fix: skip backports the release branch already has

scripts/release.ts

@@ -126,14 +126,17 @@ export const release = (cwd: string, { type, bumpEngine }: Options, deps: Deps)
                 continue;
             }
             git('checkout', '-q', '--detach', head);
-            if (!ok('cherry-pick', '-x', sha)) {
+
+            // a fix backported by hand under a different patch applies as nothing, so it's dropped
+            if (!ok('cherry-pick', '-x', '--empty=drop', sha)) {
                 git('cherry-pick', '--abort');
                 throw new Error(
                     `Backport of #${number} conflicts on ${branch}; backport it by hand or remove its "${BACKPORT_LABEL}" label`
                 );
             }
-            head = git('rev-parse', 'HEAD');
-            console.log(`Backported #${number}`);
+            const picked = git('rev-parse', 'HEAD');
+            console.log(picked === head ? `Skipping #${number}: already on ${branch}` : `Backported #${number}`);
+            head = picked;
         }
         head = withEngine(head);
         if (!git('rev-list', '-1', `${latest}..${head}`)) {

test/release/release.test.ts

@@ -91,6 +91,15 @@ describe('release', function () {
         expect(refs()).to.equal(before);
     });
 
+    it('skips a backport the branch already has under a different patch', () => {
+        run('minor');
+        picks = [{ number: 9, title: 'fix: b', sha: land('main', 'b.txt', 'b') }];
+        land('release-2.34', 'b.txt', 'old');
+        land('release-2.34', 'b.txt', 'b');
+        expect(run('patch')).to.deep.equal({ tag: 'v2.34.1', released: true });
+        expect(sh(remote, 'show', 'release-2.34:b.txt')).to.equal('b');
+    });
+
     it('does nothing when there is nothing to release', () => {
         run('minor');
         const before = refs();