feat(mcp): expose entity creation schemas on demand

Expose creation fields, constraints and examples for the 11 supported types without expanding startup tool schemas. Share the creation contract and constructor with execution to keep accepted inputs consistent.

Validation: MCP, contract/factory and entity creation regression tests.

docs/automation/guides/workflow.md

@@ -4,6 +4,12 @@ Call ocs_sessions, then pass its session_id as ocs_session_id to ocs_read, ocs_e
 
 Use commands with parameters.name for a command manifest. Use batch when several steps are known, and request changed_entities when resulting geometry is needed.
 
+Before creating an unfamiliar entity, use `ocs_read` with `op: entity_schema` and
+`parameters.type` (for example, `Circle`) to get its creation fields, required
+values, units, defaults and example. Omit type for the catalog. Creation schemas
+describe the inputs to `entities_create`; `record_schema` describes stored records.
+Schema discovery runs locally and can omit `ocs_session_id`.
+
 For interactive work, call start and follow state.command.accepts, options and input_example. To have the person at the screen pick entities for you, call user_select and keep polling until it completes; running means they are still picking. A run.cmd contains the command name followed by prompt answers separated by spaces; points use x,y or x,y,z.
 
 After a timeout, query the existing operation and never replay a mutation with a new request_id. waiting_input and running are not completion. Let OCS and its geometry kernel calculate geometry; use query near, contains_point and intersections for exact relationships. 

docs/automation/mcp_smoke.py

@@ -135,6 +135,15 @@ def legacy(server: Path) -> None:
     assert not guide_tool["result"].get("isError"), guide_tool
     assert guide_tool["result"]["structuredContent"]["ok"] is True
     assert "resource_link" in guide_tool["result"]["structuredContent"]["contents"][0]["text"]
+    entity_schema = request(process, {
+        "jsonrpc": "2.0", "id": "entity-schema", "method": "tools/call",
+        "params": {"name": "ocs_read", "arguments": {
+            "op": "entity_schema", "parameters": {"type": "Circle"},
+        }},
+    })
+    assert not entity_schema["result"].get("isError"), entity_schema
+    contract = entity_schema["result"]["structuredContent"]["schema"]
+    assert contract["required"] == ["type", "center", "radius"]
     close(process)