diff --git a/src/matrix.zig b/src/matrix.zig
index becf4a1..bcecf6d 100644
--- a/src/matrix.zig
+++ b/src/matrix.zig
@@ -67,28 +67,143 @@ pub fn login(alloc: std.mem.Allocator, io: Io, user: []const u8, password: []con
 }
 
 /// Send a text message. Returns event id (allocated; caller frees).
+/// Escape text for embedding inside a JSON string literal.
+fn jsonEscape(alloc: std.mem.Allocator, out: *std.ArrayList(u8), text: []const u8) !void {
+    for (text) |c| {
+        switch (c) {
+            '"' => try out.appendSlice(alloc, "\\\""),
+            '\\' => try out.appendSlice(alloc, "\\\\"),
+            '\n' => try out.appendSlice(alloc, "\\n"),
+            '\r', '\t' => try out.append(alloc, ' '),
+            // Any other control char is invalid raw in a JSON string —
+            // escape as \u00XX so the server never rejects the send.
+            // (Ranges disjoint from \t \n \r handled above.)
+            0x00...0x08, 0x0b, 0x0c, 0x0e...0x1f => {
+                var buf: [6]u8 = undefined;
+                const s = std.fmt.bufPrint(&buf, "\\u{x:0>4}", .{c}) catch unreachable;
+                try out.appendSlice(alloc, s);
+            },
+            else => try out.append(alloc, c),
+        }
+    }
+}
+
+/// Minimal markdown → HTML for formatted_body: **bold**, *italic*,
+/// `code`, ``` fences, paragraphs. Element only renders styling via
+/// org.matrix.custom.html — plain m.text bodies show raw asterisks.
+fn markdownToHtml(alloc: std.mem.Allocator, md: []const u8) ![]u8 {
+    var out: std.ArrayList(u8) = .empty;
+    errdefer out.deinit(alloc);
+    var in_code = false;
+    var i: usize = 0;
+    while (i < md.len) {
+        // Fenced code blocks
+        if (std.mem.startsWith(u8, md[i..], "```")) {
+            try out.appendSlice(alloc, if (in_code) "</pre>" else "<pre>");
+            in_code = !in_code;
+            i += 3;
+            // Skip to end of line (language tag when opening).
+            if (!in_code) {
+                while (i < md.len and md[i] != '\n') i += 1;
+                if (i < md.len) i += 1;
+            } else {
+                if (i < md.len and md[i] == '\n') i += 1;
+            }
+            continue;
+        }
+        if (in_code) {
+            try out.append(alloc, md[i]);
+            i += 1;
+            continue;
+        }
+        switch (md[i]) {
+            '\n' => {
+                try out.appendSlice(alloc, "<br>");
+                i += 1;
+            },
+            '<' => {
+                try out.appendSlice(alloc, "&lt;");
+                i += 1;
+            },
+            '>' => {
+                try out.appendSlice(alloc, "&gt;");
+                i += 1;
+            },
+            '&' => {
+                try out.appendSlice(alloc, "&amp;");
+                i += 1;
+            },
+            '`' => {
+                // Inline code: `...`
+                if (std.mem.indexOfScalarPos(u8, md, i + 1, '`')) |end| {
+                    try out.appendSlice(alloc, "<code>");
+                    try out.appendSlice(alloc, md[i + 1 .. end]);
+                    try out.appendSlice(alloc, "</code>");
+                    i = end + 1;
+                } else {
+                    try out.append(alloc, '`');
+                    i += 1;
+                }
+            },
+            '*' => {
+                if (std.mem.startsWith(u8, md[i..], "**")) {
+                    if (std.mem.indexOfPos(u8, md, i + 2, "**")) |end| {
+                        try out.appendSlice(alloc, "<strong>");
+                        try out.appendSlice(alloc, md[i + 2 .. end]);
+                        try out.appendSlice(alloc, "</strong>");
+                        i = end + 2;
+                    } else {
+                        try out.appendSlice(alloc, "**");
+                        i += 2;
+                    }
+                } else if (std.mem.indexOfScalarPos(u8, md, i + 1, '*')) |end| {
+                    try out.appendSlice(alloc, "<em>");
+                    try out.appendSlice(alloc, md[i + 1 .. end]);
+                    try out.appendSlice(alloc, "</em>");
+                    i = end + 1;
+                } else {
+                    try out.append(alloc, '*');
+                    i += 1;
+                }
+            },
+            else => {
+                try out.append(alloc, md[i]);
+                i += 1;
+            },
+        }
+    }
+    if (in_code) try out.appendSlice(alloc, "</pre>");
+    return out.toOwnedSlice(alloc);
+}
+
 pub fn sendText(alloc: std.mem.Allocator, io: Io, token: []const u8, room: []const u8, body: []const u8) ![]u8 {
     const ts = Io.Clock.now(.real, io).nanoseconds;
     const url = try std.fmt.allocPrint(alloc, "{s}/_matrix/client/v3/rooms/{s}/send/m.room.message/infr-{d}", .{ HOMESERVER, room, ts });
     defer alloc.free(url);
 
-    var esc: std.ArrayList(u8) = .empty;
-    defer esc.deinit(alloc);
-    for (body) |c| {
-        switch (c) {
-            '"' => try esc.appendSlice(alloc, "\\\""),
-            '\\' => try esc.appendSlice(alloc, "\\\\"),
-            '\n' => try esc.appendSlice(alloc, "\\n"),
-            '\r', '\t' => try esc.appendSlice(alloc, " "),
-            else => try esc.append(alloc, c),
-        }
-    }
-    const payload = try std.fmt.allocPrint(alloc, "{{\"msgtype\":\"m.text\",\"body\":\"{s}\"}}", .{esc.items});
-    defer alloc.free(payload);
+    const html = markdownToHtml(alloc, body) catch |e| switch (e) {
+        error.OutOfMemory => return e,
+    };
+    defer alloc.free(html);
 
-    const resp = try http(alloc, io, "PUT", url, token, payload);
+    var payload: std.ArrayList(u8) = .empty;
+    defer payload.deinit(alloc);
+    try payload.appendSlice(alloc, "{\"msgtype\":\"m.text\",\"body\":\"");
+    try jsonEscape(alloc, &payload, body);
+    try payload.appendSlice(alloc, "\",\"format\":\"org.matrix.custom.html\",\"formatted_body\":\"");
+    try jsonEscape(alloc, &payload, html);
+    try payload.append(alloc, '"');
+    try payload.append(alloc, '}');
+
+    const resp = try http(alloc, io, "PUT", url, token, payload.items);
     defer alloc.free(resp);
-    const ev = letta.jsonStr(alloc, resp, 0, "event_id") orelse return error.SendFailed;
+    const ev = letta.jsonStr(alloc, resp, 0, "event_id") orelse {
+        // Diagnose silently-rejected sends: dump first 400 bytes of the
+        // server response (errcode/message) and payload head to stderr.
+        std.debug.print("matrix: send failed, resp: {s}\n", .{resp[0..@min(resp.len, 400)]});
+        std.debug.print("matrix: payload head: {s}\n", .{payload.items[0..@min(payload.items.len, 400)]});
+        return error.SendFailed;
+    };
     return ev.val;
 }
 
@@ -100,10 +215,14 @@ pub fn joinRoom(alloc: std.mem.Allocator, io: Io, token: []const u8, room: []con
     alloc.free(resp);
 }
 
-pub const Event = struct { sender: []u8, body: []u8 }; // both allocated
+pub const Event = struct { sender: []u8, body: []u8, ts: i64 = 0 }; // sender/body allocated
 
 /// One sync poll. Returns message events + next `since` token. Caller frees.
 /// (Sync first without a since token to establish one, then poll.)
+///
+/// Proper JSON parsing (std.json): the previous string-window scraper
+/// misattributed senders and duplicated events when multiple messages shared
+/// a response — sender/body could be scraped from different events.
 pub fn sync(alloc: std.mem.Allocator, io: Io, token: []const u8, since: []const u8, timeout_ms: u32) !struct { events: []Event, next: []u8 } {
     const url = if (since.len > 0)
         try std.fmt.allocPrint(alloc, "{s}/_matrix/client/v3/sync?timeout={d}&since={s}", .{ HOMESERVER, timeout_ms, since })
@@ -113,28 +232,96 @@ pub fn sync(alloc: std.mem.Allocator, io: Io, token: []const u8, since: []const
     const resp = try http(alloc, io, "GET", url, token, null);
     defer alloc.free(resp);
 
-    const next = if (letta.jsonStr(alloc, resp, 0, "next_batch")) |nb| nb.val else try alloc.dupe(u8, since);
-
     var events: std.ArrayList(Event) = .empty;
     errdefer events.deinit(alloc);
 
-    var i: usize = 0;
-    while (std.mem.indexOfPos(u8, resp, i, "\"m.room.message\"")) |pos| {
-        defer i = pos + 15;
-        // Event layout: sender (and event_id) come BEFORE the type marker,
-        // body comes after it in content — window spans both sides.
-        const win_start = pos -| 600;
-        const win_end = @min(resp.len, pos + 1500);
-        const win = resp[win_start..win_end];
-        const sender = letta.jsonStr(alloc, win, 0, "sender") orelse continue;
-        const body = letta.jsonStr(alloc, win, 0, "body") orelse {
-            alloc.free(sender.val);
-            continue;
-        };
-        events.append(alloc, .{ .sender = sender.val, .body = body.val }) catch {
-            alloc.free(sender.val);
-            alloc.free(body.val);
+    var arena_state = std.heap.ArenaAllocator.init(alloc);
+    defer arena_state.deinit();
+    const jalloc = arena_state.allocator();
+
+    var parsed = std.json.parseFromSlice(std.json.Value, jalloc, resp, .{}) catch return error.BadSyncJson;
+    defer parsed.deinit();
+
+    const root = switch (parsed.value) {
+        .object => |o| o,
+        else => return error.BadSyncJson,
+    };
+
+    var next: []u8 = try alloc.dupe(u8, since);
+    if (root.get("next_batch")) |nb| switch (nb) {
+        .string => |s| {
+            alloc.free(next);
+            next = try alloc.dupe(u8, s);
+        },
+        else => {},
+    };
+
+    // Walk rooms.join.*.timeline.events[] — every room, in order.
+    const join = if (root.get("rooms")) |rooms| switch (rooms) {
+        .object => |o| o.get("join") orelse return .{ .events = try events.toOwnedSlice(alloc), .next = next },
+        else => return .{ .events = try events.toOwnedSlice(alloc), .next = next },
+    } else return .{ .events = try events.toOwnedSlice(alloc), .next = next };
+
+    const join_obj = switch (join) {
+        .object => |o| o,
+        else => return .{ .events = try events.toOwnedSlice(alloc), .next = next },
+    };
+
+    var room_it = join_obj.iterator();
+    while (room_it.next()) |room_entry| {
+        const room = switch (room_entry.value_ptr.*) {
+            .object => |o| o,
+            else => continue,
         };
+        const timeline = if (room.get("timeline")) |t| switch (t) {
+            .object => |o| o,
+            else => continue,
+        } else continue;
+        const evs = if (timeline.get("events")) |e| switch (e) {
+            .array => |a| a,
+            else => continue,
+        } else continue;
+
+        for (evs.items) |ev| {
+            const obj = switch (ev) {
+                .object => |o| o,
+                else => continue,
+            };
+            // Only m.room.message events.
+            const ty = if (obj.get("type")) |t| switch (t) {
+                .string => |s| s,
+                else => continue,
+            } else continue;
+            if (!std.mem.eql(u8, ty, "m.room.message")) continue;
+
+            const sender_raw = if (obj.get("sender")) |s| switch (s) {
+                .string => |v| v,
+                else => continue,
+            } else continue;
+
+            const content = if (obj.get("content")) |c| switch (c) {
+                .object => |o| o,
+                else => continue,
+            } else continue;
+            const body_raw = if (content.get("body")) |b| switch (b) {
+                .string => |v| v,
+                else => continue,
+            } else continue;
+            const ts: i64 = if (obj.get("origin_server_ts")) |t| switch (t) {
+                .integer => |v| v,
+                else => 0,
+            } else 0;
+
+            const sender_copy = alloc.dupe(u8, sender_raw) catch continue;
+            const body_copy = alloc.dupe(u8, body_raw) catch {
+                alloc.free(sender_copy);
+                continue;
+            };
+            events.append(alloc, .{ .sender = sender_copy, .body = body_copy, .ts = ts }) catch {
+                alloc.free(sender_copy);
+                alloc.free(body_copy);
+            };
+        }
     }
     return .{ .events = try events.toOwnedSlice(alloc), .next = next };
 }
diff --git a/src/matrix_harness.zig b/src/matrix_harness.zig
index 05eece3..1040230 100644
--- a/src/matrix_harness.zig
+++ b/src/matrix_harness.zig
@@ -55,13 +55,42 @@ pub fn main(init: std.process.Init) !void {
     defer if (owned_room) |r| alloc.free(r);
     std.debug.print("matrix_harness: room {s}\n", .{room_id});
 
-    _ = try matrix.sendText(alloc, io, session.token, room_id, "matrix_harness online in persistent room. Messages reach the agent, replies come back here.");
+    // No room banner on startup — restarts (deploys, watchdog) would spam
+    // the DM. Startup is logged to journald instead.
 
-    // Establish a sync point (drop history before now).
+    // Establish a sync point. RECENT peer messages (last 30 min only, so
+    // harness restarts don't re-forward ancient history every boot) are
+    // forwarded to the agent as one [matrix backlog] context message
+    // (reply suppressed).
     const first = try matrix.sync(alloc, io, session.token, "", 0);
-    for (first.events) |ev| {
-        alloc.free(ev.sender);
-        alloc.free(ev.body);
+    {
+        const now_ms: i64 = @intCast(@divTrunc(std.Io.Clock.now(.real, io).nanoseconds, std.time.ns_per_ms));
+        var backlog: std.ArrayListUnmanaged(u8) = .empty;
+        defer backlog.deinit(alloc);
+        for (first.events) |ev| {
+            defer alloc.free(ev.sender);
+            defer alloc.free(ev.body);
+            if (!std.mem.eql(u8, ev.sender, peer)) continue;
+            if (ev.body.len == 0) continue;
+            if (ev.ts > 0 and now_ms - ev.ts > 30 * 60 * 1000) continue; // stale
+            try backlog.appendSlice(alloc, ev.sender);
+            try backlog.appendSlice(alloc, ": ");
+            try backlog.appendSlice(alloc, ev.body);
+            try backlog.append(alloc, '\n');
+        }
+        if (backlog.items.len > 0) {
+            std.debug.print("matrix_harness: forwarding backlog ({d} bytes) to agent\n", .{backlog.items.len});
+            const hist_msg = try std.fmt.allocPrint(alloc, "[matrix backlog — messages received while harness was offline]\n{s}", .{backlog.items});
+            defer alloc.free(hist_msg);
+            // Do NOT exit on backlog failure: with systemd Restart=on-failure
+            // this would re-forward the same backlog every 3s forever.
+            // Log, skip, keep polling.
+            if (letta.infer(io, alloc, agent, hist_msg)) |reply| {
+                alloc.free(reply); // backlog replies are not sent back
+            } else |e| {
+                std.debug.print("matrix_harness: backlog letta failed: {s} (skipping)\n", .{@errorName(e)});
+            }
+        }
     }
     alloc.free(first.events);
     var since = first.next;
@@ -86,7 +115,20 @@ pub fn main(init: std.process.Init) !void {
 
             std.debug.print("matrix_harness: [{s}] {s}\n", .{ ev.sender, ev.body });
 
-            const reply = letta.infer(io, alloc, agent, ev.body) catch |e| {
+            // Prefix with origin + event UTC timestamp so the agent can tell
+            // Matrix-origin messages from CLI ones (and when they were sent).
+            var ts_buf: [16]u8 = undefined;
+            const ts_str: []const u8 = blk: {
+                if (ev.ts <= 0) break :blk "";
+                const secs: u64 = @intCast(@divTrunc(ev.ts, 1000));
+                const epoch = std.time.epoch.EpochSeconds{ .secs = secs };
+                const sod = epoch.getDaySeconds();
+                break :blk std.fmt.bufPrint(&ts_buf, " {d:0>2}:{d:0>2}Z", .{ sod.getHoursIntoDay(), sod.getMinutesIntoHour() }) catch "";
+            };
+            const prefixed = try std.fmt.allocPrint(alloc, "[matrix{s}] {s}", .{ ts_str, ev.body });
+            defer alloc.free(prefixed);
+
+            const reply = letta.infer(io, alloc, agent, prefixed) catch |e| {
                 std.debug.print("matrix_harness: letta failed: {s}\n", .{@errorName(e)});
                 const err_txt = "agent failed — see harness logs";
                 if (matrix.sendText(alloc, io, session.token, room_id, err_txt)) |ev_id| alloc.free(ev_id) else |_| {}