Contain provider errors at the LLM adapter

internal/framework/llm/promptkit_client.go

@@ -142,7 +142,7 @@ func (c *PromptKitClient) CompleteStructured(ctx context.Context, req contracts.
 		if ctxErr := ctx.Err(); ctxErr != nil {
 			return contracts.StructuredCompletionResponse{}, ctxErr
 		}
-		return contracts.StructuredCompletionResponse{}, fmt.Errorf("prepare PromptKit prompt %q: %w", promptID, redactPromptKitError(err))
+		return contracts.StructuredCompletionResponse{}, fmt.Errorf("prepare PromptKit prompt %q: %v", promptID, redactPromptKitError(err))
 	}
 	defer prepared.Discard()
 	preparedDetails := prepared.Details()
@@ -169,7 +169,7 @@ func (c *PromptKitClient) CompleteStructured(ctx context.Context, req contracts.
 				redactPromptKitError(err),
 			)
 		}
-		return contracts.StructuredCompletionResponse{}, fmt.Errorf("run PromptKit prompt %q: %w", promptID, redactPromptKitError(err))
+		return contracts.StructuredCompletionResponse{}, fmt.Errorf("run PromptKit prompt %q: %v", promptID, redactPromptKitError(err))
 	}
 	if result == nil {
 		return contracts.StructuredCompletionResponse{}, fmt.Errorf("run PromptKit prompt %q: %w: empty result", promptID, contracts.ErrInvalidStructuredOutput)
@@ -427,17 +427,13 @@ func redactPromptKitError(err error) error {
 	if err == nil {
 		return nil
 	}
-	return redactedProviderError{err: err}
+	return sanitizedProviderDiagnostic{message: bearerTokenPattern.ReplaceAllString(err.Error(), "Bearer "+secretReplacement)}
 }
 
-type redactedProviderError struct {
-	err error
+type sanitizedProviderDiagnostic struct {
+	message string
 }
 
-func (e redactedProviderError) Error() string {
-	return bearerTokenPattern.ReplaceAllString(e.err.Error(), "Bearer "+secretReplacement)
-}
-
-func (e redactedProviderError) Unwrap() error {
-	return e.err
+func (e sanitizedProviderDiagnostic) Error() string {
+	return e.message
 }

internal/framework/llm/promptkit_client_test.go

@@ -741,6 +741,11 @@ model: local-model
 		!strings.Contains(err.Error(), promptkit.BackendLocal) {
 		t.Fatalf("CompleteStructured() without registration error = %v, want preparation failure with local backend context", err)
 	}
+	for _, sentinel := range []error{promptkit.ErrProfileLoad, promptkit.ErrInvalidRequest, promptkit.ErrPromptNotFound} {
+		if errors.Is(err, sentinel) {
+			t.Fatalf("preparation failure exposes PromptKit sentinel %v: %v", sentinel, err)
+		}
+	}
 	if providerCalls.Load() != 1 {
 		t.Fatalf("provider calls after missing-registration failure = %d, want 1", providerCalls.Load())
 	}
@@ -814,7 +819,8 @@ func TestPromptKitClientDecodeFailureReturnsRawResponse(t *testing.T) {
 }
 
 func TestPromptKitClientProviderFailureIncludesContextAndRedactsBearerToken(t *testing.T) {
-	client := newTestPromptKitClient(t, &fakePromptKitLLM{err: errors.New("provider failed with Bearer secret-token")})
+	providerErr := &credentialBearingProviderError{}
+	client := newTestPromptKitClient(t, &fakePromptKitLLM{err: providerErr})
 
 	var out map[string]any
 	resp, err := client.CompleteStructured(context.Background(), contracts.StructuredCompletionRequest{
@@ -836,6 +842,21 @@ func TestPromptKitClientProviderFailureIncludesContextAndRedactsBearerToken(t *t
 	if strings.Contains(err.Error(), "secret-token") || !strings.Contains(err.Error(), "Bearer [REDACTED]") {
 		t.Fatalf("error = %q, want redacted bearer token", err.Error())
 	}
+	for current := err; current != nil; current = errors.Unwrap(current) {
+		if strings.Contains(current.Error(), "secret-token") {
+			t.Fatalf("error chain exposes credential: %v", err)
+		}
+	}
+	if errors.Unwrap(err) != nil {
+		t.Fatalf("provider failure must not expose a wrapped diagnostic: %v", err)
+	}
+	var recoveredProviderErr *credentialBearingProviderError
+	if errors.As(err, &recoveredProviderErr) {
+		t.Fatalf("provider error escaped the adapter: %v", err)
+	}
+	if errors.Is(err, promptkit.ErrLLMGenerate) {
+		t.Fatalf("provider failure exposes PromptKit generation sentinel: %v", err)
+	}
 	if resp.Debug != nil {
 		t.Fatalf("debug material = %#v, want none for provider failure without result", resp.Debug)
 	}
@@ -1214,6 +1235,12 @@ type fakePromptKitLLM struct {
 	maxInFlight int32
 }
 
+type credentialBearingProviderError struct{}
+
+func (*credentialBearingProviderError) Error() string {
+	return "provider failed with Bearer secret-token"
+}
+
 func (f *fakePromptKitLLM) Generate(ctx context.Context, req promptkit.GenerateRequest) (*promptkit.GenerateResponse, error) {
 	f.mu.Lock()
 	f.last = req