test(08-04): add failing code-exchange RED test in wristband

- Server.Token 501 stub and TestPhase8RedCodeExchange (PHASE8_RED:code-exchange)
- Options gains AccessTokenTTL/RefreshTokenTTL with PHP-parity defaults

wristband/token_test.go

@@ -0,0 +1,127 @@
+package wristband
+
+import (
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"net/url"
+	"strings"
+	"testing"
+	"time"
+)
+
+const tokenTestRedirect = "https://chatgpt.com/connector/oauth/cb"
+
+// insertTokenTestClient inserts an already-usable ClientRecord directly into
+// backend (bypassing CreateWithCap's cap/sweep policy, which this plan's
+// tests do not exercise) and returns it.
+func insertTokenTestClient(backend *memoryBackend, clientID, authMethod string, secretHash *string, ceiling []string) *ClientRecord {
+	backend.mu.Lock()
+	defer backend.mu.Unlock()
+	backend.nextID++
+	rec := &ClientRecord{
+		ID:                      backend.nextID,
+		ClientID:                clientID,
+		ClientSecretHash:        secretHash,
+		ClientName:              "Test Client",
+		RedirectURIs:            []string{tokenTestRedirect},
+		GrantTypes:              []string{"authorization_code", "refresh_token"},
+		TokenEndpointAuthMethod: authMethod,
+		ScopeCeiling:            ceiling,
+		CreatedAt:               time.Now(),
+	}
+	backend.clients = append(backend.clients, rec)
+	return rec
+}
+
+// insertTokenTestCode seeds an already-issued (post-consent) code row
+// directly into backend, matching the shape 08-05's consent flow will
+// produce via AuthCodeStore.MarkIssued: CodeHash set, RequestID nil, UserID
+// set. mutate, when non-nil, is applied to the record before it is stored so
+// individual tests can adjust ExpiresAt/UsedAt/ClientID/etc.
+func insertTokenTestCode(t *testing.T, backend *memoryBackend, clientID string, challenge string, mutate func(*AuthCodeRecord)) (rawCode string, rec *AuthCodeRecord) {
+	t.Helper()
+	raw, err := randomBase64URL(32)
+	if err != nil {
+		t.Fatal(err)
+	}
+	backend.mu.Lock()
+	defer backend.mu.Unlock()
+	backend.nextID++
+	userID := uint(1)
+	hash := sha256Hex(raw)
+	rec = &AuthCodeRecord{
+		ID:                  backend.nextID,
+		CodeHash:            &hash,
+		ClientID:            clientID,
+		UserID:              &userID,
+		RedirectURI:         tokenTestRedirect,
+		Scopes:              []string{"read", "write"},
+		CodeChallenge:       challenge,
+		CodeChallengeMethod: "S256",
+		ExpiresAt:           time.Now().Add(5 * time.Minute),
+	}
+	if mutate != nil {
+		mutate(rec)
+	}
+	backend.codes = append(backend.codes, rec)
+	return raw, rec
+}
+
+// tokenRequest builds a POST /oauth/mcp/token request from form (encoded as
+// the body) with an optional Authorization header, matching the D-02 body
+// parser every test in this file exercises.
+func tokenRequest(form url.Values, contentType string) *http.Request {
+	if contentType == "" {
+		contentType = "application/x-www-form-urlencoded"
+	}
+	req := httptest.NewRequest(http.MethodPost, "/oauth/mcp/token", strings.NewReader(form.Encode()))
+	req.Header.Set("Content-Type", contentType)
+	return req
+}
+
+// TestPhase8RedCodeExchange is the Phase 8 Wave 4 RED anchor (08-04-PLAN.md
+// Task 1, D-02/D-04/D-05/D-07). It drives one valid S256 authorization-code
+// exchange through the real (in-memory-backed) Server.Token and asserts the
+// exact RFC 6749 success contract. It fails with the
+// PHASE8_RED:code-exchange sentinel while Token is the 501 stub;
+// scripts/check-phase8-red.sh verifies this failure is fail-closed.
+func TestPhase8RedCodeExchange(t *testing.T) {
+	backend := newMemoryBackend()
+	srv := newTestServer(backend)
+	insertTokenTestClient(backend, "cli-red", "none", nil, nil)
+	verifier, challenge := s256Pair(t)
+	rawCode, _ := insertTokenTestCode(t, backend, "cli-red", challenge, nil)
+
+	req := tokenRequest(url.Values{
+		"grant_type":    {"authorization_code"},
+		"code":          {rawCode},
+		"code_verifier": {verifier},
+		"redirect_uri":  {tokenTestRedirect},
+		"client_id":     {"cli-red"},
+	}, "")
+	rec := httptest.NewRecorder()
+	srv.Token(rec, req)
+
+	if rec.Code != http.StatusOK {
+		t.Fatalf("PHASE8_RED:code-exchange: status = %d, want %d (body=%s)", rec.Code, http.StatusOK, rec.Body.String())
+	}
+	var got map[string]any
+	if err := json.Unmarshal(rec.Body.Bytes(), &got); err != nil {
+		t.Fatalf("PHASE8_RED:code-exchange: decode response: %v", err)
+	}
+	access, _ := got["access_token"].(string)
+	refresh, _ := got["refresh_token"].(string)
+	if access == "" || refresh == "" {
+		t.Fatalf("PHASE8_RED:code-exchange: access_token/refresh_token empty in %v", got)
+	}
+	if got["token_type"] != "Bearer" {
+		t.Fatalf("PHASE8_RED:code-exchange: token_type = %v, want Bearer", got["token_type"])
+	}
+	if got["scope"] != "read write" {
+		t.Fatalf("PHASE8_RED:code-exchange: scope = %v, want %q", got["scope"], "read write")
+	}
+	if cc := rec.Header().Get("Cache-Control"); cc != "no-store" {
+		t.Fatalf("PHASE8_RED:code-exchange: Cache-Control = %q, want \"no-store\"", cc)
+	}
+}