Merge pull request #284 from leookun/fix/compress

Enhance checkpoint handling and error management in forwarder

internal/backend/forwarder/actor.go

@@ -730,6 +730,9 @@ func (service *Service) handleProviderDoneEvent(stream *ActiveStream, payload *s
 			service.setTurnPhase(stream, TurnPhaseFailed)
 			return service.closeStreamWithProviderError(stream, conversationID, turnSeq, requestID, accumulatedText, accumulatedReasoning, accumulatedReasoningSignature, accumulatedReasoningSignatureSource, accumulatedReasoningItemID, accumulatedReasoningStatus, accumulatedReasoningSummary, usage, providerErr, !hadToolInvocation)
 		}
+		if err := service.flushAssistantText(stream, conversationID, turnSeq, requestID, accumulatedText, accumulatedReasoning, accumulatedReasoningSignature, accumulatedReasoningSignatureSource, accumulatedReasoningItemID, accumulatedReasoningStatus, accumulatedReasoningSummary, !hadToolInvocation); err != nil {
+			return service.failStream(stream, "unknown", fmt.Errorf("flush failed provider output: %w", err))
+		}
 		service.setTurnPhase(stream, TurnPhaseFailed)
 		return service.failStream(stream, "unknown", payload.Err)
 	}

internal/backend/forwarder/checkpoint_blobs.go

@@ -19,15 +19,29 @@ type pendingCheckpointBlobWrite struct {
 	blob      CheckpointBlob
 }
 
-func clonePendingTurnCompletion(completion *pendingTurnCompletion) *pendingTurnCompletion {
+func successfulCheckpointTerminalAction(completion *pendingTurnCompletion) checkpointTerminalAction {
 	if completion == nil {
-		return nil
+		return checkpointTerminalAction{}
+	}
+	return checkpointTerminalAction{
+		Kind:       checkpointTerminalActionComplete,
+		Completion: *completion,
+	}
+}
+
+func failedCheckpointTerminalAction(errorCode string, errorMessage string) checkpointTerminalAction {
+	return checkpointTerminalAction{
+		Kind:         checkpointTerminalActionFail,
+		ErrorCode:    strings.TrimSpace(errorCode),
+		ErrorMessage: strings.TrimSpace(errorMessage),
 	}
-	cloned := *completion
-	return &cloned
 }
 
 func (service *Service) queueCheckpointProjection(stream *ActiveStream, projection *CheckpointProjection, completion *pendingTurnCompletion) error {
+	return service.queueCheckpointProjectionWithTerminal(stream, projection, successfulCheckpointTerminalAction(completion))
+}
+
+func (service *Service) queueCheckpointProjectionWithTerminal(stream *ActiveStream, projection *CheckpointProjection, terminal checkpointTerminalAction) error {
 	if service == nil || stream == nil || projection == nil || projection.State == nil {
 		return nil
 	}
@@ -43,8 +57,8 @@ func (service *Service) queueCheckpointProjection(stream *ActiveStream, projecti
 	if stream.ConfirmedCheckpointBlobs == nil {
 		stream.ConfirmedCheckpointBlobs = make(map[string]struct{})
 	}
-	if completion == nil && stream.PendingCheckpoint != nil {
-		completion = stream.PendingCheckpoint.Completion
+	if terminal.Kind == checkpointTerminalActionNone && stream.PendingCheckpoint != nil {
+		terminal = stream.PendingCheckpoint.Terminal
 	}
 	required := make(map[string]struct{}, len(projection.Blobs))
 	pendingKeys := make(map[string]struct{}, len(stream.PendingCheckpointBlobWrites))
@@ -74,11 +88,11 @@ func (service *Service) queueCheckpointProjection(stream *ActiveStream, projecti
 		toWrite = append(toWrite, pendingCheckpointBlobWrite{requestID: requestID, blob: blob})
 	}
 	stream.PendingCheckpoint = &pendingCheckpointPublish{
-		State:      state,
-		Required:   required,
-		Completion: clonePendingTurnCompletion(completion),
+		State:    state,
+		Required: required,
+		Terminal: terminal,
 	}
-	if completion != nil {
+	if terminal.Kind != checkpointTerminalActionNone {
 		stream.Phase = TurnPhaseCheckpointing
 	}
 	stream.UpdatedAt = time.Now().UTC()
@@ -94,13 +108,8 @@ func (service *Service) queueCheckpointProjection(stream *ActiveStream, projecti
 	if service.checkpointProjectionReady(stream) {
 		return service.publishReadyCheckpoint(stream)
 	}
-	// Keep the latest live UI state ahead of an immediate client abort. Blob writes are
-	// ordered before this snapshot; acknowledgements still gate terminal completion.
-	if completion == nil {
-		if err := service.publishPendingCheckpoint(stream); err != nil {
-			return service.finishAfterCheckpointSyncFailure(stream, fmt.Errorf("publish pending checkpoint: %w", err))
-		}
-	}
+	// Checkpoints reference these Blob IDs, so the client must confirm every
+	// required Blob before the checkpoint becomes visible.
 	service.scheduleStreamTimer(
 		stream,
 		providerTimerKey(streamTimerCheckpointBlobs, ""),
@@ -113,31 +122,6 @@ func (service *Service) queueCheckpointProjection(stream *ActiveStream, projecti
 	return nil
 }
 
-func (service *Service) publishPendingCheckpoint(stream *ActiveStream) error {
-	if service == nil || stream == nil {
-		return nil
-	}
-	stream.mu.Lock()
-	pending := stream.PendingCheckpoint
-	if pending == nil || pending.Published {
-		stream.mu.Unlock()
-		return nil
-	}
-	pending.Published = true
-	state := pending.State
-	stream.UpdatedAt = time.Now().UTC()
-	stream.mu.Unlock()
-	if err := service.broker.Publish(stream.RequestID, StreamEvent{Message: buildCheckpointMessage(state)}); err != nil {
-		stream.mu.Lock()
-		if stream.PendingCheckpoint == pending {
-			pending.Published = false
-		}
-		stream.mu.Unlock()
-		return err
-	}
-	return nil
-}
-
 func (service *Service) checkpointProjectionReady(stream *ActiveStream) bool {
 	if stream == nil {
 		return false
@@ -207,24 +191,18 @@ func (service *Service) publishReadyCheckpoint(stream *ActiveStream) error {
 	}
 	stream.PendingCheckpoint = nil
 	state := pending.State
-	completion := clonePendingTurnCompletion(pending.Completion)
-	published := pending.Published
+	terminal := pending.Terminal
 	stream.UpdatedAt = time.Now().UTC()
 	stream.mu.Unlock()
 	clearStreamTimer(stream, providerTimerKey(streamTimerCheckpointBlobs, ""))
-	if !published {
-		if err := service.broker.Publish(stream.RequestID, StreamEvent{Message: buildCheckpointMessage(state)}); err != nil {
-			if completion != nil {
-				log.Printf("forwarder checkpoint publish skipped before successful terminal request_id=%s err=%v", stream.RequestID, err)
-				return service.finishSuccessfulTurnAfterCheckpoint(stream, *completion)
-			}
-			return err
+	if err := service.broker.Publish(stream.RequestID, StreamEvent{Message: buildCheckpointMessage(state)}); err != nil {
+		if terminal.Kind != checkpointTerminalActionNone {
+			log.Printf("forwarder checkpoint publish skipped before terminal request_id=%s err=%v", stream.RequestID, err)
+			return service.finishCheckpointTerminalAction(stream, terminal)
 		}
+		return err
 	}
-	if completion != nil {
-		return service.finishSuccessfulTurnAfterCheckpoint(stream, *completion)
-	}
-	return nil
+	return service.finishCheckpointTerminalAction(stream, terminal)
 }
 
 func (service *Service) handleCheckpointBlobTimeout(stream *ActiveStream) error {
@@ -251,12 +229,23 @@ func (service *Service) finishAfterCheckpointSyncFailure(stream *ActiveStream, c
 	if cause != nil {
 		log.Printf("forwarder checkpoint blob sync skipped request_id=%s conversation_id=%s err=%v", stream.RequestID, stream.ConversationID, cause)
 	}
-	if pending != nil && pending.Completion != nil {
-		return service.finishSuccessfulTurnAfterCheckpoint(stream, *pending.Completion)
+	if pending != nil {
+		return service.finishCheckpointTerminalAction(stream, pending.Terminal)
 	}
 	return nil
 }
 
+func (service *Service) finishCheckpointTerminalAction(stream *ActiveStream, terminal checkpointTerminalAction) error {
+	switch terminal.Kind {
+	case checkpointTerminalActionComplete:
+		return service.finishSuccessfulTurnAfterCheckpoint(stream, terminal.Completion)
+	case checkpointTerminalActionFail:
+		return service.finishFailedTurnAfterCheckpoint(stream, terminal.ErrorCode, terminal.ErrorMessage)
+	default:
+		return nil
+	}
+}
+
 func (service *Service) discardPendingCheckpoint(stream *ActiveStream, reason string) {
 	if stream == nil {
 		return

internal/backend/forwarder/checkpoint_blobs_test.go

@@ -8,22 +8,43 @@ import (
 	"cursor/gen/agentv1"
 )
 
-func TestCheckpointBlobSyncPublishesNonTerminalCheckpointBeforeAcknowledgements(t *testing.T) {
+func TestCheckpointBlobSyncWaitsForAcknowledgementsBeforePublishingNonTerminalCheckpoint(t *testing.T) {
 	service, stream, projection := testCheckpointBlobProjection(t)
 	if err := service.queueCheckpointProjection(stream, projection, nil); err != nil {
 		t.Fatalf("queueCheckpointProjection() error = %v", err)
 	}
 	events := readCheckpointTestEvents(t, service, stream)
-	if len(events) != len(projection.Blobs)+1 {
-		t.Fatalf("events before ACK = %d, want %d Blob writes and one checkpoint", len(events), len(projection.Blobs))
+	if len(events) != len(projection.Blobs) {
+		t.Fatalf("events before ACK = %d, want %d Blob writes", len(events), len(projection.Blobs))
 	}
-	for _, event := range events[:len(projection.Blobs)] {
+	for _, event := range events {
 		if event.Message.GetKvServerMessage().GetSetBlobArgs() == nil {
 			t.Fatalf("event before ACK = %#v, want set_blob_args", event.Message)
 		}
 	}
-	if checkpoint := events[len(events)-1].Message.GetConversationCheckpointUpdate(); checkpoint == nil || len(checkpoint.GetTurns()) != 1 {
-		t.Fatalf("last event before ACK = %#v, want one Blob-backed turn", events[len(events)-1].Message)
+
+	stream.mu.Lock()
+	var firstRequestID uint32
+	for requestID := range stream.PendingCheckpointBlobWrites {
+		firstRequestID = requestID
+		break
+	}
+	stream.mu.Unlock()
+	if firstRequestID == 0 {
+		t.Fatal("checkpoint projection has no pending Blob writes")
+	}
+	if err := service.handleCheckpointBlobResult(stream, &agentv1.KvClientMessage{
+		Id: firstRequestID,
+		Message: &agentv1.KvClientMessage_SetBlobResult{
+			SetBlobResult: &agentv1.SetBlobResult{},
+		},
+	}); err != nil {
+		t.Fatalf("first Blob ACK error = %v", err)
+	}
+	for _, event := range readCheckpointTestEvents(t, service, stream) {
+		if event.Message.GetConversationCheckpointUpdate() != nil {
+			t.Fatal("checkpoint published after only a partial Blob acknowledgement")
+		}
 	}
 
 	acknowledgeCheckpointBlobs(t, service, stream)
@@ -98,7 +119,123 @@ func TestCheckpointBlobTimeoutDoesNotFailSuccessfulTurn(t *testing.T) {
 	}
 }
 
-func TestCancellationKeepsPublishedCheckpointAndIgnoresLateAcknowledgements(t *testing.T) {
+func TestCheckpointBlobSyncPublishesCheckpointBeforeFailedTerminal(t *testing.T) {
+	service, stream, _ := testCheckpointBlobProjection(t)
+	if err := service.failActiveStream(
+		stream,
+		stream.ConversationID,
+		stream.RequestID,
+		"model-call-1",
+		"provider_error",
+		"provider failed",
+	); err != nil {
+		t.Fatalf("failActiveStream() error = %v", err)
+	}
+
+	for _, event := range readCheckpointTestEvents(t, service, stream) {
+		if event.Message.GetConversationCheckpointUpdate() != nil || event.End {
+			t.Fatalf("event before ACK = %#v, want only Blob writes", event)
+		}
+	}
+	stream.mu.Lock()
+	phaseBeforeACK := stream.Phase
+	statusBeforeACK := stream.Status
+	stream.mu.Unlock()
+	if phaseBeforeACK != TurnPhaseCheckpointing || isTerminalStreamStatus(statusBeforeACK) {
+		t.Fatalf("before ACK phase=%s status=%s, want checkpointing and non-terminal", phaseBeforeACK, statusBeforeACK)
+	}
+
+	acknowledgeCheckpointBlobs(t, service, stream)
+	events := readCheckpointTestEvents(t, service, stream)
+	checkpointIndex, endIndex := -1, -1
+	for index, event := range events {
+		switch {
+		case event.Message.GetConversationCheckpointUpdate() != nil:
+			checkpointIndex = index
+		case event.End:
+			endIndex = index
+			if event.TerminalErrorCode != "provider_error" || event.TerminalErrorMessage != "provider failed" {
+				t.Fatalf("terminal event = %#v, want provider error", event)
+			}
+		}
+	}
+	if checkpointIndex < 0 || endIndex <= checkpointIndex {
+		t.Fatalf("terminal order checkpoint=%d end=%d", checkpointIndex, endIndex)
+	}
+	stream.mu.Lock()
+	phaseAfterACK := stream.Phase
+	statusAfterACK := stream.Status
+	stream.mu.Unlock()
+	if phaseAfterACK != TurnPhaseFailed || statusAfterACK != StreamStatusFailed {
+		t.Fatalf("after ACK phase=%s status=%s, want failed", phaseAfterACK, statusAfterACK)
+	}
+}
+
+func TestCheckpointBlobTimeoutStillPublishesFailedTerminal(t *testing.T) {
+	service, stream, _ := testCheckpointBlobProjection(t)
+	if err := service.failActiveStream(
+		stream,
+		stream.ConversationID,
+		stream.RequestID,
+		"model-call-1",
+		"provider_error",
+		"provider failed",
+	); err != nil {
+		t.Fatalf("failActiveStream() error = %v", err)
+	}
+	if err := service.handleCheckpointBlobTimeout(stream); err != nil {
+		t.Fatalf("handleCheckpointBlobTimeout() error = %v", err)
+	}
+
+	events := readCheckpointTestEvents(t, service, stream)
+	var checkpoint, failedEnd bool
+	for _, event := range events {
+		checkpoint = checkpoint || event.Message.GetConversationCheckpointUpdate() != nil
+		failedEnd = failedEnd || event.End && event.TerminalErrorCode == "provider_error" && event.TerminalErrorMessage == "provider failed"
+	}
+	if checkpoint || !failedEnd {
+		t.Fatalf("timeout events checkpoint=%v failed_end=%v", checkpoint, failedEnd)
+	}
+}
+
+func TestManualCompactionNoopWaitsForCheckpointBeforeTerminal(t *testing.T) {
+	service, stream, _ := testCheckpointBlobProjection(t)
+	conversation, _, _, err := service.snapshotCheckpointConversation(stream)
+	if err != nil {
+		t.Fatalf("snapshotCheckpointConversation() error = %v", err)
+	}
+	if _, err := service.store.SaveConversationWithEntries(stream.ConversationID, conversation, conversation.Entries); err != nil {
+		t.Fatalf("SaveConversationWithEntries() error = %v", err)
+	}
+	if err := service.finishManualCompactionNoop(stream); err != nil {
+		t.Fatalf("finishManualCompactionNoop() error = %v", err)
+	}
+
+	for _, event := range readCheckpointTestEvents(t, service, stream) {
+		if event.Message.GetInteractionUpdate().GetTurnEnded() != nil || event.End {
+			t.Fatalf("terminal event before checkpoint Blob ACK = %#v", event)
+		}
+	}
+	acknowledgeCheckpointBlobs(t, service, stream)
+
+	events := readCheckpointTestEvents(t, service, stream)
+	checkpointIndex, turnEndedIndex, endIndex := -1, -1, -1
+	for index, event := range events {
+		switch {
+		case event.Message.GetConversationCheckpointUpdate() != nil:
+			checkpointIndex = index
+		case event.Message.GetInteractionUpdate().GetTurnEnded() != nil:
+			turnEndedIndex = index
+		case event.End:
+			endIndex = index
+		}
+	}
+	if checkpointIndex < 0 || turnEndedIndex <= checkpointIndex || endIndex <= turnEndedIndex {
+		t.Fatalf("terminal order checkpoint=%d turn_ended=%d end=%d", checkpointIndex, turnEndedIndex, endIndex)
+	}
+}
+
+func TestCancellationDiscardsUnpublishedCheckpointAndIgnoresLateAcknowledgements(t *testing.T) {
 	service, stream, projection := testCheckpointBlobProjection(t)
 	if err := service.queueCheckpointProjection(stream, projection, nil); err != nil {
 		t.Fatalf("queueCheckpointProjection() error = %v", err)
@@ -110,8 +247,8 @@ func TestCancellationKeepsPublishedCheckpointAndIgnoresLateAcknowledgements(t *t
 			checkpointBeforeCancel++
 		}
 	}
-	if checkpointBeforeCancel != 1 {
-		t.Fatalf("checkpoints before cancel = %d, want 1", checkpointBeforeCancel)
+	if checkpointBeforeCancel != 0 {
+		t.Fatalf("checkpoints before cancel = %d, want 0", checkpointBeforeCancel)
 	}
 	stream.mu.Lock()
 	requestIDs := make([]uint32, 0, len(stream.PendingCheckpointBlobWrites))
@@ -149,7 +286,7 @@ func TestCancellationKeepsPublishedCheckpointAndIgnoresLateAcknowledgements(t *t
 	stream.mu.Lock()
 	pending := stream.PendingCheckpoint
 	stream.mu.Unlock()
-	if checkpointCount != 1 || !canceledEnd || pending != nil {
+	if checkpointCount != 0 || !canceledEnd || pending != nil {
 		t.Fatalf("cancel events checkpoints=%d canceled_end=%v pending=%v", checkpointCount, canceledEnd, pending != nil)
 	}
 }

internal/backend/forwarder/compaction.go

@@ -234,7 +234,7 @@ func (service *Service) buildLegacyCompactionPlan(base *compactionPlan, conversa
 	if conversation == nil || base == nil {
 		return nil, nil
 	}
-	candidates := buildContextCompactionCandidates(checkpointProjectionEntries(conversation.Entries), base.CurrentTurnSeq, base.CurrentRequestID)
+	candidates := buildContextCompactionCandidates(replayablePromptProjectionEntries(conversation.Entries), base.CurrentTurnSeq, base.CurrentRequestID)
 	if len(candidates) == 0 {
 		return nil, nil
 	}
@@ -260,7 +260,7 @@ func (service *Service) buildAutoCompactionPlanFromHistory(base *compactionPlan,
 	if err != nil {
 		return nil, err
 	}
-	currentCandidate, hasCurrentCandidate := buildCurrentTurnCompactionCandidate(checkpointProjectionEntries(conversation.Entries), base.CurrentTurnSeq, base.CurrentRequestID)
+	currentCandidate, hasCurrentCandidate := buildCurrentTurnCompactionCandidate(replayablePromptProjectionEntries(conversation.Entries), base.CurrentTurnSeq, base.CurrentRequestID)
 	if !hasCurrentCandidate {
 		return legacyPlan, nil
 	}
@@ -447,16 +447,8 @@ func (service *Service) handleCompactionEvent(stream *ActiveStream, payload *str
 		if err := service.completeManualCompactionTurn(stream); err != nil {
 			return service.failStream(stream, "unknown", err)
 		}
-		if err := service.broker.Publish(stream.RequestID, StreamEvent{
-			Message: buildTurnEndedMessage(0, 0, 0, 0),
-		}); err != nil {
-			return service.failStream(stream, "unknown", err)
-		}
-		if err := service.broker.Complete(stream.RequestID, "", ""); err != nil {
-			return service.failStream(stream, "unknown", err)
-		}
-		service.setTurnPhase(stream, TurnPhaseCompleted)
-		return nil
+		completion := manualCompactionTurnCompletion(stream)
+		return service.publishCheckpointWithCompletion(stream.RequestID, stream.ConversationID, &completion)
 	}
 	return service.requestProviderAction(stream, providerActionResume)
 }
@@ -500,12 +492,8 @@ func (service *Service) finishManualCompactionNoop(stream *ActiveStream) error {
 	if err := service.completeManualCompactionTurn(stream); err != nil {
 		return err
 	}
-	if err := service.broker.Publish(stream.RequestID, StreamEvent{
-		Message: buildTurnEndedMessage(0, 0, 0, 0),
-	}); err != nil {
-		return err
-	}
-	return service.broker.Complete(stream.RequestID, "", "")
+	completion := manualCompactionTurnCompletion(stream)
+	return service.publishCheckpointWithCompletion(stream.RequestID, stream.ConversationID, &completion)
 }
 
 func (service *Service) completeManualCompactionTurn(stream *ActiveStream) error {
@@ -530,10 +518,21 @@ func (service *Service) completeManualCompactionTurn(stream *ActiveStream) error
 	if err := service.syncSummaryCarryForward(conversationID, requestID, modelCallID); err != nil {
 		return err
 	}
-	service.setTurnPhase(stream, TurnPhaseCompleted)
 	return nil
 }
 
+func manualCompactionTurnCompletion(stream *ActiveStream) pendingTurnCompletion {
+	if stream == nil {
+		return pendingTurnCompletion{}
+	}
+	return pendingTurnCompletion{
+		ConversationID: strings.TrimSpace(stream.ConversationID),
+		RequestID:      strings.TrimSpace(stream.RequestID),
+		TurnSeq:        stream.TurnSeq,
+		ModelCallID:    "turn:" + strings.TrimSpace(stream.RequestID),
+	}
+}
+
 func (service *Service) publishSummaryCompleted(stream *ActiveStream, hookMessage string) error {
 	if service == nil || stream == nil {
 		return nil
@@ -568,6 +567,7 @@ func (service *Service) applyCompactionPlan(stream *ActiveStream, conversationID
 	if err != nil {
 		return err
 	}
+	originalEntryCount := len(candidateConversation.Entries)
 	if err := applyCompactionToConversation(candidateConversation, plan, summaryText); err != nil {
 		return err
 	}
@@ -582,9 +582,9 @@ func (service *Service) applyCompactionPlan(stream *ActiveStream, conversationID
 	if validationErr := validateCompactionCandidateBudget(recompiled, plan); validationErr != nil {
 		return validationErr
 	}
-	replacementEntries := append([]HistoryEntry(nil), candidateConversation.Entries...)
+	compactionEntries := append([]HistoryEntry(nil), candidateConversation.Entries[originalEntryCount:]...)
 	if service.store != nil {
-		persisted, err := service.store.ReplaceEntries(conversationID, replacementEntries, func(item *ConversationFile) error {
+		persisted, _, err := service.store.AppendEntriesWithUpdate(conversationID, resetEntrySequences(compactionEntries), func(item *ConversationFile) error {
 			if item == nil {
 				return nil
 			}
@@ -605,10 +605,7 @@ func (service *Service) applyCompactionPlan(stream *ActiveStream, conversationID
 		if item == nil {
 			return nil
 		}
-		item.Entries = nil
-		item.NextEntrySeq = 1
-		item.NextTurnSeq = 1
-		appendEntriesInPlace(item, resetEntrySequences(replacementEntries))
+		appendEntriesInPlace(item, resetEntrySequences(compactionEntries))
 		item.TokenDetailsUsedTokens = 0
 		clearConversationAutoCompactionState(item)
 		return nil
@@ -643,14 +640,13 @@ func applyCompactionToConversation(conversation *ConversationFile, plan *Pending
 	if conversation == nil || plan == nil {
 		return nil
 	}
-	replacementEntries, err := buildCompactedContextEntries(conversation, plan, summaryText)
+	compactionEntries, err := buildCompactedContextEntries(conversation, plan, summaryText)
 	if err != nil {
 		return err
 	}
-	conversation.Entries = nil
-	conversation.NextEntrySeq = 1
-	conversation.NextTurnSeq = 1
-	appendEntriesInPlace(conversation, resetEntrySequences(replacementEntries))
+	// Canonical history stays append-only. The prompt projector applies the
+	// latest summary marker when constructing model-visible replay.
+	appendEntriesInPlace(conversation, resetEntrySequences(compactionEntries))
 	conversation.TokenDetailsUsedTokens = 0
 	clearConversationAutoCompactionState(conversation)
 	if conversation.TokenDetailsMaxTokens == 0 {
@@ -671,40 +667,9 @@ func buildCompactedContextEntries(conversation *ConversationFile, plan *PendingC
 	if ok {
 		entries = append(entries, runtimeEntry)
 	}
-	if conversation == nil || !plan.PreserveCurrentTurnInputs {
-		return entries, nil
-	}
-	entries = append(entries, buildAutoCompactionPreservedCurrentTurnEntries(conversation.Entries, plan)...)
 	return entries, nil
 }
 
-func buildAutoCompactionPreservedCurrentTurnEntries(entries []HistoryEntry, plan *PendingCompaction) []HistoryEntry {
-	if len(entries) == 0 || plan == nil || !plan.PreserveCurrentTurnInputs {
-		return nil
-	}
-	latestToolCallID := latestCompletedToolCallIDForTurn(entries, plan.CurrentTurnSeq, plan.CurrentRequestID)
-	preservedIndexes := autoCompactionPreservedEntryIndexes(entries, plan.CurrentTurnSeq, plan.CurrentRequestID, latestToolCallID)
-	if len(preservedIndexes) == 0 {
-		return nil
-	}
-	preserved := make([]HistoryEntry, 0, len(preservedIndexes))
-	for index, entry := range entries {
-		if _, ok := preservedIndexes[index]; !ok {
-			continue
-		}
-		switch strings.TrimSpace(entry.Kind) {
-		case "compaction_summary", "compacted_summary", "compaction_request":
-			continue
-		case "tool_result":
-			if rewritten, ok := rewriteAutoCompactionToolResultEntry(entry, autoCompactionPreservedToolResultLimitBytes, false); ok {
-				entry = rewritten
-			}
-		}
-		preserved = append(preserved, entry)
-	}
-	return preserved
-}
-
 func newCompactionSummaryEntry(plan *PendingCompaction, summaryText string) HistoryEntry {
 	payload, _ := json.Marshal(compactionSummaryEntryPayload{
 		Summary:                   strings.TrimSpace(summaryText),

internal/backend/forwarder/compaction_append_only_test.go

@@ -0,0 +1,206 @@
+package forwarder
+
+import (
+	"reflect"
+	"strings"
+	"testing"
+
+	"google.golang.org/protobuf/encoding/protojson"
+
+	"cursor/gen/agentv1"
+)
+
+func TestApplyCompactionToConversationPreservesCanonicalHistory(t *testing.T) {
+	conversation := compactionAppendOnlyConversation(t)
+	originalEntries := append([]HistoryEntry(nil), conversation.Entries...)
+	plan := &PendingCompaction{
+		Trigger:          "manual",
+		CurrentTurnSeq:   2,
+		CurrentRequestID: "request-2",
+	}
+
+	if err := applyCompactionToConversation(conversation, plan, "earlier context summary"); err != nil {
+		t.Fatalf("applyCompactionToConversation() error = %v", err)
+	}
+	if len(conversation.Entries) <= len(originalEntries) {
+		t.Fatalf("entries after compaction = %d, want the %d original entries plus a summary marker", len(conversation.Entries), len(originalEntries))
+	}
+	if !reflect.DeepEqual(conversation.Entries[:len(originalEntries)], originalEntries) {
+		t.Fatal("compaction changed the canonical history prefix")
+	}
+
+	projector := NewHistoryProjector()
+	projection, err := projector.ProjectCheckpointProjection(conversation)
+	if err != nil {
+		t.Fatalf("ProjectCheckpointProjection() error = %v", err)
+	}
+	if len(projection.State.GetTurns()) != 2 {
+		t.Fatalf("checkpoint turns after compaction = %d, want 2 visible turns", len(projection.State.GetTurns()))
+	}
+	replay, err := projector.ProjectPromptReplay(conversation)
+	if err != nil {
+		t.Fatalf("ProjectPromptReplay() error = %v", err)
+	}
+	if len(replay) != 1 || replay[0].Role != "user" || !strings.Contains(replay[0].Content, "earlier context summary") {
+		t.Fatalf("prompt replay after compaction = %#v, want only the compacted summary", replay)
+	}
+}
+
+func TestCompactedPromptProjectionPlacesSummaryBeforePreservedCurrentTurn(t *testing.T) {
+	conversation := &ConversationFile{
+		ConversationID:     "conversation-1",
+		RootConversationID: "conversation-1",
+		Mode:               "agent",
+		NextTurnSeq:        1,
+		NextEntrySeq:       1,
+	}
+	appendEntriesInPlace(conversation, []HistoryEntry{
+		compactionTestUserEntry(t, 1, "request-1", "current question", "message-1"),
+		newToolCallEntry(1, "request-1", "call-1", "Read", "", "", checkpointTestReadToolCall(t, nil)),
+		newToolResultEntry(1, "request-1", "call-1", "Read", `{"path":"/tmp/example.txt"}`, "file contents", "", checkpointTestReadToolCall(t, nil)),
+	})
+	plan := &PendingCompaction{
+		Trigger:                   "auto",
+		CurrentTurnSeq:            1,
+		CurrentRequestID:          "request-1",
+		PreserveCurrentTurnInputs: true,
+	}
+	if err := applyCompactionToConversation(conversation, plan, "current progress summary"); err != nil {
+		t.Fatalf("applyCompactionToConversation() error = %v", err)
+	}
+
+	projected := compactedPromptProjectionEntries(conversation.Entries)
+	promptKinds := make([]string, 0, len(projected))
+	for _, entry := range projected {
+		if isPromptReplayEntryKind(entry.Kind) {
+			promptKinds = append(promptKinds, entry.Kind)
+		}
+	}
+	want := []string{"compacted_summary", "user_message", "tool_call", "tool_result"}
+	if !reflect.DeepEqual(promptKinds, want) {
+		t.Fatalf("compacted prompt entry order = %#v, want %#v", promptKinds, want)
+	}
+}
+
+func TestCompactionPlanningDoesNotRecompactArchivedHistory(t *testing.T) {
+	conversation := compactionAppendOnlyConversation(t)
+	if err := applyCompactionToConversation(conversation, &PendingCompaction{
+		Trigger:          "manual",
+		CurrentTurnSeq:   2,
+		CurrentRequestID: "request-2",
+	}, "archived history summary"); err != nil {
+		t.Fatalf("applyCompactionToConversation() error = %v", err)
+	}
+	appendEntriesInPlace(conversation, []HistoryEntry{
+		compactionTestUserEntry(t, 3, "request-3", "new question", "message-3"),
+	})
+
+	plan, err := (&Service{}).buildLegacyCompactionPlan(&compactionPlan{
+		CurrentTurnSeq:   3,
+		CurrentRequestID: "request-3",
+	}, conversation, false, 0)
+	if err != nil {
+		t.Fatalf("buildLegacyCompactionPlan() error = %v", err)
+	}
+	if plan != nil {
+		t.Fatalf("buildLegacyCompactionPlan() = %#v, want no already summarized candidates", plan)
+	}
+}
+
+func TestApplyCompactionPlanPersistsHistoryAppendOnly(t *testing.T) {
+	store := NewConversationFileStore(t.TempDir())
+	conversation := compactionAppendOnlyConversation(t)
+	if _, _, err := store.AppendEntries(conversation.ConversationID, resetEntrySequences(conversation.Entries)); err != nil {
+		t.Fatalf("AppendEntries() error = %v", err)
+	}
+	persisted, err := store.LoadConversation(conversation.ConversationID)
+	if err != nil {
+		t.Fatalf("initial LoadConversation() error = %v", err)
+	}
+	originalEntries := append([]HistoryEntry(nil), persisted.Entries...)
+	projector := NewHistoryProjector()
+	service := &Service{
+		store:     store,
+		projector: projector,
+		compiler:  compactionProjectionCompiler{projector: projector},
+	}
+	stream := &ActiveStream{
+		RequestID:              "request-2",
+		ConversationID:         conversation.ConversationID,
+		TurnSeq:                2,
+		Mode:                   agentv1.AgentMode_AGENT_MODE_AGENT,
+		CheckpointConversation: persisted,
+	}
+	plan := &PendingCompaction{
+		Trigger:           "manual",
+		CurrentTurnSeq:    2,
+		CurrentRequestID:  "request-2",
+		ContextWindowSize: 1_000_000,
+	}
+	if err := service.applyCompactionPlan(stream, conversation.ConversationID, plan, "persisted summary"); err != nil {
+		t.Fatalf("applyCompactionPlan() error = %v", err)
+	}
+
+	loaded, err := store.LoadConversation(conversation.ConversationID)
+	if err != nil {
+		t.Fatalf("LoadConversation() error = %v", err)
+	}
+	if len(loaded.Entries) <= len(originalEntries) {
+		t.Fatalf("persisted entries after compaction = %d, want more than %d", len(loaded.Entries), len(originalEntries))
+	}
+	for index := range originalEntries {
+		if !reflect.DeepEqual(loaded.Entries[index], originalEntries[index]) {
+			t.Fatalf("persisted history entry %d changed after compaction:\ngot  %#v\nwant %#v", index, loaded.Entries[index], originalEntries[index])
+		}
+	}
+}
+
+type compactionProjectionCompiler struct {
+	projector *HistoryProjector
+}
+
+func (compiler compactionProjectionCompiler) Compile(conversation *ConversationFile, _ agentv1.AgentMode, _ string, _ string) (CompiledConversation, error) {
+	messages, err := compiler.projector.ProjectPromptReplay(conversation)
+	return CompiledConversation{Messages: messages}, err
+}
+
+func (compactionProjectionCompiler) DerivePromptContexts(*ConversationFile, agentv1.AgentMode, string) ([]PromptContextMessage, error) {
+	return nil, nil
+}
+
+func compactionAppendOnlyConversation(t *testing.T) *ConversationFile {
+	t.Helper()
+	conversation := &ConversationFile{
+		ConversationID:         "conversation-1",
+		RootConversationID:     "conversation-1",
+		Mode:                   "agent",
+		NextTurnSeq:            1,
+		NextEntrySeq:           1,
+		TokenDetailsUsedTokens: 42_000,
+		TokenDetailsMaxTokens:  50_000,
+	}
+	appendEntriesInPlace(conversation, []HistoryEntry{
+		compactionTestUserEntry(t, 1, "request-1", "first question", "message-1"),
+		newAssistantTextEntry(1, "request-1", "first answer", "", ""),
+		compactionTestUserEntry(t, 2, "request-2", "second question", "message-2"),
+		newAssistantTextEntry(2, "request-2", "second answer", "", ""),
+	})
+	return conversation
+}
+
+func compactionTestUserEntry(t *testing.T, turnSeq int64, requestID string, text string, messageID string) HistoryEntry {
+	t.Helper()
+	payload, err := protojson.Marshal(&agentv1.UserMessage{Text: text, MessageId: messageID})
+	if err != nil {
+		t.Fatalf("marshal user message: %v", err)
+	}
+	return HistoryEntry{
+		TurnSeq:   turnSeq,
+		RequestID: requestID,
+		Role:      "user",
+		Kind:      "user_message",
+		Payload:   payload,
+	}
+}
+
+var _ PromptCompiler = compactionProjectionCompiler{}

internal/backend/forwarder/file_store.go

@@ -121,10 +121,15 @@ func (store *ConversationFileStore) LoadConversation(conversationID string) (*Co
 
 // AppendEntries 把已经发生的语义事件追加到 context.json，并同步 state.json。
 func (store *ConversationFileStore) AppendEntries(conversationID string, entries []HistoryEntry) (*ConversationFile, []HistoryEntry, error) {
+	return store.AppendEntriesWithUpdate(conversationID, entries, nil)
+}
+
+// AppendEntriesWithUpdate 原子追加 context entries，并在同一把会话锁内更新 state metadata。
+func (store *ConversationFileStore) AppendEntriesWithUpdate(conversationID string, entries []HistoryEntry, update func(*ConversationFile) error) (*ConversationFile, []HistoryEntry, error) {
 	if store == nil {
 		return nil, nil, fmt.Errorf("conversation file store is nil")
 	}
-	if len(entries) == 0 {
+	if len(entries) == 0 && update == nil {
 		conversation, err := store.LoadConversation(conversationID)
 		return conversation, nil, err
 	}
@@ -162,6 +167,11 @@ func (store *ConversationFileStore) AppendEntries(conversationID string, entries
 		conversation.Mode = alias
 	}
 	assigned := appendEntriesInPlace(conversation, entries)
+	if update != nil {
+		if err := update(conversation); err != nil {
+			return nil, nil, err
+		}
+	}
 	deriveConversationLoopState(conversation)
 	if err := store.writeConversationLocked(normalizedConversationID, conversation); err != nil {
 		return nil, nil, err
@@ -762,6 +772,7 @@ func mergeConversationMetadata(target *ConversationFile, source *ConversationFil
 	target.CurrentPlanText = source.CurrentPlanText
 	target.CurrentPlans = clonePlanRegistryEntries(source.CurrentPlans)
 	target.CurrentTodos = cloneTodoItems(source.CurrentTodos)
+	target.ImportedTurnIDs = cloneByteSlices(source.ImportedTurnIDs)
 	target.LatestRequestPrefix = cloneConversationRequestPrefix(source.LatestRequestPrefix)
 	target.LastProviderCall = cloneConversationProviderCall(source.LastProviderCall)
 	if !source.CreatedAt.IsZero() && (target.CreatedAt.IsZero() || source.CreatedAt.Before(target.CreatedAt)) {
@@ -894,6 +905,7 @@ func cloneConversationFile(conversation *ConversationFile) *ConversationFile {
 	cloned := *conversation
 	cloned.CurrentPlans = clonePlanRegistryEntries(conversation.CurrentPlans)
 	cloned.CurrentTodos = cloneTodoItems(conversation.CurrentTodos)
+	cloned.ImportedTurnIDs = cloneByteSlices(conversation.ImportedTurnIDs)
 	cloned.LatestRequestPrefix = cloneConversationRequestPrefix(conversation.LatestRequestPrefix)
 	cloned.LastProviderCall = cloneConversationProviderCall(conversation.LastProviderCall)
 	cloned.Entries = append([]HistoryEntry(nil), conversation.Entries...)

internal/backend/forwarder/imported_blobs.go

@@ -0,0 +1,167 @@
+package forwarder
+
+import (
+	"crypto/sha256"
+	"fmt"
+
+	"google.golang.org/protobuf/proto"
+
+	"cursor/gen/agentv1"
+	modeladapter "cursor/internal/backend/agent/model"
+	promptengine "cursor/internal/backend/agent/prompt"
+)
+
+type importedBlobStore map[string][]byte
+
+func newImportedBlobStore(items []*agentv1.PreFetchedBlob) (importedBlobStore, error) {
+	if len(items) == 0 {
+		return nil, nil
+	}
+	store := make(importedBlobStore, len(items))
+	for _, item := range items {
+		if item == nil || len(item.GetId()) == 0 {
+			continue
+		}
+		if len(item.GetId()) != sha256.Size {
+			return nil, fmt.Errorf("prefetched blob id length %d, want %d", len(item.GetId()), sha256.Size)
+		}
+		digest := sha256.Sum256(item.GetValue())
+		if string(digest[:]) != string(item.GetId()) {
+			return nil, fmt.Errorf("prefetched blob %x failed SHA-256 validation", item.GetId())
+		}
+		store[string(item.GetId())] = append([]byte(nil), item.GetValue()...)
+	}
+	return store, nil
+}
+
+func (store importedBlobStore) resolve(id []byte) ([]byte, bool) {
+	if len(id) == 0 || len(store) == 0 {
+		return nil, false
+	}
+	value, ok := store[string(id)]
+	return append([]byte(nil), value...), ok
+}
+
+func decodeImportedTurn(raw []byte, blobs importedBlobStore) (*agentv1.ConversationTurnStructure, []byte, error) {
+	if data, ok := blobs.resolve(raw); ok {
+		turn := &agentv1.ConversationTurnStructure{}
+		if err := proto.Unmarshal(data, turn); err != nil || turn.GetTurn() == nil {
+			return nil, nil, fmt.Errorf("decode imported turn blob %x: %w", raw, firstNonNilError(err, fmt.Errorf("turn payload is empty")))
+		}
+		return turn, append([]byte(nil), raw...), nil
+	}
+	turn := &agentv1.ConversationTurnStructure{}
+	if err := proto.Unmarshal(raw, turn); err == nil && turn.GetTurn() != nil {
+		return turn, nil, nil
+	}
+	if len(raw) == sha256.Size {
+		return nil, append([]byte(nil), raw...), nil
+	}
+	return nil, nil, fmt.Errorf("decode imported inline turn")
+}
+
+func decodeImportedUserMessage(raw []byte, blobs importedBlobStore) (*agentv1.UserMessage, error) {
+	data := raw
+	if resolved, ok := blobs.resolve(raw); ok {
+		data = resolved
+	} else if len(raw) == sha256.Size {
+		candidate := &agentv1.UserMessage{}
+		if err := proto.Unmarshal(raw, candidate); err != nil || !hasKnownUserMessageContent(candidate) {
+			return nil, fmt.Errorf("missing prefetched user message blob %x", raw)
+		}
+		return candidate, nil
+	}
+	message := &agentv1.UserMessage{}
+	if err := proto.Unmarshal(data, message); err != nil {
+		return nil, fmt.Errorf("decode imported turn user_message: %w", err)
+	}
+	return message, nil
+}
+
+func decodeImportedStep(raw []byte, blobs importedBlobStore) (*agentv1.ConversationStep, error) {
+	data := raw
+	if resolved, ok := blobs.resolve(raw); ok {
+		data = resolved
+	} else if len(raw) == sha256.Size {
+		candidate := &agentv1.ConversationStep{}
+		if err := proto.Unmarshal(raw, candidate); err != nil || candidate.GetMessage() == nil {
+			return nil, fmt.Errorf("missing prefetched conversation step blob %x", raw)
+		}
+		return candidate, nil
+	}
+	step := &agentv1.ConversationStep{}
+	if err := proto.Unmarshal(data, step); err != nil {
+		return nil, fmt.Errorf("decode imported turn step: %w", err)
+	}
+	if step.GetMessage() == nil {
+		return nil, fmt.Errorf("decode imported turn step: payload is empty")
+	}
+	return step, nil
+}
+
+func importedBlobTurnMessages(turn *agentv1.ConversationTurnStructure, blobs importedBlobStore) ([]modeladapter.Message, error) {
+	if turn == nil || turn.GetAgentConversationTurn() == nil {
+		return nil, nil
+	}
+	agentTurn := turn.GetAgentConversationTurn()
+	messages := make([]modeladapter.Message, 0, 1+len(agentTurn.GetSteps()))
+	if len(agentTurn.GetUserMessage()) > 0 {
+		userMessage, err := decodeImportedUserMessage(agentTurn.GetUserMessage(), blobs)
+		if err != nil {
+			return nil, err
+		}
+		if replay, ok := promptengine.BuildUserMessageReplayMessage(userMessage); ok {
+			messages = append(messages, toModelMessage(replay))
+		}
+	}
+	for _, rawStep := range agentTurn.GetSteps() {
+		if len(rawStep) == 0 {
+			continue
+		}
+		step, err := decodeImportedStep(rawStep, blobs)
+		if err != nil {
+			return nil, err
+		}
+		for _, replay := range promptengine.BuildLegacyMessagesFromConversationStep(step) {
+			messages = append(messages, toModelMessage(replay))
+		}
+	}
+	return messages, nil
+}
+
+func importedTurnIDs(turns [][]byte, blobs importedBlobStore) ([][]byte, error) {
+	ids := make([][]byte, 0, len(turns))
+	for _, raw := range turns {
+		if len(raw) == 0 {
+			continue
+		}
+		_, id, err := decodeImportedTurn(raw, blobs)
+		if err != nil {
+			return nil, err
+		}
+		if len(id) > 0 {
+			ids = append(ids, id)
+		}
+	}
+	return ids, nil
+}
+
+func hasKnownUserMessageContent(message *agentv1.UserMessage) bool {
+	if message == nil {
+		return false
+	}
+	return message.GetText() != "" ||
+		message.GetMessageId() != "" ||
+		message.GetSelectedContext() != nil ||
+		message.GetRichText() != "" ||
+		len(message.GetConversationStateBlobId()) > 0 ||
+		len(message.GetTextBlobId()) > 0 ||
+		len(message.GetRichTextBlobId()) > 0
+}
+
+func firstNonNilError(err error, fallback error) error {
+	if err != nil {
+		return err
+	}
+	return fallback
+}

internal/backend/forwarder/imported_history_test.go

@@ -0,0 +1,109 @@
+package forwarder
+
+import (
+	"crypto/sha256"
+	"testing"
+
+	"google.golang.org/protobuf/proto"
+
+	"cursor/gen/agentv1"
+)
+
+func TestImportedConversationStateRestoresBlobOnlyForkAndCheckpointPrefix(t *testing.T) {
+	parent := compactionAppendOnlyConversation(t)
+	parent.Entries = parent.Entries[:2]
+	parent.NextEntrySeq = 3
+	parent.NextTurnSeq = 2
+	projection, err := NewHistoryProjector().ProjectCheckpointProjection(parent)
+	if err != nil {
+		t.Fatalf("ProjectCheckpointProjection() error = %v", err)
+	}
+	prefetched := make([]*agentv1.PreFetchedBlob, 0, len(projection.Blobs))
+	for _, blob := range projection.Blobs {
+		prefetched = append(prefetched, &agentv1.PreFetchedBlob{Id: blob.ID, Value: blob.Data})
+	}
+	state := proto.Clone(projection.State).(*agentv1.ConversationStateStructure)
+	state.RootPromptMessagesJson = nil
+	conversation, err := newRuntimeConversation("fork-conversation", agentv1.AgentMode_AGENT_MODE_AGENT)
+	if err != nil {
+		t.Fatalf("newRuntimeConversation() error = %v", err)
+	}
+	entries, err := (&Service{}).importConversationState(conversation, state, prefetched)
+	if err != nil {
+		t.Fatalf("importConversationState() error = %v", err)
+	}
+	if len(conversation.ImportedTurnIDs) != 1 || conversation.NextTurnSeq != 2 {
+		t.Fatalf("imported prefix turns=%d next_turn_seq=%d, want 1 and 2", len(conversation.ImportedTurnIDs), conversation.NextTurnSeq)
+	}
+	if len(entries) != 2 {
+		t.Fatalf("imported model entries = %d, want parent user and assistant", len(entries))
+	}
+	appendEntriesInPlace(conversation, append(entries,
+		compactionTestUserEntry(t, 2, "request-2", "fork question", "message-2"),
+	))
+	forkProjection, err := NewHistoryProjector().ProjectCheckpointProjection(conversation)
+	if err != nil {
+		t.Fatalf("fork ProjectCheckpointProjection() error = %v", err)
+	}
+	if len(forkProjection.State.GetTurns()) != 2 {
+		t.Fatalf("fork checkpoint turns = %d, want imported parent plus local fork turn", len(forkProjection.State.GetTurns()))
+	}
+	if string(forkProjection.State.GetTurns()[0]) != string(projection.State.GetTurns()[0]) {
+		t.Fatal("fork checkpoint did not preserve the imported parent turn ID as its prefix")
+	}
+}
+
+func TestImportedConversationStateRejectsUnresolvedBlobTurn(t *testing.T) {
+	turnID := sha256.Sum256([]byte("missing imported turn"))
+	conversation, err := newRuntimeConversation("fork-conversation", agentv1.AgentMode_AGENT_MODE_AGENT)
+	if err != nil {
+		t.Fatalf("newRuntimeConversation() error = %v", err)
+	}
+	if _, err := (&Service{}).importConversationState(conversation, &agentv1.ConversationStateStructure{
+		Turns: [][]byte{turnID[:]},
+	}, nil); err == nil {
+		t.Fatal("importConversationState() accepted an unresolved Blob turn")
+	}
+}
+
+func TestImportedTurnIDsPersistThroughConversationStore(t *testing.T) {
+	store := NewConversationFileStore(t.TempDir())
+	turnID := sha256.Sum256([]byte("parent turn"))
+	conversation, err := newRuntimeConversation("fork-conversation", agentv1.AgentMode_AGENT_MODE_AGENT)
+	if err != nil {
+		t.Fatalf("newRuntimeConversation() error = %v", err)
+	}
+	conversation.ImportedTurnIDs = [][]byte{turnID[:]}
+	persisted, err := store.SaveConversationWithEntries(conversation.ConversationID, conversation, []HistoryEntry{
+		compactionTestUserEntry(t, 2, "request-2", "fork question", "message-2"),
+	})
+	if err != nil {
+		t.Fatalf("SaveConversationWithEntries() error = %v", err)
+	}
+	if len(persisted.ImportedTurnIDs) != 1 || string(persisted.ImportedTurnIDs[0]) != string(turnID[:]) {
+		t.Fatalf("persisted ImportedTurnIDs = %x, want %x", persisted.ImportedTurnIDs, turnID)
+	}
+	loaded, err := store.LoadConversation(conversation.ConversationID)
+	if err != nil {
+		t.Fatalf("LoadConversation() error = %v", err)
+	}
+	if len(loaded.ImportedTurnIDs) != 1 || string(loaded.ImportedTurnIDs[0]) != string(turnID[:]) {
+		t.Fatalf("loaded ImportedTurnIDs = %x, want %x", loaded.ImportedTurnIDs, turnID)
+	}
+}
+
+func TestRewindImportedTurnPrefixUsesClientForkPoint(t *testing.T) {
+	ids := make([][]byte, 3)
+	for index := range ids {
+		digest := sha256.Sum256([]byte{byte(index + 1)})
+		ids[index] = digest[:]
+	}
+	trimmed := rewindImportedTurnPrefix(ids, runRewindDecision{
+		TargetTurnSeq:      4,
+		HasClientTurnCount: true,
+		ClientTurnCount:    1,
+	})
+	if len(trimmed) != 1 || string(trimmed[0]) != string(ids[0]) {
+		t.Fatalf("rewindImportedTurnPrefix() = %x, want first imported turn only", trimmed)
+	}
+}

internal/backend/forwarder/interrupted_output_test.go

@@ -2,6 +2,7 @@ package forwarder
 
 import (
 	"encoding/json"
+	"errors"
 	"strings"
 	"testing"
 )
@@ -125,6 +126,53 @@ func TestCancelPersistsInterruptedProviderOutputIdempotently(t *testing.T) {
 	}
 }
 
+func TestGenericProviderFailurePersistsAccumulatedOutput(t *testing.T) {
+	service, stream, _ := testCheckpointBlobProjection(t)
+	conversation, _, _, err := service.snapshotCheckpointConversation(stream)
+	if err != nil {
+		t.Fatalf("snapshotCheckpointConversation() error = %v", err)
+	}
+	if _, err := service.store.SaveConversationWithEntries(stream.ConversationID, conversation, conversation.Entries); err != nil {
+		t.Fatalf("SaveConversationWithEntries() error = %v", err)
+	}
+
+	stream.mu.Lock()
+	stream.CurrentModelCallID = "model-call-1"
+	stream.ProviderActive = true
+	stream.ProviderAccumulatedText = "partial answer before transport failure"
+	stream.Status = StreamStatusStreaming
+	stream.Phase = TurnPhaseProviderRunning
+	stream.mu.Unlock()
+	if err := service.handleProviderDoneEvent(stream, &streamProviderEvent{
+		Done: true,
+		Err:  errors.New("transport failed"),
+	}); err != nil {
+		t.Fatalf("handleProviderDoneEvent() error = %v", err)
+	}
+
+	persisted, err := service.store.LoadConversation(stream.ConversationID)
+	if err != nil {
+		t.Fatalf("LoadConversation() error = %v", err)
+	}
+	foundPartialOutput := false
+	for _, entry := range persisted.Entries {
+		if entry.Kind != "assistant_text" {
+			continue
+		}
+		var payload assistantTextPayload
+		if err := json.Unmarshal(entry.Payload, &payload); err != nil {
+			t.Fatalf("decode assistant entry: %v", err)
+		}
+		if payload.Text == "partial answer before transport failure" {
+			foundPartialOutput = true
+			break
+		}
+	}
+	if !foundPartialOutput {
+		t.Fatal("generic provider failure discarded accumulated assistant output")
+	}
+}
+
 func TestCancelPreservesPersistedTurnActivityWithoutLiveAccumulator(t *testing.T) {
 	service, stream, _ := testCheckpointBlobProjection(t)
 	conversation, _, _, err := service.snapshotCheckpointConversation(stream)

internal/backend/forwarder/projector.go

@@ -326,20 +326,24 @@ func compactedPromptProjectionEntries(entries []HistoryEntry) []HistoryEntry {
 		latestToolCallID := latestCompletedToolCallIDForTurn(entries, compactionPayload.CurrentTurnSeq, compactionPayload.CurrentRequestID)
 		preservedIndexes = autoCompactionPreservedEntryIndexes(entries, compactionPayload.CurrentTurnSeq, compactionPayload.CurrentRequestID, latestToolCallID)
 	}
-	filtered := make([]HistoryEntry, 0, len(entries)-compactionIndex)
-	for index, entry := range entries {
-		if index < compactionIndex && isPromptReplayEntryKind(entry.Kind) {
-			if _, ok := preservedIndexes[index]; !ok {
-				continue
-			}
+	filtered := make([]HistoryEntry, 0, len(entries)-compactionIndex+len(preservedIndexes))
+	for index := 0; index < compactionIndex; index++ {
+		if !isPromptReplayEntryKind(entries[index].Kind) {
+			filtered = append(filtered, entries[index])
 		}
-		if index < compactionIndex {
-			if rewritten, ok := compactedProjectionPreservedEntry(entry); ok {
-				entry = rewritten
-			}
+	}
+	filtered = append(filtered, entries[compactionIndex])
+	for index := 0; index < compactionIndex; index++ {
+		if _, ok := preservedIndexes[index]; !ok || isCompactionSummaryKind(entries[index].Kind) {
+			continue
+		}
+		entry := entries[index]
+		if rewritten, ok := compactedProjectionPreservedEntry(entry); ok {
+			entry = rewritten
 		}
 		filtered = append(filtered, entry)
 	}
+	filtered = append(filtered, entries[compactionIndex+1:]...)
 	return filtered
 }
 
@@ -575,7 +579,7 @@ func (projector *HistoryProjector) ProjectCheckpointProjection(conversation *Con
 	if err != nil {
 		return nil, err
 	}
-	state.Turns = turnIDs
+	state.Turns = append(cloneByteSlices(conversation.ImportedTurnIDs), turnIDs...)
 	replayMessages, err := projector.ProjectPromptReplay(conversation)
 	if err != nil {
 		return nil, err
@@ -1292,7 +1296,7 @@ func filterCheckpointPersistentToolReplay(messages []promptengine.Message) []pro
 	return filtered
 }
 
-func restoreImportedReplayUserMessages(messages []promptengine.Message, importedTurns [][]byte) []promptengine.Message {
+func restoreImportedReplayUserMessages(messages []promptengine.Message, importedTurns [][]byte, blobs importedBlobStore) []promptengine.Message {
 	if len(messages) == 0 || len(importedTurns) == 0 {
 		return messages
 	}
@@ -1301,16 +1305,16 @@ func restoreImportedReplayUserMessages(messages []promptengine.Message, imported
 		if len(rawTurn) == 0 {
 			continue
 		}
-		turn := &agentv1.ConversationTurnStructure{}
-		if err := proto.Unmarshal(rawTurn, turn); err != nil {
+		turn, _, err := decodeImportedTurn(rawTurn, blobs)
+		if err != nil || turn == nil {
 			continue
 		}
 		agentTurn := turn.GetAgentConversationTurn()
 		if agentTurn == nil || len(agentTurn.GetUserMessage()) == 0 {
 			continue
 		}
-		userMessage := &agentv1.UserMessage{}
-		if err := proto.Unmarshal(agentTurn.GetUserMessage(), userMessage); err != nil {
+		userMessage, err := decodeImportedUserMessage(agentTurn.GetUserMessage(), blobs)
+		if err != nil {
 			continue
 		}
 		replay, ok := promptengine.BuildUserMessageReplayMessage(userMessage)

internal/backend/forwarder/rewind.go

@@ -224,6 +224,7 @@ func (service *Service) applyRunRewindToConversation(conversation *ConversationF
 	conversation.Entries = nil
 	conversation.NextEntrySeq = 1
 	conversation.NextTurnSeq = 1
+	conversation.ImportedTurnIDs = rewindImportedTurnPrefix(conversation.ImportedTurnIDs, decision)
 	appendEntriesInPlace(conversation, appendReplacementRunEntries(decision.PrefixEntries, entries))
 	applyRunRewindConversationState(conversation, intent, turnSeq)
 	deriveConversationLoopState(conversation)
@@ -269,10 +270,30 @@ func applyRunRewindMetadata(conversation *ConversationFile, source *Conversation
 		if source.TokenDetailsMaxTokens > 0 {
 			conversation.TokenDetailsMaxTokens = source.TokenDetailsMaxTokens
 		}
+		decision := runRewindDecision{TargetTurnSeq: turnSeq}
+		if intent.ConversationState != nil {
+			decision.HasClientTurnCount = true
+			decision.ClientTurnCount = len(intent.ConversationState.GetTurns())
+		}
+		conversation.ImportedTurnIDs = rewindImportedTurnPrefix(source.ImportedTurnIDs, decision)
 	}
 	applyRunRewindConversationState(conversation, intent, turnSeq)
 }
 
+func rewindImportedTurnPrefix(importedTurnIDs [][]byte, decision runRewindDecision) [][]byte {
+	keep := decision.TargetTurnSeq - 1
+	if decision.HasClientTurnCount {
+		keep = int64(decision.ClientTurnCount)
+	}
+	if keep <= 0 || len(importedTurnIDs) == 0 {
+		return nil
+	}
+	if keep > int64(len(importedTurnIDs)) {
+		keep = int64(len(importedTurnIDs))
+	}
+	return cloneByteSlices(importedTurnIDs[:keep])
+}
+
 func (service *Service) logRunRewindDecision(requestID string, conversationID string, eventName string, decision runRewindDecision) {
 	if service == nil || !decision.Evaluated {
 		return

internal/backend/forwarder/runtime_summary.go

@@ -50,7 +50,7 @@ func (service *Service) bootstrapRuntimeConversation(intent InboundIntent) (*Con
 	}
 	importedEntries := []HistoryEntry(nil)
 	if len(conversation.Entries) == 0 && intent.ConversationState != nil {
-		importedEntries, err = service.importConversationState(conversation, intent.ConversationState)
+		importedEntries, err = service.importConversationState(conversation, intent.ConversationState, intent.PreFetchedBlobs)
 		if err != nil {
 			return nil, agentv1.AgentMode_AGENT_MODE_AGENT, 0, nil, err
 		}
@@ -138,6 +138,7 @@ func (service *Service) syncConversationRecord(conversationID string, conversati
 		item.AutoCompactionReserveTokens = conversation.AutoCompactionReserveTokens
 		item.AutoCompactionTriggeredAt = conversation.AutoCompactionTriggeredAt
 		item.AutoCompactionSourceModelCallID = conversation.AutoCompactionSourceModelCallID
+		item.ImportedTurnIDs = cloneByteSlices(conversation.ImportedTurnIDs)
 		item.LatestRequestPrefix = cloneConversationRequestPrefix(conversation.LatestRequestPrefix)
 		item.LastProviderCall = cloneConversationProviderCall(conversation.LastProviderCall)
 		item.CreatedAt = conversation.CreatedAt

internal/backend/forwarder/service.go

@@ -559,6 +559,7 @@ func (service *Service) decodeInboundIntent(requestID string, message *agentv1.A
 		}
 		intent.ConversationID = conversationID
 		intent.ConversationState = runRequest.GetConversationState()
+		intent.PreFetchedBlobs = runRequest.GetPreFetchedBlobs()
 		intent.UserMessage = extractUserMessage(message)
 		intent.RequestContext = extractRequestContext(message)
 		if service.shouldIgnoreEmptyResumeRunRequest(requestID, runRequest, intent.UserMessage, intent.RequestContext) {
@@ -606,6 +607,7 @@ func (service *Service) decodeInboundIntent(requestID string, message *agentv1.A
 		intent.ConversationID = conversationID
 		intent.SubagentTypeName = strings.TrimSpace(prewarmRequest.GetSubagentTypeName())
 		intent.ConversationState = prewarmRequest.GetConversationState()
+		intent.PreFetchedBlobs = prewarmRequest.GetPreFetchedBlobs()
 		intent.Mode, intent.ModeSource, intent.HasExplicitMode, err = extractPrewarmMode(prewarmRequest)
 		if err != nil {
 			return InboundIntent{}, err
@@ -2246,6 +2248,15 @@ func (service *Service) finishSuccessfulTurnAfterCheckpoint(stream *ActiveStream
 	return nil
 }
 
+func (service *Service) finishFailedTurnAfterCheckpoint(stream *ActiveStream, terminalCode string, terminalMessage string) error {
+	if stream == nil {
+		return nil
+	}
+	err := service.broker.Fail(stream.RequestID, terminalCode, terminalMessage)
+	service.setTurnPhase(stream, TurnPhaseFailed)
+	return err
+}
+
 func (service *Service) failStreamIfNonTerminal(stream *ActiveStream, terminalCode string, cause error) error {
 	if stream == nil || cause == nil {
 		return nil
@@ -2265,6 +2276,10 @@ func (service *Service) publishCheckpoint(requestID string, conversationID strin
 }
 
 func (service *Service) publishCheckpointWithCompletion(requestID string, _ string, completion *pendingTurnCompletion) error {
+	return service.publishCheckpointWithTerminalAction(requestID, successfulCheckpointTerminalAction(completion))
+}
+
+func (service *Service) publishCheckpointWithTerminalAction(requestID string, terminal checkpointTerminalAction) error {
 	stream, ok := service.broker.Get(requestID)
 	if !ok || stream == nil {
 		return fmt.Errorf("request is not active: %s", requestID)
@@ -2282,7 +2297,7 @@ func (service *Service) publishCheckpointWithCompletion(requestID string, _ stri
 	}
 	projection.State.PendingToolCalls = buildPendingToolCalls(pendingExecs, pendingInteractions)
 	service.rewriteCheckpointTokenDetailsForClient(stream, conversation, projection.State)
-	return service.queueCheckpointProjection(stream, projection, completion)
+	return service.queueCheckpointProjectionWithTerminal(stream, projection, terminal)
 }
 
 func (service *Service) rewriteCheckpointTokenDetailsForClient(stream *ActiveStream, conversation *ConversationFile, state *agentv1.ConversationStateStructure) {
@@ -2422,18 +2437,20 @@ func (service *Service) failActiveStream(stream *ActiveStream, conversationID st
 	if cancel != nil {
 		cancel()
 	}
-	service.setTurnPhase(stream, TurnPhaseFailed)
-	var firstErr error
-	if err := service.syncSummaryCarryForward(conversationID, requestID, modelCallID); err != nil && firstErr == nil {
-		firstErr = err
+	if err := service.syncSummaryCarryForward(conversationID, requestID, modelCallID); err != nil {
+		log.Printf(
+			"forwarder summary sync before failed terminal skipped request_id=%s model_call_id=%s err=%v",
+			strings.TrimSpace(requestID),
+			strings.TrimSpace(modelCallID),
+			err,
+		)
 	}
-	if err := service.publishCheckpoint(requestID, conversationID); err != nil && firstErr == nil {
-		firstErr = err
+	terminal := failedCheckpointTerminalAction(terminalCode, terminalMessage)
+	if err := service.publishCheckpointWithTerminalAction(requestID, terminal); err != nil {
+		log.Printf("forwarder checkpoint queue before failed terminal skipped request_id=%s err=%v", strings.TrimSpace(requestID), err)
+		return service.finishFailedTurnAfterCheckpoint(stream, terminalCode, terminalMessage)
 	}
-	if err := service.broker.Fail(requestID, terminalCode, terminalMessage); err != nil && firstErr == nil {
-		firstErr = err
-	}
-	return firstErr
+	return nil
 }
 
 // buildRunEntries 构造一次 run intent 需要写入 history 的首批 entry。

internal/backend/forwarder/token_usage.go

@@ -45,13 +45,25 @@ func (snapshot turnUsageSnapshot) requestTokensTotal() int64 {
 	return snapshot.promptTokensTotal() + nonNegativeInt64(snapshot.OutputTokens)
 }
 
-func (service *Service) importConversationState(item *ConversationFile, state *agentv1.ConversationStateStructure) ([]HistoryEntry, error) {
+func (service *Service) importConversationState(item *ConversationFile, state *agentv1.ConversationStateStructure, prefetchedBlobs []*agentv1.PreFetchedBlob) ([]HistoryEntry, error) {
 	if item == nil || state == nil {
 		return nil, nil
 	}
+	blobs, err := newImportedBlobStore(prefetchedBlobs)
+	if err != nil {
+		return nil, err
+	}
+	importedIDs, err := importedTurnIDs(state.GetTurns(), blobs)
+	if err != nil {
+		return nil, err
+	}
 	item.TokenDetailsUsedTokens = state.GetTokenDetails().GetUsedTokens()
+	item.ImportedTurnIDs = importedIDs
+	if minimumNextTurnSeq := int64(len(item.ImportedTurnIDs)) + 1; item.NextTurnSeq < minimumNextTurnSeq {
+		item.NextTurnSeq = minimumNextTurnSeq
+	}
 	entries := make([]HistoryEntry, 0, 2)
-	if messages, err := importedConversationStateModelMessages(state); err != nil {
+	if messages, err := importedConversationStateModelMessagesWithBlobs(state, blobs); err != nil {
 		return nil, err
 	} else {
 		for _, message := range messages {
@@ -105,6 +117,10 @@ func (service *Service) importConversationState(item *ConversationFile, state *a
 }
 
 func importedConversationStateModelMessages(state *agentv1.ConversationStateStructure) ([]modeladapter.Message, error) {
+	return importedConversationStateModelMessagesWithBlobs(state, nil)
+}
+
+func importedConversationStateModelMessagesWithBlobs(state *agentv1.ConversationStateStructure, blobs importedBlobStore) ([]modeladapter.Message, error) {
 	if state == nil {
 		return nil, nil
 	}
@@ -113,7 +129,7 @@ func importedConversationStateModelMessages(state *agentv1.ConversationStateStru
 		if err != nil {
 			return nil, fmt.Errorf("decode imported replay messages: %w", err)
 		}
-		decoded = restoreImportedReplayUserMessages(decoded, state.GetTurns())
+		decoded = restoreImportedReplayUserMessages(decoded, state.GetTurns(), blobs)
 		decoded = filterLegacyPlainWriteReplay(decoded)
 		decoded = filterInternalPromptContextReplay(decoded)
 		messages := make([]modeladapter.Message, 0, len(decoded))
@@ -133,35 +149,18 @@ func importedConversationStateModelMessages(state *agentv1.ConversationStateStru
 		if len(rawTurn) == 0 {
 			continue
 		}
-		turn := &agentv1.ConversationTurnStructure{}
-		if err := proto.Unmarshal(rawTurn, turn); err != nil {
-			return nil, fmt.Errorf("decode imported turn: %w", err)
+		turn, turnID, err := decodeImportedTurn(rawTurn, blobs)
+		if err != nil {
+			return nil, err
 		}
-		agentTurn := turn.GetAgentConversationTurn()
-		if agentTurn == nil {
-			continue
+		if turn == nil && len(turnID) > 0 {
+			return nil, fmt.Errorf("missing prefetched turn blob %x", turnID)
 		}
-		if rawUser := agentTurn.GetUserMessage(); len(rawUser) > 0 {
-			userMessage := &agentv1.UserMessage{}
-			if err := proto.Unmarshal(rawUser, userMessage); err != nil {
-				return nil, fmt.Errorf("decode imported turn user_message: %w", err)
-			}
-			if replay, ok := promptengine.BuildUserMessageReplayMessage(userMessage); ok {
-				messages = append(messages, toModelMessage(replay))
-			}
-		}
-		for _, rawStep := range agentTurn.GetSteps() {
-			if len(rawStep) == 0 {
-				continue
-			}
-			step := &agentv1.ConversationStep{}
-			if err := proto.Unmarshal(rawStep, step); err != nil {
-				return nil, fmt.Errorf("decode imported turn step: %w", err)
-			}
-			for _, replay := range promptengine.BuildLegacyMessagesFromConversationStep(step) {
-				messages = append(messages, toModelMessage(replay))
-			}
+		turnMessages, err := importedBlobTurnMessages(turn, blobs)
+		if err != nil {
+			return nil, err
 		}
+		messages = append(messages, turnMessages...)
 	}
 	return normalizeReplayMessageSequence(messages), nil
 }

internal/backend/forwarder/types.go

@@ -39,6 +39,7 @@ type ConversationFile struct {
 	CurrentPlanText                 string                                `json:"current_plan_text,omitempty"`
 	CurrentPlans                    map[string]*agentv1.PlanRegistryEntry `json:"current_plans,omitempty"`
 	CurrentTodos                    []*agentv1.TodoItem                   `json:"current_todos,omitempty"`
+	ImportedTurnIDs                 [][]byte                              `json:"imported_turn_ids,omitempty"`
 	LatestRequestPrefix             *ConversationRequestPrefix            `json:"latest_request_prefix,omitempty"`
 	LastProviderCall                *ConversationProviderCall             `json:"last_provider_call,omitempty"`
 	CreatedAt                       time.Time                             `json:"created_at"`
@@ -224,11 +225,25 @@ type pendingTurnCompletion struct {
 	Disposition    pendingCompletionDisposition
 }
 
+type checkpointTerminalActionKind uint8
+
+const (
+	checkpointTerminalActionNone checkpointTerminalActionKind = iota
+	checkpointTerminalActionComplete
+	checkpointTerminalActionFail
+)
+
+type checkpointTerminalAction struct {
+	Kind         checkpointTerminalActionKind
+	Completion   pendingTurnCompletion
+	ErrorCode    string
+	ErrorMessage string
+}
+
 type pendingCheckpointPublish struct {
-	State      *agentv1.ConversationStateStructure
-	Required   map[string]struct{}
-	Completion *pendingTurnCompletion
-	Published  bool
+	State    *agentv1.ConversationStateStructure
+	Required map[string]struct{}
+	Terminal checkpointTerminalAction
 }
 
 type PendingCompaction struct {
@@ -430,6 +445,7 @@ type InboundIntent struct {
 	SubagentTypeName         string
 	SubagentModelOverrides   map[string]runtimecore.SubagentModelOverrideSelection
 	ConversationState        *agentv1.ConversationStateStructure
+	PreFetchedBlobs          []*agentv1.PreFetchedBlob
 	UserMessage              *agentv1.UserMessage
 	RequestContext           *agentv1.RequestContext
 	ClientMessage            *agentv1.AgentClientMessage