fix(abcip): budget expected reply size in RequestScheduler.TakeBatch (#582); private lock + struct-handle check across read fragments (#567)

Claude-Session: https://claude.ai/code/session_01Ef2ozxS7QPanGT8uoATbTe

docs/drivers/AbCip.md

@@ -157,6 +157,17 @@ The driver has two interchangeable wire transports, selected by one `DriverConfi
 - **One CIP connection and one request scheduler per device** (`DeviceSessionPool`), shared by reads,
   writes, browse and template reads. The Multiple Service Packet scheduler coalesces requests with one
   request in flight; large reads (listing pages, Read Template) are sent unpacked and exclusive.
+  **Packing budgets the expected reply as well as the request (#582):** each queued request declares an
+  upper bound on its reply (`expectedReplyBytes`; reads: elements x element width, STRING = 88 bytes per
+  element, BOOL counted as 4) and a batch is closed when the summed MSP reply (`6 + 2n + sum`) would exceed
+  the connection size. A read whose size cannot be bounded (structure / unknown authored type) is sent
+  alone; writes and status-only replies count their 4-byte header. Pinned by
+  `RequestSchedulerTests.Mixed_scalar_string_and_array_replies_are_packed_within_the_reply_budget`.
+  ⚠️ RESIDUAL: mixed STRING/array packing has not been exercised against a real controller (the real-press
+  gate predates the budget); the budget is unit-tested against the scheduler and fake channel only.
+- **Fragmented-read integrity (#567):** `Read Tag Fragmented` replies are compared against the first reply;
+  a changed type code *or* structure handle mid-read fails the read with `BadReply` rather than stitching
+  two types into one value.
 - **Forward Open throttle:** at most one attempt in flight, at least 1 s between starts, bounded by the
   open budget.
 - `ConnectionSize` / `Timeout` / `AllowPacking` are honoured per pooled connection, and the **first**
@@ -194,7 +205,9 @@ The driver has two interchangeable wire transports, selected by one `DriverConfi
   (2026-10-08) and nothing else. Results:
   [native-ab-transport-gate-results](../plans/2026-10-07-native-ab-transport-gate-results.md).
 - **libplctag cannot be deleted** until a bench controller allows write verification.
-- Wide-struct fragmented writes (8-byte alignment) are unit-tested only, never proven on a controller (#567).
+- ⚠️ RESIDUAL (#567): wide-struct **fragmented writes** (8-byte alignment) are unit-tested only. Production
+  presses are read-only and there is no bench controller, so this cannot be proven; it stays open until a
+  bench controller exists.
 - Native browse: listing pages are unpaced, and template reads outside an enumeration open a connection per
   call (#572).
 - Micro800, routed and `logixpccc` paths are covered by `ab_server` only. The Micro800 profile passes