diff --git a/.github/workflows/validate.yml b/.github/workflows/validate.yml
index 9178b34..aa6a853 100644
--- a/.github/workflows/validate.yml
+++ b/.github/workflows/validate.yml
@@ -14,6 +14,12 @@ on:
 permissions:
   contents: read
 
+# A new push to a pull request cancels the run on the commit it replaces. Each master push
+# gets its own group, so master runs are never cancelled.
+concurrency:
+  group: validate-${{ github.event.pull_request.number || github.sha }}
+  cancel-in-progress: ${{ github.event_name == 'pull_request' }}
+
 jobs:
   validate:
     name: Repository validation
diff --git a/AGENTS.md b/AGENTS.md
index d3fb317..e018596 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -60,6 +60,8 @@ nub run format
 
 Open a pull request as a draft. Keep it a draft while you work. GitHub Actions does not run jobs on a draft pull request.
 
+`nub install` installs a lefthook pre-push hook (`lefthook.yml`) that runs `nub run typecheck`, `nub run lint`, and `nub run format`.
+
 When the work is done, mark the pull request ready for review.
 
 ## Release management
diff --git a/lefthook.yml b/lefthook.yml
new file mode 100644
index 0000000..056f972
--- /dev/null
+++ b/lefthook.yml
@@ -0,0 +1,12 @@
+# Runs the fast repository checks before a push, so a lint, type or format error fails
+# here and not in CI. Skip once with `git push --no-verify` or `LEFTHOOK=0 git push`.
+# `nub install` installs the hook (the `prepare` script).
+pre-push:
+  parallel: true
+  jobs:
+    - name: typecheck
+      run: nub run typecheck
+    - name: lint
+      run: nub run lint
+    - name: format
+      run: nub run format
diff --git a/nub.lock b/nub.lock
index cce06eb..1bf9165 100644
--- a/nub.lock
+++ b/nub.lock
@@ -15,6 +15,9 @@ importers:
       '@types/node':
         specifier: 24.19.2
         version: 24.19.2
+      lefthook:
+        specifier: ^2.2.2
+        version: 2.2.2
       oxfmt:
         specifier: 0.74.0
         version: 0.74.0
@@ -479,6 +482,65 @@ packages:
       picomatch:
         optional: true
 
+  lefthook-android-arm64@2.2.2:
+    resolution: {integrity: sha512-wb9rQQFLX7u1dJLxvMrq9VUfMYi5kxM7tJQ6Y4mWEOwaU+SmIm2wjoT/nromKq27Y8fh2Qd7FgCD3G1wfW8CnQ==}
+    cpu: [arm64]
+    os: [android]
+
+  lefthook-darwin-arm64@2.2.2:
+    resolution: {integrity: sha512-6V8D3bLnD/60Xhqn0o2EQD6H3Fe/U9LGkt4WF1O/3eBHbux+5ZJqoH0hfrC+Bi9Dy1Ve1AWxiAY7U2asYl8qVA==}
+    cpu: [arm64]
+    os: [darwin]
+
+  lefthook-darwin-x64@2.2.2:
+    resolution: {integrity: sha512-fH/kArZ9ZZ65wCFtvBMgGcq25qwQpkQ5jp93ba+8wpjgxxzjczYGluwHvM/NQDJWLOFXuKXW0yFs76SramQkyQ==}
+    cpu: [x64]
+    os: [darwin]
+
+  lefthook-freebsd-arm64@2.2.2:
+    resolution: {integrity: sha512-MCRsU01ju989QQffOfS3gCeFfyVDXs5B/FzR65fmrNvqcxb98fldvfzzoAbnK2q6SBJlRT3QT1tNEMCxddCwlA==}
+    cpu: [arm64]
+    os: [freebsd]
+
+  lefthook-freebsd-x64@2.2.2:
+    resolution: {integrity: sha512-LkKuJU0S2oLimeoHwPTy1TLWB6GcN0t5lLxiXNlsBKUkr6R47QRcvPMZMoXmu3IetQtd+WliXMLE8qTwi2fqBg==}
+    cpu: [x64]
+    os: [freebsd]
+
+  lefthook-linux-arm64@2.2.2:
+    resolution: {integrity: sha512-d+HFtS2DEKaOnD7vRU0tUz8pNgHwsUYmQ22+1dyXpOrXGyzNXR0AqX5KsIRF36JGhVvO5X5Anw5QYgR3mxVSuA==}
+    cpu: [arm64]
+    os: [linux]
+
+  lefthook-linux-x64@2.2.2:
+    resolution: {integrity: sha512-N/OlQyAhcU6RAXjrwFxLsh70sn96rBoi+XkuLJ8CVBkk9Ci3VDXQayDZTNz5B1xML8RwoMcV8Wblniy1xFOmSA==}
+    cpu: [x64]
+    os: [linux]
+
+  lefthook-openbsd-arm64@2.2.2:
+    resolution: {integrity: sha512-6G/gKXcpIwC+XcODg7ELZYP/hIrVIHQxhy2GoRdVyecmpGMFj+BZo3iqcUmeWusQMuL+UdNexbkrUaeJalIkNw==}
+    cpu: [arm64]
+    os: [openbsd]
+
+  lefthook-openbsd-x64@2.2.2:
+    resolution: {integrity: sha512-eMJGi3/tqKEqu7XCZlqwQWRtK5JlL/9diaqqgRlEdlRD7GxwzHZN21z6awbITum9emea3lALvXFe6V8odQLGOA==}
+    cpu: [x64]
+    os: [openbsd]
+
+  lefthook-windows-arm64@2.2.2:
+    resolution: {integrity: sha512-4P1EaQb5xG1zhYD1RLJ6TEGdFkmHkB+Slqx6yRDPKuBDNxMiD0+kTAAdUY2E8xPuRR35xHpVPR+b3/HtzPrjQQ==}
+    cpu: [arm64]
+    os: [win32]
+
+  lefthook-windows-x64@2.2.2:
+    resolution: {integrity: sha512-9Ck4zancQilBfXT3ZeRipm7Lcq4RQfxyMpy8SAVINw0t/BrbjsT25V46ZuziERcwdajnE4myfMzC33GoCBwr7g==}
+    cpu: [x64]
+    os: [win32]
+
+  lefthook@2.2.2:
+    resolution: {integrity: sha512-37fYHAhL12r1twaEV0PA5TwoIT491eTGGYjhhXxlYNMq3DSkiGZBQ++Jfk5maXj0vq52NRauLtMikBKtbNJs3Q==}
+    hasBin: true
+
   oxfmt@0.74.0:
     resolution: {integrity: sha512-G4OP7FgwGYZR5ttRpCOOfJdyRsSyvtn34vSXnjDq6Oqed5Dufg5mB44mank+51nAdHOKuTJ0lj0mksY7L+N61A==}
     engines: {node: ^20.19.0 || >=22.12.0}
@@ -784,6 +846,53 @@ snapshots:
     dependencies:
       picomatch: 4.0.7
 
+  lefthook-android-arm64@2.2.2:
+    optional: true
+
+  lefthook-darwin-arm64@2.2.2:
+    optional: true
+
+  lefthook-darwin-x64@2.2.2:
+    optional: true
+
+  lefthook-freebsd-arm64@2.2.2:
+    optional: true
+
+  lefthook-freebsd-x64@2.2.2:
+    optional: true
+
+  lefthook-linux-arm64@2.2.2:
+    optional: true
+
+  lefthook-linux-x64@2.2.2:
+    optional: true
+
+  lefthook-openbsd-arm64@2.2.2:
+    optional: true
+
+  lefthook-openbsd-x64@2.2.2:
+    optional: true
+
+  lefthook-windows-arm64@2.2.2:
+    optional: true
+
+  lefthook-windows-x64@2.2.2:
+    optional: true
+
+  lefthook@2.2.2:
+    optionalDependencies:
+      lefthook-android-arm64: 2.2.2
+      lefthook-darwin-arm64: 2.2.2
+      lefthook-darwin-x64: 2.2.2
+      lefthook-freebsd-arm64: 2.2.2
+      lefthook-freebsd-x64: 2.2.2
+      lefthook-linux-arm64: 2.2.2
+      lefthook-linux-x64: 2.2.2
+      lefthook-openbsd-arm64: 2.2.2
+      lefthook-openbsd-x64: 2.2.2
+      lefthook-windows-arm64: 2.2.2
+      lefthook-windows-x64: 2.2.2
+
   oxfmt@0.74.0:
     dependencies:
       tinypool: 2.2.0
diff --git a/package.json b/package.json
index 5afff8e..e000065 100644
--- a/package.json
+++ b/package.json
@@ -42,6 +42,7 @@
   },
   "scripts": {
     "build": "tsc -p tsconfig.build.json",
+    "prepare": "lefthook install",
     "typecheck": "tsrs --noEmit",
     "test": "node --test \"tests/**/*.test.ts\"",
     "lint": "nub run build && oxlint --deny-warnings",
@@ -56,6 +57,7 @@
   },
   "devDependencies": {
     "@types/node": "24.19.2",
+    "lefthook": "^2.2.2",
     "oxfmt": "0.74.0",
     "oxlint": "1.89.0",
     "tegami": "1.5.0",