diff --git a/pkg/memory/jsonl.go b/pkg/memory/jsonl.go
new file mode 100644
index 000000000..266f453d9
--- /dev/null
+++ b/pkg/memory/jsonl.go
@@ -0,0 +1,386 @@
+package memory
+
+import (
+	"bufio"
+	"context"
+	"encoding/json"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/sipeed/picoclaw/pkg/providers"
+)
+
+// sessionMeta holds per-session metadata stored in a .meta.json file.
+type sessionMeta struct {
+	Key       string    `json:"key"`
+	Summary   string    `json:"summary"`
+	Skip      int       `json:"skip"`
+	Count     int       `json:"count"`
+	CreatedAt time.Time `json:"created_at"`
+	UpdatedAt time.Time `json:"updated_at"`
+}
+
+// JSONLStore implements Store using append-only JSONL files.
+//
+// Each session is stored as two files:
+//
+//	{sanitized_key}.jsonl      — one JSON-encoded message per line, append-only
+//	{sanitized_key}.meta.json  — session metadata (summary, logical truncation offset)
+//
+// Messages are never physically deleted from the JSONL file. Instead,
+// TruncateHistory records a "skip" offset in the metadata file and
+// GetHistory ignores lines before that offset. This keeps all writes
+// append-only, which is both fast and crash-safe.
+type JSONLStore struct {
+	dir string
+
+	mu    sync.Mutex
+	locks map[string]*sync.Mutex
+}
+
+// NewJSONLStore creates a new JSONL-backed store rooted at dir.
+func NewJSONLStore(dir string) (*JSONLStore, error) {
+	err := os.MkdirAll(dir, 0o755)
+	if err != nil {
+		return nil, fmt.Errorf("memory: create directory: %w", err)
+	}
+	return &JSONLStore{
+		dir:   dir,
+		locks: make(map[string]*sync.Mutex),
+	}, nil
+}
+
+// sessionLock returns (or creates) a per-session mutex.
+func (s *JSONLStore) sessionLock(key string) *sync.Mutex {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	l, ok := s.locks[key]
+	if !ok {
+		l = &sync.Mutex{}
+		s.locks[key] = l
+	}
+	return l
+}
+
+func (s *JSONLStore) jsonlPath(key string) string {
+	return filepath.Join(s.dir, sanitizeKey(key)+".jsonl")
+}
+
+func (s *JSONLStore) metaPath(key string) string {
+	return filepath.Join(s.dir, sanitizeKey(key)+".meta.json")
+}
+
+// sanitizeKey converts a session key to a safe filename component.
+// Mirrors pkg/session.sanitizeFilename so that migration paths match.
+func sanitizeKey(key string) string {
+	return strings.ReplaceAll(key, ":", "_")
+}
+
+// readMeta loads the metadata file for a session.
+// Returns a zero-value sessionMeta if the file does not exist.
+func (s *JSONLStore) readMeta(key string) (sessionMeta, error) {
+	data, err := os.ReadFile(s.metaPath(key))
+	if os.IsNotExist(err) {
+		return sessionMeta{Key: key}, nil
+	}
+	if err != nil {
+		return sessionMeta{}, fmt.Errorf("memory: read meta: %w", err)
+	}
+	var meta sessionMeta
+	err = json.Unmarshal(data, &meta)
+	if err != nil {
+		return sessionMeta{}, fmt.Errorf("memory: decode meta: %w", err)
+	}
+	return meta, nil
+}
+
+// writeMeta atomically writes the metadata file (temp + rename).
+func (s *JSONLStore) writeMeta(key string, meta sessionMeta) error {
+	data, err := json.MarshalIndent(meta, "", "  ")
+	if err != nil {
+		return fmt.Errorf("memory: encode meta: %w", err)
+	}
+
+	target := s.metaPath(key)
+	tmp := target + ".tmp"
+
+	err = os.WriteFile(tmp, data, 0o644)
+	if err != nil {
+		return fmt.Errorf("memory: write meta tmp: %w", err)
+	}
+
+	err = os.Rename(tmp, target)
+	if err != nil {
+		_ = os.Remove(tmp)
+		return fmt.Errorf("memory: rename meta: %w", err)
+	}
+	return nil
+}
+
+// readMessages reads all valid JSON lines from a .jsonl file.
+// Malformed trailing lines (e.g. from a crash) are silently skipped.
+func readMessages(path string) ([]providers.Message, error) {
+	f, err := os.Open(path)
+	if os.IsNotExist(err) {
+		return []providers.Message{}, nil
+	}
+	if err != nil {
+		return nil, fmt.Errorf("memory: open jsonl: %w", err)
+	}
+	defer f.Close()
+
+	var msgs []providers.Message
+	scanner := bufio.NewScanner(f)
+	// Allow up to 1 MB per line for messages with large content.
+	scanner.Buffer(make([]byte, 0, 64*1024), 1024*1024)
+
+	for scanner.Scan() {
+		line := scanner.Bytes()
+		if len(line) == 0 {
+			continue
+		}
+		var msg providers.Message
+		if json.Unmarshal(line, &msg) != nil {
+			// Corrupt line — likely a partial write from a crash.
+			// Skip it; this is the standard JSONL recovery pattern.
+			continue
+		}
+		msgs = append(msgs, msg)
+	}
+	if scanner.Err() != nil {
+		return nil, fmt.Errorf("memory: scan jsonl: %w", scanner.Err())
+	}
+
+	if msgs == nil {
+		msgs = []providers.Message{}
+	}
+	return msgs, nil
+}
+
+func (s *JSONLStore) AddMessage(
+	_ context.Context, sessionKey, role, content string,
+) error {
+	return s.addMsg(sessionKey, providers.Message{
+		Role:    role,
+		Content: content,
+	})
+}
+
+func (s *JSONLStore) AddFullMessage(
+	_ context.Context, sessionKey string, msg providers.Message,
+) error {
+	return s.addMsg(sessionKey, msg)
+}
+
+// addMsg is the shared implementation for AddMessage and AddFullMessage.
+func (s *JSONLStore) addMsg(sessionKey string, msg providers.Message) error {
+	l := s.sessionLock(sessionKey)
+	l.Lock()
+	defer l.Unlock()
+
+	// Append the message as a single JSON line.
+	line, err := json.Marshal(msg)
+	if err != nil {
+		return fmt.Errorf("memory: marshal message: %w", err)
+	}
+	line = append(line, '\n')
+
+	f, err := os.OpenFile(
+		s.jsonlPath(sessionKey),
+		os.O_CREATE|os.O_WRONLY|os.O_APPEND,
+		0o644,
+	)
+	if err != nil {
+		return fmt.Errorf("memory: open jsonl for append: %w", err)
+	}
+	_, writeErr := f.Write(line)
+	closeErr := f.Close()
+	if writeErr != nil {
+		return fmt.Errorf("memory: append message: %w", writeErr)
+	}
+	if closeErr != nil {
+		return fmt.Errorf("memory: close jsonl: %w", closeErr)
+	}
+
+	// Update metadata.
+	meta, err := s.readMeta(sessionKey)
+	if err != nil {
+		return err
+	}
+	now := time.Now()
+	if meta.Count == 0 && meta.CreatedAt.IsZero() {
+		meta.CreatedAt = now
+	}
+	meta.Count++
+	meta.UpdatedAt = now
+
+	return s.writeMeta(sessionKey, meta)
+}
+
+func (s *JSONLStore) GetHistory(
+	_ context.Context, sessionKey string,
+) ([]providers.Message, error) {
+	l := s.sessionLock(sessionKey)
+	l.Lock()
+	defer l.Unlock()
+
+	meta, err := s.readMeta(sessionKey)
+	if err != nil {
+		return nil, err
+	}
+
+	msgs, err := readMessages(s.jsonlPath(sessionKey))
+	if err != nil {
+		return nil, err
+	}
+
+	// Apply logical truncation: skip the first meta.Skip messages.
+	if meta.Skip > 0 && meta.Skip < len(msgs) {
+		msgs = msgs[meta.Skip:]
+	} else if meta.Skip >= len(msgs) {
+		msgs = []providers.Message{}
+	}
+
+	return msgs, nil
+}
+
+func (s *JSONLStore) GetSummary(
+	_ context.Context, sessionKey string,
+) (string, error) {
+	l := s.sessionLock(sessionKey)
+	l.Lock()
+	defer l.Unlock()
+
+	meta, err := s.readMeta(sessionKey)
+	if err != nil {
+		return "", err
+	}
+	return meta.Summary, nil
+}
+
+func (s *JSONLStore) SetSummary(
+	_ context.Context, sessionKey, summary string,
+) error {
+	l := s.sessionLock(sessionKey)
+	l.Lock()
+	defer l.Unlock()
+
+	meta, err := s.readMeta(sessionKey)
+	if err != nil {
+		return err
+	}
+	now := time.Now()
+	if meta.CreatedAt.IsZero() {
+		meta.CreatedAt = now
+	}
+	meta.Summary = summary
+	meta.UpdatedAt = now
+
+	return s.writeMeta(sessionKey, meta)
+}
+
+func (s *JSONLStore) TruncateHistory(
+	_ context.Context, sessionKey string, keepLast int,
+) error {
+	l := s.sessionLock(sessionKey)
+	l.Lock()
+	defer l.Unlock()
+
+	meta, err := s.readMeta(sessionKey)
+	if err != nil {
+		return err
+	}
+
+	// If the meta count might be stale (e.g. after a crash during
+	// addMsg), reconcile with the actual line count on disk.
+	if meta.Count == 0 {
+		msgs, readErr := readMessages(s.jsonlPath(sessionKey))
+		if readErr != nil {
+			return readErr
+		}
+		meta.Count = len(msgs)
+	}
+
+	if keepLast <= 0 {
+		meta.Skip = meta.Count
+	} else {
+		effective := meta.Count - meta.Skip
+		if keepLast < effective {
+			meta.Skip = meta.Count - keepLast
+		}
+	}
+	meta.UpdatedAt = time.Now()
+
+	return s.writeMeta(sessionKey, meta)
+}
+
+func (s *JSONLStore) SetHistory(
+	_ context.Context,
+	sessionKey string,
+	history []providers.Message,
+) error {
+	l := s.sessionLock(sessionKey)
+	l.Lock()
+	defer l.Unlock()
+
+	// Rewrite the JSONL file atomically (temp + rename).
+	target := s.jsonlPath(sessionKey)
+	tmp := target + ".tmp"
+
+	f, err := os.Create(tmp)
+	if err != nil {
+		return fmt.Errorf("memory: create jsonl tmp: %w", err)
+	}
+
+	for i, msg := range history {
+		line, marshalErr := json.Marshal(msg)
+		if marshalErr != nil {
+			f.Close()
+			_ = os.Remove(tmp)
+			return fmt.Errorf("memory: marshal message %d: %w", i, marshalErr)
+		}
+		line = append(line, '\n')
+		_, writeErr := f.Write(line)
+		if writeErr != nil {
+			f.Close()
+			_ = os.Remove(tmp)
+			return fmt.Errorf("memory: write message %d: %w", i, writeErr)
+		}
+	}
+
+	err = f.Close()
+	if err != nil {
+		_ = os.Remove(tmp)
+		return fmt.Errorf("memory: close jsonl tmp: %w", err)
+	}
+
+	err = os.Rename(tmp, target)
+	if err != nil {
+		_ = os.Remove(tmp)
+		return fmt.Errorf("memory: rename jsonl: %w", err)
+	}
+
+	// Reset metadata: skip=0, count=len(history).
+	meta, err := s.readMeta(sessionKey)
+	if err != nil {
+		return err
+	}
+	now := time.Now()
+	if meta.CreatedAt.IsZero() {
+		meta.CreatedAt = now
+	}
+	meta.Skip = 0
+	meta.Count = len(history)
+	meta.UpdatedAt = now
+
+	return s.writeMeta(sessionKey, meta)
+}
+
+func (s *JSONLStore) Close() error {
+	return nil
+}