diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
new file mode 100644
index 0000000..fc38784
--- /dev/null
+++ b/.pre-commit-config.yaml
@@ -0,0 +1,30 @@
+repos:
+  - repo: https://github.com/pre-commit/pre-commit-hooks
+    rev: v5.0.0
+    hooks:
+      - id: trailing-whitespace
+      - id: end-of-file-fixer
+      - id: check-yaml
+      - id: check-merge-conflict
+      - id: mixed-line-ending
+        args: [--fix=lf]
+
+  - repo: https://github.com/AleksaC/hadolint-py
+    rev: v2.15.1
+    hooks:
+      - id: hadolint
+
+  - repo: https://github.com/shellcheck-py/shellcheck-py
+    rev: v0.11.0.1
+    hooks:
+      - id: shellcheck
+
+  # No upstream equivalent: a distro added under distros/ but left out of a
+  # Woodpecker matrix silently never gets built.
+  - repo: local
+    hooks:
+      - id: check-distros
+        name: distros match the woodpecker matrices
+        entry: ci/check-distros.sh
+        language: system
+        pass_filenames: false
diff --git a/.woodpecker/build.yaml b/.woodpecker/build.yaml
new file mode 100644
index 0000000..3946f8e
--- /dev/null
+++ b/.woodpecker/build.yaml
@@ -0,0 +1,35 @@
+when:
+  - event: pull_request
+
+matrix:
+  include:
+    # One entry per distro. Adding a distro: add distros/<name>/ and one entry here.
+    - DISTRO: alma9
+      BASE_IMAGE_NAME: almalinux9
+      TAG_SUFFIX: alma9
+      DEFAULT: "true"
+
+steps:
+  - name: build
+    image: "artifactapi.k8s.syd1.au.unkin.net/docker-internal/plugin-docker-buildx:latest"
+    settings:
+      # registry is what gets the internal CA into the buildkit container: the plugin
+      # writes a buildkit.toml pointing at /etc/docker/certs.d/<registry>/ca.crt only
+      # when it is set. The plugin has no buildkit_config setting.
+      registry: artifactapi.k8s.syd1.au.unkin.net
+      repo: "artifactapi.k8s.syd1.au.unkin.net/docker-internal/gobuilder"
+      target: image
+      dry_run: true
+      build_args:
+        BASE_IMAGE_NAME: "${BASE_IMAGE_NAME}"
+        DISTRO: "${DISTRO}"
+    backend_options:
+      kubernetes:
+        serviceAccountName: default
+        resources:
+          requests:
+            memory: 1Gi
+            cpu: 1
+          limits:
+            memory: 4Gi
+            cpu: 2
diff --git a/.woodpecker/docker.yaml b/.woodpecker/docker.yaml
new file mode 100644
index 0000000..12b4a86
--- /dev/null
+++ b/.woodpecker/docker.yaml
@@ -0,0 +1,63 @@
+when:
+  - event: tag
+    ref: refs/tags/v*
+
+matrix:
+  include:
+    # One entry per distro. Adding a distro: add distros/<name>/ and one entry here.
+    - DISTRO: alma9
+      BASE_IMAGE_NAME: almalinux9
+      TAG_SUFFIX: alma9
+      DEFAULT: "true"
+
+steps:
+  - name: docker
+    image: "artifactapi.k8s.syd1.au.unkin.net/docker-internal/plugin-docker-buildx:latest"
+    settings:
+      # registry is what gets the internal CA into the buildkit container: the plugin
+      # writes a buildkit.toml pointing at /etc/docker/certs.d/<registry>/ca.crt only
+      # when it is set. The plugin has no buildkit_config setting.
+      registry: artifactapi.k8s.syd1.au.unkin.net
+      repo: "artifactapi.k8s.syd1.au.unkin.net/docker-internal/gobuilder"
+      target: image
+      build_args:
+        BASE_IMAGE_NAME: "${BASE_IMAGE_NAME}"
+        DISTRO: "${DISTRO}"
+      tags:
+        - "${CI_COMMIT_TAG##v}-${TAG_SUFFIX}"
+    backend_options:
+      kubernetes:
+        serviceAccountName: default
+        resources:
+          requests:
+            memory: 1Gi
+            cpu: 1
+          limits:
+            memory: 4Gi
+            cpu: 2
+
+  # The default distro also carries the unsuffixed tags.
+  - name: docker-default
+    image: "artifactapi.k8s.syd1.au.unkin.net/docker-internal/plugin-docker-buildx:latest"
+    when:
+      - evaluate: 'DEFAULT == "true"'
+    settings:
+      registry: artifactapi.k8s.syd1.au.unkin.net
+      repo: "artifactapi.k8s.syd1.au.unkin.net/docker-internal/gobuilder"
+      target: image
+      build_args:
+        BASE_IMAGE_NAME: "${BASE_IMAGE_NAME}"
+        DISTRO: "${DISTRO}"
+      tags:
+        - "${CI_COMMIT_TAG##v}"
+        - latest
+    backend_options:
+      kubernetes:
+        serviceAccountName: default
+        resources:
+          requests:
+            memory: 1Gi
+            cpu: 1
+          limits:
+            memory: 4Gi
+            cpu: 2
diff --git a/.woodpecker/pre-commit.yaml b/.woodpecker/pre-commit.yaml
new file mode 100644
index 0000000..e4446ad
--- /dev/null
+++ b/.woodpecker/pre-commit.yaml
@@ -0,0 +1,18 @@
+when:
+  - event: pull_request
+
+steps:
+  - name: pre-commit
+    image: "git.unkin.net/unkin/almalinux9-gobuilder:20260606"
+    commands:
+      - uvx pre-commit run --all-files
+    backend_options:
+      kubernetes:
+        serviceAccountName: default
+        resources:
+          requests:
+            memory: 512Mi
+            cpu: 1
+          limits:
+            memory: 2Gi
+            cpu: 2
diff --git a/Dockerfile b/Dockerfile
new file mode 100644
index 0000000..d03f216
--- /dev/null
+++ b/Dockerfile
@@ -0,0 +1,24 @@
+ARG REGISTRY=artifactapi.k8s.syd1.au.unkin.net/docker-internal
+# The container-base release this image is built on — the one place to bump it.
+ARG BASE_VERSION=0.1.0
+ARG BASE_IMAGE_NAME=almalinux9
+
+FROM ${REGISTRY}/${BASE_IMAGE_NAME}:${BASE_VERSION} AS image
+ARG DISTRO=alma9
+ARG GO_CACHE_PLUGIN_VERSION=v0.1.0
+ARG GO_CACHE_PLUGIN_SHA256=0eb23d06a0dcf395559cb6447864579c220e60148fdcd6a6f841c2b17169b9b8
+COPY distros/${DISTRO}/ /tmp/distro/
+# DL3041: versions are pinned by the estate dnf repos, not here. SC2086: $PACKAGES is a
+# word list on purpose. DL4006: the only pipe ends in sha256sum, whose status is the
+# pipeline's, and set -e catches it.
+# hadolint ignore=DL3041,DL4006,SC2086
+RUN set -eux; \
+    . /tmp/distro/distro.env; \
+    dnf install -y $PACKAGES; \
+    dnf clean all; \
+    curl -fsSL -o /usr/local/bin/go-cache-plugin \
+      "https://git.unkin.net/unkin/go-cache-plugin/releases/download/${GO_CACHE_PLUGIN_VERSION}/go-cache-plugin-linux-amd64"; \
+    echo "$GO_CACHE_PLUGIN_SHA256  /usr/local/bin/go-cache-plugin" | sha256sum -c -; \
+    chmod 0755 /usr/local/bin/go-cache-plugin; \
+    rm -rf /var/cache/dnf /tmp/distro
+CMD ["/bin/bash"]
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..e9577ff
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,39 @@
+REGISTRY := artifactapi.k8s.syd1.au.unkin.net/docker-internal
+DISTROS  := $(notdir $(wildcard distros/*))
+VERSION  ?= $(patsubst v%,%,$(or $(shell git describe --tags --exact-match 2>/dev/null),0.1.0-dev))
+
+.PHONY: build clean pre-commit patch minor major
+build: $(addprefix build-,$(DISTROS))
+clean: $(addprefix clean-,$(DISTROS))
+
+pre-commit:
+	@uvx pre-commit run --all-files
+
+# Not .PHONY: GNU make skips implicit-rule search for phony targets.
+
+build-%:
+	@set -eu; . ./distros/$*/distro.env; \
+	docker build --build-arg "BASE_IMAGE_NAME=$$BASE_IMAGE_NAME" --build-arg "DISTRO=$*" \
+	  -t "$(REGISTRY)/$$IMAGE:$(VERSION)-$$TAG_SUFFIX" .
+
+clean-%:
+	@set -eu; . ./distros/$*/distro.env; \
+	docker rmi "$(REGISTRY)/$$IMAGE:$(VERSION)-$$TAG_SUFFIX" 2>/dev/null || true
+
+_LATEST := $(shell git tag --sort=-v:refname | grep -E '^v[0-9]+\.[0-9]+\.[0-9]+$$' | head -1)
+_BASE   := $(if $(_LATEST),$(_LATEST),v0.0.0)
+_MAJ    := $(shell echo $(_BASE) | sed 's/^v//' | cut -d. -f1)
+_MIN    := $(shell echo $(_BASE) | sed 's/^v//' | cut -d. -f2)
+_PAT    := $(shell echo $(_BASE) | sed 's/^v//' | cut -d. -f3)
+
+patch:
+	@NEW=v$(_MAJ).$(_MIN).$(shell expr $(_PAT) + 1); \
+	git tag $$NEW && echo "Tagged $$NEW" && git push origin $$NEW
+
+minor:
+	@NEW=v$(_MAJ).$(shell expr $(_MIN) + 1).0; \
+	git tag $$NEW && echo "Tagged $$NEW" && git push origin $$NEW
+
+major:
+	@NEW=v$(shell expr $(_MAJ) + 1).0.0; \
+	git tag $$NEW && echo "Tagged $$NEW" && git push origin $$NEW
diff --git a/README.md b/README.md
index 2fade9a..1f0aaee 100644
--- a/README.md
+++ b/README.md
@@ -1,3 +1,30 @@
 # container-gobuilder
 
-Go toolchain builder container image, built on each supported container-base distro image, used by Woodpecker pipelines to compile Go projects.
\ No newline at end of file
+The estate's Go toolchain image, built on each `container-base` distro image.
+Published as `artifactapi.k8s.syd1.au.unkin.net/docker-internal/gobuilder:<version>-<suffix>`;
+the default distro also gets the unsuffixed `:<version>` and `:latest`.
+
+| distro | from | tag suffix | default |
+| --- | --- | --- | --- |
+| `alma9` | `docker-internal/almalinux9:<base version>` | `alma9` | yes |
+
+Adds `golang`, `gcc` and `nfpm`, and bakes in the `go-cache-plugin` binary on `PATH`
+so Go pipelines get the shared build cache with no download step. No credentials and no
+`GOCACHEPROG` value are baked in — consumers set those.
+
+The `container-base` release this image builds on is `BASE_VERSION` in the `Dockerfile`.
+
+## Adding a distro
+
+1. `distros/<name>/distro.env` — `BASE_IMAGE_NAME`, `IMAGE`, `TAG_SUFFIX`, `DEFAULT`, `PACKAGES`, `GO_MIN`.
+2. One `include` entry in each of `.woodpecker/{build,docker}.yaml`.
+
+The `check-distros` pre-commit hook fails if step 1 or 2 is incomplete, or if more than
+one distro claims `DEFAULT`.
+
+## Make
+
+    make build          # build every distro
+    make pre-commit     # uvx pre-commit run --all-files
+    make build-alma9    # one distro
+    make patch|minor|major
diff --git a/ci/check-distros.sh b/ci/check-distros.sh
new file mode 100755
index 0000000..6948081
--- /dev/null
+++ b/ci/check-distros.sh
@@ -0,0 +1,43 @@
+#!/usr/bin/env bash
+# Every distros/<name>/ needs a complete distro.env and an entry in every Woodpecker
+# matrix, or a newly added distro silently never gets built.
+set -uo pipefail
+
+KEYS="BASE_IMAGE_NAME IMAGE TAG_SUFFIX DEFAULT ESTATE_REPO PACKAGES GO_MIN"
+WORKFLOWS=(.woodpecker/build.yaml .woodpecker/docker.yaml)
+
+fail=0
+for d in distros/*/; do
+  n=$(basename "$d")
+  for k in $KEYS; do
+    grep -q "^${k}=" "${d}distro.env" || { echo "${d}distro.env: missing ${k}"; fail=1; }
+  done
+  for wf in "${WORKFLOWS[@]}"; do
+    grep -q "DISTRO: ${n}\$" "$wf" || { echo "${wf}: distro ${n} missing from matrix"; fail=1; }
+
+    # A matrix entry that restates a distro.env key must not drift from it — a stale
+    # BASE_IMAGE here silently overrides distro.env for every CI build.
+    while IFS='=' read -r k v; do
+      [ -n "$k" ] || continue
+      grep -q "^${k}=" "${d}distro.env" || continue
+      ev=$(sed -n "s/^${k}=//p" "${d}distro.env" | head -1 | sed 's/^"//;s/"$//')
+      [ "$v" = "$ev" ] || { echo "${wf}: matrix ${k}=\"${v}\" for ${n} disagrees with ${d}distro.env (\"${ev}\")"; fail=1; }
+    done <<EOF
+$(awk -v d="$n" '
+  $0 ~ "^[[:space:]]*-[[:space:]]+DISTRO:[[:space:]]*"d"[[:space:]]*$" { inb=1; next }
+  inb && /^[[:space:]]*-/ { inb=0 }
+  inb && match($0, /^[[:space:]]+[A-Z_]+:/) {
+    k=$1; sub(/:$/,"",k)
+    v=$0; sub(/^[[:space:]]*[A-Z_]+:[[:space:]]*/,"",v); gsub(/^"|"$/,"",v)
+    print k "=" v
+  }
+' "$wf")
+EOF
+  done
+done
+
+# Exactly one distro owns the unsuffixed :<version> and :latest tags.
+defaults=$(grep -l 'DEFAULT="true"' distros/*/distro.env | wc -l)
+[ "$defaults" -eq 1 ] || { echo "expected exactly one distro with DEFAULT=\"true\", found ${defaults}"; fail=1; }
+
+exit "$fail"
diff --git a/distros/alma9/distro.env b/distros/alma9/distro.env
new file mode 100644
index 0000000..62fd458
--- /dev/null
+++ b/distros/alma9/distro.env
@@ -0,0 +1,12 @@
+# alma9 — built on the container-base almalinux9 image
+BASE_IMAGE_NAME="almalinux9"
+IMAGE="gobuilder"
+TAG_SUFFIX="alma9"
+# The default distro also gets the unsuffixed :<version> and :latest tags.
+DEFAULT="true"
+
+# Estate local repo used to prove inherited HTTPS trust.
+ESTATE_REPO="rpm-vendor-el9"
+
+PACKAGES="golang gcc nfpm"
+GO_MIN="1.24"