Auto: abcip-3.1 — configurable CIP connection size per device

Closes #235

docs/Driver.AbCip.Cli.md

@@ -81,3 +81,25 @@ otopcua-abcip-cli subscribe -g ab://10.0.0.5/1,0 -t Motor01_Speed --type Real -i
 - **"Is this GuardLogix safety tag writable from non-safety?"** → `write` and
   read the status code — safety tags surface `BadNotWritable` / CIP errors,
   non-safety tags surface `Good`.
+
+## Connection Size
+
+PR abcip-3.1 introduced a per-device `ConnectionSize` override on the driver
+side (`AbCipDeviceOptions.ConnectionSize`, range `500..4002`). The CLI does
+not expose a flag for it — every CLI invocation uses the family-default
+Connection Size (4002 / 504 / 488 depending on `--family`). When a Forward
+Open is rejected with a CIP error like `0x01/0x113` ("connection request
+size invalid"), the symptom is almost always a **mismatch between the chosen
+family default and the controller firmware**:
+
+- **v19-and-earlier ControlLogix** caps at 504 — pick `--family CompactLogix`
+  on the CLI to fall back to that narrower default.
+- **5069-L1/L2/L3 CompactLogix** narrow-buffer parts also cap at 504, which
+  is the family default already.
+- **FW20+ ControlLogix** accepts the full 4002.
+
+For the warning *"AbCip device 'X' family 'Y' uses a narrow-buffer profile
+(default ConnectionSize Z); the configured ConnectionSize N exceeds the
+511-byte legacy-firmware cap..."* see
+[`docs/drivers/AbCip-Performance.md`](drivers/AbCip-Performance.md) — that
+warning is fired by the driver host, not the CLI.