Commit the events queued by a ProjectionScenario's final step

[jeremydmiller]

Closes #5126

The bug

ScenarioAction only flushes the session when the step after it is an assertion:

_action(scenario.Session.Events);
if (scenario.NextStep is ScenarioAssertion)   // null for the last step
{
    await scenario.Session.SaveChangesAsync(ct);
    await scenario.WaitForNonStaleData();
}

NextStep peeks the queue after the current step was dequeued, so it is null on the final step and the branch never runs. Execute's finally then disposes the session, and Marten's dispose does not commit.

Consequences: a scenario ending in an append silently loses those events, and an arrange-only scenario is a complete no-op that passes.

The fix

Flush once more after the step loop. Unconditional on purpose — SaveChangesAsync returns immediately when the unit of work is empty (DocumentSessionBase.SaveChangesAsync checks HasOutstandingWork before doing anything) and WaitForNonStaleData is already a no-op when no daemon is running, so scenarios that already flushed pay nothing for it.

The flush sits inside the try and aggregates into ProjectionScenarioException like any other step, so a failing commit is reported as a scenario failure with the rest rather than escaping raw.

Tests

Two regression tests, both verified to fail on master before the fix:

• trailing_append_is_committed — an append after an assertion, with nothing following it
• arrange_only_scenario_actually_writes — a scenario with no assertions at all

None of the eight existing tests covered this, because every one of them happens to end with an assertion.

net9.0: DaemonTests 262 / 0 / 0.

Not addressed here

The same NextStep is ScenarioAssertion rule means consecutive actions batch into a single transaction, so a scenario cannot express "two separate commits" — which is what you would want for optimistic concurrency or per-batch projection behaviour. That is a design decision rather than a defect, and it is called out in #5126 and #5127 rather than changed silently here.

🤖 Generated with Claude Code

https://claude.ai/code/session_01VpDCvJcBDZerieJB4JEHde