fix(gateway): persist watcher metadata in checkpoint for crash recovery (#1706)

Salvaged from PR #1573 by @eren-karakus0. Cherry-picked with authorship preserved.

Fixes #1143 — background process notifications resume after gateway restart.

Co-authored-by: Muhammet Eren Karakuş <erenkar950@gmail.com>

tests/tools/test_process_registry.py

@@ -294,6 +294,61 @@ class TestCheckpoint:
             recovered = registry.recover_from_checkpoint()
             assert recovered == 0
 
+    def test_write_checkpoint_includes_watcher_metadata(self, registry, tmp_path):
+        with patch("tools.process_registry.CHECKPOINT_PATH", tmp_path / "procs.json"):
+            s = _make_session()
+            s.watcher_platform = "telegram"
+            s.watcher_chat_id = "999"
+            s.watcher_thread_id = "42"
+            s.watcher_interval = 60
+            registry._running[s.id] = s
+            registry._write_checkpoint()
+
+            data = json.loads((tmp_path / "procs.json").read_text())
+            assert len(data) == 1
+            assert data[0]["watcher_platform"] == "telegram"
+            assert data[0]["watcher_chat_id"] == "999"
+            assert data[0]["watcher_thread_id"] == "42"
+            assert data[0]["watcher_interval"] == 60
+
+    def test_recover_enqueues_watchers(self, registry, tmp_path):
+        checkpoint = tmp_path / "procs.json"
+        checkpoint.write_text(json.dumps([{
+            "session_id": "proc_live",
+            "command": "sleep 999",
+            "pid": os.getpid(),  # current process — guaranteed alive
+            "task_id": "t1",
+            "session_key": "sk1",
+            "watcher_platform": "telegram",
+            "watcher_chat_id": "123",
+            "watcher_thread_id": "42",
+            "watcher_interval": 60,
+        }]))
+        with patch("tools.process_registry.CHECKPOINT_PATH", checkpoint):
+            recovered = registry.recover_from_checkpoint()
+            assert recovered == 1
+            assert len(registry.pending_watchers) == 1
+            w = registry.pending_watchers[0]
+            assert w["session_id"] == "proc_live"
+            assert w["platform"] == "telegram"
+            assert w["chat_id"] == "123"
+            assert w["thread_id"] == "42"
+            assert w["check_interval"] == 60
+
+    def test_recover_skips_watcher_when_no_interval(self, registry, tmp_path):
+        checkpoint = tmp_path / "procs.json"
+        checkpoint.write_text(json.dumps([{
+            "session_id": "proc_live",
+            "command": "sleep 999",
+            "pid": os.getpid(),
+            "task_id": "t1",
+            "watcher_interval": 0,
+        }]))
+        with patch("tools.process_registry.CHECKPOINT_PATH", checkpoint):
+            recovered = registry.recover_from_checkpoint()
+            assert recovered == 1
+            assert len(registry.pending_watchers) == 0
+
 
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 # Kill process