refactor: move proxy block message rendering to presentation layer (#364)

* refactor: move proxy block message rendering to presentation layer

* refactor: introduce ui.ProxyPresenter with injected advisory source

* feat: friendly ecosystem labels in proxy block messages

* test: cover ecosystemLabel derivation

* fix: address review feedback on block context assertions and empty reference line

config/config.go

@@ -795,6 +795,12 @@ func Get() *RuntimeConfig {
 	return globalConfig
 }
 
+// AdvisoryMessage returns the org-configured advisory message appended to
+// policy block output. Empty when not configured.
+func AdvisoryMessage() string {
+	return globalConfig.Config.AdvisoryMessage
+}
+
 func ConfigureSandbox(mayDownloadPackages bool) {
 	if globalConfig.Config.Sandbox.Enabled {
 		// Apply sandbox to all commands if EnforceAlways=true, otherwise only to

internal/flows/proxy_flow.go

@@ -348,6 +348,8 @@ func (f *proxyFlow) createAndStartProxyServer(
 	proxyConfig := proxy.DefaultProxyConfig()
 	proxyConfig.CertManager = certMgr
 	proxyConfig.Interceptors = interceptorsList
+	presenter := ui.ProxyPresenter{Advisory: config.AdvisoryMessage}
+	proxyConfig.BlockMessageRenderer = presenter.BlockMessage
 
 	proxyServer, err := proxy.NewProxyServer(proxyConfig)
 	if err != nil {

internal/proxyserver/server.go

@@ -16,6 +16,7 @@ import (
 	"github.com/safedep/pmg/internal/audit"
 	"github.com/safedep/pmg/internal/flows"
 	"github.com/safedep/pmg/internal/localstore"
+	"github.com/safedep/pmg/internal/ui"
 	pmgproxy "github.com/safedep/pmg/proxy"
 	"github.com/safedep/pmg/proxy/certmanager"
 	"github.com/safedep/pmg/proxy/interceptors"
@@ -115,6 +116,8 @@ func Run(ctx context.Context, cfg *config.RuntimeConfig, statePath, host string,
 	proxyConfig.ListenAddr = listenAddr(host, port)
 	proxyConfig.CertManager = certMgr
 	proxyConfig.Interceptors = interceptorList
+	presenter := ui.ProxyPresenter{Advisory: config.AdvisoryMessage}
+	proxyConfig.BlockMessageRenderer = presenter.BlockMessage
 
 	server, err := pmgproxy.NewProxyServer(proxyConfig)
 	if err != nil {

internal/ui/proxy_presenter.go

@@ -0,0 +1,71 @@
+package ui
+
+import (
+	"fmt"
+	"strings"
+
+	packagev1 "buf.build/gen/go/safedep/api/protocolbuffers/go/safedep/messages/package/v1"
+	"github.com/safedep/pmg/proxy"
+)
+
+// ecosystemLabel maps the ecosystem enum to the label users know the
+// registry by (npm, pypi, go, ...) instead of the raw enum name.
+func ecosystemLabel(ecosystem packagev1.Ecosystem) string {
+	return strings.ToLower(strings.TrimPrefix(ecosystem.String(), "ECOSYSTEM_"))
+}
+
+// ProxyPresenter composes all user-facing text authored by the proxy layer.
+// Interceptors return structured decisions; any new proxy-emitted message
+// belongs here, not in the proxy layer.
+type ProxyPresenter struct {
+	// Advisory returns the org-configured advisory message appended to
+	// policy block messages. Read at render time so config changes apply
+	// to subsequent blocks. nil means no advisory.
+	Advisory func() string
+}
+
+// BlockMessage renders the response body for a blocked proxy request
+// from the interceptor's structured block decision.
+func (p ProxyPresenter) BlockMessage(reason proxy.BlockReason, blockCtx *proxy.BlockContext) string {
+	if blockCtx == nil {
+		return ""
+	}
+
+	ecosystem := ecosystemLabel(blockCtx.Ecosystem)
+
+	var message string
+	switch reason {
+	case proxy.BlockReasonMalware, proxy.BlockReasonUserDeclined:
+		prefix := "Malicious package blocked"
+		if reason == proxy.BlockReasonUserDeclined {
+			prefix = "Installation blocked by user"
+		}
+
+		message = fmt.Sprintf("%s: %s/%s@%s\n\nReason: %s",
+			prefix, ecosystem, blockCtx.PackageName, blockCtx.PackageVersion, blockCtx.MalwareSummary)
+		if blockCtx.MalwareReferenceURL != "" {
+			message += "\n\nReference: " + blockCtx.MalwareReferenceURL
+		}
+
+	case proxy.BlockReasonConfirmationFailed:
+		// Operational failure rather than a policy decision; the advisory
+		// message is intentionally not appended.
+		return fmt.Sprintf("Failed to get user confirmation for suspicious package %s/%s@%s",
+			ecosystem, blockCtx.PackageName, blockCtx.PackageVersion)
+
+	case proxy.BlockReasonDependencyCooldown:
+		message = fmt.Sprintf("Package blocked by dependency cooldown: %s/%s@%s\n\nPublished %d day(s) ago; cooldown window is %d day(s) (%d remaining).",
+			ecosystem, blockCtx.PackageName, blockCtx.PackageVersion,
+			blockCtx.CooldownDaysAgo, blockCtx.CooldownDays, blockCtx.CooldownDaysLeft)
+
+	default:
+		return ""
+	}
+
+	if p.Advisory != nil {
+		if advisory := p.Advisory(); advisory != "" {
+			message += "\n\n" + advisory
+		}
+	}
+	return message
+}

internal/ui/proxy_presenter_test.go

@@ -0,0 +1,130 @@
+package ui
+
+import (
+	"testing"
+
+	packagev1 "buf.build/gen/go/safedep/api/protocolbuffers/go/safedep/messages/package/v1"
+	"github.com/safedep/pmg/proxy"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestEcosystemLabel(t *testing.T) {
+	tests := []struct {
+		ecosystem packagev1.Ecosystem
+		expected  string
+	}{
+		{packagev1.Ecosystem_ECOSYSTEM_NPM, "npm"},
+		{packagev1.Ecosystem_ECOSYSTEM_PYPI, "pypi"},
+		{packagev1.Ecosystem_ECOSYSTEM_GO, "go"},
+		{packagev1.Ecosystem_ECOSYSTEM_RUBYGEMS, "rubygems"},
+		{packagev1.Ecosystem_ECOSYSTEM_GITHUB_ACTIONS, "github_actions"},
+		{packagev1.Ecosystem_ECOSYSTEM_UNSPECIFIED, "unspecified"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.expected, func(t *testing.T) {
+			assert.Equal(t, tt.expected, ecosystemLabel(tt.ecosystem))
+		})
+	}
+}
+
+func TestProxyPresenterBlockMessage(t *testing.T) {
+	malwareCtx := &proxy.BlockContext{
+		Ecosystem:           packagev1.Ecosystem_ECOSYSTEM_NPM,
+		PackageName:         "evil",
+		PackageVersion:      "1.0.0",
+		MalwareSummary:      "Contains known malware",
+		MalwareReferenceURL: "https://example.com/malware-report",
+	}
+
+	tests := []struct {
+		name     string
+		reason   proxy.BlockReason
+		blockCtx *proxy.BlockContext
+		advisory string
+		expected string
+	}{
+		{
+			name:     "malware",
+			reason:   proxy.BlockReasonMalware,
+			blockCtx: malwareCtx,
+			expected: "Malicious package blocked: npm/evil@1.0.0\n\nReason: Contains known malware\n\nReference: https://example.com/malware-report",
+		},
+		{
+			name:     "malware with advisory",
+			reason:   proxy.BlockReasonMalware,
+			blockCtx: malwareCtx,
+			advisory: "Contact #security-help",
+			expected: "Malicious package blocked: npm/evil@1.0.0\n\nReason: Contains known malware\n\nReference: https://example.com/malware-report\n\nContact #security-help",
+		},
+		{
+			name:     "user declined",
+			reason:   proxy.BlockReasonUserDeclined,
+			blockCtx: malwareCtx,
+			advisory: "Contact #security-help",
+			expected: "Installation blocked by user: npm/evil@1.0.0\n\nReason: Contains known malware\n\nReference: https://example.com/malware-report\n\nContact #security-help",
+		},
+		{
+			name:   "malware without reference URL omits reference line",
+			reason: proxy.BlockReasonMalware,
+			blockCtx: &proxy.BlockContext{
+				Ecosystem:      packagev1.Ecosystem_ECOSYSTEM_NPM,
+				PackageName:    "evil",
+				PackageVersion: "1.0.0",
+				MalwareSummary: "Contains known malware",
+			},
+			advisory: "Contact #security-help",
+			expected: "Malicious package blocked: npm/evil@1.0.0\n\nReason: Contains known malware\n\nContact #security-help",
+		},
+		{
+			name:     "confirmation failed carries no advisory",
+			reason:   proxy.BlockReasonConfirmationFailed,
+			blockCtx: malwareCtx,
+			advisory: "Contact #security-help",
+			expected: "Failed to get user confirmation for suspicious package npm/evil@1.0.0",
+		},
+		{
+			name:   "dependency cooldown",
+			reason: proxy.BlockReasonDependencyCooldown,
+			blockCtx: &proxy.BlockContext{
+				Ecosystem:        packagev1.Ecosystem_ECOSYSTEM_GO,
+				PackageName:      "example.com/fresh",
+				PackageVersion:   "v1.1.0",
+				CooldownDays:     7,
+				CooldownDaysAgo:  2,
+				CooldownDaysLeft: 5,
+			},
+			advisory: "Request an exemption at go/pmg-exceptions",
+			expected: "Package blocked by dependency cooldown: go/example.com/fresh@v1.1.0\n\nPublished 2 day(s) ago; cooldown window is 7 day(s) (5 remaining).\n\nRequest an exemption at go/pmg-exceptions",
+		},
+		{
+			name:     "nil context",
+			reason:   proxy.BlockReasonMalware,
+			blockCtx: nil,
+			expected: "",
+		},
+		{
+			name:     "no reason",
+			reason:   proxy.BlockReasonNone,
+			blockCtx: malwareCtx,
+			expected: "",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			p := ProxyPresenter{Advisory: func() string { return tt.advisory }}
+			assert.Equal(t, tt.expected, p.BlockMessage(tt.reason, tt.blockCtx))
+		})
+	}
+}
+
+func TestProxyPresenterNilAdvisory(t *testing.T) {
+	message := ProxyPresenter{}.BlockMessage(proxy.BlockReasonMalware, &proxy.BlockContext{
+		Ecosystem:      packagev1.Ecosystem_ECOSYSTEM_NPM,
+		PackageName:    "evil",
+		PackageVersion: "1.0.0",
+		MalwareSummary: "verified malware",
+	})
+	assert.Equal(t, "Malicious package blocked: npm/evil@1.0.0\n\nReason: verified malware", message)
+}

proxy/interceptor.go

@@ -4,6 +4,8 @@ import (
 	"net/http"
 	"net/url"
 	"time"
+
+	packagev1 "buf.build/gen/go/safedep/api/protocolbuffers/go/safedep/messages/package/v1"
 )
 
 // ResponseAction determines how the proxy should handle a request
@@ -41,12 +43,46 @@ type RequestContext struct {
 	Data map[string]interface{}
 }
 
+// BlockReason identifies why an interceptor blocked a request
+type BlockReason int
+
+const (
+	BlockReasonNone BlockReason = iota
+	BlockReasonMalware
+	BlockReasonUserDeclined
+	BlockReasonConfirmationFailed
+	BlockReasonDependencyCooldown
+)
+
+// BlockContext carries the structured facts of a block decision so a
+// presentation layer can render the user-facing message. Interceptors
+// populate it instead of composing message text themselves.
+type BlockContext struct {
+	Ecosystem      packagev1.Ecosystem
+	PackageName    string
+	PackageVersion string
+
+	// For BlockReasonMalware and BlockReasonUserDeclined
+	MalwareSummary      string
+	MalwareReferenceURL string
+
+	// For BlockReasonDependencyCooldown
+	CooldownDays     int
+	CooldownDaysAgo  int
+	CooldownDaysLeft int
+}
+
 // InterceptorResponse defines how the proxy should handle the request
 type InterceptorResponse struct {
 	// Action to take
 	Action ResponseAction
 
-	// For Action = Block: error message to return
+	// For Action = Block: why and what was blocked. The proxy renders the
+	// response body from these via ProxyConfig.BlockMessageRenderer.
+	BlockReason  BlockReason
+	BlockContext *BlockContext
+
+	// BlockMessage overrides the rendered message when non-empty
 	BlockMessage string
 	BlockCode    int
 

proxy/interceptors/base_registry.go

@@ -101,15 +101,6 @@ func (b *baseRegistryInterceptor) fastAllow(
 	return nil, false
 }
 
-// appendAdvisoryMessage appends the org-configured advisory_message, when set,
-// to a block message body.
-func appendAdvisoryMessage(message, advisory string) string {
-	if advisory == "" {
-		return message
-	}
-	return message + "\n\n" + advisory
-}
-
 // analyzePackage analyzes a package using the configured analyzer with caching
 // This method is ecosystem-agnostic and can be used by any registry interceptor
 func (b *baseRegistryInterceptor) analyzePackage(
@@ -203,16 +194,17 @@ func (b *baseRegistryInterceptor) handleAnalysisResult(
 			b.statsCollector.RecordBlocked(result)
 		}
 
-		message := appendAdvisoryMessage(fmt.Sprintf("Malicious package blocked: %s/%s@%s\n\nReason: %s\n\nReference: %s",
-			ecosystem.String(),
-			packageName, packageVersion,
-			result.Summary,
-			result.ReferenceURL), config.Get().Config.AdvisoryMessage)
-
 		return &proxy.InterceptorResponse{
 			Action:      proxy.ActionBlock,
 			BlockCode:   http.StatusForbidden,
-			BlockMessage: message,
+			BlockReason: proxy.BlockReasonMalware,
+			BlockContext: &proxy.BlockContext{
+				Ecosystem:           ecosystem,
+				PackageName:         packageName,
+				PackageVersion:      packageVersion,
+				MalwareSummary:      result.Summary,
+				MalwareReferenceURL: result.ReferenceURL,
+			},
 		}, nil
 
 	case analyzer.ActionConfirm:
@@ -229,7 +221,12 @@ func (b *baseRegistryInterceptor) handleAnalysisResult(
 			return &proxy.InterceptorResponse{
 				Action:      proxy.ActionBlock,
 				BlockCode:   http.StatusForbidden,
-				BlockMessage: fmt.Sprintf("Failed to get user confirmation for suspicious package %s/%s@%s", ecosystem.String(), packageName, packageVersion),
+				BlockReason: proxy.BlockReasonConfirmationFailed,
+				BlockContext: &proxy.BlockContext{
+					Ecosystem:      ecosystem,
+					PackageName:    packageName,
+					PackageVersion: packageVersion,
+				},
 			}, nil
 		}
 
@@ -242,16 +239,17 @@ func (b *baseRegistryInterceptor) handleAnalysisResult(
 				b.statsCollector.RecordUserCancelled(result)
 			}
 
-			message := appendAdvisoryMessage(fmt.Sprintf("Installation blocked by user: %s/%s@%s\n\nReason: %s\n\nReference: %s",
-				ecosystem.String(),
-				packageName, packageVersion,
-				result.Summary,
-				result.ReferenceURL), config.Get().Config.AdvisoryMessage)
-
 			return &proxy.InterceptorResponse{
 				Action:      proxy.ActionBlock,
 				BlockCode:   http.StatusForbidden,
-				BlockMessage: message,
+				BlockReason: proxy.BlockReasonUserDeclined,
+				BlockContext: &proxy.BlockContext{
+					Ecosystem:           ecosystem,
+					PackageName:         packageName,
+					PackageVersion:      packageVersion,
+					MalwareSummary:      result.Summary,
+					MalwareReferenceURL: result.ReferenceURL,
+				},
 			}, nil
 		}
 

proxy/interceptors/base_registry_test.go

@@ -70,7 +70,7 @@ func TestBaseRegistryInterceptor_HandleAnalysisResult(t *testing.T) {
 		userConfirms        bool
 		expectedAction      proxy.ResponseAction
 		expectedBlockCode   int
-		expectBlockMessage bool
+		expectedBlockReason proxy.BlockReason
 	}{
 		{
 			name:           "ActionBlock - malicious package",
@@ -84,7 +84,7 @@ func TestBaseRegistryInterceptor_HandleAnalysisResult(t *testing.T) {
 			},
 			expectedAction:      proxy.ActionBlock,
 			expectedBlockCode:   http.StatusForbidden,
-			expectBlockMessage: true,
+			expectedBlockReason: proxy.BlockReasonMalware,
 		},
 		{
 			name:           "ActionConfirm - user confirms installation",
@@ -99,7 +99,7 @@ func TestBaseRegistryInterceptor_HandleAnalysisResult(t *testing.T) {
 			userConfirms:        true,
 			expectedAction:      proxy.ActionAllow,
 			expectedBlockCode:   0,
-			expectBlockMessage: false,
+			expectedBlockReason: proxy.BlockReasonNone,
 		},
 		{
 			name:           "ActionConfirm - user declines installation",
@@ -114,7 +114,7 @@ func TestBaseRegistryInterceptor_HandleAnalysisResult(t *testing.T) {
 			userConfirms:        false,
 			expectedAction:      proxy.ActionBlock,
 			expectedBlockCode:   http.StatusForbidden,
-			expectBlockMessage: true,
+			expectedBlockReason: proxy.BlockReasonUserDeclined,
 		},
 		// Note: Timeout test case is skipped as it would require waiting 5 minutes
 		// The timeout behavior is covered by the implementation but not tested here
@@ -131,7 +131,7 @@ func TestBaseRegistryInterceptor_HandleAnalysisResult(t *testing.T) {
 			},
 			expectedAction:      proxy.ActionAllow,
 			expectedBlockCode:   0,
-			expectBlockMessage: false,
+			expectedBlockReason: proxy.BlockReasonNone,
 		},
 		{
 			name:           "ActionUnknown - default to allow",
@@ -145,7 +145,7 @@ func TestBaseRegistryInterceptor_HandleAnalysisResult(t *testing.T) {
 			},
 			expectedAction:      proxy.ActionAllow,
 			expectedBlockCode:   0,
-			expectBlockMessage: false,
+			expectedBlockReason: proxy.BlockReasonNone,
 		},
 		{
 			name:           "ActionBlock - pypi ecosystem",
@@ -159,7 +159,7 @@ func TestBaseRegistryInterceptor_HandleAnalysisResult(t *testing.T) {
 			},
 			expectedAction:      proxy.ActionBlock,
 			expectedBlockCode:   http.StatusForbidden,
-			expectBlockMessage: true,
+			expectedBlockReason: proxy.BlockReasonMalware,
 		},
 	}
 
@@ -200,35 +200,25 @@ func TestBaseRegistryInterceptor_HandleAnalysisResult(t *testing.T) {
 			assert.NoError(t, err)
 			assert.Equal(t, tt.expectedAction, response.Action)
 			assert.Equal(t, tt.expectedBlockCode, response.BlockCode)
-			assert.Equal(t, tt.expectBlockMessage, response.BlockMessage != "")
+			assert.Equal(t, tt.expectedBlockReason, response.BlockReason)
+			assert.Empty(t, response.BlockMessage)
+
+			switch tt.expectedBlockReason {
+			case proxy.BlockReasonNone:
+				assert.Nil(t, response.BlockContext)
+			case proxy.BlockReasonMalware, proxy.BlockReasonUserDeclined:
+				require.NotNil(t, response.BlockContext)
+				assert.Equal(t, tt.ecosystem, response.BlockContext.Ecosystem)
+				assert.Equal(t, tt.packageName, response.BlockContext.PackageName)
+				assert.Equal(t, tt.packageVersion, response.BlockContext.PackageVersion)
+				assert.Equal(t, tt.analysisResult.Summary, response.BlockContext.MalwareSummary)
+				assert.Equal(t, tt.analysisResult.ReferenceURL, response.BlockContext.MalwareReferenceURL)
+			default:
+				require.NotNil(t, response.BlockContext)
+				assert.Equal(t, tt.ecosystem, response.BlockContext.Ecosystem)
+				assert.Equal(t, tt.packageName, response.BlockContext.PackageName)
+				assert.Equal(t, tt.packageVersion, response.BlockContext.PackageVersion)
+			}
 		})
 	}
 }
-
-func TestAppendAdvisoryMessage(t *testing.T) {
-	assert.Equal(t, "base", appendAdvisoryMessage("base", ""))
-	assert.Equal(t, "base\n\ncustom", appendAdvisoryMessage("base", "custom"))
-}
-
-func TestHandleAnalysisResultBlockCarriesAdvisoryMessage(t *testing.T) {
-	origMsg := pmgconfig.Get().Config.AdvisoryMessage
-	pmgconfig.Get().Config.AdvisoryMessage = "Contact #security-help"
-	t.Cleanup(func() { pmgconfig.Get().Config.AdvisoryMessage = origMsg })
-
-	b := &baseRegistryInterceptor{}
-	ctx := makeTestRequestContext("https://registry.npmjs.org/evil/-/evil-1.0.0.tgz")
-
-	result := &analyzer.PackageVersionAnalysisResult{
-		PackageVersion: &packagev1.PackageVersion{
-			Package: &packagev1.Package{Name: "evil", Ecosystem: packagev1.Ecosystem_ECOSYSTEM_NPM},
-			Version: "1.0.0",
-		},
-		Action:  analyzer.ActionBlock,
-		Summary: "verified malware",
-	}
-
-	resp, err := b.handleAnalysisResult(ctx, packagev1.Ecosystem_ECOSYSTEM_NPM, "evil", "1.0.0", result)
-	require.NoError(t, err)
-	assert.Equal(t, proxy.ActionBlock, resp.Action)
-	assert.Contains(t, resp.BlockMessage, "Contact #security-help")
-}

proxy/interceptors/go_cooldown.go

@@ -126,15 +126,18 @@ func (h *goCooldownHandler) CheckZipDownload(ctx *proxy.RequestContext, baseURL,
 	pv.SetVersion(version)
 	audit.LogDependencyCooldown(pv, publishTime, cooldownDays, daysAgo, daysLeft)
 
-	message := appendAdvisoryMessage(
-		fmt.Sprintf("Package blocked by dependency cooldown: GO/%s@%s\n\nPublished %d day(s) ago; cooldown window is %d day(s) (%d remaining).",
-			module, version, daysAgo, cooldownDays, daysLeft),
-		pmgconfig.Get().Config.AdvisoryMessage)
-
 	return &proxy.InterceptorResponse{
 		Action:      proxy.ActionBlock,
 		BlockCode:   http.StatusForbidden,
-		BlockMessage: message,
+		BlockReason: proxy.BlockReasonDependencyCooldown,
+		BlockContext: &proxy.BlockContext{
+			Ecosystem:        packagev1.Ecosystem_ECOSYSTEM_GO,
+			PackageName:      module,
+			PackageVersion:   version,
+			CooldownDays:     cooldownDays,
+			CooldownDaysAgo:  daysAgo,
+			CooldownDaysLeft: daysLeft,
+		},
 	}, true
 }
 

proxy/interceptors/go_cooldown_test.go

@@ -7,6 +7,7 @@ import (
 	"testing"
 	"time"
 
+	packagev1 "buf.build/gen/go/safedep/api/protocolbuffers/go/safedep/messages/package/v1"
 	"github.com/safedep/pmg/proxy"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
@@ -39,6 +40,15 @@ func TestGoCooldownCheckZipDownloadSideFetch(t *testing.T) {
 		require.True(t, handled)
 		assert.Equal(t, proxy.ActionBlock, resp.Action)
 		assert.Equal(t, http.StatusForbidden, resp.BlockCode)
+		assert.Equal(t, proxy.BlockReasonDependencyCooldown, resp.BlockReason)
+
+		require.NotNil(t, resp.BlockContext)
+		assert.Equal(t, packagev1.Ecosystem_ECOSYSTEM_GO, resp.BlockContext.Ecosystem)
+		assert.Equal(t, "example.com/fresh", resp.BlockContext.PackageName)
+		assert.Equal(t, "v1.1.0", resp.BlockContext.PackageVersion)
+		assert.Equal(t, 7, resp.BlockContext.CooldownDays)
+		assert.Equal(t, 1, resp.BlockContext.CooldownDaysAgo)
+		assert.Equal(t, 6, resp.BlockContext.CooldownDaysLeft)
 	})
 
 	t.Run("fails open when the out-of-band fetch fails", func(t *testing.T) {

proxy/proxy.go

@@ -62,6 +62,11 @@ type ProxyConfig struct {
 	// Interceptors
 	Interceptors []Interceptor
 
+	// BlockMessageRenderer composes the response body for blocked requests
+	// from the interceptor's structured block decision. nil falls back to
+	// the generic block message.
+	BlockMessageRenderer func(BlockReason, *BlockContext) string
+
 	// Other configuration
 	EnableMITM     bool
 	RequestTimeout time.Duration
@@ -561,6 +566,9 @@ func (ps *proxyServer) registerHandlers() {
 				}
 
 				message := resp.BlockMessage
+				if message == "" && ps.config.BlockMessageRenderer != nil {
+					message = ps.config.BlockMessageRenderer(resp.BlockReason, resp.BlockContext)
+				}
 				if message == "" {
 					message = "Blocked by proxy interceptor"
 				}

test/proxye2e/harness.go

@@ -14,7 +14,9 @@ import (
 
 	packagev1 "buf.build/gen/go/safedep/api/protocolbuffers/go/safedep/messages/package/v1"
 	"github.com/safedep/pmg/analyzer"
+	"github.com/safedep/pmg/config"
 	"github.com/safedep/pmg/internal/models"
+	"github.com/safedep/pmg/internal/ui"
 	"github.com/safedep/pmg/proxy"
 	"github.com/safedep/pmg/proxy/certmanager"
 	"github.com/safedep/pmg/proxy/interceptors"
@@ -151,6 +153,8 @@ func buildProxy(t *testing.T, certMgr certmanager.CertificateManager, upstreamAd
 	cfg := proxy.DefaultProxyConfig()
 	cfg.CertManager = certMgr
 	cfg.Interceptors = interceptorList
+	presenter := ui.ProxyPresenter{Advisory: config.AdvisoryMessage}
+	cfg.BlockMessageRenderer = presenter.BlockMessage
 
 	// All upstream connections — MITM'd round-trips and CONNECT tunnels for
 	// non-MITM hosts alike — terminate at the mock registry, so no test reaches