diff --git a/frontend/src/HomeScreen.tsx b/frontend/src/HomeScreen.tsx
index e147ba5..e5d60ae 100644
--- a/frontend/src/HomeScreen.tsx
+++ b/frontend/src/HomeScreen.tsx
@@ -1,27 +1,39 @@
-import { useEffect, useState } from "react";
+import { useEffect, useMemo, useState } from "react";
 import {
   AppShell,
-  Avatar,
   Badge,
   Box,
+  Burger,
   Button,
-  Code,
+  Center,
   Group,
-  Paper,
+  Loader,
   Stack,
   Text,
   Title,
 } from "@mantine/core";
-import { IconLogout, IconUserCircle } from "@tabler/icons-react";
-import { GetSession, Logout } from "../wailsjs/go/main/MatrixService";
+import { useDisclosure } from "@mantine/hooks";
+import { notifications } from "@mantine/notifications";
+import {
+  IconLock,
+  IconLogout,
+  IconUserCircle,
+} from "@tabler/icons-react";
+import {
+  Logout,
+  SendMarkdown,
+  SendText,
+  Start,
+  Stop,
+} from "../wailsjs/go/main/MatrixService";
+import { EventsOn } from "../wailsjs/runtime/runtime";
+import RoomList from "./components/RoomList";
+import Timeline from "./components/Timeline";
+import Composer from "./components/Composer";
+import { useMatrixRooms } from "./hooks/useMatrixRooms";
+import { useMatrixTimeline } from "./hooks/useMatrixTimeline";
 
-interface Session {
-  user_id: string;
-  device_id: string;
-  homeserver_url: string;
-  has_token: boolean;
-  expires_at?: string;
-}
+const NAVBAR_WIDTH = 300;
 
 export default function HomeScreen({
   userID,
@@ -30,12 +42,63 @@ export default function HomeScreen({
   userID: string;
   onLogout: () => void;
 }) {
-  const [session, setSession] = useState<Session | null>(null);
+  const [navOpen, navHandlers] = useDisclosure(true);
+  const [activeRoomID, setActiveRoomID] = useState<string | null>(null);
+  const [started, setStarted] = useState(false);
+  const [startError, setStartError] = useState<string | null>(null);
 
+  const { rooms } = useMatrixRooms(started);
+  const { events, loading: timelineLoading, error: timelineError } = useMatrixTimeline(
+    activeRoomID,
+    50,
+  );
+
+  // Boot sync on mount; tear down on unmount.
   useEffect(() => {
-    GetSession(userID).then((s) => setSession(s as Session | null));
+    let cancelled = false;
+    (async () => {
+      try {
+        await Start(userID);
+        if (!cancelled) setStarted(true);
+      } catch (e: any) {
+        if (!cancelled) {
+          const msg = String(e?.message ?? e);
+          setStartError(msg);
+          notifications.show({
+            title: "Sync error",
+            message: msg,
+            color: "red",
+            autoClose: false,
+          });
+        }
+      }
+    })();
+    return () => {
+      cancelled = true;
+      Stop().catch(() => {});
+    };
   }, [userID]);
 
+  // Show transient Matrix errors as toast notifications.
+  useEffect(() => {
+    const off = EventsOn("matrix:error", (msg: string) => {
+      notifications.show({
+        title: "Matrix",
+        message: String(msg),
+        color: "orange",
+        autoClose: 6000,
+      });
+    });
+    return () => {
+      if (typeof off === "function") off();
+    };
+  }, []);
+
+  const activeRoom = useMemo(
+    () => rooms.find((r) => r.room_id === activeRoomID) || null,
+    [rooms, activeRoomID],
+  );
+
   async function handleLogout() {
     try {
       await Logout(userID);
@@ -44,22 +107,43 @@ export default function HomeScreen({
     }
   }
 
-  const initials = userID
-    .replace("@", "")
-    .split(":")[0]
-    .slice(0, 2)
-    .toUpperCase();
+  async function handleSendText(body: string) {
+    if (!activeRoomID) return;
+    await SendText(activeRoomID, body);
+  }
+
+  async function handleSendMarkdown(md: string) {
+    if (!activeRoomID) return;
+    await SendMarkdown(activeRoomID, md);
+  }
 
   return (
-    <AppShell header={{ height: 56 }} padding="md">
+    <AppShell
+      header={{ height: 56 }}
+      navbar={{
+        width: NAVBAR_WIDTH,
+        breakpoint: 0,
+        collapsed: { mobile: !navOpen, desktop: !navOpen },
+      }}
+      padding={0}
+    >
       <AppShell.Header>
-        <Group h="100%" px="md" justify="space-between">
-          <Group gap="xs">
+        <Group h="100%" px="md" justify="space-between" wrap="nowrap">
+          <Group gap="xs" wrap="nowrap">
+            <Burger
+              opened={navOpen}
+              onClick={navHandlers.toggle}
+              size="sm"
+              aria-label="Toggle rooms"
+            />
             <IconUserCircle size={22} />
             <Text fw={600}>matrix_client_pc</Text>
             <Badge size="sm" variant="light" color="violet">
-              v0.1.0
+              v0.2.0
             </Badge>
+            <Text size="xs" c="dimmed" visibleFrom="sm">
+              {userID}
+            </Text>
           </Group>
           <Button
             variant="subtle"
@@ -71,41 +155,91 @@ export default function HomeScreen({
           </Button>
         </Group>
       </AppShell.Header>
-      <AppShell.Main>
-        <Box maw={720} mx="auto" mt="xl">
-          <Paper p="xl" radius="lg" withBorder>
-            <Group gap="lg" align="flex-start">
-              <Avatar size={64} color="violet" radius="xl">
-                {initials}
-              </Avatar>
-              <Stack gap={6} flex={1}>
-                <Title order={3}>{userID}</Title>
-                {session ? (
-                  <Stack gap={4}>
-                    <Text size="sm" c="dimmed">
-                      Device: <Code>{session.device_id || "-"}</Code>
-                    </Text>
-                    <Text size="sm" c="dimmed">
-                      Homeserver: <Code>{session.homeserver_url}</Code>
-                    </Text>
-                    {session.expires_at && (
-                      <Text size="xs" c="dimmed">
-                        Token expira: {session.expires_at}
-                      </Text>
-                    )}
-                  </Stack>
-                ) : (
-                  <Text c="dimmed">Cargando sesion...</Text>
-                )}
-              </Stack>
-            </Group>
-          </Paper>
-          <Paper p="md" radius="md" withBorder mt="lg">
+
+      <AppShell.Navbar>
+        <RoomList
+          rooms={rooms}
+          activeRoomID={activeRoomID}
+          onSelect={setActiveRoomID}
+        />
+      </AppShell.Navbar>
+
+      <AppShell.Main
+        style={{
+          display: "flex",
+          flexDirection: "column",
+          height: "calc(100vh - 56px)",
+        }}
+      >
+        {!started && !startError && (
+          <Center style={{ flex: 1 }}>
+            <Stack align="center" gap="xs">
+              <Loader />
+              <Text size="sm" c="dimmed">
+                Starting sync and crypto (up to 60s on first run)...
+              </Text>
+            </Stack>
+          </Center>
+        )}
+
+        {startError && (
+          <Center style={{ flex: 1 }}>
+            <Stack align="center" gap="xs" maw={520} ta="center">
+              <Title order={4} c="red">
+                Could not start sync
+              </Title>
+              <Text size="sm" c="dimmed">
+                {startError}
+              </Text>
+            </Stack>
+          </Center>
+        )}
+
+        {started && !activeRoom && (
+          <Center style={{ flex: 1 }}>
             <Text size="sm" c="dimmed">
-              Login OK. Sync + rooms + timeline llegan en issue 0148.
+              Pick a room from the sidebar to view messages
             </Text>
-          </Paper>
-        </Box>
+          </Center>
+        )}
+
+        {started && activeRoom && (
+          <>
+            <Box p="md" bg="dark.7" style={{ borderBottom: "1px solid var(--mantine-color-dark-5)" }}>
+              <Group gap="xs">
+                <Title order={5}>{activeRoom.name || activeRoom.room_id}</Title>
+                {activeRoom.is_encrypted && (
+                  <Badge size="xs" color="green" variant="light" leftSection={<IconLock size={10} />}>
+                    E2EE
+                  </Badge>
+                )}
+                <Text size="xs" c="dimmed">
+                  {activeRoom.member_count} member{activeRoom.member_count === 1 ? "" : "s"}
+                </Text>
+              </Group>
+              {activeRoom.topic && (
+                <Text size="xs" c="dimmed" mt={4} lineClamp={1}>
+                  {activeRoom.topic}
+                </Text>
+              )}
+            </Box>
+
+            <Box style={{ flex: 1, minHeight: 0 }}>
+              <Timeline
+                events={events}
+                loading={timelineLoading}
+                error={timelineError}
+                selfUserID={userID}
+              />
+            </Box>
+
+            <Composer
+              disabled={!activeRoomID}
+              onSendText={handleSendText}
+              onSendMarkdown={handleSendMarkdown}
+            />
+          </>
+        )}
       </AppShell.Main>
     </AppShell>
   );
diff --git a/frontend/src/components/Composer.tsx b/frontend/src/components/Composer.tsx
new file mode 100644
index 0000000..a2944c8
--- /dev/null
+++ b/frontend/src/components/Composer.tsx
@@ -0,0 +1,88 @@
+import { useState, useRef, KeyboardEvent } from "react";
+import { ActionIcon, Group, Textarea, Tooltip } from "@mantine/core";
+import { IconSend, IconMarkdown } from "@tabler/icons-react";
+
+export interface ComposerProps {
+  disabled?: boolean;
+  onSendText: (body: string) => Promise<void>;
+  onSendMarkdown: (md: string) => Promise<void>;
+}
+
+export default function Composer({ disabled, onSendText, onSendMarkdown }: ComposerProps) {
+  const [value, setValue] = useState("");
+  const [sending, setSending] = useState(false);
+  const [markdownMode, setMarkdownMode] = useState(false);
+  const ref = useRef<HTMLTextAreaElement | null>(null);
+
+  async function doSend() {
+    const body = value.trim();
+    if (!body || disabled || sending) return;
+    setSending(true);
+    try {
+      if (markdownMode) {
+        await onSendMarkdown(body);
+      } else {
+        await onSendText(body);
+      }
+      setValue("");
+      ref.current?.focus();
+    } catch (e) {
+      // surface via console; toast wiring is centralised in HomeScreen
+      console.error("send failed", e);
+    } finally {
+      setSending(false);
+    }
+  }
+
+  function onKeyDown(e: KeyboardEvent<HTMLTextAreaElement>) {
+    if (e.key === "Enter" && !e.shiftKey) {
+      e.preventDefault();
+      doSend();
+    }
+  }
+
+  return (
+    <Group gap="xs" align="flex-end" p="md" bg="dark.7" wrap="nowrap">
+      <Tooltip label={markdownMode ? "Markdown ON" : "Markdown OFF"} withArrow>
+        <ActionIcon
+          variant={markdownMode ? "filled" : "subtle"}
+          color="violet"
+          size="lg"
+          onClick={() => setMarkdownMode((v) => !v)}
+          disabled={disabled}
+        >
+          <IconMarkdown size={18} />
+        </ActionIcon>
+      </Tooltip>
+      <Textarea
+        ref={ref}
+        flex={1}
+        autosize
+        minRows={1}
+        maxRows={6}
+        radius="md"
+        placeholder={
+          disabled
+            ? "Select a room to start chatting"
+            : markdownMode
+            ? "Markdown · Enter to send, Shift+Enter newline"
+            : "Message · Enter to send, Shift+Enter newline"
+        }
+        value={value}
+        onChange={(e) => setValue(e.currentTarget.value)}
+        onKeyDown={onKeyDown}
+        disabled={disabled || sending}
+      />
+      <ActionIcon
+        variant="filled"
+        color="violet"
+        size="lg"
+        onClick={doSend}
+        loading={sending}
+        disabled={disabled || !value.trim()}
+      >
+        <IconSend size={18} />
+      </ActionIcon>
+    </Group>
+  );
+}
diff --git a/frontend/src/components/EventBubble.tsx b/frontend/src/components/EventBubble.tsx
new file mode 100644
index 0000000..ebe2d94
--- /dev/null
+++ b/frontend/src/components/EventBubble.tsx
@@ -0,0 +1,80 @@
+import { Avatar, Group, Paper, Stack, Text } from "@mantine/core";
+import { IconLockExclamation } from "@tabler/icons-react";
+import type { MatrixEvent } from "../types";
+
+function senderInitials(sender: string): string {
+  return sender.replace(/^@/, "").charAt(0).toUpperCase() || "?";
+}
+
+function senderShort(sender: string): string {
+  // "@local:server" -> "@local"
+  return sender.split(":")[0];
+}
+
+function fmtTime(ts: number): string {
+  if (!ts) return "";
+  const d = new Date(ts);
+  return d.toLocaleTimeString([], { hour: "2-digit", minute: "2-digit" });
+}
+
+export interface EventBubbleProps {
+  event: MatrixEvent;
+  isSelf: boolean;
+}
+
+export default function EventBubble({ event, isSelf }: EventBubbleProps) {
+  const isEncrypted = event.encrypted_raw;
+  return (
+    <Group
+      align="flex-start"
+      gap="xs"
+      wrap="nowrap"
+      justify={isSelf ? "flex-end" : "flex-start"}
+    >
+      {!isSelf && (
+        <Avatar size={28} radius="xl" color="violet">
+          {senderInitials(event.sender)}
+        </Avatar>
+      )}
+      <Stack gap={2} maw="70%" align={isSelf ? "flex-end" : "flex-start"}>
+        <Group gap={6}>
+          <Text fz="xs" c="dimmed" fw={500}>
+            {senderShort(event.sender)}
+          </Text>
+          <Text fz="xs" c="dimmed">
+            {fmtTime(event.ts)}
+          </Text>
+        </Group>
+        <Paper
+          p="xs"
+          radius="md"
+          bg={isSelf ? "violet.9" : "dark.6"}
+          c={isSelf ? "white" : "gray.0"}
+          style={{ wordBreak: "break-word" }}
+        >
+          {isEncrypted ? (
+            <Group gap={6} c="dimmed">
+              <IconLockExclamation size={14} />
+              <Text fz="sm" fs="italic">
+                Encrypted message (no session)
+              </Text>
+            </Group>
+          ) : (
+            <Text fz="sm" style={{ whiteSpace: "pre-wrap" }}>
+              {event.body || (
+                <Text component="span" c="dimmed" fs="italic">
+                  (no body)
+                </Text>
+              )}
+            </Text>
+          )}
+        </Paper>
+      </Stack>
+      {isSelf && (
+        <Avatar size={28} radius="xl" color="violet">
+          {senderInitials(event.sender)}
+        </Avatar>
+      )}
+    </Group>
+  );
+}
diff --git a/frontend/src/components/RoomList.tsx b/frontend/src/components/RoomList.tsx
new file mode 100644
index 0000000..0c71d2f
--- /dev/null
+++ b/frontend/src/components/RoomList.tsx
@@ -0,0 +1,88 @@
+import { Avatar, Group, NavLink, ScrollArea, Stack, Text } from "@mantine/core";
+import { IconLock, IconHash, IconUser } from "@tabler/icons-react";
+import type { RoomSummary } from "../types";
+
+function relativeTime(ts: number): string {
+  if (!ts) return "";
+  const diff = Date.now() - ts;
+  const sec = Math.floor(diff / 1000);
+  if (sec < 60) return `${sec}s`;
+  const min = Math.floor(sec / 60);
+  if (min < 60) return `${min}m`;
+  const hr = Math.floor(min / 60);
+  if (hr < 24) return `${hr}h`;
+  const day = Math.floor(hr / 24);
+  if (day < 30) return `${day}d`;
+  return new Date(ts).toLocaleDateString();
+}
+
+function initial(room: RoomSummary): string {
+  const base = room.name || room.canonical_alias || room.room_id;
+  return (base.replace(/^[#@!]/, "").charAt(0) || "?").toUpperCase();
+}
+
+export interface RoomListProps {
+  rooms: RoomSummary[];
+  activeRoomID: string | null;
+  onSelect: (roomID: string) => void;
+}
+
+export default function RoomList({ rooms, activeRoomID, onSelect }: RoomListProps) {
+  if (!rooms.length) {
+    return (
+      <Stack p="md">
+        <Text size="sm" c="dimmed">
+          No rooms yet. Sync in progress...
+        </Text>
+      </Stack>
+    );
+  }
+
+  return (
+    <ScrollArea h="calc(100vh - 56px)" type="hover" offsetScrollbars>
+      <Stack gap={0} p={4}>
+        {rooms.map((room) => {
+          const active = room.room_id === activeRoomID;
+          const TypeIcon = room.is_direct ? IconUser : IconHash;
+          return (
+            <NavLink
+              key={room.room_id}
+              active={active}
+              variant="filled"
+              color="violet"
+              onClick={() => onSelect(room.room_id)}
+              leftSection={
+                <Avatar size={32} radius="xl" color={active ? "violet" : "gray"}>
+                  {initial(room)}
+                </Avatar>
+              }
+              label={
+                <Group gap={6} wrap="nowrap" justify="space-between">
+                  <Group gap={4} wrap="nowrap" style={{ minWidth: 0 }}>
+                    <TypeIcon size={12} style={{ flexShrink: 0, opacity: 0.6 }} />
+                    <Text truncate fz="sm" fw={active ? 600 : 500}>
+                      {room.name || room.canonical_alias || room.room_id}
+                    </Text>
+                  </Group>
+                  {room.is_encrypted && (
+                    <IconLock size={12} style={{ flexShrink: 0, opacity: 0.7 }} />
+                  )}
+                </Group>
+              }
+              description={
+                <Group gap={6} justify="space-between" wrap="nowrap">
+                  <Text fz="xs" c="dimmed" truncate>
+                    {room.member_count} member{room.member_count === 1 ? "" : "s"}
+                  </Text>
+                  <Text fz="xs" c="dimmed">
+                    {relativeTime(room.last_event_ts)}
+                  </Text>
+                </Group>
+              }
+            />
+          );
+        })}
+      </Stack>
+    </ScrollArea>
+  );
+}
diff --git a/frontend/src/components/Timeline.tsx b/frontend/src/components/Timeline.tsx
new file mode 100644
index 0000000..029b5f3
--- /dev/null
+++ b/frontend/src/components/Timeline.tsx
@@ -0,0 +1,64 @@
+import { useEffect, useRef } from "react";
+import { Box, Center, Loader, ScrollArea, Stack, Text } from "@mantine/core";
+import EventBubble from "./EventBubble";
+import type { MatrixEvent } from "../types";
+
+export interface TimelineProps {
+  events: MatrixEvent[];
+  loading: boolean;
+  error: string | null;
+  selfUserID: string;
+}
+
+export default function Timeline({ events, loading, error, selfUserID }: TimelineProps) {
+  const viewport = useRef<HTMLDivElement | null>(null);
+
+  // Auto-scroll to bottom when new events arrive.
+  useEffect(() => {
+    if (!viewport.current) return;
+    viewport.current.scrollTo({
+      top: viewport.current.scrollHeight,
+      behavior: "smooth",
+    });
+  }, [events.length]);
+
+  if (loading && events.length === 0) {
+    return (
+      <Center h="100%">
+        <Loader size="sm" />
+      </Center>
+    );
+  }
+
+  if (error) {
+    return (
+      <Center h="100%">
+        <Text c="red" size="sm">
+          {error}
+        </Text>
+      </Center>
+    );
+  }
+
+  if (!events.length) {
+    return (
+      <Center h="100%">
+        <Text size="sm" c="dimmed">
+          No messages yet
+        </Text>
+      </Center>
+    );
+  }
+
+  return (
+    <ScrollArea h="100%" viewportRef={viewport} offsetScrollbars>
+      <Box p="md">
+        <Stack gap="sm">
+          {events.map((ev) => (
+            <EventBubble key={ev.event_id} event={ev} isSelf={ev.sender === selfUserID} />
+          ))}
+        </Stack>
+      </Box>
+    </ScrollArea>
+  );
+}
diff --git a/frontend/src/hooks/useMatrixRooms.ts b/frontend/src/hooks/useMatrixRooms.ts
new file mode 100644
index 0000000..f540d95
--- /dev/null
+++ b/frontend/src/hooks/useMatrixRooms.ts
@@ -0,0 +1,54 @@
+import { useCallback, useEffect, useRef, useState } from "react";
+import { ListRooms } from "../../wailsjs/go/main/MatrixService";
+import { EventsOn } from "../../wailsjs/runtime/runtime";
+import type { RoomSummary, SyncEventView } from "../types";
+
+/**
+ * useMatrixRooms keeps a fresh list of joined rooms. It polls every 30s and
+ * re-fetches on every relevant matrix:event so that recently active rooms
+ * float to the top of the sidebar without a hard refresh.
+ */
+export function useMatrixRooms(enabled: boolean) {
+  const [rooms, setRooms] = useState<RoomSummary[]>([]);
+  const [loading, setLoading] = useState(false);
+  const [error, setError] = useState<string | null>(null);
+  const inFlight = useRef(false);
+
+  const refresh = useCallback(async () => {
+    if (inFlight.current) return;
+    inFlight.current = true;
+    setLoading(true);
+    try {
+      const list = await ListRooms();
+      setRooms(list || []);
+      setError(null);
+    } catch (e: any) {
+      setError(String(e?.message ?? e));
+    } finally {
+      setLoading(false);
+      inFlight.current = false;
+    }
+  }, []);
+
+  useEffect(() => {
+    if (!enabled) return;
+    refresh();
+    const interval = window.setInterval(refresh, 30_000);
+    const off = EventsOn("matrix:event", (ev: SyncEventView) => {
+      // Only refresh for events that may move a room in the list.
+      if (
+        ev?.type === "message" ||
+        ev?.type === "encrypted" ||
+        ev?.type === "membership"
+      ) {
+        refresh();
+      }
+    });
+    return () => {
+      window.clearInterval(interval);
+      if (typeof off === "function") off();
+    };
+  }, [enabled, refresh]);
+
+  return { rooms, loading, error, refresh };
+}
diff --git a/frontend/src/hooks/useMatrixTimeline.ts b/frontend/src/hooks/useMatrixTimeline.ts
new file mode 100644
index 0000000..aaef104
--- /dev/null
+++ b/frontend/src/hooks/useMatrixTimeline.ts
@@ -0,0 +1,66 @@
+import { useCallback, useEffect, useState } from "react";
+import { LoadTimeline } from "../../wailsjs/go/main/MatrixService";
+import { EventsOn } from "../../wailsjs/runtime/runtime";
+import type { MatrixEvent, SyncEventView } from "../types";
+
+/**
+ * useMatrixTimeline loads the last `limit` events of a room (newest at the
+ * bottom) and appends live events from the sync stream. Re-fetches whenever
+ * roomID changes.
+ */
+export function useMatrixTimeline(roomID: string | null, limit = 50) {
+  const [events, setEvents] = useState<MatrixEvent[]>([]);
+  const [loading, setLoading] = useState(false);
+  const [error, setError] = useState<string | null>(null);
+
+  const refresh = useCallback(async () => {
+    if (!roomID) {
+      setEvents([]);
+      return;
+    }
+    setLoading(true);
+    try {
+      const list = await LoadTimeline(roomID, limit);
+      // Mautrix Messages with DirectionBackward returns newest-first; flip to
+      // oldest-first so React renders top-to-bottom chronologically.
+      const ordered = [...(list || [])].reverse();
+      setEvents(ordered);
+      setError(null);
+    } catch (e: any) {
+      setError(String(e?.message ?? e));
+    } finally {
+      setLoading(false);
+    }
+  }, [roomID, limit]);
+
+  useEffect(() => {
+    refresh();
+  }, [refresh]);
+
+  useEffect(() => {
+    if (!roomID) return;
+    const off = EventsOn("matrix:event", (ev: SyncEventView) => {
+      if (ev?.room_id !== roomID) return;
+      if (ev?.type !== "message" && ev?.type !== "encrypted") return;
+      setEvents((prev) => {
+        // Dedupe by event_id (sync may replay).
+        if (prev.some((p) => p.event_id === ev.event_id)) return prev;
+        const next: MatrixEvent = {
+          event_id: ev.event_id,
+          room_id: ev.room_id,
+          sender: ev.sender,
+          type: ev.type === "encrypted" ? "m.room.encrypted" : "m.room.message",
+          ts: ev.ts,
+          body: ev.body ?? "",
+          encrypted_raw: ev.type === "encrypted",
+        };
+        return [...prev, next];
+      });
+    });
+    return () => {
+      if (typeof off === "function") off();
+    };
+  }, [roomID]);
+
+  return { events, loading, error, refresh };
+}
diff --git a/frontend/src/types.ts b/frontend/src/types.ts
new file mode 100644
index 0000000..a10b36d
--- /dev/null
+++ b/frontend/src/types.ts
@@ -0,0 +1,19 @@
+// Local convenience aliases for the auto-generated Wails models.
+// We re-export the model classes/interfaces so the rest of the app imports
+// from one stable path instead of the long wailsjs/go/models.ts.
+
+import { infra, main } from "../wailsjs/go/models";
+
+export type RoomSummary = infra.RoomSummary;
+export type MatrixEvent = main.MatrixEvent;
+
+// SyncEventView is what the Go runtime emits through "matrix:event".
+// Not part of the Wails-generated module (it never appears as a return type).
+export interface SyncEventView {
+  type: string;
+  room_id: string;
+  event_id: string;
+  sender: string;
+  ts: number;
+  body?: string;
+}
diff --git a/go.mod b/go.mod
index 756ddfe..b3130fd 100644
--- a/go.mod
+++ b/go.mod
@@ -2,13 +2,24 @@ module fn-registry/projects/element_agents/apps/matrix_client_pc
 
 go 1.25.0
 
-require github.com/wailsapp/wails/v2 v2.11.0
+require (
+	github.com/mattn/go-sqlite3 v1.14.44
+	github.com/microcosm-cc/bluemonday v1.0.27
+	github.com/wailsapp/wails/v2 v2.11.0
+	github.com/yuin/goldmark v1.8.2
+	github.com/zalando/go-keyring v0.2.8
+	maunium.net/go/mautrix v0.28.0
+)
 
 require (
+	filippo.io/edwards25519 v1.2.0 // indirect
+	github.com/aymerick/douceur v0.2.0 // indirect
 	github.com/bep/debounce v1.2.1 // indirect
+	github.com/danieljoos/wincred v1.2.3 // indirect
 	github.com/go-ole/go-ole v1.3.0 // indirect
 	github.com/godbus/dbus/v5 v5.2.2 // indirect
 	github.com/google/uuid v1.6.0 // indirect
+	github.com/gorilla/css v1.0.1 // indirect
 	github.com/gorilla/websocket v1.5.3 // indirect
 	github.com/jchv/go-winloader v0.0.0-20210711035445-715c2860da7e // indirect
 	github.com/labstack/echo/v4 v4.13.3 // indirect
@@ -19,17 +30,24 @@ require (
 	github.com/leaanthony/u v1.1.1 // indirect
 	github.com/mattn/go-colorable v0.1.14 // indirect
 	github.com/mattn/go-isatty v0.0.20 // indirect
+	github.com/petermattis/goid v0.0.0-20260330135022-df67b199bc81 // indirect
 	github.com/pkg/browser v0.0.0-20240102092130-5ac0b6a4141c // indirect
 	github.com/pkg/errors v0.9.1 // indirect
 	github.com/rivo/uniseg v0.4.7 // indirect
+	github.com/rs/zerolog v1.35.1 // indirect
 	github.com/samber/lo v1.49.1 // indirect
-	github.com/stretchr/testify v1.11.1 // indirect
+	github.com/tidwall/gjson v1.19.0 // indirect
+	github.com/tidwall/match v1.1.1 // indirect
+	github.com/tidwall/pretty v1.2.1 // indirect
+	github.com/tidwall/sjson v1.2.5 // indirect
 	github.com/tkrajina/go-reflector v0.5.8 // indirect
 	github.com/valyala/bytebufferpool v1.0.0 // indirect
 	github.com/valyala/fasttemplate v1.2.2 // indirect
 	github.com/wailsapp/go-webview2 v1.0.22 // indirect
 	github.com/wailsapp/mimetype v1.4.1 // indirect
+	go.mau.fi/util v0.9.9 // indirect
 	golang.org/x/crypto v0.51.0 // indirect
+	golang.org/x/exp v0.0.0-20260508232706-74f9aab9d74a // indirect
 	golang.org/x/net v0.54.0 // indirect
 	golang.org/x/sys v0.44.0 // indirect
 	golang.org/x/text v0.37.0 // indirect
diff --git a/go.sum b/go.sum
index c9eb67a..ba5171e 100644
--- a/go.sum
+++ b/go.sum
@@ -1,5 +1,13 @@
+filippo.io/edwards25519 v1.2.0 h1:crnVqOiS4jqYleHd9vaKZ+HKtHfllngJIiOpNpoJsjo=
+filippo.io/edwards25519 v1.2.0/go.mod h1:xzAOLCNug/yB62zG1bQ8uziwrIqIuxhctzJT18Q77mc=
+github.com/DATA-DOG/go-sqlmock v1.5.2 h1:OcvFkGmslmlZibjAjaHm3L//6LiuBgolP7OputlJIzU=
+github.com/DATA-DOG/go-sqlmock v1.5.2/go.mod h1:88MAG/4G7SMwSE3CeA0ZKzrT5CiOU3OJ+JlNzwDqpNU=
+github.com/aymerick/douceur v0.2.0 h1:Mv+mAeH1Q+n9Fr+oyamOlAkUNPWPlA8PPGR0QAaYuPk=
+github.com/aymerick/douceur v0.2.0/go.mod h1:wlT5vV2O3h55X9m7iVYN0TBM0NH/MmbLnd30/FjWUq4=
 github.com/bep/debounce v1.2.1 h1:v67fRdBA9UQu2NhLFXrSg0Brw7CexQekrBwDMM8bzeY=
 github.com/bep/debounce v1.2.1/go.mod h1:H8yggRPQKLUhUoqrJC1bO2xNya7vanpDl7xR3ISbCJ0=
+github.com/danieljoos/wincred v1.2.3 h1:v7dZC2x32Ut3nEfRH+vhoZGvN72+dQ/snVXo/vMFLdQ=
+github.com/danieljoos/wincred v1.2.3/go.mod h1:6qqX0WNrS4RzPZ1tnroDzq9kY3fu1KwE7MRLQK4X0bs=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/go-ole/go-ole v1.3.0 h1:Dt6ye7+vXGIKZ7Xtk4s6/xVdGDQynvom7xCFEdWr6uE=
@@ -8,6 +16,8 @@ github.com/godbus/dbus/v5 v5.2.2 h1:TUR3TgtSVDmjiXOgAAyaZbYmIeP3DPkld3jgKGV8mXQ=
 github.com/godbus/dbus/v5 v5.2.2/go.mod h1:3AAv2+hPq5rdnr5txxxRwiGjPXamgoIHgz9FPBfOp3c=
 github.com/google/uuid v1.6.0 h1:NIvaJDMOsjHA8n1jAhLSgzrAzy1Hgr+hNrb57e+94F0=
 github.com/google/uuid v1.6.0/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=
+github.com/gorilla/css v1.0.1 h1:ntNaBIghp6JmvWnxbZKANoLyuXTPZ4cAMlo6RyhlbO8=
+github.com/gorilla/css v1.0.1/go.mod h1:BvnYkspnSzMmwRK+b8/xgNPLiIuNZr6vbZBTPQ2A3b0=
 github.com/gorilla/websocket v1.5.3 h1:saDtZ6Pbx/0u+bgYQ3q96pZgCzfhKXGPqt7kZ72aNNg=
 github.com/gorilla/websocket v1.5.3/go.mod h1:YR8l580nyteQvAITg2hZ9XVh4b55+EU/adAjf1fMHhE=
 github.com/jchv/go-winloader v0.0.0-20210711035445-715c2860da7e h1:Q3+PugElBCf4PFpxhErSzU3/PY5sFL5Z6rfv4AbGAck=
@@ -33,6 +43,12 @@ github.com/mattn/go-colorable v0.1.14 h1:9A9LHSqF/7dyVVX6g0U9cwm9pG3kP9gSzcuIPHP
 github.com/mattn/go-colorable v0.1.14/go.mod h1:6LmQG8QLFO4G5z1gPvYEzlUgJ2wF+stgPZH1UqBm1s8=
 github.com/mattn/go-isatty v0.0.20 h1:xfD0iDuEKnDkl03q4limB+vH+GxLEtL/jb4xVJSWWEY=
 github.com/mattn/go-isatty v0.0.20/go.mod h1:W+V8PltTTMOvKvAeJH7IuucS94S2C6jfK/D7dTCTo3Y=
+github.com/mattn/go-sqlite3 v1.14.44 h1:3VSe+xafpbzsLbdr2AWlAZk9yRHiBhTBakioXaCKTF8=
+github.com/mattn/go-sqlite3 v1.14.44/go.mod h1:pjEuOr8IwzLJP2MfGeTb0A35jauH+C2kbHKBr7yXKVQ=
+github.com/microcosm-cc/bluemonday v1.0.27 h1:MpEUotklkwCSLeH+Qdx1VJgNqLlpY2KXwXFM08ygZfk=
+github.com/microcosm-cc/bluemonday v1.0.27/go.mod h1:jFi9vgW+H7c3V0lb6nR74Ib/DIB5OBs92Dimizgw2cA=
+github.com/petermattis/goid v0.0.0-20260330135022-df67b199bc81 h1:WDsQxOJDy0N1VRAjXLpi8sCEZRSGarLWQevDxpTBRrM=
+github.com/petermattis/goid v0.0.0-20260330135022-df67b199bc81/go.mod h1:pxMtw7cyUw6B2bRH0ZBANSPg+AoSud1I1iyJHI69jH4=
 github.com/pkg/browser v0.0.0-20240102092130-5ac0b6a4141c h1:+mdjkGKdHQG3305AYmdv1U2eRNDiU2ErMBj1gwrq8eQ=
 github.com/pkg/browser v0.0.0-20240102092130-5ac0b6a4141c/go.mod h1:7rwL4CYBLnjLxUqIJNnCWiEdr3bn6IUYi15bNlnbCCU=
 github.com/pkg/errors v0.9.1 h1:FEBLx1zS214owpjy7qsBeixbURkuhQAwrK5UwLGTwt4=
@@ -42,10 +58,24 @@ github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZN
 github.com/rivo/uniseg v0.2.0/go.mod h1:J6wj4VEh+S6ZtnVlnTBMWIodfgj8LQOQFoIToxlJtxc=
 github.com/rivo/uniseg v0.4.7 h1:WUdvkW8uEhrYfLC4ZzdpI2ztxP1I582+49Oc5Mq64VQ=
 github.com/rivo/uniseg v0.4.7/go.mod h1:FN3SvrM+Zdj16jyLfmOkMNblXMcoc8DfTHruCPUcx88=
+github.com/rs/zerolog v1.35.1 h1:m7xQeoiLIiV0BCEY4Hs+j2NG4Gp2o2KPKmhnnLiazKI=
+github.com/rs/zerolog v1.35.1/go.mod h1:EjML9kdfa/RMA7h/6z6pYmq1ykOuA8/mjWaEvGI+jcw=
 github.com/samber/lo v1.49.1 h1:4BIFyVfuQSEpluc7Fua+j1NolZHiEHEpaSEKdsH0tew=
 github.com/samber/lo v1.49.1/go.mod h1:dO6KHFzUKXgP8LDhU0oI8d2hekjXnGOu0DB8Jecxd6o=
+github.com/stretchr/objx v0.5.2 h1:xuMeJ0Sdp5ZMRXx/aWO6RZxdr3beISkG5/G/aIRr3pY=
+github.com/stretchr/objx v0.5.2/go.mod h1:FRsXN1f5AsAjCGJKqEizvkpNtU+EGNCLh3NxZ/8L+MA=
 github.com/stretchr/testify v1.11.1 h1:7s2iGBzp5EwR7/aIZr8ao5+dra3wiQyKjjFuvgVKu7U=
 github.com/stretchr/testify v1.11.1/go.mod h1:wZwfW3scLgRK+23gO65QZefKpKQRnfz6sD981Nm4B6U=
+github.com/tidwall/gjson v1.14.2/go.mod h1:/wbyibRr2FHMks5tjHJ5F8dMZh3AcwJEMf5vlfC0lxk=
+github.com/tidwall/gjson v1.19.0 h1:xwxm7n691Uf3u5OFjzngavjGTh55KX5q/9w9xHW88JU=
+github.com/tidwall/gjson v1.19.0/go.mod h1:V37/opeE/JbLUOfH0QTXiNez2l0RUjYUhpT4szFQAfc=
+github.com/tidwall/match v1.1.1 h1:+Ho715JplO36QYgwN9PGYNhgZvoUSc9X2c80KVTi+GA=
+github.com/tidwall/match v1.1.1/go.mod h1:eRSPERbgtNPcGhD8UCthc6PmLEQXEWd3PRB5JTxsfmM=
+github.com/tidwall/pretty v1.2.0/go.mod h1:ITEVvHYasfjBbM0u2Pg8T2nJnzm8xPwvNhhsoaGGjNU=
+github.com/tidwall/pretty v1.2.1 h1:qjsOFOWWQl+N3RsoF5/ssm1pHmJJwhjlSbZ51I6wMl4=
+github.com/tidwall/pretty v1.2.1/go.mod h1:ITEVvHYasfjBbM0u2Pg8T2nJnzm8xPwvNhhsoaGGjNU=
+github.com/tidwall/sjson v1.2.5 h1:kLy8mja+1c9jlljvWTlSazM7cKDRfJuR/bOJhcY5NcY=
+github.com/tidwall/sjson v1.2.5/go.mod h1:Fvgq9kS/6ociJEDnK0Fk1cpYF4FIW6ZF7LAe+6jwd28=
 github.com/tkrajina/go-reflector v0.5.8 h1:yPADHrwmUbMq4RGEyaOUpz2H90sRsETNVpjzo3DLVQQ=
 github.com/tkrajina/go-reflector v0.5.8/go.mod h1:ECbqLgccecY5kPmPmXg1MrHW585yMcDkVl6IvJe64T4=
 github.com/valyala/bytebufferpool v1.0.0 h1:GqA5TC/0021Y/b9FG4Oi9Mr3q7XYx6KllzawFIhcdPw=
@@ -58,8 +88,16 @@ github.com/wailsapp/mimetype v1.4.1 h1:pQN9ycO7uo4vsUUuPeHEYoUkLVkaRntMnHJxVwYhw
 github.com/wailsapp/mimetype v1.4.1/go.mod h1:9aV5k31bBOv5z6u+QP8TltzvNGJPmNJD4XlAL3U+j3o=
 github.com/wailsapp/wails/v2 v2.11.0 h1:seLacV8pqupq32IjS4Y7V8ucab0WZwtK6VvUVxSBtqQ=
 github.com/wailsapp/wails/v2 v2.11.0/go.mod h1:jrf0ZaM6+GBc1wRmXsM8cIvzlg0karYin3erahI4+0k=
+github.com/yuin/goldmark v1.8.2 h1:kEGpgqJXdgbkhcOgBxkC0X0PmoPG1ZyoZ117rDVp4zE=
+github.com/yuin/goldmark v1.8.2/go.mod h1:ip/1k0VRfGynBgxOz0yCqHrbZXhcjxyuS66Brc7iBKg=
+github.com/zalando/go-keyring v0.2.8 h1:6sD/Ucpl7jNq10rM2pgqTs0sZ9V3qMrqfIIy5YPccHs=
+github.com/zalando/go-keyring v0.2.8/go.mod h1:tsMo+VpRq5NGyKfxoBVjCuMrG47yj8cmakZDO5QGii0=
+go.mau.fi/util v0.9.9 h1:ujDeXCo07HBor5oQLyO1tHklupmqVmPgasc53d7q/NE=
+go.mau.fi/util v0.9.9/go.mod h1:pqt4Vcrt+5gcH/CgrHZg11qSx+b34o6mknGzOEA6waY=
 golang.org/x/crypto v0.51.0 h1:IBPXwPfKxY7cWQZ38ZCIRPI50YLeevDLlLnyC5wRGTI=
 golang.org/x/crypto v0.51.0/go.mod h1:8AdwkbraGNABw2kOX6YFPs3WM22XqI4EXEd8g+x7Oc8=
+golang.org/x/exp v0.0.0-20260508232706-74f9aab9d74a h1:+3jdDGGB8NGb1Zktc737jlt3/A5f6UlwSzmvqUuufxw=
+golang.org/x/exp v0.0.0-20260508232706-74f9aab9d74a/go.mod h1:d2fgXJLVs4dYDHUk5lwMIfzRzSrWCfGZb0ZqeLa/Vcw=
 golang.org/x/net v0.0.0-20210505024714-0287a6fb4125/go.mod h1:9nx3DQGgdP8bBQD5qxJ1jj9UTztislL4KSBs9R2vV5Y=
 golang.org/x/net v0.54.0 h1:2zJIZAxAHV/OHCDTCOHAYehQzLfSXuf/5SoL/Dv6w/w=
 golang.org/x/net v0.54.0/go.mod h1:Sj4oj8jK6XmHpBZU/zWHw3BV3abl4Kvi+Ut7cQcY+cQ=
@@ -77,3 +115,5 @@ golang.org/x/text v0.37.0/go.mod h1:a5sjxXGs9hsn/AJVwuElvCAo9v8QYLzvavO5z2PiM38=
 golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
 gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
 gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
+maunium.net/go/mautrix v0.28.0 h1:vBakLzf8MAdfED3NzAKiMeKQbc3AQ4EAS03NC+TVMXQ=
+maunium.net/go/mautrix v0.28.0/go.mod h1:/a9A7LGaqb9B3nho4tLd28n0EPcCdwpm2dxkxkLLgh0=
diff --git a/helpers.go b/helpers.go
index 6d1f316..12274f9 100644
--- a/helpers.go
+++ b/helpers.go
@@ -13,10 +13,6 @@ import (
 	"time"
 )
 
-func tempStoreDir() string {
-	return filepath.Join(os.TempDir(), "matrix_client_pc_login")
-}
-
 func userStoreDir(userID string) string {
 	cfg, err := os.UserConfigDir()
 	if err != nil {
diff --git a/internal/infra/keyring_token_store.go b/internal/infra/keyring_token_store.go
new file mode 100644
index 0000000..90230ad
--- /dev/null
+++ b/internal/infra/keyring_token_store.go
@@ -0,0 +1,84 @@
+package infra
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"time"
+
+	keyring "github.com/zalando/go-keyring"
+)
+
+// ErrNotFound is returned by Load when no token exists for the given account.
+var ErrNotFound = errors.New("token not found in keyring")
+
+// Token holds OAuth/OIDC credentials that need to survive app restarts.
+type Token struct {
+	AccessToken   string    `json:"access_token"`
+	RefreshToken  string    `json:"refresh_token,omitempty"`
+	ExpiresAt     time.Time `json:"expires_at,omitempty"` // zero = never expires
+	UserID        string    `json:"user_id"`
+	DeviceID      string    `json:"device_id,omitempty"`
+	HomeserverURL string    `json:"homeserver_url"`
+	Issuer        string    `json:"issuer,omitempty"`   // MAS/OIDC issuer URL
+	ClientID      string    `json:"client_id,omitempty"` // MAS client_id used
+	// PickleKeyHex is the 32-byte hex-encoded key used by cryptohelper to
+	// pickle Olm/Megolm sessions at-rest in the SQLite crypto store.
+	// MUST persist across restarts. If lost, the crypto store is unusable
+	// and a fresh device login is required.
+	PickleKeyHex string `json:"pickle_key_hex,omitempty"`
+}
+
+// KeyringTokenStore persists tokens in the OS keyring (Secret Service on Linux,
+// Keychain on macOS, Credential Manager on Windows).
+type KeyringTokenStore struct {
+	// Service is the keyring namespace. Keep it stable across app versions.
+	// Example: "fn_registry.matrix_client_pc"
+	Service string
+}
+
+// NewKeyringTokenStore returns a store scoped to the given service name.
+func NewKeyringTokenStore(service string) *KeyringTokenStore {
+	return &KeyringTokenStore{Service: service}
+}
+
+// Save serialises t to JSON and writes it to the keyring under (service, account).
+// Overwrites silently if an entry already exists.
+// account is typically the user ID, e.g. "@user:homeserver.example.com".
+func (s *KeyringTokenStore) Save(account string, t Token) error {
+	b, err := json.Marshal(t)
+	if err != nil {
+		return fmt.Errorf("keyring save: marshal: %w", err)
+	}
+	if err := keyring.Set(s.Service, account, string(b)); err != nil {
+		return fmt.Errorf("keyring save: %w", err)
+	}
+	return nil
+}
+
+// Load retrieves and deserialises the token stored under (service, account).
+// Returns ErrNotFound if no entry exists. Callers should check with errors.Is.
+func (s *KeyringTokenStore) Load(account string) (*Token, error) {
+	raw, err := keyring.Get(s.Service, account)
+	if err != nil {
+		if errors.Is(err, keyring.ErrNotFound) {
+			return nil, ErrNotFound
+		}
+		return nil, fmt.Errorf("keyring load: %w", err)
+	}
+	var t Token
+	if err := json.Unmarshal([]byte(raw), &t); err != nil {
+		return nil, fmt.Errorf("keyring load: unmarshal: %w", err)
+	}
+	return &t, nil
+}
+
+// Delete removes the token for account from the keyring.
+// Idempotent: if no entry exists, returns nil.
+func (s *KeyringTokenStore) Delete(account string) error {
+	err := keyring.Delete(s.Service, account)
+	if err != nil && !errors.Is(err, keyring.ErrNotFound) {
+		return fmt.Errorf("keyring delete: %w", err)
+	}
+	return nil
+}
diff --git a/internal/infra/mas_oidc_loopback.go b/internal/infra/mas_oidc_loopback.go
new file mode 100644
index 0000000..b1f5d84
--- /dev/null
+++ b/internal/infra/mas_oidc_loopback.go
@@ -0,0 +1,382 @@
+package infra
+
+import (
+	"context"
+	"crypto/rand"
+	"crypto/sha256"
+	"encoding/base64"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net"
+	"net/http"
+	"net/url"
+	"os/exec"
+	"runtime"
+	"strings"
+	"time"
+)
+
+// MasOidcLoopbackConfig configura el flujo OAuth2 PKCE con loopback HTTP
+// contra Matrix Authentication Service (MAS).
+type MasOidcLoopbackConfig struct {
+	// Issuer es la URL base del MAS. Debe terminar en "/".
+	// La funcion hace GET a {Issuer}.well-known/openid-configuration para descubrir endpoints.
+	Issuer string
+
+	// ClientID es el ULID del client registrado en MAS.
+	// El client debe tener client_auth_method: none (public client PKCE).
+	ClientID string
+
+	// Scopes a solicitar. Si vacio usa ["openid", "urn:matrix:org.matrix.msc2967.client:api:*"].
+	Scopes []string
+
+	// LoopbackPort es el puerto local donde escucha el callback.
+	// Debe coincidir con el redirect_uri registrado en MAS (http://127.0.0.1:{port}/callback).
+	// Si 0, elige un puerto libre dinamicamente.
+	LoopbackPort int
+
+	// OpenBrowser abre el browser del SO automaticamente si es true.
+	// Si false, imprime la URL a stdout y espera que el caller la abra.
+	OpenBrowser bool
+
+	// TimeoutSeconds es el tiempo maximo esperando el callback. Default 300.
+	TimeoutSeconds int
+}
+
+// MasOidcLoopbackResult contiene los tokens devueltos por MAS tras el intercambio.
+type MasOidcLoopbackResult struct {
+	// AccessToken es el Bearer token para usar contra Synapse.
+	AccessToken string `json:"access_token"`
+
+	// RefreshToken permite renovar el access token sin re-autenticar.
+	RefreshToken string `json:"refresh_token"`
+
+	// ExpiresIn es el tiempo de vida del access token en segundos.
+	ExpiresIn int `json:"expires_in"`
+
+	// TokenType es el tipo de token, normalmente "Bearer".
+	TokenType string `json:"token_type"`
+
+	// Scope es la lista de scopes concedidos (space-separated).
+	Scope string `json:"scope"`
+
+	// IDToken es el JWT de identidad OIDC (puede estar vacio si no se pidio openid).
+	IDToken string `json:"id_token,omitempty"`
+}
+
+// oidcDiscovery es la respuesta de .well-known/openid-configuration.
+type oidcDiscovery struct {
+	AuthorizationEndpoint string `json:"authorization_endpoint"`
+	TokenEndpoint         string `json:"token_endpoint"`
+}
+
+// MasOidcLoopback ejecuta el flujo OAuth2 Authorization Code + PKCE contra MAS
+// usando un servidor HTTP loopback para recibir el callback.
+//
+// Flujo:
+//  1. Discovery de endpoints via .well-known/openid-configuration.
+//  2. Generacion de code_verifier/challenge PKCE y state anti-CSRF.
+//  3. Arranque de servidor loopback en 127.0.0.1:{LoopbackPort}.
+//  4. Apertura del browser (o impresion de URL si OpenBrowser=false).
+//  5. Espera del callback con el authorization code.
+//  6. Intercambio del code por tokens via POST al token_endpoint.
+//  7. Devolucion de MasOidcLoopbackResult.
+func MasOidcLoopback(cfg MasOidcLoopbackConfig) (*MasOidcLoopbackResult, error) {
+	// 1. Validar inputs
+	if cfg.Issuer == "" {
+		return nil, fmt.Errorf("mas_oidc_loopback: Issuer no puede estar vacio")
+	}
+	if !strings.HasSuffix(cfg.Issuer, "/") {
+		return nil, fmt.Errorf("mas_oidc_loopback: Issuer debe terminar en '/' (got %q)", cfg.Issuer)
+	}
+	if cfg.ClientID == "" {
+		return nil, fmt.Errorf("mas_oidc_loopback: ClientID no puede estar vacio")
+	}
+	if cfg.LoopbackPort < 0 {
+		return nil, fmt.Errorf("mas_oidc_loopback: LoopbackPort debe ser >= 0")
+	}
+
+	timeout := time.Duration(cfg.TimeoutSeconds) * time.Second
+	if cfg.TimeoutSeconds <= 0 {
+		timeout = 300 * time.Second
+	}
+
+	scopes := cfg.Scopes
+	if len(scopes) == 0 {
+		scopes = []string{"openid", "urn:matrix:org.matrix.msc2967.client:api:*"}
+	}
+
+	// 2. Discovery OIDC
+	discovery, err := masOidcDiscover(cfg.Issuer)
+	if err != nil {
+		return nil, fmt.Errorf("mas_oidc_loopback: discovery failed: %w", err)
+	}
+
+	// 3. PKCE: code_verifier + code_challenge
+	verifier, challenge, err := masOidcPKCE()
+	if err != nil {
+		return nil, fmt.Errorf("mas_oidc_loopback: pkce generation failed: %w", err)
+	}
+
+	// 4. State anti-CSRF
+	state, err := masOidcRandomBase64URL(32)
+	if err != nil {
+		return nil, fmt.Errorf("mas_oidc_loopback: state generation failed: %w", err)
+	}
+
+	// 5. Arrancar loopback server
+	listener, port, err := masOidcStartListener(cfg.LoopbackPort)
+	if err != nil {
+		return nil, fmt.Errorf("mas_oidc_loopback: no se pudo abrir puerto loopback: %w", err)
+	}
+
+	redirectURI := fmt.Sprintf("http://127.0.0.1:%d/callback", port)
+
+	// Canal para recibir el code o error desde el handler HTTP
+	codeCh := make(chan string, 1)
+	errCh := make(chan error, 1)
+
+	mux := http.NewServeMux()
+	mux.HandleFunc("/callback", func(w http.ResponseWriter, r *http.Request) {
+		q := r.URL.Query()
+
+		// Validar state anti-CSRF
+		if q.Get("state") != state {
+			errCh <- fmt.Errorf("mas_oidc_loopback: state mismatch (posible CSRF) — esperado %q, recibido %q", state, q.Get("state"))
+			w.Header().Set("Content-Type", "text/html; charset=utf-8")
+			w.WriteHeader(http.StatusBadRequest)
+			_, _ = w.Write([]byte("<html><body><h2>Error: state mismatch. Por favor cierra esta ventana.</h2></body></html>"))
+			return
+		}
+
+		// Verificar error del proveedor
+		if errParam := q.Get("error"); errParam != "" {
+			desc := q.Get("error_description")
+			errCh <- fmt.Errorf("mas_oidc_loopback: proveedor devolvio error %q: %s", errParam, desc)
+			w.Header().Set("Content-Type", "text/html; charset=utf-8")
+			w.WriteHeader(http.StatusBadRequest)
+			_, _ = w.Write([]byte(fmt.Sprintf("<html><body><h2>Error de autorizacion: %s</h2></body></html>", desc)))
+			return
+		}
+
+		code := q.Get("code")
+		if code == "" {
+			errCh <- fmt.Errorf("mas_oidc_loopback: callback sin 'code'")
+			w.Header().Set("Content-Type", "text/html; charset=utf-8")
+			w.WriteHeader(http.StatusBadRequest)
+			_, _ = w.Write([]byte("<html><body><h2>Error: no se recibio authorization code.</h2></body></html>"))
+			return
+		}
+
+		// Responder al browser con mensaje de exito
+		w.Header().Set("Content-Type", "text/html; charset=utf-8")
+		w.WriteHeader(http.StatusOK)
+		_, _ = w.Write([]byte(`<!DOCTYPE html>
+<html lang="es">
+<head><meta charset="utf-8"><title>Login completo</title></head>
+<body style="font-family:sans-serif;text-align:center;padding:3em;">
+<h2>Login completo</h2>
+<p>Puedes cerrar esta ventana y volver a la aplicacion.</p>
+</body>
+</html>`))
+
+		codeCh <- code
+	})
+
+	srv := &http.Server{Handler: mux}
+
+	// Arrancar el servidor en goroutine
+	srvErrCh := make(chan error, 1)
+	go func() {
+		if err := srv.Serve(listener); err != nil && err != http.ErrServerClosed {
+			srvErrCh <- err
+		}
+	}()
+
+	// 6. Construir URL de autorización
+	authURL := masOidcBuildAuthURL(
+		discovery.AuthorizationEndpoint,
+		cfg.ClientID,
+		redirectURI,
+		strings.Join(scopes, " "),
+		state,
+		challenge,
+	)
+
+	// 7. Abrir browser o imprimir URL
+	if cfg.OpenBrowser {
+		if err := masOidcOpenBrowser(authURL); err != nil {
+			// No es fatal: continuamos y el usuario puede abrir manualmente
+			fmt.Printf("mas_oidc_loopback: no se pudo abrir el browser automaticamente.\nAbre esta URL manualmente:\n%s\n", authURL)
+		}
+	} else {
+		fmt.Printf("Abre esta URL en tu browser para autenticarte:\n%s\n", authURL)
+	}
+
+	// 8. Esperar callback con timeout
+	ctx, cancel := context.WithTimeout(context.Background(), timeout)
+	defer cancel()
+
+	var code string
+	select {
+	case code = <-codeCh:
+		// ok
+	case callbackErr := <-errCh:
+		_ = srv.Shutdown(context.Background())
+		return nil, callbackErr
+	case <-ctx.Done():
+		_ = srv.Shutdown(context.Background())
+		return nil, fmt.Errorf("mas_oidc_loopback: timeout esperando callback despues de %v", timeout)
+	case srvErr := <-srvErrCh:
+		return nil, fmt.Errorf("mas_oidc_loopback: servidor loopback fallo: %w", srvErr)
+	}
+
+	// 9. Shutdown graceful del servidor loopback
+	shutdownCtx, shutdownCancel := context.WithTimeout(context.Background(), 2*time.Second)
+	defer shutdownCancel()
+	_ = srv.Shutdown(shutdownCtx)
+
+	// 10. Intercambiar code por tokens
+	result, err := masOidcExchangeCode(
+		discovery.TokenEndpoint,
+		cfg.ClientID,
+		code,
+		redirectURI,
+		verifier,
+	)
+	if err != nil {
+		return nil, fmt.Errorf("mas_oidc_loopback: token exchange failed: %w", err)
+	}
+
+	return result, nil
+}
+
+// masOidcHTTPClient es el cliente HTTP usado por masOidcDiscover y masOidcExchangeCode.
+// Tiene timeout de 15s. Puede ser reemplazado en tests.
+var masOidcHTTPClient = &http.Client{Timeout: 15 * time.Second}
+
+// masOidcDiscover obtiene los endpoints OIDC desde .well-known/openid-configuration.
+func masOidcDiscover(issuer string) (*oidcDiscovery, error) {
+	discoveryURL := issuer + ".well-known/openid-configuration"
+	resp, err := masOidcHTTPClient.Get(discoveryURL) //nolint:gosec
+	if err != nil {
+		return nil, fmt.Errorf("GET %s: %w", discoveryURL, err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		body, _ := io.ReadAll(resp.Body)
+		return nil, fmt.Errorf("discovery HTTP %d: %s", resp.StatusCode, string(body))
+	}
+
+	var d oidcDiscovery
+	if err := json.NewDecoder(resp.Body).Decode(&d); err != nil {
+		return nil, fmt.Errorf("parsing discovery JSON: %w", err)
+	}
+	if d.AuthorizationEndpoint == "" {
+		return nil, fmt.Errorf("discovery: authorization_endpoint vacio")
+	}
+	if d.TokenEndpoint == "" {
+		return nil, fmt.Errorf("discovery: token_endpoint vacio")
+	}
+	return &d, nil
+}
+
+// masOidcPKCE genera un code_verifier aleatorio y su code_challenge SHA256/base64url.
+func masOidcPKCE() (verifier, challenge string, err error) {
+	verifier, err = masOidcRandomBase64URL(32) // 32 bytes -> 43 chars base64url
+	if err != nil {
+		return "", "", err
+	}
+	h := sha256.Sum256([]byte(verifier))
+	challenge = base64.RawURLEncoding.EncodeToString(h[:])
+	return verifier, challenge, nil
+}
+
+// masOidcRandomBase64URL genera n bytes aleatorios codificados en base64url sin padding.
+func masOidcRandomBase64URL(n int) (string, error) {
+	b := make([]byte, n)
+	if _, err := rand.Read(b); err != nil {
+		return "", err
+	}
+	return base64.RawURLEncoding.EncodeToString(b), nil
+}
+
+// masOidcStartListener abre un listener TCP en 127.0.0.1:{port}.
+// Si port=0, elige un puerto libre y devuelve el puerto asignado.
+func masOidcStartListener(port int) (net.Listener, int, error) {
+	addr := fmt.Sprintf("127.0.0.1:%d", port)
+	l, err := net.Listen("tcp", addr)
+	if err != nil {
+		return nil, 0, err
+	}
+	assignedPort := l.Addr().(*net.TCPAddr).Port
+	return l, assignedPort, nil
+}
+
+// masOidcBuildAuthURL construye la URL de autorización OAuth2 con PKCE.
+func masOidcBuildAuthURL(authEndpoint, clientID, redirectURI, scope, state, challenge string) string {
+	u, _ := url.Parse(authEndpoint)
+	q := u.Query()
+	q.Set("response_type", "code")
+	q.Set("client_id", clientID)
+	q.Set("redirect_uri", redirectURI)
+	q.Set("scope", scope)
+	q.Set("state", state)
+	q.Set("code_challenge", challenge)
+	q.Set("code_challenge_method", "S256")
+	u.RawQuery = q.Encode()
+	return u.String()
+}
+
+// masOidcOpenBrowser abre la URL en el browser predeterminado del SO.
+func masOidcOpenBrowser(rawURL string) error {
+	var cmd *exec.Cmd
+	switch runtime.GOOS {
+	case "linux":
+		cmd = exec.Command("xdg-open", rawURL)
+	case "darwin":
+		cmd = exec.Command("open", rawURL)
+	case "windows":
+		cmd = exec.Command("rundll32", "url.dll,FileProtocolHandler", rawURL)
+	default:
+		return fmt.Errorf("plataforma no soportada para abrir browser: %s", runtime.GOOS)
+	}
+	return cmd.Start()
+}
+
+// masOidcExchangeCode intercambia el authorization code por tokens via POST al token_endpoint.
+func masOidcExchangeCode(tokenEndpoint, clientID, code, redirectURI, verifier string) (*MasOidcLoopbackResult, error) {
+	formData := url.Values{}
+	formData.Set("grant_type", "authorization_code")
+	formData.Set("code", code)
+	formData.Set("redirect_uri", redirectURI)
+	formData.Set("client_id", clientID)
+	formData.Set("code_verifier", verifier)
+
+	resp, err := masOidcHTTPClient.PostForm(tokenEndpoint, formData) //nolint:gosec
+	if err != nil {
+		return nil, fmt.Errorf("POST %s: %w", tokenEndpoint, err)
+	}
+	defer resp.Body.Close()
+
+	body, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return nil, fmt.Errorf("leyendo respuesta del token endpoint: %w", err)
+	}
+
+	if resp.StatusCode != http.StatusOK {
+		return nil, fmt.Errorf("token endpoint HTTP %d: %s", resp.StatusCode, string(body))
+	}
+
+	var result MasOidcLoopbackResult
+	if err := json.Unmarshal(body, &result); err != nil {
+		return nil, fmt.Errorf("parsing token response JSON: %w", err)
+	}
+	if result.AccessToken == "" {
+		return nil, fmt.Errorf("token response sin access_token: %s", string(body))
+	}
+
+	return &result, nil
+}
diff --git a/internal/infra/matrix_client_init.go b/internal/infra/matrix_client_init.go
new file mode 100644
index 0000000..513767a
--- /dev/null
+++ b/internal/infra/matrix_client_init.go
@@ -0,0 +1,153 @@
+package infra
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"net/url"
+	"os"
+	"path/filepath"
+	"strings"
+	"time"
+
+	"maunium.net/go/mautrix"
+	"maunium.net/go/mautrix/id"
+)
+
+// MatrixClientInitConfig parametriza la inicializacion del cliente Matrix.
+type MatrixClientInitConfig struct {
+	// HomeserverURL es la URL base del servidor Matrix (Synapse/Dendrite/etc.).
+	// Ejemplo: "https://matrix-af2f3d.organic-machine.com"
+	HomeserverURL string
+
+	// UserID es el MXID del usuario. Formato "@local:servidor".
+	// Ejemplo: "@egutierrez:matrix-af2f3d.organic-machine.com"
+	UserID string
+
+	// AccessToken es el Bearer token obtenido del flow OIDC (mas_oidc_loopback).
+	// No puede estar vacio.
+	AccessToken string
+
+	// DeviceID del cliente Matrix. Si vacio, se descubre via /whoami al inicializar.
+	// Recomendado guardarlo en keyring tras el primer uso para evitar la llamada extra.
+	DeviceID string
+
+	// StoreDir es el directorio donde se persiste el estado de sync (next_batch, filter_id).
+	// Se crea con permisos 0700 si no existe. Puede ser relativo (se convierte a absoluto).
+	// Ejemplo: "~/.matrix_client_pc/egutierrez/" (no expandido automaticamente — usar os.UserHomeDir).
+	StoreDir string
+
+	// EnableCrypto activa el crypto store SQLite para Olm/Megolm (E2EE).
+	// En v0.1.0 devuelve error — la implementacion completa esta en issue 0150.
+	EnableCrypto bool
+}
+
+// MatrixClientInitResult contiene el cliente listo y los paths de persistencia.
+type MatrixClientInitResult struct {
+	// Client es el *mautrix.Client listo para Sync/SendMessage.
+	// UserID, AccessToken y DeviceID ya estan configurados.
+	Client *mautrix.Client
+
+	// StorePath es la ruta al directorio de persistencia de sync state.
+	StorePath string
+
+	// CryptoPath es la ruta calculada para el crypto store SQLite.
+	// Vacio si EnableCrypto=false. En v0.1.0 siempre vacio (no implementado).
+	CryptoPath string
+}
+
+// MatrixClientInit construye un *mautrix.Client listo para hacer Sync,
+// sin manejar el login (que ya hizo el flow OIDC via mas_oidc_loopback).
+//
+// Pasos:
+//  1. Valida inputs (HomeserverURL parseable, UserID formato "@x:server", AccessToken no vacio).
+//  2. Crea StoreDir con permisos 0700.
+//  3. Llama mautrix.NewClient con las credenciales.
+//  4. Si DeviceID esta vacio, hace Whoami para descubrirlo (sum latency ~100ms).
+//  5. Si EnableCrypto=true, devuelve error (issue 0150 lo implementa).
+//  6. Devuelve MatrixClientInitResult con el cliente configurado.
+func MatrixClientInit(cfg MatrixClientInitConfig) (*MatrixClientInitResult, error) {
+	// 1. Validar HomeserverURL
+	if cfg.HomeserverURL == "" {
+		return nil, fmt.Errorf("matrix_client_init: HomeserverURL no puede estar vacio")
+	}
+	if _, err := url.ParseRequestURI(cfg.HomeserverURL); err != nil {
+		return nil, fmt.Errorf("matrix_client_init: HomeserverURL invalido %q: %w", cfg.HomeserverURL, err)
+	}
+	if !strings.HasPrefix(cfg.HomeserverURL, "http://") && !strings.HasPrefix(cfg.HomeserverURL, "https://") {
+		return nil, fmt.Errorf("matrix_client_init: HomeserverURL debe empezar con http:// o https:// (got %q)", cfg.HomeserverURL)
+	}
+
+	// Validar UserID: debe ser "@local:servidor"
+	if cfg.UserID == "" {
+		return nil, fmt.Errorf("matrix_client_init: UserID no puede estar vacio")
+	}
+	if !strings.HasPrefix(cfg.UserID, "@") || !strings.Contains(cfg.UserID, ":") {
+		return nil, fmt.Errorf("matrix_client_init: UserID invalido %q — formato esperado @local:servidor", cfg.UserID)
+	}
+
+	// Validar AccessToken
+	if cfg.AccessToken == "" {
+		return nil, fmt.Errorf("matrix_client_init: AccessToken no puede estar vacio")
+	}
+
+	// Validar StoreDir
+	if cfg.StoreDir == "" {
+		return nil, fmt.Errorf("matrix_client_init: StoreDir no puede estar vacio")
+	}
+
+	// En v0.1.0 crypto no esta implementado
+	if cfg.EnableCrypto {
+		return nil, fmt.Errorf("matrix_client_init: crypto not implemented in v0.1.0, see issue 0150")
+	}
+
+	// Convertir StoreDir a absoluto si es relativo
+	storeDir := cfg.StoreDir
+	if !filepath.IsAbs(storeDir) {
+		abs, err := filepath.Abs(storeDir)
+		if err != nil {
+			return nil, fmt.Errorf("matrix_client_init: no se pudo resolver StoreDir %q: %w", storeDir, err)
+		}
+		storeDir = abs
+	}
+
+	// 2. Crear StoreDir con permisos 0700 (datos sensibles)
+	if err := os.MkdirAll(storeDir, 0700); err != nil {
+		return nil, fmt.Errorf("matrix_client_init: no se pudo crear StoreDir %q: %w", storeDir, err)
+	}
+
+	// 3. Construir cliente mautrix
+	client, err := mautrix.NewClient(cfg.HomeserverURL, id.UserID(cfg.UserID), cfg.AccessToken)
+	if err != nil {
+		return nil, fmt.Errorf("matrix_client_init: mautrix.NewClient failed: %w", err)
+	}
+
+	// 4. DeviceID: usar el proporcionado o descubrir via Whoami
+	if cfg.DeviceID != "" {
+		client.DeviceID = id.DeviceID(cfg.DeviceID)
+	} else {
+		ctx, cancel := context.WithTimeout(context.Background(), 15*time.Second)
+		defer cancel()
+
+		whoami, err := client.Whoami(ctx)
+		if err != nil {
+			// Distinguir token invalido (M_UNKNOWN_TOKEN) de error de red
+			if errors.Is(err, mautrix.MUnknownToken) {
+				return nil, fmt.Errorf("matrix_client_init: access token invalido o expirado (M_UNKNOWN_TOKEN) — refrescar via OIDC: %w", err)
+			}
+			return nil, fmt.Errorf("matrix_client_init: Whoami failed (servidor caido o token invalido): %w", err)
+		}
+		client.DeviceID = whoami.DeviceID
+	}
+
+	// Calcular CryptoPath (aunque no se use en v0.1.0)
+	cryptoPath := ""
+	// CryptoPath calculado pero no inicializado en v0.1.0
+	_ = filepath.Join(storeDir, "crypto.db") // reservado para matrix_crypto_init_go_infra (issue 0150)
+
+	return &MatrixClientInitResult{
+		Client:     client,
+		StorePath:  storeDir,
+		CryptoPath: cryptoPath,
+	}, nil
+}
diff --git a/internal/infra/matrix_crypto_init.go b/internal/infra/matrix_crypto_init.go
new file mode 100644
index 0000000..a6bf74d
--- /dev/null
+++ b/internal/infra/matrix_crypto_init.go
@@ -0,0 +1,107 @@
+//go:build goolm || libolm
+
+package infra
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"path/filepath"
+
+	"maunium.net/go/mautrix"
+	"maunium.net/go/mautrix/crypto/cryptohelper"
+)
+
+// MatrixCryptoInitConfig parametriza la inicializacion del crypto store Olm/Megolm.
+type MatrixCryptoInitConfig struct {
+	// Client es el *mautrix.Client ya inicializado via MatrixClientInit.
+	// Debe tener AccessToken, UserID y DeviceID poblados.
+	Client *mautrix.Client
+
+	// StorePath es la ruta absoluta al archivo SQLite del crypto store.
+	// Debe ser separado del state store. El SDK gestiona el schema internamente.
+	// Si el directorio padre no existe, se crea con permisos 0700.
+	// Ejemplo: "/home/lucas/.config/matrix_client_pc/egutierrez/crypto.db"
+	StorePath string
+
+	// PickleKey son exactamente 32 bytes usados por cryptohelper para cifrar las
+	// sesiones Olm en disco at-rest. DEBE persistir entre arranques (guardar en keyring).
+	// Si se pierde, el store SQLite se vuelve inutilizable y hay que crear nuevo dispositivo.
+	PickleKey []byte
+}
+
+// MatrixCryptoInitResult contiene el helper listo para usar.
+type MatrixCryptoInitResult struct {
+	// Helper es el *cryptohelper.CryptoHelper inicializado.
+	// Ya esta asignado a client.Crypto — el Sync loop cifra/descifra automaticamente.
+	Helper *cryptohelper.CryptoHelper
+
+	// StorePath es la ruta al archivo SQLite del crypto store (igual que cfg.StorePath).
+	StorePath string
+}
+
+// MatrixCryptoInit inicializa el crypto store Olm/Megolm para un cliente mautrix
+// usando cryptohelper — el wrapper oficial que abstrae SQLite + Olm identity keys +
+// one-time key upload + decrypt automatico via el Syncer.
+//
+// Pasos:
+//  1. Valida inputs (Client no nil con AccessToken/UserID/DeviceID, StorePath
+//     absoluto, PickleKey exactamente 32 bytes).
+//  2. Crea el directorio padre de StorePath con permisos 0700 si no existe.
+//  3. Construye el helper via cryptohelper.NewCryptoHelper(client, pickleKey, storePath).
+//  4. Llama helper.Init(ctx) — crea tablas SQLite, carga cuenta Olm, sube one-time keys.
+//  5. Asigna client.Crypto = helper para que SendMessageEvent cifre automaticamente.
+//  6. Devuelve MatrixCryptoInitResult con el helper listo.
+func MatrixCryptoInit(ctx context.Context, cfg MatrixCryptoInitConfig) (*MatrixCryptoInitResult, error) {
+	// 1. Validar Client
+	if cfg.Client == nil {
+		return nil, fmt.Errorf("matrix_crypto_init: Client no puede ser nil")
+	}
+	if cfg.Client.AccessToken == "" {
+		return nil, fmt.Errorf("matrix_crypto_init: Client.AccessToken no puede estar vacio")
+	}
+	if cfg.Client.UserID == "" {
+		return nil, fmt.Errorf("matrix_crypto_init: Client.UserID no puede estar vacio")
+	}
+	if cfg.Client.DeviceID == "" {
+		return nil, fmt.Errorf("matrix_crypto_init: Client.DeviceID no puede estar vacio — descubrirlo via MatrixClientInit o Whoami antes de llamar MatrixCryptoInit")
+	}
+
+	// Validar StorePath
+	if cfg.StorePath == "" {
+		return nil, fmt.Errorf("matrix_crypto_init: StorePath no puede estar vacio")
+	}
+	if !filepath.IsAbs(cfg.StorePath) {
+		return nil, fmt.Errorf("matrix_crypto_init: StorePath debe ser una ruta absoluta (got %q)", cfg.StorePath)
+	}
+
+	// Validar PickleKey: exactamente 32 bytes
+	if len(cfg.PickleKey) != 32 {
+		return nil, fmt.Errorf("matrix_crypto_init: PickleKey debe tener exactamente 32 bytes (got %d)", len(cfg.PickleKey))
+	}
+
+	// 2. Crear directorio padre con permisos 0700 (datos sensibles)
+	storeDir := filepath.Dir(cfg.StorePath)
+	if err := os.MkdirAll(storeDir, 0700); err != nil {
+		return nil, fmt.Errorf("matrix_crypto_init: no se pudo crear directorio del store %q: %w", storeDir, err)
+	}
+
+	// 3. Construir CryptoHelper — acepta string como path SQLite directamente (v0.28 API)
+	helper, err := cryptohelper.NewCryptoHelper(cfg.Client, cfg.PickleKey, cfg.StorePath)
+	if err != nil {
+		return nil, fmt.Errorf("matrix_crypto_init: NewCryptoHelper failed: %w", err)
+	}
+
+	// 4. Init: crea tablas SQLite, carga cuenta Olm, sube one-time keys al servidor
+	if err := helper.Init(ctx); err != nil {
+		return nil, fmt.Errorf("matrix_crypto_init: helper.Init failed (comprueba conectividad con Synapse y validez del token): %w", err)
+	}
+
+	// 5. Asignar client.Crypto para que SendMessageEvent cifre automaticamente
+	cfg.Client.Crypto = helper
+
+	return &MatrixCryptoInitResult{
+		Helper:    helper,
+		StorePath: cfg.StorePath,
+	}, nil
+}
diff --git a/internal/infra/matrix_message_send.go b/internal/infra/matrix_message_send.go
new file mode 100644
index 0000000..ce4ba5c
--- /dev/null
+++ b/internal/infra/matrix_message_send.go
@@ -0,0 +1,121 @@
+package infra
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+
+	"github.com/microcosm-cc/bluemonday"
+	"github.com/yuin/goldmark"
+	"maunium.net/go/mautrix"
+	"maunium.net/go/mautrix/event"
+	"maunium.net/go/mautrix/id"
+)
+
+// matrixMarkdownToHTML convierte Markdown a HTML sanitizado con goldmark + bluemonday.
+// El HTML resultante es seguro para incluir en formatted_body de un evento Matrix.
+// Allowlist: bluemonday UGCPolicy + <details>, <summary>, <code>, <pre>.
+func matrixMarkdownToHTML(markdown string) (string, error) {
+	var buf bytes.Buffer
+	if err := goldmark.Convert([]byte(markdown), &buf); err != nil {
+		return "", fmt.Errorf("matrix_message_send: goldmark convert: %w", err)
+	}
+	p := bluemonday.UGCPolicy()
+	p.AllowElements("details", "summary", "code", "pre")
+	sanitized := p.SanitizeBytes(buf.Bytes())
+	return string(sanitized), nil
+}
+
+// matrixSendEvent es el helper interno que llama a client.SendMessageEvent
+// y devuelve el id.EventID asignado por Synapse.
+func matrixSendEvent(ctx context.Context, client *mautrix.Client, roomID id.RoomID, eventType event.Type, content interface{}) (id.EventID, error) {
+	resp, err := client.SendMessageEvent(ctx, roomID, eventType, content)
+	if err != nil {
+		return "", err
+	}
+	return resp.EventID, nil
+}
+
+// MatrixSendText envía un mensaje de texto plano (m.text) al room indicado.
+// Si el room tiene E2EE activo y client.Crypto != nil, mautrix cifra automáticamente.
+func MatrixSendText(ctx context.Context, client *mautrix.Client, roomID id.RoomID, body string) (id.EventID, error) {
+	if client == nil {
+		return "", fmt.Errorf("matrix_message_send: client no puede ser nil")
+	}
+	content := &event.MessageEventContent{
+		MsgType: event.MsgText,
+		Body:    body,
+	}
+	return matrixSendEvent(ctx, client, roomID, event.EventMessage, content)
+}
+
+// MatrixSendMarkdown convierte markdown a HTML con goldmark, lo sanitiza con bluemonday
+// (UGCPolicy + <details>, <summary>, <code>, <pre>) y envía con format=org.matrix.custom.html.
+// El campo Body contiene el markdown original como fallback para clientes sin HTML.
+func MatrixSendMarkdown(ctx context.Context, client *mautrix.Client, roomID id.RoomID, markdown string) (id.EventID, error) {
+	if client == nil {
+		return "", fmt.Errorf("matrix_message_send: client no puede ser nil")
+	}
+	htmlBody, err := matrixMarkdownToHTML(markdown)
+	if err != nil {
+		return "", fmt.Errorf("matrix_message_send.MatrixSendMarkdown: %w", err)
+	}
+	content := &event.MessageEventContent{
+		MsgType:       event.MsgText,
+		Body:          markdown,
+		Format:        event.FormatHTML,
+		FormattedBody: htmlBody,
+	}
+	return matrixSendEvent(ctx, client, roomID, event.EventMessage, content)
+}
+
+// MatrixSendReply envía un mensaje con m.relates_to.m.in_reply_to apuntando a replyTo.
+// El body es el texto de la respuesta. En v0.1.0 el caller construye la cita si la necesita.
+// El cifrado E2EE es automático si client.Crypto está configurado.
+func MatrixSendReply(ctx context.Context, client *mautrix.Client, roomID id.RoomID, replyTo id.EventID, body string) (id.EventID, error) {
+	if client == nil {
+		return "", fmt.Errorf("matrix_message_send: client no puede ser nil")
+	}
+	content := &event.MessageEventContent{
+		MsgType:   event.MsgText,
+		Body:      body,
+		RelatesTo: (&event.RelatesTo{}).SetReplyTo(replyTo),
+	}
+	return matrixSendEvent(ctx, client, roomID, event.EventMessage, content)
+}
+
+// MatrixEditMessage envía un replacement event (m.replace) compatible con Element y la spec Matrix.
+// NewContent contiene el texto nuevo; Body es el fallback "* newBody" para clientes sin soporte de edición.
+// eventID es el evento original a reemplazar.
+func MatrixEditMessage(ctx context.Context, client *mautrix.Client, roomID id.RoomID, eventID id.EventID, newBody string) (id.EventID, error) {
+	if client == nil {
+		return "", fmt.Errorf("matrix_message_send: client no puede ser nil")
+	}
+	content := &event.MessageEventContent{
+		MsgType: event.MsgText,
+		Body:    "* " + newBody,
+		NewContent: &event.MessageEventContent{
+			MsgType: event.MsgText,
+			Body:    newBody,
+		},
+		RelatesTo: (&event.RelatesTo{}).SetReplace(eventID),
+	}
+	return matrixSendEvent(ctx, client, roomID, event.EventMessage, content)
+}
+
+// MatrixSendReaction envía un evento m.reaction con m.relates_to.rel_type=m.annotation.
+// key debe ser el emoji unicode raw (ej. "👍"), no shortcode (:thumbsup:).
+// Las reactions no se cifran aunque el room sea E2EE (comportamiento de mautrix-go).
+func MatrixSendReaction(ctx context.Context, client *mautrix.Client, roomID id.RoomID, targetEventID id.EventID, key string) (id.EventID, error) {
+	if client == nil {
+		return "", fmt.Errorf("matrix_message_send: client no puede ser nil")
+	}
+	content := &event.ReactionEventContent{
+		RelatesTo: event.RelatesTo{
+			Type:    event.RelAnnotation,
+			EventID: targetEventID,
+			Key:     key,
+		},
+	}
+	return matrixSendEvent(ctx, client, roomID, event.EventReaction, content)
+}
diff --git a/internal/infra/matrix_room_list.go b/internal/infra/matrix_room_list.go
new file mode 100644
index 0000000..216d279
--- /dev/null
+++ b/internal/infra/matrix_room_list.go
@@ -0,0 +1,300 @@
+package infra
+
+import (
+	"context"
+	"fmt"
+	"log"
+	"sort"
+	"strings"
+
+	"maunium.net/go/mautrix"
+	"maunium.net/go/mautrix/event"
+	"maunium.net/go/mautrix/id"
+)
+
+// RoomSummary es el resumen de una room Matrix para renderizar en el sidebar de un cliente.
+type RoomSummary struct {
+	RoomID         string   `json:"room_id"`
+	Name           string   `json:"name,omitempty"`            // m.room.name o fallback
+	CanonicalAlias string   `json:"canonical_alias,omitempty"` // #room:server
+	AvatarMxc      string   `json:"avatar_mxc,omitempty"`      // mxc://...
+	Topic          string   `json:"topic,omitempty"`
+	IsDirect       bool     `json:"is_direct"`    // m.direct account_data
+	IsSpace        bool     `json:"is_space"`     // m.room.type == m.space
+	IsEncrypted    bool     `json:"is_encrypted"` // m.room.encryption state event presente
+	MemberCount    int      `json:"member_count"`
+	LastEventTs    int64    `json:"last_event_ts"` // unix ms del ultimo evento conocido
+	UnreadCount    int      `json:"unread_count"`  // notifications.unread + highlight
+	Tags           []string `json:"tags,omitempty"` // m.tag account_data
+}
+
+// MatrixRoomListConfig agrupa los parametros de MatrixRoomList.
+type MatrixRoomListConfig struct {
+	Client *mautrix.Client
+}
+
+// MatrixRoomList devuelve todos los rooms en los que el usuario esta unido,
+// ordenados por LastEventTs DESC (recientes primero).
+//
+// Estrategia:
+//  1. JoinedRooms() para la lista de room IDs.
+//  2. m.direct account_data para detectar DMs.
+//  3. Para cada room: State() -> nombre, alias, topic, avatar, encryption, space, members.
+//  4. Messages(limit=1) -> LastEventTs (TODO: coste N*HTTP; cachear con TTL 30s).
+//  5. GetRoomAccountData("m.tag") -> Tags.
+//
+// Sub-operaciones que fallan por room concreto no abortan el global.
+// LastEventTs puede ser 0 si el store no lo cachea (ver ## Gotchas del .md).
+func MatrixRoomList(ctx context.Context, cfg MatrixRoomListConfig) ([]RoomSummary, error) {
+	if cfg.Client == nil {
+		return nil, fmt.Errorf("matrix_room_list: client no puede ser nil")
+	}
+	client := cfg.Client
+
+	// 1. Rooms unidos
+	respJoined, err := client.JoinedRooms(ctx)
+	if err != nil {
+		return nil, fmt.Errorf("matrix_room_list: JoinedRooms: %w", err)
+	}
+	if len(respJoined.JoinedRooms) == 0 {
+		return []RoomSummary{}, nil
+	}
+
+	// 2. m.direct -> set roomID -> true
+	directSet := loadDirectRooms(ctx, client)
+
+	// 3. Construir summaries (secuencial para v0.1.0)
+	results := make([]RoomSummary, 0, len(respJoined.JoinedRooms))
+	for _, roomID := range respJoined.JoinedRooms {
+		s := buildRoomSummaryFromState(ctx, client, roomID, directSet)
+		results = append(results, s)
+	}
+
+	// 4. Ordenar DESC por LastEventTs; si empatan (ej. todo 0) -> alfabetico por Name
+	sort.Slice(results, func(i, j int) bool {
+		if results[i].LastEventTs != results[j].LastEventTs {
+			return results[i].LastEventTs > results[j].LastEventTs
+		}
+		return results[i].Name < results[j].Name
+	})
+
+	return results, nil
+}
+
+// loadDirectRooms carga m.direct account_data y devuelve un set roomID -> true.
+// Falla silenciosamente: si hay error devuelve mapa vacio (IsDirect quedara false).
+func loadDirectRooms(ctx context.Context, client *mautrix.Client) map[id.RoomID]bool {
+	result := make(map[id.RoomID]bool)
+	var directContent event.DirectChatsEventContent
+	if err := client.GetAccountData(ctx, "m.direct", &directContent); err != nil {
+		log.Printf("matrix_room_list: GetAccountData(m.direct) warning: %v", err)
+		return result
+	}
+	for _, rooms := range directContent {
+		for _, rid := range rooms {
+			result[rid] = true
+		}
+	}
+	return result
+}
+
+// buildRoomSummaryFromState construye el RoomSummary para un room concreto.
+// Si State() falla usa el roomID como Name de emergencia.
+func buildRoomSummaryFromState(ctx context.Context, client *mautrix.Client, roomID id.RoomID, directSet map[id.RoomID]bool) RoomSummary {
+	s := RoomSummary{
+		RoomID:   string(roomID),
+		IsDirect: directSet[roomID],
+	}
+
+	// State del room
+	stateMap, err := client.State(ctx, roomID)
+	if err != nil {
+		log.Printf("matrix_room_list: State(%s) warning: %v", roomID, err)
+		s.Name = deriveRoomName(&s, nil)
+		return s
+	}
+
+	fillStateFields(&s, stateMap)
+	s.Name = deriveRoomName(&s, stateMap)
+
+	// Tags: m.tag room account_data
+	s.Tags = loadRoomTags(ctx, client, roomID)
+
+	// LastEventTs: Messages(limit=1, dir=backward)
+	// TODO(0148): caro N*HTTP -> cachear en backend con TTL 30s.
+	msgs, err := client.Messages(ctx, roomID, "", "", mautrix.DirectionBackward, nil, 1)
+	if err != nil {
+		log.Printf("matrix_room_list: Messages(%s) warning: %v", roomID, err)
+		// No fatal: LastEventTs queda 0 y el room cae al fondo del orden
+	} else if msgs != nil && len(msgs.Chunk) > 0 {
+		s.LastEventTs = msgs.Chunk[0].Timestamp
+	}
+
+	return s
+}
+
+// ensureParsed llama ParseRaw si el contenido no esta aun parseado.
+// ParseRaw devuelve ErrContentAlreadyParsed cuando ya fue parseado (p.ej.
+// por parseRoomStateArray al deserializar el state); en ese caso ignoramos
+// el error y usamos el Parsed existente.
+func ensureParsed(c *event.Content, evtType event.Type) {
+	if c.Parsed == nil {
+		_ = c.ParseRaw(evtType)
+	}
+}
+
+// fillStateFields rellena los campos del RoomSummary a partir del state map.
+// parseRoomStateArray ya llama ParseRaw al deserializar, por lo que es posible
+// que Content.Parsed este ya populado. ensureParsed maneja ambos casos.
+func fillStateFields(s *RoomSummary, stateMap mautrix.RoomStateMap) {
+	// m.room.name
+	if nameEvts, ok := stateMap[event.StateRoomName]; ok {
+		if nameEvt, ok := nameEvts[""]; ok {
+			ensureParsed(&nameEvt.Content, event.StateRoomName)
+			if c := nameEvt.Content.AsRoomName(); c != nil {
+				s.Name = c.Name
+			}
+		}
+	}
+
+	// m.room.canonical_alias
+	if aliasEvts, ok := stateMap[event.StateCanonicalAlias]; ok {
+		if aliasEvt, ok := aliasEvts[""]; ok {
+			ensureParsed(&aliasEvt.Content, event.StateCanonicalAlias)
+			if c := aliasEvt.Content.AsCanonicalAlias(); c != nil {
+				s.CanonicalAlias = string(c.Alias)
+			}
+		}
+	}
+
+	// m.room.avatar
+	if avatarEvts, ok := stateMap[event.StateRoomAvatar]; ok {
+		if avatarEvt, ok := avatarEvts[""]; ok {
+			ensureParsed(&avatarEvt.Content, event.StateRoomAvatar)
+			if c := avatarEvt.Content.AsRoomAvatar(); c != nil {
+				s.AvatarMxc = string(c.URL)
+			}
+		}
+	}
+
+	// m.room.topic
+	if topicEvts, ok := stateMap[event.StateTopic]; ok {
+		if topicEvt, ok := topicEvts[""]; ok {
+			ensureParsed(&topicEvt.Content, event.StateTopic)
+			if c := topicEvt.Content.AsTopic(); c != nil {
+				s.Topic = c.Topic
+			}
+		}
+	}
+
+	// m.room.encryption (existence = encrypted)
+	if encEvts, ok := stateMap[event.StateEncryption]; ok {
+		if _, ok := encEvts[""]; ok {
+			s.IsEncrypted = true
+		}
+	}
+
+	// m.room.create -> IsSpace si type == "m.space"
+	if createEvts, ok := stateMap[event.StateCreate]; ok {
+		if createEvt, ok := createEvts[""]; ok {
+			ensureParsed(&createEvt.Content, event.StateCreate)
+			if c := createEvt.Content.AsCreate(); c != nil {
+				s.IsSpace = c.Type == event.RoomTypeSpace
+			}
+		}
+	}
+
+	// m.room.member: contar membership == join
+	if memberEvts, ok := stateMap[event.StateMember]; ok {
+		count := 0
+		for _, memberEvt := range memberEvts {
+			ensureParsed(&memberEvt.Content, event.StateMember)
+			if c := memberEvt.Content.AsMember(); c != nil && c.Membership == event.MembershipJoin {
+				count++
+			}
+		}
+		s.MemberCount = count
+	}
+}
+
+// deriveRoomName calcula el nombre display para el room siguiendo la jerarquia:
+//  1. Name (ya seteado desde m.room.name).
+//  2. CanonicalAlias.
+//  3. "Direct Message" si IsDirect.
+//  4. Lista de otros miembros si los hay (max 3).
+//  5. "Empty room" si MemberCount <= 1.
+func deriveRoomName(s *RoomSummary, stateMap mautrix.RoomStateMap) string {
+	if s.Name != "" {
+		return s.Name
+	}
+	if s.CanonicalAlias != "" {
+		return s.CanonicalAlias
+	}
+	if s.IsDirect {
+		// Intentar obtener displayname del otro miembro desde el state
+		if stateMap != nil {
+			if memberEvts, ok := stateMap[event.StateMember]; ok {
+				for userKey, memberEvt := range memberEvts {
+					ensureParsed(&memberEvt.Content, event.StateMember)
+					if c := memberEvt.Content.AsMember(); c != nil &&
+						c.Membership == event.MembershipJoin &&
+						userKey != "" {
+						if c.Displayname != "" {
+							return c.Displayname
+						}
+						return userKey // user ID como fallback
+					}
+				}
+			}
+		}
+		return "Direct Message"
+	}
+	if stateMap != nil && s.MemberCount > 1 {
+		// Lista de displaynames de otros miembros (max 3)
+		names := collectMemberNames(stateMap, 3)
+		if len(names) > 0 {
+			return strings.Join(names, ", ")
+		}
+	}
+	return "Empty room"
+}
+
+// collectMemberNames extrae hasta maxN displaynames de joined members del state.
+func collectMemberNames(stateMap mautrix.RoomStateMap, maxN int) []string {
+	names := make([]string, 0, maxN)
+	if memberEvts, ok := stateMap[event.StateMember]; ok {
+		for userKey, memberEvt := range memberEvts {
+			if len(names) >= maxN {
+				break
+			}
+			ensureParsed(&memberEvt.Content, event.StateMember)
+			if c := memberEvt.Content.AsMember(); c != nil && c.Membership == event.MembershipJoin {
+				if c.Displayname != "" {
+					names = append(names, c.Displayname)
+				} else if userKey != "" {
+					names = append(names, userKey)
+				}
+			}
+		}
+	}
+	return names
+}
+
+// loadRoomTags carga m.tag room account_data y devuelve los tag names como []string.
+// Falla silenciosamente devolviendo nil.
+func loadRoomTags(ctx context.Context, client *mautrix.Client, roomID id.RoomID) []string {
+	var tagContent event.TagEventContent
+	if err := client.GetRoomAccountData(ctx, roomID, "m.tag", &tagContent); err != nil {
+		// No fatal: rooms sin tags dan 404, lo cual es normal
+		return nil
+	}
+	if len(tagContent.Tags) == 0 {
+		return nil
+	}
+	tags := make([]string, 0, len(tagContent.Tags))
+	for tag := range tagContent.Tags {
+		tags = append(tags, string(tag))
+	}
+	sort.Strings(tags) // orden determinista
+	return tags
+}
diff --git a/internal/infra/matrix_sync_service.go b/internal/infra/matrix_sync_service.go
new file mode 100644
index 0000000..4a32a99
--- /dev/null
+++ b/internal/infra/matrix_sync_service.go
@@ -0,0 +1,366 @@
+package infra
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"strings"
+	"sync"
+	"time"
+
+	"maunium.net/go/mautrix"
+	"maunium.net/go/mautrix/event"
+	"maunium.net/go/mautrix/id"
+)
+
+// MatrixSyncEvent es un evento normalizado emitido por MatrixSyncService.
+// Cubre mensajes, pertenencia a sala, redacciones, reacciones, tipeo y estado.
+type MatrixSyncEvent struct {
+	Type    string      `json:"type"`           // "message" | "membership" | "redaction" | "reaction" | "edit" | "encrypted" | "presence" | "typing" | "read_receipt" | "room_state"
+	RoomID  string      `json:"room_id"`        // ID de la sala (vacio para presencia global)
+	EventID string      `json:"event_id"`       // event_id unico Matrix (vacio para eventos efimeros)
+	Sender  string      `json:"sender"`         // MXID del emisor (vacio para eventos efimeros)
+	Ts      int64       `json:"ts"`             // origin_server_ts en milisegundos
+	Body    string      `json:"body,omitempty"` // contenido de texto del evento (mensajes)
+	Raw     interface{} `json:"raw,omitempty"`  // *event.Event original para acceso completo
+}
+
+// MatrixSyncServiceConfig configura el servicio de sync loop de Matrix.
+type MatrixSyncServiceConfig struct {
+	// Client es el *mautrix.Client ya inicializado con credenciales.
+	// Obligatorio.
+	Client *mautrix.Client
+
+	// InitialBackoffMS es el tiempo inicial de espera entre reintentos tras error (ms).
+	// Default: 1000 (1 segundo).
+	InitialBackoffMS int
+
+	// MaxBackoffMS es el techo del backoff exponencial (ms).
+	// Default: 60000 (60 segundos).
+	MaxBackoffMS int
+
+	// ChannelBuffer es la capacidad del canal Events.
+	// Si el consumer va lento y el buffer se llena, el sync se bloquea hasta
+	// que el consumer drene. Default: 256.
+	ChannelBuffer int
+}
+
+// MatrixSyncServiceHandle es el handle devuelto por MatrixSyncService.
+type MatrixSyncServiceHandle struct {
+	// Events es el canal de eventos normalizados (cierra al Stop).
+	Events <-chan MatrixSyncEvent
+
+	// Errors recibe errores transitorios (red, 5xx, etc.).
+	// No fatal: el servicio reintenta con backoff. El caller decide si actuar.
+	// El canal cierra al Stop.
+	Errors <-chan error
+
+	// Stop cancela el sync loop de forma limpia e idempotente.
+	// Cierra Events y Errors. Seguro llamar varias veces.
+	Stop func()
+}
+
+// matrixSyncerWrapper envuelve DefaultSyncer para interceptar OnFailedSync
+// e inyectar nuestro backoff exponencial y emision de errores al canal.
+type matrixSyncerWrapper struct {
+	*mautrix.DefaultSyncer
+	errCh      chan<- error
+	innerCtx   context.Context
+	backoffMs  *int
+	initialMS  int
+	maxMS      int
+	lastSyncOK *time.Time
+}
+
+// OnFailedSync implementa mautrix.Syncer. Emite el error al canal y devuelve
+// el proximo backoff. Para errores fatales (401, M_FORBIDDEN) devuelve el
+// backoff maximo y emite al canal — el caller decide via Stop().
+func (w *matrixSyncerWrapper) OnFailedSync(_ *mautrix.RespSync, err error) (time.Duration, error) {
+	if w.innerCtx.Err() != nil {
+		return 0, fmt.Errorf("matrix_sync_service: context cancelado")
+	}
+
+	// Emitir error al canal de forma no-bloqueante
+	select {
+	case w.errCh <- fmt.Errorf("matrix_sync_service: %w", err):
+	default:
+	}
+
+	// Reset backoff si el ultimo sync exitoso fue reciente
+	if time.Since(*w.lastSyncOK) < 30*time.Second {
+		*w.backoffMs = w.initialMS
+	}
+
+	// Calcular duracion de espera
+	wait := time.Duration(*w.backoffMs) * time.Millisecond
+
+	// Backoff exponencial con techo
+	*w.backoffMs *= 2
+	if *w.backoffMs > w.maxMS {
+		*w.backoffMs = w.maxMS
+	}
+
+	// Para errores fatales, esperar el maximo pero no retornar error
+	// (dejamos al caller decidir via Stop)
+	if isFatalMatrixError(err) {
+		return time.Duration(w.maxMS) * time.Millisecond, nil
+	}
+
+	return wait, nil
+}
+
+// GetFilterJSON delega al DefaultSyncer.
+func (w *matrixSyncerWrapper) GetFilterJSON(userID id.UserID) *mautrix.Filter {
+	return w.DefaultSyncer.GetFilterJSON(userID)
+}
+
+// ProcessResponse delega al DefaultSyncer. Actualiza lastSyncOK en exito.
+func (w *matrixSyncerWrapper) ProcessResponse(ctx context.Context, resp *mautrix.RespSync, since string) error {
+	err := w.DefaultSyncer.ProcessResponse(ctx, resp, since)
+	if err == nil {
+		now := time.Now()
+		*w.lastSyncOK = now
+	}
+	return err
+}
+
+// MatrixSyncService arranca el sync loop de mautrix contra Synapse en background.
+// Registra handlers para los tipos de evento mas comunes y los emite via canal.
+// Implementa reconnect con backoff exponencial para errores transitorios.
+//
+// Requiere un *mautrix.Client ya inicializado (ver matrix_client_init).
+// Opcionalmente combinar con matrix_crypto_init para descifrar m.room.encrypted.
+//
+// La goroutine interna vive hasta que ctx sea cancelado o se llame Stop.
+// Ambas acciones cierran los canales Events y Errors.
+func MatrixSyncService(ctx context.Context, cfg MatrixSyncServiceConfig) (*MatrixSyncServiceHandle, error) {
+	if cfg.Client == nil {
+		return nil, fmt.Errorf("matrix_sync_service: Client no puede ser nil")
+	}
+
+	// Aplicar defaults
+	initialBackoff := cfg.InitialBackoffMS
+	if initialBackoff <= 0 {
+		initialBackoff = 1000
+	}
+	maxBackoff := cfg.MaxBackoffMS
+	if maxBackoff <= 0 {
+		maxBackoff = 60000
+	}
+	bufSize := cfg.ChannelBuffer
+	if bufSize <= 0 {
+		bufSize = 256
+	}
+
+	// Context cancelable derivado del pasado
+	innerCtx, cancel := context.WithCancel(ctx)
+
+	// Channels
+	evtCh := make(chan MatrixSyncEvent, bufSize)
+	errCh := make(chan error, 8)
+
+	// Stop idempotente via sync.Once
+	var once sync.Once
+	stopFn := func() {
+		once.Do(func() {
+			cancel()
+		})
+	}
+
+	// Estado de backoff compartido con el wrapper
+	backoffMs := initialBackoff
+	lastSyncOK := time.Now()
+
+	// Configurar el Syncer: usar DefaultSyncer base (existente o nuevo)
+	var baseSyncer *mautrix.DefaultSyncer
+	if ds, ok := cfg.Client.Syncer.(*mautrix.DefaultSyncer); ok {
+		baseSyncer = ds
+	} else {
+		baseSyncer = mautrix.NewDefaultSyncer()
+	}
+
+	// Crear wrapper que intercepta OnFailedSync
+	wrapper := &matrixSyncerWrapper{
+		DefaultSyncer: baseSyncer,
+		errCh:         errCh,
+		innerCtx:      innerCtx,
+		backoffMs:     &backoffMs,
+		initialMS:     initialBackoff,
+		maxMS:         maxBackoff,
+		lastSyncOK:    &lastSyncOK,
+	}
+	cfg.Client.Syncer = wrapper
+
+	// Helper: emitir evento de forma no-bloqueante respetando ctx
+	emit := func(ev MatrixSyncEvent) {
+		select {
+		case evtCh <- ev:
+		case <-innerCtx.Done():
+		}
+	}
+
+	// Helper: extraer body de texto de Content.VeryRaw
+	extractBody := func(evt *event.Event) string {
+		raw := evt.Content.VeryRaw
+		if raw == nil {
+			return ""
+		}
+		var m map[string]interface{}
+		if err := json.Unmarshal(raw, &m); err != nil {
+			return ""
+		}
+		if b, ok := m["body"].(string); ok {
+			return b
+		}
+		return ""
+	}
+
+	// Registrar event handlers sobre el DefaultSyncer base
+
+	// m.room.message — mensajes de texto, imagen, archivo
+	baseSyncer.OnEventType(event.EventMessage, func(_ context.Context, evt *event.Event) {
+		emit(MatrixSyncEvent{
+			Type:    "message",
+			RoomID:  evt.RoomID.String(),
+			EventID: evt.ID.String(),
+			Sender:  evt.Sender.String(),
+			Ts:      evt.Timestamp,
+			Body:    extractBody(evt),
+			Raw:     evt,
+		})
+	})
+
+	// m.room.encrypted — mensajes cifrados (crypto helper los descifra si esta init)
+	baseSyncer.OnEventType(event.EventEncrypted, func(_ context.Context, evt *event.Event) {
+		emit(MatrixSyncEvent{
+			Type:    "encrypted",
+			RoomID:  evt.RoomID.String(),
+			EventID: evt.ID.String(),
+			Sender:  evt.Sender.String(),
+			Ts:      evt.Timestamp,
+			Raw:     evt,
+		})
+	})
+
+	// m.room.redaction — redacciones de mensajes
+	baseSyncer.OnEventType(event.EventRedaction, func(_ context.Context, evt *event.Event) {
+		emit(MatrixSyncEvent{
+			Type:    "redaction",
+			RoomID:  evt.RoomID.String(),
+			EventID: evt.ID.String(),
+			Sender:  evt.Sender.String(),
+			Ts:      evt.Timestamp,
+			Raw:     evt,
+		})
+	})
+
+	// m.reaction — reacciones emoji
+	baseSyncer.OnEventType(event.EventReaction, func(_ context.Context, evt *event.Event) {
+		emit(MatrixSyncEvent{
+			Type:    "reaction",
+			RoomID:  evt.RoomID.String(),
+			EventID: evt.ID.String(),
+			Sender:  evt.Sender.String(),
+			Ts:      evt.Timestamp,
+			Raw:     evt,
+		})
+	})
+
+	// m.room.member — cambios de pertenencia a sala
+	baseSyncer.OnEventType(event.StateMember, func(_ context.Context, evt *event.Event) {
+		emit(MatrixSyncEvent{
+			Type:    "membership",
+			RoomID:  evt.RoomID.String(),
+			EventID: evt.ID.String(),
+			Sender:  evt.Sender.String(),
+			Ts:      evt.Timestamp,
+			Raw:     evt,
+		})
+	})
+
+	// m.typing — efimero: quien esta escribiendo en una sala
+	baseSyncer.OnEventType(event.EphemeralEventTyping, func(_ context.Context, evt *event.Event) {
+		emit(MatrixSyncEvent{
+			Type:   "typing",
+			RoomID: evt.RoomID.String(),
+			Ts:     evt.Timestamp,
+			Raw:    evt,
+		})
+	})
+
+	// m.receipt — read receipts
+	baseSyncer.OnEventType(event.EphemeralEventReceipt, func(_ context.Context, evt *event.Event) {
+		emit(MatrixSyncEvent{
+			Type:   "read_receipt",
+			RoomID: evt.RoomID.String(),
+			Ts:     evt.Timestamp,
+			Raw:    evt,
+		})
+	})
+
+	// m.presence — presencia de usuarios
+	baseSyncer.OnEventType(event.EphemeralEventPresence, func(_ context.Context, evt *event.Event) {
+		emit(MatrixSyncEvent{
+			Type:   "presence",
+			Sender: evt.Sender.String(),
+			Ts:     evt.Timestamp,
+			Raw:    evt,
+		})
+	})
+
+	// Goroutine principal
+	// SyncWithContext ya es un loop bloqueante que incluye retry via OnFailedSync.
+	// Esta goroutine solo reinicia si SyncWithContext retorna con error inesperado.
+	go func() {
+		defer func() {
+			cancel()
+			close(evtCh)
+			close(errCh)
+		}()
+
+		for {
+			select {
+			case <-innerCtx.Done():
+				return
+			default:
+			}
+
+			err := cfg.Client.SyncWithContext(innerCtx)
+
+			// ctx cancelado = salida limpia
+			if innerCtx.Err() != nil {
+				return
+			}
+
+			// SyncWithContext retorna nil si otro Sync() lo cancelo
+			if err == nil {
+				return
+			}
+
+			// Cualquier otro error: pequeno delay antes de reiniciar
+			select {
+			case <-innerCtx.Done():
+				return
+			case <-time.After(time.Duration(initialBackoff) * time.Millisecond):
+			}
+		}
+	}()
+
+	return &MatrixSyncServiceHandle{
+		Events: evtCh,
+		Errors: errCh,
+		Stop:   stopFn,
+	}, nil
+}
+
+// isFatalMatrixError devuelve true si el error indica que no tiene sentido
+// reintentar (token invalido, forbidden).
+func isFatalMatrixError(err error) bool {
+	if err == nil {
+		return false
+	}
+	msg := err.Error()
+	return strings.Contains(msg, "M_UNKNOWN_TOKEN") ||
+		strings.Contains(msg, "M_FORBIDDEN") ||
+		strings.Contains(msg, "401")
+}
diff --git a/matrix_service.go b/matrix_service.go
index 1e9d78c..b72adaa 100644
--- a/matrix_service.go
+++ b/matrix_service.go
@@ -2,22 +2,30 @@ package main
 
 import (
 	"context"
+	"crypto/rand"
+	"encoding/hex"
 	"errors"
 	"fmt"
+	"path/filepath"
 	"sync"
 	"time"
 
-	"fn-registry/functions/infra"
+	"fn-registry/projects/element_agents/apps/matrix_client_pc/internal/infra"
+
+	"github.com/wailsapp/wails/v2/pkg/runtime"
+	"maunium.net/go/mautrix"
+	"maunium.net/go/mautrix/event"
+	"maunium.net/go/mautrix/id"
 )
 
 // Constants are operator-configurable later via settings UI. Hardcoded for issue 0147 MVP.
 const (
-	homeserverURL       = "https://matrix-af2f3d.organic-machine.com"
-	masIssuer           = "https://auth-af2f3d.organic-machine.com/"
-	masClientID         = "VDC4XQ2ZKN2TJ0BYVJ54FK7M6Y"
-	loopbackPort        = 8765
-	keyringServiceName  = "fn_registry.matrix_client_pc"
-	oidcTimeoutSeconds  = 300
+	homeserverURL      = "https://matrix-af2f3d.organic-machine.com"
+	masIssuer          = "https://auth-af2f3d.organic-machine.com/"
+	masClientID        = "VDC4XQ2ZKN2TJ0BYVJ54FK7M6Y"
+	loopbackPort       = 8765
+	keyringServiceName = "fn_registry.matrix_client_pc"
+	oidcTimeoutSeconds = 300
 )
 
 var defaultScopes = []string{
@@ -27,9 +35,13 @@ var defaultScopes = []string{
 
 // MatrixService is bound to the Wails frontend.
 type MatrixService struct {
-	ctx   context.Context
-	mu    sync.Mutex
-	store *infra.KeyringTokenStore
+	ctx    context.Context
+	mu     sync.Mutex
+	store  *infra.KeyringTokenStore
+	client *mautrix.Client
+	sync   *infra.MatrixSyncServiceHandle
+	crypto *infra.MatrixCryptoInitResult
+	userID string
 }
 
 func NewMatrixService() *MatrixService {
@@ -51,6 +63,28 @@ type SessionView struct {
 	ExpiresAt     string `json:"expires_at,omitempty"`
 }
 
+// MatrixEvent is the exportable, JSON-friendly shape of a Matrix event for the frontend.
+type MatrixEvent struct {
+	EventID      string `json:"event_id"`
+	RoomID       string `json:"room_id"`
+	Sender       string `json:"sender"`
+	Type         string `json:"type"`
+	Ts           int64  `json:"ts"`
+	Body         string `json:"body,omitempty"`
+	EncryptedRaw bool   `json:"encrypted_raw"`
+}
+
+// SyncEventView is what we emit through Wails events. Mirrors MatrixSyncEvent but without
+// the raw event pointer that wouldn't survive JSON serialization.
+type SyncEventView struct {
+	Type    string `json:"type"`
+	RoomID  string `json:"room_id"`
+	EventID string `json:"event_id"`
+	Sender  string `json:"sender"`
+	Ts      int64  `json:"ts"`
+	Body    string `json:"body,omitempty"`
+}
+
 // Login launches the OAuth2 PKCE flow against MAS. Blocks until completion or timeout.
 // Returns the user_id of the authenticated session.
 func (s *MatrixService) Login() (string, error) {
@@ -70,29 +104,20 @@ func (s *MatrixService) Login() (string, error) {
 		return "", fmt.Errorf("oidc: %w", err)
 	}
 
-	// Initialize Matrix client to discover user_id + device_id via whoami.
-	tmpStore := tempStoreDir()
-	clientCfg := infra.MatrixClientInitConfig{
-		HomeserverURL: homeserverURL,
-		// UserID is unknown until whoami. mautrix-go requires it pre-set, but we'll
-		// use Whoami via the Wails service directly. As shortcut: parse id_token if present.
-		// For v0.1.0 use a placeholder + Whoami after; mautrix accepts empty UserID, then
-		// updates after whoami call.
-		UserID:       "",
-		AccessToken:  res.AccessToken,
-		StoreDir:     tmpStore,
-		EnableCrypto: false,
-	}
-
 	// 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 {
 		return "", fmt.Errorf("whoami: %w", err)
 	}
-	clientCfg.UserID = userID
-	clientCfg.DeviceID = deviceID
-	clientCfg.StoreDir = userStoreDir(userID)
 
+	clientCfg := infra.MatrixClientInitConfig{
+		HomeserverURL: homeserverURL,
+		UserID:        userID,
+		DeviceID:      deviceID,
+		AccessToken:   res.AccessToken,
+		StoreDir:      userStoreDir(userID),
+		EnableCrypto:  false, // crypto goes through MatrixCryptoInit in Start()
+	}
 	if _, err := infra.MatrixClientInit(clientCfg); err != nil {
 		return "", fmt.Errorf("matrix init: %w", err)
 	}
@@ -115,10 +140,9 @@ func (s *MatrixService) Login() (string, error) {
 	return userID, nil
 }
 
-// GetSession returns the persisted session for the given user_id (or last-known if empty).
+// GetSession returns the persisted session for the given user_id.
 func (s *MatrixService) GetSession(userID string) (*SessionView, error) {
 	if userID == "" {
-		// v0.1.0: no multi-account index. Frontend must pass the user_id once known.
 		return nil, errors.New("user_id required (v0.1.0 multi-account index TODO)")
 	}
 	tok, err := s.store.Load(userID)
@@ -140,12 +164,248 @@ func (s *MatrixService) GetSession(userID string) (*SessionView, error) {
 	return view, nil
 }
 
-// Logout deletes the persisted token for the given user_id.
+// Logout deletes the persisted token + stops sync.
 func (s *MatrixService) Logout(userID string) error {
 	s.mu.Lock()
 	defer s.mu.Unlock()
 	if userID == "" {
 		return errors.New("user_id required")
 	}
+	if s.sync != nil {
+		s.sync.Stop()
+		s.sync = nil
+	}
+	s.client = nil
+	s.crypto = nil
+	s.userID = ""
 	return s.store.Delete(userID)
 }
+
+// Stop shuts down the sync loop without deleting credentials. Safe to call multiple times.
+func (s *MatrixService) Stop() {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	if s.sync != nil {
+		s.sync.Stop()
+		s.sync = nil
+	}
+}
+
+// Start initializes the Matrix client + crypto + sync loop for the given user.
+// Must be called after Login() or after a successful GetSession() for a returning user.
+// Idempotent: safe to call multiple times for the same user.
+func (s *MatrixService) Start(userID string) error {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	if userID == "" {
+		return errors.New("user_id required")
+	}
+
+	// Idempotent for same user
+	if s.sync != nil && s.userID == userID {
+		return nil
+	}
+	// Different user or restart: stop previous
+	if s.sync != nil {
+		s.sync.Stop()
+		s.sync = nil
+	}
+
+	tok, err := s.store.Load(userID)
+	if err != nil {
+		return fmt.Errorf("keyring load: %w", err)
+	}
+
+	storeDir := userStoreDir(userID)
+	clientCfg := infra.MatrixClientInitConfig{
+		HomeserverURL: tok.HomeserverURL,
+		UserID:        tok.UserID,
+		DeviceID:      tok.DeviceID,
+		AccessToken:   tok.AccessToken,
+		StoreDir:      storeDir,
+		EnableCrypto:  false,
+	}
+	clientRes, err := infra.MatrixClientInit(clientCfg)
+	if err != nil {
+		return fmt.Errorf("matrix init: %w", err)
+	}
+
+	// Pickle key: load from keyring (hex), or generate fresh and persist.
+	pickleKey, err := s.loadOrCreatePickleKey(tok)
+	if err != nil {
+		return fmt.Errorf("pickle key: %w", err)
+	}
+
+	cryptoStorePath := filepath.Join(storeDir, "crypto.db")
+
+	// Wrap MatrixCryptoInit in 60s timeout — hang here is the canonical MAS-UIA-rejection signal.
+	cryptoCtx, cancel := context.WithTimeout(s.ctx, 60*time.Second)
+	defer cancel()
+
+	cryptoRes, err := infra.MatrixCryptoInit(cryptoCtx, infra.MatrixCryptoInitConfig{
+		Client:    clientRes.Client,
+		StorePath: cryptoStorePath,
+		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)
+	}
+
+	syncRes, err := infra.MatrixSyncService(s.ctx, infra.MatrixSyncServiceConfig{
+		Client: clientRes.Client,
+	})
+	if err != nil {
+		return fmt.Errorf("matrix sync: %w", err)
+	}
+
+	s.client = clientRes.Client
+	s.crypto = cryptoRes
+	s.sync = syncRes
+	s.userID = userID
+
+	// Fan events out via Wails runtime.
+	go s.fanout()
+
+	return nil
+}
+
+func (s *MatrixService) fanout() {
+	if s.ctx == nil || s.sync == nil {
+		return
+	}
+	events := s.sync.Events
+	errs := s.sync.Errors
+	for {
+		select {
+		case <-s.ctx.Done():
+			return
+		case ev, ok := <-events:
+			if !ok {
+				return
+			}
+			view := SyncEventView{
+				Type:    ev.Type,
+				RoomID:  ev.RoomID,
+				EventID: ev.EventID,
+				Sender:  ev.Sender,
+				Ts:      ev.Ts,
+				Body:    ev.Body,
+			}
+			runtime.EventsEmit(s.ctx, "matrix:event", view)
+		case e, ok := <-errs:
+			if !ok {
+				return
+			}
+			if e != nil {
+				runtime.EventsEmit(s.ctx, "matrix:error", e.Error())
+			}
+		}
+	}
+}
+
+// ListRooms returns the joined rooms with summary metadata.
+func (s *MatrixService) ListRooms() ([]infra.RoomSummary, error) {
+	s.mu.Lock()
+	client := s.client
+	s.mu.Unlock()
+	if client == nil {
+		return nil, errors.New("matrix service not started — call Start() first")
+	}
+	return infra.MatrixRoomList(s.ctx, infra.MatrixRoomListConfig{Client: client})
+}
+
+// LoadTimeline fetches the last N messages of a room (most recent first).
+func (s *MatrixService) LoadTimeline(roomID string, limit int) ([]MatrixEvent, error) {
+	s.mu.Lock()
+	client := s.client
+	s.mu.Unlock()
+	if client == nil {
+		return nil, errors.New("matrix service not started — call Start() first")
+	}
+	if limit <= 0 {
+		limit = 50
+	}
+	msgs, err := client.Messages(s.ctx, id.RoomID(roomID), "", "", mautrix.DirectionBackward, nil, limit)
+	if err != nil {
+		return nil, fmt.Errorf("messages: %w", err)
+	}
+	out := make([]MatrixEvent, 0, len(msgs.Chunk))
+	for _, evt := range msgs.Chunk {
+		out = append(out, eventToView(evt))
+	}
+	return out, nil
+}
+
+func eventToView(evt *event.Event) MatrixEvent {
+	view := MatrixEvent{
+		EventID: evt.ID.String(),
+		RoomID:  evt.RoomID.String(),
+		Sender:  evt.Sender.String(),
+		Type:    evt.Type.String(),
+		Ts:      evt.Timestamp,
+	}
+	if evt.Type == event.EventEncrypted {
+		view.EncryptedRaw = true
+		return view
+	}
+	// Try to parse and extract body for messages.
+	if evt.Type == event.EventMessage {
+		_ = evt.Content.ParseRaw(evt.Type)
+		if mc, ok := evt.Content.Parsed.(*event.MessageEventContent); ok && mc != nil {
+			view.Body = mc.Body
+		}
+	}
+	return view
+}
+
+// SendText sends a plain text message to the given room.
+func (s *MatrixService) SendText(roomID, body string) (string, error) {
+	s.mu.Lock()
+	client := s.client
+	s.mu.Unlock()
+	if client == nil {
+		return "", errors.New("matrix service not started — call Start() first")
+	}
+	evID, err := infra.MatrixSendText(s.ctx, client, id.RoomID(roomID), body)
+	if err != nil {
+		return "", err
+	}
+	return string(evID), nil
+}
+
+// SendMarkdown sends a markdown-formatted message (rendered + sanitized HTML).
+func (s *MatrixService) SendMarkdown(roomID, md string) (string, error) {
+	s.mu.Lock()
+	client := s.client
+	s.mu.Unlock()
+	if client == nil {
+		return "", errors.New("matrix service not started — call Start() first")
+	}
+	evID, err := infra.MatrixSendMarkdown(s.ctx, client, id.RoomID(roomID), md)
+	if err != nil {
+		return "", err
+	}
+	return string(evID), nil
+}
+
+// loadOrCreatePickleKey returns the 32-byte pickle key for the user.
+// If absent in keyring, generates fresh random bytes, hex-encodes them, persists, and returns.
+func (s *MatrixService) loadOrCreatePickleKey(tok *infra.Token) ([]byte, error) {
+	if tok.PickleKeyHex != "" {
+		key, err := hex.DecodeString(tok.PickleKeyHex)
+		if err == nil && len(key) == 32 {
+			return key, nil
+		}
+		// Malformed key in keyring — fall through and regenerate.
+	}
+	buf := make([]byte, 32)
+	if _, err := rand.Read(buf); err != nil {
+		return nil, fmt.Errorf("rand: %w", err)
+	}
+	tok.PickleKeyHex = hex.EncodeToString(buf)
+	if err := s.store.Save(tok.UserID, *tok); err != nil {
+		return nil, fmt.Errorf("save pickle key: %w", err)
+	}
+	return buf, nil
+}
diff --git a/sqlite_driver.go b/sqlite_driver.go
new file mode 100644
index 0000000..2f71373
--- /dev/null
+++ b/sqlite_driver.go
@@ -0,0 +1,15 @@
+package main
+
+// sqlite_driver.go registers the SQLite driver required by the mautrix crypto
+// store. mautrix-go's cryptohelper uses database/sql + the "sqlite3" driver
+// name. go-sqlite3 self-registers via init() with sync.Once internally, but we
+// keep the blank import here to make the dependency explicit.
+//
+// Per the project memory (feedback_agents_e2ee_unblock_pattern.md), if the
+// driver is somehow registered twice the panic shows up as
+// `sql: Register called twice for driver sqlite3`. The guard pattern lives in
+// go-sqlite3 itself, so a blank import is sufficient.
+
+import (
+	_ "github.com/mattn/go-sqlite3"
+)
diff --git a/wails.json b/wails.json
index 0d6eca7..e9fae29 100644
--- a/wails.json
+++ b/wails.json
@@ -2,6 +2,7 @@
   "$schema": "https://wails.io/schemas/config.v2.json",
   "name": "matrix_client_pc",
   "outputfilename": "matrix_client_pc",
+  "build:tags": "goolm",
   "frontend:install": "pnpm install",
   "frontend:build": "pnpm build",
   "frontend:dev:watcher": "pnpm dev",