fix(codex): close reasoning with Done deltas instead of Full to avoid duplicate message

Codex reasoning emitted Start(active) then Full(static) at the open index with
no Done. auto_send routes a Full into its own throwaway streaming context
(ignoring the index), so the Start context survived until end-of-turn teardown
and persisted a second, near-empty reasoning message (user-visible duplicate +
out-of-order).

Mirror the claude_code pattern: stream the final reasoning as summary + content
deltas on the open index, then close with a Done, so the open context
accumulates the final ReasoningContent and closes cleanly as one message. The
no-started case opens the Start lazily and closes it the same way.

Updated tests assert the Start + deltas + Done sequence and that no
Full(ReasoningContent) is emitted.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: declan-scale

src/agentex/lib/adk/_modules/_codex_sync.py

@@ -48,7 +48,9 @@
   reasoning               -> reasoning:
                                item.started                 -> StreamTaskMessageStart(ReasoningContent)
                                item.updated                 -> (no-op; final text arrives on completed)
-                               item.completed               -> StreamTaskMessageFull(ReasoningContent)
+                               item.completed               -> StreamTaskMessageDelta(ReasoningSummaryDelta)
+                                                              + StreamTaskMessageDelta(ReasoningContentDelta)
+                                                              + StreamTaskMessageDone
   command_execution       -> tool request + response:
                                item.started                 -> StreamTaskMessageStart(ToolRequestContent)
                                                               + StreamTaskMessageDone
@@ -96,6 +98,7 @@
 from agentex.types.tool_request_content import ToolRequestContent
 from agentex.types.tool_response_content import ToolResponseContent
 from agentex.types.reasoning_content_delta import ReasoningContentDelta
+from agentex.types.reasoning_summary_delta import ReasoningSummaryDelta
 
 logger = make_logger(__name__)
 
@@ -366,18 +369,6 @@ def _handle_item(self, evt_type: str, item: dict[str, Any]) -> list[StreamTaskMe
                         ),
                     )
                 )
-                if current:
-                    out.append(
-                        StreamTaskMessageDelta(
-                            type="delta",
-                            index=idx,
-                            delta=ReasoningContentDelta(
-                                type="reasoning_content",
-                                content_index=0,
-                                content_delta=current,
-                            ),
-                        )
-                    )
 
             elif evt_type == "item.updated":
                 # Accumulate silently; final text arrives on item.completed.
@@ -389,30 +380,53 @@ def _handle_item(self, evt_type: str, item: dict[str, Any]) -> list[StreamTaskMe
                 if text:
                     self.reasoning_count += 1
                     summary = text.strip().split("\n", 1)[0][:300]
-                    final_content = ReasoningContent(
-                        type="reasoning",
-                        author="agent",
-                        summary=[summary],
-                        content=[text],
-                        style="static",
-                    )
-                    if idx is not None:
+                    if idx is None:
+                        # No started event was seen; open the message now.
+                        idx = self._alloc()
                         out.append(
-                            StreamTaskMessageFull(
-                                type="full",
+                            StreamTaskMessageStart(
+                                type="start",
                                 index=idx,
-                                content=final_content,
+                                content=ReasoningContent(
+                                    type="reasoning",
+                                    author="agent",
+                                    summary=[],
+                                    content=[],
+                                    style="active",
+                                ),
                             )
                         )
-                    else:
-                        # No started event was seen; emit a standalone Full.
-                        out.append(
-                            StreamTaskMessageFull(
-                                type="full",
-                                index=self._alloc(),
-                                content=final_content,
-                            )
+                    # Deliver the reasoning as deltas, then close with a Done.
+                    # Emitting a Full here instead would leave the open Start
+                    # context dangling: auto_send routes Full into its own
+                    # throwaway streaming context (ignoring the index), so the
+                    # Start context survives until end-of-turn teardown and
+                    # persists a second, near-empty reasoning message. Streaming
+                    # the content as deltas lets the open context accumulate the
+                    # final ReasoningContent and close cleanly as one message.
+                    out.append(
+                        StreamTaskMessageDelta(
+                            type="delta",
+                            index=idx,
+                            delta=ReasoningSummaryDelta(
+                                type="reasoning_summary",
+                                summary_index=0,
+                                summary_delta=summary,
+                            ),
                         )
+                    )
+                    out.append(
+                        StreamTaskMessageDelta(
+                            type="delta",
+                            index=idx,
+                            delta=ReasoningContentDelta(
+                                type="reasoning_content",
+                                content_index=0,
+                                content_delta=text,
+                            ),
+                        )
+                    )
+                    out.append(StreamTaskMessageDone(type="done", index=idx))
                 elif idx is not None:
                     # Empty reasoning block — still need to close with a Done.
                     out.append(StreamTaskMessageDone(type="done", index=idx))

tests/lib/adk/test_codex_sync.py

@@ -35,6 +35,7 @@
     convert_codex_to_agentex_events,
 )
 from agentex.types.reasoning_content_delta import ReasoningContentDelta
+from agentex.types.reasoning_summary_delta import ReasoningSummaryDelta
 
 
 async def _aiter(items: list[Any]) -> AsyncIterator[Any]:
@@ -365,7 +366,15 @@ async def test_tool_indices_request_before_response(self) -> None:
 
 
 class TestReasoningStreaming:
-    async def test_reasoning_start_full(self) -> None:
+    async def test_reasoning_start_deltas_done(self) -> None:
+        """A reasoning block opens with a Start, streams the final text as
+        summary + content deltas, and closes with a Done.
+
+        It must NOT emit a Full at the open Start's index: auto_send routes a
+        Full into a throwaway streaming context (ignoring the index), which
+        would leave the Start context dangling and persist a duplicate, empty
+        reasoning message (AGX1 codex reasoning duplicate bug).
+        """
         events = [
             {"type": "item.started", "item": {"id": "r1", "type": "reasoning", "text": ""}},
             {
@@ -380,44 +389,58 @@ async def test_reasoning_start_full(self) -> None:
         out = await _collect(convert_codex_to_agentex_events(_aiter(events)))
 
         starts = [e for e in out if isinstance(e, StreamTaskMessageStart)]
-        fulls = [e for e in out if isinstance(e, StreamTaskMessageFull) and isinstance(e.content, ReasoningContent)]
+        dones = [e for e in out if isinstance(e, StreamTaskMessageDone)]
+        reasoning_fulls = [
+            e for e in out if isinstance(e, StreamTaskMessageFull) and isinstance(e.content, ReasoningContent)
+        ]
+        content_deltas = [
+            e for e in out if isinstance(e, StreamTaskMessageDelta) and isinstance(e.delta, ReasoningContentDelta)
+        ]
+        summary_deltas = [
+            e for e in out if isinstance(e, StreamTaskMessageDelta) and isinstance(e.delta, ReasoningSummaryDelta)
+        ]
 
+        # Exactly one message: Start + deltas + Done, all on the same index, no Full.
         assert len(starts) == 1
         assert isinstance(starts[0].content, ReasoningContent)
-        assert len(fulls) == 1
-        assert isinstance(fulls[0].content, ReasoningContent)
-        reasoning_content = fulls[0].content.content
-        assert reasoning_content is not None
-        assert any("thinking... done" in s for s in reasoning_content)
-
-    async def test_reasoning_initial_text_emits_delta(self) -> None:
-        events = [
-            {
-                "type": "item.started",
-                "item": {"id": "r1", "type": "reasoning", "text": "seed"},
-            },
-        ]
-        out = await _collect(convert_codex_to_agentex_events(_aiter(events)))
-        deltas = [e for e in out if isinstance(e, StreamTaskMessageDelta)]
-        assert len(deltas) == 1
-        assert isinstance(deltas[0].delta, ReasoningContentDelta)
-        assert deltas[0].delta.content_delta == "seed"
-
-    async def test_reasoning_no_started_emits_standalone_full(self) -> None:
-        """If item.completed arrives without item.started, emit a standalone Full."""
+        assert reasoning_fulls == []
+        assert len(content_deltas) == 1
+        assert content_deltas[0].delta.content_delta == "thinking... done"
+        assert len(summary_deltas) == 1
+        assert summary_deltas[0].delta.summary_delta == "thinking... done"
+        assert len(dones) == 1
+        idx = starts[0].index
+        assert content_deltas[0].index == idx
+        assert summary_deltas[0].index == idx
+        assert dones[0].index == idx
+
+    async def test_reasoning_no_started_opens_and_closes_one_message(self) -> None:
+        """If item.completed arrives without item.started, the converter opens a
+        Start lazily and closes it with a Done (still one clean message, no Full)."""
         events = [
             {
                 "type": "item.completed",
                 "item": {"id": "r_orphan", "type": "reasoning", "text": "orphan thought"},
             }
         ]
         out = await _collect(convert_codex_to_agentex_events(_aiter(events)))
-        fulls = [e for e in out if isinstance(e, StreamTaskMessageFull) and isinstance(e.content, ReasoningContent)]
-        assert len(fulls) == 1
-        assert isinstance(fulls[0].content, ReasoningContent)
-        orphan_content = fulls[0].content.content
-        assert orphan_content is not None
-        assert any("orphan thought" in s for s in orphan_content)
+
+        starts = [e for e in out if isinstance(e, StreamTaskMessageStart)]
+        dones = [e for e in out if isinstance(e, StreamTaskMessageDone)]
+        reasoning_fulls = [
+            e for e in out if isinstance(e, StreamTaskMessageFull) and isinstance(e.content, ReasoningContent)
+        ]
+        content_deltas = [
+            e for e in out if isinstance(e, StreamTaskMessageDelta) and isinstance(e.delta, ReasoningContentDelta)
+        ]
+
+        assert len(starts) == 1
+        assert isinstance(starts[0].content, ReasoningContent)
+        assert reasoning_fulls == []
+        assert len(content_deltas) == 1
+        assert content_deltas[0].delta.content_delta == "orphan thought"
+        assert len(dones) == 1
+        assert dones[0].index == starts[0].index
 
     async def test_reasoning_summary_is_first_line(self) -> None:
         events = [
@@ -428,9 +451,27 @@ async def test_reasoning_summary_is_first_line(self) -> None:
             },
         ]
         out = await _collect(convert_codex_to_agentex_events(_aiter(events)))
-        full = next(e for e in out if isinstance(e, StreamTaskMessageFull) and isinstance(e.content, ReasoningContent))
-        assert isinstance(full.content, ReasoningContent)
-        assert full.content.summary == ["line one"]
+        summary_delta = next(
+            e for e in out if isinstance(e, StreamTaskMessageDelta) and isinstance(e.delta, ReasoningSummaryDelta)
+        )
+        assert summary_delta.delta.summary_delta == "line one"
+
+    async def test_reasoning_empty_block_closes_with_done_only(self) -> None:
+        """A reasoning block that completes with no text still closes its Start."""
+        events = [
+            {"type": "item.started", "item": {"id": "r3", "type": "reasoning", "text": ""}},
+            {"type": "item.completed", "item": {"id": "r3", "type": "reasoning", "text": ""}},
+        ]
+        out = await _collect(convert_codex_to_agentex_events(_aiter(events)))
+
+        starts = [e for e in out if isinstance(e, StreamTaskMessageStart)]
+        dones = [e for e in out if isinstance(e, StreamTaskMessageDone)]
+        deltas = [e for e in out if isinstance(e, StreamTaskMessageDelta)]
+
+        assert len(starts) == 1
+        assert deltas == []
+        assert len(dones) == 1
+        assert dones[0].index == starts[0].index
 
 
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