Add getParent() API to TaskOrchestrationContext for parent instance support

[bachuv]

Issue describing the changes in this PR

Adds getParent() API to TaskOrchestrationContext, bringing the Java SDK to parity with .NET's TaskOrchestrationContext.Parent property. This allows sub-orchestrations to discover their parent orchestration's name and instance ID at runtime.

Changes:

• New class ParentOrchestrationInstance — immutable model with getName() and getInstanceId()
• New default method getParent() on TaskOrchestrationContext — returns null for standalone orchestrations (non-breaking, backward-compatible)
• Wiring in TaskOrchestrationExecutor — populates parent from ExecutionStartedEvent.parentInstance protobuf field
• 7 unit tests covering: parent present, parent absent, exact value preservation, empty fields, default method compatibility, replay stability, and equals/hashCode
• ParentInstanceSample — runnable sample demonstrating both sub-orchestration (parent detected) and standalone (null parent) scenarios

Pull request checklist

• My changes do not require documentation changes
  • Otherwise: Documentation issue linked to PR
• My changes are added to the CHANGELOG.md
• I have added all required tests (Unit tests, E2E tests)

Additional information

• Uses a default interface method to avoid breaking existing TaskOrchestrationContext implementers
• The protobuf ParentInstanceInfo fields (taskScheduledId, version) used for internal completion routing are intentionally not exposed, matching .NET's public API surface
• Verified end-to-end against the DTS emulator — both sub-orchestration and standalone paths work correctly
• Run the sample: ./gradlew runParentInstanceSample

[Copilot]

Pull request overview

Adds parent-orchestration discovery for sub-orchestrations by introducing a TaskOrchestrationContext#getParent() API (modeled after .NET), wiring it from the ExecutionStartedEvent.parentInstance protobuf field, and providing tests + a runnable sample to demonstrate parent-present vs standalone behavior.

Changes:

• Introduces ParentOrchestrationInstance (name + instanceId) and a non-breaking default TaskOrchestrationContext#getParent() method (returns null when absent).
• Populates parent instance info in TaskOrchestrationExecutor during EXECUTIONSTARTED event processing.
• Adds unit tests and a new sample + Gradle run task to validate and demonstrate the feature.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
samples/src/main/java/io/durabletask/samples/ParentInstanceSample.java	New runnable sample demonstrating ctx.getParent() for sub-orchestrations vs standalone runs.
samples/build.gradle	Adds runParentInstanceSample JavaExec task to run the new sample.
client/src/test/java/com/microsoft/durabletask/TaskOrchestrationExecutorTest.java	Adds unit tests covering parent present/absent, replay stability, and model equality.
client/src/main/java/com/microsoft/durabletask/TaskOrchestrationExecutor.java	Wires parent instance extraction from ExecutionStartedEvent.parentInstance into context implementation.
client/src/main/java/com/microsoft/durabletask/TaskOrchestrationContext.java	Adds default getParent() API returning null when not a sub-orchestration.
client/src/main/java/com/microsoft/durabletask/ParentOrchestrationInstance.java	Adds the new immutable parent instance model type.