Mission Run Overview
Mission Run: CI Main Concurrency + Fleet Fan-out Cap (Stage 1)
Stage 1 of the main-tip verdict-topology cluster (#4437): give each landed main tip its own terminal CI evaluation via per-SHA concurrency (#4347) and cap the fleet-verdict fan-out those extra runs would otherwise multiply (#4371).
On a merge burst, main-branch CI runs cancel each other (shared refs/heads/main concurrency group), so content lands with zero terminal evaluation; and the fleet-verdict workflow fans out into dozens of redundant runs per tip (measured: 60 for one main tip). These two levers are coupled — removing the cancel-cascade adds concurrent main runs, which the fan-out cap must bound, so they land together as one stage. This mission delivers per-SHA main concurrency plus a fleet-verdict top-level concurrency block, trimmed workflow_run event types, and reinforced dedup, verified on the merged main tip.