diff --git a/.gitea/workflows/ci.yml b/.gitea/workflows/ci.yml
index cb147a2..b6085d6 100644
--- a/.gitea/workflows/ci.yml
+++ b/.gitea/workflows/ci.yml
@@ -49,11 +49,16 @@ jobs:
         needs: release-gate
         if: needs.release-gate.outputs.skip != 'true'
         runs-on: ubuntu-latest
-        # Bind-mount the shared pages tree so the coverage step below can write
-        # into it. The runner whitelists this path via `container.valid_volumes`
-        # (docker-space `setup/gitea.sh`); `image` is omitted on purpose so the
-        # runner keeps using its default job image.
+        # `image` extends the runner's default job image (catthehacker/act)
+        # with Node 26 pre-planted in the tool cache layout, so setup-node's
+        # version probe hits and never downloads (see docker/Dockerfile). The
+        # tag MUST equal the exact version pinned in `.node-version`; rebuild
+        # via `npm run build:runner-image -- --push` and repoint here on every
+        # Node bump. The volume bind-mounts the shared pages tree so the
+        # coverage step below can write into it; the runner whitelists this
+        # path via `container.valid_volumes` (docker-space `setup/gitea.sh`).
         container:
+            image: gitea.e1nsnull.de/tmu/act-ci:26.8.2
             volumes:
                 - /data/gitea-pages:/data/gitea-pages
         steps:
@@ -108,6 +113,10 @@ jobs:
         if: needs.release-gate.outputs.skip != 'true'
         runs-on: ubuntu-latest
         continue-on-error: true
+        # Same baked image as `build` — without it this job re-downloads Node
+        # per run (see docker/Dockerfile).
+        container:
+            image: gitea.e1nsnull.de/tmu/act-ci:26.8.2
         steps:
             - uses: actions/checkout@v4
             - uses: actions/setup-node@v4
@@ -121,6 +130,10 @@ jobs:
         if: startsWith(gitea.ref, 'refs/tags/')
         needs: build
         runs-on: ubuntu-latest
+        # Same baked image as `build` — setup-node still owns the registry-url
+        # `.npmrc` rewrite here; only the Node download is skipped.
+        container:
+            image: gitea.e1nsnull.de/tmu/act-ci:26.8.2
         # The release page is created with the run's automatic Gitea token
         # (`github.token`), not `NPM_TOKEN`, so it needs `contents: write`.
         permissions:
diff --git a/.node-version b/.node-version
index 978b4e8..707210d 100644
--- a/.node-version
+++ b/.node-version
@@ -1 +1 @@
-26
\ No newline at end of file
+26.8.2
diff --git a/cspell.json b/cspell.json
index 58d50e3..a31d295 100644
--- a/cspell.json
+++ b/cspell.json
@@ -27,6 +27,12 @@
         "knope",
         "runwisp",
         "glab",
+        "hostedtoolcache",
+        "catthehacker",
+        "nsnull",
+        "dedup",
+        "dedupe",
+        "repoint",
         "postversion",
         "prebuild",
         "Zilla",
diff --git a/docker/Dockerfile b/docker/Dockerfile
new file mode 100644
index 0000000..2650cb5
--- /dev/null
+++ b/docker/Dockerfile
@@ -0,0 +1,30 @@
+# CI job image for the Gitea act_runner: the runner's default job image with
+# Node pre-planted where actions/setup-node looks first.
+#
+# Why this layout: setup-node ignores `node` on PATH; its only fast path is a
+# probe of /opt/hostedtoolcache/node/<version>/<arch>. Without an entry there
+# it downloads the ~50 MB distribution on EVERY job (the runner's job
+# containers are ephemeral, so its tool cache never survives a job). The
+# official node images keep exactly the layout setup-node expects under
+# /usr/local, so this layer is a pure file overlay — no scripts, no env.
+#
+# Why not a host bind of /opt/hostedtoolcache: binds never self-prune. Docker
+# images are content-addressed: the base layers dedupe against the act image
+# the host already has, and `docker image prune` / re-pulls are the cleanup
+# story.
+#
+# NODE_VERSION must match `.node-version` exactly. setup-node resolves a float
+# like `26` to the latest known patch at runtime, so a bump silently busts the
+# baked entry; `.node-version` is pinned to x.y.z and scripts/runner-image.sh
+# guards the coupling. Rebuild + repoint `container.image` in
+# .gitea/workflows/ci.yml on every bump.
+FROM catthehacker/ubuntu:act-latest
+
+ARG NODE_VERSION=26.8.2
+
+# node image: bin/ + lib/ under /usr/local → tool cache: bin/ + lib/ under <ver>/x64.
+COPY --from=node:${NODE_VERSION} /usr/local /opt/hostedtoolcache/node/${NODE_VERSION}/x64
+
+# Fail the build (not CI) if the overlay or the version arg were wrong.
+# Shell form on purpose: exec form (`RUN [...]`) does not expand ARG values.
+RUN "/opt/hostedtoolcache/node/${NODE_VERSION}/x64/bin/node" --version
diff --git a/package.json b/package.json
index aca4c28..3a9db00 100644
--- a/package.json
+++ b/package.json
@@ -38,6 +38,7 @@
     },
     "scripts": {
         "build": "tsc -p tsconfig.build.json",
+        "build:runner-image": "./scripts/runner-image.sh",
         "prebuild": "rm -rf dist",
         "check": "npm run check:tsc && npm run check:oxlint && npm run check:oxfmt && npm run check:cspell",
         "check:cspell": "cspell lint ${LEFTHOOK_FILES:-.}",
diff --git a/scripts/runner-image.sh b/scripts/runner-image.sh
new file mode 100755
index 0000000..6205cbd
--- /dev/null
+++ b/scripts/runner-image.sh
@@ -0,0 +1,33 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+# Build (and optionally push) the CI job image from docker/Dockerfile.
+# Run wherever docker + registry credentials live (the runner host, or any
+# machine that can reach the registry). The registry/repo below MUST match
+# the `container.image` references in .gitea/workflows/ci.yml — the runner
+# pulls the image by name.
+#
+# Usage: scripts/runner-image.sh [--push]
+
+IMAGE_REPO="gitea.e1nsnull.de/tmu/act-ci"
+
+NODE_VERSION="$(tr -d '[:space:]' < .node-version)"
+if [[ ! "${NODE_VERSION}" =~ ^[0-9]+\.[0-9]+\.[0-9]+$ ]]; then
+    echo "error: .node-version must be pinned to an exact x.y.z, got '${NODE_VERSION}'." >&2
+    echo "       setup-node resolves floats like '26' to the latest patch at runtime," >&2
+    echo "       which silently busts the tool-cache entry baked into the image." >&2
+    exit 1
+fi
+
+IMAGE="${IMAGE_REPO}:${NODE_VERSION}"
+
+# --pull: refresh the act base layer so the derivative does not float on an
+# aging default image forever (layer dedup keeps this cheap).
+docker build --pull --build-arg "NODE_VERSION=${NODE_VERSION}" -t "${IMAGE}" -f docker/Dockerfile .
+
+if [[ "${1:-}" == "--push" ]]; then
+    docker push "${IMAGE}"
+fi
+
+echo "built ${IMAGE}"
+echo "reminder: bump container.image in .gitea/workflows/ci.yml to this tag"