diff --git a/crates/engine/src/cmd/edit.rs b/crates/engine/src/cmd/edit.rs
index f878cc9691..bcc9cff404 100644
--- a/crates/engine/src/cmd/edit.rs
+++ b/crates/engine/src/cmd/edit.rs
@@ -79,12 +79,14 @@ pub fn specs() -> Vec<CommandSpec> {
                 Some("the Spike is empty")
             }
         }),
-        CommandSpec::new("edit.paste", "Paste", "Home › Clipboard", paste).key("Mod+V / Shift+Insert").params(r#"{"text"?: string, "html"?: string, "rtf"?: string}"#),
+        CommandSpec::new("edit.paste", "Paste", "Home › Clipboard", paste)
+            .key("Mod+V / Shift+Insert")
+            .params(r#"{"text"?: string, "html"?: string, "rtf"?: string, "privateClipboard"?: bool}"#),
         CommandSpec::new("edit.pasteText", "Paste: Keep Text Only", "Home › Clipboard › Paste", paste_text)
             .params(r#"{"text"?: string}"#)
             .key("Mod+Shift+Alt+V"),
         CommandSpec::new("edit.pasteMerge", "Paste: Merge Formatting", "Home › Clipboard › Paste", paste_merge)
-            .params(r#"{"text"?: string, "html"?: string, "rtf"?: string}"#),
+            .params(r#"{"text"?: string, "html"?: string, "rtf"?: string, "privateClipboard"?: bool}"#),
         CommandSpec::new("edit.clipboardPane", "Clipboard Pane", "Home › Clipboard", |s, v| {
             let on = p::bool(v, "value").unwrap_or(!s.view.clipboard_pane);
             s.view.clipboard_pane = on;
diff --git a/crates/engine/src/cmd/paste.rs b/crates/engine/src/cmd/paste.rs
index 4a8aad3b02..e4df30bd95 100644
--- a/crates/engine/src/cmd/paste.rs
+++ b/crates/engine/src/cmd/paste.rs
@@ -37,7 +37,7 @@ pub fn specs() -> Vec<CommandSpec> {
     vec![
         CommandSpec::new("edit.pasteSpecial", "Paste Special", "Home › Clipboard › Paste", paste_special)
             .key("Mod+Alt+V")
-            .params(r#"{"as"?: "formatted"|"rtf"|"html"|"picture"|"text", "text"?: string, "html"?: string, "rtf"?: string, "picture"?: base64}"#),
+            .params(r#"{"as"?: "formatted"|"rtf"|"html"|"picture"|"text", "text"?: string, "html"?: string, "rtf"?: string, "picture"?: base64, "privateClipboard"?: bool}"#),
     ]
 }
 
@@ -58,11 +58,18 @@ fn looks_like_html(t: &str) -> bool {
     t.starts_with('<') && (t.contains("</") || t.contains("/>"))
 }
 
+/// Whether the system clipboard still holds this window's copy. A front end that can check says
+/// so in `privateClipboard`; callers that cannot (an agent, the CLI) omit it, and the session's
+/// copy is used as before.
+fn owns_clipboard(v: &Value) -> bool {
+    p::bool(v, "privateClipboard").unwrap_or(true)
+}
+
 /// The source for a format, if the clipboard has it.
 fn source(s: &Session, v: &Value, fmt: &str) -> Option<String> {
     let non_empty = |t: String| if t.is_empty() { None } else { Some(t) };
     match fmt {
-        "formatted" => {
+        "formatted" if owns_clipboard(v) => {
             let f = s.clipboard.as_ref()?;
             // System clipboard text that isn't our own copy means someone else copied since.
             match p::str(v, "text") {
@@ -70,6 +77,7 @@ fn source(s: &Session, v: &Value, fmt: &str) -> Option<String> {
                 _ => Some(String::new()),
             }
         }
+        "formatted" => None,
         "rtf" => p::str(v, "rtf").map(str::to_string).or_else(|| clip_text(s, v).filter(|t| looks_like_rtf(t))).and_then(non_empty),
         "html" => p::str(v, "html").map(str::to_string).or_else(|| clip_text(s, v).filter(|t| looks_like_html(t))).and_then(non_empty),
         "picture" => p::str(v, "picture").map(str::to_string).and_then(non_empty),
@@ -105,6 +113,10 @@ fn paste_special(s: &mut Session, v: &Value) -> CmdResult {
                 req[k] = json!(t);
             }
         }
+        // Keep the ownership result so the dialog's list is the same as this one.
+        if let Some(own) = p::bool(v, "privateClipboard") {
+            req["privateClipboard"] = json!(own);
+        }
         // Only the newest dialog request matters; older ones would pin their payloads.
         s.ui_requests.retain(|r| r["open"] != "pasteSpecial");
         s.push_ui_request(req);
@@ -265,10 +277,13 @@ pub enum Pasted {
 }
 
 /// What Paste inserts: WordCraft's own copy while the system clipboard still holds it, else
-/// another program's formatted copy (HTML, RTF), else the system clipboard's text.
+/// another program's formatted copy (HTML, RTF), else the system clipboard's text. A front end
+/// that knows another program owns the clipboard passes `privateClipboard: false`, which keeps
+/// the fragment out even when the text matches.
 pub fn paste_content(s: &mut Session, v: &Value) -> Result<Pasted, CmdError> {
     let text = p::str(v, "text").map(|t| t.replace("\r\n", "\n"));
-    if let Some(f) = &s.clipboard
+    if owns_clipboard(v)
+        && let Some(f) = &s.clipboard
         && text.as_ref().is_none_or(|t| f.clipboard_text() == *t)
         && (text.is_some() || (p::str(v, "html").is_none() && p::str(v, "rtf").is_none()))
     {
diff --git a/crates/engine/src/tests.rs b/crates/engine/src/tests.rs
index 6439b3de9e..5fe96f0729 100644
--- a/crates/engine/src/tests.rs
+++ b/crates/engine/src/tests.rs
@@ -1193,6 +1193,52 @@ fn clipboard_round_trip() {
     assert_eq!(text(&s), "plain\ntext");
 }
 
+/// Whether any run in the body is bold.
+fn any_bold(s: &Session) -> bool {
+    s.doc.body.iter().filter_map(|b| b.as_para()).flat_map(|p| p.runs.iter()).any(|r| r.props.bold == Some(true))
+}
+
+#[test]
+fn paste_from_another_program_does_not_bring_back_our_fragment() {
+    // Review on #6225: when another program owns the clipboard, matching text must not make
+    // Paste put WordCraft's own formatted fragment back.
+    let mut s = s();
+    run(&mut s, "document.setText", json!({"text": "Bold"}));
+    run(&mut s, "select.all", json!({}));
+    run(&mut s, "format.bold", json!({}));
+    run(&mut s, "edit.copy", json!({}));
+    assert_eq!(s.clipboard_text, "Bold");
+
+    // The same text, copied by another program: paste it as plain text, not our bold fragment.
+    run(&mut s, "document.setText", json!({"text": "Plain "}));
+    run(&mut s, "caret.docEnd", json!({}));
+    run(&mut s, "edit.paste", json!({"text": "Bold", "privateClipboard": false}));
+    assert_eq!(text(&s), "Plain Bold");
+    assert!(!any_bold(&s), "{:?}", s.doc.body);
+
+    // Callers that omit the flag (an agent, the CLI) still get the session's own copy.
+    run(&mut s, "caret.docEnd", json!({}));
+    run(&mut s, "edit.paste", json!({"text": "Bold"}));
+    assert!(any_bold(&s), "{:?}", s.doc.body);
+}
+
+#[test]
+fn paste_special_does_not_offer_our_fragment_for_another_programs_copy() {
+    let mut s = s();
+    run(&mut s, "document.setText", json!({"text": "Bold"}));
+    run(&mut s, "select.all", json!({}));
+    run(&mut s, "format.bold", json!({}));
+    run(&mut s, "edit.copy", json!({}));
+
+    let r = run(&mut s, "edit.pasteSpecial", json!({"text": "Bold", "privateClipboard": false}));
+    let ids: Vec<&str> = r["formats"].as_array().map(|a| a.iter().filter_map(|f| f["id"].as_str()).collect()).unwrap_or_default();
+    assert!(!ids.contains(&"formatted"), "{ids:?}");
+    assert_eq!(s.ui_requests.last().and_then(|r| r.get("privateClipboard")), Some(&json!(false)), "{:?}", s.ui_requests);
+
+    let e = s.run("edit.pasteSpecial", &json!({"as": "formatted", "text": "Bold", "privateClipboard": false}));
+    assert!(e.is_err(), "another program's copy cannot be pasted as our fragment");
+}
+
 /// Equations in the paragraphs of a session's body, as linear text.
 fn equations(s: &Session) -> Vec<String> {
     let mut out = Vec::new();
diff --git a/crates/ui-egui/src/dialogs.rs b/crates/ui-egui/src/dialogs.rs
index 8f20dc4ecb..c9872347a9 100644
--- a/crates/ui-egui/src/dialogs.rs
+++ b/crates/ui-egui/src/dialogs.rs
@@ -869,6 +869,9 @@ impl Dialog {
                 kept[k] = json!(t);
             }
         }
+        if let Some(own) = payload.get("privateClipboard").and_then(Value::as_bool) {
+            kept["privateClipboard"] = json!(own);
+        }
         let note = if formats.is_empty() { crate::system_clipboard::nothing_to_paste(app) } else { String::new() };
         Dialog::PasteSpecial { formats, choice: 0, payload: kept, note }
     }
diff --git a/crates/ui-egui/src/dialogs/tests.rs b/crates/ui-egui/src/dialogs/tests.rs
index eb31a99c32..7154033a25 100644
--- a/crates/ui-egui/src/dialogs/tests.rs
+++ b/crates/ui-egui/src/dialogs/tests.rs
@@ -3,6 +3,19 @@ use wordcraft_doc::Pos;
 use wordcraft_doc::props::Align;
 use wordcraft_engine::Session;
 
+/// Paste Special lists and pastes the same formats the engine chose: the clipboard ownership
+/// result must survive into the dialog's payload, or another program's copy could be replaced
+/// by WordCraft's own fragment.
+#[test]
+fn paste_special_dialog_keeps_the_clipboard_ownership_result() {
+    let a = WordApp::new(Session::new(wordcraft_doc::Document::from_text("")), crate::Services::default());
+    let d = Dialog::paste_special(&a, &json!({"text": "Bold", "privateClipboard": false}));
+    let Dialog::PasteSpecial { formats, payload, .. } = d else { panic!("not Paste Special") };
+    assert_eq!(formats, ["text"], "another program's copy isn't our fragment");
+    assert_eq!(payload.get("privateClipboard"), Some(&json!(false)));
+    assert_eq!(payload.get("text").and_then(Value::as_str), Some("Bold"));
+}
+
 /// #3931: hovering Insert › Table's grid asks the page for a preview of that table (rows by
 /// columns) and changes nothing; leaving the grid drops it; a click inserts the table with no
 /// preview left over for the page to show on top of it.