fix(analyze): refuse to compare attributed and unattributed denominators

One arm's actions may include the login the spec's setup drove and the
other's cannot, so a per-action rate over the two divides by different
things and the tests rank the bookkeeping.

cmd/internal-tools/analyze/analysis.go

@@ -29,6 +29,7 @@ type armSummary struct {
 	ViolationRate               *float64        `json:"violation_rate"`
 	TotalSteps                  int             `json:"total_steps"`
 	TotalActions                int             `json:"total_actions"`
+	UnattributedActions         int             `json:"unattributed_actions"`
 	TotalRunHours               float64         `json:"total_run_hours"`
 	Detections                  int             `json:"detections"`
 	DefectsPerThousandActions   *float64        `json:"defects_per_thousand_actions"`
@@ -127,6 +128,9 @@ func baseAnalysis(arms []arm, now time.Time) (analysis, []arm, error) {
 	if err := sameBudget(testable); err != nil {
 		return analysis{}, nil, err
 	}
+	if err := sameAttribution(testable); err != nil {
+		return analysis{}, nil, err
+	}
 	if len(testable) >= 2 {
 		names := make([]string, len(testable))
 		groups := make([][]observation, len(testable))
@@ -157,6 +161,28 @@ func sameBudget(arms []arm) error {
 	return nil
 }
 
+// sameAttribution refuses arms whose actions were counted against different
+// denominators. An arm recorded before an action named its producer counts
+// whatever the spec's setup dispatched among its actions, and an arm recorded
+// after leaves the login out, so the same rate over the two divides by
+// different things and the tests rank a bookkeeping difference. Two arms of the
+// same unknown provenance are diluted alike and compare; one of each does not.
+func sameAttribution(arms []arm) error {
+	for index := 1; index < len(arms); index++ {
+		unknown, attributed := arms[0], arms[index]
+		if (unknown.unattributedActions() == 0) == (attributed.unattributedActions() == 0) {
+			continue
+		}
+		if unknown.unattributedActions() == 0 {
+			unknown, attributed = attributed, unknown
+		}
+		return fmt.Errorf("arm %q counts %d action(s) of unknown provenance and arm %q counts none: "+
+			"a denominator that may include the spec's setup cannot be compared against one that excludes it",
+			unknown.Name, unknown.unattributedActions(), attributed.Name)
+	}
+	return nil
+}
+
 func countCorrected(pairs []pairwiseResult) int {
 	corrected := 0
 	for _, pair := range pairs {
@@ -212,6 +238,7 @@ func summarize(current arm) armSummary {
 		Directories:         current.Directories,
 		Recorded:            len(current.Runs),
 		MissingSeeds:        current.MissingSeeds,
+		UnattributedActions: current.unattributedActions(),
 	}
 	runsPerDefect := map[string]int{}
 	for _, item := range current.Runs {

cmd/internal-tools/analyze/analysis_test.go

@@ -352,6 +352,67 @@ func TestRun_RefusesToCompareArmsCensoredAtDifferentBudgets(t *testing.T) {
 	}
 }
 
+func writeSourcedCampaign(t *testing.T, directory, name string, steps, unattributed int) {
+	t.Helper()
+	const budget, runs, actions = 40, 6, 20
+	seeds := make([]int, 0, runs)
+	records := make([]map[string]any, 0, runs)
+	for seed := 1; seed <= runs; seed++ {
+		seeds = append(seeds, seed)
+		records = append(records, map[string]any{
+			"seed": seed, "exit_code": 0, "steps": steps, "actions": actions,
+			"monotonic_millis": 60_000, "unattributed_actions": unattributed,
+		})
+	}
+	writeCampaign(t, directory, map[string]any{"arm": name, "max_steps": budget, "seeds": seeds}, records)
+}
+
+// An arm whose actions name no producer counts whatever the spec's setup
+// dispatched in the denominator of every per-action rate, and an arm whose
+// actions name one leaves the login out of it. The two denominators measure
+// different things, so a test that ranks one arm against the other reads a
+// difference in what was counted as a difference in what the arms found.
+func TestRun_RefusesToCompareArmsWhoseActionsWereCountedDifferently(t *testing.T) {
+	cases := []struct {
+		name      string
+		arguments []string
+	}{
+		{name: "independent samples"},
+		{name: "paired", arguments: []string{"--paired"}},
+	}
+	for _, test := range cases {
+		root := t.TempDir()
+		attributed := filepath.Join(root, "attributed")
+		legacy := filepath.Join(root, "legacy")
+		writeSourcedCampaign(t, attributed, "attributed", 40, 0)
+		writeSourcedCampaign(t, legacy, "legacy", 30, 20)
+
+		err := run(append(test.arguments, attributed, legacy), io.Discard, io.Discard)
+		if err == nil {
+			t.Fatalf("%s: an arm of unknown provenance was tested against an attributed one without complaint", test.name)
+		}
+		for _, fragment := range []string{"attributed", "legacy", "120", "unknown provenance"} {
+			if !strings.Contains(err.Error(), fragment) {
+				t.Errorf("%s: error %q is missing %q", test.name, err, fragment)
+			}
+		}
+	}
+}
+
+// Two arms recorded before actions named their producer are on the same
+// denominator as each other, diluted the same way, so they compare.
+func TestRun_ComparesTwoArmsThatBothNameNoProducer(t *testing.T) {
+	root := t.TempDir()
+	first := filepath.Join(root, "first")
+	second := filepath.Join(root, "second")
+	writeSourcedCampaign(t, first, "first", 40, 20)
+	writeSourcedCampaign(t, second, "second", 30, 20)
+
+	if err := run([]string{first, second}, io.Discard, io.Discard); err != nil {
+		t.Fatalf("two arms of the same unknown provenance were refused: %v", err)
+	}
+}
+
 func manyRuns(count, originStep int) []classifiedRun {
 	runs := make([]classifiedRun, 0, count)
 	for index := 0; index < count; index++ {