Fix missing _is_not_supported and harden WinUSB config cache

Restores the helper accidentally removed when adding access-denied
handling, retries I/O after seeding pyusb config index on Windows, and
handles USB overflow reads without crashing the HELLO loop.

Co-authored-by: Cursor <cursoragent@cursor.com>

juc500_xfer/usb_link.py

@@ -194,6 +194,24 @@ def _is_access_denied(exc: BaseException) -> bool:
     )
 
 
+def _is_not_supported(exc: BaseException) -> bool:
+    """WinUSB often returns LIBUSB_ERROR_NOT_SUPPORTED for get_configuration etc."""
+    text = _usb_err_text(exc)
+    errno = getattr(exc, "errno", None)
+    return (
+        errno in (95, 40)  # ENOTSUP / Windows ERROR_NOT_SUPPORTED-ish
+        or "not supported" in text
+        or "unimplemented" in text
+        or "enosys" in text
+    )
+
+
+def _is_overflow(exc: BaseException) -> bool:
+    text = _usb_err_text(exc)
+    errno = getattr(exc, "errno", None)
+    return errno == 84 or "overflow" in text
+
+
 def _claim_failure_message(ifnum: int, exc: BaseException) -> str:
     base = f"USB interface {ifnum} 점유 실패: {exc}"
     if not _IS_WIN:
@@ -211,6 +229,12 @@ def _claim_failure_message(ifnum: int, exc: BaseException) -> str:
             "6) 케이블 뽑았다가 다시 꽂고 JUC500 재실행 → 연결\n"
             "장치 관리자에서 Interface 5가 'WinUSB' / 'libusb-winusb' 인지도 확인하세요."
         )
+    if _is_not_supported(exc):
+        return (
+            f"{base}\n\n"
+            "WinUSB가 해당 libusb API를 지원하지 않습니다. Interface 5(MI_05)에 "
+            "WinUSB가 맞는지 Zadig로 확인하고, 최신 JUC500 빌드를 사용하세요."
+        )
     return (
         f"{base}\n"
         f"Zadig에서 Smart Data Link → Interface {ifnum} (MI_0{ifnum}) 에 WinUSB를 설치하세요."
@@ -431,14 +455,28 @@ class Juc500Link:
         self._claim(IF_CDC_COMM, required=False)
 
     def _configure_windows(self) -> None:
+        """Avoid libusb_get_configuration — unimplemented on WinUSB.
+
+        Every pyusb read/write resolves endpoints via get_active_configuration(),
+        which calls backend.get_configuration() when the cache is empty and then
+        raises 'Operation not supported or unimplemented on this platform'.
+        Always seed _active_cfg_index after open.
+        """
         assert self._dev is not None
         try:
             self._dev.set_configuration(1)
-        except usb.core.USBError:
+        except (usb.core.USBError, NotImplementedError):
             pass
+        self._ensure_cfg_cache(force=True)
+
+    def _ensure_cfg_cache(self, *, force: bool = False) -> None:
+        """Seed pyusb config index so I/O never calls get_configuration on WinUSB."""
+        if self._dev is None:
+            return
         try:
             ctx = self._dev._ctx
-            if getattr(ctx, "_active_cfg_index", None) is None:
+            if force or getattr(ctx, "_active_cfg_index", None) is None:
+                # Composite JUC500 exposes a single configuration at index 0.
                 ctx._active_cfg_index = 0
         except Exception:
             pass
@@ -506,6 +544,8 @@ class Juc500Link:
 
     def _bulk_write(self, ep: int, payload: bytes, timeout_ms: Optional[int]) -> int:
         assert self._dev is not None
+        if _IS_WIN:
+            self._ensure_cfg_cache()
         to = self.timeout_ms if timeout_ms is None else timeout_ms
         sent = 0
         view = memoryview(payload)
@@ -514,12 +554,22 @@ class Juc500Link:
             try:
                 n = self._dev.write(ep, chunk.tobytes(), timeout=to)
             except usb.core.USBError as exc:
-                if _is_not_supported(exc):
+                if _IS_WIN and _is_not_supported(exc):
+                    self._ensure_cfg_cache(force=True)
+                    try:
+                        n = self._dev.write(ep, chunk.tobytes(), timeout=to)
+                    except usb.core.USBError as exc2:
+                        raise RuntimeError(
+                            f"USB 쓰기 실패(EP 0x{ep:02x}): {exc2}\n"
+                            "Windows: Interface 5에 WinUSB가 잡혀 있는지 Zadig로 확인하세요."
+                        ) from exc2
+                elif _is_not_supported(exc):
                     raise RuntimeError(
                         f"USB 쓰기 실패(EP 0x{ep:02x}): {exc}\n"
                         "Windows: Interface 5에 WinUSB가 잡혀 있는지 Zadig로 확인하세요."
                     ) from exc
-                raise
+                else:
+                    raise
             sent += n
             if n == 0:
                 break
@@ -527,6 +577,8 @@ class Juc500Link:
 
     def _bulk_read(self, ep: int, size: int, timeout_ms: Optional[int]) -> bytes:
         assert self._dev is not None
+        if _IS_WIN:
+            self._ensure_cfg_cache()
         to = self.timeout_ms if timeout_ms is None else timeout_ms
         try:
             data = self._dev.read(ep, size, timeout=to)
@@ -534,7 +586,36 @@ class Juc500Link:
         except usb.core.USBTimeoutError:
             return b""
         except usb.core.USBError as exc:
+            if _is_overflow(exc):
+                for bigger in (max(size, 512) * 2, 4096, 16384, 65536):
+                    if bigger <= size:
+                        continue
+                    try:
+                        data = self._dev.read(ep, bigger, timeout=to)
+                        return bytes(data)
+                    except usb.core.USBTimeoutError:
+                        return b""
+                    except usb.core.USBError as exc2:
+                        if _is_overflow(exc2):
+                            size = bigger
+                            continue
+                        if _is_not_supported(exc2):
+                            break
+                        return b""
+                return b""
             if _is_not_supported(exc):
+                if _IS_WIN:
+                    self._ensure_cfg_cache(force=True)
+                    try:
+                        data = self._dev.read(ep, size, timeout=to)
+                        return bytes(data)
+                    except usb.core.USBTimeoutError:
+                        return b""
+                    except usb.core.USBError as exc2:
+                        raise RuntimeError(
+                            f"USB 읽기 실패(EP 0x{ep:02x}): {exc2}\n"
+                            "Windows: Interface 5에 WinUSB가 잡혀 있는지 Zadig로 확인하세요."
+                        ) from exc2
                 raise RuntimeError(
                     f"USB 읽기 실패(EP 0x{ep:02x}): {exc}\n"
                     "Windows: Interface 5에 WinUSB가 잡혀 있는지 Zadig로 확인하세요."