fix(bpmn): let the graph hash alone decide BPMN source staleness

[sfmskywalker]

Closes #8073. Part of #7909.

Problem

Publishing at version N and then saving anything through the designer, such as a rename or a variable change, creates draft N+1. That draft still carries Bpmn:SourceVersion = N. Because staleness required the version and the graph hash to match, the untouched BPMN source counted as stale. Export and the document GET refused, and Studio's binding editor told the user to re-import.

Fix

In BpmnInterchangeDocumentService.ResolveSourceXml, the single place staleness is decided for export, document GET and document PUT: when the Bpmn:SourceGraphHash marker is present, the graph hash alone decides. The version comparison applies only to definitions imported before the marker existed. The document ETag and the refusal codes are unchanged.

A graph change in the same draft, or in a new draft, still changes the hash, so it is still stale.

Tests

• A published definition renamed through the designer: export 200, document GET 200.
• Published, then the graph changed: 422 bpmn.export.source-stale, at both the service and endpoint levels.
• No marker: the version-only behaviour is kept.
• The Studio W11 flow (feat(workflows): bind BPMN tasks to Elsa activities from a Performed by section elsa-studio#1031): after a metadata-only save on draft N+1, GET returns an ETag, a PUT with it succeeds, and a fresh marker is recorded.
• Mutation-tested: reverting to the unconditional version check turns the new tests red.
• Elsa.Bpmn.Interchange.IntegrationTests: 103/103 after rebasing onto fix(bpmn): keep subprocess bodies through the document PUT #8077.

The tests simulate publishing by setting IsPublished on the stored row, through one shared helper (Support/PublishSimulation). The real publisher refuses a none-start BPMN process because of a separate defect, filed as #8078. The helper becomes a real PublishAsync call once that lands.

🤖 Generated with Claude Code

[greptile-apps]

Confidence Score: 5/5

Safe to merge: the changed graph-hash behavior satisfies the metadata-only draft flow while preserving stale-source protections for graph edits.

What we checked:

• The pre-change test run showed 3 selected tests with 2 passing and 1 failing; the new-draft metadata-only test expected OK but received UnprocessableEntity.
• The post-change test run showed 5 selected tests, all 5 passed.
• Compared the BPMN document and export contract before and after this change; the pre-change behavior returned 422 for metadata-only saves, while the current revision yields all five tests passing with the expected statuses.

Summary

• BPMN document access now remains available after a metadata-only designer save creates a new draft version without changing the activity graph.
• BPMN document and export requests continue to reject stored source after an activity-graph edit, preventing callers from receiving BPMN that no longer represents the workflow.
• Focused integration coverage passed for the metadata-only draft flow and the changed-graph refusal paths.

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