diff --git a/crates/op-orchestrator/src/append.rs b/crates/op-orchestrator/src/append.rs
new file mode 100644
index 000000000..158831b38
--- /dev/null
+++ b/crates/op-orchestrator/src/append.rs
@@ -0,0 +1,313 @@
+//! Append-to-document mode — `apply_append_context_to_plan`.
+//!
+//! Faithful port of `apps/web/src/services/ai/orchestrator-append.ts`.
+//! Mutates an [`OrchestratorPlan`] in-place when an [`AppendContext`] is
+//! present; returns an [`AppendPlanResult`] that `run.rs` uses to skip
+//! root-frame insertion and status-bar scaffold (Task B2).
+
+#![allow(dead_code)] // callers land in Task B2
+
+use crate::plan::OrchestratorPlan;
+use crate::types::AppendContext;
+
+/// Result of applying append context to a plan.
+///
+/// Port of the three-field return in `orchestrator-append.ts`.
+/// `plan` is mutated in-place; these flags tell `run.rs` what to skip.
+pub(crate) struct AppendPlanResult {
+    pub skip_root_insertion: bool,
+    pub skip_status_bar: bool,
+}
+
+/// Returns `true` when `id + " " + label` (lowercased) matches any of the
+/// status-bar keyword alternatives.
+///
+/// Port of `STATUS_BAR_SUBTASK_RE = /(status\s*bar|status_bar|status-bar|system chrome|系统栏|状态栏)/i`.
+/// We avoid the `regex` crate: the only non-literal in the original is `\s*`
+/// between "status" and "bar".  We cover that with two literals:
+/// `"status bar"` (single space) and `"statusbar"` (zero spaces).
+fn is_status_bar_subtask(id: &str, label: &str) -> bool {
+    let haystack = format!("{id} {label}").to_lowercase();
+    haystack.contains("status bar")
+        || haystack.contains("statusbar")
+        || haystack.contains("status_bar")
+        || haystack.contains("status-bar")
+        || haystack.contains("system chrome")
+        || haystack.contains("系统栏")
+        || haystack.contains("状态栏")
+}
+
+/// Mutates `plan` according to `append` and returns skip-flags for `run.rs`.
+///
+/// - `None` → returns `{ false, false }`, plan unmutated.
+/// - `Some(a)`:
+///   - `plan.root_frame.id` ← `a.target_parent_id`
+///   - `plan.root_frame.width` ← `a.target_width`
+///   - status-bar subtasks filtered out
+///   - every remaining subtask's `existing_section_labels` ← `Some(a.existing_section_labels.clone())`
+///   - returns `{ skip_root_insertion: true, skip_status_bar: true }`
+///
+/// Port of `applyAppendContextToPlan` in `orchestrator-append.ts`.
+pub(crate) fn apply_append_context_to_plan(
+    plan: &mut OrchestratorPlan,
+    append: Option<&AppendContext>,
+) -> AppendPlanResult {
+    let Some(a) = append else {
+        return AppendPlanResult {
+            skip_root_insertion: false,
+            skip_status_bar: false,
+        };
+    };
+
+    plan.root_frame.id = a.target_parent_id.clone();
+    plan.root_frame.width = a.target_width;
+    plan.subtasks
+        .retain(|st| !is_status_bar_subtask(&st.id, &st.label));
+    for st in &mut plan.subtasks {
+        st.existing_section_labels = Some(a.existing_section_labels.clone());
+    }
+
+    AppendPlanResult {
+        skip_root_insertion: true,
+        skip_status_bar: true,
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::plan::{OrchestratorPlan, Region, RootFrameSpec, Subtask};
+
+    fn make_plan(subtask_ids_labels: &[(&str, &str)]) -> OrchestratorPlan {
+        OrchestratorPlan {
+            root_frame: RootFrameSpec {
+                id: "original-root".into(),
+                name: "Design".into(),
+                width: 1200.0,
+                height: 800.0,
+                layout: Some("vertical".into()),
+                gap: None,
+                padding: None,
+                fill: None,
+            },
+            subtasks: subtask_ids_labels
+                .iter()
+                .map(|(id, label)| Subtask {
+                    id: id.to_string(),
+                    label: label.to_string(),
+                    region: Region {
+                        width: 1200.0,
+                        height: 400.0,
+                    },
+                    id_prefix: id.to_string(),
+                    parent_frame_id: None,
+                    elements: None,
+                    screen: None,
+                    generated_root_id: None,
+                    existing_section_labels: None,
+                })
+                .collect(),
+            style_guide_name: None,
+        }
+    }
+
+    fn make_ctx(id: &str, width: f64, labels: &[&str]) -> AppendContext {
+        AppendContext {
+            target_parent_id: id.into(),
+            target_width: width,
+            existing_section_labels: labels.iter().map(|s| s.to_string()).collect(),
+            is_mobile: false,
+        }
+    }
+
+    // ── None case ─────────────────────────────────────────────────────────────
+
+    /// None → returns { false, false }, plan unmutated.
+    #[test]
+    fn none_returns_false_flags_and_no_mutation() {
+        let mut plan = make_plan(&[("hero", "Hero"), ("features", "Features")]);
+        let original_id = plan.root_frame.id.clone();
+        let original_width = plan.root_frame.width;
+        let original_subtask_count = plan.subtasks.len();
+
+        let result = apply_append_context_to_plan(&mut plan, None);
+
+        assert!(!result.skip_root_insertion);
+        assert!(!result.skip_status_bar);
+        assert_eq!(plan.root_frame.id, original_id, "root id must be unmutated");
+        assert_eq!(
+            plan.root_frame.width, original_width,
+            "root width must be unmutated"
+        );
+        assert_eq!(
+            plan.subtasks.len(),
+            original_subtask_count,
+            "subtask count must be unmutated"
+        );
+        assert!(
+            plan.subtasks
+                .iter()
+                .all(|st| st.existing_section_labels.is_none()),
+            "existing_section_labels must remain None"
+        );
+    }
+
+    // ── Some case: basic mutation ──────────────────────────────────────────────
+
+    /// Some(ctx) → returns { true, true }, root_frame repointed, labels propagated.
+    #[test]
+    fn some_returns_true_flags_and_mutates_plan() {
+        let mut plan = make_plan(&[("hero", "Hero"), ("pricing", "Pricing")]);
+        let ctx = make_ctx("existing-frame-abc", 390.0, &["Hero", "About"]);
+
+        let result = apply_append_context_to_plan(&mut plan, Some(&ctx));
+
+        assert!(result.skip_root_insertion);
+        assert!(result.skip_status_bar);
+        assert_eq!(plan.root_frame.id, "existing-frame-abc");
+        assert_eq!(plan.root_frame.width, 390.0);
+    }
+
+    /// Each remaining subtask gets existing_section_labels = Some(ctx labels).
+    #[test]
+    fn some_propagates_existing_section_labels_to_all_remaining_subtasks() {
+        let mut plan = make_plan(&[("hero", "Hero"), ("pricing", "Pricing")]);
+        let ctx = make_ctx("frame-1", 1200.0, &["Hero", "Pricing"]);
+
+        apply_append_context_to_plan(&mut plan, Some(&ctx));
+
+        for st in &plan.subtasks {
+            let labels = st.existing_section_labels.as_ref().expect("labels set");
+            assert_eq!(labels, &vec!["Hero", "Pricing"]);
+        }
+    }
+
+    // ── Status-bar filter ─────────────────────────────────────────────────────
+
+    /// "status-bar" in id is matched and filtered.
+    #[test]
+    fn status_bar_subtask_filtered_by_id_hyphen() {
+        let mut plan = make_plan(&[("status-bar", "Top Area"), ("hero", "Hero")]);
+        let ctx = make_ctx("frame-1", 390.0, &[]);
+        apply_append_context_to_plan(&mut plan, Some(&ctx));
+        assert_eq!(plan.subtasks.len(), 1);
+        assert_eq!(plan.subtasks[0].id, "hero");
+    }
+
+    /// "Status Bar" in label (case-insensitive) is matched and filtered.
+    #[test]
+    fn status_bar_subtask_filtered_by_label_case_insensitive() {
+        let mut plan = make_plan(&[("chrome", "Status Bar"), ("hero", "Hero")]);
+        let ctx = make_ctx("frame-1", 390.0, &[]);
+        apply_append_context_to_plan(&mut plan, Some(&ctx));
+        assert_eq!(plan.subtasks.len(), 1);
+        assert_eq!(plan.subtasks[0].id, "hero");
+    }
+
+    /// CJK 状态栏 in label is matched.
+    #[test]
+    fn status_bar_subtask_filtered_by_cjk_zhuangtailan() {
+        let mut plan = make_plan(&[("chrome", "状态栏"), ("hero", "Hero")]);
+        let ctx = make_ctx("frame-1", 390.0, &[]);
+        apply_append_context_to_plan(&mut plan, Some(&ctx));
+        assert_eq!(plan.subtasks.len(), 1);
+        assert_eq!(plan.subtasks[0].id, "hero");
+    }
+
+    /// CJK 系统栏 in label is matched.
+    #[test]
+    fn status_bar_subtask_filtered_by_cjk_xitonglan() {
+        let mut plan = make_plan(&[("chrome", "系统栏"), ("content", "Content")]);
+        let ctx = make_ctx("frame-1", 390.0, &[]);
+        apply_append_context_to_plan(&mut plan, Some(&ctx));
+        assert_eq!(plan.subtasks.len(), 1);
+        assert_eq!(plan.subtasks[0].id, "content");
+    }
+
+    /// "system chrome" in label is matched.
+    #[test]
+    fn status_bar_subtask_filtered_by_system_chrome() {
+        let mut plan = make_plan(&[("top-bar", "System Chrome"), ("footer", "Footer")]);
+        let ctx = make_ctx("frame-1", 390.0, &[]);
+        apply_append_context_to_plan(&mut plan, Some(&ctx));
+        assert_eq!(plan.subtasks.len(), 1);
+        assert_eq!(plan.subtasks[0].id, "footer");
+    }
+
+    /// "statusbar" (zero space) in label is matched (covers `\s*` zero-space case).
+    #[test]
+    fn status_bar_subtask_filtered_by_statusbar_no_space() {
+        let mut plan = make_plan(&[("s", "statusbar"), ("hero", "Hero")]);
+        let ctx = make_ctx("frame-1", 390.0, &[]);
+        apply_append_context_to_plan(&mut plan, Some(&ctx));
+        assert_eq!(plan.subtasks.len(), 1);
+        assert_eq!(plan.subtasks[0].id, "hero");
+    }
+
+    /// "status_bar" (underscore) in id is matched.
+    #[test]
+    fn status_bar_subtask_filtered_by_underscore() {
+        let mut plan = make_plan(&[("status_bar", "Chrome"), ("hero", "Hero")]);
+        let ctx = make_ctx("frame-1", 390.0, &[]);
+        apply_append_context_to_plan(&mut plan, Some(&ctx));
+        assert_eq!(plan.subtasks.len(), 1);
+        assert_eq!(plan.subtasks[0].id, "hero");
+    }
+
+    /// "Status Mention" should NOT match (no false positive).
+    #[test]
+    fn status_mention_is_not_filtered() {
+        let mut plan = make_plan(&[("status-mention", "Status Mention"), ("hero", "Hero")]);
+        let ctx = make_ctx("frame-1", 390.0, &[]);
+        apply_append_context_to_plan(&mut plan, Some(&ctx));
+        // Neither subtask matches the status-bar pattern
+        assert_eq!(plan.subtasks.len(), 2);
+    }
+
+    /// Multiple status-bar subtasks all get filtered.
+    #[test]
+    fn multiple_status_bar_subtasks_all_filtered() {
+        let mut plan = make_plan(&[
+            ("status-bar", "Status Bar"),
+            ("hero", "Hero"),
+            ("system-chrome", "System Chrome"),
+            ("footer", "Footer"),
+        ]);
+        let ctx = make_ctx("frame-1", 390.0, &[]);
+        apply_append_context_to_plan(&mut plan, Some(&ctx));
+        assert_eq!(plan.subtasks.len(), 2);
+        let ids: Vec<_> = plan.subtasks.iter().map(|st| st.id.as_str()).collect();
+        assert!(ids.contains(&"hero"));
+        assert!(ids.contains(&"footer"));
+    }
+
+    // ── Full integration: all mutations together ───────────────────────────────
+
+    /// Full append scenario: root repointed, status-bar filtered, labels propagated.
+    #[test]
+    fn full_append_scenario() {
+        let mut plan = make_plan(&[
+            ("status-bar", "Status Bar"),
+            ("hero", "Hero"),
+            ("pricing", "Pricing"),
+        ]);
+        let ctx = make_ctx("target-frame-xyz", 390.0, &["Nav", "Hero"]);
+
+        let result = apply_append_context_to_plan(&mut plan, Some(&ctx));
+
+        assert!(result.skip_root_insertion);
+        assert!(result.skip_status_bar);
+        assert_eq!(plan.root_frame.id, "target-frame-xyz");
+        assert_eq!(plan.root_frame.width, 390.0);
+        // status-bar filtered out; 2 remaining
+        assert_eq!(plan.subtasks.len(), 2);
+        let ids: Vec<_> = plan.subtasks.iter().map(|st| st.id.as_str()).collect();
+        assert!(ids.contains(&"hero"));
+        assert!(ids.contains(&"pricing"));
+        // labels propagated to all remaining
+        for st in &plan.subtasks {
+            let labels = st.existing_section_labels.as_ref().unwrap();
+            assert_eq!(labels, &vec!["Nav", "Hero"]);
+        }
+    }
+}
diff --git a/crates/op-orchestrator/src/lib.rs b/crates/op-orchestrator/src/lib.rs
index 4fd2fc486..ac7d4d7a9 100644
--- a/crates/op-orchestrator/src/lib.rs
+++ b/crates/op-orchestrator/src/lib.rs
@@ -24,6 +24,7 @@ pub mod timeouts;
 pub mod types;
 pub mod variables;
 
+pub mod append;
 pub mod cleanup;
 pub mod concurrent;
 pub mod prompt;