refactor(client): commit probe sends transactionally

crates/irtt-client/src/error.rs

@@ -152,6 +152,16 @@ pub enum ClientError {
     /// can be reused.
     #[error("wire sequence {seq} is still pending")]
     PendingSequenceCollision { seq: u32 },
+    /// A prepared probe no longer matches the session's next wire sequence.
+    ///
+    /// Prepare the probe again after any intervening successful send.
+    #[error(
+        "prepared probe sequence {prepared_seq} is stale; next wire sequence is {next_wire_seq}"
+    )]
+    StalePreparedProbe {
+        prepared_seq: u32,
+        next_wire_seq: u32,
+    },
     /// Reserving memory required by an operation failed before any datagram was
     /// sent or logical protocol state was changed.
     #[error("failed to reserve memory for {operation}: {source}")]
@@ -160,6 +170,13 @@ pub enum ClientError {
         #[source]
         source: TryReserveError,
     },
+    /// UDP reported successful acceptance of a datagram with an unexpected
+    /// byte count.
+    ///
+    /// The send is committed locally before this transport invariant failure
+    /// is returned because the kernel reported success.
+    #[error("UDP accepted {actual} bytes for a {expected}-byte datagram")]
+    DatagramLengthMismatch { expected: usize, actual: usize },
     /// Client configuration failed validation before the requested operation.
     ///
     /// The reported reason names a value that must be changed before retrying.