diff --git a/internal/runtime/compact_generator.go b/internal/runtime/compact_generator.go
index 6ef580ed..321cc7b0 100644
--- a/internal/runtime/compact_generator.go
+++ b/internal/runtime/compact_generator.go
@@ -149,13 +149,33 @@ func cloneStringSlice(items []string) []string {
 	return append([]string(nil), items...)
 }
 
-// extractJSONObject 从模型响应中提取最外层 JSON 对象，容忍前后噪音。
+// extractJSONObject 从模型响应中提取首个满足 compact 协议的 JSON 对象，容忍前后噪音。
 func extractJSONObject(text string) (string, error) {
-	start := strings.Index(text, "{")
+	start := strings.IndexByte(text, '{')
 	if start < 0 {
 		return "", errors.New("runtime: compact summary response does not contain a JSON object")
 	}
 
+	for {
+		candidate, err := extractJSONObjectCandidate(text, start)
+		if err == nil {
+			if _, decodeErr := decodeCompactSummaryResponse(candidate); decodeErr == nil {
+				return candidate, nil
+			}
+		}
+
+		next := strings.IndexByte(text[start+1:], '{')
+		if next < 0 {
+			break
+		}
+		start += next + 1
+	}
+
+	return "", errors.New("runtime: compact summary response does not contain a valid compact JSON object")
+}
+
+// extractJSONObjectCandidate 从给定起点抽取平衡的 JSON 对象片段。
+func extractJSONObjectCandidate(text string, start int) (string, error) {
 	depth := 0
 	inString := false
 	escaped := false
diff --git a/internal/runtime/compact_generator_test.go b/internal/runtime/compact_generator_test.go
index ac2c908a..6c389467 100644
--- a/internal/runtime/compact_generator_test.go
+++ b/internal/runtime/compact_generator_test.go
@@ -258,3 +258,20 @@ func TestParseCompactSummaryOutputRejectsUnknownTaskStateField(t *testing.T) {
 		t.Fatal("expected unknown task_state field to be rejected")
 	}
 }
+
+func TestParseCompactSummaryOutputSkipsNonCompactJSONPreface(t *testing.T) {
+	t.Parallel()
+
+	content := strings.Join([]string{
+		`preface with braces {"hint":"not compact"}`,
+		`{"task_state":{"goal":"g","progress":[],"open_items":[],"next_step":"","blockers":[],"key_artifacts":[],"decisions":[],"user_constraints":[]},"display_summary":"[compact_summary]\nok"}`,
+	}, "\n")
+
+	output, err := parseCompactSummaryOutput(content)
+	if err != nil {
+		t.Fatalf("expected parser to recover valid compact payload, got %v", err)
+	}
+	if output.TaskState.Goal != "g" {
+		t.Fatalf("expected parsed goal, got %+v", output.TaskState)
+	}
+}
diff --git a/internal/session/store.go b/internal/session/store.go
index 2ea97169..a5018040 100644
--- a/internal/session/store.go
+++ b/internal/session/store.go
@@ -81,7 +81,7 @@ func (s *JSONStore) Save(ctx context.Context, session *Session) error {
 		return err
 	}
 
-	session.TaskState = NormalizeTaskState(session.TaskState)
+	session.TaskState = normalizeAndClampTaskState(session.TaskState)
 
 	s.mu.Lock()
 	defer s.mu.Unlock()
@@ -236,29 +236,59 @@ func validateSessionSchema(session Session) error {
 
 // decodeStoredSession 严格校验持久化会话所需字段，并拒绝缺少 schema_version 或 task_state 的旧数据。
 func decodeStoredSession(data []byte) (Session, error) {
-	var envelope map[string]json.RawMessage
-	if err := json.Unmarshal(data, &envelope); err != nil {
+	type storedSession struct {
+		SchemaVersion *int                    `json:"schema_version"`
+		ID            string                  `json:"id"`
+		Title         string                  `json:"title"`
+		Provider      string                  `json:"provider,omitempty"`
+		Model         string                  `json:"model,omitempty"`
+		CreatedAt     time.Time               `json:"created_at"`
+		UpdatedAt     time.Time               `json:"updated_at"`
+		Workdir       string                  `json:"workdir,omitempty"`
+		TaskState     *TaskState              `json:"task_state"`
+		Messages      []providertypes.Message `json:"messages"`
+		TokenInput    int                     `json:"token_input_total,omitempty"`
+		TokenOutput   int                     `json:"token_output_total,omitempty"`
+	}
+
+	var stored storedSession
+	if err := json.Unmarshal(data, &stored); err != nil {
 		return Session{}, err
 	}
 
-	if _, ok := envelope["schema_version"]; !ok {
+	if stored.SchemaVersion == nil {
 		return Session{}, errors.New("missing required field schema_version")
 	}
-	if _, ok := envelope["task_state"]; !ok {
+	if stored.TaskState == nil {
 		return Session{}, errors.New("missing required field task_state")
 	}
 
-	var session Session
-	if err := json.Unmarshal(data, &session); err != nil {
-		return Session{}, err
+	session := Session{
+		SchemaVersion:    *stored.SchemaVersion,
+		ID:               stored.ID,
+		Title:            stored.Title,
+		Provider:         stored.Provider,
+		Model:            stored.Model,
+		CreatedAt:        stored.CreatedAt,
+		UpdatedAt:        stored.UpdatedAt,
+		Workdir:          stored.Workdir,
+		TaskState:        *stored.TaskState,
+		Messages:         stored.Messages,
+		TokenInputTotal:  stored.TokenInput,
+		TokenOutputTotal: stored.TokenOutput,
 	}
 	if err := validateSessionSchema(session); err != nil {
 		return Session{}, err
 	}
-	session.TaskState = NormalizeTaskState(session.TaskState)
+	session.TaskState = normalizeAndClampTaskState(session.TaskState)
 	return session, nil
 }
 
+// normalizeAndClampTaskState 先规范化再限幅，保证持久化前后的 task_state 行为一致。
+func normalizeAndClampTaskState(state TaskState) TaskState {
+	return ClampTaskStateBoundaries(NormalizeTaskState(state))
+}
+
 // decodeStoredSummary 只解析会话列表所需的摘要元数据，避免为列表视图反序列化完整消息历史。
 func decodeStoredSummary(data []byte) (Summary, error) {
 	var stored struct {
diff --git a/internal/session/store_test.go b/internal/session/store_test.go
index dccb6571..5a0dc1e6 100644
--- a/internal/session/store_test.go
+++ b/internal/session/store_test.go
@@ -679,6 +679,111 @@ func TestDecodeStoredSummaryUsesLightweightMetadataPath(t *testing.T) {
 	}
 }
 
+func TestJSONStoreSaveClampsOversizedTaskState(t *testing.T) {
+	t.Parallel()
+
+	baseDir := t.TempDir()
+	workspaceRoot := t.TempDir()
+	store := NewJSONStore(baseDir, workspaceRoot)
+
+	progress := make([]string, 0, taskStateMaxListItems+8)
+	for i := 0; i < taskStateMaxListItems+8; i++ {
+		progress = append(progress, strings.Repeat("p", taskStateMaxListItemChars-4)+buildIndexedSuffix(i))
+	}
+	session := &Session{
+		SchemaVersion: CurrentSchemaVersion,
+		ID:            "task-state-clamp-save",
+		Title:         "Clamp Save",
+		CreatedAt:     time.Now().Add(-time.Minute),
+		UpdatedAt:     time.Now(),
+		TaskState: TaskState{
+			Goal:      strings.Repeat("g", taskStateMaxFieldChars+50),
+			NextStep:  strings.Repeat("n", taskStateMaxFieldChars+50),
+			Progress:  progress,
+			OpenItems: progress,
+		},
+	}
+
+	if err := store.Save(context.Background(), session); err != nil {
+		t.Fatalf("save session: %v", err)
+	}
+
+	if len([]rune(session.TaskState.Goal)) != taskStateMaxFieldChars {
+		t.Fatalf("expected goal to be clamped to %d runes, got %d", taskStateMaxFieldChars, len([]rune(session.TaskState.Goal)))
+	}
+	if len(session.TaskState.Progress) != taskStateMaxListItems {
+		t.Fatalf("expected progress list clamped to %d, got %d", taskStateMaxListItems, len(session.TaskState.Progress))
+	}
+	if len([]rune(session.TaskState.Progress[0])) != taskStateMaxListItemChars {
+		t.Fatalf(
+			"expected progress item clamped to %d runes, got %d",
+			taskStateMaxListItemChars,
+			len([]rune(session.TaskState.Progress[0])),
+		)
+	}
+}
+
+func TestJSONStoreLoadClampsOversizedTaskState(t *testing.T) {
+	t.Parallel()
+
+	baseDir := t.TempDir()
+	workspaceRoot := t.TempDir()
+	store := NewJSONStore(baseDir, workspaceRoot)
+
+	payload := strings.Join([]string{
+		`{`,
+		`  "schema_version": 1,`,
+		`  "id": "task-state-clamp-load",`,
+		`  "title": "Clamp Load",`,
+		`  "created_at": "2026-04-13T08:00:00Z",`,
+		`  "updated_at": "2026-04-13T09:00:00Z",`,
+		`  "task_state": {`,
+		`    "goal": "` + strings.Repeat("g", taskStateMaxFieldChars+30) + `",`,
+		`    "progress": [` + buildQuotedRepeatedWithIndex("p", taskStateMaxListItemChars+30, taskStateMaxListItems+3) + `],`,
+		`    "open_items": [],`,
+		`    "next_step": "",`,
+		`    "blockers": [],`,
+		`    "key_artifacts": [],`,
+		`    "decisions": [],`,
+		`    "user_constraints": [],`,
+		`    "last_updated_at": "2026-04-13T09:00:00Z"`,
+		`  },`,
+		`  "messages": []`,
+		`}`,
+	}, "\n")
+	mustWriteSessionFile(
+		t,
+		filepath.Join(sessionDirectory(baseDir, workspaceRoot), "task-state-clamp-load.json"),
+		payload,
+	)
+
+	loaded, err := store.Load(context.Background(), "task-state-clamp-load")
+	if err != nil {
+		t.Fatalf("load session: %v", err)
+	}
+	if len([]rune(loaded.TaskState.Goal)) != taskStateMaxFieldChars {
+		t.Fatalf("expected loaded goal to be clamped to %d runes, got %d", taskStateMaxFieldChars, len([]rune(loaded.TaskState.Goal)))
+	}
+	if len(loaded.TaskState.Progress) != taskStateMaxListItems {
+		t.Fatalf("expected loaded progress list clamped to %d, got %d", taskStateMaxListItems, len(loaded.TaskState.Progress))
+	}
+}
+
+func buildQuotedRepeatedWithIndex(ch string, itemLen int, count int) string {
+	items := make([]string, 0, count)
+	for i := 0; i < count; i++ {
+		items = append(items, `"`+strings.Repeat(ch, itemLen-4)+buildIndexedSuffix(i)+`"`)
+	}
+	return strings.Join(items, ",")
+}
+
+func buildIndexedSuffix(index int) string {
+	chars := []rune("abcdefghijklmnopqrstuvwxyz0123456789")
+	hi := chars[(index/len(chars))%len(chars)]
+	lo := chars[index%len(chars)]
+	return string([]rune{hi, lo, 'x', 'x'})
+}
+
 func mustWriteSessionFile(t *testing.T, path string, content string) {
 	t.Helper()
 	if err := os.MkdirAll(filepath.Dir(path), 0o755); err != nil {
diff --git a/internal/session/task_state.go b/internal/session/task_state.go
index de96b8a7..76c2f2fd 100644
--- a/internal/session/task_state.go
+++ b/internal/session/task_state.go
@@ -8,6 +8,13 @@ import (
 const (
 	// CurrentSchemaVersion 表示当前会话持久化结构的唯一合法版本。
 	CurrentSchemaVersion = 1
+
+	// taskStateMaxFieldChars 限制 TaskState 单值字段的最大字符数，避免异常大文本污染持久化与后续 prompt。
+	taskStateMaxFieldChars = 2000
+	// taskStateMaxListItems 限制 TaskState 列表字段的最大条目数，避免模型输出超大数组导致上下文膨胀。
+	taskStateMaxListItems = 32
+	// taskStateMaxListItemChars 限制 TaskState 列表单条目的最大字符数，避免单项异常放大。
+	taskStateMaxListItemChars = 400
 )
 
 // TaskState 表示会话级、可持久化的任务续航状态。
@@ -59,6 +66,19 @@ func NormalizeTaskState(state TaskState) TaskState {
 	return state
 }
 
+// ClampTaskStateBoundaries 对 TaskState 做尺寸与数量限幅，避免持久化状态无限增长。
+func ClampTaskStateBoundaries(state TaskState) TaskState {
+	state.Goal = truncateRunes(state.Goal, taskStateMaxFieldChars)
+	state.NextStep = truncateRunes(state.NextStep, taskStateMaxFieldChars)
+	state.Progress = truncateTaskStateList(state.Progress)
+	state.OpenItems = truncateTaskStateList(state.OpenItems)
+	state.Blockers = truncateTaskStateList(state.Blockers)
+	state.KeyArtifacts = truncateTaskStateList(state.KeyArtifacts)
+	state.Decisions = truncateTaskStateList(state.Decisions)
+	state.UserConstraints = truncateTaskStateList(state.UserConstraints)
+	return state
+}
+
 // normalizeTaskStateList 对任务状态中的字符串列表做去空、去重并保留顺序。
 func normalizeTaskStateList(items []string) []string {
 	if len(items) == 0 {
@@ -84,3 +104,30 @@ func normalizeTaskStateList(items []string) []string {
 	}
 	return result
 }
+
+// truncateTaskStateList 在保持顺序前提下裁剪列表长度与每项字符数。
+func truncateTaskStateList(items []string) []string {
+	if len(items) == 0 {
+		return nil
+	}
+	if len(items) > taskStateMaxListItems {
+		items = items[:taskStateMaxListItems]
+	}
+	result := make([]string, 0, len(items))
+	for _, item := range items {
+		result = append(result, truncateRunes(item, taskStateMaxListItemChars))
+	}
+	return result
+}
+
+// truncateRunes 按 rune 长度截断字符串，避免截断多字节字符。
+func truncateRunes(value string, limit int) string {
+	if limit <= 0 || value == "" {
+		return ""
+	}
+	runes := []rune(value)
+	if len(runes) <= limit {
+		return value
+	}
+	return string(runes[:limit])
+}
diff --git a/internal/session/task_state_test.go b/internal/session/task_state_test.go
new file mode 100644
index 00000000..69416f9e
--- /dev/null
+++ b/internal/session/task_state_test.go
@@ -0,0 +1,69 @@
+package session
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestClampTaskStateBoundariesTruncatesFieldsAndLists(t *testing.T) {
+	t.Parallel()
+
+	input := TaskState{
+		Goal:            strings.Repeat("g", taskStateMaxFieldChars+10),
+		NextStep:        strings.Repeat("n", taskStateMaxFieldChars+5),
+		Progress:        []string{strings.Repeat("p", taskStateMaxListItemChars+10)},
+		OpenItems:       []string{strings.Repeat("o", taskStateMaxListItemChars+10)},
+		Blockers:        []string{strings.Repeat("b", taskStateMaxListItemChars+10)},
+		KeyArtifacts:    []string{strings.Repeat("k", taskStateMaxListItemChars+10)},
+		Decisions:       []string{strings.Repeat("d", taskStateMaxListItemChars+10)},
+		UserConstraints: []string{strings.Repeat("u", taskStateMaxListItemChars+10)},
+	}
+
+	for i := 0; i < taskStateMaxListItems+6; i++ {
+		input.Progress = append(input.Progress, strings.Repeat("x", taskStateMaxListItemChars-4)+buildIndexedSuffix(i))
+	}
+
+	clamped := ClampTaskStateBoundaries(input)
+	if len([]rune(clamped.Goal)) != taskStateMaxFieldChars {
+		t.Fatalf("expected goal to be clamped to %d runes, got %d", taskStateMaxFieldChars, len([]rune(clamped.Goal)))
+	}
+	if len([]rune(clamped.NextStep)) != taskStateMaxFieldChars {
+		t.Fatalf("expected next_step to be clamped to %d runes, got %d", taskStateMaxFieldChars, len([]rune(clamped.NextStep)))
+	}
+	if len(clamped.Progress) != taskStateMaxListItems {
+		t.Fatalf("expected progress length %d, got %d", taskStateMaxListItems, len(clamped.Progress))
+	}
+	if len([]rune(clamped.Progress[0])) != taskStateMaxListItemChars {
+		t.Fatalf(
+			"expected progress item to be clamped to %d runes, got %d",
+			taskStateMaxListItemChars,
+			len([]rune(clamped.Progress[0])),
+		)
+	}
+	if len([]rune(clamped.OpenItems[0])) != taskStateMaxListItemChars {
+		t.Fatalf("expected open item clamped to %d runes, got %d", taskStateMaxListItemChars, len([]rune(clamped.OpenItems[0])))
+	}
+}
+
+func TestClampTaskStateBoundariesKeepsZeroValueListsNil(t *testing.T) {
+	t.Parallel()
+
+	clamped := ClampTaskStateBoundaries(TaskState{})
+	if clamped.Progress != nil || clamped.OpenItems != nil || clamped.Blockers != nil {
+		t.Fatalf("expected empty list fields to stay nil, got %+v", clamped)
+	}
+}
+
+func TestTruncateRunesHandlesBoundaryConditions(t *testing.T) {
+	t.Parallel()
+
+	if got := truncateRunes("abc", 0); got != "" {
+		t.Fatalf("expected zero limit to return empty string, got %q", got)
+	}
+	if got := truncateRunes("", 10); got != "" {
+		t.Fatalf("expected empty input to stay empty, got %q", got)
+	}
+	if got := truncateRunes("你好世界", 2); got != "你好" {
+		t.Fatalf("expected unicode-safe truncate result %q, got %q", "你好", got)
+	}
+}