p5-03: docker-only release path (drop goreleaser)

Single public deliverable per tag: a multi-arch server image, with
cross-compiled agent binaries + install scripts + the systemd unit
baked under /opt/restic-manager/dist/. The /agent/binary and
/install/* handlers fall back from <DataDir>/... to that read-only
path so a fresh container Just Works without first-run staging;
operators can still drop a custom build into <DataDir>/ to override
per-host.

Architecture rationale: agent distribution already routes through
the running server, so the release surface mirrors that — there's
no second source of truth to keep in sync.

Workflow .gitea/workflows/release.yml triggers on v*.*.* tag-push
(fan-out :vX.Y.Z / :X.Y / :X, plus :latest once MAJOR>=1) and
workflow_dispatch (snapshot tag only). Pushes to the Gitea
container registry on this instance.

Both binaries grow main.commit + main.date ldflag targets. Makefile
and Dockerfile fill them; release workflow forwards from gitea.sha
plus a UTC timestamp.

Spec : docs/superpowers/specs/2026-05-05-p5-03-docker-only-release.md
Plan : docs/superpowers/plans/2026-05-05-p5-03-docker-only-release.md

.gitea/workflows/release.yml

@@ -0,0 +1,107 @@
+# Release workflow — P5-03 (docker-only release path).
+#
+# Spec : docs/superpowers/specs/2026-05-05-p5-03-docker-only-release.md
+# Plan : docs/superpowers/plans/2026-05-05-p5-03-docker-only-release.md
+#
+# What it does
+#   * Triggered by either:
+#       - tag push matching v[0-9]+.[0-9]+.[0-9]+ (real release), or
+#       - workflow_dispatch (snapshot iteration without tagging).
+#   * Cross-builds a multi-arch (linux/amd64,linux/arm64) image of the
+#     server, with three agent binaries (linux amd64+arm64, windows amd64)
+#     plus install.sh / install.ps1 / the systemd unit baked in under
+#     /opt/restic-manager/dist (the read-only fallback path the server
+#     handlers use when <DataDir>/... is empty).
+#   * Pushes to this Gitea instance's container registry under
+#     <gitea-host>/<owner>/restic-manager.
+#
+# Tag fan-out
+#   * tag push: :vX.Y.Z, :X.Y, :X
+#   * tag push and X >= 1: also :latest
+#   * workflow_dispatch: only :snapshot-<shortsha>; nothing else moves.
+#
+# Why no goreleaser
+#   The architecture already routes agent distribution through the
+#   server's /agent/binary endpoint. The image is the only deliverable;
+#   binary archives would just be a second source of truth.
+
+name: Release
+
+on:
+  push:
+    tags:
+      - 'v[0-9]+.[0-9]+.[0-9]+'
+  workflow_dispatch:
+
+env:
+  REGISTRY: gitea.dcglab.co.uk
+  IMAGE_NAME: ${{ gitea.repository }}
+
+jobs:
+  image:
+    name: Build + push image
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: docker/setup-qemu-action@v3
+      - uses: docker/setup-buildx-action@v3
+
+      - name: Log in to Gitea registry
+        uses: docker/login-action@v3
+        with:
+          registry: ${{ env.REGISTRY }}
+          username: ${{ gitea.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Compute tags + version
+        id: meta
+        shell: bash
+        run: |
+          set -euo pipefail
+          REG="${REGISTRY}/${IMAGE_NAME}"
+          DATE="$(date -u +%Y-%m-%dT%H:%M:%SZ)"
+          SHORT_SHA="${GITHUB_SHA::7}"
+
+          if [ "${GITHUB_EVENT_NAME}" = "push" ] && [ "${GITHUB_REF_TYPE}" = "tag" ]; then
+            TAG="${GITHUB_REF_NAME}"            # vX.Y.Z
+            VER="${TAG#v}"                       # X.Y.Z
+            MAJOR="${VER%%.*}"
+            MINOR="${VER#${MAJOR}.}"; MINOR="${MINOR%%.*}"
+
+            TAGS="${REG}:${TAG}"
+            TAGS="${TAGS},${REG}:${MAJOR}.${MINOR}"
+            TAGS="${TAGS},${REG}:${MAJOR}"
+            # Pre-1.0 holds back :latest by design; operators must
+            # pin a version explicitly until v1.0.0.
+            if [ "${MAJOR}" -ge 1 ]; then
+              TAGS="${TAGS},${REG}:latest"
+            fi
+            VERSION="${TAG}"
+          else
+            TAGS="${REG}:snapshot-${SHORT_SHA}"
+            VERSION="0.0.0-snapshot-${SHORT_SHA}"
+          fi
+
+          {
+            echo "tags=${TAGS}"
+            echo "version=${VERSION}"
+            echo "date=${DATE}"
+          } >> "${GITHUB_OUTPUT}"
+
+      - name: Build + push
+        uses: docker/build-push-action@v6
+        with:
+          context: .
+          file: deploy/Dockerfile.server
+          platforms: linux/amd64,linux/arm64
+          push: true
+          tags: ${{ steps.meta.outputs.tags }}
+          build-args: |
+            VERSION=${{ steps.meta.outputs.version }}
+            COMMIT=${{ gitea.sha }}
+            DATE=${{ steps.meta.outputs.date }}
+          labels: |
+            org.opencontainers.image.version=${{ steps.meta.outputs.version }}
+            org.opencontainers.image.revision=${{ gitea.sha }}
+            org.opencontainers.image.created=${{ steps.meta.outputs.date }}

Makefile

@@ -5,9 +5,11 @@ BIN_DIR        := bin
 SERVER_BIN     := $(BIN_DIR)/restic-manager-server
 AGENT_BIN      := $(BIN_DIR)/restic-manager-agent
 VERSION        ?= $(shell git describe --tags --always --dirty 2>/dev/null || echo dev)
-LDFLAGS        := -s -w -X main.version=$(VERSION)
+COMMIT         ?= $(shell git rev-parse HEAD 2>/dev/null || echo none)
+DATE           ?= $(shell date -u +%Y-%m-%dT%H:%M:%SZ)
+LDFLAGS        := -s -w -X main.version=$(VERSION) -X main.commit=$(COMMIT) -X main.date=$(DATE)
 GOFLAGS        := -trimpath
-DOCKER_IMAGE   ?= ghcr.io/dcglab/restic-manager
+DOCKER_IMAGE   ?= gitea.dcglab.co.uk/steve/restic-manager
 DOCKER_TAG     ?= dev
 
 # Tailwind standalone CLI — single binary, no Node toolchain.
@@ -84,7 +86,11 @@ run-agent: agent ## Build and run the agent
 	$(AGENT_BIN)
 
 docker: ## Build the server Docker image
-	docker build -f deploy/Dockerfile.server --build-arg VERSION=$(VERSION) -t $(DOCKER_IMAGE):$(DOCKER_TAG) .
+	docker build -f deploy/Dockerfile.server \
+	  --build-arg VERSION=$(VERSION) \
+	  --build-arg COMMIT=$(COMMIT) \
+	  --build-arg DATE=$(DATE) \
+	  -t $(DOCKER_IMAGE):$(DOCKER_TAG) .
 
 release: ## Cross-compile for all supported platforms
 	@mkdir -p $(BIN_DIR)

cmd/agent/main.go

@@ -24,7 +24,11 @@ import (
 	"gitea.dcglab.co.uk/steve/restic-manager/internal/restic"
 )
 
-var version = "dev"
+var (
+	version = "dev"
+	commit  = "none"
+	date    = "unknown"
+)
 
 func main() {
 	if err := run(); err != nil {
@@ -62,7 +66,7 @@ func run() error {
 	flag.Parse()
 
 	if *showVersion {
-		fmt.Println("restic-manager-agent", version)
+		fmt.Printf("restic-manager-agent %s (commit %s, built %s)\n", version, commit, date)
 		return nil
 	}
 

cmd/server/main.go

@@ -25,7 +25,11 @@ import (
 	"gitea.dcglab.co.uk/steve/restic-manager/internal/store"
 )
 
-var version = "dev"
+var (
+	version = "dev"
+	commit  = "none"
+	date    = "unknown"
+)
 
 func main() {
 	if err := run(); err != nil {
@@ -40,7 +44,7 @@ func run() error {
 	flag.Parse()
 
 	if *showVersion {
-		fmt.Println("restic-manager-server", version)
+		fmt.Printf("restic-manager-server %s (commit %s, built %s)\n", version, commit, date)
 		return nil
 	}
 

deploy/Dockerfile.server

@@ -1,14 +1,17 @@
 # syntax=docker/dockerfile:1.7
 
 # ---- Build stage --------------------------------------------------------
-FROM golang:1.25-alpine AS build
+# Cross-compiles:
+#   * the server binary for the image's TARGETARCH (linux/amd64 or arm64),
+#   * three agent binaries (linux/amd64, linux/arm64, windows/amd64) that
+#     the running server hands out via /agent/binary.
+# Pure-Go SQLite (modernc.org/sqlite) means CGO stays off; static binaries
+# run on distroless/static.
+FROM --platform=$BUILDPLATFORM golang:1.25-alpine AS build
 
 WORKDIR /src
 
-# Pure-Go SQLite (modernc.org/sqlite) means we can keep CGO off and build a
-# fully static binary that runs on distroless/static.
 ENV CGO_ENABLED=0 \
-    GOOS=linux \
     GOFLAGS="-trimpath"
 
 # Cache module downloads in a separate layer.
@@ -18,10 +21,35 @@ RUN go mod download
 COPY . .
 
 ARG VERSION=dev
-RUN go build -ldflags="-s -w -X main.version=${VERSION}" \
+ARG COMMIT=none
+ARG DATE=unknown
+ARG TARGETOS
+ARG TARGETARCH
+
+ENV LDFLAGS="-s -w -X main.version=${VERSION} -X main.commit=${COMMIT} -X main.date=${DATE}"
+
+# Server: built for the image's runtime arch.
+RUN GOOS=${TARGETOS} GOARCH=${TARGETARCH} \
+    go build -ldflags="${LDFLAGS}" \
         -o /out/restic-manager-server \
         ./cmd/server
 
+# Agents: identical across image arches — an arm64 server image still
+# ships an amd64 agent binary for amd64 endpoints to download.
+RUN mkdir -p /out/agent-binaries && \
+    GOOS=linux GOARCH=amd64 \
+        go build -ldflags="${LDFLAGS}" \
+            -o /out/agent-binaries/restic-manager-agent-linux-amd64 \
+            ./cmd/agent && \
+    GOOS=linux GOARCH=arm64 \
+        go build -ldflags="${LDFLAGS}" \
+            -o /out/agent-binaries/restic-manager-agent-linux-arm64 \
+            ./cmd/agent && \
+    GOOS=windows GOARCH=amd64 \
+        go build -ldflags="${LDFLAGS}" \
+            -o /out/agent-binaries/restic-manager-agent-windows-amd64.exe \
+            ./cmd/agent
+
 # ---- Runtime stage ------------------------------------------------------
 FROM gcr.io/distroless/static-debian12:nonroot
 
@@ -31,7 +59,18 @@ LABEL org.opencontainers.image.licenses="PolyForm-Noncommercial-1.0.0"
 USER nonroot:nonroot
 WORKDIR /
 
+# Server binary on PATH.
 COPY --from=build /out/restic-manager-server /usr/local/bin/restic-manager-server
 
+# Image-baked bundled assets (P5-03). Read-only; the /agent/binary and
+# /install/* handlers fall back here when <DataDir>/... is empty, so a
+# fresh container Just Works without first-run staging. Operators can
+# still drop a custom build under <DataDir>/agent-binaries/<name> to
+# override per-host.
+COPY --from=build --chmod=0755 /out/agent-binaries/ /opt/restic-manager/dist/agent-binaries/
+COPY --chmod=0755 deploy/install/install.sh /opt/restic-manager/dist/install/install.sh
+COPY --chmod=0644 deploy/install/install.ps1 /opt/restic-manager/dist/install/install.ps1
+COPY --chmod=0644 deploy/install/restic-manager-agent.service /opt/restic-manager/dist/install/restic-manager-agent.service
+
 EXPOSE 8443
 ENTRYPOINT ["/usr/local/bin/restic-manager-server"]

docs/superpowers/plans/2026-05-05-p5-03-docker-only-release.md

@@ -0,0 +1,131 @@
+# P5-03 implementation plan — Docker-only release
+
+Spec: `docs/superpowers/specs/2026-05-05-p5-03-docker-only-release.md`.
+
+Branch: `p5-03-docker-release`. Do not auto-open a PR (see CLAUDE.md
+memory: CI runs are expensive on the self-hosted cluster).
+
+---
+
+## Slice 1 — Server config + handler fallback
+
+**Goal:** server can serve agent binaries / install scripts from a
+read-only "bundled assets" path when `<DataDir>` doesn't have them.
+
+1. `internal/server/config/config.go` (or wherever `Cfg` lives) gains
+   a `BundledAssetsDir string` field, defaulting to
+   `/opt/restic-manager/dist`. Wire from `RM_BUNDLED_ASSETS_DIR` env
+   var, mirroring the existing env-var conventions.
+2. `internal/server/http/agent_assets.go`:
+   - `handleAgentBinary`: try `<DataDir>/agent-binaries/<name>`
+     first; on `os.Stat` ENOENT, try
+     `<BundledAssetsDir>/agent-binaries/<name>`; on second ENOENT,
+     existing 404.
+   - `handleInstallAsset`: same dual-path, with `install/` subpath.
+3. Tests in `internal/server/http/agent_assets_test.go` (new file):
+   - DataDir hit serves DataDir bytes.
+   - DataDir miss + bundled hit serves bundled bytes.
+   - DataDir hit shadows bundled.
+   - Both miss → 404 + existing error envelope.
+   - Path-traversal still rejected for `install/*` (regression check).
+
+**Verify:** `go vet ./...` + `go test ./internal/server/http/...`.
+
+---
+
+## Slice 2 — Version ldflags on both binaries
+
+1. `cmd/server/main.go`: keep `var version`, add
+   `var commit = "none"` and `var date = "unknown"`. Surface via
+   existing version-log line.
+2. `cmd/agent/main.go`: same three vars. Agent already reports
+   `agent_version` in the WS hello — extend to include commit if
+   it's already plumbed through `internal/api`; otherwise leave the
+   commit out of the wire and just log it on startup.
+3. `Makefile`: extend the `make build` `-ldflags` to set all three
+   from `git describe --tags --always` + `git rev-parse HEAD` +
+   UTC timestamp. Source-build users get real values, not "dev".
+4. `deploy/Dockerfile.server`: add `ARG COMMIT=none` and
+   `ARG DATE=unknown`; pass through `-ldflags`.
+
+**Verify:** `make build && ./bin/restic-manager-server -version`
+(or whatever the existing flag is) prints non-`dev` values.
+
+---
+
+## Slice 3 — Dockerfile bakes agents + install assets
+
+1. Build stage cross-compiles three agents:
+
+   ```dockerfile
+   RUN go build -trimpath -ldflags="-s -w \
+         -X main.version=${VERSION} -X main.commit=${COMMIT} -X main.date=${DATE}" \
+       -o /out/agent/restic-manager-agent-linux-amd64 ./cmd/agent
+   ENV GOARCH=arm64
+   RUN go build ... -o /out/agent/restic-manager-agent-linux-arm64 ./cmd/agent
+   ENV GOOS=windows GOARCH=amd64
+   RUN go build ... -o /out/agent/restic-manager-agent-windows-amd64.exe ./cmd/agent
+   ```
+
+   (Reset `GOOS`/`GOARCH` between layers via `ENV`. Server build
+   stays at `GOOS=linux GOARCH=$TARGETARCH`.)
+
+2. Final stage `COPY --from=build`:
+   - `/out/restic-manager-server` → `/usr/local/bin/`
+   - `/out/agent/*` → `/opt/restic-manager/dist/agent-binaries/`
+   - `deploy/install/install.sh` →
+     `/opt/restic-manager/dist/install/install.sh`
+   - `deploy/install/install.ps1` →
+     `/opt/restic-manager/dist/install/install.ps1`
+   - `deploy/install/restic-manager-agent.service` →
+     `/opt/restic-manager/dist/install/restic-manager-agent.service`
+
+3. Set `--chmod=0755` on the agent binaries and `install.sh`,
+   `--chmod=0644` on the unit file and `install.ps1`. Distroless
+   final stage runs as `nonroot`; bundled assets are readable by
+   anyone (mode `o+r`), so the user switch doesn't break reads.
+
+**Verify:**
+```sh
+docker build -f deploy/Dockerfile.server -t rm:dev .
+docker run --rm -d -p 18080:8080 \
+    -e RM_LISTEN=:8080 -e RM_DATA_DIR=/data \
+    -e RM_BASE_URL=http://127.0.0.1:18080 \
+    -v rm-test:/data rm:dev
+curl -fsSL "http://127.0.0.1:18080/agent/binary?os=linux&arch=amd64" | wc -c
+curl -fsSL "http://127.0.0.1:18080/install/install.sh" | head -1
+```
+
+Both should succeed against a fresh volume (no operator staging).
+
+---
+
+## Slice 4 — Release workflow
+
+`.gitea/workflows/release.yml` per the spec. Two jobs:
+
+1. **`image`**: checkout → setup-qemu → setup-buildx → login → compute
+   tags → buildx build+push.
+2. (Future) `release-notes`: stub left as a TODO comment for now.
+   Operator can hand-write release notes via the Gitea UI on first
+   cut.
+
+The `compute tags` shell step is the only non-trivial bit; tested
+inline by running the script with mocked `GITHUB_REF_TYPE` /
+`GITHUB_REF_NAME` env vars before committing.
+
+**Verify on first dispatch:** trigger `workflow_dispatch` from the
+Gitea UI, check the runner produces `:snapshot-<sha>` and pushes
+multi-arch.
+
+---
+
+## Slice 5 — Tasks.md + commit + push
+
+1. `tasks.md`: tick P5-03; add a one-line note that goreleaser was
+   dropped in favour of Docker-only after a 2026-05-05 design pass
+   (link the spec).
+2. `git add -A && git commit -m "p5-03: docker-only release path"`
+   (no Co-Authored-By trailer — CLAUDE.md rule).
+3. `git push -u origin p5-03-docker-release`.
+4. **Stop.** Do not open a PR. Wait for operator review.

docs/superpowers/specs/2026-05-05-p5-03-docker-only-release.md

@@ -0,0 +1,229 @@
+# P5-03 — Docker-only release path
+
+**Status:** approved 2026-05-05. Pivots P5-03 away from `goreleaser` +
+binary archives toward a single Docker image as the only public
+deliverable.
+
+## Goal
+
+One artifact per tag: the `restic-manager` server image, multi-arch
+(linux amd64 + arm64), published to the Gitea container registry of
+this self-hosted instance. The image bakes in cross-compiled agent
+binaries (linux amd64, linux arm64, windows amd64), the install
+scripts, and the systemd unit at a read-only image path. The running
+server distributes those agents and scripts via its existing
+`/agent/binary` and `/install/*` endpoints; operators on N hosts never
+download a release artifact directly.
+
+Source builds via `make build` remain a first-class path for anyone
+who wants binaries.
+
+## Non-goals
+
+- Standalone binary archives (`.tar.gz`, `.zip`) on the release page.
+- darwin / windows-arm64 agent targets — neither is service-tested.
+- `goreleaser`. Not used.
+- `cosign`, `SBOM`, `in-toto`, `minisign`. Re-promote when we ship
+  binaries outside an image (Phase 6 candidate).
+- GHCR / GitHub mirror. Single source of truth = Gitea.
+
+## Decisions captured (with one-line rationale)
+
+| ID | Decision | Why |
+|----|----------|-----|
+| D1 | One artifact: server Docker image | Architecture already routes agent distribution through the server (`/agent/binary`); release surface should mirror that. |
+| D2 | Trigger: `tag-push` (`v*.*.*`) **plus** `workflow_dispatch` | Tag for real cuts; dispatch for snapshot iteration without polluting tag history. |
+| D3 | Build matrix: linux amd64+arm64 server image; agent cross-compiles for linux amd64+arm64+windows amd64 | Mirrors the existing CI build matrix; nothing ships that hasn't been service-tested. |
+| D4 | Image-baked, separate path (`/opt/restic-manager/dist/`); HTTP handler reads `<DataDir>/...` first, falls back to `/opt/...` | Volume stays purely operator state; image content is immutable per tag; eliminates the smoke-env "stale agent" footgun in production. |
+| D5 | Tag fan-out: `vX.Y.Z`, `X.Y`, `X`, `latest` — but `latest` is held back until `v1.0.0` | Standard rolling-minor pattern; pre-1.0 forces explicit pinning. |
+| D6 | Snapshot tag: `:snapshot-<shortsha>`, never moves `latest` | Operator can never accidentally pull an unblessed build. |
+| D7 | Version embedding via `-ldflags`: `main.version`, `main.commit`, `main.date` on both `cmd/server` and `cmd/agent` | Server already had `version`; add `commit`/`date` to both for parity and traceability. |
+| D8 | Registry: Gitea container registry on this instance, under `<host>/<owner>/restic-manager` | One source of truth, no external creds. |
+| D9 | Integrity: a `SHA256SUMS` file + the manifest digest in the release notes; nothing else | Image is the unit of trust; pull-by-digest is the verification primitive. |
+| D10 | P1-31 (signed binaries) stays deferred | Re-promote the day we ship binaries outside an image. |
+
+## Image layout
+
+Multi-stage Dockerfile (extends today's `deploy/Dockerfile.server`):
+
+```
+build stage (golang:1.25-alpine):
+    cross-compile cmd/server for $TARGETARCH (linux)
+    cross-compile cmd/agent for linux/amd64
+    cross-compile cmd/agent for linux/arm64
+    cross-compile cmd/agent for windows/amd64
+    (CGO_ENABLED=0 throughout — pure-Go SQLite)
+
+final stage (gcr.io/distroless/static-debian12:nonroot):
+    /usr/local/bin/restic-manager-server                   (matches image arch)
+    /opt/restic-manager/dist/agent-binaries/
+        restic-manager-agent-linux-amd64
+        restic-manager-agent-linux-arm64
+        restic-manager-agent-windows-amd64.exe
+    /opt/restic-manager/dist/install/
+        install.sh
+        install.ps1
+        restic-manager-agent.service
+```
+
+`/opt/restic-manager/dist/` is owned by `root:root`, mode `0755` for
+directories, `0755` for `install.sh` (script must be executable when
+the install path uses `curl ... | sh` semantics) and `0644` for the
+unit file and `install.ps1`. The agent binaries are mode `0755`.
+
+`<DataDir>` keeps holding only operator state: `restic-manager.db`,
+`secret.key`, `secrets.enc`, `audit/`, `tls/`. Nothing the image
+owns gets written into the volume.
+
+## Server-side handler change
+
+`internal/server/http/agent_assets.go` today reads from
+`<DataDir>/agent-binaries/<name>` and `<DataDir>/install/<name>`.
+
+Change: if the file isn't present in `<DataDir>`, fall back to
+`/opt/restic-manager/dist/<subpath>/<name>`. The fallback path is a
+new server-config field defaulted to `/opt/restic-manager/dist`,
+overridable via `RM_BUNDLED_ASSETS_DIR` for tests and source-build
+deployments. If neither path resolves, return 404 (existing
+`binary_not_published` / `not_found` body unchanged).
+
+This means:
+- A fresh container without any operator-staged overrides serves the
+  baked-in agents. No first-run setup needed.
+- An operator can still drop a custom-built agent into
+  `<DataDir>/agent-binaries/` to override the image's copy (handy for
+  pre-release agent testing without rebuilding the server image).
+- Source-build dev (`bin/restic-manager-server` running out of the
+  working tree) still works exactly as today — the fallback dir is
+  configurable, and the `<DataDir>` path remains the primary lookup.
+
+Tests cover four cases: (a) DataDir hit, (b) fallback hit, (c) DataDir
+hit shadows fallback, (d) neither — 404.
+
+## Versioning
+
+Both binaries grow `commit` and `date` ldflag-targets next to the
+existing `version`:
+
+```go
+var (
+    version = "dev"
+    commit  = "none"
+    date    = "unknown"
+)
+```
+
+Dockerfile gains `ARG VERSION`, `ARG COMMIT`, `ARG DATE`, all
+`""`-defaulted; the `go build` line passes them via `-ldflags`. The
+release workflow fills them from `${{ gitea.ref_name }}`,
+`${{ gitea.sha }}`, and a UTC ISO-8601 timestamp.
+
+Snapshot builds (workflow_dispatch) compute
+`VERSION=0.0.0-snapshot-${SHORTSHA}` and tag the image as
+`:snapshot-${SHORTSHA}` only. They never touch `latest` or any
+`vX.Y.Z` tag.
+
+## Workflow (`.gitea/workflows/release.yml`)
+
+```yaml
+name: Release
+
+on:
+  push:
+    tags: ['v[0-9]+.[0-9]+.[0-9]+']
+  workflow_dispatch:
+
+env:
+  IMAGE: gitea.dcglab.co.uk/${{ gitea.repository }}
+
+jobs:
+  image:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: docker/setup-qemu-action@v3
+      - uses: docker/setup-buildx-action@v3
+      - uses: docker/login-action@v3
+        with:
+          registry: gitea.dcglab.co.uk
+          username: ${{ gitea.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+      - name: compute tags
+        id: meta
+        run: |
+          # tag-push  → :vX.Y.Z, :X.Y, :X (only :latest if X >= 1)
+          # dispatch  → :snapshot-<shortsha>
+          ...
+      - uses: docker/build-push-action@v6
+        with:
+          context: .
+          file: deploy/Dockerfile.server
+          platforms: linux/amd64,linux/arm64
+          push: true
+          tags: ${{ steps.meta.outputs.tags }}
+          build-args: |
+            VERSION=${{ steps.meta.outputs.version }}
+            COMMIT=${{ gitea.sha }}
+            DATE=${{ steps.meta.outputs.date }}
+```
+
+The `compute tags` step:
+
+- For `push:tags`: extract `vMAJOR.MINOR.PATCH`. Always emit
+  `:vMAJOR.MINOR.PATCH`, `:MAJOR.MINOR`, `:MAJOR`. Emit `:latest`
+  only when `MAJOR >= 1`.
+- For `workflow_dispatch`: emit `:snapshot-<shortsha>`. Nothing else.
+
+No release-asset upload step yet — the GHCR-equivalent registry push
+is the deliverable. A future iteration may attach a `SHA256SUMS` file
+to a Gitea release object once `tea release create` is wired in;
+that's not in scope for the first cut.
+
+## Tests / verification
+
+1. `go vet ./...` (CLAUDE.md rule, runs locally pre-commit).
+2. `go test ./internal/server/http/...` covers the new fallback
+   logic.
+3. Local manual smoke: `docker build -f deploy/Dockerfile.server .`
+   produces an image; `docker run --rm <image>` starts the server;
+   `curl http://127.0.0.1:8080/agent/binary?os=linux&arch=amd64`
+   serves bytes; `curl http://127.0.0.1:8080/install/install.sh`
+   serves the script.
+4. Release workflow itself is exercised on first tag-push; until
+   then, `workflow_dispatch` is the smoke test.
+
+## Operator-facing changes
+
+- `README.md` install snippet becomes
+  `docker run -v rm-data:/var/lib/restic-manager ...
+  gitea.dcglab.co.uk/<owner>/restic-manager:vX.Y.Z`. Pre-1.0
+  releases are pinned by exact tag; no `:latest` is published.
+- The CLAUDE.md "restage" block is dev-only (smoke env runs the
+  server out of `bin/`). Production users on the image never see
+  it.
+- `RM_BUNDLED_ASSETS_DIR` is documented in the server config
+  reference (defaults to `/opt/restic-manager/dist`).
+
+## Risks / footguns
+
+- **Image size growth.** Three agent binaries (~15-20 MB each
+  stripped) add ~50 MB. Acceptable; we're already shipping a
+  distroless server. Watch the trajectory once Phase 4 alerting is
+  in.
+- **Dockerfile cross-compile multiplies build time** on the runner.
+  Pure-Go means each leg is just a `go build`; total stage time
+  should stay under 60s on the self-hosted runner.
+- **`ARG VERSION` leakage.** The current Dockerfile already accepts
+  `ARG VERSION=dev`; we're tightening, not loosening.
+- **Operator overriding `<DataDir>/agent-binaries/<name>`** with a
+  stale binary will silently shadow the image's copy. Documented in
+  the server config reference; this is a feature (lets operators
+  hot-patch a pre-release agent) not a bug.
+
+## Out of scope (tracked for follow-up)
+
+- Cosign / SBOM / in-toto provenance — defer to Phase 6 with the rest
+  of the supply-chain hardening.
+- GHCR mirror — defer until P5-01 docs site goes public.
+- `tea release create` integration — pending until we have something
+  worth attaching beyond the image digest.

internal/server/config/config.go

@@ -33,6 +33,14 @@ type Config struct {
 	CookieSecure bool        `yaml:"cookie_secure"`
 	OIDCRaw      *OIDCConfig `yaml:"oidc"`
 	OIDC         *OIDCConfig `yaml:"-"`
+
+	// BundledAssetsDir is the read-only path inside the image that
+	// holds agent binaries (under agent-binaries/) and install
+	// scripts (under install/). The /agent/binary and /install/*
+	// handlers fall back here when the file is not present in
+	// DataDir. Source-build deployments can override via
+	// RM_BUNDLED_ASSETS_DIR.
+	BundledAssetsDir string `yaml:"bundled_assets_dir"`
 }
 
 // Load resolves config in this order:
@@ -47,6 +55,7 @@ func Load(yamlPath string) (Config, error) {
 		Listen:           ":8080",
 		DataDir:          "/data",
 		CookieSecure:     true,
+		BundledAssetsDir: "/opt/restic-manager/dist",
 	}
 
 	if yamlPath != "" {
@@ -81,6 +90,9 @@ func Load(yamlPath string) (Config, error) {
 			c.CookieSecure = true
 		}
 	}
+	if v, ok := os.LookupEnv("RM_BUNDLED_ASSETS_DIR"); ok {
+		c.BundledAssetsDir = v
+	}
 	if v, ok := os.LookupEnv("RM_TRUSTED_PROXY"); ok {
 		// Comma-separated CIDRs; allow whitespace for readability.
 		parts := strings.Split(v, ",")

internal/server/http/agent_assets.go

@@ -11,19 +11,23 @@ import (
 )
 
 // agent_assets.go serves the agent binary (one per OS/arch) and the
-// install scripts. The binaries live under <DataDir>/agent-binaries/,
-// laid down by the release pipeline (or copied by hand for now).
-// The install scripts live in <DataDir>/install/ alongside the
-// systemd unit.
+// install scripts. Lookup is dual-path:
+//
+//  1. <DataDir>/agent-binaries/<name>  (or <DataDir>/install/<name>) —
+//     operator-managed override; lets the operator hot-patch a
+//     pre-release agent without rebuilding the server image.
+//  2. <BundledAssetsDir>/agent-binaries/<name> — read-only, baked
+//     into the server image at build time (P5-03). This is what
+//     makes a fresh container Just Work without first-run staging.
 //
 // Both endpoints are intentionally unauthenticated: the install
 // payload is unprivileged on its own — it's the one-time enrollment
 // token that grants access. Anyone can pull the binary; only
 // someone with a valid token can use it productively.
 //
-// P1-31: signed-binary verification is deferred. Today we serve
-// whatever the operator dropped on disk. Future work bumps this to
-// minisign/cosign signed bundles.
+// P1-31: signed-binary verification is deferred. The image is the
+// unit of trust; pull-by-digest is the verification primitive.
+// Future work bumps standalone-binary delivery to minisign/cosign.
 
 // installAssetsRoutes adds /agent/binary and /install/* to r.
 func (s *Server) handleAgentBinary(w stdhttp.ResponseWriter, r *stdhttp.Request) {
@@ -45,8 +49,8 @@ func (s *Server) handleAgentBinary(w stdhttp.ResponseWriter, r *stdhttp.Request)
 		ext = ".exe"
 	}
 	name := fmt.Sprintf("restic-manager-agent-%s-%s%s", osTag, archTag, ext)
-	path := filepath.Join(s.deps.Cfg.DataDir, "agent-binaries", name)
-	if _, err := os.Stat(path); err != nil {
+	path, ok := s.resolveBundledAsset("agent-binaries", name)
+	if !ok {
 		writeJSONError(w, stdhttp.StatusNotFound, "binary_not_published",
 			fmt.Sprintf("agent binary for %s/%s not published on this server", osTag, archTag))
 		return
@@ -64,14 +68,34 @@ func (s *Server) handleInstallAsset(w stdhttp.ResponseWriter, r *stdhttp.Request
 		writeJSONError(w, stdhttp.StatusBadRequest, "bad_path", "")
 		return
 	}
-	path := filepath.Join(s.deps.Cfg.DataDir, "install", rel)
-	if _, err := os.Stat(path); err != nil {
+	path, ok := s.resolveBundledAsset("install", rel)
+	if !ok {
 		writeJSONError(w, stdhttp.StatusNotFound, "not_found", "")
 		return
 	}
 	stdhttp.ServeFile(w, r, path)
 }
 
+// resolveBundledAsset looks up an asset by (subdir, name). DataDir
+// wins so an operator can override the image-baked copy by dropping
+// a file into <DataDir>/<subdir>/<name>. If neither path resolves,
+// returns ("", false).
+func (s *Server) resolveBundledAsset(subdir, name string) (string, bool) {
+	candidates := []string{
+		filepath.Join(s.deps.Cfg.DataDir, subdir, name),
+	}
+	if s.deps.Cfg.BundledAssetsDir != "" {
+		candidates = append(candidates,
+			filepath.Join(s.deps.Cfg.BundledAssetsDir, subdir, name))
+	}
+	for _, p := range candidates {
+		if _, err := os.Stat(p); err == nil {
+			return p, true
+		}
+	}
+	return "", false
+}
+
 func validOS(s string) bool {
 	switch api.HostOS(s) {
 	case api.OSLinux, api.OSWindows:

internal/server/http/agent_assets_test.go

@@ -0,0 +1,167 @@
+package http
+
+import (
+	"context"
+	"io"
+	stdhttp "net/http"
+	"net/http/httptest"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"gitea.dcglab.co.uk/steve/restic-manager/internal/crypto"
+	"gitea.dcglab.co.uk/steve/restic-manager/internal/server/config"
+	"gitea.dcglab.co.uk/steve/restic-manager/internal/server/ws"
+	"gitea.dcglab.co.uk/steve/restic-manager/internal/store"
+)
+
+// newAssetsTestServer is a minimal scaffold for the /agent/binary and
+// /install/* handlers. Two roots: one acts as DataDir, the other as
+// the image-baked BundledAssetsDir. Either or both may be empty.
+func newAssetsTestServer(t *testing.T, populate func(dataDir, bundleDir string)) string {
+	t.Helper()
+	root := t.TempDir()
+	dataDir := filepath.Join(root, "data")
+	bundleDir := filepath.Join(root, "dist")
+	for _, d := range []string{
+		filepath.Join(dataDir, "agent-binaries"),
+		filepath.Join(dataDir, "install"),
+		filepath.Join(bundleDir, "agent-binaries"),
+		filepath.Join(bundleDir, "install"),
+	} {
+		if err := os.MkdirAll(d, 0o755); err != nil {
+			t.Fatalf("mkdir: %v", err)
+		}
+	}
+	if populate != nil {
+		populate(dataDir, bundleDir)
+	}
+
+	st, err := store.Open(context.Background(), filepath.Join(root, "rm.db"))
+	if err != nil {
+		t.Fatalf("store: %v", err)
+	}
+	t.Cleanup(func() { _ = st.Close() })
+
+	keyPath := filepath.Join(root, "secret.key")
+	_ = crypto.GenerateKeyFile(keyPath)
+	key, _ := crypto.LoadKeyFromFile(keyPath)
+	aead, _ := crypto.NewAEAD(key)
+
+	deps := Deps{
+		Cfg: config.Config{
+			Listen:           ":0",
+			DataDir:          dataDir,
+			SecretKeyFile:    keyPath,
+			BundledAssetsDir: bundleDir,
+		},
+		Store:          st,
+		AEAD:           aead,
+		Hub:            ws.NewHub(),
+		BootstrapToken: "test-token",
+	}
+	s := New(deps)
+	ts := httptest.NewServer(s.srv.Handler)
+	t.Cleanup(ts.Close)
+	return ts.URL
+}
+
+func writeFile(t *testing.T, path string, body []byte) {
+	t.Helper()
+	if err := os.WriteFile(path, body, 0o644); err != nil {
+		t.Fatalf("write %s: %v", path, err)
+	}
+}
+
+func get(t *testing.T, url string) (int, []byte) {
+	t.Helper()
+	res, err := stdhttp.Get(url)
+	if err != nil {
+		t.Fatalf("GET %s: %v", url, err)
+	}
+	defer res.Body.Close()
+	body, _ := io.ReadAll(res.Body)
+	return res.StatusCode, body
+}
+
+func TestAgentBinary_DataDirHit(t *testing.T) {
+	t.Parallel()
+	url := newAssetsTestServer(t, func(dataDir, _ string) {
+		writeFile(t, filepath.Join(dataDir, "agent-binaries", "restic-manager-agent-linux-amd64"),
+			[]byte("from-datadir"))
+	})
+	code, body := get(t, url+"/agent/binary?os=linux&arch=amd64")
+	if code != 200 || string(body) != "from-datadir" {
+		t.Fatalf("got %d %q", code, string(body))
+	}
+}
+
+func TestAgentBinary_BundleFallback(t *testing.T) {
+	t.Parallel()
+	url := newAssetsTestServer(t, func(_, bundleDir string) {
+		writeFile(t, filepath.Join(bundleDir, "agent-binaries", "restic-manager-agent-linux-amd64"),
+			[]byte("from-bundle"))
+	})
+	code, body := get(t, url+"/agent/binary?os=linux&arch=amd64")
+	if code != 200 || string(body) != "from-bundle" {
+		t.Fatalf("got %d %q", code, string(body))
+	}
+}
+
+func TestAgentBinary_DataDirShadowsBundle(t *testing.T) {
+	t.Parallel()
+	url := newAssetsTestServer(t, func(dataDir, bundleDir string) {
+		writeFile(t, filepath.Join(dataDir, "agent-binaries", "restic-manager-agent-linux-amd64"),
+			[]byte("from-datadir"))
+		writeFile(t, filepath.Join(bundleDir, "agent-binaries", "restic-manager-agent-linux-amd64"),
+			[]byte("from-bundle"))
+	})
+	code, body := get(t, url+"/agent/binary?os=linux&arch=amd64")
+	if code != 200 || string(body) != "from-datadir" {
+		t.Fatalf("operator override should win: got %d %q", code, string(body))
+	}
+}
+
+func TestAgentBinary_BothMiss(t *testing.T) {
+	t.Parallel()
+	url := newAssetsTestServer(t, nil)
+	code, _ := get(t, url+"/agent/binary?os=linux&arch=amd64")
+	if code != 404 {
+		t.Fatalf("expected 404, got %d", code)
+	}
+}
+
+func TestAgentBinary_WindowsNameHasExe(t *testing.T) {
+	t.Parallel()
+	url := newAssetsTestServer(t, func(_, bundleDir string) {
+		writeFile(t, filepath.Join(bundleDir, "agent-binaries", "restic-manager-agent-windows-amd64.exe"),
+			[]byte("win"))
+	})
+	code, body := get(t, url+"/agent/binary?os=windows&arch=amd64")
+	if code != 200 || string(body) != "win" {
+		t.Fatalf("got %d %q", code, string(body))
+	}
+}
+
+func TestInstallAsset_BundleFallback(t *testing.T) {
+	t.Parallel()
+	url := newAssetsTestServer(t, func(_, bundleDir string) {
+		writeFile(t, filepath.Join(bundleDir, "install", "install.sh"), []byte("#!/bin/sh\n"))
+	})
+	code, body := get(t, url+"/install/install.sh")
+	if code != 200 || string(body) != "#!/bin/sh\n" {
+		t.Fatalf("got %d %q", code, string(body))
+	}
+}
+
+func TestInstallAsset_PathTraversalRejected(t *testing.T) {
+	t.Parallel()
+	url := newAssetsTestServer(t, nil)
+	// chi will normalise some traversal attempts, but the handler
+	// also rejects any rel containing a slash or backslash. The
+	// path component of the URL after /install/ is the rel.
+	code, _ := get(t, url+"/install/..%2fpasswd")
+	if code == 200 {
+		t.Fatalf("traversal should not return 200")
+	}
+}

tasks.md

@@ -328,7 +328,7 @@ Sizes: **S** = under a day, **M** = 1–3 days, **L** = 3–7 days.
 
 - [ ] **P5-01** (M) Documentation site (mdBook or similar) with install, concepts, security model, screenshots
 - [ ] **P5-02** (S) `CONTRIBUTING.md`, `CODE_OF_CONDUCT.md`, issue + PR templates
-- [ ] **P5-03** (S) Release automation: `goreleaser` for binaries + Docker image to GHCR
+- [x] **P5-03** (S) Release automation — **pivoted away from goreleaser/binary archives** on 2026-05-05 (spec: `docs/superpowers/specs/2026-05-05-p5-03-docker-only-release.md`). Single deliverable per tag: a multi-arch (linux amd64+arm64) server image, with cross-compiled agent binaries (linux amd64+arm64, windows amd64) + `install.sh` + `install.ps1` + the systemd unit baked under `/opt/restic-manager/dist/`. The `/agent/binary` and `/install/*` handlers fall back from `<DataDir>/...` to `<BundledAssetsDir>/...` so a fresh container Just Works. Workflow `.gitea/workflows/release.yml` triggers on `v*.*.*` tag-push (real release: fan-out `:vX.Y.Z`, `:X.Y`, `:X`, plus `:latest` once `MAJOR>=1`) and `workflow_dispatch` (snapshot: `:snapshot-<shortsha>` only). Pushed to the Gitea container registry on this instance — no external creds, no GHCR mirror. Cosign / SBOM / minisign / GHCR mirror deferred to Phase 6. Source builds via `make build` remain a first-class path.
 - [ ] **P5-04** (S) Demo screenshots / short Loom walkthrough in README
 - [ ] **P5-05** (S) `SECURITY.md` with disclosure process
 - [ ] **P5-06** (M) End-to-end test suite in CI (Playwright vs. compose stack with sibling Linux agent)