fix: ground-truth CI-V offset/tone on live ID-5100

- offset amount (0x0D) is REJECTED (NG) by the radio -> removed the offset
  codec + set_offset/get_offset; tune_repeater now sets only duplex direction
  (radio applies its configured auto-offset)
- repeater tone (0x1B/00) uses a 3-byte field (00 + 2-byte BCD); set_tone
  prepends the pad, get_tone strips it
- duplex (0x0F) and tone-switch (0x16/42) verified working
- added get_duplex; verified full tune_repeater on a live repeater (all steps OK)

civ.py

@@ -24,15 +24,17 @@ SUB_SQL_LEVEL = 0x03
 SUB_SQL_STATUS = 0x01
 SUB_SMETER = 0x02
 
-# --- repeater config (candidate commands; verify on live radio) ---
-CMD_OFFSET = 0x0D       # set duplex offset frequency
-CMD_DUPLEX = 0x0F       # set duplex direction
+# --- repeater config (verified on live ID-5100 2026-06-14) ---
+# NOTE: offset-amount cmd 0x0D is REJECTED (NG) by the ID-5100 — the offset
+# amount is not CI-V-settable; the radio applies its configured auto-offset
+# (default 0.6 MHz / 5 MHz) when a duplex direction is selected via 0x0F.
+CMD_DUPLEX = 0x0F       # set/read duplex direction (verified: read -> 0x10 simplex)
 DUP_SIMPLEX = 0x10
 DUP_MINUS = 0x11
 DUP_PLUS = 0x12
-CMD_TONE_PARAM = 0x1B   # sub 0x00 = repeater (TX) tone frequency
+CMD_TONE_PARAM = 0x1B   # sub 0x00 = repeater (TX) tone freq (verified)
 SUB_RPT_TONE = 0x00
-CMD_TONE_SWITCH = 0x16  # sub 0x42 = tone encode on/off
+CMD_TONE_SWITCH = 0x16  # sub 0x42 = tone encode on/off (verified)
 SUB_TONE_ENC = 0x42
 
 Frame = namedtuple("Frame", "to frm cn data")
@@ -77,28 +79,12 @@ def bcd_to_level(data):
     return value
 
 
-def offset_to_bcd(hz):
-    """Duplex offset Hz -> 3-byte little-endian BCD in 100 Hz units (PROVISIONAL)."""
-    if hz < 0:
-        raise ValueError(f"offset {hz} must be >= 0")
-    units = round(hz / 100)
-    digits = f"{units:06d}"
-    out = bytearray()
-    for i in range(0, 6, 2):
-        out.append((int(digits[4 - i]) << 4) | int(digits[5 - i]))
-    return bytes(out)
-
-
-def bcd_to_offset(data):
-    """3-byte little-endian BCD (100 Hz units) -> Hz (PROVISIONAL)."""
-    units = 0
-    for i, byte in enumerate(data[:3]):
-        units += (byte & 0x0F) * (10 ** (2 * i)) + (byte >> 4) * (10 ** (2 * i + 1))
-    return units * 100
-
-
 def tone_to_bcd(hz):
-    """CTCSS tone Hz -> 2-byte BCD of tone*10 (88.5 -> 08 85)."""
+    """CTCSS tone Hz -> 2-byte BCD of tone*10 (88.5 -> 08 85).
+
+    The ID-5100 wire format for cmd 0x1B/0x00 prepends a 0x00 pad byte before
+    these two (so 88.5 Hz reads/writes as `00 08 85`); radio.py adds/strips it.
+    """
     digits = f"{round(hz * 10):04d}"
     return bytes([(int(digits[0]) << 4) | int(digits[1]),
                   (int(digits[2]) << 4) | int(digits[3])])