diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index 467efc0c1a..f48f7fed3e 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -36,11 +36,11 @@ jobs:
         uses: actions/cache/restore@27d5ce7f107fe9357f9df03efb73ab90386fccae  # v5.0.5
         with:
           path: test_durations.json
-          key: test-durations-${{ github.sha }}
-          # Any previous cache from any branch works — caches from main
-          # are visible to all PRs; branch caches are visible to PRs
-          # targeting that branch.
-          restore-keys: test-durations-
+          # Single stable key — main always overwrites, PRs always find it.
+          # No SHA in the key: durations are about *files*, not commits,
+          # and SHA-keyed caches miss on every new commit (and on PR merge
+          # commits which have a different SHA than the head).
+          key: test-durations
 
       - name: Install ripgrep (prebuilt binary)
         run: |
@@ -139,7 +139,7 @@ jobs:
         uses: actions/cache/save@27d5ce7f107fe9357f9df03efb73ab90386fccae  # v5.0.5
         with:
           path: test_durations.json
-          key: test-durations-${{ github.sha }}
+          key: test-durations
 
   e2e:
     runs-on: ubuntu-latest