feat(ble_log_console): add BUF_UTIL internal frame decoding

Add BUF_UTIL=5 to InternalSource, BufUtilPool enum, BufUtilResult
TypedDict, BufUtilEntry dataclass, and name resolution helpers.
Add decode branch in internal_decoder with pool/index extraction
from the packed lbm_id field. Tests cover valid decode, pool/index
extraction, and truncated payload handling.

tools/bt/ble_log_console/src/backend/internal_decoder.py

@@ -9,6 +9,7 @@ See Spec Section 9.
 
 import struct
 
+from src.backend.models import BufUtilResult
 from src.backend.models import EnhStatResult
 from src.backend.models import InfoResult
 from src.backend.models import InternalDecoderResult
@@ -23,6 +24,9 @@ _INFO_STRUCT = struct.Struct('<BB')
 # ble_log_enh_stat_t: [1B int_src_code][1B src_code][4B written][4B lost][4B written_bytes][4B lost_bytes]
 _ENH_STAT_STRUCT = struct.Struct('<BBIIII')
 
+# ble_log_buf_util_t: [1B int_src_code][1B lbm_id][1B trans_cnt][1B inflight_peak]
+_BUF_UTIL_STRUCT = struct.Struct('<BBBB')
+
 
 def decode_internal_frame(payload: bytes) -> InternalDecoderResult | None:
     """Decode an INTERNAL frame payload.
@@ -74,4 +78,20 @@ def decode_internal_frame(payload: bytes) -> InternalDecoderResult | None:
             os_ts_ms=os_ts_ms,
         )
 
+    if int_src == InternalSource.BUF_UTIL:
+        if len(sub_payload) < _BUF_UTIL_STRUCT.size:
+            return None
+        _, lbm_id, trans_cnt, inflight_peak = _BUF_UTIL_STRUCT.unpack_from(sub_payload, 0)
+        pool = (lbm_id >> 4) & 0x0F
+        index = lbm_id & 0x0F
+        return BufUtilResult(
+            int_src=int_src,
+            lbm_id=lbm_id,
+            pool=pool,
+            index=index,
+            trans_cnt=trans_cnt,
+            inflight_peak=inflight_peak,
+            os_ts_ms=os_ts_ms,
+        )
+
     return None

tools/bt/ble_log_console/src/backend/models.py

@@ -117,6 +117,14 @@ class InternalSource(int, Enum):
     ENH_STAT = 2
     INFO = 3
     FLUSH = 4
+    BUF_UTIL = 5
+
+
+class BufUtilPool(int, Enum):
+    COMMON_TASK = 0
+    COMMON_ISR = 1
+    LL = 2
+    REDIR = 3
 
 
 # --- Data classes ---
@@ -154,6 +162,46 @@ class SourceStats:
     lost_bytes: int = 0
 
 
+@dataclass(frozen=True)
+class BufUtilEntry:
+    """Single LBM buffer utilization snapshot."""
+
+    lbm_id: int
+    pool: int
+    index: int
+    trans_cnt: int
+    inflight_peak: int
+
+
+# --- Buffer utilization name resolution ---
+
+_LBM_NAMES: dict[tuple[int, int], str] = {
+    (0, 0): 'spin',
+    (1, 0): 'spin',
+    (2, 0): 'll_task',
+    (2, 1): 'll_hci',
+    (3, 0): 'redir',
+}
+
+
+def resolve_pool_name(pool: int) -> str:
+    """Resolve pool code to BufUtilPool name, with fallback for unknown codes."""
+    try:
+        return BufUtilPool(pool).name
+    except ValueError:
+        return f'POOL_{pool}'
+
+
+def resolve_lbm_name(pool: int, index: int) -> str:
+    """Resolve pool + index to human-readable LBM name."""
+    key = (pool, index)
+    if key in _LBM_NAMES:
+        return _LBM_NAMES[key]
+    if pool in (0, 1) and index >= 1:
+        return f'atomic[{index - 1}]'
+    return f'lbm_{pool}_{index}'
+
+
 @dataclass(slots=True)
 class TransportSnapshot:
     """Snapshot of transport-layer metrics for the current stats interval."""
@@ -265,7 +313,17 @@ class EnhStatResult(TypedDict):
     os_ts_ms: int
 
 
-InternalDecoderResult = InfoResult | EnhStatResult
+class BufUtilResult(TypedDict):
+    int_src: InternalSource
+    lbm_id: int
+    pool: int
+    index: int
+    trans_cnt: int
+    inflight_peak: int
+    os_ts_ms: int
+
+
+InternalDecoderResult = InfoResult | EnhStatResult | BufUtilResult
 
 
 # --- Textual Messages (backend -> frontend) ---
@@ -278,10 +336,16 @@ class SyncStateChanged(Message):
 
 
 class StatsUpdated(Message):
-    def __init__(self, stats: FrameStats, funnel_snapshots: list[FunnelSnapshot] | None = None) -> None:
+    def __init__(
+        self,
+        stats: FrameStats,
+        funnel_snapshots: list[FunnelSnapshot] | None = None,
+        buf_util_snapshots: list[BufUtilEntry] | None = None,
+    ) -> None:
         super().__init__()
         self.stats = stats
         self.funnel_snapshots = funnel_snapshots or []
+        self.buf_util_snapshots = buf_util_snapshots or []
 
 
 class InternalFrameDecoded(Message):

tools/bt/ble_log_console/tests/test_internal_decoder.py

@@ -69,6 +69,38 @@ class TestUnknown:
         assert result is None
 
 
+class TestBufUtil:
+    def test_decode_buf_util(self) -> None:
+        # lbm_id=0x01 (pool=0, index=1), trans_cnt=4, inflight_peak=3
+        sub = b'\x01\x04\x03'
+        payload = _make_internal_payload(os_ts=7777, int_src=5, sub_payload=sub)
+        result = decode_internal_frame(payload)
+        assert result is not None
+        assert result['int_src'] == InternalSource.BUF_UTIL
+        assert result['lbm_id'] == 0x01
+        assert result['pool'] == 0
+        assert result['index'] == 1
+        assert result['trans_cnt'] == 4
+        assert result['inflight_peak'] == 3
+        assert result['os_ts_ms'] == 7777
+
+    def test_buf_util_pool_index_extraction(self) -> None:
+        # lbm_id=0x21 -> pool=2 (LL), index=1 (ll_hci)
+        sub = b'\x21\x04\x02'
+        payload = _make_internal_payload(os_ts=0, int_src=5, sub_payload=sub)
+        result = decode_internal_frame(payload)
+        assert result is not None
+        assert result['pool'] == 2
+        assert result['index'] == 1
+
+    def test_buf_util_too_short(self) -> None:
+        # Only 2 bytes of sub_payload (need 3 after int_src_code)
+        sub = b'\x00\x04'
+        payload = _make_internal_payload(os_ts=0, int_src=5, sub_payload=sub)
+        result = decode_internal_frame(payload)
+        assert result is None
+
+
 class TestMalformed:
     def test_too_short_payload(self) -> None:
         result = decode_internal_frame(b'\x00\x00\x00')