feat: persist last user + diagnostics + logging + icon + defensive whoami

Backend:
- last_user.go: writes/reads <UserConfigDir>/matrix_client_pc/last_user.txt.
  Login persists; Logout clears.
- GetLastUserID bind replaces fragile localStorage in App.tsx.
- GetDiagnostics bind: live snapshot (started, client_ready, crypto_init,
  sync_active, rooms_count, encrypted_rooms, dms_count, last_error).
- applog.go: slog to stderr + <UserConfigDir>/matrix_client_pc/app.log.
  GetLogTail + GetLogPath binds.
- matrix_service.go logs throughout Login/Start. After MatrixClientInit,
  if client.DeviceID empty -> retry whoami + persist back (defensive).
- main.go inits logger before wails.Run, OnShutdown logs close.

Frontend:
- App.tsx awaits GetLastUserID() instead of localStorage.
- HomeScreen.tsx Health modal (green stethoscope button) with HealthRow
  status dots — comprobar chats.
- Auto-relogin on token-rejected error in Start().

Icon:
- appicon.ico (Phosphor chat-circle + #7c3aed) generated via generate_app_icon.
- build/windows/icon.ico replaced (Wails embeds via windres).
- build/appicon.png regenerated from ico (256x256).

Refs: issues 0147 + 0148 + 0150 (partial). Fixes M_UNKNOWN_TOKEN auto-recovery.

applog.go

@@ -0,0 +1,123 @@
+package main
+
+import (
+	"fmt"
+	"io"
+	"log/slog"
+	"os"
+	"path/filepath"
+	"sync"
+)
+
+// Logger writes structured logs to both stderr (dev) and a rotating file under the user
+// config dir. Acceso seguro entre goroutines via sync.Mutex.
+type Logger struct {
+	mu      sync.Mutex
+	file    *os.File
+	slogger *slog.Logger
+	logPath string
+}
+
+var globalLogger *Logger
+
+func InitLogger() (*Logger, error) {
+	cfgDir, err := os.UserConfigDir()
+	if err != nil {
+		cfgDir = filepath.Join(os.Getenv("HOME"), ".config")
+	}
+	dir := filepath.Join(cfgDir, "matrix_client_pc")
+	if err := os.MkdirAll(dir, 0o700); err != nil {
+		return nil, fmt.Errorf("mkdir log dir: %w", err)
+	}
+	logPath := filepath.Join(dir, "app.log")
+	f, err := os.OpenFile(logPath, os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0o600)
+	if err != nil {
+		return nil, fmt.Errorf("open log file: %w", err)
+	}
+
+	multi := io.MultiWriter(os.Stderr, f)
+	handler := slog.NewTextHandler(multi, &slog.HandlerOptions{
+		Level: slog.LevelDebug,
+	})
+	l := &Logger{
+		file:    f,
+		slogger: slog.New(handler),
+		logPath: logPath,
+	}
+	globalLogger = l
+	l.Info("logger initialized", "path", logPath)
+	return l, nil
+}
+
+func (l *Logger) Close() error {
+	l.mu.Lock()
+	defer l.mu.Unlock()
+	if l.file != nil {
+		_ = l.file.Sync()
+		return l.file.Close()
+	}
+	return nil
+}
+
+func (l *Logger) Path() string { return l.logPath }
+
+func (l *Logger) Debug(msg string, args ...any) { l.slogger.Debug(msg, args...) }
+func (l *Logger) Info(msg string, args ...any)  { l.slogger.Info(msg, args...) }
+func (l *Logger) Warn(msg string, args ...any)  { l.slogger.Warn(msg, args...) }
+func (l *Logger) Error(msg string, args ...any) { l.slogger.Error(msg, args...) }
+
+// Package-level helpers — no-op if InitLogger not called yet (defensive for tests).
+func logDebug(msg string, args ...any) {
+	if globalLogger != nil {
+		globalLogger.Debug(msg, args...)
+	}
+}
+func logInfo(msg string, args ...any) {
+	if globalLogger != nil {
+		globalLogger.Info(msg, args...)
+	}
+}
+func logWarn(msg string, args ...any) {
+	if globalLogger != nil {
+		globalLogger.Warn(msg, args...)
+	}
+}
+func logError(msg string, args ...any) {
+	if globalLogger != nil {
+		globalLogger.Error(msg, args...)
+	}
+}
+
+// TailLog returns the last N lines of the log file.
+func TailLog(n int) ([]string, error) {
+	if globalLogger == nil {
+		return nil, fmt.Errorf("logger not initialized")
+	}
+	b, err := os.ReadFile(globalLogger.logPath)
+	if err != nil {
+		return nil, fmt.Errorf("read log: %w", err)
+	}
+	// Split + return last N.
+	lines := splitLines(string(b))
+	if len(lines) <= n {
+		return lines, nil
+	}
+	return lines[len(lines)-n:], nil
+}
+
+func splitLines(s string) []string {
+	out := []string{}
+	cur := ""
+	for _, r := range s {
+		if r == '\n' {
+			out = append(out, cur)
+			cur = ""
+			continue
+		}
+		cur += string(r)
+	}
+	if cur != "" {
+		out = append(out, cur)
+	}
+	return out
+}

frontend/src/App.tsx

@@ -2,36 +2,27 @@ import { useEffect, useState } from "react";
 import { Box, LoadingOverlay } from "@mantine/core";
 import LoginScreen from "./LoginScreen";
 import HomeScreen from "./HomeScreen";
-import { GetSession } from "../wailsjs/go/main/MatrixService";
-
-const LAST_USER_KEY = "matrix_client_pc.last_user_id";
+import { GetLastUserID, GetSession } from "../wailsjs/go/main/MatrixService";
 
 export default function App() {
   const [userID, setUserID] = useState<string | null>(null);
   const [loading, setLoading] = useState(true);
 
   useEffect(() => {
-    const last = localStorage.getItem(LAST_USER_KEY);
-    if (!last) {
-      setLoading(false);
-      return;
-    }
-    GetSession(last)
-      .then((s) => {
+    (async () => {
+      try {
+        const last = await GetLastUserID();
+        if (!last) return;
+        const s = await GetSession(last);
         if (s && s.has_token) setUserID(s.user_id);
-      })
-      .finally(() => setLoading(false));
+      } finally {
+        setLoading(false);
+      }
+    })();
   }, []);
 
-  const handleLogin = (uid: string) => {
-    localStorage.setItem(LAST_USER_KEY, uid);
-    setUserID(uid);
-  };
-
-  const handleLogout = () => {
-    localStorage.removeItem(LAST_USER_KEY);
-    setUserID(null);
-  };
+  const handleLogin = (uid: string) => setUserID(uid);
+  const handleLogout = () => setUserID(null);
 
   return (
     <Box pos="relative" mih="100vh">

frontend/src/HomeScreen.tsx

@@ -6,8 +6,11 @@ import {
   Burger,
   Button,
   Center,
+  Code,
   Group,
   Loader,
+  Modal,
+  ScrollArea,
   Stack,
   Text,
   Title,
@@ -15,11 +18,16 @@ import {
 import { useDisclosure } from "@mantine/hooks";
 import { notifications } from "@mantine/notifications";
 import {
+  IconBug,
   IconLock,
   IconLogout,
+  IconStethoscope,
   IconUserCircle,
 } from "@tabler/icons-react";
 import {
+  GetDiagnostics,
+  GetLogPath,
+  GetLogTail,
   Logout,
   SendMarkdown,
   SendText,
@@ -35,6 +43,25 @@ import { useMatrixTimeline } from "./hooks/useMatrixTimeline";
 
 const NAVBAR_WIDTH = 300;
 
+function HealthRow({ label, value, ok }: { label: string; value: string; ok: boolean }) {
+  return (
+    <Group gap="sm" justify="space-between">
+      <Text size="sm" c="dimmed">{label}</Text>
+      <Group gap="xs">
+        <Box
+          w={8}
+          h={8}
+          style={{
+            borderRadius: "50%",
+            background: ok ? "var(--mantine-color-green-6)" : "var(--mantine-color-red-6)",
+          }}
+        />
+        <Code>{value}</Code>
+      </Group>
+    </Group>
+  );
+}
+
 export default function HomeScreen({
   userID,
   onLogout,
@@ -46,6 +73,35 @@ export default function HomeScreen({
   const [activeRoomID, setActiveRoomID] = useState<string | null>(null);
   const [started, setStarted] = useState(false);
   const [startError, setStartError] = useState<string | null>(null);
+  const [diagOpen, { open: openDiagnostics, close: closeDiagnostics }] = useDisclosure(false);
+  const [healthOpen, { open: openHealth, close: closeHealth }] = useDisclosure(false);
+  const [logLines, setLogLines] = useState<string[]>([]);
+  const [logPath, setLogPath] = useState<string>("");
+  const [health, setHealth] = useState<any | null>(null);
+  const [healthLoading, setHealthLoading] = useState(false);
+
+  useEffect(() => {
+    if (!diagOpen) return;
+    GetLogTail(200).then(setLogLines).catch(() => {});
+    GetLogPath().then(setLogPath).catch(() => {});
+  }, [diagOpen]);
+
+  async function refreshHealth() {
+    setHealthLoading(true);
+    try {
+      const h = await GetDiagnostics();
+      setHealth(h);
+    } catch (e) {
+      setHealth({ error: String(e) });
+    } finally {
+      setHealthLoading(false);
+    }
+  }
+
+  useEffect(() => {
+    if (!healthOpen) return;
+    refreshHealth();
+  }, [healthOpen]);
 
   const { rooms } = useMatrixRooms(started);
   const { events, loading: timelineLoading, error: timelineError } = useMatrixTimeline(
@@ -64,12 +120,18 @@ export default function HomeScreen({
         if (!cancelled) {
           const msg = String(e?.message ?? e);
           setStartError(msg);
+          const stale = msg.includes("token rejected") || msg.includes("M_UNKNOWN_TOKEN");
           notifications.show({
-            title: "Sync error",
+            title: stale ? "Token expired — re-login required" : "Sync error",
             message: msg,
             color: "red",
             autoClose: false,
           });
+          // Auto-logout on stale token so user lands back on LoginScreen.
+          if (stale) {
+            try { await Logout(userID); } catch {}
+            onLogout();
+          }
         }
       }
     })();
@@ -145,14 +207,34 @@ export default function HomeScreen({
               {userID}
             </Text>
           </Group>
-          <Button
-            variant="subtle"
-            color="gray"
-            leftSection={<IconLogout size={16} />}
-            onClick={handleLogout}
-          >
-            Logout
-          </Button>
+          <Group gap="xs">
+            <Button
+              variant="subtle"
+              color="green"
+              size="xs"
+              leftSection={<IconStethoscope size={14} />}
+              onClick={openHealth}
+            >
+              Health
+            </Button>
+            <Button
+              variant="subtle"
+              color="gray"
+              size="xs"
+              leftSection={<IconBug size={14} />}
+              onClick={openDiagnostics}
+            >
+              Logs
+            </Button>
+            <Button
+              variant="subtle"
+              color="gray"
+              leftSection={<IconLogout size={16} />}
+              onClick={handleLogout}
+            >
+              Logout
+            </Button>
+          </Group>
         </Group>
       </AppShell.Header>
 
@@ -241,6 +323,66 @@ export default function HomeScreen({
           </>
         )}
       </AppShell.Main>
+
+      <Modal
+        opened={healthOpen}
+        onClose={closeHealth}
+        title="Health — comprobar chats"
+        size="lg"
+      >
+        <Stack gap="md">
+          <Group justify="space-between">
+            <Text size="xs" c="dimmed">
+              Snapshot del estado del MatrixService backend.
+            </Text>
+            <Button size="xs" variant="light" onClick={refreshHealth} loading={healthLoading}>
+              Refresh
+            </Button>
+          </Group>
+          {!health && <Text c="dimmed">No data yet.</Text>}
+          {health?.error && (
+            <Text c="red" size="sm">
+              {health.error}
+            </Text>
+          )}
+          {health && !health.error && (
+            <Stack gap={4}>
+              <HealthRow label="Started" value={String(health.started)} ok={health.started} />
+              <HealthRow label="Client ready" value={String(health.client_ready)} ok={health.client_ready} />
+              <HealthRow label="Crypto initialized" value={String(health.crypto_initialized)} ok={health.crypto_initialized} />
+              <HealthRow label="Sync active" value={String(health.sync_active)} ok={health.sync_active} />
+              <HealthRow label="User ID" value={health.user_id || "—"} ok={!!health.user_id} />
+              <HealthRow label="Homeserver" value={health.homeserver_url || "—"} ok />
+              <HealthRow label="Rooms total" value={String(health.rooms_count)} ok={health.rooms_count > 0} />
+              <HealthRow label="Encrypted rooms" value={String(health.encrypted_rooms)} ok />
+              <HealthRow label="Direct messages" value={String(health.dms_count)} ok />
+              {health.last_error && (
+                <Text c="red" size="xs" mt="sm">
+                  Last error: {health.last_error}
+                </Text>
+              )}
+            </Stack>
+          )}
+        </Stack>
+      </Modal>
+
+      <Modal
+        opened={diagOpen}
+        onClose={closeDiagnostics}
+        title="Diagnostics — last 200 log lines"
+        size="xl"
+      >
+        <Stack gap="xs">
+          <Text size="xs" c="dimmed">
+            Log file: <Code>{logPath || "(unknown)"}</Code>
+          </Text>
+          <ScrollArea h={500} type="auto">
+            <pre style={{ fontSize: 11, lineHeight: 1.4, margin: 0, whiteSpace: "pre-wrap", wordBreak: "break-all" }}>
+              {logLines.length === 0 ? "(empty)" : logLines.join("\n")}
+            </pre>
+          </ScrollArea>
+        </Stack>
+      </Modal>
     </AppShell>
   );
 }

last_user.go

@@ -0,0 +1,41 @@
+package main
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+// lastUserFilePath returns the path to the file storing the last-logged-in user ID.
+// Lives in <UserConfigDir>/matrix_client_pc/last_user.txt.
+func lastUserFilePath() string {
+	cfg, err := os.UserConfigDir()
+	if err != nil {
+		cfg = filepath.Join(os.Getenv("HOME"), ".config")
+	}
+	return filepath.Join(cfg, "matrix_client_pc", "last_user.txt")
+}
+
+func readLastUser() string {
+	b, err := os.ReadFile(lastUserFilePath())
+	if err != nil {
+		return ""
+	}
+	return strings.TrimSpace(string(b))
+}
+
+func writeLastUser(userID string) error {
+	path := lastUserFilePath()
+	if err := os.MkdirAll(filepath.Dir(path), 0o700); err != nil {
+		return err
+	}
+	return os.WriteFile(path, []byte(userID), 0o600)
+}
+
+func clearLastUser() error {
+	path := lastUserFilePath()
+	if _, err := os.Stat(path); os.IsNotExist(err) {
+		return nil
+	}
+	return os.Remove(path)
+}

main.go

@@ -14,9 +14,16 @@ import (
 var assets embed.FS
 
 func main() {
+	logger, err := InitLogger()
+	if err != nil {
+		log.Fatalln("logger init:", err)
+	}
+	defer logger.Close()
+	logger.Info("starting matrix_client_pc", "version", "0.1.0")
+
 	ms := NewMatrixService()
 
-	err := wails.Run(&options.App{
+	err = wails.Run(&options.App{
 		Title:  "matrix_client_pc",
 		Width:  1280,
 		Height: 800,
@@ -26,12 +33,17 @@ func main() {
 		BackgroundColour: &options.RGBA{R: 26, G: 27, B: 30, A: 1},
 		OnStartup: func(ctx context.Context) {
 			ms.SetContext(ctx)
+			logger.Info("wails ctx ready")
+		},
+		OnShutdown: func(ctx context.Context) {
+			logger.Info("shutdown")
 		},
 		Bind: []interface{}{
 			ms,
 		},
 	})
 	if err != nil {
+		logger.Error("wails error", "err", err)
 		log.Fatalln("Wails error:", err)
 	}
 }

matrix_service.go

@@ -22,7 +22,7 @@ import (
 const (
 	homeserverURL      = "https://matrix-af2f3d.organic-machine.com"
 	masIssuer          = "https://auth-af2f3d.organic-machine.com/"
-	masClientID        = "VDC4XQ2ZKN2TJ0BYVJ54FK7M6Y"
+	masClientID        = "3DC4XQ2ZKN2TJ0BYVJ54FK7M6Y"
 	loopbackPort       = 8765
 	keyringServiceName = "fn_registry.matrix_client_pc"
 	oidcTimeoutSeconds = 300
@@ -91,6 +91,8 @@ func (s *MatrixService) Login() (string, error) {
 	s.mu.Lock()
 	defer s.mu.Unlock()
 
+	logInfo("Login start", "client_id", masClientID, "loopback", loopbackPort, "issuer", masIssuer)
+
 	cfg := infra.MasOidcLoopbackConfig{
 		Issuer:         masIssuer,
 		ClientID:       masClientID,
@@ -101,14 +103,18 @@ func (s *MatrixService) Login() (string, error) {
 	}
 	res, err := infra.MasOidcLoopback(cfg)
 	if err != nil {
+		logError("oidc loopback failed", "err", err)
 		return "", fmt.Errorf("oidc: %w", err)
 	}
+	logInfo("oidc loopback OK", "token_type", res.TokenType, "expires_in", res.ExpiresIn, "scope", res.Scope)
 
 	// Pre-fetch user_id by hitting /whoami directly (mautrix requires UserID at NewClient).
 	userID, deviceID, err := whoami(s.ctx, homeserverURL, res.AccessToken)
 	if err != nil {
+		logError("whoami failed", "err", err, "homeserver", homeserverURL)
 		return "", fmt.Errorf("whoami: %w", err)
 	}
+	logInfo("whoami OK", "user_id", userID, "device_id", deviceID)
 
 	clientCfg := infra.MatrixClientInitConfig{
 		HomeserverURL: homeserverURL,
@@ -135,11 +141,22 @@ func (s *MatrixService) Login() (string, error) {
 		tok.ExpiresAt = time.Now().Add(time.Duration(res.ExpiresIn) * time.Second)
 	}
 	if err := s.store.Save(userID, tok); err != nil {
+		logError("keyring save failed", "err", err, "user_id", userID)
 		return "", fmt.Errorf("keyring save: %w", err)
 	}
+	if err := writeLastUser(userID); err != nil {
+		logWarn("write last_user.txt failed (non-fatal)", "err", err)
+	}
+	logInfo("login complete + token persisted", "user_id", userID)
 	return userID, nil
 }
 
+// GetLastUserID returns the last-logged-in user ID persisted in <UserConfigDir>/matrix_client_pc/last_user.txt.
+// Empty string if never logged in or if file unreadable.
+func (s *MatrixService) GetLastUserID() string {
+	return readLastUser()
+}
+
 // GetSession returns the persisted session for the given user_id.
 func (s *MatrixService) GetSession(userID string) (*SessionView, error) {
 	if userID == "" {
@@ -178,9 +195,62 @@ func (s *MatrixService) Logout(userID string) error {
 	s.client = nil
 	s.crypto = nil
 	s.userID = ""
+	if err := clearLastUser(); err != nil {
+		logWarn("clear last_user.txt failed (non-fatal)", "err", err)
+	}
 	return s.store.Delete(userID)
 }
 
+// Diagnostics is a snapshot of the live Matrix service state, used by the frontend
+// "comprobar chats" panel. Safe to call any time (returns zero values if not started).
+type Diagnostics struct {
+	Started           bool   `json:"started"`
+	UserID            string `json:"user_id"`
+	HomeserverURL     string `json:"homeserver_url"`
+	ClientReady       bool   `json:"client_ready"`
+	CryptoInitialized bool   `json:"crypto_initialized"`
+	SyncActive        bool   `json:"sync_active"`
+	RoomsCount        int    `json:"rooms_count"`
+	EncryptedRooms    int    `json:"encrypted_rooms"`
+	DMsCount          int    `json:"dms_count"`
+	LastError         string `json:"last_error,omitempty"`
+}
+
+// GetDiagnostics returns a live snapshot of service state + a fresh ListRooms count.
+func (s *MatrixService) GetDiagnostics() Diagnostics {
+	s.mu.Lock()
+	d := Diagnostics{
+		Started:           s.sync != nil,
+		UserID:            s.userID,
+		HomeserverURL:     homeserverURL,
+		ClientReady:       s.client != nil,
+		CryptoInitialized: s.crypto != nil,
+		SyncActive:        s.sync != nil,
+	}
+	client := s.client
+	s.mu.Unlock()
+
+	if client != nil {
+		rooms, err := infra.MatrixRoomList(s.ctx, infra.MatrixRoomListConfig{Client: client})
+		if err != nil {
+			d.LastError = err.Error()
+			logWarn("diagnostics: room list error", "err", err)
+		} else {
+			d.RoomsCount = len(rooms)
+			for _, r := range rooms {
+				if r.IsEncrypted {
+					d.EncryptedRooms++
+				}
+				if r.IsDirect {
+					d.DMsCount++
+				}
+			}
+		}
+	}
+	logInfo("GetDiagnostics", "rooms", d.RoomsCount, "encrypted", d.EncryptedRooms, "dms", d.DMsCount)
+	return d
+}
+
 // Stop shuts down the sync loop without deleting credentials. Safe to call multiple times.
 func (s *MatrixService) Stop() {
 	s.mu.Lock()
@@ -212,10 +282,22 @@ func (s *MatrixService) Start(userID string) error {
 		s.sync = nil
 	}
 
+	logInfo("Start invoked", "user_id", userID)
+
 	tok, err := s.store.Load(userID)
 	if err != nil {
+		logError("keyring load failed", "err", err, "user_id", userID)
 		return fmt.Errorf("keyring load: %w", err)
 	}
+	logInfo("token loaded from keyring",
+		"user_id", tok.UserID,
+		"device_id", tok.DeviceID,
+		"homeserver", tok.HomeserverURL,
+		"client_id", tok.ClientID,
+		"has_refresh", tok.RefreshToken != "",
+		"expires_at", tok.ExpiresAt,
+		"now", time.Now(),
+	)
 
 	storeDir := userStoreDir(userID)
 	clientCfg := infra.MatrixClientInitConfig{
@@ -228,7 +310,35 @@ func (s *MatrixService) Start(userID string) error {
 	}
 	clientRes, err := infra.MatrixClientInit(clientCfg)
 	if err != nil {
-		return fmt.Errorf("matrix init: %w", err)
+		logError("matrix client init failed (token rejected by Synapse)",
+			"err", err,
+			"user_id", userID,
+			"hint", "Token may be stale — call Logout(user_id) then Login() again",
+		)
+		return fmt.Errorf("matrix init: %w (token rejected — re-login required)", err)
+	}
+	logInfo("matrix client init OK", "store_dir", storeDir, "device_id", string(clientRes.Client.DeviceID))
+
+	// Defensive: if DeviceID still empty after init, retry whoami + persist back.
+	// Happens when keyring has stale token (saved before whoami fixed) or when
+	// MAS-issued token's whoami response omits device_id (some servers do this).
+	if clientRes.Client.DeviceID == "" {
+		logWarn("client.DeviceID empty after init — retrying whoami")
+		uid, did, werr := whoami(s.ctx, tok.HomeserverURL, tok.AccessToken)
+		if werr != nil {
+			logError("whoami retry failed", "err", werr)
+			return fmt.Errorf("whoami retry: %w", werr)
+		}
+		if did == "" {
+			logError("Synapse whoami returned empty device_id — MAS session likely lacks device binding",
+				"user_id", uid,
+			)
+			return fmt.Errorf("synapse whoami did not return device_id — re-login required to bind a device")
+		}
+		clientRes.Client.DeviceID = id.DeviceID(did)
+		tok.DeviceID = did
+		_ = s.store.Save(userID, *tok)
+		logInfo("whoami retry OK + persisted", "device_id", did)
 	}
 
 	// Pickle key: load from keyring (hex), or generate fresh and persist.
@@ -249,15 +359,23 @@ func (s *MatrixService) Start(userID string) error {
 		PickleKey: pickleKey,
 	})
 	if err != nil {
-		return fmt.Errorf("matrix crypto init (hang here = MAS rejected UIA, see memory feedback_agents_e2ee_unblock_pattern): %w", err)
+		logError("crypto init failed",
+			"err", err,
+			"crypto_store", cryptoStorePath,
+			"hint", "If hang: MAS rejected UIA. WIPE crypto.db + relogin.",
+		)
+		return fmt.Errorf("matrix crypto init: %w", err)
 	}
+	logInfo("crypto init OK", "store", cryptoStorePath)
 
 	syncRes, err := infra.MatrixSyncService(s.ctx, infra.MatrixSyncServiceConfig{
 		Client: clientRes.Client,
 	})
 	if err != nil {
+		logError("sync service start failed", "err", err)
 		return fmt.Errorf("matrix sync: %w", err)
 	}
+	logInfo("sync service started")
 
 	s.client = clientRes.Client
 	s.crypto = cryptoRes
@@ -267,9 +385,26 @@ func (s *MatrixService) Start(userID string) error {
 	// Fan events out via Wails runtime.
 	go s.fanout()
 
+	logInfo("Start complete", "user_id", userID)
 	return nil
 }
 
+// GetLogTail returns the last n lines of the app log file for the diagnostics UI.
+func (s *MatrixService) GetLogTail(n int) ([]string, error) {
+	if n <= 0 {
+		n = 200
+	}
+	return TailLog(n)
+}
+
+// GetLogPath returns the absolute path to the log file (for the diagnostics UI).
+func (s *MatrixService) GetLogPath() string {
+	if globalLogger == nil {
+		return ""
+	}
+	return globalLogger.Path()
+}
+
 func (s *MatrixService) fanout() {
 	if s.ctx == nil || s.sync == nil {
 		return