diff --git a/agent/chat_completion_helpers.py b/agent/chat_completion_helpers.py
index 72e962c62b..48c7517827 100644
--- a/agent/chat_completion_helpers.py
+++ b/agent/chat_completion_helpers.py
@@ -46,7 +46,10 @@ from agent.message_sanitization import (
     _sanitize_messages_surrogates, _sanitize_surrogates, _repair_tool_call_arguments,
     normalize_finish_reason as _normalize_finish_reason, sanitize_outbound_kwargs, strip_images_for_rejecting_model,
 )
-from agent.reasoning_summaries import append_streamed_reasoning_detail, separate_glued_reasoning_blocks
+from agent.reasoning_summaries import (
+    append_streamed_reasoning_detail, separate_glued_reasoning_blocks,
+    streamed_reasoning_detail_text,
+)
 from agent.repetition_guard import is_repetition_dominated
 from agent.stream_single_writer import claim_stream_writer, stream_writer_is_current
 from tools.terminal_tool_lifecycle import is_persistent_env
@@ -3230,7 +3233,6 @@ class _StreamingCall(StreamingWaitMonitor):
                 reasoning_text = separate_glued_reasoning_blocks(
                     reasoning_parts[-1] if reasoning_parts else "", reasoning_text)
                 reasoning_parts.append(reasoning_text)
-                self._emit_reasoning(reasoning_text)
             # Structured reasoning_details deltas carry the provider's replay data; the
             # non-streaming path already keeps them, so dropping them here lost
             # reasoning continuity on nearly every turn. Pydantic parks unknown fields
@@ -3238,8 +3240,16 @@ class _StreamingCall(StreamingWaitMonitor):
             rd_delta = getattr(delta, "reasoning_details", None)
             if rd_delta is None and isinstance(getattr(delta, "model_extra", None), dict):
                 rd_delta = delta.model_extra.get("reasoning_details")
+            detail_text_parts = []
             for rd in rd_delta if isinstance(rd_delta, (list, tuple)) else ():
+                detail_text_parts.append(streamed_reasoning_detail_text(rd))
                 append_streamed_reasoning_detail(reasoning_details, rd)
+            # Details may carry the full text while ordinary reasoning is only
+            # a sparse fragment or a mirror. Deliver one representation per
+            # chunk, without rewriting either persisted/replayed field.
+            display_reasoning = "".join(detail_text_parts) or reasoning_text
+            if display_reasoning:
+                self._emit_reasoning(display_reasoning)
             # Not routed to the live display: the transport promotes a sole-payload
             # refusal to content + ``content_filter`` and the loop surfaces it terminally.
             delta_refusal = getattr(delta, "refusal", None)
diff --git a/agent/reasoning_summaries.py b/agent/reasoning_summaries.py
index 72258ee48d..1ed51eb200 100644
--- a/agent/reasoning_summaries.py
+++ b/agent/reasoning_summaries.py
@@ -36,6 +36,16 @@ _MERGEABLE_DETAIL_TEXT_KEYS = {"reasoning.text": "text", "reasoning.summary": "s
 _BACKFILL_DETAIL_KEYS = ("signature", "id", "format", "index")
 
 
+def streamed_reasoning_detail_text(detail: Any) -> str:
+    """Readable text from a detail delta; never expose opaque replay material."""
+    dtype = detail.get("type") if isinstance(detail, dict) else getattr(detail, "type", None)
+    key = _MERGEABLE_DETAIL_TEXT_KEYS.get(dtype) if isinstance(dtype, str) else None
+    if key is None:
+        return ""
+    text = detail.get(key) if isinstance(detail, dict) else getattr(detail, key, None)
+    return text if isinstance(text, str) else ""
+
+
 def append_streamed_reasoning_detail(details_acc: list, detail: Any) -> None:
     """Accumulate one streamed ``reasoning_details`` delta entry into *details_acc*.
 
diff --git a/tests/agent/test_streamed_reasoning_details.py b/tests/agent/test_streamed_reasoning_details.py
index 4470630b87..b12fc8a47d 100644
--- a/tests/agent/test_streamed_reasoning_details.py
+++ b/tests/agent/test_streamed_reasoning_details.py
@@ -56,7 +56,20 @@ def test_streamed_details_land_on_final_message_and_persist(_mock_close, mock_cr
     mock_create.return_value = mock_client
 
     agent = _agent()
+    delivered = []
+    agent.reasoning_callback = delivered.append
+    agent.stream_delta_callback = lambda text: None
+
+    def streamed_chunks():
+        yield chunks[0]
+        assert delivered == ["I should "]
+        yield chunks[1]
+        assert delivered == ["I should ", "answer."]
+        yield chunks[2]
+
+    mock_client.chat.completions.create.return_value = streamed_chunks()
     response = agent._interruptible_streaming_api_call({})
+    assert "".join(delivered) == "I should answer."
     msg = response.choices[0].message
     assert msg.content == "Hello!"
     assert msg.reasoning_details == [{"type": "reasoning.text", "text": "I should answer.", "signature": "sigZ"}]
@@ -74,3 +87,46 @@ def test_no_details_leaves_attribute_absent(_mock_close, mock_create):
     mock_create.return_value = mock_client
     response = _agent()._interruptible_streaming_api_call({})
     assert not hasattr(response.choices[0].message, "reasoning_details")
+
+
+@patch("run_agent.AIAgent._create_request_openai_client")
+@patch("run_agent.AIAgent._close_request_openai_client")
+def test_live_details_keep_plain_fallback_and_opaque_replay(_mock_close, mock_create):
+    agent = _agent()
+    client = MagicMock()
+    mock_create.return_value = client
+    cases = [
+        ([{"type": "reasoning.text", "text": "Complete thought"}], "C", "Complete thought"),
+        ([{"type": "reasoning.text", "text": "Same"}], "Same", "Same"),
+        ([SimpleNamespace(type="reasoning.summary", summary="Summary")], None, "Summary"),
+        ([{"type": "reasoning.encrypted", "data": "secret", "text": "not readable"}], "Plain", "Plain"),
+        ([{"type": "unknown", "text": "not readable"}], "Plain", "Plain"),
+        ([{"type": "reasoning.text", "text": ""}], "Plain", "Plain"),
+        ([], "Plain", "Plain"),
+        ([{"type": "reasoning.encrypted", "data": "secret"}], None, ""),
+    ]
+    for details, plain, expected in cases:
+        chunk = _make_chunk(content="Answer", finish_reason="stop")
+        chunk.choices[0].delta.reasoning = plain
+        chunk.choices[0].delta.model_extra = {"reasoning_details": details}
+        client.chat.completions.create.return_value = iter([chunk])
+        delivered = []
+        agent.reasoning_callback = delivered.append
+        response = agent._interruptible_streaming_api_call({})
+        assert "".join(delivered) == expected
+        assert response.choices[0].message.content == "Answer"
+        assert response.choices[0].message.reasoning_content == plain
+        preserved = []
+        for detail in details:
+            append_streamed_reasoning_detail(preserved, detail)
+        assert getattr(response.choices[0].message, "reasoning_details", []) == preserved
+
+    def broken_callback(text):
+        raise RuntimeError("consumer failed")
+
+    for callback in (None, broken_callback):
+        agent.reasoning_callback = callback
+        client.chat.completions.create.return_value = iter([
+            _make_chunk(content="Answer", finish_reason="stop", reasoning_details=[
+                {"type": "reasoning.text", "text": "Thought"}])])
+        assert agent._interruptible_streaming_api_call({}).choices[0].message.content == "Answer"