diff --git a/backend/internal/service/openai_ws_forwarder_ingress.go b/backend/internal/service/openai_ws_forwarder_ingress.go
index ca6135352b..87d733b539 100644
--- a/backend/internal/service/openai_ws_forwarder_ingress.go
+++ b/backend/internal/service/openai_ws_forwarder_ingress.go
@@ -1340,6 +1340,7 @@ func (s *OpenAIGatewayService) ProxyResponsesWebSocketFromClient(
 	turnPrevRecoveryTried := false
 	lastTurnFinishedAt := time.Time{}
 	lastTurnResponseID := ""
+	lastTurnWindowID := ""
 	lastTurnPayload := []byte(nil)
 	var lastTurnStrictState *openAIWSIngressPreviousTurnStrictState
 	lastTurnReplayInput := []json.RawMessage(nil)
@@ -1484,8 +1485,33 @@ func (s *OpenAIGatewayService) ProxyResponsesWebSocketFromClient(
 				lastTurnReplayInput, _ = stripOpenAIInvalidEncryptedContentFromReplayItems(lastTurnReplayInput, invalidDigests)
 			}
 		}
+		boundaryPayload, contextWindowBoundary, boundaryErr := normalizeOpenAIWSContextWindowBoundary(
+			currentPayload,
+			lastTurnWindowID,
+		)
+		if boundaryErr != nil {
+			return fmt.Errorf("normalize Codex websocket context-window boundary: %w", boundaryErr)
+		}
+		if contextWindowBoundary.Changed {
+			currentPayload = boundaryPayload
+			currentPayloadBytes = len(boundaryPayload)
+			logOpenAIWSModeInfo(
+				"ingress_ws_context_window_changed account_id=%d turn=%d conn_id=%s action=break_previous_response_chain previous_window_id=%s current_window_id=%s previous_response_id_removed=%v",
+				account.ID,
+				turn,
+				truncateOpenAIWSLogValue(sessionConnID, openAIWSIDValueMaxLen),
+				truncateOpenAIWSLogValue(lastTurnWindowID, openAIWSIDValueMaxLen),
+				truncateOpenAIWSLogValue(contextWindowBoundary.WindowID, openAIWSIDValueMaxLen),
+				contextWindowBoundary.PreviousResponseIDRemoved,
+			)
+		}
 		currentPreviousResponseID := openAIWSPayloadStringFromRaw(currentPayload, "previous_response_id")
 		expectedPrev := strings.TrimSpace(lastTurnResponseID)
+		if contextWindowBoundary.Changed {
+			// A context-window rollover is a new Responses root. Do not infer a
+			// continuation anchor from the response produced in the old window.
+			expectedPrev = ""
+		}
 		toolSignals := ToolContinuationSignals{
 			HasFunctionCallOutput: openAIWSRawPayloadHasToolCallOutput(currentPayload),
 		}
@@ -1822,6 +1848,9 @@ func (s *OpenAIGatewayService) ProxyResponsesWebSocketFromClient(
 		}
 		responseID := strings.TrimSpace(result.RequestID)
 		lastTurnResponseID = responseID
+		if contextWindowBoundary.WindowID != "" {
+			lastTurnWindowID = contextWindowBoundary.WindowID
+		}
 		// 正文共享：currentPayload/currentTurnReplayInput 均不可变，历史直接引用；
 		// collector 增量经 combine 合并（新头数组）。
 		lastTurnReplayInput = currentTurnReplayInput
diff --git a/backend/internal/service/openai_ws_forwarder_ingress_test.go b/backend/internal/service/openai_ws_forwarder_ingress_test.go
index b70f83659a..915a4edf24 100644
--- a/backend/internal/service/openai_ws_forwarder_ingress_test.go
+++ b/backend/internal/service/openai_ws_forwarder_ingress_test.go
@@ -144,6 +144,49 @@ func TestDropPreviousResponseIDFromRawPayload(t *testing.T) {
 	})
 }
 
+func TestNormalizeOpenAIWSContextWindowBoundary(t *testing.T) {
+	t.Parallel()
+
+	t.Run("same_window_keeps_previous_response_id", func(t *testing.T) {
+		payload := []byte("{\"type\":\"response.create\",\"previous_response_id\":\"resp_old\",\"client_metadata\":{\"x-codex-window-id\":\"window-a\"}}")
+		updated, boundary, err := normalizeOpenAIWSContextWindowBoundary(payload, "window-a")
+		require.NoError(t, err)
+		require.False(t, boundary.Changed)
+		require.False(t, boundary.PreviousResponseIDRemoved)
+		require.Equal(t, "window-a", boundary.WindowID)
+		require.Equal(t, "resp_old", gjson.GetBytes(updated, "previous_response_id").String())
+	})
+
+	t.Run("new_window_drops_previous_response_id", func(t *testing.T) {
+		payload := []byte("{\"type\":\"response.create\",\"previous_response_id\":\"resp_old\",\"client_metadata\":{\"x-codex-window-id\":\"window-b\"}}")
+		updated, boundary, err := normalizeOpenAIWSContextWindowBoundary(payload, "window-a")
+		require.NoError(t, err)
+		require.True(t, boundary.Changed)
+		require.True(t, boundary.PreviousResponseIDRemoved)
+		require.Equal(t, "window-b", boundary.WindowID)
+		require.False(t, gjson.GetBytes(updated, "previous_response_id").Exists())
+	})
+
+	t.Run("new_window_without_previous_response_id_still_marks_boundary", func(t *testing.T) {
+		payload := []byte("{\"type\":\"response.create\",\"client_metadata\":{\"x-codex-window-id\":\"window-b\"}}")
+		updated, boundary, err := normalizeOpenAIWSContextWindowBoundary(payload, "window-a")
+		require.NoError(t, err)
+		require.True(t, boundary.Changed)
+		require.False(t, boundary.PreviousResponseIDRemoved)
+		require.Equal(t, string(payload), string(updated))
+	})
+
+	t.Run("embedded_turn_metadata_is_fallback", func(t *testing.T) {
+		payload := []byte("{\"type\":\"response.create\",\"previous_response_id\":\"resp_old\",\"client_metadata\":{\"x-codex-turn-metadata\":\"{\\\"window_id\\\":\\\"window-b\\\"}\"}}")
+		updated, boundary, err := normalizeOpenAIWSContextWindowBoundary(payload, "window-a")
+		require.NoError(t, err)
+		require.True(t, boundary.Changed)
+		require.True(t, boundary.PreviousResponseIDRemoved)
+		require.Equal(t, "window-b", boundary.WindowID)
+		require.False(t, gjson.GetBytes(updated, "previous_response_id").Exists())
+	})
+}
+
 func TestStripCodexSparkImageGenerationToolFromRawPayload(t *testing.T) {
 	t.Run("strips_image_generation_for_spark", func(t *testing.T) {
 		payload := []byte(`{"type":"response.create","model":"gpt-5.3-codex-spark","tools":[{"type":"function","name":"shell"},{"type":"image_generation","output_format":"png"}]}`)
diff --git a/backend/internal/service/openai_ws_forwarder_payload.go b/backend/internal/service/openai_ws_forwarder_payload.go
index bc24ebc265..16ca9c8a63 100644
--- a/backend/internal/service/openai_ws_forwarder_payload.go
+++ b/backend/internal/service/openai_ws_forwarder_payload.go
@@ -378,6 +378,48 @@ func setPreviousResponseIDToRawPayload(payload []byte, previousResponseID string
 	return rebuilt, nil
 }
 
+type openAIWSContextWindowBoundary struct {
+	WindowID                  string
+	Changed                   bool
+	PreviousResponseIDRemoved bool
+}
+
+func openAIWSPayloadCodexWindowID(payload []byte) string {
+	if len(payload) == 0 {
+		return ""
+	}
+	if windowID := strings.TrimSpace(gjson.GetBytes(payload, "client_metadata.x-codex-window-id").String()); windowID != "" {
+		return windowID
+	}
+	turnMetadata := strings.TrimSpace(gjson.GetBytes(payload, "client_metadata.x-codex-turn-metadata").String())
+	if turnMetadata == "" {
+		return ""
+	}
+	return strings.TrimSpace(gjson.Get(turnMetadata, "window_id").String())
+}
+
+// normalizeOpenAIWSContextWindowBoundary breaks a Responses continuation chain
+// when Codex moves to a new local context window. WebSocket response.create can
+// still carry the previous window's previous_response_id after new_context,
+// while HTTP starts the new window without that continuation anchor.
+func normalizeOpenAIWSContextWindowBoundary(
+	payload []byte,
+	previousWindowID string,
+) ([]byte, openAIWSContextWindowBoundary, error) {
+	currentWindowID := openAIWSPayloadCodexWindowID(payload)
+	boundary := openAIWSContextWindowBoundary{WindowID: currentWindowID}
+	if previousWindowID == "" || currentWindowID == "" || currentWindowID == previousWindowID {
+		return payload, boundary, nil
+	}
+	boundary.Changed = true
+	updated, removed, err := dropPreviousResponseIDFromRawPayload(payload)
+	if err != nil {
+		return payload, boundary, err
+	}
+	boundary.PreviousResponseIDRemoved = removed
+	return updated, boundary, nil
+}
+
 func shouldInferIngressFunctionCallOutputPreviousResponseID(
 	storeDisabled bool,
 	turn int,