Fix flush spacing regression while preserving auto-restore

The auto-restore merge reintroduced the spacing bug: on every flush char
the engine re-emitted a Replace and the daemon backspaced+retyped the
already-on-screen composed word, racing against the separately-forwarded
flush char and eating spaces (mất sự->mấtsự, đầu ngã xuống->đầungãxuống).

Now flush only backspaces+retypes when auto-restore actually changes the
word (English/invalid Vietnamese -> raw keystrokes). For a normal composed
word the engine returns None and the daemon types only the flush char,
leaving the correct word untouched on screen.

Co-Authored-By: vndangkhoa <vonguyendangkhoa@gmail.com>

daemon/src/main.rs

@@ -285,15 +285,17 @@ impl Daemon {
     fn replay_and_inject(&mut self, ch: char) -> Vec<OutputCommand> {
         let mut commands = Vec::new();
 
-        // Flush characters: commit current word, type the character, clear state.
+        // Flush characters: commit the current word and type the flush char.
-        // The composed word is already correctly on screen, so we must NOT
+        // Only backspace + retype when auto-restore actually CHANGES the word
-        // backspace and retype it — doing so eats the spacing and shifts the
+        // (English / invalid Vietnamese). For a normal composed word it is
-        // finished word left. Just type the flush char and clear state.
+        // already correctly on screen, so retyping it would eat the spacing and
+        // shift the finished word left.
         if is_flush_char(ch) {
-            if !self.screen_output.is_empty() {
+            let to_commit = self.word_to_commit();
+            if !self.screen_output.is_empty() && to_commit != self.screen_output {
                 let backspaces = self.screen_output.chars().count();
                 commands.push(OutputCommand::Backspace(backspaces));
-                commands.push(OutputCommand::Type(self.word_to_commit()));
+                commands.push(OutputCommand::Type(to_commit));
             }
             // Type the flush character itself
             commands.push(OutputCommand::Type(ch.to_string()));
@@ -317,16 +319,15 @@ impl Daemon {
         );
 
         if did_flush {
-            // Engine flushed a word — it is already correctly on screen, so
+            // Engine flushed a word. Only backspace + retype when auto-restore
-            // just clear state without backspacing/retyping it (retyping eats
+            // actually CHANGES the word; otherwise the composed word is already
-            // spacing and shifts the finished word left).
+            // correct on screen and retyping it eats spacing and shifts the
-            // Engine flushed a word — commit it and clear state
+            // finished word left.
-            // The flush char (space/period/etc) was NOT in history, so we need to
+            let to_commit = self.word_to_commit();
-            // type whatever was on screen + the flush char
+            if !self.screen_output.is_empty() && to_commit != self.screen_output {
-            if !self.screen_output.is_empty() {
                 let backspaces = self.screen_output.chars().count();
                 commands.push(OutputCommand::Backspace(backspaces));
-                commands.push(OutputCommand::Type(self.word_to_commit()));
+                commands.push(OutputCommand::Type(to_commit));
             }
             self.keystroke_history.clear();
             self.screen_output.clear();

engine/src/engine.rs

@@ -213,25 +213,21 @@ impl Engine {
 
             let raw = self.raw_buffer.clone();
             self.reset();
-            // The composed word is already correctly on screen — re-typing it
-            // here would trigger a redundant backspace + clipboard-paste cycle
-            // that races against the separately-forwarded flush char, eating
-            // spaces and merging words. Just finalize and let the flush char
-            // through untouched.
             if prev_len > 0 {
                 // Auto-restore: if the committed word is English / not valid
-                // Vietnamese, revert to the raw keystrokes the user typed.
+                // Vietnamese, revert to the raw keystrokes the user typed. This
+                // genuinely changes the on-screen word, so a Replace is needed.
                 if self.auto_restore && Engine::should_restore_word(&previous, &raw) {
                     return Some(EngineEvent::Replace {
                         backspaces: prev_len,
                         insert: raw,
                     });
                 }
-                // Don't include flush char in insert — daemon forwards it separately
+                // Normal case: the composed word is already correctly on screen.
-                return Some(EngineEvent::Replace {
+                // Re-typing it would trigger a redundant backspace + retype that
-                    backspaces: prev_len,
+                // races against the separately-forwarded flush char, eating
-                    insert: previous,
+                // spaces and merging words. Finalize and let the flush char
-                });
+                // through untouched.
             }
             return None;
         }

engine/tests/auto_restore.rs

@@ -91,11 +91,15 @@ fn auto_restore_can_be_disabled() {
     for ch in "cargo".chars() {
         engine.process_key(ch);
     }
+    // With auto-restore off the Vietnamese composition is kept on screen
+    // (no restore back to the raw English keystrokes).
+    assert_eq!(engine.buffer(), "cảgo");
+    // The composed word is already correct on screen, so flushing emits no
+    // Replace — re-typing it would race with the forwarded flush char and eat
+    // the spacing. (Contrast with auto-restore on, which emits Replace→"cargo".)
     let event = engine.process_key(' ');
-    match event {
+    assert!(
-        Some(vietc_engine::EngineEvent::Replace { insert, .. }) => {
+        event.is_none(),
-            assert_eq!(insert, "cảgo", "with auto-restore off the VN form is kept");
+        "with auto-restore off the composed VN word stays untouched on flush, got {event:?}"
-        }
+    );
-        other => panic!("expected Replace to 'cảgo', got {other:?}"),
-    }
 }