Add comment, update from review

Signed-off-by: Jacob Gillespie <[email protected]>

Author: jacobwgillespie

solver/jobs.go

@@ -343,11 +343,10 @@ func (jl *Solver) loadUnlocked(v, parent Vertex, j *Job, cache map[Vertex]Vertex
 	st, ok := jl.actives[dgstWithoutCache]
 
 	if ok {
-		v = &vertexWithCacheOptions{
-			Vertex: v,
-			dgst:   dgstWithoutCache,
-			inputs: inputs,
-		}
+		// When matching an existing active vertext by dgstWithoutCache, set v to the
+		// existing active vertex, as otherwise the original vertex will use an
+		// incorrect digest and can incorrectly delete it while it is still in use.
+		v = st.vtx
 	}
 
 	if !ok {