feat(node): log what a transfer moved when it ends

One INFO line per lease: bytes, duration, rate, and the SCTP
association's window, round trip, losses and T3 expirations.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

1 files changed, 23 insertions, 0 deletions

diff --git a/packages/meshbay-node/src/meshbay_node/transfers.py b/packages/meshbay-node/src/meshbay_node/transfers.py
index 3345cb9..477ec92 100644
--- a/packages/meshbay-node/src/meshbay_node/transfers.py
+++ b/packages/meshbay-node/src/meshbay_node/transfers.py
@@ -102,11 +102,24 @@ class Lease:
     # later, for ever. Seen doing exactly that in a node's log, every 30 s,
     # minutes after the transfers involved had finished.
     missed_grants: int = 0
+    # What moved under this lease and over how long, for the line the node logs
+    # when it ends. Counted here because nothing else spans a transfer: a
+    # download is a run of independent chunk requests.
+    moved: int = 0
+    first_used: float | None = None
+    last_moved: float = 0.0
 
     @property
     def member(self) -> tuple[str, str]:
         return (self.group_id, self.user_id)
 
+    @property
+    def elapsed(self) -> float:
+        """Seconds from the first request under this lease to the last byte."""
+        if self.first_used is None:
+            return 0.0
+        return max(0.0, self.last_moved - self.first_used)
+
 
 @dataclass
 class TransferSlots:
@@ -223,8 +236,18 @@ class TransferSlots:
         lease.used = True
         lease.missed_grants = 0
         lease.last_seen = time.monotonic() if now is None else now
+        if lease.first_used is None:
+            lease.first_used = lease.last_seen
         return True
 
+    def account(self, tr: str, nbytes: int, now: float | None = None) -> None:
+        """`nbytes` were served or received under this lease."""
+        lease = self.leases.get(tr)
+        if lease is None:
+            return
+        lease.moved += nbytes
+        lease.last_moved = time.monotonic() if now is None else now
+
     def close(self, tr: str, reason: str = REASON_DONE,
               now: float | None = None) -> tuple[Lease | None, list[Lease]]:
         """Give a slot back. Returns (the closed lease, newly granted ones).