diff --git a/.doc/system-design/module-boundaries.yaml b/.doc/system-design/module-boundaries.yaml
index 440ae23e..9fba27c8 100644
--- a/.doc/system-design/module-boundaries.yaml
+++ b/.doc/system-design/module-boundaries.yaml
@@ -90,6 +90,7 @@ imports:
     - taskrun
     - workflowdef
     - workspace
+    - sysadmin
   app/chatflow:
     - coordinator
     - ctxmgr
@@ -202,6 +203,7 @@ imports:
     - workflowdef
     - workspace
     - artifactvault
+    - sysadmin
   squad:
     - agent
     - config
@@ -244,6 +246,8 @@ imports:
   dataset:
     - artifactvault
     - app/uow
+  sysadmin:
+    - config
 
 table_owners:
   document_records:
@@ -326,6 +330,8 @@ table_owners:
     - app/intentflow
   intent_plan_shadow:
     - app/intentflow
+  system_settings:
+    - sysadmin
 
 path_owners:
   output.md:
diff --git a/deploy/postgres/goose/00049_2026-09-17-system-settings.sql b/deploy/postgres/goose/00049_2026-09-17-system-settings.sql
new file mode 100644
index 00000000..8e078e3f
--- /dev/null
+++ b/deploy/postgres/goose/00049_2026-09-17-system-settings.sql
@@ -0,0 +1,12 @@
+-- +goose Up
+-- 系统管理台（一期）：白名单化系统设置存储。键空间由 internal/sysadmin SettingSpec 注册表约束。
+
+CREATE TABLE IF NOT EXISTS system_settings (
+    key         TEXT PRIMARY KEY,
+    value       JSONB NOT NULL,
+    updated_by  BIGINT,
+    updated_at  TIMESTAMPTZ NOT NULL DEFAULT now()
+);
+
+-- +goose Down
+DROP TABLE IF EXISTS system_settings;
diff --git a/internal/app/app.go b/internal/app/app.go
index 06b33410..16ba6ba3 100644
--- a/internal/app/app.go
+++ b/internal/app/app.go
@@ -4,6 +4,7 @@ import (
 	"context"
 	"fmt"
 	"log/slog"
+	"strconv"
 	"strings"
 	"sync"
 	"time"
@@ -33,6 +34,7 @@ import (
 	"chat-agent-system/internal/projectinstance"
 	"chat-agent-system/internal/projectworkflow"
 	"chat-agent-system/internal/storage"
+	"chat-agent-system/internal/sysadmin"
 	"chat-agent-system/internal/taskrun"
 	"chat-agent-system/internal/workflowdef"
 	"chat-agent-system/internal/workspace"
@@ -73,6 +75,7 @@ type Runtime struct {
 	CAS         *storage.CAS
 	FreeDoc     *freedoc.Service
 	KB          *kb.Client
+	SysAdmin    *sysadmin.Service
 
 	mu             sync.Mutex
 	running        bool
@@ -208,6 +211,15 @@ func Assemble(cfg *config.Config, svc *bizdev.Service) (*Runtime, error) {
 		FreeDoc:    parts.FreeDoc,
 		KB:         parts.KB,
 	}
+	rt.SysAdmin = sysadmin.NewService(cfg, sysadmin.Options{
+		Pool:   pool,
+		Status: svc,
+		KB:     parts.KB,
+		TaskStoreReady: func(ctx context.Context) bool {
+			return taskrun.TablesReady(ctx, pool)
+		},
+		FeatureValues: sysadminFeatureValues(cfg),
+	})
 	rt.DocNotify = &docnotify.Subscriber{Notify: rt.Notify, Docs: parts.Gov}
 	rt.DocNotify.SkipWrite = func(ctx context.Context) bool {
 		return rt.WriterLive(ctx, events.ConsumerNotify)
@@ -257,6 +269,43 @@ func (r *Runtime) bindWorkflowApprovalHook() {
 	r.hookBound = true
 }
 
+// sysadminFeatureValues 在组合根解析各业务包公开 flag 的生效值，供 sysadmin 聚合层
+// 只读消费；sysadmin 不 import 业务包。
+func sysadminFeatureValues(cfg *config.Config) func() map[string]string {
+	return func() map[string]string {
+		iflags := intent.CurrentFeatureFlags()
+		pflags := intentflow.CurrentFeatureFlags()
+		sflags := ctxmgr.CurrentSummaryFlags()
+		values := map[string]string{
+			"INTENT_V2_SHADOW":             strconv.FormatBool(iflags.IntentV2Shadow),
+			"INTENT_V2_DECISION":           strconv.FormatBool(iflags.IntentV2Decision),
+			"INTENT_V2_DECISION_TIER":      string(iflags.V2DecisionTier),
+			"WORKFLOW_INTENTS_ENABLED":     strconv.FormatBool(iflags.WorkflowIntentsEnabled),
+			"MULTI_INTENT_ENABLED":         strconv.FormatBool(iflags.MultiIntentEnabled),
+			"SEMANTIC_FALLBACK_ENABLED":    strconv.FormatBool(iflags.SemanticFallbackEnabled),
+			"MULTI_INTENT_PLAN_TIER":       string(pflags.PlanTier),
+			"MULTI_INTENT_U9_SEGMENT":      strconv.FormatBool(pflags.U9Segment),
+			"MULTI_INTENT_U10_MUTATE":      strconv.FormatBool(pflags.U10Mutate),
+			"MULTI_INTENT_U11_DOCGOV":      strconv.FormatBool(pflags.U11DocGov),
+			"MULTI_INTENT_U12_RUN_CONTROL": strconv.FormatBool(pflags.U12RunControl),
+			"SEMANTIC_SUMMARY_SHADOW":      strconv.FormatBool(sflags.Shadow),
+			"SEMANTIC_SUMMARY_REPLACE":     strconv.FormatBool(sflags.Replace),
+			"PI_CHANGE_REPORT_NARRATIVE":   strconv.FormatBool(docrevision.PIChangeReportNarrativeEnabled()),
+		}
+		if cfg != nil {
+			values["AGENT_BACKEND"] = cfg.AgentBackend
+			values["MAX_CONCURRENT_AGENTS"] = strconv.Itoa(cfg.MaxConcurrentAgents)
+			values["PI_AGENT_RUNNER_URL"] = cfg.PiAgentRunnerURL
+			values["ALLOW_IN_MEMORY"] = strconv.FormatBool(cfg.AllowInMemory)
+			values["AUTH_REGISTRATION_ENABLED"] = strconv.FormatBool(cfg.AuthRegistrationEnabled)
+			values["AUTH_REQUIRE_APPROVAL"] = strconv.FormatBool(cfg.AuthRequireApproval)
+			values["FAV_PUBLISHER_ENABLED"] = strconv.FormatBool(cfg.FAVPublisherEnabled)
+			values["FAV_DEGRADED_READ"] = strconv.FormatBool(cfg.FAVDegradedRead)
+		}
+		return values
+	}
+}
+
 // WriterLive reports whether the durable consumer already owns the visible write.
 func (r *Runtime) WriterLive(ctx context.Context, consumer string) bool {
 	if r == nil {
diff --git a/internal/server/admin_system_handlers.go b/internal/server/admin_system_handlers.go
new file mode 100644
index 00000000..2d7327f3
--- /dev/null
+++ b/internal/server/admin_system_handlers.go
@@ -0,0 +1,94 @@
+package server
+
+import (
+	"encoding/json"
+	"errors"
+	"net/http"
+
+	"chat-agent-system/internal/sysadmin"
+)
+
+// 系统管理台（一期）：全部端点要求系统管理员。
+
+func (s *Server) handleAdminSystemOverview(w http.ResponseWriter, r *http.Request) {
+	if _, ok := s.requireSystemAdmin(w, r); !ok {
+		return
+	}
+	if s.sysadmin == nil {
+		writeSafeError(w, r, http.StatusServiceUnavailable, "sysadmin service unavailable")
+		return
+	}
+	writeJSONResponse(w, http.StatusOK, s.sysadmin.Overview(r.Context()))
+}
+
+func (s *Server) handleAdminSystemKB(w http.ResponseWriter, r *http.Request) {
+	if _, ok := s.requireSystemAdmin(w, r); !ok {
+		return
+	}
+	if s.sysadmin == nil {
+		writeSafeError(w, r, http.StatusServiceUnavailable, "sysadmin service unavailable")
+		return
+	}
+	writeJSONResponse(w, http.StatusOK, s.sysadmin.KBInfo())
+}
+
+func (s *Server) handleAdminSystemFeatures(w http.ResponseWriter, r *http.Request) {
+	if _, ok := s.requireSystemAdmin(w, r); !ok {
+		return
+	}
+	if s.sysadmin == nil {
+		writeSafeError(w, r, http.StatusServiceUnavailable, "sysadmin service unavailable")
+		return
+	}
+	writeJSONResponse(w, http.StatusOK, map[string]any{"features": s.sysadmin.Features()})
+}
+
+func (s *Server) handleAdminSystemSettings(w http.ResponseWriter, r *http.Request) {
+	if _, ok := s.requireSystemAdmin(w, r); !ok {
+		return
+	}
+	if s.sysadmin == nil {
+		writeSafeError(w, r, http.StatusServiceUnavailable, "sysadmin service unavailable")
+		return
+	}
+	settings, err := s.sysadmin.ListSettings(r.Context())
+	if err != nil {
+		writeSafeError(w, r, http.StatusInternalServerError, err.Error())
+		return
+	}
+	writeJSONResponse(w, http.StatusOK, map[string]any{"settings": settings})
+}
+
+func (s *Server) handleAdminSystemSettingByKey(w http.ResponseWriter, r *http.Request) {
+	user, ok := s.requireSystemAdmin(w, r)
+	if !ok {
+		return
+	}
+	if s.sysadmin == nil {
+		writeSafeError(w, r, http.StatusServiceUnavailable, "sysadmin service unavailable")
+		return
+	}
+	key := r.PathValue("key")
+	var req struct {
+		Value json.RawMessage `json:"value"`
+	}
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		writeSafeError(w, r, http.StatusBadRequest, "无效的请求体")
+		return
+	}
+	setting, err := s.sysadmin.UpdateSetting(r.Context(), key, req.Value, user.ID)
+	switch {
+	case errors.Is(err, sysadmin.ErrUnknownSetting):
+		writeSafeError(w, r, http.StatusBadRequest, "未知的设置键")
+	case errors.Is(err, sysadmin.ErrSettingReadOnly):
+		writeSafeError(w, r, http.StatusForbidden, "该设置为只读")
+	case errors.Is(err, sysadmin.ErrInvalidSettingValue):
+		writeSafeError(w, r, http.StatusBadRequest, "设置值类型不匹配")
+	case errors.Is(err, sysadmin.ErrStoreUnavailable):
+		writeSafeError(w, r, http.StatusServiceUnavailable, "设置存储不可用")
+	case err != nil:
+		writeSafeError(w, r, http.StatusInternalServerError, err.Error())
+	default:
+		writeJSONResponse(w, http.StatusOK, setting)
+	}
+}
diff --git a/internal/server/admin_system_handlers_test.go b/internal/server/admin_system_handlers_test.go
new file mode 100644
index 00000000..b0f0731c
--- /dev/null
+++ b/internal/server/admin_system_handlers_test.go
@@ -0,0 +1,244 @@
+package server
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"sync"
+	"testing"
+	"time"
+
+	"chat-agent-system/internal/auth"
+	"chat-agent-system/internal/sysadmin"
+)
+
+type fakeSettingsStore struct {
+	mu    sync.Mutex
+	items map[string]json.RawMessage
+}
+
+func newFakeSettingsStore() *fakeSettingsStore {
+	return &fakeSettingsStore{items: map[string]json.RawMessage{}}
+}
+
+func (f *fakeSettingsStore) Get(_ context.Context, key string) (json.RawMessage, *int64, *time.Time, error) {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	raw, ok := f.items[key]
+	if !ok {
+		return nil, nil, nil, sysadmin.ErrSettingNotFound
+	}
+	at := time.Now()
+	by := int64(1)
+	return raw, &by, &at, nil
+}
+
+func (f *fakeSettingsStore) Upsert(_ context.Context, key string, value json.RawMessage, _ int64) (time.Time, error) {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	f.items[key] = append(json.RawMessage(nil), value...)
+	return time.Now(), nil
+}
+
+// registerTestUser 注册并登录一个普通用户，返回其 Bearer Token。
+func registerTestUser(t *testing.T, srv *Server, username string) string {
+	t.Helper()
+	if err := srv.AuthService().UpdateConfig(context.Background(), auth.SystemAuthConfig{
+		AllowRegistration: true,
+		RequireApproval:   false,
+	}); err != nil {
+		t.Fatalf("enable registration: %v", err)
+	}
+	body, _ := json.Marshal(map[string]string{
+		"username": username,
+		"password": "PlainPass123",
+		"name":     "普通用户",
+	})
+	req := httptest.NewRequest(http.MethodPost, "/api/v1/auth/register", bytes.NewReader(body))
+	w := httptest.NewRecorder()
+	srv.Routes().ServeHTTP(w, req)
+	if w.Code != http.StatusOK {
+		t.Fatalf("register %s failed: %d %s", username, w.Code, w.Body.String())
+	}
+
+	loginBody, _ := json.Marshal(map[string]string{"username": username, "password": "PlainPass123"})
+	req = httptest.NewRequest(http.MethodPost, "/api/v1/auth/login", bytes.NewReader(loginBody))
+	w = httptest.NewRecorder()
+	srv.Routes().ServeHTTP(w, req)
+	if w.Code != http.StatusOK {
+		t.Fatalf("login %s failed: %d %s", username, w.Code, w.Body.String())
+	}
+	var session auth.SessionInfo
+	if err := json.NewDecoder(w.Body).Decode(&session); err != nil || session.Token == "" {
+		t.Fatalf("decode login session: %v", err)
+	}
+	return session.Token
+}
+
+func doSysadminRequest(t *testing.T, srv *Server, method, path, token, body string) *httptest.ResponseRecorder {
+	t.Helper()
+	var req *http.Request
+	if body != "" {
+		req = httptest.NewRequest(method, path, bytes.NewReader([]byte(body)))
+		req.Header.Set("Content-Type", "application/json")
+	} else {
+		req = httptest.NewRequest(method, path, nil)
+	}
+	if token != "" {
+		withBearerAuth(req, token)
+	}
+	w := httptest.NewRecorder()
+	srv.Routes().ServeHTTP(w, req)
+	return w
+}
+
+func TestAdminSystemEndpoints_RequireSystemAdmin(t *testing.T) {
+	srv := newTestServer(t)
+	srv.cfg.AllowInMemory = false // 关闭 legacy 未认证兜底，严格鉴权
+	plainToken := registerTestUser(t, srv, "plain_sysadmin_probe")
+	endpoints := []struct {
+		method string
+		path   string
+	}{
+		{http.MethodGet, "/api/v1/admin/system/overview"},
+		{http.MethodGet, "/api/v1/admin/system/kb"},
+		{http.MethodGet, "/api/v1/admin/system/features"},
+		{http.MethodGet, "/api/v1/admin/system/settings"},
+		{http.MethodPut, "/api/v1/admin/system/settings/ui.maintenance_notice"},
+	}
+	for _, ep := range endpoints {
+		// 未认证 → 401
+		if w := doSysadminRequest(t, srv, ep.method, ep.path, "", ""); w.Code != http.StatusUnauthorized {
+			t.Fatalf("%s %s: expected 401 without auth, got %d", ep.method, ep.path, w.Code)
+		}
+		// 非管理员 → 403
+		if w := doSysadminRequest(t, srv, ep.method, ep.path, plainToken, ""); w.Code != http.StatusForbidden {
+			t.Fatalf("%s %s: expected 403 for non-admin, got %d %s", ep.method, ep.path, w.Code, w.Body.String())
+		}
+	}
+}
+
+func TestAdminSystemOverview_AdminGetsCamelCasePayload(t *testing.T) {
+	srv := newTestServer(t)
+	srv.cfg.AllowInMemory = false // 关闭 legacy 未认证兜底，严格鉴权
+	token := loginTestAdmin(t, srv)
+	w := doSysadminRequest(t, srv, http.MethodGet, "/api/v1/admin/system/overview", token, "")
+	if w.Code != http.StatusOK {
+		t.Fatalf("expected 200, got %d %s", w.Code, w.Body.String())
+	}
+	var body map[string]any
+	if err := json.Unmarshal(w.Body.Bytes(), &body); err != nil {
+		t.Fatalf("decode: %v", err)
+	}
+	for _, key := range []string{"status", "env", "agentBackend", "databaseReady", "schemaVersion", "taskStoreReady", "kbOnline", "uptimeSeconds"} {
+		if _, ok := body[key]; !ok {
+			t.Fatalf("overview missing camelCase key %s: %v", key, body)
+		}
+	}
+	if body["env"] != "test" || body["agentBackend"] != "stub" {
+		t.Fatalf("unexpected overview payload: %v", body)
+	}
+}
+
+func TestAdminSystemKB_NoSecretMaterial(t *testing.T) {
+	srv := newTestServer(t)
+	srv.cfg.AllowInMemory = false // 关闭 legacy 未认证兜底，严格鉴权
+	token := loginTestAdmin(t, srv)
+	w := doSysadminRequest(t, srv, http.MethodGet, "/api/v1/admin/system/kb", token, "")
+	if w.Code != http.StatusOK {
+		t.Fatalf("expected 200, got %d %s", w.Code, w.Body.String())
+	}
+	var body map[string]any
+	if err := json.Unmarshal(w.Body.Bytes(), &body); err != nil {
+		t.Fatalf("decode: %v", err)
+	}
+	for _, key := range []string{"online", "host", "port", "database", "user", "embeddingModel", "rerankerEnabled", "sslMode"} {
+		if _, ok := body[key]; !ok {
+			t.Fatalf("kb payload missing key %s: %v", key, body)
+		}
+	}
+	if bytes.Contains(w.Body.Bytes(), []byte("assword")) {
+		t.Fatalf("kb payload leaks secret material: %s", w.Body.String())
+	}
+}
+
+func TestAdminSystemFeatures_Payload(t *testing.T) {
+	srv := newTestServer(t)
+	srv.cfg.AllowInMemory = false // 关闭 legacy 未认证兜底，严格鉴权
+	token := loginTestAdmin(t, srv)
+	w := doSysadminRequest(t, srv, http.MethodGet, "/api/v1/admin/system/features", token, "")
+	if w.Code != http.StatusOK {
+		t.Fatalf("expected 200, got %d %s", w.Code, w.Body.String())
+	}
+	var body struct {
+		Features []sysadmin.Feature `json:"features"`
+	}
+	if err := json.Unmarshal(w.Body.Bytes(), &body); err != nil {
+		t.Fatalf("decode features: %v", err)
+	}
+	found := false
+	for _, f := range body.Features {
+		if f.Key == "FAV_PUBLISHER_ENABLED" && f.Group == "artifact-vault" && f.Source == "env" {
+			found = true
+		}
+	}
+	if !found {
+		t.Fatal("features payload must include FAV_PUBLISHER_ENABLED in artifact-vault group")
+	}
+}
+
+func TestAdminSystemSettings_ListAndUpdate(t *testing.T) {
+	srv := newTestServer(t)
+	srv.cfg.AllowInMemory = false // 关闭 legacy 未认证兜底，严格鉴权
+	// 用带内存 store 的 sysadmin 服务替换装配产物（无 DB 时 store 为 nil）。
+	srv.sysadmin = sysadmin.NewService(srv.cfg, sysadmin.Options{Store: newFakeSettingsStore()})
+	token := loginTestAdmin(t, srv)
+
+	w := doSysadminRequest(t, srv, http.MethodGet, "/api/v1/admin/system/settings", token, "")
+	if w.Code != http.StatusOK {
+		t.Fatalf("list: expected 200, got %d %s", w.Code, w.Body.String())
+	}
+	var list struct {
+		Settings []sysadmin.Setting `json:"settings"`
+	}
+	if err := json.Unmarshal(w.Body.Bytes(), &list); err != nil {
+		t.Fatalf("decode list: %v", err)
+	}
+	if len(list.Settings) == 0 {
+		t.Fatal("expected whitelist settings")
+	}
+
+	// 合法写 → 200，返回更新后的 setting
+	w = doSysadminRequest(t, srv, http.MethodPut, "/api/v1/admin/system/settings/ui.maintenance_notice", token, `{"value":"停机维护"}`)
+	if w.Code != http.StatusOK {
+		t.Fatalf("update: expected 200, got %d %s", w.Code, w.Body.String())
+	}
+	var updated sysadmin.Setting
+	if err := json.Unmarshal(w.Body.Bytes(), &updated); err != nil {
+		t.Fatalf("decode updated: %v", err)
+	}
+	if updated.Value != "停机维护" || !updated.Writable {
+		t.Fatalf("unexpected updated setting: %+v", updated)
+	}
+
+	// 未知 key → 400
+	if w := doSysadminRequest(t, srv, http.MethodPut, "/api/v1/admin/system/settings/no.such.key", token, `{"value":"x"}`); w.Code != http.StatusBadRequest {
+		t.Fatalf("unknown key: expected 400, got %d %s", w.Code, w.Body.String())
+	}
+
+	// 类型不匹配 → 400
+	if w := doSysadminRequest(t, srv, http.MethodPut, "/api/v1/admin/system/settings/ui.read_only_mode", token, `{"value":"yes"}`); w.Code != http.StatusBadRequest {
+		t.Fatalf("type mismatch: expected 400, got %d %s", w.Code, w.Body.String())
+	}
+}
+
+func TestAdminSystemSettings_UpdateWithoutStoreReturns503(t *testing.T) {
+	srv := newTestServer(t) // 无 DB：sysadmin store 为 nil
+	token := loginTestAdmin(t, srv)
+	w := doSysadminRequest(t, srv, http.MethodPut, "/api/v1/admin/system/settings/ui.maintenance_notice", token, `{"value":"x"}`)
+	if w.Code != http.StatusServiceUnavailable {
+		t.Fatalf("expected 503 without settings store, got %d %s", w.Code, w.Body.String())
+	}
+}
diff --git a/internal/server/server.go b/internal/server/server.go
index 480a74ca..05cc2722 100644
--- a/internal/server/server.go
+++ b/internal/server/server.go
@@ -31,6 +31,7 @@ import (
 	"chat-agent-system/internal/projectinstance"
 	"chat-agent-system/internal/projectworkflow"
 	"chat-agent-system/internal/storage"
+	"chat-agent-system/internal/sysadmin"
 	"chat-agent-system/internal/taskrun"
 	"chat-agent-system/internal/workflowdef"
 	"chat-agent-system/internal/workspace"
@@ -68,16 +69,17 @@ type Server struct {
 	pool               *pgxpool.Pool
 	freeDoc            *freedoc.Service
 	kb                 *kb.Client
+	sysadmin           *sysadmin.Service
 	httpServer         *http.Server
 	intentPlans        intentflow.Service
 	planAccessFn       func(ctx context.Context, projectID, userID int64) error
 	planSessionOwnerFn func(ctx context.Context, sessionID string) (int64, error)
 
 	// FAV stubs (U7 incremental): nil / off unless FAV_PUBLISHER_ENABLED.
-	vaultReg               artifactvault.Registry
-	vaultStore             *artifactvault.FilesystemStore
-	vaultPub               *artifactvault.Publisher
-	vaultPublisherStarted  int32
+	vaultReg              artifactvault.Registry
+	vaultStore            *artifactvault.FilesystemStore
+	vaultPub              *artifactvault.Publisher
+	vaultPublisherStarted int32
 }
 
 // NewFromRuntime attaches the HTTP adapter to an already-wired composition root.
@@ -111,6 +113,7 @@ func NewFromRuntime(rt *app.Runtime) *Server {
 		pool:        rt.Pool,
 		freeDoc:     rt.FreeDoc,
 		kb:          rt.KB,
+		sysadmin:    rt.SysAdmin,
 		intentPlans: rt.IntentPlans,
 	}
 	s.chatLog = chatflow.NewAdapter(s.ctxMgr, s.resolveStageAccess, s.failClosedAuthz())
@@ -323,6 +326,13 @@ func (s *Server) Routes() http.Handler {
 	mux.HandleFunc("GET /api/v1/admin/config", s.handleAdminConfig)
 	mux.HandleFunc("PUT /api/v1/admin/config", s.handleAdminConfig)
 
+	// 9.1 系统管理台（一期）：只读聚合 + 白名单设置
+	mux.HandleFunc("GET /api/v1/admin/system/overview", s.handleAdminSystemOverview)
+	mux.HandleFunc("GET /api/v1/admin/system/kb", s.handleAdminSystemKB)
+	mux.HandleFunc("GET /api/v1/admin/system/features", s.handleAdminSystemFeatures)
+	mux.HandleFunc("GET /api/v1/admin/system/settings", s.handleAdminSystemSettings)
+	mux.HandleFunc("PUT /api/v1/admin/system/settings/{key}", s.handleAdminSystemSettingByKey)
+
 	// 10. 现代 SPA 前端页面与静态资产托管
 	mux.HandleFunc("GET /", s.serveSPA)
 
diff --git a/internal/sysadmin/features.go b/internal/sysadmin/features.go
new file mode 100644
index 00000000..cd541ddd
--- /dev/null
+++ b/internal/sysadmin/features.go
@@ -0,0 +1,78 @@
+package sysadmin
+
+import "os"
+
+// Feature 功能开关视图；value 统一用字符串表示。
+type Feature struct {
+	Key             string `json:"key"`
+	Label           string `json:"label"`
+	Group           string `json:"group"`
+	Value           string `json:"value"`
+	Source          string `json:"source"`
+	RequiresRestart bool   `json:"requiresRestart"`
+	Description     string `json:"description"`
+}
+
+type featureSpec struct {
+	key         string // 环境变量名
+	label       string
+	group       string
+	fallback    string // 组合根未提供生效值时的兜底
+	description string
+}
+
+// featureCatalog 覆盖 config.Config 主要开关与各业务包灰度 flag（宁全勿缺）。
+// 生效值由组合根（app）解析后注入，避免本包反向依赖业务模块。
+var featureCatalog = []featureSpec{
+	{key: "AGENT_BACKEND", label: "Agent 执行后端", group: "agent", fallback: "pi-agent", description: "对话与任务执行的 Agent 后端（stub / cursor / pi-agent）"},
+	{key: "MAX_CONCURRENT_AGENTS", label: "Agent 全局并发上限", group: "agent", fallback: "8", description: "保护 pi-agent / GPU / API 的并发闸"},
+	{key: "PI_AGENT_RUNNER_URL", label: "PI Runner 地址", group: "agent", fallback: "", description: "产品内 PI Agent Runner 服务地址；空表示未接入"},
+	{key: "ALLOW_IN_MEMORY", label: "允许内存降级模式", group: "system", fallback: "false", description: "数据库不可用时降级内存模式（仅限本地 Demo）"},
+	{key: "AUTH_REGISTRATION_ENABLED", label: "开放注册", group: "auth", fallback: "true", description: "是否允许用户自主注册"},
+	{key: "AUTH_REQUIRE_APPROVAL", label: "注册需审核", group: "auth", fallback: "false", description: "新注册用户是否需要管理员审核后激活"},
+	{key: "FAV_PUBLISHER_ENABLED", label: "FAV 发布器", group: "artifact-vault", fallback: "false", description: "Final Artifact Vault 后台发布器；默认关闭"},
+	{key: "FAV_DEGRADED_READ", label: "FAV 降级读", group: "artifact-vault", fallback: "false", description: "FAV 缺失时允许降级读取；默认关闭"},
+	{key: "INTENT_V2_SHADOW", label: "意图 V2 影子模式", group: "intent", fallback: "false", description: "V2 意图识别影子运行，仅观测不接管"},
+	{key: "INTENT_V2_DECISION", label: "意图 V2 决策", group: "intent", fallback: "false", description: "V2 意图识别接管路由决策"},
+	{key: "INTENT_V2_DECISION_TIER", label: "意图 V2 决策档位", group: "intent", fallback: "none", description: "V2 灰度风险档位：none/query/generate/write_low/write_high/all"},
+	{key: "WORKFLOW_INTENTS_ENABLED", label: "工作流意图", group: "intent", fallback: "true", description: "识别工作流类意图"},
+	{key: "MULTI_INTENT_ENABLED", label: "多意图识别", group: "intent", fallback: "true", description: "单条消息多意图拆解"},
+	{key: "SEMANTIC_FALLBACK_ENABLED", label: "语义兜底", group: "intent", fallback: "false", description: "规则意图未命中时的语义兜底"},
+	{key: "MULTI_INTENT_PLAN_TIER", label: "多意图计划档位", group: "intentflow", fallback: "legacy", description: "意图计划灰度：legacy/shadow/auto_read/confirm/full"},
+	{key: "MULTI_INTENT_U9_SEGMENT", label: "U9 LLM 分段", group: "intentflow", fallback: "false", description: "LLM 意图分段提议"},
+	{key: "MULTI_INTENT_U10_MUTATE", label: "U10 变更适配器", group: "intentflow", fallback: "false", description: "低/中风险 mutate 动作适配器"},
+	{key: "MULTI_INTENT_U11_DOCGOV", label: "U11 文档治理适配器", group: "intentflow", fallback: "false", description: "docgov 动作适配器"},
+	{key: "MULTI_INTENT_U12_RUN_CONTROL", label: "U12 运行控制适配器", group: "intentflow", fallback: "false", description: "workflow/run-control 动作适配器"},
+	{key: "SEMANTIC_SUMMARY_SHADOW", label: "语义摘要影子", group: "ctxmgr", fallback: "false", description: "上下文语义摘要影子生成"},
+	{key: "SEMANTIC_SUMMARY_REPLACE", label: "语义摘要替换", group: "ctxmgr", fallback: "false", description: "语义摘要替换确定性叙事（保留位，未接线）"},
+	{key: "PI_CHANGE_REPORT_NARRATIVE", label: "PI 变更报告叙事", group: "docrevision", fallback: "false", description: "变更报告 PI 叙事增强；默认仅确定性回退"},
+}
+
+// Features 返回功能开关快照；source 恒为 env，均需重启生效。
+func (s *Service) Features() []Feature {
+	values := map[string]string{}
+	if s.featureValues != nil {
+		values = s.featureValues()
+	}
+	out := make([]Feature, 0, len(featureCatalog))
+	for _, spec := range featureCatalog {
+		value, ok := values[spec.key]
+		if !ok {
+			if env, set := os.LookupEnv(spec.key); set {
+				value = env
+			} else {
+				value = spec.fallback
+			}
+		}
+		out = append(out, Feature{
+			Key:             spec.key,
+			Label:           spec.label,
+			Group:           spec.group,
+			Value:           value,
+			Source:          "env",
+			RequiresRestart: true,
+			Description:     spec.description,
+		})
+	}
+	return out
+}
diff --git a/internal/sysadmin/service.go b/internal/sysadmin/service.go
new file mode 100644
index 00000000..da636643
--- /dev/null
+++ b/internal/sysadmin/service.go
@@ -0,0 +1,142 @@
+// Package sysadmin 系统管理台（一期）薄聚合层：只通过小接口读取其他模块的
+// 公开状态，业务包不得 import 本包。
+package sysadmin
+
+import (
+	"context"
+	"time"
+
+	"chat-agent-system/internal/config"
+
+	"github.com/jackc/pgx/v5/pgxpool"
+)
+
+// StatusProvider 业务服务的数据库/schema 公开状态（*bizdev.Service 满足）。
+type StatusProvider interface {
+	DatabaseReady() bool
+	SchemaVersion() int64
+	LiveSchemaVersion(ctx context.Context) int64
+}
+
+// KBProber 知识库在线探针（*kb.Client 满足）。
+type KBProber interface {
+	Online() bool
+}
+
+// Options 装配根注入的依赖；全部为只读探针，聚合层不持有业务写路径。
+type Options struct {
+	Pool           *pgxpool.Pool
+	Store          SettingsStore // 测试可直接注入；为空且 Pool 非空时使用 PG store
+	Status         StatusProvider
+	KB             KBProber
+	TaskStoreReady func(ctx context.Context) bool
+	FeatureValues  func() map[string]string // 组合根解析后的功能开关生效值（key 为环境变量名）
+}
+
+// Service 系统管理台聚合服务。
+type Service struct {
+	cfg            *config.Config
+	store          SettingsStore
+	status         StatusProvider
+	kb             KBProber
+	taskStoreReady func(ctx context.Context) bool
+	featureValues  func() map[string]string
+	specs          []SettingSpec
+	startedAt      time.Time
+}
+
+// NewService 构建聚合服务；cfg 允许为 nil（测试）。
+func NewService(cfg *config.Config, opts Options) *Service {
+	store := opts.Store
+	if store == nil && opts.Pool != nil {
+		store = newPGSettingsStore(opts.Pool)
+	}
+	return &Service{
+		cfg:            cfg,
+		store:          store,
+		status:         opts.Status,
+		kb:             opts.KB,
+		taskStoreReady: opts.TaskStoreReady,
+		featureValues:  opts.FeatureValues,
+		specs:          defaultSettingSpecs(),
+		startedAt:      time.Now(),
+	}
+}
+
+// Overview 系统总览，字段对齐前端 camelCase 契约。
+type Overview struct {
+	Status         string `json:"status"`
+	Env            string `json:"env"`
+	AgentBackend   string `json:"agentBackend"`
+	DatabaseReady  bool   `json:"databaseReady"`
+	SchemaVersion  int64  `json:"schemaVersion"`
+	TaskStoreReady bool   `json:"taskStoreReady"`
+	KBOnline       bool   `json:"kbOnline"`
+	UptimeSeconds  int64  `json:"uptimeSeconds"`
+}
+
+// Overview 聚合 /health 同源信号。
+func (s *Service) Overview(ctx context.Context) Overview {
+	dbReady := s.status != nil && s.status.DatabaseReady()
+	schemaVersion := int64(0)
+	if s.status != nil {
+		if dbReady {
+			schemaVersion = s.status.LiveSchemaVersion(ctx)
+		} else {
+			schemaVersion = s.status.SchemaVersion()
+		}
+	}
+	taskStoreReady := false
+	if s.taskStoreReady != nil {
+		taskStoreReady = s.taskStoreReady(ctx)
+	}
+
+	status := "ok"
+	if s.cfg != nil && s.cfg.ContextDbHost != "" && !s.cfg.AllowInMemory && !dbReady {
+		status = "degraded"
+	}
+
+	out := Overview{
+		Status:         status,
+		DatabaseReady:  dbReady,
+		SchemaVersion:  schemaVersion,
+		TaskStoreReady: taskStoreReady,
+		KBOnline:       s.kb != nil && s.kb.Online(),
+		UptimeSeconds:  int64(time.Since(s.startedAt).Seconds()),
+	}
+	if s.cfg != nil {
+		out.Env = s.cfg.Env
+		out.AgentBackend = s.cfg.AgentBackend
+	}
+	return out
+}
+
+// KBInfo 知识库连接视图；密码等敏感信息绝不输出。
+type KBInfo struct {
+	Online          bool   `json:"online"`
+	Host            string `json:"host"`
+	Port            int    `json:"port"`
+	Database        string `json:"database"`
+	User            string `json:"user"`
+	EmbeddingModel  string `json:"embeddingModel"`
+	RerankerEnabled bool   `json:"rerankerEnabled"`
+	SSLMode         string `json:"sslMode"`
+}
+
+// KBInfo 返回 KB 连接与模型配置（脱敏）。
+func (s *Service) KBInfo() KBInfo {
+	out := KBInfo{
+		Online: s.kb != nil && s.kb.Online(),
+		// KbDSN 固定 sslmode=disable，如实暴露
+		SSLMode: "disable",
+	}
+	if s.cfg != nil {
+		out.Host = s.cfg.KbDbHost
+		out.Port = s.cfg.KbDbPort
+		out.Database = s.cfg.KbDbName
+		out.User = s.cfg.KbDbUser
+		out.EmbeddingModel = s.cfg.EmbeddingModel
+		out.RerankerEnabled = s.cfg.RerankerEndpointURL != ""
+	}
+	return out
+}
diff --git a/internal/sysadmin/service_test.go b/internal/sysadmin/service_test.go
new file mode 100644
index 00000000..7827cf17
--- /dev/null
+++ b/internal/sysadmin/service_test.go
@@ -0,0 +1,151 @@
+package sysadmin
+
+import (
+	"context"
+	"encoding/json"
+	"strings"
+	"testing"
+
+	"chat-agent-system/internal/config"
+)
+
+type fakeStatus struct {
+	ready   bool
+	version int64
+}
+
+func (f fakeStatus) DatabaseReady() bool { return f.ready }
+func (f fakeStatus) SchemaVersion() int64 {
+	return f.version
+}
+func (f fakeStatus) LiveSchemaVersion(_ context.Context) int64 { return f.version + 1 }
+
+type fakeKB struct{ online bool }
+
+func (f fakeKB) Online() bool { return f.online }
+
+func testConfig() *config.Config {
+	return &config.Config{
+		Env:           "test",
+		AgentBackend:  "stub",
+		AllowInMemory: true,
+		KbDbHost:      "kb.internal",
+		KbDbPort:      5432,
+		KbDbUser:      "regkb",
+		KbDbPassword:  "super-secret",
+		KbDbName:      "regulations",
+	}
+}
+
+func TestOverview_AggregatesSources(t *testing.T) {
+	svc := NewService(testConfig(), Options{
+		Status: fakeStatus{ready: true, version: 48},
+		KB:     fakeKB{online: true},
+		TaskStoreReady: func(context.Context) bool {
+			return true
+		},
+	})
+	ov := svc.Overview(context.Background())
+	if ov.Status != "ok" {
+		t.Fatalf("expected ok, got %s", ov.Status)
+	}
+	if ov.Env != "test" || ov.AgentBackend != "stub" {
+		t.Fatalf("unexpected env/backend: %+v", ov)
+	}
+	if !ov.DatabaseReady || !ov.TaskStoreReady || !ov.KBOnline {
+		t.Fatalf("expected all ready: %+v", ov)
+	}
+	// dbReady 时使用 LiveSchemaVersion（fake 返回 version+1）
+	if ov.SchemaVersion != 49 {
+		t.Fatalf("expected live schema version 49, got %d", ov.SchemaVersion)
+	}
+	if ov.UptimeSeconds < 0 {
+		t.Fatalf("uptime must be >= 0, got %d", ov.UptimeSeconds)
+	}
+}
+
+func TestOverview_DegradedWhenDBDownAndNotInMemory(t *testing.T) {
+	cfg := testConfig()
+	cfg.AllowInMemory = false
+	cfg.ContextDbHost = "127.0.0.1"
+	svc := NewService(cfg, Options{Status: fakeStatus{ready: false, version: 48}})
+	ov := svc.Overview(context.Background())
+	if ov.Status != "degraded" {
+		t.Fatalf("expected degraded, got %s", ov.Status)
+	}
+	// 未就绪时回退启动缓存版本
+	if ov.SchemaVersion != 48 {
+		t.Fatalf("expected cached schema version 48, got %d", ov.SchemaVersion)
+	}
+	if ov.TaskStoreReady || ov.KBOnline {
+		t.Fatalf("expected nil probes to report not-ready: %+v", ov)
+	}
+}
+
+func TestKBInfo_NeverLeaksSecrets(t *testing.T) {
+	svc := NewService(testConfig(), Options{KB: fakeKB{online: true}})
+	info := svc.KBInfo()
+	if !info.Online {
+		t.Fatal("expected online")
+	}
+	if info.Host != "kb.internal" || info.Port != 5432 || info.Database != "regulations" || info.User != "regkb" {
+		t.Fatalf("unexpected connection view: %+v", info)
+	}
+	if info.SSLMode != "disable" {
+		t.Fatalf("expected sslMode=disable (KbDSN fixed), got %s", info.SSLMode)
+	}
+	if info.RerankerEnabled {
+		t.Fatal("reranker endpoint empty must report disabled")
+	}
+	// 结构体无密码字段；序列化结果也不得出现密码值
+	raw, err := json.Marshal(info)
+	if err != nil {
+		t.Fatalf("marshal: %v", err)
+	}
+	if s := string(raw); strings.Contains(s, "super-secret") || strings.Contains(s, "assword") {
+		t.Fatalf("KBInfo leaks secret material: %s", s)
+	}
+}
+
+func TestFeatures_CoversCatalogAndInjectedValues(t *testing.T) {
+	svc := NewService(testConfig(), Options{
+		FeatureValues: func() map[string]string {
+			return map[string]string{
+				"AGENT_BACKEND":          "stub",
+				"FAV_PUBLISHER_ENABLED":  "true",
+				"MULTI_INTENT_PLAN_TIER": "shadow",
+			}
+		},
+	})
+	features := svc.Features()
+	if len(features) != len(featureCatalog) {
+		t.Fatalf("expected %d features, got %d", len(featureCatalog), len(features))
+	}
+	byKey := map[string]Feature{}
+	for _, f := range features {
+		byKey[f.Key] = f
+		if f.Source != "env" || !f.RequiresRestart {
+			t.Fatalf("feature %s must be env-sourced and restart-bound: %+v", f.Key, f)
+		}
+		if f.Label == "" || f.Group == "" {
+			t.Fatalf("feature %s missing label/group: %+v", f.Key, f)
+		}
+	}
+	if byKey["FAV_PUBLISHER_ENABLED"].Value != "true" {
+		t.Fatalf("expected injected FAV value, got %+v", byKey["FAV_PUBLISHER_ENABLED"])
+	}
+	if byKey["FAV_PUBLISHER_ENABLED"].Group != "artifact-vault" {
+		t.Fatalf("unexpected group: %+v", byKey["FAV_PUBLISHER_ENABLED"])
+	}
+	if byKey["MULTI_INTENT_PLAN_TIER"].Value != "shadow" {
+		t.Fatalf("expected injected plan tier, got %+v", byKey["MULTI_INTENT_PLAN_TIER"])
+	}
+	if byKey["INTENT_V2_SHADOW"].Value != "false" {
+		t.Fatalf("expected catalog fallback false, got %+v", byKey["INTENT_V2_SHADOW"])
+	}
+	for _, key := range []string{"AGENT_BACKEND", "AUTH_REGISTRATION_ENABLED", "FAV_DEGRADED_READ", "SEMANTIC_SUMMARY_SHADOW", "PI_CHANGE_REPORT_NARRATIVE"} {
+		if _, ok := byKey[key]; !ok {
+			t.Fatalf("catalog must cover %s", key)
+		}
+	}
+}
diff --git a/internal/sysadmin/settings.go b/internal/sysadmin/settings.go
new file mode 100644
index 00000000..cd22e093
--- /dev/null
+++ b/internal/sysadmin/settings.go
@@ -0,0 +1,198 @@
+package sysadmin
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"os"
+	"strconv"
+	"time"
+)
+
+// 设置读写错误；HTTP 适配层据此映射状态码。
+var (
+	ErrUnknownSetting      = errors.New("sysadmin: unknown setting key")
+	ErrSettingReadOnly     = errors.New("sysadmin: setting is read-only")
+	ErrInvalidSettingValue = errors.New("sysadmin: invalid setting value")
+	ErrStoreUnavailable    = errors.New("sysadmin: settings store unavailable")
+)
+
+// 设置值类型。
+const (
+	SettingTypeString = "string"
+	SettingTypeBool   = "bool"
+	SettingTypeNumber = "number"
+)
+
+// SettingSpec 白名单注册表条目；只有登记在册的 key 才可读写。
+type SettingSpec struct {
+	Key             string
+	Label           string
+	Group           string
+	Type            string
+	Default         any
+	Writable        bool
+	RequiresRestart bool
+	EnvVar          string // 可选 env 中间层：DB > env > default
+	Description     string
+}
+
+// Setting 设置视图，字段对齐前端 camelCase 契约。
+type Setting struct {
+	Key             string     `json:"key"`
+	Label           string     `json:"label"`
+	Group           string     `json:"group"`
+	Type            string     `json:"type"`
+	Value           any        `json:"value"`
+	Default         any        `json:"default"`
+	Writable        bool       `json:"writable"`
+	RequiresRestart bool       `json:"requiresRestart"`
+	Description     string     `json:"description"`
+	UpdatedAt       *time.Time `json:"updatedAt,omitempty"`
+	UpdatedBy       *int64     `json:"updatedBy,omitempty"`
+}
+
+// defaultSettingSpecs 一期白名单：先做机制，键空间可后续扩展。
+func defaultSettingSpecs() []SettingSpec {
+	return []SettingSpec{
+		{Key: "ui.maintenance_notice", Label: "维护公告", Group: "ui", Type: SettingTypeString, Default: "", Writable: true, RequiresRestart: false, Description: "全站维护公告横幅文案；空字符串表示关闭"},
+		{Key: "ui.read_only_mode", Label: "只读模式提示", Group: "ui", Type: SettingTypeBool, Default: false, Writable: true, RequiresRestart: false, Description: "开启后前端进入只读提示模式，阻断写操作入口"},
+		{Key: "chat.default_session_role", Label: "新会话默认职责", Group: "chat", Type: SettingTypeString, Default: "engineer", Writable: true, RequiresRestart: false, Description: "未显式指定职责时新会话的默认角色"},
+		{Key: "tasks.default_auto_repair", Label: "任务默认自动修复", Group: "tasks", Type: SettingTypeBool, Default: false, Writable: true, RequiresRestart: false, Description: "独立任务运行未传 auto_repair 时的默认值"},
+		{Key: "kb.default_search_limit", Label: "KB 检索默认条数", Group: "kb", Type: SettingTypeNumber, Default: 8.0, Writable: true, RequiresRestart: false, Description: "知识库检索未指定 limit 时的默认返回条数"},
+		{Key: "notifications.stage_advance_reminder", Label: "阶段推进提醒总开关", Group: "notification", Type: SettingTypeBool, Default: true, Writable: true, RequiresRestart: false, Description: "阶段就绪 24h 提醒的总开关（一期先落机制）"},
+	}
+}
+
+func (s *Service) findSpec(key string) (SettingSpec, bool) {
+	for _, spec := range s.specs {
+		if spec.Key == key {
+			return spec, true
+		}
+	}
+	return SettingSpec{}, false
+}
+
+// ListSettings 返回白名单全部设置；读优先级 DB > env > default。
+func (s *Service) ListSettings(ctx context.Context) ([]Setting, error) {
+	out := make([]Setting, 0, len(s.specs))
+	for _, spec := range s.specs {
+		setting, err := s.resolve(ctx, spec)
+		if err != nil {
+			return nil, err
+		}
+		out = append(out, setting)
+	}
+	return out, nil
+}
+
+// UpdateSetting 校验并写入白名单设置，返回更新后的视图。
+func (s *Service) UpdateSetting(ctx context.Context, key string, raw json.RawMessage, updatedBy int64) (Setting, error) {
+	spec, ok := s.findSpec(key)
+	if !ok {
+		return Setting{}, ErrUnknownSetting
+	}
+	if !spec.Writable {
+		return Setting{}, ErrSettingReadOnly
+	}
+	if err := validateSettingValue(spec.Type, raw); err != nil {
+		return Setting{}, err
+	}
+	if s.store == nil {
+		return Setting{}, ErrStoreUnavailable
+	}
+	if _, err := s.store.Upsert(ctx, key, raw, updatedBy); err != nil {
+		return Setting{}, err
+	}
+	return s.resolve(ctx, spec)
+}
+
+// resolve 按 DB > env > default 解析单个设置的当前值。
+func (s *Service) resolve(ctx context.Context, spec SettingSpec) (Setting, error) {
+	setting := Setting{
+		Key:             spec.Key,
+		Label:           spec.Label,
+		Group:           spec.Group,
+		Type:            spec.Type,
+		Value:           spec.Default,
+		Default:         spec.Default,
+		Writable:        spec.Writable,
+		RequiresRestart: spec.RequiresRestart,
+		Description:     spec.Description,
+	}
+	if spec.EnvVar != "" {
+		if raw, set := os.LookupEnv(spec.EnvVar); set {
+			if v, err := parseSettingValue(spec.Type, raw); err == nil {
+				setting.Value = v
+			}
+		}
+	}
+	if s.store == nil {
+		return setting, nil
+	}
+	raw, updatedBy, updatedAt, err := s.store.Get(ctx, spec.Key)
+	if err != nil {
+		if errors.Is(err, ErrSettingNotFound) {
+			return setting, nil
+		}
+		return Setting{}, err
+	}
+	var value any
+	if err := json.Unmarshal(raw, &value); err != nil {
+		return Setting{}, fmt.Errorf("sysadmin: decode stored value for %s: %w", spec.Key, err)
+	}
+	setting.Value = value
+	setting.UpdatedBy = updatedBy
+	setting.UpdatedAt = updatedAt
+	return setting, nil
+}
+
+// validateSettingValue 按声明类型校验 JSON 值。
+func validateSettingValue(valueType string, raw json.RawMessage) error {
+	if len(raw) == 0 {
+		return ErrInvalidSettingValue
+	}
+	switch valueType {
+	case SettingTypeString:
+		var v string
+		if err := json.Unmarshal(raw, &v); err != nil {
+			return ErrInvalidSettingValue
+		}
+	case SettingTypeBool:
+		var v bool
+		if err := json.Unmarshal(raw, &v); err != nil {
+			return ErrInvalidSettingValue
+		}
+	case SettingTypeNumber:
+		var v float64
+		if err := json.Unmarshal(raw, &v); err != nil {
+			return ErrInvalidSettingValue
+		}
+	default:
+		return ErrInvalidSettingValue
+	}
+	return nil
+}
+
+// parseSettingValue 将 env 字符串按类型解析。
+func parseSettingValue(valueType, raw string) (any, error) {
+	switch valueType {
+	case SettingTypeString:
+		return raw, nil
+	case SettingTypeBool:
+		v, err := strconv.ParseBool(raw)
+		if err != nil {
+			return nil, err
+		}
+		return v, nil
+	case SettingTypeNumber:
+		v, err := strconv.ParseFloat(raw, 64)
+		if err != nil {
+			return nil, err
+		}
+		return v, nil
+	default:
+		return nil, ErrInvalidSettingValue
+	}
+}
diff --git a/internal/sysadmin/settings_test.go b/internal/sysadmin/settings_test.go
new file mode 100644
index 00000000..e26a6a95
--- /dev/null
+++ b/internal/sysadmin/settings_test.go
@@ -0,0 +1,210 @@
+package sysadmin
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"sync"
+	"testing"
+	"time"
+)
+
+// memStore 进程内 SettingsStore，用于读优先级与写路径测试。
+type memStore struct {
+	mu    sync.Mutex
+	items map[string]memEntry
+}
+
+type memEntry struct {
+	value     json.RawMessage
+	updatedBy *int64
+	updatedAt time.Time
+}
+
+func newMemStore() *memStore {
+	return &memStore{items: map[string]memEntry{}}
+}
+
+func (m *memStore) Get(_ context.Context, key string) (json.RawMessage, *int64, *time.Time, error) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	entry, ok := m.items[key]
+	if !ok {
+		return nil, nil, nil, ErrSettingNotFound
+	}
+	at := entry.updatedAt
+	return entry.value, entry.updatedBy, &at, nil
+}
+
+func (m *memStore) Upsert(_ context.Context, key string, value json.RawMessage, updatedBy int64) (time.Time, error) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	at := time.Now()
+	m.items[key] = memEntry{value: append(json.RawMessage(nil), value...), updatedBy: &updatedBy, updatedAt: at}
+	return at, nil
+}
+
+func findSetting(t *testing.T, settings []Setting, key string) Setting {
+	t.Helper()
+	for _, s := range settings {
+		if s.Key == key {
+			return s
+		}
+	}
+	t.Fatalf("setting %s not found", key)
+	return Setting{}
+}
+
+func TestListSettings_FallsBackToDefaultWithoutStore(t *testing.T) {
+	svc := NewService(nil, Options{})
+	settings, err := svc.ListSettings(context.Background())
+	if err != nil {
+		t.Fatalf("ListSettings: %v", err)
+	}
+	if len(settings) != len(defaultSettingSpecs()) {
+		t.Fatalf("expected %d settings, got %d", len(defaultSettingSpecs()), len(settings))
+	}
+	notice := findSetting(t, settings, "ui.maintenance_notice")
+	if notice.Value != "" || notice.Default != "" {
+		t.Fatalf("expected empty default notice, got value=%v default=%v", notice.Value, notice.Default)
+	}
+	if notice.UpdatedAt != nil || notice.UpdatedBy != nil {
+		t.Fatalf("default-resolved setting must not carry update metadata: %+v", notice)
+	}
+	reminder := findSetting(t, settings, "notifications.stage_advance_reminder")
+	if reminder.Value != true {
+		t.Fatalf("expected bool default true, got %v", reminder.Value)
+	}
+}
+
+func TestListSettings_DBOverridesDefault(t *testing.T) {
+	store := newMemStore()
+	if _, err := store.Upsert(context.Background(), "ui.maintenance_notice", json.RawMessage(`"停机维护中"`), 7); err != nil {
+		t.Fatalf("seed store: %v", err)
+	}
+	svc := NewService(nil, Options{Store: store})
+	settings, err := svc.ListSettings(context.Background())
+	if err != nil {
+		t.Fatalf("ListSettings: %v", err)
+	}
+	notice := findSetting(t, settings, "ui.maintenance_notice")
+	if notice.Value != "停机维护中" {
+		t.Fatalf("expected DB value, got %v", notice.Value)
+	}
+	if notice.UpdatedBy == nil || *notice.UpdatedBy != 7 {
+		t.Fatalf("expected updatedBy=7, got %+v", notice.UpdatedBy)
+	}
+	if notice.UpdatedAt == nil {
+		t.Fatal("expected updatedAt from DB row")
+	}
+	// 未写入的 key 仍回退 default
+	limit := findSetting(t, settings, "kb.default_search_limit")
+	if limit.Value != 8.0 {
+		t.Fatalf("expected default 8, got %v", limit.Value)
+	}
+}
+
+func TestListSettings_EnvLayerBetweenDBAndDefault(t *testing.T) {
+	t.Setenv("SYSADMIN_TEST_FLAG", "true")
+	specs := []SettingSpec{
+		{Key: "test.env_flag", Label: "env 中间层", Group: "test", Type: SettingTypeBool, Default: false, Writable: true, EnvVar: "SYSADMIN_TEST_FLAG"},
+	}
+	svc := &Service{specs: specs}
+	settings, err := svc.ListSettings(context.Background())
+	if err != nil {
+		t.Fatalf("ListSettings: %v", err)
+	}
+	if settings[0].Value != true {
+		t.Fatalf("expected env override true, got %v", settings[0].Value)
+	}
+
+	// DB 优先于 env
+	store := newMemStore()
+	if _, err := store.Upsert(context.Background(), "test.env_flag", json.RawMessage(`false`), 1); err != nil {
+		t.Fatalf("seed store: %v", err)
+	}
+	svc = &Service{specs: specs, store: store}
+	settings, err = svc.ListSettings(context.Background())
+	if err != nil {
+		t.Fatalf("ListSettings: %v", err)
+	}
+	if settings[0].Value != false {
+		t.Fatalf("expected DB to win over env, got %v", settings[0].Value)
+	}
+}
+
+func TestUpdateSetting_UnknownKey(t *testing.T) {
+	svc := NewService(nil, Options{Store: newMemStore()})
+	_, err := svc.UpdateSetting(context.Background(), "no.such.key", json.RawMessage(`"x"`), 1)
+	if !errors.Is(err, ErrUnknownSetting) {
+		t.Fatalf("expected ErrUnknownSetting, got %v", err)
+	}
+}
+
+func TestUpdateSetting_ReadOnlyRejected(t *testing.T) {
+	specs := []SettingSpec{
+		{Key: "test.locked", Label: "只读项", Group: "test", Type: SettingTypeString, Default: "a", Writable: false},
+	}
+	svc := &Service{specs: specs, store: newMemStore()}
+	_, err := svc.UpdateSetting(context.Background(), "test.locked", json.RawMessage(`"b"`), 1)
+	if !errors.Is(err, ErrSettingReadOnly) {
+		t.Fatalf("expected ErrSettingReadOnly, got %v", err)
+	}
+}
+
+func TestUpdateSetting_TypeValidation(t *testing.T) {
+	svc := NewService(nil, Options{Store: newMemStore()})
+	cases := []struct {
+		key string
+		raw string
+	}{
+		{"ui.maintenance_notice", `123`},     // string 声明收到 number
+		{"ui.read_only_mode", `"true"`},      // bool 声明收到 string
+		{"kb.default_search_limit", `"8"`},   // number 声明收到 string
+		{"ui.maintenance_notice", ``},        // 空 body value
+		{"ui.maintenance_notice", `{"a":1}`}, // string 声明收到 object
+	}
+	for _, tc := range cases {
+		_, err := svc.UpdateSetting(context.Background(), tc.key, json.RawMessage(tc.raw), 1)
+		if !errors.Is(err, ErrInvalidSettingValue) {
+			t.Fatalf("%s <- %s: expected ErrInvalidSettingValue, got %v", tc.key, tc.raw, err)
+		}
+	}
+}
+
+func TestUpdateSetting_WithoutStore(t *testing.T) {
+	svc := NewService(nil, Options{})
+	_, err := svc.UpdateSetting(context.Background(), "ui.maintenance_notice", json.RawMessage(`"x"`), 1)
+	if !errors.Is(err, ErrStoreUnavailable) {
+		t.Fatalf("expected ErrStoreUnavailable, got %v", err)
+	}
+}
+
+func TestUpdateSetting_PersistsAndReturnsUpdatedView(t *testing.T) {
+	svc := NewService(nil, Options{Store: newMemStore()})
+	setting, err := svc.UpdateSetting(context.Background(), "kb.default_search_limit", json.RawMessage(`12`), 42)
+	if err != nil {
+		t.Fatalf("UpdateSetting: %v", err)
+	}
+	if setting.Value != 12.0 {
+		t.Fatalf("expected 12, got %v", setting.Value)
+	}
+	if setting.Default != 8.0 {
+		t.Fatalf("default must stay 8, got %v", setting.Default)
+	}
+	if setting.UpdatedBy == nil || *setting.UpdatedBy != 42 {
+		t.Fatalf("expected updatedBy=42, got %+v", setting.UpdatedBy)
+	}
+	if setting.UpdatedAt == nil {
+		t.Fatal("expected updatedAt after write")
+	}
+
+	// 覆盖写：值更新、审计字段跟随
+	setting, err = svc.UpdateSetting(context.Background(), "kb.default_search_limit", json.RawMessage(`20`), 43)
+	if err != nil {
+		t.Fatalf("second UpdateSetting: %v", err)
+	}
+	if setting.Value != 20.0 || setting.UpdatedBy == nil || *setting.UpdatedBy != 43 {
+		t.Fatalf("expected overwrite (20, by 43), got (%v, %+v)", setting.Value, setting.UpdatedBy)
+	}
+}
diff --git a/internal/sysadmin/store.go b/internal/sysadmin/store.go
new file mode 100644
index 00000000..9d30f6ce
--- /dev/null
+++ b/internal/sysadmin/store.go
@@ -0,0 +1,56 @@
+package sysadmin
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"time"
+
+	"github.com/jackc/pgx/v5"
+	"github.com/jackc/pgx/v5/pgxpool"
+)
+
+// ErrSettingNotFound DB 中无该 key 的行（回退 env/default）。
+var ErrSettingNotFound = errors.New("sysadmin: setting not found")
+
+// SettingsStore system_settings 表读写（表 owner 为 sysadmin）。
+type SettingsStore interface {
+	Get(ctx context.Context, key string) (value json.RawMessage, updatedBy *int64, updatedAt *time.Time, err error)
+	Upsert(ctx context.Context, key string, value json.RawMessage, updatedBy int64) (time.Time, error)
+}
+
+type pgSettingsStore struct {
+	pool *pgxpool.Pool
+}
+
+func newPGSettingsStore(pool *pgxpool.Pool) SettingsStore {
+	return &pgSettingsStore{pool: pool}
+}
+
+func (s *pgSettingsStore) Get(ctx context.Context, key string) (json.RawMessage, *int64, *time.Time, error) {
+	var raw []byte
+	var updatedBy *int64
+	var updatedAt time.Time
+	err := s.pool.QueryRow(ctx, `
+		SELECT value, updated_by, updated_at FROM system_settings WHERE key = $1
+	`, key).Scan(&raw, &updatedBy, &updatedAt)
+	if err != nil {
+		if errors.Is(err, pgx.ErrNoRows) {
+			return nil, nil, nil, ErrSettingNotFound
+		}
+		return nil, nil, nil, err
+	}
+	return json.RawMessage(raw), updatedBy, &updatedAt, nil
+}
+
+func (s *pgSettingsStore) Upsert(ctx context.Context, key string, value json.RawMessage, updatedBy int64) (time.Time, error) {
+	var updatedAt time.Time
+	err := s.pool.QueryRow(ctx, `
+		INSERT INTO system_settings (key, value, updated_by, updated_at)
+		VALUES ($1, $2, $3, now())
+		ON CONFLICT (key) DO UPDATE
+		SET value = EXCLUDED.value, updated_by = EXCLUDED.updated_by, updated_at = now()
+		RETURNING updated_at
+	`, key, []byte(value), updatedBy).Scan(&updatedAt)
+	return updatedAt, err
+}
diff --git a/internal/sysadmin/store_pg_test.go b/internal/sysadmin/store_pg_test.go
new file mode 100644
index 00000000..e4c02df5
--- /dev/null
+++ b/internal/sysadmin/store_pg_test.go
@@ -0,0 +1,57 @@
+package sysadmin
+
+import (
+	"context"
+	"encoding/json"
+	"testing"
+
+	"chat-agent-system/internal/db"
+
+	"github.com/jackc/pgx/v5/pgxpool"
+)
+
+func TestPGSettingsStore_RoundTrip(t *testing.T) {
+	dsn := db.SkipIfNoTestDatabaseURL(t)
+	db.RefuseSharedEnvDSN(t, dsn)
+	ctx := context.Background()
+	pool, err := pgxpool.New(ctx, dsn)
+	if err != nil {
+		t.Fatalf("connect: %v", err)
+	}
+	defer pool.Close()
+	if err := db.RunMigrationsOnceForTest(ctx, pool, dsn); err != nil {
+		t.Fatalf("migrate: %v", err)
+	}
+
+	store := newPGSettingsStore(pool)
+	key := "ui.maintenance_notice"
+	if _, _, _, err := store.Get(ctx, key); err != ErrSettingNotFound {
+		t.Fatalf("expected ErrSettingNotFound, got %v", err)
+	}
+	if _, err := store.Upsert(ctx, key, json.RawMessage(`"维护中"`), 1); err != nil {
+		t.Fatalf("upsert: %v", err)
+	}
+	raw, updatedBy, updatedAt, err := store.Get(ctx, key)
+	if err != nil {
+		t.Fatalf("get: %v", err)
+	}
+	if string(raw) != `"维护中"` {
+		t.Fatalf("unexpected value: %s", raw)
+	}
+	if updatedBy == nil || *updatedBy != 1 {
+		t.Fatalf("expected updatedBy=1, got %+v", updatedBy)
+	}
+	if updatedAt == nil {
+		t.Fatal("expected updatedAt")
+	}
+	if _, err := store.Upsert(ctx, key, json.RawMessage(`"恢复"`), 2); err != nil {
+		t.Fatalf("second upsert: %v", err)
+	}
+	raw, updatedBy, _, err = store.Get(ctx, key)
+	if err != nil {
+		t.Fatalf("get after overwrite: %v", err)
+	}
+	if string(raw) != `"恢复"` || updatedBy == nil || *updatedBy != 2 {
+		t.Fatalf("expected overwrite, got %s by %+v", raw, updatedBy)
+	}
+}