Commit a completed events export even if Cancel is clicked late

[jschick04]

Summary

MauiMenuActionService.ExportEventsAsync passed the export's cancellation token to SaveStreamingAsync, so AtomicFileWriter's post-write cancellation gate (a ThrowIfCancellationRequested immediately before the atomic commit) could throw in the tiny window between the streaming write finishing and the commit. A Cancel click landing there discarded a fully written export and reported it canceled. A finished flag tried to disarm the banner Cancel after the write, but it was set a few instructions too late to close the race.

Fix

Scope cancellation to the write phase only:

• Pass the CTS token directly to EventTableExporter.ExportAsync — it throws per row on Cancel, so a mid-write Cancel discards the temp file (unchanged behavior).
• Pass CancellationToken.None to SaveStreamingAsync, so once the write completes the atomic commit is unconditional — a late Cancel is now a no-op and the completed export is saved.

This matches Windows Event Viewer (a finished export shouldn't be thrown away) and the two other SaveStreamingAsync callers (DebugLogModal, DatabaseToolsLogView), which already pass None. The banner Cancel callback now swallows ObjectDisposedException (only) to stay safe against the CTS being disposed during teardown, replacing the racy finished flag; any other throw still reaches BannerActionGuard.

Behavior

• Cancel during the write -> ExportAsync throws -> temp discarded, "Export canceled". (unchanged)
• Cancel after the write completes -> ignored -> the finished export is saved. (the fix)
• AtomicFileWriter (shared, safety-critical) is unchanged; the other callers are unaffected.

Testing

The MAUI action has no unit-test harness, so the two guarantees are locked at the Runtime layer:

• EventTableExporterTests.ExportAsync_CancelledToken_ThrowsAndWritesNothing — a canceled token aborts the export and writes nothing (so AtomicFileWriter discards the temp).
• AtomicFileWriterTests.WriteAsync_NoneToken_CommitsCompletedWriteEvenWhenASeparateSourceIsCancelled — a completed write commits under CancellationToken.None even when a separate source is canceled (complements the existing WriteAsync_CancelledAfterWrite, which proves the gate fires for a real token).

Full solution builds; Runtime.Tests 2032/2032.

[Copilot]

Pull request overview

Fixes a race in the MAUI “Export events” flow where a late Cancel click could discard a fully-written export by triggering AtomicFileWriter’s post-write cancellation gate. The change scopes cancellation to the export/write phase only, ensuring that once streaming finishes the atomic commit always proceeds.

Changes:

• In MauiMenuActionService.ExportEventsAsync, pass CancellationToken.None to SaveStreamingAsync so AtomicFileWriter commits unconditionally after the write completes, while still canceling the export write via a separate CTS token.
• Replace the racy finished flag with an ObjectDisposedException guard around the Cancel callback to handle CTS disposal during teardown safely.
• Add unit tests covering (1) exporter behavior with an already-canceled token and (2) AtomicFileWriter committing under CancellationToken.None even if a separate cancellation source is triggered.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
tests/Unit/EventLogExpert.Runtime.Tests/Export/EventTableExporterTests.cs	Adds coverage ensuring a canceled token aborts export and writes nothing.
tests/Unit/EventLogExpert.Runtime.Tests/Common/Files/AtomicFileWriterTests.cs	Adds coverage confirming CancellationToken.None allows commit even if an unrelated CTS is canceled.
src/EventLogExpert/Adapters/Menu/MauiMenuActionService.cs	Scopes cancellation to the export/write phase and prevents late Cancel from aborting the atomic commit.

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[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated no new comments.