node-tools: say whose words a refused event is (hq issue 276)

"plex did not take radarr.download.completed: Unexpected end of JSON input"
read as the runtime failing to parse the bundle's answer. It was plex's own
handler error, relayed. A bundle's error answer is now a launch.Refused, and
the line says the handler answered an error, quotes it, names the event id
and the delay before the next offer; the runtime's own failures (no answer
in time, bundle exited) are said as before.

The rule, unchanged and now tested: any mesh/event answer that is not an
error takes the event, whatever its result says, including none.

node-tools/internal/launch/launch.go

@@ -65,6 +65,17 @@ type Bus interface {
 // EventTimeout bounds how long a bundle has to handle one event before it is offered again.
 var EventTimeout = 2 * time.Minute
 
+// Refused is a bundle's error answer to what the runtime asked it: the bundle's own words, as opposed
+// to the runtime not reaching it (not running, exited, no answer in time). For `mesh/event` it is the
+// one way a bundle says it did not take an event: any answer that is not an error — `{}`, `null`, no
+// result at all — takes it (mesh-sdk, "Taking an event"; novox/hq issue 276).
+type Refused struct {
+	Method  string
+	Message string
+}
+
+func (r *Refused) Error() string { return r.Message }
+
 // Restart backoff: a bundle that exits is started again at once, then after growing pauses while it
 // keeps exiting, back to at once once it has run a while.
 var (
@@ -144,6 +155,7 @@ func Start(module, entry string, env []string, mesh Bus, logf func(string, ...an
 		if c == nil {
 			return errors.New(module + "'s bundle is not running to take its events")
 		}
+		// Taken unless the answer is an error; what a result says is not read (see Refused).
 		_, err := c.ask(module, "mesh/event", map[string]any{"envelope": envelope}, EventTimeout)
 		return err
 	}
@@ -528,7 +540,7 @@ func (c *child) ask(module, method string, params any, timeout time.Duration) (j
 			if msg == "" {
 				msg = "the bundle refused the request"
 			}
-			return nil, errors.New(msg)
+			return nil, &Refused{Method: method, Message: msg}
 		}
 		return m.Result, nil
 	case <-c.dead: