Problem

The XCTest runner process can exit without XCTest delivering its completion callbacks — testCaseDidFinish, testRetryGroupDidFinish, testSuiteDidFinish, testBundleDidFinish. This is not a crash: the process exits in an orderly way, so our binary-unload hook (__AutoUnloadHook → FrameworkLoadHandler.libraryUnloaded()) still runs and SessionManager.stop() closes the session and module spans. But any in-flight suite / retry-group / test is left open, never end()ed, and therefore dropped from the trace.

This is a general premature-exit problem, not a single vendor bug. Equivalent triggers:

• a test (or its setup) calling exit(...) directly;
• a failure in an async setUp/tearDown under recent Xcode, which terminates the runner after tearDown (forum thread — the "crash" framing there is inaccurate, it's an orderly exit).

Fix

DDXCTestObserver.stop() previously hit default: break for the .suite/.group/.test states and did nothing. It now detects the premature exit and:

1. Logs a generic premature-exit warning — deliberately not attributed to any specific Xcode/vendor bug, since a user exit() produces the identical fault.
2. Force-closes the open test and suite as failed, attaching a PrematureTestProcessExit error so the backend records why they failed.
3. Ends the module the way testBundleDidFinish does (session.end(module:)); the failure propagates up to the session via set(failed:). The session/module spans are then closed by the unload path as before.

State is extended so .group/.test carry the references needed to recover from stop() (they previously held none). The suite-end mirrors testSuiteDidFinish but skips the feature hooks — those can't run meaningfully once the process is terminating.

Test

Adds testWhenProcessExitsMidTest_activeTestAndSuiteAreSealedAsFailed, which drives the observer into .test and then forces shutdown, asserting both spans are ended, failed, and carry an error.

It is intentionally synchronous: stop() unregisters the observer, which XCTest only permits on the main thread (sync tests run there). An async test crashes off-main on the unregister; a @MainActor async test deadlocks against XCTest's main-thread wait at the first await.

All 8 DDXCTestObserverTests pass; no regression to the normal completion flow.

Ref: SDTEST-3844

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