diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 46d4d05a..43b1c870 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -19,8 +19,43 @@ permissions:
   contents: read
 
 jobs:
+  verified:
+    name: Already verified
+    # A push to main whose tree is the tree its pull request was merged with, and whose pull request passed Required Checks on that head, has nothing new to check: the same files give the same result. Every other push, and every pull request, runs the full set. A failure here runs the full set too (the other jobs only skip on an explicit "true").
+    if: github.event_name == 'push'
+    runs-on: ubuntu-latest
+    timeout-minutes: 5
+    permissions:
+      contents: read
+      pull-requests: read
+      checks: read
+    outputs:
+      skip: ${{ steps.compare.outputs.skip }}
+    steps:
+      - id: compare
+        env:
+          GH_TOKEN: ${{ github.token }}
+          REPO: ${{ github.repository }}
+          SHA: ${{ github.sha }}
+        run: |
+          set -euo pipefail
+          skip=false
+          head=$(gh api "repos/${REPO}/commits/${SHA}/pulls" --jq '.[0].head.sha // empty')
+          if [ -n "$head" ]; then
+            pushed_tree=$(gh api "repos/${REPO}/git/commits/${SHA}" --jq .tree.sha)
+            merged_tree=$(gh api "repos/${REPO}/git/commits/${head}" --jq .tree.sha)
+            verdict=$(gh api "repos/${REPO}/commits/${head}/check-runs?filter=latest&check_name=Required%20Checks" --jq '.check_runs[0].conclusion // empty')
+            echo "pushed tree ${pushed_tree}, pull request head ${head} tree ${merged_tree}, its Required Checks: ${verdict:-none}"
+            if [ "$pushed_tree" = "$merged_tree" ] && [ "$verdict" = success ]; then
+              skip=true
+            fi
+          fi
+          echo "skip=${skip}" >> "$GITHUB_OUTPUT"
+
   shellcheck:
     name: Shellcheck
+    needs: verified
+    if: ${{ !cancelled() && needs.verified.outputs.skip != 'true' }}
     runs-on: ubuntu-latest
     timeout-minutes: 10
     steps:
@@ -28,8 +63,6 @@ jobs:
       - name: Lint every shell script
         run: |
           set -euo pipefail
-          sudo apt-get update -qq
-          sudo apt-get install -y -qq shellcheck
           mapfile -t scripts < <(find . -type f -name '*.sh' -not -path './.git/*')
           echo "Found ${#scripts[@]} shell script(s)."
           if [ "${#scripts[@]}" -gt 0 ]; then
@@ -38,17 +71,21 @@ jobs:
 
   actionlint:
     name: actionlint
+    needs: verified
+    if: ${{ !cancelled() && needs.verified.outputs.skip != 'true' }}
     runs-on: ubuntu-latest
     timeout-minutes: 10
     steps:
       - uses: actions/checkout@v7
       - name: Install actionlint
-        run: bash <(curl -fsSL https://raw.githubusercontent.com/rhysd/actionlint/main/scripts/download-actionlint.bash)
+        run: bash <(curl -fsSL https://raw.githubusercontent.com/rhysd/actionlint/v1.7.12/scripts/download-actionlint.bash) 1.7.12
       - name: Lint every workflow file
         run: ./actionlint -color
 
   yamllint:
     name: YAML lint
+    needs: verified
+    if: ${{ !cancelled() && needs.verified.outputs.skip != 'true' }}
     runs-on: ubuntu-latest
     timeout-minutes: 10
     steps:
@@ -56,12 +93,12 @@ jobs:
       - name: Lint every YAML file
         run: |
           set -euo pipefail
-          sudo apt-get update -qq
-          sudo apt-get install -y -qq yamllint
           yamllint .
 
   hadolint:
     name: hadolint
+    needs: verified
+    if: ${{ !cancelled() && needs.verified.outputs.skip != 'true' }}
     runs-on: ubuntu-latest
     timeout-minutes: 10
     steps:
@@ -89,6 +126,8 @@ jobs:
 
   ansible-syntax-check:
     name: Ansible syntax check
+    needs: verified
+    if: ${{ !cancelled() && needs.verified.outputs.skip != 'true' }}
     runs-on: ubuntu-latest
     timeout-minutes: 10
     steps:
@@ -104,19 +143,11 @@ jobs:
             echo "Syntax-checking ${playbook}"
             ansible-playbook -i ../examples/three-server-tailscale/inventory.yml "${playbook}" --syntax-check
           done
-      - name: Build the collection
-        # Proves galaxy.yml's build_ignore still ships what the roles need at runtime, such as the k3s node's Compose file and build context under roles/github_runner_cluster/files.
-        run: |
-          set -euo pipefail
-          ansible-galaxy collection build --output-path "${RUNNER_TEMP}/collection"
-          tar -tzf "${RUNNER_TEMP}"/collection/*.tar.gz | grep -Fx roles/github_runner_cluster/files/docker-compose.yml
-          tar -tzf "${RUNNER_TEMP}"/collection/*.tar.gz | grep -Fx roles/github_runner_cluster/files/k3s/node-entrypoint.sh
-          for file in Dockerfile fleet-regrade.sh fleet-regrade-core.sh fleet-regrade-docker.sh; do
-            tar -tzf "${RUNNER_TEMP}"/collection/*.tar.gz | grep -Fx "roles/github_runner_cluster/files/regrade/${file}"
-          done
 
   unit-tests:
     name: Unit tests (shard ${{ matrix.shard }})
+    needs: verified
+    if: ${{ !cancelled() && needs.verified.outputs.skip != 'true' }}
     runs-on: ubuntu-latest
     # Each module is run on its own by discovery, dealt out by size so that the shards take about the same amount of work: the tests that run Ansible playbooks cost a process each, and the suite no longer fits one job.
     timeout-minutes: 20
@@ -149,6 +180,8 @@ jobs:
 
   ansible-lint:
     name: ansible-lint
+    needs: verified
+    if: ${{ !cancelled() && needs.verified.outputs.skip != 'true' }}
     runs-on: ubuntu-latest
     timeout-minutes: 10
     steps:
@@ -167,17 +200,25 @@ jobs:
 
   collection-build:
     name: Collection build check
+    needs: verified
+    if: ${{ !cancelled() && needs.verified.outputs.skip != 'true' }}
     runs-on: ubuntu-latest
     timeout-minutes: 10
     steps:
       - uses: actions/checkout@v7
-      - name: Install Ansible
-        run: |
-          set -euo pipefail
-          sudo apt-get update -qq
-          sudo apt-get install -y -qq ansible
       - name: Build the collection tarball
+        # ansible-galaxy and ansible-doc come with the ansible-core the ubuntu-latest image already has: building, installing and reading a collection's own plugins needs no other collection.
         run: ansible-galaxy collection build --force
+      - name: Check the tarball ships what the roles need at runtime
+        # Proves galaxy.yml's build_ignore still ships what the roles need at runtime, such as the k3s node's Compose file and build context under roles/github_runner_cluster/files.
+        run: |
+          set -euo pipefail
+          tarball=$(ls exadev-github_runner-*.tar.gz)
+          tar -tzf "$tarball" | grep -Fx roles/github_runner_cluster/files/docker-compose.yml
+          tar -tzf "$tarball" | grep -Fx roles/github_runner_cluster/files/k3s/node-entrypoint.sh
+          for file in Dockerfile fleet-regrade.sh fleet-regrade-core.sh fleet-regrade-docker.sh; do
+            tar -tzf "$tarball" | grep -Fx "roles/github_runner_cluster/files/regrade/${file}"
+          done
       - name: Install the built tarball and verify its content
         run: |
           set -euo pipefail
@@ -210,19 +251,6 @@ jobs:
           BASE_SHA: ${{ github.event.pull_request.base.sha }}
           HEAD_SHA: ${{ github.event.pull_request.head.sha }}
         run: npx --no-install commitlint --from "$BASE_SHA" --to "$HEAD_SHA" --verbose
-
-  commitlint-pr-title:
-    name: Lint PR title
-    if: github.event_name == 'pull_request'
-    runs-on: ubuntu-latest
-    timeout-minutes: 5
-    steps:
-      - uses: actions/checkout@v7
-      - uses: actions/setup-node@v7
-        with:
-          node-version: '22'
-          cache: npm
-      - run: npm ci
       # Rebase-merges keep each commit's own message, so the title isn't what lands on main; it's still checked so the PR list reads consistently. Passed through env, never interpolated into the script.
       - name: Lint the pull request title
         env:
@@ -231,7 +259,7 @@ jobs:
 
   required-checks:
     name: Required Checks
-    needs: [shellcheck, actionlint, yamllint, hadolint, ansible-syntax-check, unit-tests, ansible-lint, collection-build, commitlint, commitlint-pr-title]
+    needs: [shellcheck, actionlint, yamllint, hadolint, ansible-syntax-check, unit-tests, ansible-lint, collection-build, commitlint]
     # Always runs, even if a dependency failed or was skipped, so it can report that failure itself rather than being skipped - a required check that's silently absent blocks a PR indefinitely instead of failing it visibly.
     if: always()
     runs-on: ubuntu-latest
diff --git a/README.md b/README.md
index e7faa3b2..27cd2244 100644
--- a/README.md
+++ b/README.md
@@ -78,7 +78,7 @@ There is no application test suite in this repo; the checks above are the projec
 
 ## Releases
 
-Every push to `main` runs `.github/workflows/release.yml`, driven by [semantic-release](https://semantic-release.gitbook.io/) (`.releaserc.json`) against [Conventional Commits](https://www.conventionalcommits.org/) (`commitlint.config.js`, enforced by the `commitlint`/`commitlint-pr-title` CI jobs above). Almost every conventional-commit type triggers at least a patch release (see `.releaserc.json`'s `commit-analyzer` `releaseRules`: `feat` is minor, a breaking change (`!` or a `BREAKING CHANGE:` footer) is major, everything else conventional is patch), so in practice nearly every push to `main` produces a release.
+Every push to `main` runs `.github/workflows/release.yml`, driven by [semantic-release](https://semantic-release.gitbook.io/) (`.releaserc.json`) against [Conventional Commits](https://www.conventionalcommits.org/) (`commitlint.config.js`, enforced by the `commitlint` CI job above, which checks every commit and the pull request title). Almost every conventional-commit type triggers at least a patch release (see `.releaserc.json`'s `commit-analyzer` `releaseRules`: `feat` is minor, a breaking change (`!` or a `BREAKING CHANGE:` footer) is major, everything else conventional is patch), so in practice nearly every push to `main` produces a release.
 
 A release: