diff --git a/static/messages.js b/static/messages.js
index 79addad4..d89badf8 100644
--- a/static/messages.js
+++ b/static/messages.js
@@ -3403,6 +3403,29 @@ function attachLiveStream(activeSid, streamId, uploaded=[], options={}){
       }
     }
   }
+  function _anchorSceneHasWorklogWorthyRows(scene){
+    // A worklog (the collapsible "已处理 …" rail) is only meaningful when the turn
+    // actually DID worklog-worthy work — a tool call, a thinking/reasoning pass, or
+    // a compression lifecycle card. A turn that only streamed prose (e.g. a long
+    // plain-text answer, or a degeneration burst that flooded the body with repeated
+    // tokens) projects an activity scene whose rows are ALL `prose`/`terminal`. Folding
+    // such a turn into a collapsed worklog hides the whole answer and, at STREAM_DONE,
+    // shrinks the transcript by the full streamed height → the browser clamps a
+    // bottom-pinned viewport back to the top (the "jump back" report). Require at least
+    // one genuinely worklog-worthy row before promoting the turn to a worklog.
+    const rows=Array.isArray(scene&&scene.activity_rows)?scene.activity_rows:[];
+    for(const row of rows){
+      if(!row||typeof row!=='object') continue;
+      const role=String(row.role||'');
+      if(role==='tool'||role==='thinking') return true;
+      if(role==='lifecycle'){
+        const source=String(row.source_event_type||'');
+        // compression cards are worklog-worthy; a bare terminal/done lifecycle is not.
+        if(source==='compressing'||source==='compressed') return true;
+      }
+    }
+    return false;
+  }
   function _attachProjectedAnchorSceneToLastAssistant(messages){
     if(!_anchorRegistry||!Array.isArray(messages)) return false;
     let lastAsst=null;
@@ -3418,7 +3441,8 @@ function attachLiveStream(activeSid, streamId, uploaded=[], options={}){
     if(!lastAsst) return false;
     const projectedScene=_projectLiveAnchorActivityScene();
     const scene=_completeSettledAnchorSceneForTurn(messages,lastAsstIndex,projectedScene);
-    if(scene&&Array.isArray(scene.activity_rows)&&scene.activity_rows.length){
+    if(scene&&Array.isArray(scene.activity_rows)&&scene.activity_rows.length
+        &&_anchorSceneHasWorklogWorthyRows(scene)){
       lastAsst._anchor_stream_id=streamId;
       lastAsst._anchor_activity_scene=scene;
       _persistSettledAnchorScene(lastAsst, scene, lastAsstIndex);
diff --git a/static/ui.js b/static/ui.js
index 31e53b36..5ddbc453 100644
--- a/static/ui.js
+++ b/static/ui.js
@@ -10330,8 +10330,28 @@ if(typeof window!=='undefined'){
   window._projectLiveAnchorActivitySceneForStream=_projectLiveAnchorActivitySceneForStream;
   window.isLiveAnchorActivitySceneOwner=isLiveAnchorActivitySceneOwner;
 }
+function _anchorSceneSceneHasWorklogWorthyRows(scene){
+  // Mirror of messages.js _anchorSceneHasWorklogWorthyRows for the RENDER side:
+  // a settled scene that was persisted (or hydrated from the backend) before the
+  // generation-side guard existed can still be all-prose. Such a scene must NOT be
+  // promoted to a collapsed worklog at render time (it would hide the whole answer
+  // and shrink the transcript at settle → bottom-pinned jump-back). Require at least
+  // one tool/thinking/compression row. (defense-in-depth for already-persisted scenes)
+  const rows=Array.isArray(scene&&scene.activity_rows)?scene.activity_rows:[];
+  for(const row of rows){
+    if(!row||typeof row!=='object') continue;
+    const role=String(row.role||'');
+    if(role==='tool'||role==='thinking') return true;
+    if(role==='lifecycle'){
+      const source=String(row.source_event_type||'');
+      if(source==='compressing'||source==='compressed') return true;
+    }
+  }
+  return false;
+}
 function _renderSettledAnchorSceneTransparentForMessage(message, segment, rawIdx){
   if(!message||!message._anchor_activity_scene||!segment) return false;
+  if(!_anchorSceneSceneHasWorklogWorthyRows(message._anchor_activity_scene)) return false;
   const blocks=_assistantTurnBlocks(segment.closest('.assistant-turn'));
   if(!blocks) return false;
   const scene=message._anchor_activity_scene;
@@ -10409,6 +10429,7 @@ if(typeof window!=='undefined'){
 }
 function _renderSettledAnchorSceneForMessage(message, segment, rawIdx){
   if(!message||!message._anchor_activity_scene||!segment) return false;
+  if(!_anchorSceneSceneHasWorklogWorthyRows(message._anchor_activity_scene)) return false;
   if(typeof isTransparentStream==='function'&&isTransparentStream()){
     return _renderSettledAnchorSceneTransparentForMessage(message,segment,rawIdx);
   }
diff --git a/tests/test_pure_prose_turn_not_worklog.py b/tests/test_pure_prose_turn_not_worklog.py
new file mode 100644
index 00000000..c508a78b
--- /dev/null
+++ b/tests/test_pure_prose_turn_not_worklog.py
@@ -0,0 +1,150 @@
+"""Regression locks: a pure-prose assistant turn must NOT become a collapsed worklog.
+
+Follow-up to the #4970/#5058 stream-end worklog collapse jump. Root cause of a
+recurring "jump back" report: a turn that streamed ONLY prose (a long plain-text
+answer, or a degeneration burst that floods the body with repeated tokens) still
+projected an anchor activity scene whose `activity_rows` were all `prose`/`terminal`
+— zero tool/thinking rows. The settle path promoted it to a collapsed worklog
+anyway (the gate only checked `activity_rows.length`), hiding the whole answer and
+shrinking the transcript by the full streamed height at STREAM_DONE → the browser
+clamps a bottom-pinned viewport back to the top.
+
+The fix adds a worklog-worthiness predicate at BOTH the generation gate
+(`_anchorSceneHasWorklogWorthyRows` in messages.js, decides whether to attach a
+scene at all) and the render gate (`_anchorSceneSceneHasWorklogWorthyRows` in
+ui.js, defense-in-depth for already-persisted all-prose scenes). A scene is
+worklog-worthy only if it has >=1 tool/thinking row or a compression lifecycle
+card; pure prose is not.
+
+These tests are BEHAVIORAL: they extract the real predicate functions from the
+static JS and execute them in Node against representative scenes.
+"""
+import json
+import shutil
+import subprocess
+import textwrap
+from pathlib import Path
+
+import pytest
+
+ROOT = Path(__file__).resolve().parent.parent
+UI_JS = (ROOT / "static" / "ui.js").read_text(encoding="utf-8")
+MESSAGES_JS = (ROOT / "static" / "messages.js").read_text(encoding="utf-8")
+
+
+def _function_body(src: str, name: str) -> str:
+    marker = f"function {name}"
+    start = src.index(marker)
+    brace = src.index("{", start)
+    depth = 0
+    for idx in range(brace, len(src)):
+        ch = src[idx]
+        if ch == "{":
+            depth += 1
+        elif ch == "}":
+            depth -= 1
+            if depth == 0:
+                return src[brace + 1 : idx]
+    raise AssertionError(f"function {name} body not found")
+
+
+def _extract(src: str, name: str) -> str:
+    marker = f"function {name}"
+    start = src.index(marker)
+    body = _function_body(src, name)
+    sig = src[start : src.index("{", start)]
+    return f"{sig}{{{body}}}"
+
+
+def test_gates_call_worklog_worthy_predicate():
+    # Structural lock: BOTH the generation gate and the render gates must be
+    # guarded by a worklog-worthiness predicate, not just `activity_rows.length`.
+    # (Counting only the helper DEFINITION is the orphan-definition trap — assert
+    # the CALL SITES too.)
+    attach_fn = _function_body(MESSAGES_JS, "_attachProjectedAnchorSceneToLastAssistant")
+    assert "_anchorSceneHasWorklogWorthyRows(scene)" in attach_fn, (
+        "generation gate must require a worklog-worthy scene before attaching"
+    )
+    render_fn = _function_body(UI_JS, "_renderSettledAnchorSceneForMessage")
+    assert "_anchorSceneSceneHasWorklogWorthyRows(message._anchor_activity_scene)" in render_fn, (
+        "compact render gate must reject an all-prose persisted scene"
+    )
+    transparent_fn = _function_body(UI_JS, "_renderSettledAnchorSceneTransparentForMessage")
+    assert "_anchorSceneSceneHasWorklogWorthyRows(message._anchor_activity_scene)" in transparent_fn, (
+        "transparent render gate must reject an all-prose persisted scene"
+    )
+    # The predicate definitions exist on both sides.
+    assert "function _anchorSceneHasWorklogWorthyRows" in MESSAGES_JS
+    assert "function _anchorSceneSceneHasWorklogWorthyRows" in UI_JS
+
+
+@pytest.mark.skipif(shutil.which("node") is None, reason="node required for behavioral test")
+def test_pure_prose_scene_is_not_worklog_worthy():
+    """Pure-prose scene → false; tool/thinking/compression scene → true."""
+    predicate = _extract(UI_JS, "_anchorSceneSceneHasWorklogWorthyRows")
+    harness = textwrap.dedent(f"""
+        {predicate}
+        const out = {{}};
+        // (1) The exact shape that caused the jump: long prose flood + a terminal/done row.
+        out.pure_prose = _anchorSceneSceneHasWorklogWorthyRows({{
+          activity_rows: [
+            {{ role: 'prose', source_event_type: 'token', text: 'call\\ncall\\ncall' }},
+            {{ role: 'terminal', source_event_type: 'done', text: '' }},
+          ]
+        }});                                  // expect false
+        // (2) A real worklog: has a tool row.
+        out.with_tool = _anchorSceneSceneHasWorklogWorthyRows({{
+          activity_rows: [
+            {{ role: 'prose', text: 'let me check' }},
+            {{ role: 'tool', name: 'terminal', text: '' }},
+          ]
+        }});                                  // expect true
+        // (3) A reasoning pass is worklog-worthy.
+        out.with_thinking = _anchorSceneSceneHasWorklogWorthyRows({{
+          activity_rows: [ {{ role: 'thinking', text: 'reasoning...' }} ]
+        }});                                  // expect true
+        // (4) A compression lifecycle card is worklog-worthy.
+        out.with_compression = _anchorSceneSceneHasWorklogWorthyRows({{
+          activity_rows: [ {{ role: 'lifecycle', source_event_type: 'compressed', text: '' }} ]
+        }});                                  // expect true
+        // (5) A bare terminal/done lifecycle is NOT worklog-worthy.
+        out.bare_lifecycle = _anchorSceneSceneHasWorklogWorthyRows({{
+          activity_rows: [ {{ role: 'lifecycle', source_event_type: 'done', text: '' }} ]
+        }});                                  // expect false
+        // (6) Empty / missing rows → false (no worklog for nothing).
+        out.empty = _anchorSceneSceneHasWorklogWorthyRows({{ activity_rows: [] }});  // false
+        out.no_scene = _anchorSceneSceneHasWorklogWorthyRows(null);                  // false
+        console.log(JSON.stringify(out));
+    """)
+    res = subprocess.run(["node", "-e", harness], capture_output=True, text=True, timeout=30)
+    assert res.returncode == 0, res.stderr
+    out = json.loads(res.stdout.strip())
+    assert out["pure_prose"] is False, "pure-prose turn must NOT be promoted to a collapsed worklog"
+    assert out["with_tool"] is True, "a turn with a tool row is a real worklog"
+    assert out["with_thinking"] is True, "a turn with a thinking row is a real worklog"
+    assert out["with_compression"] is True, "a compression lifecycle card is worklog-worthy"
+    assert out["bare_lifecycle"] is False, "a bare terminal/done lifecycle is not worklog-worthy"
+    assert out["empty"] is False
+    assert out["no_scene"] is False
+
+
+@pytest.mark.skipif(shutil.which("node") is None, reason="node required for behavioral test")
+def test_generation_side_predicate_matches_render_side():
+    """The messages.js generation predicate must classify identically to ui.js."""
+    gen = _extract(MESSAGES_JS, "_anchorSceneHasWorklogWorthyRows")
+    harness = textwrap.dedent(f"""
+        {gen}
+        const out = {{}};
+        out.pure_prose = _anchorSceneHasWorklogWorthyRows({{
+          activity_rows: [ {{ role: 'prose', text: 'call\\ncall' }}, {{ role: 'terminal', source_event_type: 'done' }} ]
+        }});
+        out.with_tool = _anchorSceneHasWorklogWorthyRows({{
+          activity_rows: [ {{ role: 'tool', name: 'x' }} ]
+        }});
+        console.log(JSON.stringify(out));
+    """)
+    res = subprocess.run(["node", "-e", harness], capture_output=True, text=True, timeout=30)
+    assert res.returncode == 0, res.stderr
+    out = json.loads(res.stdout.strip())
+    assert out["pure_prose"] is False
+    assert out["with_tool"] is True