Add serializable project commands

docs/project-history-and-external-model-architecture.md

@@ -140,6 +140,11 @@ Completed foundation:
 - projects carry a monotonic `currentRevision` counter starting at zero
 - project revision metadata and versioned forward/inverse change-set payloads
   have separate persistence entities
+- forward and inverse payloads store complete serialized command envelopes;
+  command type and schema version are derived from those envelopes rather than
+  duplicated caller metadata
+- command serialization rejects non-finite numbers, `undefined`, non-plain
+  objects and cyclic payloads before a revision transaction starts
 - the SQLite revision repository advances the project counter and stores both
   history records atomically
 - revision appends use an expected-revision compare-and-set and reject stale
@@ -147,7 +152,8 @@ Completed foundation:
 
 Remaining constraints before implementing history:
 
-- model project-scoped command descriptions independently from React callbacks
+- define concrete project-scoped command unions and executors independently
+  from React callbacks; the generic versioned command envelope is complete
 - route domain writes and revision recording through one shared project
   transaction boundary; the current revision repository only commits history
   records and the counter together