Neither Test Run form implemented IDisposable, so navigating away mid-run left
_runCts uncancelled: the sandbox kept the run alive until its own internal
script timeout, and the eventual continuation touched a torn-down component's
_running/_runResult fields. TemplateScriptDialog already got this right — both
forms now mirror it exactly: @implements IDisposable plus a Dispose() that
cancels + disposes _runCts.
ScriptAnalysisService.RunInSandboxAsync is marked virtual (test-only seam,
mirroring the existing virtual on DebugStreamService.StartStreamAsync/
StopStream) so a TaskCompletionSource-gated stub can hold a run open
deterministically. New bUnit tests (ScriptFormSandboxDisposalTests) prove, for
both forms: disposing mid-run cancels the token the sandbox observed, and the
cancelled continuation resolves with no unhandled exception and no _runResult/
_running mutation. Proof of failure: reverting only the two .razor changes
(keeping the virtual seam) reproduces all 4 failures — the token is never
cancelled and the no-op assertions time out.
Joseph Doherty