Require secrets for ProviderError redaction and omit unredactable bodies

NewProviderError now takes the secrets to redact as a required []string
instead of an optional variadic. When no non-empty secret is given the
body cannot be redacted, so no excerpt is stored and Body()/Error() never
expose raw vendor output.

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

internal/ai/llm/errors.go

@@ -56,17 +56,24 @@ type ProviderError struct {
 	body   string
 }
 
-// NewProviderError returns the error for an unexpected HTTP status. Every
-// occurrence of each non-empty secret (the API key, at least) in body is
-// replaced before the body is cut to MaxBodyExcerpt bytes, so no part of a
-// secret survives.
-func NewProviderError(status int, body []byte, secrets ...string) *ProviderError {
+// NewProviderError returns the error for an unexpected HTTP status.
+// secrets must hold the API key (and any other credential sent with the
+// request). Every occurrence of each non-empty secret in body is replaced
+// before the body is cut to MaxBodyExcerpt bytes, so no part of a secret
+// survives. If secrets holds no non-empty value the body cannot be
+// redacted, so no excerpt is kept at all.
+func NewProviderError(status int, body []byte, secrets []string) *ProviderError {
 	s := string(body)
+	redactedAny := false
 	for _, secret := range secrets {
 		if secret != "" {
 			s = strings.ReplaceAll(s, secret, redacted)
+			redactedAny = true
 		}
 	}
+	if !redactedAny {
+		return &ProviderError{status: status}
+	}
 	s = strings.TrimSpace(s)
 	if len(s) > MaxBodyExcerpt {
 		cut := MaxBodyExcerpt
@@ -81,7 +88,8 @@ func NewProviderError(status int, body []byte, secrets ...string) *ProviderError
 // Status returns the HTTP status code.
 func (e *ProviderError) Status() int { return e.status }
 
-// Body returns the redacted, truncated response-body excerpt.
+// Body returns the redacted, truncated response-body excerpt; it is empty
+// when the vendor sent no body or no secret was given to redact it with.
 func (e *ProviderError) Body() string { return e.body }
 
 func (e *ProviderError) Error() string {

internal/ai/llm/errors_test.go

@@ -46,7 +46,7 @@ func TestRateLimitedError(t *testing.T) {
 }
 
 func TestProviderError(t *testing.T) {
-	err := fmt.Errorf("gemini: %w", NewProviderError(503, []byte(` {"error":"overloaded"} `)))
+	err := fmt.Errorf("gemini: %w", NewProviderError(503, []byte(` {"error":"overloaded"} `), []string{"sk-test"}))
 	if !errors.Is(err, ErrProvider) {
 		t.Fatal("errors.Is(err, ErrProvider) = false")
 	}
@@ -63,7 +63,7 @@ func TestProviderError(t *testing.T) {
 	if got := err.Error(); got != `gemini: llm: provider error: HTTP 503: {"error":"overloaded"}` {
 		t.Fatalf("Error() = %q", got)
 	}
-	if got := NewProviderError(500, nil).Error(); got != "llm: provider error: HTTP 500" {
+	if got := NewProviderError(500, nil, []string{"sk-test"}).Error(); got != "llm: provider error: HTTP 500" {
 		t.Fatalf("Error() without body = %q", got)
 	}
 }
@@ -71,7 +71,7 @@ func TestProviderError(t *testing.T) {
 func TestProviderErrorRedactsSecrets(t *testing.T) {
 	const key = "sk-live-0123456789abcdef"
 	body := []byte(`{"error":"invalid key sk-live-0123456789abcdef","echo":"Bearer sk-live-0123456789abcdef"}`)
-	pe := NewProviderError(400, body, key, "")
+	pe := NewProviderError(400, body, []string{key, ""})
 	for _, s := range []string{pe.Error(), pe.Body()} {
 		if strings.Contains(s, key) {
 			t.Fatalf("secret leaked: %q", s)
@@ -88,7 +88,7 @@ func TestProviderErrorRedactsBeforeTruncating(t *testing.T) {
 	// The key starts just before the excerpt limit, so truncating first
 	// would leave its prefix in the excerpt.
 	body := strings.Repeat("x", MaxBodyExcerpt-5) + key
-	pe := NewProviderError(500, []byte(body), key)
+	pe := NewProviderError(500, []byte(body), []string{key})
 	if strings.Contains(pe.Body(), "sk-se") {
 		t.Fatalf("secret prefix leaked: %q", pe.Body())
 	}
@@ -96,9 +96,26 @@ func TestProviderErrorRedactsBeforeTruncating(t *testing.T) {
 
 func TestProviderErrorTruncatesOnRuneBoundary(t *testing.T) {
 	body := strings.Repeat("a", MaxBodyExcerpt-1) + "é" + strings.Repeat("b", 100)
-	pe := NewProviderError(500, []byte(body))
+	pe := NewProviderError(500, []byte(body), []string{"sk-test"})
 	want := strings.Repeat("a", MaxBodyExcerpt-1) + "…"
 	if pe.Body() != want {
 		t.Fatalf("Body() has %d bytes, want %d", len(pe.Body()), len(want))
 	}
 }
+
+func TestProviderErrorOmitsBodyWithoutSecret(t *testing.T) {
+	const key = "sk-live-0123456789abcdef"
+	body := []byte(`{"error":"invalid key sk-live-0123456789abcdef"}`)
+	for _, secrets := range [][]string{nil, {}, {""}} {
+		pe := NewProviderError(401, body, secrets)
+		if pe.Body() != "" {
+			t.Fatalf("secrets %q: Body() = %q, want empty", secrets, pe.Body())
+		}
+		if got := pe.Error(); got != "llm: provider error: HTTP 401" {
+			t.Fatalf("secrets %q: Error() = %q", secrets, got)
+		}
+		if strings.Contains(pe.Error(), key) {
+			t.Fatalf("secrets %q: secret leaked: %q", secrets, pe.Error())
+		}
+	}
+}