Harden smooth text fade before merge

PR_NOTES.md

@@ -20,16 +20,16 @@ Adds an opt-in `Fade text effect` preference for live assistant responses. When
 - Uses Hermes' existing incremental `streaming-markdown` parser with a custom renderer instead of full markdown re-renders.
 - Only newly appended words are wrapped and animated.
 - Animated spans are replaced with plain text by a delegated `animationend` handler, avoiding long-lived wrapper buildup without per-word listeners.
-- Reduced-motion preference is cached with a media-query listener instead of checked for every appended text node.
+- Reduced-motion preference is cached with a media-query listener instead of checked for every appended text node, and terminal stream paths remove the listener.
 - Unsafe streamed `href`/`src` values are blocked in the fade renderer `set_attr` path.
 - On `done`, fade mode drains buffered text, ends the parser to flush pending markdown, and waits for the final fade/stagger window before the final `renderMessages()` replacement.
 
 ## Performance/readability tuning
 
-- Normal fade duration: `160ms`
-- Word stagger: `12ms`
-- Done drain wait cap: `220ms`
-- Visual playback is capped at `100 wps`.
+- Normal fade duration: `200ms`
+- Word stagger: `16ms`
+- Done drain wait cap: `320ms`
+- Visual playback is capped at `160 wps`.
 - Reveals at most `2 words/frame`, or `3 words/frame` only with very large backlog.
 - Reveal steps pause briefly after sentence punctuation and paragraph breaks so very fast models feel less overwhelming.
 - Target word counts reuse the already-visible word count plus backlog count, avoiding repeated full-response word scans on each tick.
@@ -46,7 +46,7 @@ git diff --check
 Latest focused result:
 
 ```text
-68 passed
+69 passed
 ```
 
 ## Manual QA suggested

static/messages.js

@@ -538,6 +538,7 @@ function attachLiveStream(activeSid, streamId, uploaded=[], options={}){
   let _streamFadeHoldUntilMs=0;
   let _streamFadeReduceMotionMql=null;
   let _streamFadeReduceMotion=false;
+  let _streamFadeReduceMotionOnChange=null;
   const _STREAM_FADE_MS=200;
   const _STREAM_FADE_STAGGER_MS=16;
   const _STREAM_FADE_DONE_MAX_MS=320;
@@ -727,12 +728,19 @@ function attachLiveStream(activeSid, streamId, uploaded=[], options={}){
     if(!_streamFadeReduceMotionMql){
       _streamFadeReduceMotionMql=window.matchMedia('(prefers-reduced-motion: reduce)');
       _streamFadeReduceMotion=!!_streamFadeReduceMotionMql.matches;
-      const onChange=e=>{_streamFadeReduceMotion=!!e.matches;};
-      try{_streamFadeReduceMotionMql.addEventListener('change',onChange);}
-      catch(_){try{_streamFadeReduceMotionMql.addListener(onChange);}catch(_){}}
+      _streamFadeReduceMotionOnChange=e=>{_streamFadeReduceMotion=!!e.matches;};
+      try{_streamFadeReduceMotionMql.addEventListener('change',_streamFadeReduceMotionOnChange);}
+      catch(_){try{_streamFadeReduceMotionMql.addListener(_streamFadeReduceMotionOnChange);}catch(_){}}
     }
     return _streamFadeReduceMotion;
   }
+  function _streamFadeCleanupReduceMotionListener(){
+    if(!_streamFadeReduceMotionMql||!_streamFadeReduceMotionOnChange) return;
+    try{_streamFadeReduceMotionMql.removeEventListener('change',_streamFadeReduceMotionOnChange);}
+    catch(_){try{_streamFadeReduceMotionMql.removeListener(_streamFadeReduceMotionOnChange);}catch(_){}}
+    _streamFadeReduceMotionMql=null;
+    _streamFadeReduceMotionOnChange=null;
+  }
   function _streamFadeBindCleanup(el){
     if(!el||el._streamFadeCleanupBound) return;
     el._streamFadeCleanupBound=true;
@@ -1245,6 +1253,7 @@ function attachLiveStream(activeSid, streamId, uploaded=[], options={}){
         // can reintroduce a stale thinking card or duplicate content.
         _streamFinalized=true;
         _cancelAnimationFramePendingStreamRender();
+        _streamFadeCleanupReduceMotionListener();
         if(typeof finalizeThinkingCard==='function') finalizeThinkingCard();
         // Finalize smd parser — flushes any remaining buffered markdown state
         // and runs Prism + copy buttons on the live segment before the DOM is replaced
@@ -1489,6 +1498,7 @@ function attachLiveStream(activeSid, streamId, uploaded=[], options={}){
       if(_persistTimer){clearTimeout(_persistTimer);_persistTimer=null;}
       _streamFinalized=true;
       _cancelAnimationFramePendingStreamRender();
+      _streamFadeCleanupReduceMotionListener();
       _smdEndParser();
       if(typeof finalizeThinkingCard==='function') finalizeThinkingCard();
       // Application-level error sent explicitly by the server (rate limit, crash, etc.)
@@ -1575,6 +1585,7 @@ function attachLiveStream(activeSid, streamId, uploaded=[], options={}){
       if(_persistTimer){clearTimeout(_persistTimer);_persistTimer=null;}
       _streamFinalized=true;
       _cancelAnimationFramePendingStreamRender();
+      _streamFadeCleanupReduceMotionListener();
       _smdEndParser();
       if(typeof finalizeThinkingCard==='function') finalizeThinkingCard();
       source.close();
@@ -1669,6 +1680,7 @@ function attachLiveStream(activeSid, streamId, uploaded=[], options={}){
     if(_persistTimer){clearTimeout(_persistTimer);_persistTimer=null;}
     _streamFinalized=true;
     _cancelAnimationFramePendingStreamRender();
+    _streamFadeCleanupReduceMotionListener();
     if(typeof finalizeThinkingCard==='function') finalizeThinkingCard();
     _clearOwnerInflightState();
     _closeSource();

tests/test_smooth_text_fade.py

@@ -77,9 +77,9 @@ let _streamFadeLatestAnimationEndAt=0;
 let _streamFadeAppendOffset=0;
 let _streamFadeVisibleWords=0;
 let _streamFadeHoldUntilMs=0;
-const _STREAM_FADE_MS=160;
-const _STREAM_FADE_STAGGER_MS=12;
-const _STREAM_FADE_DONE_MAX_MS=220;
+const _STREAM_FADE_MS=200;
+const _STREAM_FADE_STAGGER_MS=16;
+const _STREAM_FADE_DONE_MAX_MS=320;
 const performance={performance_stub};
 {helpers}
 """
@@ -187,7 +187,7 @@ def test_stream_fade_css_is_opacity_only_and_hides_live_cursor():
         [
             "@keyframes stream-fade-word-in",
             ".stream-fade-word.is-new",
-            "var(--stream-fade-ms,160ms) cubic-bezier(.2,.7,.2,1)",
+            "var(--stream-fade-ms,240ms) cubic-bezier(.2,.7,.2,1)",
             "prefers-reduced-motion: reduce",
             ".msg-body.stream-fade-active > :last-child::after",
             "display:none",
@@ -197,6 +197,14 @@ def test_stream_fade_css_is_opacity_only_and_hides_live_cursor():
     assert ".stream-fade-active .stream-fade-word{display:inline;}" in fade_css
 
 
+def test_stream_fade_reduced_motion_listener_is_cleaned_up_on_terminal_paths():
+    assert "_streamFadeReduceMotionOnChange" in MESSAGES_JS
+    assert "function _streamFadeCleanupReduceMotionListener()" in MESSAGES_JS
+    assert "removeEventListener('change',_streamFadeReduceMotionOnChange)" in MESSAGES_JS
+    assert "removeListener(_streamFadeReduceMotionOnChange)" in MESSAGES_JS
+    assert MESSAGES_JS.count("_streamFadeCleanupReduceMotionListener();") >= 4
+
+
 def test_stream_fade_playout_handles_fast_models_without_paragraph_pops():
     script = (
         fade_helper_script()