(pattern string, handle func(jetstream.Msg)) error
+}
+
+type processBus struct {
+	call func(string, any) (json.RawMessage, error)
+	hub  EventHandlers
+}
+
+// ProcessBus is the bus of a process on its own credential: a verb of the seat is called through its connection
+// (process.Conn.Call), and the seat's events are heard as handlers of the module's event hub, on the seat's own subject
+// (`mesh.seat.<seat>.event.<event>`). The process starts the hub after the reader is started, so every handler is registered.
+func ProcessBus(call func(string, any) (json.RawMessage, error), hub EventHandlers) Bus {
+	return processBus{call: call, hub: hub}
+}
+
+func (b processBus) Ask(key string, body any) (json.RawMessage, error) { return b.call(key, body) }
+
+func (b processBus) Subscribe(pattern string, handle func(key string, body json.RawMessage) error) error {
+	seat, event, ok := strings.Cut(pattern, ".")
+	if !ok || seat == "" || event == "" {
+		return fmt.Errorf("%q is no seat event's pattern, <seat>.<event>", pattern)
+	}
+	return b.hub.Handle(seatdef.EventSubject(seat, event), func(m jetstream.Msg) {
+		// A reader that could not take the event says so in its status and reads again at the next event or by hand
+		// (Reload): the message is not delivered again for it.
+		_ = handle(pattern, m.Data())
+		_ = m.Ack()
+	})
+}
diff --git a/go/seatlist/processbus_test.go b/go/seatlist/processbus_test.go
new file mode 100644
index 0000000..478bfa9
--- /dev/null
+++ b/go/seatlist/processbus_test.go
@@ -0,0 +1,46 @@
+package seatlist
+
+import (
+	"encoding/json"
+	"testing"
+
+	"github.com/nats-io/nats.go/jetstream"
+)
+
+type hubStub map[string]func(jetstream.Msg)
+
+func (h hubStub) Handle(pattern string, f func(jetstream.Msg)) error { h[pattern] = f; return nil }
+
+type msgStub struct {
+	jetstream.Msg
+	data  []byte
+	acked *int
+}
+
+func (m msgStub) Data() []byte { return m.data }
+func (m msgStub) Ack() error   { *m.acked++; return nil }
+
+func TestAProcessBusAsksByKeyAndHearsTheSeatsEventsOnTheHub(t *testing.T) {
+	var asked string
+	hub := hubStub{}
+	bus := ProcessBus(func(key string, body any) (json.RawMessage, error) { asked = key; return json.RawMessage(`{}`), nil }, hub)
+	if _, err := bus.Ask(Key(), nil); err != nil || asked != Key() {
+		t.Fatalf("asked %q, %v", asked, err)
+	}
+	var got []string
+	if err := bus.Subscribe(Pattern(ChangedEvent), func(key string, body json.RawMessage) error { got = append(got, key+" "+string(body)); return nil }); err != nil {
+		t.Fatal(err)
+	}
+	h := hub["mesh.seat."+Seat+".event."+ChangedEvent]
+	if h == nil {
+		t.Fatalf("handlers on %v, want the seat's own subject", hub)
+	}
+	acked := 0
+	h(msgStub{data: []byte(`{"seat":"x"}`), acked: &acked})
+	if len(got) != 1 || got[0] != Pattern(ChangedEvent)+` {"seat":"x"}` || acked != 1 {
+		t.Errorf("heard %v, acked %d", got, acked)
+	}
+	if err := bus.Subscribe("nodot", nil); err == nil {
+		t.Error("a pattern that names no seat event was taken")
+	}
+}