diff --git a/crates/op-orchestrator/src/lib.rs b/crates/op-orchestrator/src/lib.rs
index ad9cafc35..76ed3a5f1 100644
--- a/crates/op-orchestrator/src/lib.rs
+++ b/crates/op-orchestrator/src/lib.rs
@@ -56,5 +56,8 @@ pub use intent::classify_intent;
 pub use model_profile::{resolve_model_profile, ModelProfile, ModelTier};
 pub use prompt::build_orchestrator_prompt;
 pub use run::Orchestrator;
-pub use stub_providers::{SkippedPreValidator, SkippedScreenshotProvider, SkippedVisionLlmClient};
+pub use stub_providers::{
+    SkippedPreValidator, SkippedScreenshotProvider, SkippedVisionLlmClient,
+    SkippedVisualRefProvider,
+};
 pub use types::*;
diff --git a/crates/op-orchestrator/src/stub_providers.rs b/crates/op-orchestrator/src/stub_providers.rs
index 1abbcc721..1c0aed3c3 100644
--- a/crates/op-orchestrator/src/stub_providers.rs
+++ b/crates/op-orchestrator/src/stub_providers.rs
@@ -1,5 +1,5 @@
 //! Production-visible stub provider implementations for the vision
-//! validation pipeline (S3c).
+//! validation pipeline (S3c) and visual-ref pipeline (S4).
 //!
 //! Hosts use these when the real implementations are not yet wired —
 //! `op-design-lint` integration is pending host wiring, screenshot
@@ -14,6 +14,8 @@
 //!   loop exits before any vision round.
 //! - `SkippedVisionLlmClient::validate` → `VisionResponse::Skipped`
 //!   (defensive in case `capture_root_frame` ever returns `Some`).
+//! - `SkippedVisualRefProvider::render_html_to_screenshot` → `None`,
+//!   so the visual-ref pipeline skips immediately to plain orchestration.
 //!
 //! Net result: the Progress stream emits `ValidationStarted` →
 //! `ValidationPreCheckDone { applied: 0, .. }` →
@@ -23,7 +25,7 @@
 
 use crate::types::{
     DocSink, PreValidationResult, PreValidator, ScreenshotProvider, VisionCallRequest,
-    VisionLlmClient, VisionResponse,
+    VisionLlmClient, VisionResponse, VisualRefProvider,
 };
 
 /// Stub `PreValidator` — always returns zero fixes; no side effects.
@@ -53,3 +55,13 @@ impl VisionLlmClient for SkippedVisionLlmClient {
         VisionResponse::Skipped { reason: None }
     }
 }
+
+/// Stub `VisualRefProvider` — always returns `None`. Visual-ref pipeline
+/// short-circuits to plain orchestration without rendering any HTML.
+pub struct SkippedVisualRefProvider;
+
+impl VisualRefProvider for SkippedVisualRefProvider {
+    fn render_html_to_screenshot(&self, _html: &str, _width: f64, _height: f64) -> Option<String> {
+        None
+    }
+}
diff --git a/crates/op-orchestrator/src/types.rs b/crates/op-orchestrator/src/types.rs
index f068306e0..cb22a8cab 100644
--- a/crates/op-orchestrator/src/types.rs
+++ b/crates/op-orchestrator/src/types.rs
@@ -160,6 +160,23 @@ pub struct ValidationProviders<'a> {
     pub system_prompt: String,
 }
 
+// ── S4: VisualRefProvider ─────────────────────────────────────────────────────
+
+/// Visual-reference rendering outlet.
+///
+/// host 实现把 HTML 字符串渲染成 base64 PNG 截图;stub 返回 `None`
+/// 表示"跳过视觉参考阶段"。
+///
+/// Port of the `renderHtmlToScreenshot` call-site shape in
+/// `visual-ref-orchestrator.ts:108-122` + spec §4.5.
+pub trait VisualRefProvider: Send + Sync {
+    /// 将 HTML 字符串渲染为给定像素尺寸的截图,返回 base64 PNG;
+    /// `None` 表示不可用 / 跳过。
+    fn render_html_to_screenshot(&self, html: &str, width: f64, height: f64) -> Option<String>;
+}
+
+// ── S4 end ────────────────────────────────────────────────────────────────────
+
 // ── S3c end ───────────────────────────────────────────────────────────────────
 
 /// 廉价可克隆的中止句柄(`Arc<AtomicBool>` 语义)。
@@ -564,6 +581,42 @@ mod tests {
         }
     }
 
+    // ── Task A2: VisualRefProvider trait + SkippedVisualRefProvider stub ─────────
+
+    /// `SkippedVisualRefProvider` returns `None` for any input.
+    #[test]
+    fn skipped_visual_ref_provider_returns_none() {
+        use crate::stub_providers::SkippedVisualRefProvider;
+        let p = SkippedVisualRefProvider;
+        assert!(p
+            .render_html_to_screenshot("<html></html>", 1280.0, 800.0)
+            .is_none());
+        assert!(p.render_html_to_screenshot("", 0.0, 0.0).is_none());
+        assert!(p
+            .render_html_to_screenshot("<html><body>Hello</body></html>", 390.0, 844.0)
+            .is_none());
+    }
+
+    /// `VisualRefProvider` trait is `Send + Sync`.
+    #[test]
+    fn visual_ref_provider_is_send_sync() {
+        use crate::types::VisualRefProvider;
+        fn assert_send_sync<T: Send + Sync + ?Sized>() {}
+        assert_send_sync::<dyn VisualRefProvider>();
+    }
+
+    /// `op_orchestrator::SkippedVisualRefProvider` resolves from a host-style import.
+    #[test]
+    fn skipped_visual_ref_provider_resolves_from_crate_root() {
+        use crate::{SkippedVisualRefProvider, VisualRefProvider};
+        let p: &dyn VisualRefProvider = &SkippedVisualRefProvider;
+        assert!(p
+            .render_html_to_screenshot("<p>test</p>", 800.0, 600.0)
+            .is_none());
+    }
+
+    // ── Task A2 end ───────────────────────────────────────────────────────────────
+
     /// `DesignRequest.validation_enabled` defaults to `true` when omitted from JSON.
     #[test]
     fn design_request_validation_enabled_defaults_true() {