[CONNECT] CommandPlugin et al.

docs/connect/CommandPlugin.md

@@ -1,3 +1,22 @@
 # CommandPlugin
 
-`CommandPlugin` is...FIXME
+`CommandPlugin` is an [abstraction](#contract) of [command processors](#implementations) in [Spark Connect](./index.md) that can [process a command](#process).
+
+## Contract
+
+### Process Command { #process }
+
+```scala
+process(
+  command: protobuf.Any,
+  planner: SparkConnectPlanner): Option[Unit]
+```
+
+Used when:
+
+* `SparkConnectPlanner` is requested to [handleCommandPlugin](SparkConnectPlanner.md#handleCommandPlugin)
+
+## Implementations
+
+!!! note
+    No built-in implementations available.

docs/connect/ExecuteHolder.md

@@ -0,0 +1,12 @@
+# ExecuteHolder
+
+## Creating Instance
+
+`ExecuteHolder` takes the following to be created:
+
+* <span id="request"> `ExecutePlanRequest`
+* <span id="sessionHolder"> `SessionHolder`
+
+`ExecuteHolder` is created when:
+
+* `SparkConnectExecutionManager` is requested to [create an ExecuteHolder](SparkConnectExecutionManager.md#createExecuteHolder)

docs/connect/ExecuteThreadRunner.md

@@ -0,0 +1,9 @@
+# ExecuteThreadRunner
+
+`ExecuteThreadRunner` is created alongside [ExecuteHolder](ExecuteHolder.md#runner).
+
+## Creating Instance
+
+`ExecuteThreadRunner` takes the following to be created:
+
+* <span id="executeHolder"> `ExecuteHolder`

docs/connect/SparkConnectExecutionManager.md

@@ -0,0 +1,9 @@
+# SparkConnectExecutionManager
+
+## Creating Instance
+
+`SparkConnectExecutionManager` takes no arguments to be created.
+
+`SparkConnectExecutionManager` is created when:
+
+* `SparkConnectService` is requested for the [executionManager](SparkConnectService.md#executionManager)

docs/connect/SparkConnectPlanner.md

@@ -74,3 +74,44 @@ transformPythonFunction(
 `transformPythonFunction` is used when:
 
 * `SparkConnectPlanner` is requested to [transformPythonUDF](#transformPythonUDF) and [handleRegisterPythonUDF](#handleRegisterPythonUDF)
+
+## Process Command { #process }
+
+```scala
+process(
+  command: proto.Command,
+  responseObserver: StreamObserver[ExecutePlanResponse],
+  executeHolder: ExecuteHolder): Unit
+```
+
+`process` handles the input `Command` based on its type.
+
+Command Type | Handler
+-|-
+ `REGISTER_FUNCTION` | [handleRegisterUserDefinedFunction](#handleRegisterUserDefinedFunction)
+ `REGISTER_TABLE_FUNCTION` | [handleRegisterUserDefinedTableFunction](#handleRegisterUserDefinedTableFunction)
+ `WRITE_OPERATION` | [handleWriteOperation](#handleWriteOperation)
+ `CREATE_DATAFRAME_VIEW` | [handleCreateViewCommand](#handleCreateViewCommand)
+ `WRITE_OPERATION_V2` | [handleWriteOperationV2](#handleWriteOperationV2)
+ `EXTENSION` | [handleCommandPlugin](#handleCommandPlugin)
+ `SQL_COMMAND` | [handleSqlCommand](#handleSqlCommand)
+ `WRITE_STREAM_OPERATION_START` | [handleWriteStreamOperationStart](#handleWriteStreamOperationStart)
+ `STREAMING_QUERY_COMMAND` | [handleStreamingQueryCommand](#handleStreamingQueryCommand)
+ `STREAMING_QUERY_MANAGER_COMMAND` | [handleStreamingQueryManagerCommand](#handleStreamingQueryManagerCommand)
+ `GET_RESOURCES_COMMAND` | [handleGetResourcesCommand](#handleGetResourcesCommand)
+
+---
+
+`process` is used when:
+
+* `ExecuteThreadRunner` is requested to [handle a command](ExecuteThreadRunner.md#handleCommand)
+
+### handleCommandPlugin { #handleCommandPlugin }
+
+```scala
+handleCommandPlugin(
+  extension: ProtoAny,
+  executeHolder: ExecuteHolder): Unit
+```
+
+`handleCommandPlugin`...FIXME