fixes #7743: stop overwriting workflow parentId with Spark variable name

[mattcasters]

Summary

Fixes #7743 (thanks @nadment for the report and repro).

With Caching Database execution info location, workflow rows were stored with:

parent_id = Internal.Spark.TransformOwnerId

instead of:

• null for a top-level parent workflow
• the parent workflow’s log-channel id for a nested child workflow

Root cause

This is not a bug in the Caching Database location. The denormalized parent_id column only made a registration bug obvious.

In LocalWorkflowEngine (from the Native Spark engine work), parent rebind used:

resolve("Internal.Spark.TransformOwnerId")

IVariables.resolve() only expands ${...} / %%...%% tokens. A bare name is returned unchanged, so every local workflow execution overwrote the correct parent id with that literal string.

Spark is supposed to set the real owner id via HopMapPartitionsFn when a workflow runs nested under a mapPartitions Workflow Executor. Rebind should only run when that variable is actually set.

Fix

• Look up with getVariable(...) (returns null when unset) instead of resolve(...)
• Centralize the variable name as VAR_SPARK_TRANSFORM_OWNER_ID (kept in sync with SparkConst in the spark plugin; engine cannot depend on that plugin)
• Unit tests for unset / set / empty variable, and documenting the resolve vs getVariable distinction

Expected after fix

Scenario	Before	After
Top-level workflow	parent_id = Internal.Spark.TransformOwnerId	null
Child workflow (local)	same literal	parent log-channel id
Nested under Spark Workflow Executor	same literal	synthetic pipeId|name|copy

Test plan

• LocalWorkflowEngineSparkParentRebindTest (7 tests)
• Repro from [Bug]: Bad PARENT_ID when using DatabaseExecutionInfoLocation with Hop-Gui #7743 (workflows.zip): parent → child local workflows, Caching Database execution info location, hop-gui
  • Parent row: parent_id null/empty
  • Child row: parent_id = parent’s id
• Optional: nested workflow under Spark Workflow Executor still parents to synthetic owner id

[nadment]

I haven't encountered “Internal.Spark.TransformOwnerId” since that patch.