A2: S2F49/F50 Enhanced Remote Command

Adds the OBJSPEC-scoped sibling of S2F41 with extended per-parameter
ack shape (CPACK + CEPACK).  Wire:

  S2F49  body <DATAID OBJSPEC RCMD <L,n <CPNAME CPVAL>>>
  S2F50  body <HCACK <L,n <CPNAME CPACK CEPACK>>>

Server delegates to the existing HostCommandRegistry, logs OBJSPEC for
audit, and currently returns empty cpacks (all-OK).  Per-parameter
failures will be wired when the command registry grows CEPACK-level
validation; this commit is the catalog + dispatch scaffolding.

secsgem-py defines these in its catalog but never dispatches them; this
puts the C++ port marginally ahead on remote-command coverage.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

data/messages.yaml

@@ -433,6 +433,56 @@ messages:
                 - {name: name, shape: {kind: scalar, item_type: ASCII}}
                 - {name: code, shape: {kind: scalar, item_type: BINARY_BYTE}}
 
+  # S2F49 / S2F50 — Enhanced Remote Command (E30 §6.4, E5 §10.4).  Same
+  # intent as S2F41/F42 but routes a command at a specific object via
+  # OBJSPEC, carries a DATAID transaction handle, and the reply uses
+  # extended per-CP acks (CPACK + CEPACK) so the equipment can flag both
+  # "name unknown" (CPACK) and "value invalid" (CEPACK) independently.
+  - id: S2F49
+    stream: 2
+    function: 49
+    w: true
+    builder: s2f49_enhanced_host_command
+    parser: parse_s2f49
+    body:
+      kind: list
+      struct_name: EnhancedHostCommand
+      fields:
+        - {name: dataid,  shape: {kind: scalar, item_type: U4}}
+        - {name: objspec, shape: {kind: scalar, item_type: ASCII}}
+        - {name: rcmd,    shape: {kind: scalar, item_type: ASCII}}
+        - name: params
+          shape:
+            kind: list_of
+            element:
+              kind: list
+              struct_name: CommandParameter
+              external_struct: true
+              fields:
+                - {name: name,  shape: {kind: scalar, item_type: ASCII}}
+                - {name: value, shape: {kind: scalar, item_type: ITEM}}
+
+  - id: S2F50
+    stream: 2
+    function: 50
+    builder: s2f50_enhanced_host_command_ack
+    parser: parse_s2f50
+    body:
+      kind: list
+      struct_name: EnhancedHostCommandReply
+      fields:
+        - {name: hcack, shape: {kind: scalar, item_type: BINARY_BYTE, enum: HostCmdAck}}
+        - name: cpacks
+          shape:
+            kind: list_of
+            element:
+              kind: list
+              struct_name: EnhancedCommandParameterAck
+              fields:
+                - {name: name,   shape: {kind: scalar, item_type: ASCII}}
+                - {name: cpack,  shape: {kind: scalar, item_type: BINARY_BYTE}}
+                - {name: cepack, shape: {kind: scalar, item_type: BINARY_BYTE}}
+
   # S2F23 / S2F24 — Trace Initialize Send (E30 §6.12).  Host requests
   # periodic SVID sampling: every DSPER, equipment captures the SVID
   # values; every REPGSZ samples it emits an S6F1 batch; after TOTSMP