Changesets: staged deletes of gone records count as done, name stale ops

A web changeset with a staged record delete could not be applied after
the record was deleted elsewhere (e.g. with the CLI), and the error only
said "record N does not exist", so it was hard to find the operation to
remove. A delete of a record that is already gone is now a no-op with a
warning. Other operations that no longer apply fail with their number and
summary (op_summary in the API), and the Changes page marks that row and
offers to remove it from the error.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/engine/stale_test.go

@@ -0,0 +1,51 @@
+package engine
+
+import (
+	"strings"
+	"testing"
+
+	"jarl/internal/model"
+)
+
+// Records deleted or changed after a change to them was staged (in the
+// CLI while a web UI changeset is open, say).
+func TestStaleChangeset(t *testing.T) {
+	env := newEnv(t)
+	setupZone(env)
+	env.submit(env.admin, rec("example.com", "one", "A", "192.0.2.51"), rec("example.com", "two", "A", "192.0.2.52"), rec("example.com", "three", "A", "192.0.2.53"))
+	st := env.state()
+	one, two, three := findRec(st, "one.example.com.", "A"), findRec(st, "two.example.com.", "A"), findRec(st, "three.example.com.", "A")
+
+	// Two deletes staged; one of the records is deleted elsewhere first.
+	cs, err := env.e.CreateChangeset(env.ctx, env.admin, "web", "")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if _, err := env.e.Stage(env.ctx, cs.ID, []Request{NewRequest(OpRecordDelete, one.ID, nil), NewRequest(OpRecordDelete, two.ID, nil)}, env.admin); err != nil {
+		t.Fatal(err)
+	}
+	env.submit(env.admin, NewRequest(OpRecordDelete, one.ID, nil))
+	res, err := env.e.Apply(env.ctx, cs.ID, env.admin, ApplyOptions{})
+	if err != nil {
+		t.Fatalf("apply after the record was deleted elsewhere: %v", err)
+	}
+	if len(res.Warnings) != 1 || !strings.Contains(res.Warnings[0], "one.example.com. A 192.0.2.51: the record was already deleted") {
+		t.Errorf("warnings = %q", res.Warnings)
+	}
+	if st := env.state(); st.Records[two.ID] != nil {
+		t.Error("two was not deleted")
+	}
+
+	// A staged edit of a record deleted elsewhere names the operation.
+	cs, _ = env.e.CreateChangeset(env.ctx, env.admin, "web", "")
+	env.e.Stage(env.ctx, cs.ID, []Request{NewRequest(OpRecordUpdate, three.ID, RecordInput{Data: model.Ptr("192.0.2.54")})}, env.admin)
+	env.submit(env.admin, NewRequest(OpRecordDelete, three.ID, nil))
+	p, err := env.e.Preview(env.ctx, cs.ID, env.admin)
+	if err != nil || p.Error == nil || p.Error.OpSeq != 1 || !strings.HasPrefix(p.Error.OpSummary, "change three.example.com. A 192.0.2.53") {
+		t.Fatalf("preview = %+v, %v", p, err)
+	}
+	_, err = env.e.Apply(env.ctx, cs.ID, env.admin, ApplyOptions{})
+	if ee, ok := AsError(err); !ok || ee.Kind != KindConflict || !strings.Contains(err.Error(), "operation 1 (change three.example.com. A") || !strings.Contains(err.Error(), "remove this operation") {
+		t.Errorf("apply = %v", err)
+	}
+}