test(08-07): add failing repeatable-flag RED anchor for bonfire

- TestPhase8RedBonfireFlags asserts Input.Flags preserves ordered
  repeated --redirect-uri/--scope values while existing scalar --mode
  flags via Input.Flag stay unaffected
- Adds the compiling seam (Flag.Repeatable, Input.Flags,
  cobraInput.Flags) without wiring Cobra StringSlice registration yet,
  so the test fails with PHASE8_RED:bonfire-flags (D-19)

bonfire/output_test.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"context"
 	"errors"
+	"slices"
 	"strings"
 	"testing"
 )
@@ -244,6 +245,61 @@ func TestNonTTYProgressSkipsIntraDecile(t *testing.T) {
 	}
 }
 
+// TestPhase8RedBonfireFlags is the Phase 8 Wave 7 RED anchor (08-07-PLAN.md
+// Task 1, D-19). bonfire.Flag/Input are scalar-only today
+// (08-PATTERNS.md "bonfire repeatable-flag gap"): a Repeatable flag
+// registered through Command.Flags must preserve every repeated
+// `--name=value` occurrence in order via Input.Flags, while an ordinary
+// scalar flag declared alongside it keeps working through Input.Flag
+// unmodified. It fails with the PHASE8_RED:bonfire-flags sentinel while
+// Repeatable is not yet wired into Cobra registration;
+// scripts/check-phase8-red.sh verifies this failure is fail-closed.
+func TestPhase8RedBonfireFlags(t *testing.T) {
+	var buf bytes.Buffer
+	var gotRedirect, gotScope []string
+	var gotMode string
+	var gotModeOK bool
+	root, err := NewRootIO("app", []Command{{
+		Name:        "demo:repeat",
+		Description: "Demo repeatable flags",
+		Flags: []Flag{
+			{Name: "redirect-uri", Repeatable: true, Description: "repeatable redirect URI"},
+			{Name: "scope", Repeatable: true, Description: "repeatable scope"},
+			{Name: "mode", Default: "slow", Description: "scalar, unaffected by D-19"},
+		},
+		Run: func(ctx context.Context, in Input, out Output) error {
+			gotRedirect = in.Flags("redirect-uri")
+			gotScope = in.Flags("scope")
+			gotMode, gotModeOK = in.Flag("mode")
+			return nil
+		},
+	}}, strings.NewReader(""), &buf, &buf)
+	if err != nil {
+		t.Fatal(err)
+	}
+	root.SetArgs([]string{
+		"demo:repeat",
+		"--redirect-uri=https://a.example/callback",
+		"--redirect-uri=https://b.example/callback",
+		"--scope=read",
+		"--mode=fast",
+	})
+	if err := root.Execute(); err != nil {
+		t.Fatal(err)
+	}
+
+	wantRedirect := []string{"https://a.example/callback", "https://b.example/callback"}
+	if !slices.Equal(gotRedirect, wantRedirect) {
+		t.Fatalf("PHASE8_RED:bonfire-flags: repeated --redirect-uri via Input.Flags = %v, want %v in insertion order", gotRedirect, wantRedirect)
+	}
+	if !slices.Equal(gotScope, []string{"read"}) {
+		t.Fatalf("PHASE8_RED:bonfire-flags: repeated --scope via Input.Flags = %v, want [read]", gotScope)
+	}
+	if !gotModeOK || gotMode != "fast" {
+		t.Fatalf("PHASE8_RED:bonfire-flags: existing scalar --mode via Input.Flag = (%q, %v), want (\"fast\", true) unaffected by Repeatable", gotMode, gotModeOK)
+	}
+}
+
 func TestHelpUsesSharedAdapter(t *testing.T) {
 	var buf bytes.Buffer
 	root, err := NewRoot("hello", []Command{{