cache and skip commits that have passed already

Commits marked as passed can be re-run by changing their hash or
clearing the cache.

bin/job

@@ -30,6 +30,19 @@ bail() (
     exit 1
 )
 
+mark_commit_passed() (
+    set -euo pipefail
+
+    mkdir -p ".gitlab-ci.d/passed/$1"
+    touch ".gitlab-ci.d/passed/$1/$(git rev-parse HEAD)"
+)
+
+commit_passed() (
+    set -euo pipefail
+
+    [[ -f ".gitlab-ci.d/passed/$1/$(git rev-parse HEAD)" ]]
+)
+
 run() (
     set -euo pipefail
 
@@ -59,7 +72,15 @@ run() (
             <(git rev-list --reverse "$CI_MERGE_REQUEST_DIFF_BASE_SHA..HEAD")
         for commit in "${commits[@]}"; do
             git checkout "$commit"
+
+            if commit_passed "$job"; then
+                echo "Skipping commit because it already passed: $commit"
+                continue
+            fi
+
             job_"$job" || bail
+
+            mark_commit_passed "$job"
         done
     fi
 )