diff --git a/static/ui.js b/static/ui.js
index 97c8980d..b1951f4a 100644
--- a/static/ui.js
+++ b/static/ui.js
@@ -7275,10 +7275,19 @@ function _syncWorklogReasonFromAnchor(group, anchor, displayTextOverride){
   const list=_toolWorklogListEl(group);
   if(!group||!list) return;
   const anchorKey=_worklogReasonAnchorKey(anchor);
+  const selector=anchorKey?`:scope > .wl-reason[data-worklog-anchor-key="${CSS.escape(anchorKey)}"]`:':scope > .wl-reason[data-worklog-anchor-reason="1"]';
+  // When reasoning/thinking display is turned off (#3903), do not render Worklog
+  // reasoning rows on the live OR settled path — remove any existing one and bail
+  // before building. (The gate must live here, in the actual render path, not in
+  // the unused _worklogReasonNodeFromText helper.)
+  if(window._showThinking===false){
+    const existing=list.querySelector(selector);
+    if(existing) existing.remove();
+    return;
+  }
   const html=arguments.length>2
     ? _worklogReasonHtmlFromAnchor(anchor, displayTextOverride)
     : _worklogReasonHtmlFromAnchor(anchor);
-  const selector=anchorKey?`:scope > .wl-reason[data-worklog-anchor-key="${CSS.escape(anchorKey)}"]`:':scope > .wl-reason[data-worklog-anchor-reason="1"]';
   let reason=list.querySelector(selector);
   if(!html){
     if(reason) reason.remove();
@@ -7344,6 +7353,8 @@ function _migrateLegacyLiveActivityGroupsToWorklog(blocks, worklog){
 }
 function _appendWorklogReason(list, anchor){
   if(!list) return null;
+  // Reasoning display off (#3903): never append a Worklog reasoning row.
+  if(window._showThinking===false) return null;
   const html=_worklogReasonHtmlFromAnchor(anchor);
   if(!html) return null;
   const reason=document.createElement('div');
@@ -9288,7 +9299,7 @@ function renderMessages(options){
     // regression vs master; same content-loss-on-switch class as #3668). The
     // `:not([data-live-thinking="1"])` / live-card guards below keep the active
     // turn's own live nodes from being double-built.
-    inner.querySelectorAll('.tool-worklog-group:not([data-compression-card]),.tool-call-group:not([data-compression-card]),.tool-card-row:not([data-compression-card]),.agent-activity-thinking:not([data-live-thinking="1"]):not([data-event-type="thinking"]),.wl-reason[data-worklog-reason-source="reasoning"]').forEach(el=>el.remove());
+    inner.querySelectorAll('.tool-worklog-group:not([data-compression-card]),.tool-call-group:not([data-compression-card]),.tool-card-row:not([data-compression-card]),.agent-activity-thinking:not([data-live-thinking="1"]):not([data-event-type="thinking"]),.wl-reason[data-worklog-anchor-reason="1"],.wl-reason[data-worklog-reason-source="reasoning"]').forEach(el=>el.remove());
     const byActivity = new Map();
     const assistantIdxs=[...assistantSegments.keys()].sort((a,b)=>a-b);
     const _assistantAnchorForActivity=(aIdx,segmentSeq,burstId)=>{
@@ -11478,7 +11489,7 @@ function removeThinking(){
   const turn=$('liveAssistantTurn');
   const blocks=_assistantTurnBlocks(turn);
   if(blocks) blocks.querySelectorAll('.agent-activity-thinking').forEach(el=>el.remove());
-  if(blocks) blocks.querySelectorAll('.wl-reason[data-worklog-reason-source="reasoning"]').forEach(el=>el.remove());
+  if(blocks) blocks.querySelectorAll('.wl-reason[data-worklog-anchor-reason="1"],.wl-reason[data-worklog-reason-source="reasoning"]').forEach(el=>el.remove());
   if(blocks) blocks.querySelectorAll('.live-worklog[data-live-worklog-shell="1"],.tool-worklog-group[data-live-tool-call-group="1"],.tool-call-group[data-live-tool-call-group="1"],.tool-call-group[data-agent-activity-group="1"]').forEach(group=>{
     _syncToolCallGroupSummary(group);
     if(!group.querySelector('.tool-card-row,.agent-activity-thinking,.wl-reason')){
diff --git a/tests/test_reasoning_show_hide.py b/tests/test_reasoning_show_hide.py
index 69fa1f3d..87660586 100644
--- a/tests/test_reasoning_show_hide.py
+++ b/tests/test_reasoning_show_hide.py
@@ -99,9 +99,17 @@ class TestUiJsThinkingGate:
 
     def test_worklog_reasoning_rows_are_gated_by_show_thinking(self):
         src = read('static/ui.js')
-        node_fn = function_body(src, "_worklogReasonNodeFromText")
-        assert 'window._showThinking===false' in node_fn and 'return null' in node_fn, (
-            "reasoning-source Worklog rows must not be created when thinking is hidden"
+        # The gate must sit in the ACTUAL render paths that build Worklog reasoning
+        # rows — _syncWorklogReasonFromAnchor (live + settled) and _appendWorklogReason
+        # (settled rebuild) — not in the unused _worklogReasonNodeFromText helper.
+        sync_fn = function_body(src, "_syncWorklogReasonFromAnchor")
+        assert 'window._showThinking===false' in sync_fn and 'return' in sync_fn, (
+            "_syncWorklogReasonFromAnchor must bail (and remove any existing row) "
+            "when thinking display is off"
+        )
+        append_fn = function_body(src, "_appendWorklogReason")
+        assert 'window._showThinking===false' in append_fn and 'return null' in append_fn, (
+            "_appendWorklogReason must not build a reasoning row when thinking is hidden"
         )
 
     def test_show_thinking_gate_does_not_hide_worklog_anchor_text(self):
@@ -115,8 +123,12 @@ class TestUiJsThinkingGate:
     def test_remove_thinking_prunes_reasoning_rows_but_preserves_tool_or_anchor_rows(self):
         src = read('static/ui.js')
         fn = function_body(src, "removeThinking")
-        assert '.wl-reason[data-worklog-reason-source="reasoning"]' in fn, (
-            "removeThinking must sweep already-rendered reasoning Worklog rows"
+        # The live/settled reasoning rows are tagged data-worklog-anchor-reason="1"
+        # (by _syncWorklogReasonFromAnchor / _appendWorklogReason); the sweep MUST
+        # target that attribute, not only the legacy data-worklog-reason-source.
+        assert '.wl-reason[data-worklog-anchor-reason="1"]' in fn, (
+            "removeThinking must sweep the actually-rendered reasoning Worklog rows "
+            '(data-worklog-anchor-reason="1")'
         )
         assert '.tool-card-row,.agent-activity-thinking,.wl-reason' in fn, (
             "empty-group cleanup must preserve groups that still contain tool cards "