Mission Run Overview
Mission Run: CI suite stability & test-isolation
Fix the ensure_runtime shared-home concurrency crash (#4017) and finish moving flaky wall-clock budget guards off the per-PR path (#4015).
Reinstated CI surfaced a real runtime TOCTOU race (#4017): concurrent installed-CLI invocations sharing one spec-kitty-home abort with 'Global asset input changed' because the runtime's asset-input recheck observes the HOME destination tree (an output), not just package sources. It also left a residual of mixed and timing-only budget guards (#4015, now incl. the flaky wall-clock/NFR gates bullet) on the per-PR path. This mission narrows the asset-input observation scope so the race cannot occur and un-quarantines the concurrency tests, and sweeps the timing-guard residual (split mixed tests, a shared timing-budget helper, delete persistently-flaky low-value gates). Parent epic #1931.