fix(CLI-40,CLI-41,CLI-44): exact-secret scrub, uniform malformed-reply contract, Go terminal-error mislabel

CLI-40: port the exact-secret credential scrub to Rust/Java/.NET (Go/Python
already did it). AuthenticateUser/WriteSecured(2) helpers now redact the exact
caller-supplied secret from any surfaced error, as defense-in-depth on top of the
by-construction guarantee. Rust hand-writes a redacting Debug (derived Debug would
leak the reply); Java/.NET rebuild the same exception type with the redacted
message and do not carry the secret-bearing original forward (so ToString/stack
traces stay clean too).

CLI-41: uniform malformed-reply contract for AuthenticateUser/ArchestrAUserToId/
AddBufferedItem across all five clients — typed payload, else a present int32
return_value, else a typed malformed-reply error. Fixes Go/Java silent-0, .NET
NRE, and Rust's own internal inconsistency.

CLI-44: the Go event goroutine's Recv-error path now uses a non-blocking
sendTerminalEventResult on the reserved slot, so a genuine terminal stream error
is reported as itself instead of being mislabeled ErrSlowConsumer under overflow.

Riders from the CLI-37/38 review: (a) .NET ToDiagnosticSummary and Python
_mxaccess_message surface the raw success member (diagnostics-only parity with
Rust); (b) the status-conversion fixture carries an independent wantSuccess
boolean and the Go/.NET fixture tests assert against it instead of recomputing
the formula under test.

Shared fixtures (authenticate-user.{echoed-credential,missing-payload,
return-value-only}.reply.json) + manifest + ClientBehaviorFixtures.md +
ClientLibrariesDesign.md updated in the same change. Tracking: CLI-40/41/44 -> Done.

clients/python/src/zb_mom_ww_mxgateway/errors.py

@@ -53,6 +53,10 @@ class MxAccessError(MxGatewayCommandError):
     """MXAccess HRESULT or status failure."""
 
 
+class MalformedReplyError(MxGatewayError):
+    """Raised when an OK reply lacks the expected typed payload and any usable return_value fallback."""
+
+
 def map_rpc_error(operation: str, error: grpc.RpcError) -> MxGatewayTransportError:
     """Map a generated gRPC exception to the client exception hierarchy."""
 
@@ -153,8 +157,18 @@ def ensure_mxaccess_success(operation: str, reply: pb.MxCommandReply) -> pb.MxCo
 def _mxaccess_message(operation: str, reply: pb.MxCommandReply) -> str:
     status_text = reply.protocol_status.message or "MXAccess command failed"
     hresult = reply.hresult if reply.HasField("hresult") else None
-    return (
+    message = (
         f"{operation} failed: {status_text}; "
         f"session={reply.session_id}; correlation={reply.correlation_id}; "
         f"hresult={hresult}; statuses={len(reply.statuses)}"
     )
+    # Append a per-status breakdown that carries the raw `success` COM member
+    # verbatim for diagnostic parity with the other clients. `category` remains
+    # the authoritative verdict; `success` is diagnostics only.
+    for status in reply.statuses:
+        category = pb.MxStatusCategory.Name(status.category)
+        message += (
+            f" [success={status.success}, category={category}, "
+            f"detail={status.detail}, {status.diagnostic_text}]"
+        )
+    return message