Dropped the single-active-run fallback that claimed unrelated stackless rejections in the shared main-process realm, matching the eval inline-mode invariant. Only guest-file stack frames attribute a rejection now; stackless reasons keep the fatal path. Restored the probe to an Error rejection carrying a guest stack.
Fixes#7365
Attributed unmatched rejection reasons when exactly one cmux guest run is active, covering primitive and library-created failures without guessing between concurrent runs. Updated the process probe to reject with a primitive value.
Fixes#7365
Captured browser-run-attributable promise rejections before the global fatal handler and surfaced active failures as tool errors. Retained finished run filenames so late rejections remain isolated without consuming unrelated process failures.
Fixes#7365
roboomp