Stabilize KTX seat lookup review fixes

Constraint: PR #293 review found fallback korail2 imports failed under PYTHONNOUSERSITE and seat lookup needed clearer Dynapath/power-seat contracts.
Rejected: Leave research endpoints outside DYNAPATH_PATHS | would keep the auth-header behavior ambiguous for live seat lookup.
Confidence: high
Scope-risk: narrow
Directive: Keep fallback-only tests independent of installed korail2 so CI catches missing dependency behavior.
Tested: PYTHONPATH=.:scripts python3 -m unittest scripts.test_ktx_booking; PYTHONPATH=.:scripts PYTHONNOUSERSITE=1 python3 -m unittest discover -s scripts -p 'test_ktx_booking.py'; python3 -m py_compile scripts/ktx_booking.py scripts/test_ktx_booking.py; PYTHONPATH=.:scripts python3 scripts/ktx_booking.py seats --help; node --test scripts/skill-docs.test.js
Not-tested: live Korail seat lookup against production endpoints

docs/features/ktx-booking.md

@@ -97,7 +97,7 @@ python3 scripts/ktx_booking.py seats 서울 부산 20260328 090000 --train-id <t
 python3 scripts/ktx_booking.py seats 서울 부산 20260328 090000 --train-id <train_id> --available-only --power-only
 ```
 
-특실 좌석을 확인하려면 `--room special`, KTX 외 열차를 조회했다면 `search` 와 같은 `--train-type` 을 함께 넘긴다.
+`--power-only` 는 KTX/KTX-산천에서 알려진 호차 배치 힌트 기반의 best-effort 필터다. 특실 좌석을 확인하려면 `--room special`, KTX 외 열차를 조회했다면 `search` 와 같은 `--train-type` 을 함께 넘긴다.
 
 ```bash
 python3 scripts/ktx_booking.py seats 남춘천 용산 20260503 150000 \

ktx-booking/SKILL.md

@@ -141,7 +141,7 @@ python3 scripts/ktx_booking.py seats 서울 부산 20260328 090000 --train-id <t
 python3 scripts/ktx_booking.py seats 서울 부산 20260328 090000 --train-id <train_id> --car-no 5 --available-only
 ```
 
-콘센트 꿀팁 자리부터 확인하려면 `--power-only` 를 붙인다. 응답의 `power_outlet` 은 `direct`, `adjacent`, `none` 중 하나다.
+콘센트 꿀팁 자리부터 확인하려면 `--power-only` 를 붙인다. 응답의 `power_outlet` 은 `direct`, `adjacent`, `none` 중 하나다. 이 필터는 KTX/KTX-산천에서 알려진 호차 배치 힌트 기반 best-effort 이다.
 
 ```bash
 python3 scripts/ktx_booking.py seats 서울 부산 20260328 090000 --train-id <train_id> --available-only --power-only

scripts/ktx_booking.py

@@ -103,7 +103,7 @@ except ModuleNotFoundError as exc:
 
     class _FallbackKorailModule:
         EMAIL_REGEX = re.compile(r".+@.+")
-        PHONE_NUMBER_REGEX = re.compile(r"^\d+$")
+        PHONE_NUMBER_REGEX = re.compile(r"^01\d-?\d{3,4}-?\d{4}$")
 
     korail_mod = _FallbackKorailModule()
 else:
@@ -127,6 +127,8 @@ DEFAULT_USER_AGENT = "Dalvik/2.1.0 (Linux; U; Android 13; SM-S928N Build/UP1A.23
 DYNAPATH_PATHS = [
     "/classes/com.korail.mobile.certification.TicketReservation",
     "/classes/com.korail.mobile.nonMember.NonMemTicket",
+    "/classes/com.korail.mobile.research.ResidualSeatsResearch.do",
+    "/classes/com.korail.mobile.research.TrainResearch",
     "/classes/com.korail.mobile.seatMovie.ScheduleView",
     "/classes/com.korail.mobile.seatMovie.ScheduleViewSpecial",
     "/classes/com.korail.mobile.trn.prcFare.do",
@@ -899,10 +901,15 @@ def command_seats(args: argparse.Namespace) -> None:
     car_payloads: list[dict[str, object]] = []
     for car in cars:
         raw = client.car_seats(raw_train, str(car["car_no_raw"]), passenger_count, room_class)
-        raw_seats = raw.get("seat_infos", {}).get("seat_info", [])
+        seat_infos = raw.get("seat_infos", {}) if isinstance(raw, dict) else {}
+        raw_seats = seat_infos.get("seat_info", []) if isinstance(seat_infos, dict) else []
         if isinstance(raw_seats, dict):
             raw_seats = [raw_seats]
-        all_seats = [normalize_seat(seat) for seat in raw_seats if seat.get("h_con_seat_no") != "0A"]
+        all_seats = [
+            normalize_seat(seat)
+            for seat in raw_seats
+            if isinstance(seat, dict) and seat.get("h_con_seat_no") != "0A"
+        ]
         available_seats = [seat for seat in all_seats if seat["available"]]
         seats = all_seats
         if args.available_only:

scripts/test_ktx_booking.py

@@ -327,6 +327,10 @@ class KtxBookingTests(unittest.TestCase):
         self.assertFalse(ktx_booking.is_phone_login_id("1234567890"))
         self.assertFalse(ktx_booking.is_phone_login_id("user@example.com"))
 
+    def test_seat_lookup_urls_receive_dynapath_headers(self):
+        self.assertTrue(any(path in ktx_booking.KORAIL_CARS_INFO for path in ktx_booking.DYNAPATH_PATHS))
+        self.assertTrue(any(path in ktx_booking.KORAIL_CAR_DETAIL for path in ktx_booking.DYNAPATH_PATHS))
+
     def test_command_search_replays_selected_train_type(self):
         selected = FakeTrain(
             train_no="2080",
@@ -598,6 +602,43 @@ class KtxBookingTests(unittest.TestCase):
 
         self.assertIn("car_no 5", str(exc.exception))
 
+    def test_command_seats_treats_malformed_seat_infos_as_empty(self):
+        selected = FakeTrain(train_no="009", dep_time="090000", arr_time="113000", label="selected")
+        raw_train = {"h_trn_no": "009", "h_dpt_dt": "20260328"}
+        train_id = ktx_booking.normalize_train(selected, index=1)["train_id"]
+        client = FakeClient(
+            [],
+            train_details=[(selected, raw_train)],
+            cars=[{"h_srcar_no": "05", "h_psrm_cl_cd": "1", "h_seat_cnt": "48", "h_rest_seat_cnt": "9"}],
+        )
+        client.car_seats = lambda *args, **kwargs: {"seat_infos": []}
+        args = argparse.Namespace(
+            dep="서울",
+            arr="부산",
+            date="20260328",
+            time="090000",
+            adults=1,
+            children=0,
+            toddlers=0,
+            seniors=0,
+            train_id=train_id,
+            room="general",
+            train_type="ktx",
+            car_no=None,
+            available_only=True,
+            power_only=False,
+            limit=10,
+        )
+        output = io.StringIO()
+
+        with patch.object(ktx_booking, "build_client", return_value=client):
+            with redirect_stdout(output):
+                ktx_booking.command_seats(args)
+
+        result = json.loads(output.getvalue())
+        self.assertEqual(result["cars"][0]["available_seat_count"], 0)
+        self.assertEqual(result["cars"][0]["seats"], [])
+
     def test_build_parser_has_ncard_commands(self):
         parser = ktx_booking.build_parser()
         help_text = parser.format_help()