fix(cr-2026-04-22): paste_text_replacing snapshots and restores prior clipboard

MAJOR from the 2026-04-22 review (paste.rs:181-217): unlike
paste_text, the replace flow did not snapshot the user's clipboard
before writing the raw transcript. A successful revert left the raw
transcript on the clipboard and destroyed whatever the user had
copied before invoking it — inconsistent with paste_text's Handy-#921
contract (brief item #3).

Extracts the snapshot+restore pattern into two helpers shared
between paste_text and paste_text_replacing:

- snapshot_clipboard_text() -> Option<String>
- schedule_clipboard_restore(prior, transcript)

Both paste_text and paste_text_replacing now run the same
capture-before-stomp, restore-after-fire sequence. The restore-
guard (only restore if clipboard still holds the transcript we set)
is shared too, so a user who copies something new within the 300 ms
window is still respected.

DRY: removes ~15 lines of inline clipboard bookkeeping from
paste_text while making the replace flow identical.

src-tauri/src/commands/paste.rs

@@ -72,18 +72,7 @@ pub async fn paste_text(app: tauri::AppHandle, text: String) -> Result<PasteOutc
         message: None,
     };
 
-    // Snapshot the user's existing clipboard text BEFORE we stomp it
-    // with the transcript, so a background task can restore it after
-    // the paste keystroke has landed. `arboard::Clipboard::get_text`
-    // returns Err when the clipboard holds non-text content (images,
-    // files, empty) — in those cases we skip the restore step
-    // entirely rather than trying to coerce. This is the "never
-    // silently clobber the user's clipboard" contract from Handy
-    // #921 (Workstream B brief item #3).
-    let prior_clipboard: Option<String> = match Clipboard::new() {
-        Ok(mut cb) => cb.get_text().ok(),
-        Err(_) => None,
-    };
+    let prior_clipboard = snapshot_clipboard_text();
 
     match Clipboard::new().and_then(|mut cb| cb.set_text(&text)) {
         Ok(()) => outcome.copied = true,
@@ -121,25 +110,40 @@ pub async fn paste_text(app: tauri::AppHandle, text: String) -> Result<PasteOutc
         Err(err) => outcome.message = Some(err),
     }
 
-    // Fire-and-forget: restore the prior clipboard in the background
-    // after CLIPBOARD_RESTORE_MS, regardless of whether the paste
-    // succeeded. If paste failed, the transcript is still on the
-    // clipboard and Kon's own "Copy" button remains the user's
-    // recovery path; overwriting it with the restore would undo that.
-    // So only restore when the keystroke actually fired.
     if outcome.pasted {
-        if let Some(prior) = prior_clipboard.clone() {
-            let transcript_clone = text.clone();
-            tokio::spawn(async move {
-                tokio::time::sleep(Duration::from_millis(CLIPBOARD_RESTORE_MS)).await;
-                restore_prior_clipboard(&prior, &transcript_clone);
-            });
-        }
+        schedule_clipboard_restore(prior_clipboard, text);
     }
 
     Ok(outcome)
 }
 
+/// Snapshot the clipboard's current text, or `None` when the clipboard
+/// holds non-text content (images, files, empty). Shared between
+/// `paste_text` and `paste_text_replacing` so both halves of the
+/// dictation flow obey the "never silently clobber the user's
+/// clipboard" contract from Handy #921 (brief item #3).
+fn snapshot_clipboard_text() -> Option<String> {
+    match Clipboard::new() {
+        Ok(mut cb) => cb.get_text().ok(),
+        Err(_) => None,
+    }
+}
+
+/// Fire-and-forget: restore `prior` to the clipboard after
+/// `CLIPBOARD_RESTORE_MS`, but only if the clipboard still holds the
+/// `transcript` we set (i.e., the user hasn't copied something new in
+/// the window). No-op when `prior` is `None` — nothing safe to
+/// restore.
+fn schedule_clipboard_restore(prior: Option<String>, transcript: String) {
+    let Some(prior) = prior else {
+        return;
+    };
+    tokio::spawn(async move {
+        tokio::time::sleep(Duration::from_millis(CLIPBOARD_RESTORE_MS)).await;
+        restore_prior_clipboard(&prior, &transcript);
+    });
+}
+
 /// Write `prior` back to the clipboard only if the current clipboard
 /// content is still the transcript we just set — i.e. the user hasn't
 /// already copied something new themselves in the last 300 ms. This
@@ -189,6 +193,14 @@ pub async fn paste_text_replacing(
         message: None,
     };
 
+    // Same clipboard-preservation contract as `paste_text`: snapshot
+    // the user's prior clipboard before we write the raw transcript,
+    // restore it in the background after the paste keystroke fires.
+    // Without this, a successful revert leaves the raw transcript on
+    // the clipboard permanently — stomping whatever the user had
+    // copied before invoking replace-with-raw.
+    let prior_clipboard = snapshot_clipboard_text();
+
     match Clipboard::new().and_then(|mut cb| cb.set_text(&text)) {
         Ok(()) => outcome.copied = true,
         Err(err) => {
@@ -214,6 +226,10 @@ pub async fn paste_text_replacing(
         Err(err) => outcome.message = Some(err),
     }
 
+    if outcome.pasted {
+        schedule_clipboard_restore(prior_clipboard, text);
+    }
+
     Ok(outcome)
 }