D4b: a row that a candidate taken out ends its check with a named cause, so the asker drops its asks (ADR 0664 §5, issue 1748)

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

modules/mesh-delivery-checker/internal/check/checker_test.go

@@ -3,6 +3,7 @@ package check
 import (
 	"context"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"strings"
 	"sync"
@@ -362,6 +363,20 @@ func TestARepositoryWithNoTrunkCannotBeJudgedLoudlyUntilItsTrunkIsKnown(t *testi
 			}
 		})
 	}
+
+	// ADR 0664 §5 (issue 1748): a candidate taken out (its pull request merged or closed) ends the check running for it with a
+	// cause its asks' wait names, never a plain cancel, so its asker drops the asks it put on the build nodes.
+	t.Run("a candidate taken out ends its check with a named cause", func(t *testing.T) {
+		ch := &Checker{}
+		ch.init()
+		run, end := context.WithCancelCause(context.Background())
+		ch.live["g.heads"] = liveCheck{group: "g", end: end}
+		ch.Forget("g")
+		var s superseded
+		if cause := context.Cause(run); !errors.As(cause, &s) || s.by != "" || errors.Is(cause, context.Canceled) {
+			t.Errorf("the check was ended with %v, want superseded with no heads, not a plain cancel", cause)
+		}
+	})
 }
 
 func countWith(lines []string, words string) int {