go/asks: whole details never digest as another ask's Whole and Details (the review of #25)

WholeDetails was written after a tag, so an ask with only whole details "+ x: 1" encoded as one whose Whole
was "whole-details" and Details "+ x: 1". Whole and Details are now written whenever whole details are
given, then the whole details, untagged: the number of trailing values tells the three shapes apart, and an
ask without whole details digests as before. The note's comment says what ADR 0347 §5 holds of cuts.

go/asks/asks.go

@@ -170,14 +170,16 @@ func (a Ask) Digest() string {
 			canonical(&b, v)
 		}
 	}
-	if a.Whole != "" || a.Details != "" {
+	// Whole and Details are written whenever either or WholeDetails is given, and WholeDetails after them whenever
+	// it is given (novox/hq ADR 0347): the fields after the options are then always one of three fixed shapes —
+	// none, the two, or the three — and the count of values the sequence holds tells them apart, so no two asks
+	// encode the same (the review of mesh-sdk #25). An ask with none of them digests as before they existed, and
+	// one without WholeDetails as before it existed.
+	if a.Whole != "" || a.Details != "" || a.WholeDetails != "" {
 		canonical(&b, a.Whole)
 		canonical(&b, a.Details)
 	}
-	// WholeDetails (novox/hq issue 383, the review of mesh-controller #304) follows only when given, so every
-	// ask without it digests as it did before it existed.
 	if a.WholeDetails != "" {
-		canonical(&b, "whole-details")
 		canonical(&b, a.WholeDetails)
 	}
 	sum := sha256.Sum256([]byte(b.String()))
@@ -493,7 +495,9 @@ type Message struct {
 	Buttons []Button `json:"buttons,omitempty"`
 	// Note is the message's secondary words, after its body and its buttons: who asked and when, what each
 	// answer does, when it expires, and the ask's Details. A channel shows it smaller, collapsed or set apart
-	// where it can, and after the body where it cannot; it is never left out (novox/hq issue 639).
+	// where it can, and after the body where it cannot (novox/hq issue 639). A channel that bounds a message's
+	// length cuts the body first and the note only when the title and the note alone do not fit, saying each
+	// cut (novox/hq ADR 0347 §5).
 	Note   string `json:"note,omitempty"`
 	Urgent bool   `json:"urgent,omitempty"`
 	Silent bool   `json:"silent,omitempty"`

go/asks/asks_test.go

@@ -337,3 +337,31 @@ func TestWholeDetailsAreDigestedOnlyWhenGiven(t *testing.T) {
 		t.Fatal("an ask without whole details digests otherwise than before")
 	}
 }
+
+// No two asks encode the same (the review of mesh-sdk #25): whole details given beside nothing else are not read as
+// a Whole and Details that happen to spell the same values, nor as any other split of the three fields.
+func TestWholeDetailsCollideWithNoOtherAsk(t *testing.T) {
+	base := Ask{ID: "a", Headline: "h", Explanation: "e"}
+	shapes := []Ask{}
+	for _, f := range []struct{ whole, details, wholeDetails string }{
+		{"", "", "+ x: 1"},
+		{"whole-details", "+ x: 1", ""},
+		{"", "+ x: 1", ""},
+		{"+ x: 1", "", ""},
+		{"", "", "whole-details"},
+		{"", "+ x: 1", "+ x: 1"},
+		{"+ x: 1", "+ x: 1", ""},
+		{"", "", ""},
+	} {
+		a := base
+		a.Whole, a.Details, a.WholeDetails = f.whole, f.details, f.wholeDetails
+		shapes = append(shapes, a)
+	}
+	seen := map[string]int{}
+	for i, a := range shapes {
+		if j, ok := seen[a.Digest()]; ok {
+			t.Errorf("asks %d and %d digest the same: %+v / %+v", j, i, shapes[j], a)
+		}
+		seen[a.Digest()] = i
+	}
+}