diff --git a/.github/workflows/connectivity.yml b/.github/workflows/connectivity.yml
new file mode 100644
index 0000000..d272d71
--- /dev/null
+++ b/.github/workflows/connectivity.yml
@@ -0,0 +1,127 @@
+---
+# Diagnostics, for when a deploy job hangs instead of failing.
+#
+# Two jobs, deliberately separate:
+#
+#   ping   uses the real deploy key and asks Ansible to talk to every host. This
+#          is the right first thing to run after setting the secrets up, and the
+#          right first thing to run when a deploy misbehaves. It changes nothing.
+#   probe  uses no credentials at all and answers a narrower question: where do
+#          the packets stop? Run it when ping times out.
+#
+# The distinction that matters, and the reason `probe` exists:
+#
+#   Permission denied (publickey)  the key is wrong — you reached sshd
+#   Connection refused             you reached the host, nothing is listening
+#   Connection timed out           packets are being dropped in transit
+#
+# Only the third is a network problem, and no amount of re-pasting the key will
+# fix it. See docs/connectivity.md.
+name: connectivity
+
+on:
+  workflow_dispatch:
+    inputs:
+      hosts:
+        description: Space-separated hosts to probe (defaults to the inventory)
+        required: false
+        default: edge.example.com app.example.com
+
+permissions:
+  contents: read
+
+jobs:
+  ping:
+    name: ansible ping
+    runs-on: ${{ vars.DEPLOY_RUNNER || 'ubuntu-latest' }}
+    environment: production
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+      - name: Install the pinned toolchain
+        run: |
+          set -eu
+          scripts/check.sh --print-specs | head -1 | xargs -d '\n' pip install --quiet
+      - name: Load the deploy key
+        env:
+          SSH_KEY_BACKEND: ci
+          SSH_PRIVATE_KEY_B64: ${{ secrets.SSH_PRIVATE_KEY_B64 }}
+        run: |
+          set -eu
+          SSH_KEY_PATH="$(scripts/load-ssh-key.sh)"
+          echo "SSH_KEY_PATH=$SSH_KEY_PATH" >> "$GITHUB_ENV"
+      # Success looks like `SUCCESS => {"ping": "pong"}` for every host. That
+      # proves the runner decoded the key, reached port 22, authenticated, and
+      # ran Python on the far side — which is everything a deploy needs except
+      # the playbook itself.
+      - name: Ping every host in the inventory
+        working-directory: ansible
+        run: ansible all -m ansible.builtin.ping
+
+  probe:
+    name: network probe
+    runs-on: ${{ vars.DEPLOY_RUNNER || 'ubuntu-latest' }}
+    # A report, not a gate. Every section must run even when the thing it probes
+    # is unreachable, which is the normal case when you are running this.
+    continue-on-error: true
+    steps:
+      - name: Probe
+        env:
+          HOSTS: ${{ github.event.inputs.hosts }}
+        run: |
+          set +e
+
+          # A bare TCP connect can be answered by a transparent proxy that then
+          # says nothing, which looks like success and is not. Real sshd greets
+          # first, so the banner is the only honest proof you reached the server.
+          ssh_banner() {
+            b=$(timeout 6 bash -c "exec 3<>/dev/tcp/$1/${2:-22}; head -c 12 <&3" 2>/dev/null || true)
+            case "$b" in
+              SSH-*) printf '  %-26s %-5s OK, sshd replied: %s\n' "$1" "${2:-22}" "$b" ;;
+              '')    printf '  %-26s %-5s NO REPLY (dropped, or a silent proxy)\n' "$1" "${2:-22}" ;;
+              *)     printf '  %-26s %-5s answered, but not sshd: %s\n' "$1" "${2:-22}" "$b" ;;
+            esac
+          }
+
+          # Distinguishes "refused" (allowed out, nothing listening) from
+          # "filtered" (dropped in transit). This is the whole point of the job:
+          # if every port but 443 is filtered, you are behind an egress allowlist
+          # and no alternative SSH port will help.
+          port_state() {
+            # `rc=0; out=$(...) || rc=$?` and not `out=$(...); rc=$?` — the
+            # latter is a failing simple command, which under set -e ends the
+            # step before rc is ever read, so a filtered port aborts the report
+            # instead of describing it.
+            rc=0
+            out=$(timeout 5 bash -c "cat < /dev/null > /dev/tcp/$1/$2" 2>&1) || rc=$?
+            if [ "$rc" -eq 0 ]; then                          s='open'
+            elif printf '%s' "$out" | grep -qi refused; then
+              s='refused -> port allowed out'
+            elif [ "$rc" -eq 124 ]; then
+              s='filtered -> blocked in transit'
+            else
+              s="unclear (rc=$rc) $out"
+            fi
+            printf '  %-26s %-5s %s\n' "$1" "$2" "$s"
+          }
+
+          printf '== 0. does this runner have a network at all? ==\n'
+          printf '  DNS:            '; getent hosts github.com >/dev/null 2>&1 && echo resolves || echo 'CANNOT RESOLVE'
+          printf '  https external: '
+          curl -s -o /dev/null -w '%{http_code}\n' --max-time 10 \
+            https://github.com || echo 'NO EGRESS'
+          printf '  egress address: '; curl -s --max-time 10 https://ifconfig.me || echo unknown
+
+          printf '\n\n== 1. SSH to the target hosts ==\n'
+          for h in $HOSTS; do ssh_banner "$h"; done
+
+          printf '\n== 2. SSH elsewhere: is outbound 22 blocked wholesale? ==\n'
+          ssh_banner github.com
+
+          printf '\n== 3. Which ports are allowed out at all? ==\n'
+          for h in $HOSTS; do
+            port_state "$h" 22
+            port_state "$h" 443
+          done
diff --git a/.github/workflows/deploy.yml b/.github/workflows/deploy.yml
new file mode 100644
index 0000000..ddd64cf
--- /dev/null
+++ b/.github/workflows/deploy.yml
@@ -0,0 +1,151 @@
+---
+# Deploys. Two ways in, and only two:
+#
+#   - a human fills in the form under Actions > deploy > Run workflow
+#   - another repository asks for a stack by name, via repository_dispatch
+#
+# Nothing deploys on a push. That is the single most important property of this
+# file: a merge to the default branch changes what *would* be deployed, and a
+# person still decides when.
+#
+# GitHub has no per-job manual button, so GitLab's grid of check:<stack> and
+# deploy:<stack> buttons becomes one form with a `stack` dropdown. The list under
+# `options:` has to be kept in step with ansible/playbooks/ by hand — see
+# skills/adding-a-stack/SKILL.md. Setup: docs/ci-github-actions.md.
+name: deploy
+
+on:
+  workflow_dispatch:
+    inputs:
+      stack:
+        description: Which stack to act on
+        required: true
+        type: choice
+        options:
+          - site
+          - reverse-proxy
+          - banner
+          - metrics
+          - static-site
+          - webapp
+          - webapp-staging
+      mode:
+        description: check reports what would change; deploy does it
+        required: true
+        default: check
+        type: choice
+        options:
+          - check
+          - deploy
+      pull:
+        description: >-
+          Image pull policy. always fetches newer images and enables per-stack
+          update work (backups, migrations).
+        required: true
+        default: policy
+        type: choice
+        options:
+          - policy
+          - always
+          - missing
+          - never
+  repository_dispatch:
+    types: [deploy]
+
+# Two deploys of the same stack at once would race on the host.
+concurrency:
+  group: deploy-${{ github.event.inputs.stack || github.event.client_payload.stack }}
+  cancel-in-progress: false
+
+permissions:
+  contents: read
+
+jobs:
+  ansible:
+    name: >-
+      ${{ github.event.inputs.mode || 'deploy' }}
+      ${{ github.event.inputs.stack || github.event.client_payload.stack }}
+    # Self-hosted when the hosts are not reachable from GitHub's network — set
+    # the DEPLOY_RUNNER repository variable to the runner's label. See
+    # "Runners" in docs/ci-github-actions.md.
+    runs-on: ${{ vars.DEPLOY_RUNNER || 'ubuntu-latest' }}
+    # The Environment is what replaces GitLab's Protected variables: the deploy
+    # key is stored on it, so it exists only for jobs that name it, and its
+    # protection rules (required reviewers, allowed branches) gate every run.
+    environment: production
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+
+      # STACK, MODE and PULL reach a shell command, and under repository_dispatch
+      # they come from another repository. They go through the environment, never
+      # through ${{ }} interpolation into a run: block — an expression is
+      # substituted into the script *before* the shell sees it, so a crafted
+      # value would be executed rather than compared. Validate, then use.
+      - name: Validate the requested stack and pull policy
+        env:
+          STACK: ${{ github.event.inputs.stack || github.event.client_payload.stack }}
+          MODE: ${{ github.event.inputs.mode || github.event.client_payload.mode || 'deploy' }}
+          PULL: ${{ github.event.inputs.pull || github.event.client_payload.pull || 'policy' }}
+        run: |
+          set -eu
+          case "$STACK" in
+            ''|*[!a-z0-9_-]*) echo "refusing STACK='$STACK'"; exit 1 ;;
+          esac
+          case "$MODE" in
+            check|deploy) ;;
+            *) echo "refusing MODE='$MODE'"; exit 1 ;;
+          esac
+          # An unchecked value can smuggle extra `-e` overrides onto the command
+          # line (stack_dest, ansible_host) and redirect the deploy somewhere
+          # else entirely.
+          case "$PULL" in
+            policy|always|missing|never) ;;
+            *) echo "refusing PULL='$PULL'"; exit 1 ;;
+          esac
+          test -f "ansible/playbooks/${STACK}.yml" \
+            || { echo "no playbook for '$STACK'"; exit 1; }
+          {
+            echo "STACK=$STACK"
+            echo "MODE=$MODE"
+            echo "PULL=$PULL"
+          } >> "$GITHUB_ENV"
+
+      - name: Install the pinned toolchain
+        run: |
+          set -eu
+          scripts/check.sh --print-specs | head -1 | xargs -d '\n' pip install --quiet
+          ansible-galaxy install -r ansible/requirements.yml
+
+      # Two lines, not `export SSH_KEY_PATH="$(...)"`. export is a special
+      # builtin, so the compound command reports *its* exit status and swallows
+      # the script's — under `set -e` a loader failure goes unnoticed and the job
+      # dies much later with a per-host "Permission denied (publickey)" instead
+      # of the loader's own message saying which variable was missing.
+      - name: Load the deploy key
+        env:
+          SSH_KEY_BACKEND: ci
+          SSH_PRIVATE_KEY_B64: ${{ secrets.SSH_PRIVATE_KEY_B64 }}
+        run: |
+          set -eu
+          SSH_KEY_PATH="$(scripts/load-ssh-key.sh)"
+          echo "SSH_KEY_PATH=$SSH_KEY_PATH" >> "$GITHUB_ENV"
+
+      - name: Run the playbook
+        working-directory: ansible
+        env:
+          ANSIBLE_FORCE_COLOR: "1"
+        run: |
+          set -eu
+          # An `if`, not `[ ... ] && extra=...`: when the test fails the AND-list
+          # returns non-zero, and under `set -e` that ends the job right here
+          # with no error message and a green-looking cancel.
+          if [ "$MODE" = "check" ]; then
+            set -- --check --diff
+          else
+            set --
+          fi
+          ansible-playbook "playbooks/${STACK}.yml" "$@" -e "pull=$PULL"
diff --git a/.github/workflows/lint.yml b/.github/workflows/lint.yml
new file mode 100644
index 0000000..223fe9f
--- /dev/null
+++ b/.github/workflows/lint.yml
@@ -0,0 +1,73 @@
+---
+# The static gate. Runs on every push and pull request, needs no access to any
+# host, and is the definition of "done" for a change here.
+#
+# Everything below is `scripts/check.sh` plus two scans. Keeping the lint steps
+# in a script rather than inline is deliberate: a contributor can run the exact
+# same gate locally with `make check` before pushing, and the two cannot drift.
+name: lint
+
+on:
+  push:
+    branches: ["**"]
+  pull_request:
+
+# A second push to the same branch makes the first run pointless.
+concurrency:
+  group: lint-${{ github.ref }}
+  cancel-in-progress: true
+
+permissions:
+  contents: read
+
+jobs:
+  ansible:
+    name: yamllint + ansible-lint + syntax
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+
+      # scripts/check.sh is the single source of the version pins; it prints
+      # them so that this workflow can install exactly what a contributor runs
+      # locally. Nothing here can drift from the script.
+      - name: Install the pinned toolchain
+        run: |
+          set -eu
+          scripts/check.sh --print-specs | tee /dev/stderr | xargs -d '\n' pip install --quiet
+
+      - name: Run the static gate
+        run: RUNNER=installed scripts/check.sh
+
+  shell:
+    name: shellcheck
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      # Pre-installed on GitHub-hosted Ubuntu runners; installed explicitly so
+      # this job also works on a self-hosted runner with a bare image.
+      - name: Install shellcheck
+        run: command -v shellcheck || sudo apt-get install -y --no-install-recommends shellcheck
+      - name: Check the shell scripts
+        run: shellcheck scripts/*.sh server/*/*/app/*.sh
+
+  secrets:
+    name: secret scan
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          # detect scans history, not just the working tree. A secret that was
+          # committed and then removed is still a leaked secret.
+          fetch-depth: 0
+      # Run the upstream image directly rather than the marketplace action: the
+      # action requires a licence key for organisation-owned repositories, and
+      # silently no-ops without one. The image has no such condition.
+      - name: Scan the working tree and history for committed secrets
+        run: |
+          docker run --rm -v "$PWD:/repo" zricethezav/gitleaks:latest \
+            detect --source=/repo --config=/repo/.gitleaks.toml \
+            --redact --verbose --no-banner
diff --git a/docs/ci-github-actions.md b/docs/ci-github-actions.md
new file mode 100644
index 0000000..7fe87b5
--- /dev/null
+++ b/docs/ci-github-actions.md
@@ -0,0 +1,145 @@
+# CI on GitHub Actions
+
+Three workflows. There is a Gitea port of all three in
+[`.gitea/workflows/`](../.gitea/workflows) — see [ci-gitea.md](ci-gitea.md),
+and note that Gitea reads that directory *instead of* this one.
+
+| Workflow | Trigger | Needs host access |
+| --- | --- | --- |
+| [`lint.yml`](../.github/workflows/lint.yml) | every push and pull request | no |
+| [`deploy.yml`](../.github/workflows/deploy.yml) | manual, or `repository_dispatch` | yes |
+| [`connectivity.yml`](../.github/workflows/connectivity.yml) | manual | yes (`ping` only) |
+
+## Setup
+
+### 1. Create the `production` environment
+
+Settings → Environments → New environment → `production`.
+
+This is where the deploy key lives, and it is what replaces GitLab's "Protected
+variable" concept. A secret on an environment is invisible to any job that does
+not name that environment, and the environment's own rules gate the job:
+
+- **Required reviewers** — a deploy waits for a named person to approve it.
+  Worth turning on. It makes "press the button" a two-person operation without
+  any change to this repository.
+- **Deployment branches** — restrict to your default branch so a deploy cannot
+  be run from an arbitrary fork branch.
+
+### 2. Add the deploy key
+
+On that environment, add a secret `SSH_PRIVATE_KEY_B64` holding the base64 of
+your deploy private key. See [secrets.md](secrets.md) for how to encode it, and
+what not to use on Windows.
+
+The matching public key must be in the deploy user's `authorized_keys` on every
+host.
+
+### 3. Point at a runner
+
+Deploys need to reach your hosts over SSH. GitHub-hosted runners have general
+internet egress, so if your hosts accept SSH from the internet, nothing to do.
+
+If they do not — a private network, an IP allowlist, or a corporate egress
+filter — register a self-hosted runner somewhere that *can* reach them, and set
+a repository **variable** (not a secret) `DEPLOY_RUNNER` to its label:
+
+```
+Settings → Secrets and variables → Actions → Variables
+DEPLOY_RUNNER = my-deploy-runner
+```
+
+Both host-touching workflows read it:
+
+```yaml
+runs-on: ${{ vars.DEPLOY_RUNNER || 'ubuntu-latest' }}
+```
+
+A runner only makes *outbound* HTTPS connections to GitHub, which is why this
+works where an inbound exception would need a policy change. Do not set the
+variable before a runner carries that label — a label no runner has leaves jobs
+queued forever rather than failing.
+
+## Deploying
+
+Actions → **deploy** → Run workflow. Three fields:
+
+| Field | Values | Meaning |
+| --- | --- | --- |
+| `stack` | the dropdown | Which playbook to run. `site` is all of them. |
+| `mode` | `check`, `deploy` | `check` runs `--check --diff` and touches nothing |
+| `pull` | `policy`, `always`, `missing`, `never` | `always` fetches newer images **and** enables per-stack update work |
+
+Work up from harmless to real the first time:
+
+| Step | What to run | What it proves |
+| --- | --- | --- |
+| 1 | **connectivity** → `ping` | The runner can decode the key, reach every host over SSH, and run Python there. Changes nothing. |
+| 2 | **deploy** with `mode: check` | What that deploy *would* change. |
+| 3 | **deploy** with `mode: deploy` | The real thing. |
+
+`static-site` is the safest stack to prove this with: one container behind the
+proxy, no database and no persistent state, so redeploying it costs nothing if it
+goes wrong.
+
+## Differences from GitLab that shape this file
+
+**There is no per-job manual button.** GitLab renders a play button for every
+`when: manual` job, which is how the `.gitlab-ci.yml` here ends up with a
+`check:` and `deploy:` pair per stack. GitHub has one "Run workflow" form per
+workflow, so the stack becomes a `choice` input instead.
+
+The practical cost is that the `options:` list in `deploy.yml` has to be kept in
+step with `ansible/playbooks/` by hand. There is no way to populate a `choice`
+dynamically. Adding a stack means editing that list — it is step 4 of
+[adding a stack](../skills/adding-a-stack/SKILL.md), and forgetting it is how a
+service ends up deployable only from a laptop.
+
+**`repository_dispatch` does not wait.** GitLab's `strategy: depend` makes an
+upstream pipeline mirror the downstream result. A `repository_dispatch` returns
+as soon as the event is accepted, so the caller learns nothing about whether the
+deploy worked. If you need the caller to block, see
+[triggering-deploys.md](triggering-deploys.md).
+
+**Environments replace protected variables.** GitLab hides a Protected variable
+from pipelines on unprotected refs, which produces the confusing failure of a
+variable that exists but is empty. GitHub's equivalent is scoping the secret to
+an environment and restricting which branches may deploy to it — the job is
+blocked outright rather than running with an empty key.
+
+## Why untrusted input is validated
+
+`deploy.yml` matches `stack` against `[a-z0-9_-]+` and `pull` against a fixed
+list before running anything, and confirms the playbook exists. Under
+`workflow_dispatch` the values come from a dropdown and this looks redundant.
+Under `repository_dispatch` they come from another repository's payload, and they
+reach a shell command.
+
+More importantly, they never go into a `run:` block through `${{ }}`. A workflow
+expression is substituted into the script text *before the shell sees it*, so a
+value containing shell syntax is executed rather than compared. Values go through
+`env:` and are read as `"$STACK"`:
+
+```yaml
+        env:
+          STACK: ${{ github.event.inputs.stack || github.event.client_payload.stack }}
+        run: |
+          case "$STACK" in
+            ''|*[!a-z0-9_-]*) echo "refusing STACK='$STACK'"; exit 1 ;;
+          esac
+```
+
+Keep that shape if you restructure the job. It is the difference between a
+validated argument and remote code execution on your deploy runner.
+
+## Troubleshooting
+
+| Job fails with | Cause |
+| --- | --- |
+| `set SSH_PRIVATE_KEY_B64, or SSH_PRIVATE_KEY ...` | The secret is not on the `production` environment, or the job does not name that environment |
+| `does not look like a private key` | The value was encoded with `certutil` or `Get-Content`, or re-wrapped across lines |
+| `Permission denied (publickey)` | The matching public key is not in the deploy user's `authorized_keys` |
+| `Connection timed out` | Network path, not credentials — run **connectivity** → `probe`, and read [connectivity.md](connectivity.md) |
+| `no playbook for '...'` | The `stack` value does not match a file in `ansible/playbooks/` |
+| Job queued forever | `DEPLOY_RUNNER` names a label no runner carries |
+| Deploy succeeds, nothing changed | Images are tagged `latest` and `pull` was `policy` |