Bring the repository up to the standard of its siblings

.github/dependabot.yml

@@ -0,0 +1,33 @@
+version: 2
+
+updates:
+  - package-ecosystem: github-actions
+    directory: "/"
+    schedule:
+      interval: weekly
+      day: monday
+    commit-message:
+      prefix: "ci"
+    groups:
+      actions:
+        patterns: ["*"]
+
+  - package-ecosystem: pip
+    directory: "/"
+    schedule:
+      interval: weekly
+      day: monday
+    commit-message:
+      prefix: "deps"
+    # torch, numpy and scipy are pinned by a lower bound on purpose: it says
+    # which versions a user may already have, not which version CI runs. pip
+    # installs the newest match either way, so raising the floor buys nothing
+    # and locks users out.
+    ignore:
+      - dependency-name: torch
+      - dependency-name: numpy
+      - dependency-name: scipy
+    groups:
+      dev-tooling:
+        patterns: ["ruff", "mypy", "pytest*"]
+    open-pull-requests-limit: 5

.github/workflows/ci.yml

@@ -85,3 +85,22 @@ jobs:
               stadion run "$task" --agent "$agent" --instances 10 --episodes 8
             done
           done
+
+  ci:
+    name: CI
+    runs-on: ubuntu-latest
+    if: always()
+    needs: [lint-and-test, verify-optima, reference-controls]
+    steps:
+      # One aggregate check to require in branch protection. The matrix jobs
+      # carry their operating system and Python version in the name, so every
+      # one of them is a separate context that changes the moment the matrix
+      # does - and a required check that silently stops matching is a required
+      # check that stopped requiring anything.
+      - name: Fail if any job did not succeed
+        if: contains(needs.*.result, 'failure') || contains(needs.*.result, 'cancelled')
+        run: |
+          echo "One or more jobs failed:"
+          echo '${{ toJSON(needs) }}'
+          exit 1
+      - run: echo "All checks passed."

.github/workflows/codeql.yml

@@ -0,0 +1,41 @@
+name: CodeQL
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+  schedule:
+    # Weekly, because advisories land between pushes: a rule added after the
+    # last commit would otherwise never run against this code.
+    - cron: "17 4 * * 1"
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+jobs:
+  analyze:
+    name: Analyze Python
+    runs-on: ubuntu-latest
+    # Code scanning on a private repository needs GitHub Advanced Security.
+    # Skipped rather than left permanently red, and it starts running by itself
+    # if the repository ever goes private and comes back.
+    if: github.event.repository.visibility == 'public'
+    permissions:
+      security-events: write
+      actions: read
+      contents: read
+    steps:
+      - uses: actions/checkout@v7
+
+      - uses: github/codeql-action/init@v4
+        with:
+          languages: python
+          # security-and-quality over the default: this service parses untrusted
+          # documents and serves HTTP, so the extra checks earn their noise.
+          queries: security-and-quality
+
+      - uses: github/codeql-action/analyze@v4
+        with:
+          category: "/language:python"

.github/workflows/dependabot-auto-merge.yml

@@ -0,0 +1,115 @@
+name: Dependabot auto-merge
+
+# What this does and does not do:
+#
+#   auto-merged  - GitHub Actions bumps, and patch bumps of anything else
+#   left for you - anything with a minor or major in it
+#
+# A patch release and an action bump are the updates that pile up unread until
+# the queue is too long to review honestly. A minor bump can change behaviour,
+# so it keeps a human. Auto-merge is queued, not immediate: GitHub still waits
+# for the required checks to pass, and a red build leaves the PR open.
+#
+# Dependabot watches actions and pip here. The file is kept identical to the
+# other repositories so they stay comparable.
+
+on: pull_request_target
+
+permissions:
+  contents: read
+
+jobs:
+  auto-merge:
+    # Who opened the pull request, not who triggered the event. `github.actor`
+    # is whoever caused this run, so the moment a person touches a Dependabot
+    # pull request - reopening it, or nudging it after a base change - the job
+    # skips and the update sits there looking merged-ready and never merging.
+    # The author never changes, which is the thing actually being asserted.
+    if: github.event.pull_request.user.login == 'dependabot[bot]'
+    runs-on: ubuntu-latest
+    permissions:
+      contents: write
+      pull-requests: write
+    steps:
+      # Reads the update metadata from the PR that Dependabot opened. Nothing
+      # from the branch is checked out or executed, which is what makes
+      # pull_request_target safe to use here.
+      - id: metadata
+        uses: dependabot/fetch-metadata@v3
+
+      - id: verdict
+        name: Decide whether this one can merge itself
+        env:
+          ECOSYSTEM: ${{ steps.metadata.outputs.package-ecosystem }}
+          UPDATE_TYPE: ${{ steps.metadata.outputs.update-type }}
+          UPDATED: ${{ steps.metadata.outputs.updated-dependencies-json }}
+        # A grouped pull request has no single update type: fetch-metadata
+        # leaves `update-type` empty and puts one entry per dependency in
+        # `updated-dependencies-json`. Reading only `update-type` sent every
+        # grouped bump to a human, including a group where all seven were
+        # patches - which is exactly the group worth merging unattended, and the
+        # reason the groups exist at all.
+        run: |
+          PATCH="version-update:semver-patch"
+
+          if [ "$ECOSYSTEM" = "github_actions" ]; then
+            echo "auto=true" >> "$GITHUB_OUTPUT"
+            echo "reason=an actions bump" >> "$GITHUB_OUTPUT"
+            exit 0
+          fi
+
+          if [ -n "$UPDATE_TYPE" ] && [ "$UPDATE_TYPE" != "null" ]; then
+            if [ "$UPDATE_TYPE" = "$PATCH" ]; then
+              echo "auto=true" >> "$GITHUB_OUTPUT"
+              echo "reason=a patch bump" >> "$GITHUB_OUTPUT"
+            else
+              echo "auto=false" >> "$GITHUB_OUTPUT"
+              echo "reason=${UPDATE_TYPE#version-update:semver-} is not a patch" >> "$GITHUB_OUTPUT"
+            fi
+            exit 0
+          fi
+
+          total=$(jq 'length' <<<"$UPDATED")
+          if [ "$total" -eq 0 ]; then
+            # No metadata to read. Refusing is the only safe reading of silence.
+            echo "auto=false" >> "$GITHUB_OUTPUT"
+            echo "reason=no update metadata to read" >> "$GITHUB_OUTPUT"
+            exit 0
+          fi
+
+          patches=$(jq --arg p "$PATCH" '[.[] | select(.updateType == $p)] | length' <<<"$UPDATED")
+          if [ "$total" -eq "$patches" ]; then
+            echo "auto=true" >> "$GITHUB_OUTPUT"
+            echo "reason=a group of $total, every one a patch" >> "$GITHUB_OUTPUT"
+          else
+            echo "auto=false" >> "$GITHUB_OUTPUT"
+            echo "reason=a group of $total, $((total - patches)) beyond patch" >> "$GITHUB_OUTPUT"
+          fi
+
+      - name: Queue the merge
+        if: steps.verdict.outputs.auto == 'true'
+        env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          PR: ${{ github.event.pull_request.html_url }}
+          REASON: ${{ steps.verdict.outputs.reason }}
+        # No `gh pr review --approve`. This organisation does not permit Actions
+        # to approve pull requests, so that call fails with
+        #
+        #   GitHub Actions is not permitted to approve pull requests
+        #
+        # and under `bash -e` it took the whole step down before the merge was
+        # ever queued - which is how auto-merge came to be broken in every
+        # repository at once.
+        #
+        # The approval was never needed: branch protection here requires the CI
+        # check and no reviews. If a review requirement is ever added, this needs
+        # a token that is not GITHUB_TOKEN, not a retry.
+        run: |
+          echo "auto-merging: $REASON"
+          gh pr merge --auto --squash "$PR"
+
+      - name: Explain why this one was left alone
+        if: steps.verdict.outputs.auto != 'true'
+        env:
+          REASON: ${{ steps.verdict.outputs.reason }}
+        run: echo "not auto-merged ($REASON); this pull request needs a human."