Add orchestration send_event support

[andystaples]

Summary

• add synchronous OrchestrationContext.send_event(instance_id, event_name, *, data=None) for one-way orchestration-to-orchestration events
• emit deterministic SendEventAction records using the configured data converter and reconcile EventSent history during replay using .NET-compatible event-name matching
• record and deliver sent events in the in-memory backend without duplicate replay delivery, while dropping events for missing or terminal targets
• cover action creation, validation, custom and externalized payloads, replay nondeterminism, legacy entity-history compatibility, and end-to-end delivery

Validation

• python -m nox -s ci -- 3.14
• python -m nox -R -s core_tests-3.14 -- tests\durabletask\test_orchestration_executor.py tests\durabletask\test_orchestration_e2e.py tests\durabletask\test_large_payload.py -q
• python -m nox -R -s lint
• python -m nox -R -s typecheck_core-3.10

Closes #32

[Copilot]

Pull request overview

Adds orchestration-to-orchestration one-way event sending to the core Durable Task Python SDK, including deterministic action emission and replay reconciliation, plus in-memory backend delivery behavior and coverage.

Changes:

• Introduces OrchestrationContext.send_event(instance_id, event_name, *, data=None) and emits SendEventAction records using the configured DataConverter.
• Reconciles EventSent history during replay (including case-insensitive event-name matching) and wires action-type name resolution for sendEvent.
• Extends the in-memory backend to persist EventSent history and deliver/drop sent events safely without duplicate replay delivery; adds unit/E2E/large-payload tests and a changelog entry.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
tests/durabletask/test_orchestration_executor.py	Adds unit tests covering send-event action creation, converter usage, validation, and replay nondeterminism behavior.
tests/durabletask/test_orchestration_e2e.py	Adds E2E coverage for orchestration-to-orchestration event delivery and replay-safe non-duplication behavior.
tests/durabletask/test_large_payload.py	Verifies large send-event payloads are externalized.
durabletask/worker.py	Implements send_event, reconciles EventSent during replay, and maps sendEvent actions to the correct method name.
durabletask/testing/in_memory_backend.py	Records EventSent history and delivers/drops send-event actions in the in-memory backend.
durabletask/task.py	Declares the public send_event API on OrchestrationContext.
durabletask/internal/helpers.py	Adds helpers to build SendEventAction and enrich EventSent history with an event name.
CHANGELOG.md	Documents the new OrchestrationContext.send_event() API under Unreleased/ADDED.

[Copilot]

Pull request overview

Copilot reviewed 8 out of 8 changed files in this pull request and generated 1 comment.

[berndverst]

Making this new method abstract breaks every existing third-party or test OrchestrationContext subclass that implements the previous public contract: after upgrading, instantiation raises TypeError even when send_event() is never used. Keep a concrete default that raises NotImplementedError, or defer the abstract requirement to a major version, so this additive API remains backward compatible.

[andystaples]

I agree this can affect custom subclasses, but keeping the method abstract is consistent with this interface's contract and the project's release precedent. parent_instance_id was added as an abstract property in #168 and shipped between v1.7.0 and the v1.7.1 patch release; new_uuid was also added abstract in #83 before v1.2.0. I therefore prefer the consistent fail-fast requirement here over deferring an omitted implementation to runtime.

[berndverst]

Those precedents do not make this additive API backward compatible: a subclass built against the current public contract now fails at instantiation even when it never calls send_event(). The break is avoidable—keep a concrete default that raises NotImplementedError when invoked, and reserve adding an abstract requirement for a major release.

[Copilot]

Pull request overview

Copilot reviewed 8 out of 8 changed files in this pull request and generated no new comments.