diff --git a/tests/tui_gateway/test_gateway_owned_session_reap.py b/tests/tui_gateway/test_gateway_owned_session_reap.py
new file mode 100644
index 00000000000..81edd590f46
--- /dev/null
+++ b/tests/tui_gateway/test_gateway_owned_session_reap.py
@@ -0,0 +1,83 @@
+"""Tests for #60609: the TUI backend must not end gateway-owned sessions.
+
+``_finalize_session`` (and thus the ws-orphan reaper / session.close paths
+that funnel into it) marks the session ended in state.db.  For sessions the
+messaging gateway owns (telegram, discord, ...), that write creates the
+Groundhog Day routing loop described in #60609 — the gateway self-heal
+drops the ended-but-routed entry, recovers hours-old parent context, and
+loops.  The TUI is only a viewer of those sessions.
+"""
+
+from unittest.mock import MagicMock, patch
+
+from tui_gateway.server import _finalize_session, _is_gateway_owned_source
+
+
+class TestIsGatewayOwnedSource:
+    def test_builtin_gateway_platforms_are_owned(self):
+        for src in ("telegram", "discord", "whatsapp", "slack", "signal",
+                    "matrix", "mattermost", "bluebubbles", "sms", "email"):
+            assert _is_gateway_owned_source(src) is True, src
+
+    def test_case_and_whitespace_normalized(self):
+        assert _is_gateway_owned_source(" Telegram ") is True
+
+    def test_tui_owned_sources_are_not(self):
+        for src in ("tui", "cli", "webui", "desktop", "cron", "subagent",
+                    "test", "acp", ""):
+            assert _is_gateway_owned_source(src) is False, src
+
+    def test_local_and_server_endpoints_are_not(self):
+        # Platform enum members, but their sessions aren't owned by a remote
+        # chat surface — reaping them keeps /resume clean.
+        for src in ("local", "webhook", "api_server", "msgraph_webhook"):
+            assert _is_gateway_owned_source(src) is False, src
+
+    def test_arbitrary_strings_are_not(self):
+        assert _is_gateway_owned_source("hermesbench-task-xyz") is False
+        assert _is_gateway_owned_source(None) is False
+
+
+def _make_session(session_id="sess_1"):
+    agent = MagicMock()
+    agent.session_id = session_id
+    return {
+        "agent": agent,
+        "history": [{"role": "user", "content": "x"}],
+        "history_lock": None,
+        "session_key": session_id,
+    }
+
+
+class TestFinalizeSkipsGatewaySessions:
+    @patch("tui_gateway.server._get_db")
+    def test_gateway_session_not_ended(self, mock_get_db):
+        db = MagicMock()
+        db.get_session.return_value = {"id": "sess_1", "source": "telegram"}
+        mock_get_db.return_value = db
+
+        _finalize_session(_make_session(), end_reason="ws_orphan_reap")
+
+        db.end_session.assert_not_called()
+
+    @patch("tui_gateway.server._get_db")
+    def test_tui_session_still_ended(self, mock_get_db):
+        db = MagicMock()
+        db.get_session.return_value = {"id": "sess_1", "source": "tui"}
+        mock_get_db.return_value = db
+
+        _finalize_session(_make_session(), end_reason="ws_orphan_reap")
+
+        db.end_session.assert_called_once_with("sess_1", "ws_orphan_reap")
+
+    @patch("tui_gateway.server._get_db")
+    def test_missing_row_still_ended(self, mock_get_db):
+        """A session with no state.db row can't be gateway-owned — keep the
+        pre-existing reap behavior."""
+        db = MagicMock()
+        db.get_session.return_value = None
+        mock_get_db.return_value = db
+
+        _finalize_session(_make_session(), end_reason="tui_close")
+
+        db.end_session.assert_called_once_with("sess_1", "tui_close")
diff --git a/tui_gateway/server.py b/tui_gateway/server.py
index fcd29723bd0..412c89aaf15 100644
--- a/tui_gateway/server.py
+++ b/tui_gateway/server.py
@@ -499,6 +499,42 @@ def _transfer_active_session_slot(
     return False
 
 
+# Session sources the TUI/desktop backend must never end in state.db: the
+# messaging gateway owns those sessions' lifecycle — the TUI is only a viewer
+# (a resume of a Telegram/Discord/... session).  Ending one creates the
+# #60609 Groundhog Day routing loop (see _finalize_session).  Sources the
+# TUI backend itself creates ("tui", plus whatever a client passes as its
+# own ``source``) and the CLI's own sessions are NOT gateway-owned.
+_NON_GATEWAY_SOURCES = frozenset({
+    "", "tui", "cli", "webui", "desktop", "cron", "subagent", "test",
+    "local", "acp", "webhook", "api_server", "msgraph_webhook",
+})
+
+
+def _is_gateway_owned_source(source: str) -> bool:
+    """True when ``source`` names a messaging-gateway platform whose session
+    lifecycle belongs to the gateway, not to this TUI backend.
+
+    Structural rather than a hardcoded platform list: any source that
+    resolves to a known gateway ``Platform`` (built-in enum member OR a
+    registered platform plugin, via ``Platform._missing_``) counts, so new
+    platforms are covered automatically.  Local/self-owned sources are
+    excluded explicitly — ``local``/``webhook``/``api_server`` are Platform
+    members but their sessions are not owned by a remote chat surface that
+    routes by session_key, so reaping them is safe and keeps /resume clean.
+    """
+    src = (source or "").strip().lower()
+    if src in _NON_GATEWAY_SOURCES:
+        return False
+    try:
+        from gateway.config import Platform
+
+        Platform(src)  # raises ValueError for arbitrary non-platform strings
+        return True
+    except Exception:
+        return False
+
+
 def _finalize_session(session: dict | None, end_reason: str = "tui_close") -> None:
     """Best-effort finalize hook + memory commit for a session.
 
@@ -586,22 +622,16 @@ def _finalize_session(session: dict | None, end_reason: str = "tui_close") -> No
         try:
             db = _get_db()
             if db is not None:
-                # Don't end gateway-originated sessions — the gateway owns their
-                # lifecycle.  The TUI is a viewer, not the owner.  Ending a
-                # gateway session in state.db triggers a Groundhog Day routing
-                # loop: the gateway's #54878 self-heal detects the stale entry,
-                # recovers to the parent session, context compression splits
-                # back to the reaped child, and the cycle repeats on every
-                # inbound message.  (#60609)
-                _GATEWAY_SOURCES = frozenset({
-                    "bluebubbles", "telegram", "discord", "signal",
-                    "whatsapp", "sms", "slack", "mattermost",
-                    "matrix", "line", "wechat", "facebook",
-                    "imessage", "googlechat",
-                })
+                # Don't end gateway-originated sessions — the gateway owns
+                # their lifecycle.  The TUI is a viewer, not the owner.
+                # Ending a gateway session in state.db triggers a Groundhog
+                # Day routing loop: the gateway's #54878 self-heal detects
+                # the stale entry, recovers to the parent session, context
+                # compression splits back to the reaped child, and the cycle
+                # repeats on every inbound message.  (#60609)
                 row = db.get_session(session_id)
                 source = (row or {}).get("source", "")
-                if source not in _GATEWAY_SOURCES:
+                if not _is_gateway_owned_source(source):
                     db.end_session(session_id, end_reason)
         except Exception:
             pass