diff --git a/CHANGELOG.md b/CHANGELOG.md
index f4ca8b7f..318ac9fc 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,12 @@
 
 ## [Unreleased]
 
+## [v0.51.536] — 2026-06-20 — Release SU (transparent-stream tool-call rows persist after settle)
+
+### Fixed
+
+- **Transparent-stream tool-call rows no longer vanish on turn settle (#4539).** The settled-node cleanup sweep in `renderMessages` was removing `.tool-card-row` elements regardless of type; it now excludes rows with `data-event-type="tool"` (the transparent-stream rows) so they survive settlement. The burst-key assignment also pre-scans burst IDs into a `Set` before the tool-card loop (O(1) lookup instead of O(n) spread per card), and only uses a burst key when the matching assistant segment is present. Thanks @rodboev.
+
 ## [v0.51.535] — 2026-06-20 — Release ST (open model picker stays stable during stream sync)
 
 ### Fixed
diff --git a/static/ui.js b/static/ui.js
index 6fb23a23..9004c2c0 100644
--- a/static/ui.js
+++ b/static/ui.js
@@ -10796,7 +10796,7 @@ 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-anchor-reason="1"],.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]):not([data-event-type="tool"]),.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)=>{
@@ -10847,13 +10847,16 @@ function renderMessages(options){
       const hasValue=value!==undefined&&value!==null&&String(value)!==''&&String(value)!=='0';
       return hasValue?String(value):'';
     };
+    const knownBurstIds=new Set();
+    for(const s of assistantSegments.values()) if(s){const b=s.getAttribute('data-activity-burst-id');if(b)knownBurstIds.add(b);}
     for(const tc of (S.toolCalls||[])){
       if(!tc) continue;
       const aIdx=tc.assistant_msg_idx!==undefined?parseInt(tc.assistant_msg_idx):-1;
       if(virtualWindow.virtualized&&renderableRawIdxs.has(aIdx)&&!renderedRawIdxs.has(aIdx)) continue;
       const segmentSeq=normalizeToken(tc.activitySegmentSeq);
       const burstId=normalizeToken(tc.activityBurstId);
-      const key=segmentSeq?`segment:${segmentSeq}`:(burstId?`burst:${burstId}`:`assistant:${aIdx}`);
+      const burstResolvable=burstId&&knownBurstIds.has(burstId);
+      const key=segmentSeq?`segment:${segmentSeq}`:(burstResolvable?`burst:${burstId}`:`assistant:${aIdx}`);
       const entry=ensureActivityBucket(key,aIdx,segmentSeq,burstId);
       entry.cards.push(tc);
       entry.includeAnchorReason=true;
diff --git a/tests/test_issue3820_chat_activity_display_mode.py b/tests/test_issue3820_chat_activity_display_mode.py
index af0962e7..1b3efc94 100644
--- a/tests/test_issue3820_chat_activity_display_mode.py
+++ b/tests/test_issue3820_chat_activity_display_mode.py
@@ -420,7 +420,7 @@ def test_thinking_blocks_persist_after_renderMessages():
     assert inner_sweep in UI_JS
     # The promoted-row guard is the only thing that changed; the rest of
     # the selector must remain intact.
-    head = ".tool-worklog-group:not([data-compression-card]),.tool-call-group:not([data-compression-card]),.tool-card-row:not([data-compression-card]),.agent-activity-thinking"
+    head = ".tool-worklog-group:not([data-compression-card]),.tool-call-group:not([data-compression-card]),.tool-card-row:not([data-compression-card]):not([data-event-type=\"tool\"]),.agent-activity-thinking"
     tail = ".wl-reason[data-worklog-reason-source=\"reasoning\"]"
     assert head in UI_JS
     assert tail in UI_JS
diff --git a/tests/test_issue4539_transparent_tool_settle.py b/tests/test_issue4539_transparent_tool_settle.py
new file mode 100644
index 00000000..3c654c40
--- /dev/null
+++ b/tests/test_issue4539_transparent_tool_settle.py
@@ -0,0 +1,99 @@
+"""Regression tests for issue #4539: transparent-stream tool-call rows
+vanish on turn settle, reappear only after tab/session switch."""
+
+import re
+from pathlib import Path
+
+ROOT = Path(__file__).resolve().parents[1]
+UI_JS = (ROOT / "static" / "ui.js").read_text(encoding="utf-8")
+
+
+def _settled_cleanup_selector():
+    """Extract the settled-node cleanup querySelectorAll string."""
+    anchor = ".tool-worklog-group:not([data-compression-card])"
+    idx = UI_JS.index(anchor)
+    marker = ".forEach(el=>el.remove())"
+    end = UI_JS.index(marker, idx) + len(marker)
+    line_start = UI_JS.rfind("\n", 0, idx) + 1
+    return UI_JS[line_start:end]
+
+
+def _tool_bucketing_block():
+    """Extract the tool-call bucketing region including burst-ID pre-scan."""
+    start = UI_JS.index("const knownBurstIds=")
+    end = UI_JS.index("\n    }", UI_JS.index("for(const tc of (S.toolCalls||[])){", start)) + len("\n    }")
+    return UI_JS[start:end]
+
+
+class TestCleanupSelectorProtectsTransparentToolRows:
+    """Fix A: the settled-node cleanup must not remove transparent tool rows."""
+
+    def test_tool_card_row_arm_excludes_event_type_tool(self):
+        selector = _settled_cleanup_selector()
+        assert ".tool-card-row:not([data-compression-card]):not([data-event-type=\"tool\"])" in selector, (
+            "The .tool-card-row cleanup arm must exclude [data-event-type='tool'] "
+            "rows to protect transparent tool-call rows from deletion"
+        )
+
+    def test_thinking_arm_still_excludes_event_type_thinking(self):
+        selector = _settled_cleanup_selector()
+        assert ":not([data-event-type=\"thinking\"])" in selector, (
+            "The .agent-activity-thinking arm must still exclude "
+            "[data-event-type='thinking'] rows"
+        )
+
+    def test_tool_and_thinking_arms_follow_same_event_type_pattern(self):
+        selector = _settled_cleanup_selector()
+        assert ":not([data-event-type=\"tool\"])" in selector
+        assert ":not([data-event-type=\"thinking\"])" in selector
+
+
+class TestBurstIdFallbackWhenSegmentLacksBurstAttribute:
+    """Fix B: bucketing must fall back to assistant:${aIdx} when no segment
+    carries a matching data-activity-burst-id."""
+
+    def test_burst_resolvable_check_before_burst_key(self):
+        block = _tool_bucketing_block()
+        assert "burstResolvable" in block, (
+            "The tool-call bucketing loop must check burst-ID resolvability "
+            "before using 'burst:' as the bucket key"
+        )
+
+    def test_burst_ids_pre_scanned_from_assistant_segments(self):
+        block = _tool_bucketing_block()
+        assert "assistantSegments.values()" in block, (
+            "knownBurstIds must be built from assistantSegments before the loop"
+        )
+        assert "knownBurstIds.has(burstId)" in block, (
+            "burstResolvable must use the pre-scanned knownBurstIds set"
+        )
+
+    def test_fallback_uses_burst_resolvable_not_raw_burst_id(self):
+        block = _tool_bucketing_block()
+        assert re.search(r"burstResolvable\?.*burst:", block), (
+            "The bucket key must use burstResolvable (not raw burstId) "
+            "as the guard for the burst: key path"
+        )
+
+    def test_assistant_fallback_preserved(self):
+        block = _tool_bucketing_block()
+        assert "`assistant:${aIdx}`" in block, (
+            "The assistant:${aIdx} fallback must still be present"
+        )
+
+
+class TestDecorateTransparentEventRowSetsEventType:
+    """Confirms the decorator still sets the attributes the cleanup
+    selector depends on for its exclusion."""
+
+    def test_decorator_sets_data_event_type(self):
+        start = UI_JS.index("function _decorateTransparentEventRow(row, opts){")
+        end = UI_JS.index("\nfunction ", start + 1)
+        block = UI_JS[start:end]
+        assert "row.setAttribute('data-event-type',type)" in block
+
+    def test_tool_type_triggers_transparent_event_card(self):
+        start = UI_JS.index("function _decorateTransparentEventRow(row, opts){")
+        end = UI_JS.index("\nfunction ", start + 1)
+        block = UI_JS[start:end]
+        assert "if(type==='tool')" in block