Add I2C hot-plug detection and streaming diagnostics (firmware v3.04.0)

Phase D firmware hardening: vendor commands 0xBD (streaming diagnostics)
and 0xBE (I2C hot-plug detection) with Python library, bridge, and demo
support. All I2C operations use timeout-protected helpers, BCM4500 reads
are rate-limited during streaming, and frame counter reads use atomic
read-verify-reread pattern. Counters saturate instead of wrapping.

tools/skywalker_lib.py

@@ -63,6 +63,8 @@ CMD_MULTI_REG_READ = 0xB9
 CMD_PARAM_SWEEP = 0xBA
 CMD_ADAPTIVE_BLIND_SCAN = 0xBB
 CMD_GET_LAST_ERROR = 0xBC
+CMD_GET_STREAM_DIAG = 0xBD
+CMD_GET_HOTPLUG_STATUS = 0xBE
 
 # Error codes (returned by CMD_GET_LAST_ERROR)
 ERR_OK = 0x00
@@ -789,6 +791,68 @@ class SkyWalker1:
         """Disable east/west soft limits."""
         self.send_diseqc_message(diseqc_disable_limits())
 
+    # -- Streaming diagnostics (v3.04+) --
+
+    def get_stream_diag(self, reset: bool = False) -> dict:
+        """Read streaming diagnostics counters (0xBD).
+
+        Returns dict with poll_count, overflow_count, sync_loss,
+        last_status, last_lock, armed, had_sync.
+        Set reset=True to clear counters after read.
+        """
+        wval = 1 if reset else 0
+        data = self._vendor_in(CMD_GET_STREAM_DIAG, value=wval, length=12)
+        poll_count = struct.unpack_from('<I', data, 0)[0]
+        overflow_count = struct.unpack_from('<H', data, 4)[0]
+        sync_loss = struct.unpack_from('<H', data, 6)[0]
+        return {
+            "poll_count": poll_count,
+            "overflow_count": overflow_count,
+            "sync_loss": sync_loss,
+            "last_status": data[8],
+            "last_lock": data[9],
+            "armed": bool(data[10]),
+            "had_sync": bool(data[11]),
+        }
+
+    # -- I2C hot-plug detection (v3.04+) --
+
+    def get_hotplug_status(self, reset: bool = False,
+                           force_scan: bool = False) -> dict:
+        """Read I2C hot-plug detection status (0xBE).
+
+        Returns dict with current/previous bus bitmaps, change count,
+        devices added/removed in last scan, and decoded address lists.
+        Set reset=True to clear change counter.
+        Set force_scan=True to trigger immediate I2C rescan.
+        """
+        wval = 2 if force_scan else (1 if reset else 0)
+        data = self._vendor_in(CMD_GET_HOTPLUG_STATUS, value=wval, length=36)
+        current_bitmap = bytes(data[0:16])
+        changes = struct.unpack_from('<H', data, 16)[0]
+        added = data[18]
+        removed = data[19]
+        previous_bitmap = bytes(data[20:36])
+        return {
+            "current_bitmap": current_bitmap,
+            "previous_bitmap": previous_bitmap,
+            "changes": changes,
+            "added": added,
+            "removed": removed,
+            "current_devices": _bitmap_to_addrs(current_bitmap),
+            "previous_devices": _bitmap_to_addrs(previous_bitmap),
+        }
+
+
+def _bitmap_to_addrs(bitmap: bytes) -> list[int]:
+    """Convert 16-byte I2C address bitmap to list of 7-bit addresses."""
+    addrs = []
+    for byte_idx in range(16):
+        for bit in range(8):
+            if bitmap[byte_idx] & (1 << bit):
+                addrs.append((byte_idx << 3) | bit)
+    return addrs
+
 
 # --- DiSEqC 1.2 command builders ---