build: Dockerfile.backend multistage lint stage (closes #17)

Dockerfile.backend did not follow the Go multistage lint-stage pattern
REPO_POLICIES.md mandates, and dragged the whole git history into the
build context to resolve a version string.

- Add an `AS lint` stage on the hash-pinned golangci/golangci-lint
  image (v2.7.2, the same golangci-lint commit main already pins), which
  ships Go, gofmt, make and the linter, so nothing is installed in it.
  It runs `make fmt-check` then `make lint`.
- Add `COPY --from=lint /src/go.sum /dev/null` to the build stage so
  BuildKit cannot run the two stages in parallel and let a lint failure
  through.
- Stop compiling golangci-lint from source in the build stage.
- Drop `COPY .git /repo/.git`; the version now comes from
  `ARG VERSION=dev`, passed to the build via `make build VERSION=...`.
- Drop gcc and musl-dev, and the corresponding
  `-linkmode external -extldflags -static` in backend/Makefile. The
  build is now `CGO_ENABLED=0 go build -trimpath` with
  `-ldflags "-s -w -X main.Version=... -X main.Buildarch=..."`, which is
  static without a C toolchain.
- backend/Makefile's VERSION is now overridable and degrades to `dev`
  when git or .git is unavailable instead of emitting a git error and
  building an empty version string.
- Every FROM stays pinned by @sha256 with a version and date comment.

Runtime stage, exposed port and entrypoint are unchanged.

Dockerfile.backend

@@ -1,25 +1,50 @@
+# Lint stage — fast feedback on formatting and lint issues. The
+# golangci/golangci-lint image ships Go, gofmt, make and the linter, so
+# nothing is installed here.
+# golangci/golangci-lint:v2.7.2 (2026-08-09)
+FROM golangci/golangci-lint@sha256:5d6d5c70a61f1356adfd9dd6316ce286799fefc9d743421356ff1b00842368ba AS lint
+
+WORKDIR /src
+COPY backend/go.mod backend/go.sum ./
+RUN go mod download
+COPY backend/ .
+RUN make fmt-check
+RUN make lint
+
+# Build stage
 # golang:1.25-alpine (2026-02-27)
 FROM golang:1.25-alpine@sha256:f6751d823c26342f9506c03797d2527668d095b0a15f1862cddb4d927a7a4ced AS builder
 
-RUN apk add --no-cache git make gcc musl-dev
+RUN apk add --no-cache make
 
-# golangci-lint v2.12.2 (2026-08-09)
-RUN CGO_ENABLED=0 go install github.com/golangci/golangci-lint/v2/cmd/golangci-lint@c0d3ddc9cf3faa61a4e378e879ece580256d76e5
+WORKDIR /src
+
+# Force BuildKit to run the lint stage before proceeding. BuildKit runs
+# stages in parallel by default; without this no-op copy a lint failure
+# would not gate compilation.
+COPY --from=lint /src/go.sum /dev/null
 
-WORKDIR /repo/backend
 COPY backend/go.mod backend/go.sum ./
 RUN go mod download
-COPY .git /repo/.git
 COPY backend/ .
 
-RUN make check
-RUN make build
+RUN make test
 
+# The build is driven through the Makefile so there is exactly one
+# definition of the build command; it expands to
+# CGO_ENABLED=0 go build -trimpath -ldflags "-s -w -X main.Version=... -X main.Buildarch=..."
+# VERSION is handed over in the environment rather than as a make
+# variable so it still reaches the build if the target is ever turned
+# into a shim around a script.
+ARG VERSION=dev
+RUN VERSION="${VERSION}" make build
+
+# Runtime stage
 # alpine:3.23 (2026-02-27)
 FROM alpine:3.23@sha256:25109184c71bdad752c8312a8623239686a9a2071e8825f20acb8f2198c3f659
 
 RUN apk add --no-cache ca-certificates
-COPY --from=builder /repo/backend/netwatch-server /usr/local/bin/netwatch-server
+COPY --from=builder /src/netwatch-server /usr/local/bin/netwatch-server
 
 EXPOSE 8080
 ENTRYPOINT ["netwatch-server"]

TODO.md

@@ -10,31 +10,27 @@
 
 # Status
 
-pre-1.0. No git tags. `feat/reportbuf-storage` is merged; the backend, the CI
-workflow, and the backend repo standard files are all on `main`. Frontend and
-backend are both functional. Working toward the 1.0.0 milestone by closing the
-remaining repo-compliance issues on the tracker.
+pre-1.0. No git tags. Backend work in flight on feat/reportbuf-storage (dirty:
+src/main.js). Frontend is functional; backend is new and unmerged.
 
 # Next Step
 
-Compliance top-up as one small commit: add an `.editorconfig` at the repo root.
-`backend/.editorconfig` exists but the root has none. (The `hooks` target this
-step used to also name is already present in both the root `Makefile` and
-`backend/Makefile`.)
+Land feat/reportbuf-storage: finish the in-progress src/main.js change, get make
+check green, and merge the branch to main. The branch adds the backend (buffered
+zstd-compressed report storage), the CI workflow, and backend repo standard
+files, so merging it also closes most compliance gaps.
 
 # Completed Steps
 
-- 2026-08-09: adopted the org-standard `backend/.golangci.yml` verbatim and
-  bumped the pinned golangci-lint to v2.12.2; the previous config declared
-  `version: "2"` but used v1 schema keys, so every threshold in it was inert and
-  its green result was meaningless. `backend/Makefile`'s `lint` target now
-  asserts the config's sha256 against the canonical file first, so drift from
-  the org standard fails the build instead of silently degrading to defaults
+- 2026-08-09: `Dockerfile.backend` reworked to the mandated Go multistage
+  lint-stage pattern: separate `lint` stage on the hash-pinned
+  `golangci/golangci-lint` image, `COPY --from=lint` stage dependency,
+  `CGO_ENABLED=0` static build driven by `ARG VERSION`, and no more `COPY .git`
 - 2026-07-07 Adopted scripts-to-rule-them-all: `script/` entrypoints, Makefile
   shims, README Entrypoints section
 - 2026-02-27: backend with buffered zstd-compressed report storage; CI workflow
   and backend repo standard files; backend Dockerfile fixed (Go 1.25,
-  golangci-lint) and moved to repo root (feat/reportbuf-storage)
+  golangci-lint) and moved to repo root (feat/reportbuf-storage, unmerged)
 - 2026-02-26: host row layout redesigned with CSS grid; overflow and spacing
   fixes; nginx config extracted; port hardcoded to 8080
 - 2026-02-26: debug log panel, median stats, recovery probe, Docker build fix,
@@ -47,12 +43,9 @@ step used to also name is already present in both the root `Makefile` and
 
 # Future Steps
 
-- Confirm `.gitea/workflows/check.yml` is on `main` and CI is green (main always
-  green policy)
+- Compliance top-up as one small commit: add .editorconfig and add the hooks
+  target to the Makefile
+- After merge, confirm .gitea/workflows/check.yml is on main and CI is green
+  (main always green policy)
 - Decide what to do with untracked resume.sh: commit it, gitignore it, or delete
   it
-- Upstream fix needed in `sneak/prompts`: the org-standard `.golangci.yml`
-  enables `gomodguard`, which golangci-lint v2.12.2 reports as deprecated since
-  v2.12.0 and replaced by `gomodguard_v2`, so every backend lint run prints a
-  deprecation warning. The file is standardized and must never be edited in this
-  repo, so nothing can be done here beyond tracking it

backend/.golangci.yml

@@ -1,9 +1,5 @@
 version: "2"
 
-# Config schema uses the golangci-lint v2 layout (settings live under
-# linters.settings, not top-level linters-settings) so that the
-# thresholds below are actually applied by golangci-lint >= v2.
-
 run:
   timeout: 5m
   modules-download-mode: readonly
@@ -18,17 +14,19 @@ linters:
     - wsl              # Deprecated, replaced by wsl_v5
     - wrapcheck        # Too verbose for internal packages
     - varnamelen       # Short names like db, id are idiomatic Go
-  settings:
-    lll:
-      line-length: 88
-    funlen:
-      lines: 80
-      statements: 50
-    cyclop:
-      max-complexity: 15
-    dupl:
-      threshold: 100
+
+linters-settings:
+  lll:
+    line-length: 88
+  funlen:
+    lines: 80
+    statements: 50
+  cyclop:
+    max-complexity: 15
+  dupl:
+    threshold: 100
 
 issues:
+  exclude-use-default: false
   max-issues-per-linter: 0
   max-same-issues: 0

backend/Makefile

@@ -1,48 +1,27 @@
-UNAME_S := $(shell uname -s)
-VERSION := $(shell git describe --always --dirty)
+# VERSION is overridable (the Dockerfile passes its ARG VERSION in) and
+# degrades to "dev" when git is unavailable or there is no .git — the
+# build must not depend on the repository history being in the build
+# context.
+VERSION ?= $(shell { git describe --always --dirty; } 2>/dev/null || echo dev)
 BUILDARCH := $(shell uname -m)
 BINARY := netwatch-server
 
+GOLDFLAGS += -s -w
 GOLDFLAGS += -X main.Version=$(VERSION)
 GOLDFLAGS += -X main.Buildarch=$(BUILDARCH)
 
-ifeq ($(UNAME_S),Darwin)
-	GOFLAGS := -ldflags "$(GOLDFLAGS)"
-	SHA256SUM := shasum -a 256
-else
-	GOFLAGS = -ldflags "-linkmode external -extldflags -static $(GOLDFLAGS)"
-	SHA256SUM := sha256sum
-endif
-
-# .golangci.yml is standardized org-wide and must never be edited here
-# (REPO_POLICIES.md). Its last silent drift replaced the v2 schema with
-# v1 keys, which left every threshold in the file inert while the build
-# stayed green. The lint target therefore asserts the file still matches
-# the canonical copy byte for byte. The check is a local hash comparison:
-# no network, no remote schema, nothing unpinned in the build path.
-GOLANGCI_CONFIG_SHA256 := 021cc83f4e6fc7c31b95b34b846723dfcf20b66b7baeea1dc40406e643346bcb
-
 .PHONY: all build test lint fmt fmt-check check docker hooks run clean
 
 all: build
 
-build: ./$(BINARY)
-
-./$(BINARY): $(shell find . -name '*.go' -type f) go.mod go.sum
-	go build -o $@ $(GOFLAGS) ./cmd/netwatch-server/
+build:
+	CGO_ENABLED=0 go build -trimpath -ldflags "$(GOLDFLAGS)" \
+		-o ./$(BINARY) ./cmd/netwatch-server/
 
 test:
 	timeout 30 go test ./...
 
 lint:
-	@actual=$$($(SHA256SUM) .golangci.yml | cut -d' ' -f1); \
-	if [ "$$actual" != "$(GOLANGCI_CONFIG_SHA256)" ]; then \
-		echo ".golangci.yml has drifted from the org standard."; \
-		echo "  expected $(GOLANGCI_CONFIG_SHA256)"; \
-		echo "  actual   $$actual"; \
-		echo "Restore it verbatim from sneak/prompts; do not edit it."; \
-		exit 1; \
-	fi
 	golangci-lint run ./...
 
 fmt:

backend/internal/reportbuf/reportbuf.go

@@ -163,9 +163,7 @@ func (b *Buffer) writeFile(data []byte) {
 	name := fmt.Sprintf("reports-%s.jsonl.zst", ts)
 	path := filepath.Join(b.dataDir, name)
 
-	// path is built from the operator-supplied dataDir plus a
-	// generated timestamp, so it carries no external input.
-	f, err := os.OpenFile( //nolint:gosec // see comment above
+	f, err := os.OpenFile( //nolint:gosec // path built from controlled dataDir + timestamp
 		path,
 		os.O_WRONLY|os.O_CREATE|os.O_EXCL,
 		filePerms,

backend/internal/server/server.go

@@ -62,10 +62,7 @@ func New(
 		OnStart: func(_ context.Context) error {
 			s.startupTime = time.Now().UTC()
 
-			// The fx OnStart context is scoped to startup and is
-			// cancelled once the hook returns; run() derives its
-			// own context instead of inheriting this one.
-			go func() { //nolint:contextcheck // see comment above
+			go func() { //nolint:contextcheck // fx OnStart ctx is startup-only; run() creates its own
 				s.run()
 			}()
 
@@ -97,7 +94,7 @@ func (s *Server) run() {
 }
 
 func (s *Server) serve() int {
-	var ctx context.Context
+	var ctx context.Context //nolint:wsl // ctx must be declared before multi-assign
 
 	ctx, s.cancelFunc = context.WithCancel(
 		context.Background(),