diff --git a/internal/client/spool/events.go b/internal/client/spool/events.go
index 3b341ea..e09b038 100644
--- a/internal/client/spool/events.go
+++ b/internal/client/spool/events.go
@@ -33,6 +33,13 @@ type EventInput struct {
 	CreatedAt   time.Time
 }
 
+const (
+	// These match the CommandEvent oneof field numbers, allowing the runtime to
+	// reconstruct the envelope without a second event-kind translation table.
+	EventKindOutput           uint32 = 5
+	EventKindOutputTruncation uint32 = 10
+)
+
 type Event struct {
 	IssueUUID    domain.UUID
 	LocalOrdinal uint64
diff --git a/internal/client/spool/output.go b/internal/client/spool/output.go
new file mode 100644
index 0000000..a68d5d3
--- /dev/null
+++ b/internal/client/spool/output.go
@@ -0,0 +1,203 @@
+package spool
+
+import (
+	"bytes"
+	"context"
+	"database/sql"
+	"errors"
+	"fmt"
+	"time"
+
+	"github.com/klauspost/compress/zstd"
+	rvboxv1 "github.com/rvbox/rvbox/gen/go/rvbox/v1"
+	"github.com/rvbox/rvbox/internal/domain"
+	"google.golang.org/protobuf/proto"
+)
+
+const MaxOutputChunkBytes = 64 << 10
+
+var ErrPinnedOutput = errors.New("client output is pinned awaiting server acknowledgement")
+
+type OutputInput struct {
+	Stream     rvboxv1.StreamKind
+	Raw        []byte
+	ObservedAt time.Time
+}
+
+// AppendOutput stores one raw pipe chunk as a Zstandard OutputChunk. Under
+// offline pressure it replaces only the oldest unsequenced output with an
+// ordered loss marker; assigned wire events are immutable and never evicted.
+func (store *Store) AppendOutput(ctx context.Context, issueUUID domain.UUID, input OutputInput) (Event, error) {
+	if (input.Stream != rvboxv1.StreamKind_STREAM_STDOUT && input.Stream != rvboxv1.StreamKind_STREAM_STDERR) || uint64(len(input.Raw)) > MaxOutputChunkBytes || input.ObservedAt.IsZero() {
+		return Event{}, errors.New("invalid raw output chunk")
+	}
+	payload, err := encodeOutputChunk(input.Stream, input.Raw)
+	if err != nil {
+		return Event{}, err
+	}
+	eventInput := EventInput{Kind: EventKindOutput, Compression: 2, RawBytes: uint64(len(input.Raw)), Payload: payload, Output: true, CreatedAt: input.ObservedAt}
+	for {
+		event, err := store.AppendEvent(ctx, issueUUID, eventInput)
+		if !errors.Is(err, ErrCapacityExhausted) {
+			return event, err
+		}
+		rotated, rotateErr := store.RotateOldestUnassignedOutput(ctx, issueUUID, input.ObservedAt)
+		if rotateErr != nil {
+			return Event{}, rotateErr
+		}
+		if !rotated {
+			return Event{}, err
+		}
+	}
+}
+
+// RotateOldestUnassignedOutput replaces exactly one earliest contiguous run.
+// Retaining the first removed local ordinal for the marker preserves durable
+// command-local order while leaving every assigned event pinned.
+func (store *Store) RotateOldestUnassignedOutput(ctx context.Context, issueUUID domain.UUID, observedAt time.Time) (bool, error) {
+	if !validUUID(issueUUID) || observedAt.IsZero() {
+		return false, errors.New("invalid output rotation request")
+	}
+	tx, err := store.db.BeginTx(ctx, nil)
+	if err != nil {
+		return false, err
+	}
+	defer tx.Rollback()
+	var nextOrdinal, outputCharged, totalCharged, closeout uint64
+	err = tx.QueryRowContext(ctx, `SELECT next_local_ordinal, output_charged_bytes, total_charged_bytes, closeout_remaining_bytes FROM commands WHERE issue_uuid = ?`, issueUUID[:]).Scan(&nextOrdinal, &outputCharged, &totalCharged, &closeout)
+	if err == sql.ErrNoRows {
+		return false, ErrUnknownCommand
+	}
+	if err != nil {
+		return false, err
+	}
+	rows, err := tx.QueryContext(ctx, `SELECT local_ordinal, raw_bytes, charged_bytes, payload FROM events WHERE issue_uuid = ? AND event_seq IS NULL AND output = 1 ORDER BY local_ordinal`, issueUUID[:])
+	if err != nil {
+		return false, err
+	}
+	var run []outputRow
+	for rows.Next() {
+		var current outputRow
+		if err := rows.Scan(&current.ordinal, &current.rawBytes, &current.charge, &current.payload); err != nil {
+			_ = rows.Close()
+			return false, err
+		}
+		if len(run) > 0 && current.ordinal != run[len(run)-1].ordinal+1 {
+			break
+		}
+		run = append(run, current)
+	}
+	if err := rows.Close(); err != nil {
+		return false, err
+	}
+	if len(run) == 0 {
+		return false, ErrPinnedOutput
+	}
+	markerPayload, removedRaw, removedCompressed, removedCharge, err := outputLossMarker(run)
+	if err != nil {
+		return false, err
+	}
+	markerCharge, err := EstimateCharge(ChargeInput{EncodedBytes: uint64(len(markerPayload)), SQLiteRows: 1, IndexEntries: 2})
+	if err != nil {
+		return false, err
+	}
+	if removedCharge > totalCharged || removedCharge > outputCharged {
+		return false, fmt.Errorf("client spool output charge counter mismatch")
+	}
+	clientTotal, err := clientTotalCharge(ctx, tx)
+	if err != nil {
+		return false, err
+	}
+	if removedCharge > clientTotal {
+		return false, fmt.Errorf("client spool aggregate charge counter mismatch")
+	}
+	remainingTotal := totalCharged - removedCharge
+	remainingOutput := outputCharged - removedCharge
+	remainingClient := clientTotal - removedCharge
+	decision, err := CheckReservation(store.quotaLimits, ReservationState{CommandOutputCharged: remainingOutput, CommandTotalCharged: remainingTotal, ClientTotalCharged: remainingClient, CloseoutRemaining: closeout}, ReservationRequest{ChargedBytes: markerCharge})
+	if err != nil {
+		return false, err
+	}
+	for _, current := range run {
+		if _, err := tx.ExecContext(ctx, `DELETE FROM events WHERE issue_uuid = ? AND local_ordinal = ? AND event_seq IS NULL`, issueUUID[:], current.ordinal); err != nil {
+			return false, err
+		}
+	}
+	digest := immutableDigest(markerPayload)
+	if _, err := tx.ExecContext(ctx, `INSERT INTO events(issue_uuid, local_ordinal, event_kind, compression, raw_bytes, charged_bytes, output, payload, payload_sha256, created_at) VALUES (?, ?, ?, 2, ?, ?, 0, ?, ?, ?)`, issueUUID[:], run[0].ordinal, EventKindOutputTruncation, removedRaw, markerCharge, markerPayload, digest[:], observedAt.UnixNano()); err != nil {
+		return false, err
+	}
+	if _, err := tx.ExecContext(ctx, `UPDATE commands SET output_charged_bytes = ?, total_charged_bytes = ?, closeout_remaining_bytes = ?, next_local_ordinal = ? WHERE issue_uuid = ?`, decision.CommandOutputCharged, decision.CommandTotalCharged, decision.CloseoutRemaining, nextOrdinal, issueUUID[:]); err != nil {
+		return false, err
+	}
+	if err := updateClientTotalCharge(ctx, tx, decision.ClientTotalCharged); err != nil {
+		return false, err
+	}
+	if err := tx.Commit(); err != nil {
+		return false, err
+	}
+	_ = removedCompressed // retained in the durable marker payload.
+	return true, nil
+}
+
+type outputRow struct {
+	ordinal  uint64
+	rawBytes uint64
+	charge   uint64
+	payload  []byte
+}
+
+func encodeOutputChunk(stream rvboxv1.StreamKind, raw []byte) ([]byte, error) {
+	encoder, err := zstd.NewWriter(nil, zstd.WithEncoderConcurrency(1))
+	if err != nil {
+		return nil, err
+	}
+	compressed := encoder.EncodeAll(raw, nil)
+	encoder.Close()
+	chunk := &rvboxv1.OutputChunk{Stream: stream, Compression: rvboxv1.Compression_COMPRESSION_ZSTD, Data: compressed, UncompressedSize: uint64(len(raw)), CompressedSize: uint64(len(compressed))}
+	return proto.Marshal(chunk)
+}
+
+func outputLossMarker(rows []outputRow) ([]byte, uint64, uint64, uint64, error) {
+	var raw, compressed, charged uint64
+	for _, row := range rows {
+		var chunk rvboxv1.OutputChunk
+		if err := proto.Unmarshal(row.payload, &chunk); err != nil || chunk.Compression != rvboxv1.Compression_COMPRESSION_ZSTD || chunk.UncompressedSize != row.rawBytes || chunk.CompressedSize != uint64(len(chunk.Data)) {
+			return nil, 0, 0, 0, ErrStoredPayloadChecksum
+		}
+		if raw > ^uint64(0)-row.rawBytes || compressed > ^uint64(0)-chunk.CompressedSize || charged > ^uint64(0)-row.charge {
+			return nil, 0, 0, 0, ErrCapacityExhausted
+		}
+		raw += row.rawBytes
+		compressed += chunk.CompressedSize
+		charged += row.charge
+	}
+	marker := &rvboxv1.OutputTruncation{RemovedCompressedBytes: &compressed, RemovedUncompressedBytes: raw, Reason: "CLIENT_SPOOL", Source: rvboxv1.OutputTruncationSource_OUTPUT_TRUNCATION_SOURCE_CLIENT_SPOOL}
+	payload, err := proto.Marshal(marker)
+	return payload, raw, compressed, charged, err
+}
+
+func decodeOutputLossMarker(payload []byte) (*rvboxv1.OutputTruncation, error) {
+	var marker rvboxv1.OutputTruncation
+	if err := proto.Unmarshal(payload, &marker); err != nil || marker.Source != rvboxv1.OutputTruncationSource_OUTPUT_TRUNCATION_SOURCE_CLIENT_SPOOL || marker.FirstRemovedEventSeq != nil || marker.LastRemovedEventSeq != nil || marker.RemovedCompressedBytes == nil {
+		return nil, ErrStoredPayloadChecksum
+	}
+	return &marker, nil
+}
+
+func outputChunkRaw(payload []byte) ([]byte, error) {
+	var chunk rvboxv1.OutputChunk
+	if err := proto.Unmarshal(payload, &chunk); err != nil || (chunk.Stream != rvboxv1.StreamKind_STREAM_STDOUT && chunk.Stream != rvboxv1.StreamKind_STREAM_STDERR) || chunk.Compression != rvboxv1.Compression_COMPRESSION_ZSTD || chunk.CompressedSize != uint64(len(chunk.Data)) {
+		return nil, ErrStoredPayloadChecksum
+	}
+	decoder, err := zstd.NewReader(bytes.NewReader(chunk.Data), zstd.WithDecoderConcurrency(1), zstd.WithDecoderMaxMemory(MaxOutputChunkBytes+1))
+	if err != nil {
+		return nil, ErrStoredPayloadChecksum
+	}
+	defer decoder.Close()
+	raw, err := decoder.DecodeAll(chunk.Data, nil)
+	if err != nil || uint64(len(raw)) != chunk.UncompressedSize || uint64(len(raw)) > MaxOutputChunkBytes {
+		return nil, ErrStoredPayloadChecksum
+	}
+	return raw, nil
+}
diff --git a/internal/client/spool/output_test.go b/internal/client/spool/output_test.go
new file mode 100644
index 0000000..7a8969f
--- /dev/null
+++ b/internal/client/spool/output_test.go
@@ -0,0 +1,86 @@
+package spool
+
+import (
+	"bytes"
+	"context"
+	"errors"
+	"path/filepath"
+	"testing"
+	"time"
+
+	rvboxv1 "github.com/rvbox/rvbox/gen/go/rvbox/v1"
+)
+
+func TestAppendOutputRotatesOnlyUnsequencedRun_HP_OUT_01(t *testing.T) {
+	t.Parallel()
+	ctx := context.Background()
+	limits := QuotaLimits{HardAllocationBytes: 1_000, CommandOutputBytes: 900, CommandTotalBytes: 3_000, ClientTotalBytes: 4_000, CloseoutReserveBytes: 400}
+	store, err := Open(ctx, Options{DataDir: filepath.Join(t.TempDir(), "spool"), BusyTimeout: time.Second, QuotaLimits: limits})
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() { _ = store.Close() })
+	issue := testUUID(t, "019c46f1-1d02-7000-8000-000000000051")
+	if _, err := store.AcceptCommand(ctx, testCommand(issue, []byte("output")), time.Now().UTC()); err != nil {
+		t.Fatal(err)
+	}
+	first := bytes.Repeat([]byte("a"), 200)
+	second := bytes.Repeat([]byte("b"), 200)
+	third := bytes.Repeat([]byte("c"), 200)
+	for _, raw := range [][]byte{first, second, third} {
+		if _, err := store.AppendOutput(ctx, issue, OutputInput{Stream: rvboxv1.StreamKind_STREAM_STDOUT, Raw: raw, ObservedAt: time.Now().UTC()}); err != nil {
+			t.Fatalf("AppendOutput(%q): %v", raw[:1], err)
+		}
+	}
+	assigned, err := store.AssignSendWindow(ctx, issue, 8, 1<<20)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(assigned) != 2 || assigned[0].Kind != EventKindOutputTruncation || assigned[0].LocalOrdinal != 1 || assigned[0].EventSeq != 1 || assigned[1].Kind != EventKindOutput || assigned[1].LocalOrdinal != 3 || assigned[1].EventSeq != 2 {
+		t.Fatalf("assigned output/loss events = %#v", assigned)
+	}
+	marker, err := decodeOutputLossMarker(assigned[0].Payload)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if marker.RemovedUncompressedBytes != uint64(len(first)+len(second)) || marker.GetRemovedCompressedBytes() == 0 {
+		t.Fatalf("loss marker = %#v", marker)
+	}
+	raw, err := outputChunkRaw(assigned[1].Payload)
+	if err != nil || !bytes.Equal(raw, third) {
+		t.Fatalf("stored output = %q, %v", raw, err)
+	}
+	report, err := store.Check(ctx)
+	if err != nil || report.EventsChecked != 2 {
+		t.Fatalf("output spool Check = %#v, %v", report, err)
+	}
+}
+
+func TestAppendOutputNeverEvictsAssignedEvent_BH_OUTFLOW_02(t *testing.T) {
+	t.Parallel()
+	ctx := context.Background()
+	limits := QuotaLimits{HardAllocationBytes: 1_000, CommandOutputBytes: 600, CommandTotalBytes: 3_000, ClientTotalBytes: 4_000, CloseoutReserveBytes: 400}
+	store, err := Open(ctx, Options{DataDir: filepath.Join(t.TempDir(), "spool"), BusyTimeout: time.Second, QuotaLimits: limits})
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() { _ = store.Close() })
+	issue := testUUID(t, "019c46f1-1d02-7000-8000-000000000052")
+	if _, err := store.AcceptCommand(ctx, testCommand(issue, []byte("output")), time.Now().UTC()); err != nil {
+		t.Fatal(err)
+	}
+	raw := bytes.Repeat([]byte("x"), 200)
+	if _, err := store.AppendOutput(ctx, issue, OutputInput{Stream: rvboxv1.StreamKind_STREAM_STDERR, Raw: raw, ObservedAt: time.Now().UTC()}); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := store.AssignSendWindow(ctx, issue, 1, 1<<20); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := store.AppendOutput(ctx, issue, OutputInput{Stream: rvboxv1.StreamKind_STREAM_STDERR, Raw: raw, ObservedAt: time.Now().UTC()}); !errors.Is(err, ErrPinnedOutput) {
+		t.Fatalf("output behind assigned event error = %v, want ErrPinnedOutput", err)
+	}
+	pending, err := store.PendingEvents(ctx, issue)
+	if err != nil || len(pending) != 1 || pending[0].EventSeq != 1 || pending[0].Kind != EventKindOutput {
+		t.Fatalf("assigned event was changed: %#v, %v", pending, err)
+	}
+}
diff --git a/internal/client/spool/recovery.go b/internal/client/spool/recovery.go
index 6671867..22970a4 100644
--- a/internal/client/spool/recovery.go
+++ b/internal/client/spool/recovery.go
@@ -83,13 +83,15 @@ OR c.output_charged_bytes !=
 
 func checkPayloads(ctx context.Context, database *sql.DB, maxScriptBytes uint64) (RecoveryReport, error) {
 	var report RecoveryReport
-	rows, err := database.QueryContext(ctx, `SELECT issue_uuid, payload, payload_sha256 FROM events ORDER BY issue_uuid, local_ordinal`)
+	rows, err := database.QueryContext(ctx, `SELECT issue_uuid, event_kind, raw_bytes, payload, payload_sha256 FROM events ORDER BY issue_uuid, local_ordinal`)
 	if err != nil {
 		return report, err
 	}
 	for rows.Next() {
 		var owner, payload, digest []byte
-		if err := rows.Scan(&owner, &payload, &digest); err != nil {
+		var kind uint32
+		var rawBytes uint64
+		if err := rows.Scan(&owner, &kind, &rawBytes, &payload, &digest); err != nil {
 			_ = rows.Close()
 			return report, err
 		}
@@ -98,6 +100,20 @@ func checkPayloads(ctx context.Context, database *sql.DB, maxScriptBytes uint64)
 			_ = rows.Close()
 			return report, ErrStoredPayloadChecksum
 		}
+		switch kind {
+		case EventKindOutput:
+			raw, err := outputChunkRaw(payload)
+			if err != nil || uint64(len(raw)) != rawBytes {
+				_ = rows.Close()
+				return report, ErrStoredPayloadChecksum
+			}
+		case EventKindOutputTruncation:
+			marker, err := decodeOutputLossMarker(payload)
+			if err != nil || marker.RemovedUncompressedBytes != rawBytes {
+				_ = rows.Close()
+				return report, ErrStoredPayloadChecksum
+			}
+		}
 		report.EventsChecked++
 	}
 	if err := rows.Close(); err != nil {
diff --git a/test/coverage.toml b/test/coverage.toml
index b901c10..8ad2f89 100644
--- a/test/coverage.toml
+++ b/test/coverage.toml
@@ -215,6 +215,18 @@ tests = [
   "internal/client/spool/quota_test.go:TestSpoolAcknowledgementReleasesQuota_HP_CLIENT_08",
 ]
 
+[[requirements]]
+id = "HP-OUT-01"
+layer = "unit"
+status = "implemented"
+tests = ["internal/client/spool/output_test.go:TestAppendOutputRotatesOnlyUnsequencedRun_HP_OUT_01"]
+
+[[requirements]]
+id = "BH-OUTFLOW-02"
+layer = "unit"
+status = "implemented"
+tests = ["internal/client/spool/output_test.go:TestAppendOutputNeverEvictsAssignedEvent_BH_OUTFLOW_02"]
+
 [[requirements]]
 id = "BH-RET-01"
 layer = "unit"