feat(frontend): post collected samples to /api/v1/reports (closes #53)

A Reporter beside AppState POSTs each host's unreported, non-paused
samples to /api/v1/reports every reportInterval (default 60s).
buildReport is an exported pure function of host state; init() runs only
when #app exists, so a test can import the module. A per-host mark
advances only on a delivered POST. At most one report POST is pending at
a time and it is abandoned after half the interval, so a slow POST never
overlaps the next report and a mark never moves backwards. The samples of
an abandoned POST are sent again at the next interval, so a backend that
stored them but answered late receives them twice. Failure is quiet and
never blocks probing. vite.config.js proxies /api for yarn dev.

Model: opus-5-5

.dockerignore

@@ -1,5 +1,6 @@
 node_modules
 dist
+tmp
 .DS_Store
 *.log
 .claude

.gitignore

@@ -1,4 +1,28 @@
-node_modules/
+# OS
-dist/
 .DS_Store
+Thumbs.db
+
+# Editors
+*.swp
+*.swo
+*~
+*.bak
+.idea/
+.vscode/
+*.sublime-*
+
+# Node
+node_modules/
+
+# Environment / secrets
+.env
+.env.*
+*.pem
+*.key
+
+# Build output
+dist/
+tmp/
+
+# Logs
 *.log

.prettierignore

@@ -1,5 +1,6 @@
 backend/
 dist/
 node_modules/
+tmp/
 yarn.lock
 .claude/

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:v2.12.2 (2026-08-10)
+FROM golangci/golangci-lint@sha256:5cceeef04e53efe1470638d4b4b4f5ceefd574955ab3941b2d9a68a8c9ad5240 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 v2.7.2 (2026-02-27)
+WORKDIR /src
-RUN CGO_ENABLED=0 go install github.com/golangci/golangci-lint/v2/cmd/golangci-lint@9f61b0f53f80672872fced07b6874397c3ed197b
+
+# 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 test
-RUN make build
 
+# 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"]

Makefile

@@ -1,4 +1,5 @@
-.PHONY: bootstrap setup dev test lint fmt fmt-check check docker hooks
+.PHONY: bootstrap setup dev test lint fmt fmt-check check \
+	frontend-viewport-test docker hooks
 
 # Standard targets are thin shims; the implementations live in script/
 # per the scripts-to-rule-them-all pattern (see the Entrypoints section
@@ -28,6 +29,12 @@ fmt-check:
 check:
 	@script/check
 
+# Responsive-layout verification in a containerised browser. Kept out of
+# check: it needs Docker and takes minutes, where make test has to stay
+# under 20 seconds.
+frontend-viewport-test:
+	@script/frontend-viewport-test
+
 docker:
 	@script/docker
 

README.md

@@ -23,6 +23,9 @@ docker build -t netwatch .
 docker run -p 8080:8080 netwatch
 ```
 
+`yarn dev` proxies `/api` to `http://127.0.0.1:8080`, so a locally running
+`netwatch-server` (see `backend/`) receives the reports the page posts.
+
 ## Entrypoints
 
 This repository adheres to the
@@ -41,11 +44,25 @@ provide:
 - `script/fmt` — format all files (writes)
 - `script/fmt-check` — check formatting (read-only)
 - `script/check` — run test, lint, and fmt-check
+- `script/frontend-viewport-test` — responsive-layout verification of the built
+  frontend in a containerised headless Chrome (see
+  [test/viewport/README.md](test/viewport/README.md)). Not part of
+  `script/check`: it needs Docker and takes minutes.
 - `script/docker` — build the Docker image tagged via `script/projectname`
 - `script/cibuild` — CI entrypoint: plain `docker build .`
 - `script/precommit` — run by the git pre-commit hook; runs `script/check`
 - `script/install-precommit` — install the git pre-commit hook
 
+## Responsive layout
+
+The narrow-viewport layout lives in the `max-width: 768px` media block in
+`src/styles.css`. It is verified automatically by `make frontend-viewport-test`,
+which drives a digest-pinned headless Chrome against the built `dist/` and
+asserts on computed layout at widths derived from that CSS — one pixel either
+side of every breakpoint it declares, plus a 320px floor, a desktop baseline and
+two landscape sizes. See [test/viewport/README.md](test/viewport/README.md) for
+what it covers and what it genuinely cannot.
+
 ## Rationale
 
 When debugging network issues, it's useful to have a persistent at-a-glance view
@@ -71,6 +88,18 @@ code lives in `src/main.js` with a class-based architecture:
 - **`tick()`**: Main loop — measures all hosts in parallel via `Promise.all`,
   pushes samples, redraws UI. When paused, pushes blank markers (no probes, no
   false outage)
+- **`Reporter`**: Posts collected samples to the backend
+
+### Reporting
+
+Every `reportInterval` (default 60s) the page POSTs a JSON report to the
+same-origin path `/api/v1/reports`: a random per-browser `clientId` kept in
+`localStorage`, `geo` sent as null, and each host's unreported, non-paused
+samples (timestamp, latency, error). A per-host high-water mark makes every
+report a delta, so only new samples are sent; the mark advances only on a
+delivered report, and while paused nothing is sent. Delivery failure is quiet —
+one debug-log line per outage, retried at the next interval, never blocking
+probing. The report-building step is a pure function of host state.
 
 ### Monitoring targets
 

TODO.md

@@ -10,23 +10,91 @@
 
 # Status
 
-pre-1.0. No git tags. Backend work in flight on feat/reportbuf-storage (dirty:
+pre-1.0. No git tags. `feat/reportbuf-storage` is merged; the backend, the CI
-src/main.js). Frontend is functional; backend is new and unmerged.
+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.
 
 # Next Step
 
-Land feat/reportbuf-storage: finish the in-progress src/main.js change, get make
+Confirm the `.gitea/workflows/check.yml` run is green (main always green
-check green, and merge the branch to main. The branch adds the backend (buffered
+policy). The workflow file is already on `main`; what is unverified is that its
-zstd-compressed report storage), the CI workflow, and backend repo standard
+latest run passes.
-files, so merging it also closes most compliance gaps.
 
 # Completed Steps
 
+- 2026-09-28: frontend reporting client (issue #53): a `Reporter` class posts
+  collected samples to `/api/v1/reports` every `reportInterval` (default 60s) as
+  a per-host delta, with the report-building step a pure exported function of
+  host state; a per-host mark advances only on a delivered POST; at most one
+  report POST is pending at a time and it is abandoned after half the interval,
+  so a slow POST never overlaps the next report and a mark never moves
+  backwards; the samples of an abandoned POST are sent again at the next
+  interval, so a backend that stored them but answered late receives them twice;
+  the per-browser client id works in insecure (plain-HTTP) contexts;
+  `vite.config.js` proxies `/api` to the local backend for `yarn dev`
+- 2026-09-28: report ingest correctness (issue #23): a storage failure now
+  returns 500 instead of a false `ok`; oversize bodies return 413 (distinguished
+  from malformed JSON, which stays 400); a `MaxBodyBytes` middleware caps every
+  route, not just the report route; the raw attacker-controlled `geo` blob is no
+  longer logged (only its length), and `client_id`, `timestamp` and decode error
+  text are length-bounded before logging; a `decodeJSON` handler helper was
+  added; panic recovery now routes the stack through slog instead of chi's
+  plain-text stderr; and writing a report file now returns its error, so a
+  failed final flush on shutdown makes the process exit non-zero instead of
+  losing the buffered reports silently
+- 2026-09-21: shutdown lifecycle correctness. The process now shuts down through
+  fx instead of `os.Exit`, so every component's `OnStop` runs and buffered
+  reports are flushed to disk on `SIGTERM` — previously a full flush window of
+  telemetry was silently lost on every restart. The `http.Server` is now built
+  before its serving goroutine starts, so shutdown can no longer race or
+  nil-deref it; a listen failure exits non-zero via `fx.Shutdowner`; `reportbuf`
+  `OnStop` is idempotent; and `writeTimeout` now exceeds the chi per-request
+  budget so that budget is actually reachable. Dead `startupTime`, `exitCode`,
+  and `cancelFunc` fields were removed
+- 2026-09-21: backend HTTP hardening (issue #19): added `ReadHeaderTimeout` and
+  `IdleTimeout` to the server, a `SecurityHeaders` middleware (HSTS, tight CSP,
+  frame/sniff/referrer/permissions headers) registered before CORS, and
+  trusted-proxy client IP resolution honouring `X-Forwarded-For` / `X-Real-IP`
+  only from a `TRUSTED_PROXIES` allowlist (loopback plus RFC1918 by default)
+- 2026-08-10: adopted the org-standard `backend/.golangci.yml` verbatim and
+  moved the pinned golangci-lint from v2.7.2 to v2.12.2 (the `lint` stage of
+  `Dockerfile.backend` now pins the `golangci/golangci-lint:v2.12.2` image by
+  digest); 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
+- 2026-08-10: every interactive control now meets the 44x44 CSS px minimum tap
+  target (`.pin-btn`, `#interval-select`, the debug-log label and, on narrow
+  viewports, `#pause-btn`). The pin button's hit area grows via matching
+  negative margins, so its layout footprint and row density are unchanged
+- 2026-08-10: per-host status line wraps below the 768px breakpoint instead of
+  forcing horizontal page scroll at 320px
+- 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`
+- 2026-08-09: dotfile compliance — lifted `backend/.editorconfig` to the repo
+  root so `root = true` covers the frontend too, and replaced `.gitignore` with
+  the org model (OS, editor, node, and environment/secrets sections) plus this
+  repo's `dist/` and `*.log`. `.env`, `.env.*`, `*.pem`, and `*.key` are now
+  ignored repo-wide, not just under `backend/`. Excluding `.git` from
+  `.dockerignore` stays deferred: both images read git metadata at build time
+  (`COPY .git` in `Dockerfile.backend`, `git rev-parse` in `vite.config.js`)
+- 2026-08-09: automated responsive-layout harness
+  (`make frontend-viewport-test`): digest-pinned headless Chrome driven over CDP
+  against the built `dist/`, viewport widths derived from the breakpoints in
+  `src/styles.css` ([#13](https://git.eeqj.de/sneak/netwatch/issues/13)). Every
+  check carries a presence guard so none of them can pass against a page it is
+  not actually measuring. Found two real layout defects, filed as
+  [#42](https://git.eeqj.de/sneak/netwatch/issues/42) and
+  [#43](https://git.eeqj.de/sneak/netwatch/issues/43)
 - 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, unmerged)
+  golangci-lint) and moved to repo root (feat/reportbuf-storage)
 - 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,
@@ -39,9 +107,18 @@ files, so merging it also closes most compliance gaps.
 
 # Future Steps
 
+- Wire `script/frontend-viewport-test` into CI as its own step (deliberately not
+  part of `make check` today; the decision has real CI-runtime cost and is
+  tracked separately)
 - 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 — tracked at
+  <https://git.eeqj.de/sneak/netwatch/issues/41>

backend/.golangci.yml

@@ -1,5 +1,9 @@
 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
@@ -14,8 +18,7 @@ linters:
     - wsl              # Deprecated, replaced by wsl_v5
     - wrapcheck        # Too verbose for internal packages
     - varnamelen       # Short names like db, id are idiomatic Go
-
+  settings:
-linters-settings:
     lll:
       line-length: 88
     funlen:
@@ -27,6 +30,5 @@ linters-settings:
       threshold: 100
 
 issues:
-  exclude-use-default: false
   max-issues-per-linter: 0
   max-same-issues: 0

backend/Makefile

@@ -1,30 +1,46 @@
-UNAME_S := $(shell uname -s)
+# VERSION is overridable (the Dockerfile passes its ARG VERSION in) and
-VERSION := $(shell git describe --always --dirty)
+# 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 ($(UNAME_S),Darwin)
+# macOS ships shasum rather than sha256sum.
-	GOFLAGS := -ldflags "$(GOLDFLAGS)"
+SHA256SUM := $(shell command -v sha256sum >/dev/null 2>&1 && echo sha256sum || echo shasum -a 256)
-else
+
-	GOFLAGS = -ldflags "-linkmode external -extldflags -static $(GOLDFLAGS)"
+# .golangci.yml is standardized org-wide and must never be edited here
-endif
+# (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: ./$(BINARY)
+build:
-
+	CGO_ENABLED=0 go build -trimpath -ldflags "$(GOLDFLAGS)" \
-./$(BINARY): $(shell find . -name '*.go' -type f) go.mod go.sum
+		-o ./$(BINARY) ./cmd/netwatch-server/
-	go build -o $@ $(GOFLAGS) ./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/README.md

@@ -43,10 +43,16 @@ Internal packages in `internal/` follow standard Go project layout:
 ### Configuration
 
 | Variable          | Default              | Description                                                                                              |
-| ---------- | ------------------ | --------------------------------- |
+| ----------------- | -------------------- | -------------------------------------------------------------------------------------------------------- |
 | `PORT`            | `8080`               | HTTP listen port                                                                                         |
 | `DATA_DIR`        | `./data/reports`     | Directory for compressed reports                                                                         |
 | `DEBUG`           | `false`              | Enable debug logging                                                                                     |
+| `TRUSTED_PROXIES` | loopback + RFC1918   | Comma-separated CIDRs whose `X-Forwarded-For` / `X-Real-IP` headers are trusted for client IP resolution |
+
+`TRUSTED_PROXIES` defaults to `127.0.0.1/32,::1/128,10.0.0.0/8,172.16.0.0/12,192.168.0.0/16`.
+The loopback entries cover the reverse proxy that shares the container; the
+RFC1918 ranges match `nginx.conf`. A request whose direct peer is outside this
+set has its forwarded headers ignored, and the direct peer is logged instead.
 
 ### Report storage
 

backend/internal/config/config.go

@@ -5,6 +5,7 @@ package config
 import (
 	"errors"
 	"log/slog"
+	"strings"
 
 	"sneak.berlin/go/netwatch/internal/globals"
 	"sneak.berlin/go/netwatch/internal/logger"
@@ -14,6 +15,14 @@ import (
 	"go.uber.org/fx"
 )
 
+// defaultTrustedProxies lists the networks whose forwarded
+// headers are honoured by default. It covers the RFC1918
+// ranges (to match nginx.conf) plus IPv4 and IPv6 loopback,
+// because the reverse proxy shares the container and reaches
+// the backend over loopback.
+const defaultTrustedProxies = "127.0.0.1/32,::1/128," +
+	"10.0.0.0/8,172.16.0.0/12,192.168.0.0/16"
+
 // Params defines the dependencies for Config.
 type Params struct {
 	fx.In
@@ -30,6 +39,7 @@ type Config struct {
 	MetricsUsername string
 	Port            int
 	SentryDSN       string
+	TrustedProxies  []string
 	log             *slog.Logger
 	params          *Params
 }
@@ -56,6 +66,7 @@ func New(
 	viper.SetDefault("SENTRY_DSN", "")
 	viper.SetDefault("METRICS_USERNAME", "")
 	viper.SetDefault("METRICS_PASSWORD", "")
+	viper.SetDefault("TRUSTED_PROXIES", defaultTrustedProxies)
 
 	err := viper.ReadInConfig()
 	if err != nil {
@@ -73,6 +84,7 @@ func New(
 		MetricsUsername: viper.GetString("METRICS_USERNAME"),
 		Port:            viper.GetInt("PORT"),
 		SentryDSN:       viper.GetString("SENTRY_DSN"),
+		TrustedProxies:  splitList(viper.GetString("TRUSTED_PROXIES")),
 		log:             log,
 		params:          &params,
 	}
@@ -84,3 +96,19 @@ func New(
 
 	return s, nil
 }
+
+// splitList turns a comma-separated setting into a trimmed
+// slice, dropping empty entries.
+func splitList(raw string) []string {
+	parts := strings.Split(raw, ",")
+
+	out := make([]string, 0, len(parts))
+	for _, p := range parts {
+		p = strings.TrimSpace(p)
+		if p != "" {
+			out = append(out, p)
+		}
+	}
+
+	return out
+}

backend/internal/handlers/export_test.go

@@ -0,0 +1,13 @@
+package handlers
+
+import "log/slog"
+
+// MaxLoggedFieldBytes exposes the log bound to the external tests.
+const MaxLoggedFieldBytes = maxLoggedFieldBytes
+
+// NewForTest builds a Handlers around a report sink and logger,
+// bypassing the fx graph so handler behaviour (including the
+// storage failure path) is exercisable in unit tests.
+func NewForTest(buf reportAppender, log *slog.Logger) *Handlers {
+	return &Handlers{buf: buf, log: log}
+}

backend/internal/handlers/handlers.go

@@ -18,6 +18,13 @@ import (
 
 const jsonContentType = "application/json; charset=utf-8"
 
+// reportAppender is the subset of the report buffer the handlers
+// depend on. Defining it here keeps the storage failure path
+// exercisable with a stub in tests.
+type reportAppender interface {
+	Append(v any) error
+}
+
 // Params defines the dependencies for Handlers.
 type Params struct {
 	fx.In
@@ -30,7 +37,7 @@ type Params struct {
 
 // Handlers provides HTTP handler factories for all endpoints.
 type Handlers struct {
-	buf    *reportbuf.Buffer
+	buf    reportAppender
 	hc     *healthcheck.Healthcheck
 	log    *slog.Logger
 	params *Params
@@ -72,3 +79,15 @@ func (s *Handlers) respondJSON(
 		}
 	}
 }
+
+// decodeJSON decodes the request body into v. The body is
+// expected to already be bounded by the body-size middleware, so
+// a caller can distinguish an over-limit body from malformed
+// JSON by testing the returned error for *http.MaxBytesError.
+func (s *Handlers) decodeJSON(
+	_ http.ResponseWriter,
+	r *http.Request,
+	v any,
+) error {
+	return json.NewDecoder(r.Body).Decode(v)
+}

backend/internal/handlers/report.go

@@ -2,10 +2,14 @@ package handlers
 
 import (
 	"encoding/json"
+	"errors"
 	"net/http"
 )
 
-const maxReportBodyBytes = 1 << 20 // 1 MiB
+// maxLoggedFieldBytes bounds untrusted text (string fields,
+// decode error text) before it is logged, so a caller cannot
+// inflate log volume with an oversized value.
+const maxLoggedFieldBytes = 128
 
 type reportSample struct {
 	T       int64   `json:"t"`
@@ -35,48 +39,80 @@ func (s *Handlers) HandleReport() http.HandlerFunc {
 	}
 
 	return func(w http.ResponseWriter, r *http.Request) {
-		r.Body = http.MaxBytesReader(
-			w, r.Body, maxReportBodyBytes,
-		)
-
 		var rpt report
 
-		err := json.NewDecoder(r.Body).Decode(&rpt)
+		err := s.decodeJSON(w, r, &rpt)
 		if err != nil {
-			s.log.Error("failed to decode report",
-				"error", err,
-			)
 			s.respondJSON(w, r,
 				&response{Status: "error"},
-				http.StatusBadRequest,
+				s.decodeErrorStatus(err),
 			)
 
 			return
 		}
 
+		s.logReportReceived(rpt)
+
+		err = s.buf.Append(rpt)
+		if err != nil {
+			s.log.Error("failed to buffer report", "error", err)
+			s.respondJSON(w, r,
+				&response{Status: "error"},
+				http.StatusInternalServerError,
+			)
+
+			return
+		}
+
+		s.respondJSON(w, r, &response{Status: "ok"}, http.StatusOK)
+	}
+}
+
+// decodeErrorStatus logs a report decode failure and returns the
+// status to send: 413 when the body exceeded the size limit,
+// otherwise 400 for malformed JSON.
+func (s *Handlers) decodeErrorStatus(err error) int {
+	var tooLarge *http.MaxBytesError
+	if errors.As(err, &tooLarge) {
+		s.log.Warn("report body too large", "limit_bytes", tooLarge.Limit)
+
+		return http.StatusRequestEntityTooLarge
+	}
+
+	// The decoder's error text can quote request bytes (a whole
+	// oversized number, for example), so it is bounded too.
+	s.log.Error("failed to decode report",
+		"error", boundedForLog(err.Error()),
+	)
+
+	return http.StatusBadRequest
+}
+
+// logReportReceived logs an accepted report. Untrusted fields are
+// bounded (client_id, timestamp) or reduced to a length
+// (geo_bytes) so the raw attacker-controlled body never reaches
+// the log.
+func (s *Handlers) logReportReceived(rpt report) {
 	totalSamples := 0
 	for _, h := range rpt.Hosts {
 		totalSamples += len(h.History)
 	}
 
 	s.log.Info("report received",
-			"client_id", rpt.ClientID,
+		"client_id", boundedForLog(rpt.ClientID),
-			"timestamp", rpt.Timestamp,
+		"timestamp", boundedForLog(rpt.Timestamp),
 		"host_count", len(rpt.Hosts),
 		"total_samples", totalSamples,
-			"geo", string(rpt.Geo),
+		"geo_bytes", len(rpt.Geo),
 	)
+}
 
-		bufErr := s.buf.Append(rpt)
+// boundedForLog truncates an untrusted string to a fixed byte
-		if bufErr != nil {
+// bound so an attacker-controlled field cannot dominate the log.
-			s.log.Error("failed to buffer report",
+func boundedForLog(s string) string {
-				"error", bufErr,
+	if len(s) > maxLoggedFieldBytes {
-			)
+		return s[:maxLoggedFieldBytes]
 	}
 
-		s.respondJSON(w, r,
+	return s
-			&response{Status: "ok"},
-			http.StatusOK,
-		)
-	}
 }

backend/internal/handlers/report_test.go

@@ -0,0 +1,212 @@
+package handlers_test
+
+import (
+	"bytes"
+	"encoding/json"
+	"errors"
+	"io"
+	"log/slog"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"sneak.berlin/go/netwatch/internal/handlers"
+	"sneak.berlin/go/netwatch/internal/middleware"
+)
+
+var errStorageFailed = errors.New("storage failed")
+
+// stubAppender drives the storage success/failure path without a
+// real buffer or disk.
+type stubAppender struct {
+	err error
+}
+
+func (s stubAppender) Append(any) error { return s.err }
+
+func newTestHandlers(buf stubAppender, out io.Writer) *handlers.Handlers {
+	return handlers.NewForTest(buf, slog.New(slog.NewJSONHandler(out, nil)))
+}
+
+func decodeStatus(t *testing.T, body []byte) string {
+	t.Helper()
+
+	var resp struct {
+		Status string `json:"status"`
+	}
+
+	err := json.Unmarshal(body, &resp)
+	if err != nil {
+		t.Fatalf("response body not JSON: %v (%q)", err, body)
+	}
+
+	return resp.Status
+}
+
+func TestHandleReportStorageFailureIsNon2xx(t *testing.T) {
+	t.Parallel()
+
+	h := newTestHandlers(stubAppender{err: errStorageFailed}, io.Discard)
+
+	rec := httptest.NewRecorder()
+	req := httptest.NewRequestWithContext(t.Context(),
+		http.MethodPost, "/api/v1/reports",
+		strings.NewReader(`{"clientId":"c1","hosts":[]}`),
+	)
+
+	h.HandleReport().ServeHTTP(rec, req)
+
+	if rec.Code < 500 {
+		t.Fatalf("storage failure status = %d, want a 5xx", rec.Code)
+	}
+
+	if got := decodeStatus(t, rec.Body.Bytes()); got != "error" {
+		t.Fatalf("status field = %q, want %q", got, "error")
+	}
+}
+
+func TestHandleReportMalformedJSONIs400(t *testing.T) {
+	t.Parallel()
+
+	h := newTestHandlers(stubAppender{}, io.Discard)
+
+	rec := httptest.NewRecorder()
+	req := httptest.NewRequestWithContext(t.Context(),
+		http.MethodPost, "/api/v1/reports",
+		strings.NewReader(`{not json`),
+	)
+
+	h.HandleReport().ServeHTTP(rec, req)
+
+	if rec.Code != http.StatusBadRequest {
+		t.Fatalf("malformed status = %d, want %d",
+			rec.Code, http.StatusBadRequest)
+	}
+}
+
+func TestHandleReportOversizeIs413(t *testing.T) {
+	t.Parallel()
+
+	const limit = 32
+
+	h := newTestHandlers(stubAppender{}, io.Discard)
+	handler := (&middleware.Middleware{}).MaxBodyBytes(limit)(
+		h.HandleReport(),
+	)
+
+	rec := httptest.NewRecorder()
+	req := httptest.NewRequestWithContext(t.Context(),
+		http.MethodPost, "/api/v1/reports",
+		strings.NewReader(`{"clientId":"`+strings.Repeat("x", 200)+`"}`),
+	)
+	// No declared length, so only the middleware's read cap can
+	// stop this body.
+	req.ContentLength = -1
+
+	handler.ServeHTTP(rec, req)
+
+	if rec.Code != http.StatusRequestEntityTooLarge {
+		t.Fatalf("oversize status = %d, want %d",
+			rec.Code, http.StatusRequestEntityTooLarge)
+	}
+}
+
+func TestHandleReportDoesNotLogRawGeo(t *testing.T) {
+	t.Parallel()
+
+	const sentinel = "SENSITIVE-GEO-BLOB"
+
+	var logbuf bytes.Buffer
+
+	h := newTestHandlers(stubAppender{}, &logbuf)
+
+	rec := httptest.NewRecorder()
+	req := httptest.NewRequestWithContext(t.Context(),
+		http.MethodPost, "/api/v1/reports",
+		strings.NewReader(
+			`{"clientId":"c1","geo":{"raw":"`+sentinel+`"},"hosts":[]}`,
+		),
+	)
+
+	h.HandleReport().ServeHTTP(rec, req)
+
+	if rec.Code != http.StatusOK {
+		t.Fatalf("status = %d, want %d", rec.Code, http.StatusOK)
+	}
+
+	if strings.Contains(logbuf.String(), sentinel) {
+		t.Fatal("raw geo bytes were written to the log")
+	}
+
+	if !strings.Contains(logbuf.String(), "geo_bytes") {
+		t.Fatal("expected a bounded geo_bytes field in the log")
+	}
+}
+
+func TestHandleReportLogsClientIDCutToBound(t *testing.T) {
+	t.Parallel()
+
+	long := strings.Repeat("c", 2*handlers.MaxLoggedFieldBytes)
+
+	var logbuf bytes.Buffer
+
+	h := newTestHandlers(stubAppender{}, &logbuf)
+
+	rec := httptest.NewRecorder()
+	req := httptest.NewRequestWithContext(t.Context(),
+		http.MethodPost, "/api/v1/reports",
+		strings.NewReader(
+			`{"clientId":"`+long+`","timestamp":"`+long+`","hosts":[]}`,
+		),
+	)
+
+	h.HandleReport().ServeHTTP(rec, req)
+
+	var logged map[string]any
+
+	err := json.Unmarshal(logbuf.Bytes(), &logged)
+	if err != nil {
+		t.Fatalf("log line not JSON: %v (%q)", err, logbuf.String())
+	}
+
+	want := long[:handlers.MaxLoggedFieldBytes]
+
+	if logged["client_id"] != want {
+		t.Fatalf("logged client_id not cut to %d bytes: %q",
+			handlers.MaxLoggedFieldBytes, logged["client_id"])
+	}
+
+	if logged["timestamp"] != want {
+		t.Fatalf("logged timestamp not cut to %d bytes: %q",
+			handlers.MaxLoggedFieldBytes, logged["timestamp"])
+	}
+}
+
+func TestHandleReportDecodeErrorLogIsBounded(t *testing.T) {
+	t.Parallel()
+
+	// A number too large for its int64 field makes the decoder's
+	// error text quote the whole number.
+	huge := strings.Repeat("9", 2*handlers.MaxLoggedFieldBytes)
+
+	var logbuf bytes.Buffer
+
+	h := newTestHandlers(stubAppender{}, &logbuf)
+
+	rec := httptest.NewRecorder()
+	req := httptest.NewRequestWithContext(t.Context(),
+		http.MethodPost, "/api/v1/reports",
+		strings.NewReader(`{"hosts":[{"history":[{"t":`+huge+`}]}]}`),
+	)
+
+	h.HandleReport().ServeHTTP(rec, req)
+
+	if rec.Code != http.StatusBadRequest {
+		t.Fatalf("status = %d, want %d", rec.Code, http.StatusBadRequest)
+	}
+
+	if strings.Contains(logbuf.String(), huge) {
+		t.Fatal("the whole oversized number was written to the log")
+	}
+}

backend/internal/middleware/export_test.go

@@ -0,0 +1,28 @@
+package middleware
+
+import (
+	"log/slog"
+	"net/http"
+	"net/netip"
+)
+
+// Test-only wrappers exposing unexported helpers to the
+// external middleware_test package.
+
+// NewWithLogger builds a Middleware around a logger for tests
+// that exercise the logging paths without the fx graph.
+func NewWithLogger(log *slog.Logger) *Middleware {
+	return &Middleware{log: log}
+}
+
+func ClientIP(
+	remoteAddr string,
+	header http.Header,
+	trusted []netip.Prefix,
+) string {
+	return clientIP(remoteAddr, header, trusted)
+}
+
+func ParseTrustedProxies(cidrs []string) ([]netip.Prefix, error) {
+	return parseTrustedProxies(cidrs)
+}

backend/internal/middleware/middleware.go

@@ -3,9 +3,15 @@
 package middleware
 
 import (
+	"errors"
+	"fmt"
+	"io"
 	"log/slog"
 	"net"
 	"net/http"
+	"net/netip"
+	"runtime/debug"
+	"strings"
 	"time"
 
 	"sneak.berlin/go/netwatch/internal/config"
@@ -19,6 +25,23 @@ import (
 
 const corsMaxAgeSec = 300
 
+// jsonErrorBody is the body written for errors raised inside
+// middleware, matching the {"status":"error"} shape the handlers
+// return so clients see one error contract across the API.
+const (
+	jsonContentType = "application/json; charset=utf-8"
+	jsonErrorBody   = "{\"status\":\"error\"}\n"
+)
+
+// Security header values. The backend is a JSON API with no
+// HTML surface, so the CSP forbids every resource type and
+// framing outright.
+const (
+	hstsValue              = "max-age=31536000; includeSubDomains"
+	cspValue               = "default-src 'none'; frame-ancestors 'none'"
+	permissionsPolicyValue = "camera=(), microphone=(), geolocation=()"
+)
+
 // Params defines the dependencies for Middleware.
 type Params struct {
 	fx.In
@@ -32,6 +55,7 @@ type Params struct {
 type Middleware struct {
 	log            *slog.Logger
 	params         *Params
+	trustedProxies []netip.Prefix
 }
 
 // New creates a Middleware instance.
@@ -39,13 +63,38 @@ func New(
 	_ fx.Lifecycle,
 	params Params,
 ) (*Middleware, error) {
+	trusted, err := parseTrustedProxies(params.Config.TrustedProxies)
+	if err != nil {
+		return nil, err
+	}
+
 	s := new(Middleware)
 	s.params = &params
 	s.log = params.Logger.Get()
+	s.trustedProxies = trusted
 
 	return s, nil
 }
 
+// parseTrustedProxies converts CIDR strings into prefixes,
+// failing fast on any malformed entry.
+func parseTrustedProxies(cidrs []string) ([]netip.Prefix, error) {
+	prefixes := make([]netip.Prefix, 0, len(cidrs))
+
+	for _, cidr := range cidrs {
+		prefix, err := netip.ParsePrefix(cidr)
+		if err != nil {
+			return nil, fmt.Errorf(
+				"trusted proxy %q: %w", cidr, err,
+			)
+		}
+
+		prefixes = append(prefixes, prefix.Masked())
+	}
+
+	return prefixes, nil
+}
+
 type loggingResponseWriter struct {
 	http.ResponseWriter
 
@@ -72,6 +121,70 @@ func ipFromHostPort(hostPort string) string {
 	return host
 }
 
+// clientIP resolves the caller's address. X-Forwarded-For and
+// X-Real-IP are honoured only when the direct peer is a
+// trusted proxy; otherwise the direct peer is returned so a
+// spoofed header cannot forge the logged address.
+func clientIP(
+	remoteAddr string,
+	header http.Header,
+	trusted []netip.Prefix,
+) string {
+	peer := ipFromHostPort(remoteAddr)
+
+	if !addrInAny(peer, trusted) {
+		return peer
+	}
+
+	if xff := firstForwardedFor(header.Get("X-Forwarded-For")); xff != "" {
+		return xff
+	}
+
+	if xr := strings.TrimSpace(header.Get("X-Real-IP")); validIP(xr) {
+		return xr
+	}
+
+	return peer
+}
+
+// firstForwardedFor returns the left-most valid address in an
+// X-Forwarded-For list (the original client), or "" if none.
+func firstForwardedFor(value string) string {
+	for part := range strings.SplitSeq(value, ",") {
+		candidate := strings.TrimSpace(part)
+		if validIP(candidate) {
+			return candidate
+		}
+	}
+
+	return ""
+}
+
+func validIP(s string) bool {
+	_, err := netip.ParseAddr(s)
+
+	return err == nil
+}
+
+// addrInAny reports whether s parses as an address contained
+// in any of the trusted prefixes.
+func addrInAny(s string, trusted []netip.Prefix) bool {
+	addr, err := netip.ParseAddr(s)
+	if err != nil {
+		return false
+	}
+
+	addr = addr.Unmap()
+
+	for _, prefix := range trusted {
+		if prefix.Contains(addr) {
+			return true
+		}
+	}
+
+	return false
+}
+
 // Logging returns middleware that logs each request with
 // timing, status code, and client information.
 func (s *Middleware) Logging() func(http.Handler) http.Handler {
@@ -96,7 +209,11 @@ func (s *Middleware) Logging() func(http.Handler) http.Handler {
 						"referer", r.Referer(),
 						"proto", r.Proto,
 						"remote_ip",
-						ipFromHostPort(r.RemoteAddr),
+						clientIP(
+							r.RemoteAddr,
+							r.Header,
+							s.trustedProxies,
+						),
 						"status", lrw.statusCode,
 						"latency_ms",
 						latency.Milliseconds(),
@@ -109,6 +226,100 @@ func (s *Middleware) Logging() func(http.Handler) http.Handler {
 	}
 }
 
+// SecurityHeaders returns middleware that sets response
+// security headers. It runs before CORS so the headers are
+// present on preflight responses the CORS handler writes.
+func (s *Middleware) SecurityHeaders() func(http.Handler) http.Handler {
+	return func(next http.Handler) http.Handler {
+		return http.HandlerFunc(
+			func(w http.ResponseWriter, r *http.Request) {
+				h := w.Header()
+				h.Set("Strict-Transport-Security", hstsValue)
+				h.Set("Content-Security-Policy", cspValue)
+				h.Set("X-Frame-Options", "DENY")
+				h.Set("X-Content-Type-Options", "nosniff")
+				h.Set("Referrer-Policy", "no-referrer")
+				h.Set("Permissions-Policy", permissionsPolicyValue)
+
+				next.ServeHTTP(w, r)
+			},
+		)
+	}
+}
+
+// writeJSONError writes the shared JSON error body with the
+// given status. Used where middleware must reject a request
+// before it reaches a handler.
+func writeJSONError(w http.ResponseWriter, status int) {
+	w.Header().Set("Content-Type", jsonContentType)
+	w.WriteHeader(status)
+	_, _ = io.WriteString(w, jsonErrorBody)
+}
+
+// MaxBodyBytes returns middleware that caps the request body at
+// limit bytes. A declared Content-Length over the limit is
+// rejected immediately with 413. Bodies without a declared
+// length (or that understate it) are capped as they are read, so
+// a handler that reads the body sees a *http.MaxBytesError it can
+// map to 413. Mounted again on a route group, it can only lower
+// the limit: a cap applied earlier in the chain still holds.
+func (s *Middleware) MaxBodyBytes(
+	limit int64,
+) func(http.Handler) http.Handler {
+	return func(next http.Handler) http.Handler {
+		return http.HandlerFunc(
+			func(w http.ResponseWriter, r *http.Request) {
+				if r.ContentLength > limit {
+					writeJSONError(
+						w,
+						http.StatusRequestEntityTooLarge,
+					)
+
+					return
+				}
+
+				r.Body = http.MaxBytesReader(w, r.Body, limit)
+
+				next.ServeHTTP(w, r)
+			},
+		)
+	}
+}
+
+// Recoverer returns middleware that recovers from a panic in a
+// downstream handler, logs the panic and stack trace through
+// slog, and responds 500 with no body. http.ErrAbortHandler is
+// re-panicked so the server can abort the response as intended.
+func (s *Middleware) Recoverer() func(http.Handler) http.Handler {
+	return func(next http.Handler) http.Handler {
+		return http.HandlerFunc(
+			func(w http.ResponseWriter, r *http.Request) {
+				defer func() {
+					rec := recover()
+					if rec == nil {
+						return
+					}
+
+					err, ok := rec.(error)
+					if ok && errors.Is(err, http.ErrAbortHandler) {
+						panic(rec)
+					}
+
+					s.log.ErrorContext(r.Context(),
+						"panic recovered",
+						"panic", fmt.Sprintf("%v", rec),
+						"stack", string(debug.Stack()),
+					)
+
+					w.WriteHeader(http.StatusInternalServerError)
+				}()
+
+				next.ServeHTTP(w, r)
+			},
+		)
+	}
+}
+
 // CORS returns middleware that adds permissive CORS headers.
 func (s *Middleware) CORS() func(http.Handler) http.Handler {
 	return cors.Handler(cors.Options{

backend/internal/middleware/middleware_test.go

@@ -0,0 +1,302 @@
+package middleware_test
+
+import (
+	"bytes"
+	"encoding/json"
+	"errors"
+	"log/slog"
+	"net/http"
+	"net/http/httptest"
+	"net/netip"
+	"strings"
+	"testing"
+
+	"sneak.berlin/go/netwatch/internal/middleware"
+)
+
+const (
+	// loopbackPeer is a remote address inside the trusted-proxy allowlist.
+	loopbackPeer = "127.0.0.1:5000"
+	// forwardedIP is the client address presented via X-Forwarded-For.
+	forwardedIP = "203.0.113.7"
+	// realIP is the client address presented via X-Real-IP.
+	realIP = "203.0.113.9"
+)
+
+func mustPrefixes(t *testing.T, cidrs ...string) []netip.Prefix {
+	t.Helper()
+
+	prefixes, err := middleware.ParseTrustedProxies(cidrs)
+	if err != nil {
+		t.Fatalf("ParseTrustedProxies(%v): %v", cidrs, err)
+	}
+
+	return prefixes
+}
+
+func TestParseTrustedProxiesRejectsMalformed(t *testing.T) {
+	t.Parallel()
+
+	_, err := middleware.ParseTrustedProxies([]string{"not-a-cidr"})
+	if err == nil {
+		t.Fatal("expected error for malformed CIDR, got nil")
+	}
+}
+
+type clientIPCase struct {
+	name       string
+	remoteAddr string
+	xff        string
+	xRealIP    string
+	want       string
+}
+
+func clientIPCases() []clientIPCase {
+	return []clientIPCase{
+		{
+			name:       "trusted proxy uses forwarded-for",
+			remoteAddr: loopbackPeer,
+			xff:        forwardedIP,
+			want:       forwardedIP,
+		},
+		{
+			name:       "trusted proxy uses left-most of chain",
+			remoteAddr: "10.1.2.3:5000",
+			xff:        forwardedIP + ", 10.1.2.3",
+			want:       forwardedIP,
+		},
+		{
+			name:       "trusted proxy falls back to x-real-ip",
+			remoteAddr: loopbackPeer,
+			xRealIP:    realIP,
+			want:       realIP,
+		},
+		{
+			name:       "untrusted peer ignores forwarded-for",
+			remoteAddr: "198.51.100.4:5000",
+			xff:        forwardedIP,
+			want:       "198.51.100.4",
+		},
+		{
+			name:       "untrusted peer ignores x-real-ip",
+			remoteAddr: "198.51.100.4:5000",
+			xRealIP:    realIP,
+			want:       "198.51.100.4",
+		},
+		{
+			name:       "trusted proxy with no headers uses peer",
+			remoteAddr: "10.1.2.3:5000",
+			want:       "10.1.2.3",
+		},
+		{
+			name:       "trusted proxy with garbage header uses peer",
+			remoteAddr: loopbackPeer,
+			xff:        "not-an-ip",
+			want:       "127.0.0.1",
+		},
+	}
+}
+
+func TestClientIP(t *testing.T) {
+	t.Parallel()
+
+	trusted := mustPrefixes(t, "127.0.0.1/32", "::1/128", "10.0.0.0/8")
+
+	for _, tc := range clientIPCases() {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			header := http.Header{}
+			if tc.xff != "" {
+				header.Set("X-Forwarded-For", tc.xff)
+			}
+
+			if tc.xRealIP != "" {
+				header.Set("X-Real-IP", tc.xRealIP)
+			}
+
+			got := middleware.ClientIP(tc.remoteAddr, header, trusted)
+			if got != tc.want {
+				t.Errorf("ClientIP() = %q, want %q", got, tc.want)
+			}
+		})
+	}
+}
+
+func TestSecurityHeaders(t *testing.T) {
+	t.Parallel()
+
+	handler := (&middleware.Middleware{}).SecurityHeaders()(
+		http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+			w.WriteHeader(http.StatusOK)
+		}),
+	)
+
+	rec := httptest.NewRecorder()
+	req := httptest.NewRequestWithContext(t.Context(), http.MethodGet, "/", http.NoBody)
+	handler.ServeHTTP(rec, req)
+
+	want := map[string]string{
+		"Strict-Transport-Security": "max-age=31536000; includeSubDomains",
+		"Content-Security-Policy":   "default-src 'none'; frame-ancestors 'none'",
+		"X-Frame-Options":           "DENY",
+		"X-Content-Type-Options":    "nosniff",
+		"Referrer-Policy":           "no-referrer",
+		"Permissions-Policy":        "camera=(), microphone=(), geolocation=()",
+	}
+
+	for name, value := range want {
+		if got := rec.Header().Get(name); got != value {
+			t.Errorf("header %s = %q, want %q", name, got, value)
+		}
+	}
+}
+
+// TestMaxBodyBytesRejectsOversizeOnNonReadingRoute confirms the
+// limit is enforced even for a handler that never reads the body
+// (for example the health check), via the Content-Length check.
+func TestMaxBodyBytesRejectsOversizeOnNonReadingRoute(t *testing.T) {
+	t.Parallel()
+
+	const limit = 16
+
+	called := false
+	handler := (&middleware.Middleware{}).MaxBodyBytes(limit)(
+		http.HandlerFunc(func(_ http.ResponseWriter, _ *http.Request) {
+			called = true
+		}),
+	)
+
+	rec := httptest.NewRecorder()
+	req := httptest.NewRequestWithContext(t.Context(),
+		http.MethodPost, "/.well-known/healthcheck",
+		strings.NewReader(strings.Repeat("x", limit+1)),
+	)
+	handler.ServeHTTP(rec, req)
+
+	if rec.Code != http.StatusRequestEntityTooLarge {
+		t.Fatalf("status = %d, want %d",
+			rec.Code, http.StatusRequestEntityTooLarge)
+	}
+
+	if called {
+		t.Fatal("handler ran despite oversize body")
+	}
+
+	if got := rec.Body.String(); got != "{\"status\":\"error\"}\n" {
+		t.Errorf("body = %q, want %q", got, "{\"status\":\"error\"}\n")
+	}
+
+	got := rec.Header().Get("Content-Type")
+	if got != "application/json; charset=utf-8" {
+		t.Errorf("Content-Type = %q, want a JSON content type", got)
+	}
+}
+
+func TestMaxBodyBytesAllowsWithinLimit(t *testing.T) {
+	t.Parallel()
+
+	const limit = 64
+
+	handler := (&middleware.Middleware{}).MaxBodyBytes(limit)(
+		http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+			w.WriteHeader(http.StatusOK)
+		}),
+	)
+
+	rec := httptest.NewRecorder()
+	req := httptest.NewRequestWithContext(t.Context(),
+		http.MethodPost, "/api/v1/reports",
+		strings.NewReader(`{"clientId":"c1"}`),
+	)
+	handler.ServeHTTP(rec, req)
+
+	if rec.Code != http.StatusOK {
+		t.Fatalf("status = %d, want %d", rec.Code, http.StatusOK)
+	}
+}
+
+func TestRecovererReturns500AndLogsThroughSlog(t *testing.T) {
+	t.Parallel()
+
+	var logbuf bytes.Buffer
+
+	mw := middleware.NewWithLogger(
+		slog.New(slog.NewJSONHandler(&logbuf, nil)),
+	)
+
+	handler := mw.Recoverer()(
+		http.HandlerFunc(func(_ http.ResponseWriter, _ *http.Request) {
+			panic("boom")
+		}),
+	)
+
+	rec := httptest.NewRecorder()
+	req := httptest.NewRequestWithContext(t.Context(), http.MethodGet, "/", http.NoBody)
+	handler.ServeHTTP(rec, req)
+
+	if rec.Code != http.StatusInternalServerError {
+		t.Fatalf("status = %d, want %d",
+			rec.Code, http.StatusInternalServerError)
+	}
+
+	var record map[string]any
+
+	err := json.Unmarshal(logbuf.Bytes(), &record)
+	if err != nil {
+		t.Fatalf("panic log is not one JSON record: %v (%q)", err, logbuf.String())
+	}
+
+	if record["msg"] != "panic recovered" || record["level"] != "ERROR" {
+		t.Errorf("log record = %v, want msg %q at level ERROR",
+			record, "panic recovered")
+	}
+
+	if record["panic"] != "boom" {
+		t.Errorf("panic field = %v, want %q", record["panic"], "boom")
+	}
+
+	stack, _ := record["stack"].(string)
+	if !strings.HasPrefix(stack, "goroutine ") {
+		t.Errorf("stack field = %q, want a stack trace", stack)
+	}
+}
+
+// TestRecovererRepanicsOnAbortHandler checks that a handler aborting
+// with http.ErrAbortHandler is not treated as a crash: Recoverer
+// panics again so the server aborts the response, and logs nothing.
+func TestRecovererRepanicsOnAbortHandler(t *testing.T) {
+	t.Parallel()
+
+	var logbuf bytes.Buffer
+
+	mw := middleware.NewWithLogger(
+		slog.New(slog.NewJSONHandler(&logbuf, nil)),
+	)
+
+	handler := mw.Recoverer()(
+		http.HandlerFunc(func(_ http.ResponseWriter, _ *http.Request) {
+			panic(http.ErrAbortHandler)
+		}),
+	)
+
+	rec := httptest.NewRecorder()
+	req := httptest.NewRequestWithContext(t.Context(), http.MethodGet, "/", http.NoBody)
+
+	var recovered any
+
+	func() {
+		defer func() { recovered = recover() }()
+
+		handler.ServeHTTP(rec, req)
+	}()
+
+	err, _ := recovered.(error)
+	if !errors.Is(err, http.ErrAbortHandler) {
+		t.Errorf("Recoverer panicked with %v, want http.ErrAbortHandler", recovered)
+	}
+
+	if logbuf.Len() != 0 {
+		t.Errorf("abort was logged: %q", logbuf.String())
+	}
+}

backend/internal/reportbuf/reportbuf.go

@@ -45,6 +45,7 @@ type Buffer struct {
 	done     chan struct{}
 	log      *slog.Logger
 	mu       sync.Mutex
+	stopOnce sync.Once
 }
 
 // New creates a Buffer and registers lifecycle hooks to
@@ -76,10 +77,19 @@ func New(
 			return nil
 		},
 		OnStop: func(_ context.Context) error {
-			close(b.done)
+			// stopOnce makes OnStop idempotent: a second
-			b.flushLocked()
+			// invocation must not close an already-closed channel
+			// (which would panic) or flush again.
+			var err error
 
-			return nil
+			b.stopOnce.Do(func() {
+				close(b.done)
+				err = b.flushLocked()
+			})
+
+			// A failed final flush fails the stop, so the process
+			// exits non-zero.
+			return err
 		},
 	})
 
@@ -103,7 +113,12 @@ func (b *Buffer) Append(v any) error {
 		data := b.drainBuf()
 		b.mu.Unlock()
 
-		go b.writeFile(data)
+		go func() {
+			writeErr := b.writeFile(data)
+			if writeErr != nil {
+				b.log.Error("flush reports failed", "error", writeErr)
+			}
+		}()
 
 		return nil
 	}
@@ -122,7 +137,10 @@ func (b *Buffer) flushLoop() {
 	for {
 		select {
 		case <-ticker.C:
-			b.flushLocked()
+			err := b.flushLocked()
+			if err != nil {
+				b.log.Error("flush reports failed", "error", err)
+			}
 		case <-b.done:
 			return
 		}
@@ -131,19 +149,19 @@ func (b *Buffer) flushLoop() {
 
 // flushLocked acquires the lock, drains the buffer, and
 // writes the data to a compressed file.
-func (b *Buffer) flushLocked() {
+func (b *Buffer) flushLocked() error {
 	b.mu.Lock()
 
 	if b.buf.Len() == 0 {
 		b.mu.Unlock()
 
-		return
+		return nil
 	}
 
 	data := b.drainBuf()
 	b.mu.Unlock()
 
-	b.writeFile(data)
+	return b.writeFile(data)
 }
 
 // drainBuf copies the buffer contents and resets it.
@@ -158,42 +176,48 @@ func (b *Buffer) drainBuf() []byte {
 
 // writeFile creates a timestamped zstd-compressed JSONL file
 // in the data directory.
-func (b *Buffer) writeFile(data []byte) {
+func (b *Buffer) writeFile(data []byte) error {
 	ts := time.Now().UTC().Format("2006-01-02T15-04-05.000Z")
 	name := fmt.Sprintf("reports-%s.jsonl.zst", ts)
 	path := filepath.Join(b.dataDir, name)
 
-	f, err := os.OpenFile( //nolint:gosec // path built from controlled dataDir + timestamp
+	// 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
 		path,
 		os.O_WRONLY|os.O_CREATE|os.O_EXCL,
 		filePerms,
 	)
 	if err != nil {
-		b.log.Error("create report file", "error", err)
+		return fmt.Errorf("create report file: %w", err)
-
-		return
 	}
 
+	// Closes the file on the early returns below. The success
+	// path closes it explicitly to check the error; closing it
+	// a second time here is harmless.
 	defer func() { _ = f.Close() }()
 
 	enc, err := zstd.NewWriter(f)
 	if err != nil {
-		b.log.Error("create zstd encoder", "error", err)
+		return fmt.Errorf("create zstd encoder: %w", err)
-
-		return
 	}
 
-	_, writeErr := enc.Write(data)
+	_, err = enc.Write(data)
-	if writeErr != nil {
+	if err != nil {
-		b.log.Error("write compressed data", "error", writeErr)
-
 		_ = enc.Close()
 
-		return
+		return fmt.Errorf("write compressed data: %w", err)
 	}
 
-	closeErr := enc.Close()
+	err = enc.Close()
-	if closeErr != nil {
+	if err != nil {
-		b.log.Error("close zstd encoder", "error", closeErr)
+		return fmt.Errorf("close zstd encoder: %w", err)
 	}
+
+	err = f.Close()
+	if err != nil {
+		return fmt.Errorf("close report file: %w", err)
+	}
+
+	return nil
 }

backend/internal/reportbuf/reportbuf_test.go

@@ -1,13 +1,119 @@
 package reportbuf_test
 
 import (
+	"errors"
+	"io/fs"
+	"os"
+	"strings"
 	"testing"
 
-	_ "sneak.berlin/go/netwatch/internal/reportbuf"
+	"sneak.berlin/go/netwatch/internal/config"
+	"sneak.berlin/go/netwatch/internal/globals"
+	"sneak.berlin/go/netwatch/internal/logger"
+	"sneak.berlin/go/netwatch/internal/reportbuf"
+
+	"go.uber.org/fx"
+	"go.uber.org/fx/fxtest"
 )
 
-func TestImport(t *testing.T) {
+// TestFlushOnShutdown proves the flush-on-shutdown path: a
-	t.Parallel()
+// report appended after start but before the periodic flush
-	// Compilation check — verifies the package parses
+// window must reach disk when the fx lifecycle stops. This is
-	// and all imports resolve.
+// the exact case that silent data loss on restart used to
+// destroy.
+func TestFlushOnShutdown(t *testing.T) {
+	dir := t.TempDir()
+	t.Setenv("DATA_DIR", dir)
+
+	var buf *reportbuf.Buffer
+
+	app := fxtest.New(t,
+		fx.Provide(
+			globals.New,
+			logger.New,
+			config.New,
+			reportbuf.New,
+		),
+		fx.Populate(&buf),
+	)
+
+	app.RequireStart()
+
+	err := buf.Append(map[string]string{"probe": "shutdown"})
+	if err != nil {
+		t.Fatalf("append report: %v", err)
+	}
+
+	// RequireStop runs the reportbuf OnStop hook, which is the
+	// only code path that flushes buffered reports on shutdown.
+	app.RequireStop()
+
+	if !hasReportFile(t, dir) {
+		t.Fatal("no report file on disk after shutdown; " +
+			"the buffered report was lost")
+	}
+}
+
+// TestFailedFinalFlushFailsStop proves a final flush that cannot
+// write its file makes the stop fail, which makes the process
+// exit non-zero instead of dropping the buffered reports silently.
+func TestFailedFinalFlushFailsStop(t *testing.T) {
+	dir := t.TempDir()
+	t.Setenv("DATA_DIR", dir)
+
+	var buf *reportbuf.Buffer
+
+	app := fxtest.New(t,
+		fx.Provide(
+			globals.New,
+			logger.New,
+			config.New,
+			reportbuf.New,
+		),
+		fx.Populate(&buf),
+	)
+
+	app.RequireStart()
+
+	err := buf.Append(map[string]string{"probe": "shutdown"})
+	if err != nil {
+		t.Fatalf("append report: %v", err)
+	}
+
+	// Removing the data directory leaves the final flush nowhere to
+	// write. A read-only directory would not do: tests run as root
+	// in the backend image, and root ignores the read-only bit.
+	err = os.RemoveAll(dir)
+	if err != nil {
+		t.Fatalf("remove data dir: %v", err)
+	}
+
+	err = app.Stop(t.Context())
+	if !errors.Is(err, fs.ErrNotExist) {
+		t.Fatalf("stop error = %v, want the final flush's error", err)
+	}
+}
+
+func hasReportFile(t *testing.T, dir string) bool {
+	t.Helper()
+
+	entries, err := os.ReadDir(dir)
+	if err != nil {
+		t.Fatalf("read data dir: %v", err)
+	}
+
+	for _, e := range entries {
+		if strings.HasSuffix(e.Name(), ".jsonl.zst") {
+			info, statErr := e.Info()
+			if statErr != nil {
+				t.Fatalf("stat %s: %v", e.Name(), statErr)
+			}
+
+			if info.Size() > 0 {
+				return true
+			}
+		}
+	}
+
+	return false
 }

backend/internal/server/export_test.go

@@ -0,0 +1,5 @@
+package server
+
+// MaxRequestBodyBytes exposes the router-wide body limit to the
+// external tests.
+const MaxRequestBodyBytes = maxRequestBodyBytes

backend/internal/server/http.go

@@ -5,39 +5,62 @@ import (
 	"fmt"
 	"net/http"
 	"time"
+
+	"go.uber.org/fx"
 )
 
 const (
 	readTimeout       = 10 * time.Second
-	writeTimeout   = 10 * time.Second
+	readHeaderTimeout = 5 * time.Second
+	idleTimeout       = 60 * time.Second
 	maxHeaderBytes    = 1 << 20 // 1 MiB
+
+	// requestTimeout (routes.go) is the single per-request
+	// processing budget, enforced by chi's middleware.Timeout.
+	// writeTimeout must exceed that budget so a handler can write
+	// its 503 when the chi timeout fires; if it were shorter the
+	// server would abort the write first and the chi budget would
+	// be unreachable dead configuration.
+	writeTimeout = requestTimeout + 5*time.Second
 )
 
-func (s *Server) serveUntilShutdown() {
+// newHTTPServer constructs the http.Server. It performs no I/O
+// and does not start listening.
+func (s *Server) newHTTPServer() *http.Server {
 	listenAddr := fmt.Sprintf(":%d", s.params.Config.Port)
 
-	s.httpServer = &http.Server{
+	return &http.Server{
 		Addr:              listenAddr,
 		Handler:           s,
 		MaxHeaderBytes:    maxHeaderBytes,
 		ReadTimeout:       readTimeout,
+		ReadHeaderTimeout: readHeaderTimeout,
 		WriteTimeout:      writeTimeout,
+		IdleTimeout:       idleTimeout,
 	}
+}
 
-	s.SetupRoutes()
+// listenAndServe runs the listener until the server is shut
-
+// down. A genuine listen failure (not the expected
+// ErrServerClosed from a clean shutdown) requests process
+// shutdown through fx with a non-zero exit code, so the failure
+// is visible to any supervisor.
+func (s *Server) listenAndServe() {
 	s.log.Info("http begin listen",
-		"listenaddr", listenAddr,
+		"listenaddr", s.httpServer.Addr,
 		"version", s.params.Globals.Version,
 		"buildarch", s.params.Globals.Buildarch,
 	)
 
 	err := s.httpServer.ListenAndServe()
-	if err != nil && !errors.Is(err, http.ErrServerClosed) {
+	if err == nil || errors.Is(err, http.ErrServerClosed) {
+		return
+	}
+
 	s.log.Error("listen error", "error", err)
 
-		if s.cancelFunc != nil {
+	shutdownErr := s.shutdowner.Shutdown(fx.ExitCode(1))
-			s.cancelFunc()
+	if shutdownErr != nil {
-		}
+		s.log.Error("request shutdown failed", "error", shutdownErr)
 	}
 }

backend/internal/server/routes.go

@@ -7,17 +7,26 @@ import (
 	"github.com/go-chi/chi/v5/middleware"
 )
 
-const requestTimeout = 60 * time.Second
+const (
+	requestTimeout = 60 * time.Second
+
+	// maxRequestBodyBytes caps every request body. A route group
+	// can mount s.mw.MaxBodyBytes with a smaller value to lower
+	// its bound, but cannot raise it: this cap runs first.
+	maxRequestBodyBytes int64 = 1 << 20 // 1 MiB
+)
 
 // SetupRoutes configures the chi router with middleware and
 // all application routes.
 func (s *Server) SetupRoutes() {
 	s.router = chi.NewRouter()
 
-	s.router.Use(middleware.Recoverer)
+	s.router.Use(s.mw.Recoverer())
 	s.router.Use(middleware.RequestID)
 	s.router.Use(s.mw.Logging())
+	s.router.Use(s.mw.SecurityHeaders())
 	s.router.Use(s.mw.CORS())
+	s.router.Use(s.mw.MaxBodyBytes(maxRequestBodyBytes))
 	s.router.Use(middleware.Timeout(requestTimeout))
 
 	s.router.Get(

backend/internal/server/routes_test.go

@@ -0,0 +1,76 @@
+package server_test
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"sneak.berlin/go/netwatch/internal/config"
+	"sneak.berlin/go/netwatch/internal/globals"
+	"sneak.berlin/go/netwatch/internal/handlers"
+	"sneak.berlin/go/netwatch/internal/healthcheck"
+	"sneak.berlin/go/netwatch/internal/logger"
+	"sneak.berlin/go/netwatch/internal/middleware"
+	"sneak.berlin/go/netwatch/internal/reportbuf"
+	"sneak.berlin/go/netwatch/internal/server"
+
+	"go.uber.org/fx"
+	"go.uber.org/fx/fxtest"
+)
+
+// TestHealthCheckRejectsOversizeBody sends the health check, which
+// never reads its body, a body one byte over the limit. Only the
+// router-wide body limit can reject it.
+func TestHealthCheckRejectsOversizeBody(t *testing.T) {
+	t.Parallel()
+
+	var srv *server.Server
+
+	// The same constructors as main, never started: SetupRoutes is
+	// called directly, so nothing listens.
+	app := fxtest.New(t,
+		fx.Provide(
+			config.New,
+			globals.New,
+			handlers.New,
+			healthcheck.New,
+			logger.New,
+			middleware.New,
+			reportbuf.New,
+			server.New,
+		),
+		fx.Populate(&srv),
+	)
+
+	err := app.Err()
+	if err != nil {
+		t.Fatalf("build server: %v", err)
+	}
+
+	srv.SetupRoutes()
+
+	rec := httptest.NewRecorder()
+	req := httptest.NewRequestWithContext(t.Context(),
+		http.MethodGet, "/.well-known/healthcheck",
+		strings.NewReader(
+			strings.Repeat("x", int(server.MaxRequestBodyBytes)+1),
+		),
+	)
+
+	srv.ServeHTTP(rec, req)
+
+	if rec.Code != http.StatusRequestEntityTooLarge {
+		t.Fatalf("status = %d, want %d",
+			rec.Code, http.StatusRequestEntityTooLarge)
+	}
+
+	if got := rec.Body.String(); got != "{\"status\":\"error\"}\n" {
+		t.Errorf("body = %q, want %q", got, "{\"status\":\"error\"}\n")
+	}
+
+	got := rec.Header().Get("Content-Type")
+	if got != "application/json; charset=utf-8" {
+		t.Errorf("Content-Type = %q, want a JSON content type", got)
+	}
+}

backend/internal/server/server.go

@@ -1,16 +1,14 @@
 // Package server provides the HTTP server lifecycle,
-// including startup, routing, signal handling, and graceful
+// including startup, routing, and graceful shutdown. The
-// shutdown.
+// process lifetime is owned by fx: shutdown is requested
+// through fx.Shutdowner so every component's OnStop hook runs
+// in dependency order.
 package server
 
 import (
 	"context"
 	"log/slog"
 	"net/http"
-	"os"
-	"os/signal"
-	"syscall"
-	"time"
 
 	"sneak.berlin/go/netwatch/internal/config"
 	"sneak.berlin/go/netwatch/internal/globals"
@@ -31,19 +29,18 @@ type Params struct {
 	Handlers   *handlers.Handlers
 	Logger     *logger.Logger
 	Middleware *middleware.Middleware
+	Shutdowner fx.Shutdowner
 }
 
 // Server is the top-level HTTP server orchestrator.
 type Server struct {
-	cancelFunc  context.CancelFunc
-	exitCode    int
 	h          *handlers.Handlers
 	httpServer *http.Server
 	log        *slog.Logger
 	mw         *middleware.Middleware
 	params     Params
 	router     *chi.Mux
-	startupTime time.Time
+	shutdowner fx.Shutdowner
 }
 
 // New creates a Server and registers lifecycle hooks for
@@ -57,23 +54,25 @@ func New(
 	s.mw = params.Middleware
 	s.h = params.Handlers
 	s.log = params.Logger.Get()
+	s.shutdowner = params.Shutdowner
 
 	lc.Append(fx.Hook{
 		OnStart: func(_ context.Context) error {
-			s.startupTime = time.Now().UTC()
+			// Build the router and http.Server synchronously
+			// here, before spawning the serving goroutine, so
+			// httpServer is fully constructed by the time OnStop
+			// (or an early signal) can read it. fx guarantees
+			// OnStart returns before OnStop runs, so no
+			// synchronization or nil check is needed at shutdown.
+			s.SetupRoutes()
+			s.httpServer = s.newHTTPServer()
 
-			go func() { //nolint:contextcheck // fx OnStart ctx is startup-only; run() creates its own
+			go s.listenAndServe()
-				s.run()
-			}()
 
 			return nil
 		},
-		OnStop: func(_ context.Context) error {
+		OnStop: func(ctx context.Context) error {
-			if s.cancelFunc != nil {
+			return s.shutdown(ctx)
-				s.cancelFunc()
-			}
-
-			return nil
 		},
 	})
 
@@ -88,60 +87,17 @@ func (s *Server) ServeHTTP(
 	s.router.ServeHTTP(w, r)
 }
 
-func (s *Server) run() {
+// shutdown gracefully stops the HTTP server within the
-	exitCode := s.serve()
+// deadline of the context fx provides for OnStop.
-	os.Exit(exitCode)
+func (s *Server) shutdown(ctx context.Context) error {
-}
+	err := s.httpServer.Shutdown(ctx)
-
-func (s *Server) serve() int {
-	var ctx context.Context //nolint:wsl // ctx must be declared before multi-assign
-
-	ctx, s.cancelFunc = context.WithCancel(
-		context.Background(),
-	)
-
-	go func() {
-		c := make(chan os.Signal, 1)
-
-		signal.Ignore(syscall.SIGPIPE)
-		signal.Notify(c, os.Interrupt, syscall.SIGTERM)
-
-		sig := <-c
-		s.log.Info("signal received", "signal", sig)
-
-		if s.cancelFunc != nil {
-			s.cancelFunc()
-		}
-	}()
-
-	go func() {
-		s.serveUntilShutdown()
-	}()
-
-	<-ctx.Done()
-	s.cleanShutdown()
-
-	return s.exitCode
-}
-
-const shutdownTimeout = 5 * time.Second
-
-func (s *Server) cleanShutdown() {
-	s.exitCode = 0
-
-	ctxShutdown, shutdownCancel := context.WithTimeout(
-		context.Background(),
-		shutdownTimeout,
-	)
-	defer shutdownCancel()
-
-	err := s.httpServer.Shutdown(ctxShutdown)
 	if err != nil {
-		s.log.Error(
+		s.log.Error("server clean shutdown failed", "error", err)
-			"server clean shutdown failed",
+
-			"error", err,
+		return err
-		)
 	}
 
 	s.log.Info("server stopped")
+
+	return nil
 }

package.json

@@ -14,6 +14,7 @@
         "autoprefixer": "^10.4.23",
         "postcss": "^8.5.6",
         "prettier": "^3.8.1",
+        "puppeteer-core": "25.5.0",
         "tailwindcss": "^4.1.18",
         "vite": "^7.3.1"
     }

script/frontend-viewport-test

@@ -0,0 +1,102 @@
+#!/bin/sh
+# script/frontend-viewport-test: verify the responsive layout of the built
+# frontend in a real browser engine.
+#
+# Builds dist/, serves it with the same nginx image and the same nginx.conf
+# the shipping container uses, points a containerised headless Chrome at it
+# over CDP, and asserts on computed layout at every viewport width derived
+# from the app's own CSS. See test/viewport/README.md for what this covers
+# and what it cannot.
+#
+# Deliberately not part of script/check: it needs Docker and takes far
+# longer than the 20s budget make test has to stay inside.
+set -eu
+
+ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
+
+# chromedp/headless-shell 151.0.7922.109, 2026-08-09
+BROWSER_IMAGE="chromedp/headless-shell@sha256:2d349b544a1ea6b5b5fd7c0fe99215ff662339c57407ee2e8c0a11af93516b04"
+# nginx:stable-alpine, 2026-02-22 (the digest Dockerfile ships)
+SERVER_IMAGE="nginx@sha256:15e96e59aa3b0aada3a121296e3bce117721f42d88f5f64217ef4b18f458c6ab"
+# node:22-alpine, 2026-02-22 (the digest Dockerfile builds with)
+NODE_IMAGE="node@sha256:e4bf2a82ad0a4037d28035ae71529873c069b13eb0455466ae0bc13363826e34"
+
+RUN_ID="$$-$(date +%s)"
+NETWORK="netwatch-viewport-$RUN_ID"
+SERVER="netwatch-viewport-server-$RUN_ID"
+BROWSER="netwatch-viewport-browser-$RUN_ID"
+HARNESS="netwatch-viewport-harness-$RUN_ID"
+ARTIFACT_DIR="$ROOT/tmp/viewport"
+
+# Every container is named and removed here, including the harness itself:
+# `timeout` below kills the `docker run` client, not the container it
+# started, and an unnamed survivor keeps the --internal network in use so
+# `docker network rm` fails too. This host runs many sessions at once and
+# neither may be left behind.
+cleanup() {
+    docker rm -f "$HARNESS" > /dev/null 2>&1 || true
+    docker rm -f "$BROWSER" > /dev/null 2>&1 || true
+    docker rm -f "$SERVER" > /dev/null 2>&1 || true
+    docker network rm "$NETWORK" > /dev/null 2>&1 || true
+}
+trap cleanup EXIT INT TERM
+
+main() {
+    cd "$ROOT"
+
+    # Test what ships: the production build, not a dev server.
+    "$ROOT/script/test"
+    if [ ! -f "$ROOT/dist/index.html" ]; then
+        echo "frontend-viewport-test: dist/index.html missing after build" >&2
+        exit 1
+    fi
+
+    mkdir -p "$ARTIFACT_DIR"
+
+    # An --internal network has no route off the host, so the browser
+    # cannot reach the real internet no matter what the page asks for.
+    # Latency probes are answered by the harness instead. This also means
+    # no port can be published from it, which is why the harness itself
+    # runs as a third container on the same network rather than on the
+    # host.
+    docker network create --internal "$NETWORK" > /dev/null
+
+    docker run -d --rm --name "$SERVER" \
+        --network "$NETWORK" --network-alias netwatch \
+        -v "$ROOT/dist:/usr/share/nginx/html:ro" \
+        -v "$ROOT/nginx.conf:/etc/nginx/conf.d/default.conf:ro" \
+        "$SERVER_IMAGE" > /dev/null
+
+    # The image's own entrypoint already exposes CDP on 9222 and passes
+    # --no-sandbox, so only extra flags belong here; re-specifying the
+    # debugging port collides with it and leaves the endpoint bound to
+    # loopback only. --hide-scrollbars keeps innerWidth equal to
+    # clientWidth, so the overflow assertion has no scrollbar-sized slack
+    # to hide behind, and matches the overlay scrollbars phones use.
+    docker run -d --rm --name "$BROWSER" --init --shm-size=1g \
+        --network "$NETWORK" \
+        "$BROWSER_IMAGE" \
+        --hide-scrollbars \
+        > /dev/null
+
+    # Chrome refuses DevTools requests whose Host header is neither
+    # localhost nor an IP address, so dial the container by address rather
+    # than by its network alias.
+    browser_ip="$(docker inspect \
+        -f '{{range .NetworkSettings.Networks}}{{.IPAddress}}{{end}}' \
+        "$BROWSER")"
+
+    timeout 900 docker run --rm --init --name "$HARNESS" \
+        --network "$NETWORK" \
+        --user "$(id -u):$(id -g)" \
+        -v "$ROOT:/app" \
+        -w /app \
+        -e NETWATCH_ROOT=/app \
+        -e NETWATCH_BASE_URL=http://netwatch:8080 \
+        -e "NETWATCH_CDP_URL=http://$browser_ip:9222" \
+        -e NETWATCH_ARTIFACT_DIR=/app/tmp/viewport \
+        "$NODE_IMAGE" \
+        node test/viewport/harness.js
+}
+
+main "$@"

src/main.js

@@ -7,9 +7,11 @@ import "./styles.css";
 // graphMaxLatency — values above it pin to the top of the chart but still
 // display their real value in the latency figure. The history buffer holds
 // maxHistoryPoints samples (historyDuration / updateInterval).
+// reportInterval is how often collected samples are POSTed to the backend.
 const CONFIG = {
     updateInterval: 3000,
     maxHistoryPoints: 100,
+    reportInterval: 60000,
     get historyDuration() {
         return (this.maxHistoryPoints * this.updateInterval) / 1000;
     },
@@ -346,6 +348,159 @@ class AppState {
     }
 }
 
+// --- Reporting ---------------------------------------------------------------
+
+// A random UUIDv4. `crypto.randomUUID` exists only in secure contexts
+// (HTTPS or localhost); over plain HTTP to any other host — the normal LAN
+// deployment — it is undefined, so feature-detect it and otherwise build the
+// id from `crypto.getRandomValues`, which is available in insecure contexts.
+function randomId() {
+    if (typeof crypto !== "undefined" && crypto.randomUUID) {
+        return crypto.randomUUID();
+    }
+    const bytes = new Uint8Array(16);
+    crypto.getRandomValues(bytes);
+    bytes[6] = (bytes[6] & 0x0f) | 0x40; // version 4
+    bytes[8] = (bytes[8] & 0x3f) | 0x80; // variant 1
+    const hex = [...bytes].map((b) => b.toString(16).padStart(2, "0"));
+    return (
+        hex.slice(0, 4).join("") +
+        "-" +
+        hex.slice(4, 6).join("") +
+        "-" +
+        hex.slice(6, 8).join("") +
+        "-" +
+        hex.slice(8, 10).join("") +
+        "-" +
+        hex.slice(10, 16).join("")
+    );
+}
+
+// A random id identifying this browser across reports. Generated once and
+// kept in localStorage; if storage is unavailable (e.g. private mode) a
+// fresh id is used for this session only.
+function getClientId() {
+    const key = "netwatch-client-id";
+    try {
+        let id = localStorage.getItem(key);
+        if (!id) {
+            id = randomId();
+            localStorage.setItem(key, id);
+        }
+        return id;
+    } catch {
+        return randomId();
+    }
+}
+
+// Build the delta report body the backend decodes, plus the new per-host
+// high-water marks. Pure function of the passed state: `hosts` is an array
+// of { name, url, status, history }, `since` maps a host url to the Unix-ms
+// timestamp of the last sample already reported for it, and `now` is a Date.
+// Only non-paused samples newer than the mark are included. Returns null
+// when no host has an unreported sample.
+export function buildReport(hosts, clientId, now, since) {
+    const reportHosts = [];
+    const marks = new Map();
+    for (const host of hosts) {
+        const mark = since.get(host.url) ?? 0;
+        const samples = [];
+        let high = mark;
+        for (const p of host.history) {
+            if (p.paused) continue;
+            if (p.timestamp <= mark) continue;
+            samples.push({
+                t: p.timestamp,
+                latency: p.latency,
+                error: p.error ?? null,
+            });
+            if (p.timestamp > high) high = p.timestamp;
+        }
+        if (samples.length === 0) continue;
+        reportHosts.push({
+            name: host.name,
+            url: host.url,
+            status: host.status,
+            history: samples,
+        });
+        marks.set(host.url, high);
+    }
+    if (reportHosts.length === 0) return null;
+    return {
+        body: {
+            clientId,
+            geo: null,
+            hosts: reportHosts,
+            timestamp: now.toISOString(),
+        },
+        marks,
+    };
+}
+
+// Periodically POSTs unreported samples to the same-origin backend. Holds
+// the per-host high-water marks so each report is a delta; marks only
+// advance on a delivered report, so a failed POST simply re-sends those
+// samples next interval (bounded by the history window — whatever has since
+// fallen out is dropped). Failure is quiet: one debug line per outage, one
+// on recovery, never an alert, never a tight retry loop.
+//
+// Only one report is ever in flight, and it is abandoned after half the
+// interval, so a slow POST can neither overlap the next report (which would
+// carry the same samples) nor stall reporting for good.
+class Reporter {
+    constructor(state, clientId, intervalMs) {
+        this.state = state;
+        this.clientId = clientId;
+        this.intervalMs = intervalMs;
+        this.marks = new Map();
+        this.failing = false;
+        this.sending = false;
+        this.timerId = null;
+    }
+
+    start() {
+        if (this.timerId) return;
+        this.timerId = setInterval(() => this.flush(), this.intervalMs);
+    }
+
+    async flush() {
+        if (this.sending || this.state.paused) return;
+        const report = buildReport(
+            this.state.allHosts,
+            this.clientId,
+            new Date(),
+            this.marks,
+        );
+        if (!report) return;
+        this.sending = true;
+        try {
+            const resp = await fetch("/api/v1/reports", {
+                method: "POST",
+                headers: { "Content-Type": "application/json" },
+                credentials: "omit",
+                body: JSON.stringify(report.body),
+                signal: AbortSignal.timeout(this.intervalMs / 2),
+            });
+            if (!resp.ok) throw new Error(`HTTP ${resp.status}`);
+            for (const [url, t] of report.marks) {
+                const current = this.marks.get(url) ?? 0;
+                this.marks.set(url, Math.max(current, t));
+            }
+            if (this.failing) {
+                log.debug("Report delivery recovered");
+                this.failing = false;
+            }
+        } catch (err) {
+            if (!this.failing) {
+                log.debug(`Report delivery failed: ${err.message}`);
+                this.failing = true;
+            }
+        } finally {
+            this.sending = false;
+        }
+    }
+}
+
 // --- Latency Measurement -----------------------------------------------------
 
 async function measureLatency(url) {
@@ -537,6 +692,12 @@ class SparklineRenderer {
 
 // --- UI Renderer -------------------------------------------------------------
 
+// The per-host status line must stay wrappable: its populated content is
+// wider than the host column at a 320px viewport, and `whitespace-nowrap`
+// here overflows the element and forces the whole document to scroll
+// horizontally.
+const STATUS_TEXT_CLASS = "status-text text-xs text-right col-span-2 mt-5";
+
 function hostRowHTML(host, index, showPin = true) {
     const pinColor = host.pinned
         ? "text-blue-500"
@@ -562,7 +723,7 @@ function hostRowHTML(host, index, showPin = true) {
             <span class="text-gray-500">---</span>
           </div>
           <a href="${host.url}" target="_blank" rel="noopener" class="text-xs text-gray-500 truncate block col-span-2 -mt-2">${host.url}</a>
-          <div class="status-text text-xs text-gray-500 whitespace-nowrap text-right col-span-2 mt-5" data-host="${index}">waiting...</div>
+          <div class="${STATUS_TEXT_CLASS} text-gray-500" data-host="${index}">waiting...</div>
         </div>
         <div class="flex-grow sparkline-container rounded overflow-hidden border border-gray-700/30">
           <canvas class="sparkline-canvas w-full" data-host="${index}" height="${CONFIG.canvasHeight}"></canvas>
@@ -671,7 +832,7 @@ function buildUI(state) {
         </p>
         <p class="mt-2"><a href="https://git.eeqj.de/sneak/netwatch/commit/${__COMMIT_FULL__}" target="_blank" rel="noopener" class="text-gray-600 hover:text-gray-400">${__COMMIT_HASH__}</a></p>
         <p class="mt-2">
-          <label class="cursor-pointer">
+          <label class="debug-toggle-label cursor-pointer">
             <input type="checkbox" id="debug-toggle" class="mr-1">
             <span>Debug log</span>
           </label>
@@ -688,6 +849,26 @@ function buildUI(state) {
 
 // --- UI Updaters -------------------------------------------------------------
 
+// Renders `min 1ms / med 2ms / avg 3ms / max 4ms`. Each label, value and
+// trailing separator is one unbreakable unit, so wrapping only ever happens
+// between stats and a wrapped line never starts with a separator.
+function statusStatsHTML(stats) {
+    return stats
+        .map(([label, value], i) => {
+            const sep =
+                i < stats.length - 1
+                    ? ` <span class="text-gray-500">/</span>`
+                    : "";
+            return (
+                `<span class="whitespace-nowrap">` +
+                `<span class="text-gray-400">${label} </span>` +
+                `<span class="${latencyClass(value, "online")}">${value}ms</span>` +
+                `${sep}</span>`
+            );
+        })
+        .join(" ");
+}
+
 function updateHostRow(host, index) {
     const latencyEl = document.querySelector(
         `.latency-value[data-host="${index}"]`,
@@ -712,28 +893,22 @@ function updateHostRow(host, index) {
     const min = host.minLatency();
     const max = host.maxLatency();
     if (host.status === "online" && avg !== null) {
-        statusEl.innerHTML =
+        statusEl.innerHTML = statusStatsHTML([
-            `<span class="text-gray-400">min </span><span class="${latencyClass(min, "online")}">${min}ms</span>` +
+            ["min", min],
-            ` <span class="text-gray-500">/</span> ` +
+            ["med", med],
-            `<span class="text-gray-400">med </span><span class="${latencyClass(med, "online")}">${med}ms</span>` +
+            ["avg", avg],
-            ` <span class="text-gray-500">/</span> ` +
+            ["max", max],
-            `<span class="text-gray-400">avg </span><span class="${latencyClass(avg, "online")}">${avg}ms</span>` +
+        ]);
-            ` <span class="text-gray-500">/</span> ` +
+        statusEl.className = STATUS_TEXT_CLASS;
-            `<span class="text-gray-400">max </span><span class="${latencyClass(max, "online")}">${max}ms</span>`;
-        statusEl.className =
-            "status-text text-xs whitespace-nowrap text-right col-span-2 mt-5";
     } else if (host.status === "offline") {
         statusEl.textContent = "unreachable";
-        statusEl.className =
+        statusEl.className = `${STATUS_TEXT_CLASS} text-red-400`;
-            "status-text text-xs text-red-400 whitespace-nowrap text-right col-span-2 mt-5";
     } else if (host.status === "error") {
         statusEl.textContent = "timeout";
-        statusEl.className =
+        statusEl.className = `${STATUS_TEXT_CLASS} text-orange-400`;
-            "status-text text-xs text-orange-400 whitespace-nowrap text-right col-span-2 mt-5";
     } else {
         statusEl.textContent = "connecting...";
-        statusEl.className =
+        statusEl.className = `${STATUS_TEXT_CLASS} text-gray-500`;
-            "status-text text-xs text-gray-500 whitespace-nowrap text-right col-span-2 mt-5";
     }
 
     SparklineRenderer.draw(canvas, host.history);
@@ -1044,8 +1219,7 @@ function greyOutUI(state) {
         }
         if (statusEl) {
             statusEl.textContent = "paused";
-            statusEl.className =
+            statusEl.className = `${STATUS_TEXT_CLASS} text-gray-500`;
-                "status-text text-xs text-gray-500 whitespace-nowrap text-right col-span-2 mt-5";
         }
         // Grey out the status dot
         const row = document.querySelector(`.host-row[data-index="${i}"]`);
@@ -1143,6 +1317,19 @@ async function init() {
     buildUI(state);
     log.info("UI built, starting tick loop");
 
+    // Reporting is best-effort: any failure setting it up (e.g. no usable
+    // crypto for the client id) must never stop the monitor from probing.
+    try {
+        const reporter = new Reporter(
+            state,
+            getClientId(),
+            CONFIG.reportInterval,
+        );
+        reporter.start();
+    } catch (err) {
+        log.error(`Reporting disabled: ${err.message}`);
+    }
+
     document
         .getElementById("pause-btn")
         .addEventListener("click", () => togglePause(state));
@@ -1255,8 +1442,13 @@ async function init() {
     setTimeout(() => handleResize(state), 100);
 }
 
-if (document.readyState === "loading") {
+// Bootstrap only when loaded as the page: a real DOM containing the #app
+// mount point this module renders into. Importing the module in a unit test
+// (which has no #app) runs nothing, so buildReport can be tested in isolation.
+if (typeof document !== "undefined" && document.getElementById("app")) {
+    if (document.readyState === "loading") {
         document.addEventListener("DOMContentLoaded", init);
-} else {
+    } else {
         init();
+    }
 }

src/styles.css

@@ -14,6 +14,38 @@ body {
         ui-monospace, SFMono-Regular, "SF Mono", Menlo, Consolas, monospace;
 }
 
+/* ---- Minimum tap targets ----------------------------------------------
+   Every interactive control is at least 44x44 CSS px (Apple HIG, WCAG 2.2
+   SC 2.5.5). Not scoped to a breakpoint or to `pointer: coarse`: a large
+   phone in landscape is above the 768px breakpoint and still a touch
+   device. */
+
+/* The button grows to 44x44 while the negative margins keep its layout
+   footprint at the 16x16 of the icon inside it, so row height and the
+   icon's position are unchanged. */
+.pin-btn {
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    width: 2.75rem;
+    height: 2.75rem;
+    margin: -0.875rem;
+}
+
+/* A select paints its own background and border, so it has to actually be
+   44 tall rather than borrow the trick above. */
+#interval-select {
+    min-height: 2.75rem;
+}
+
+/* The tappable target for #debug-toggle is the label wrapping it. */
+.debug-toggle-label {
+    display: inline-flex;
+    align-items: center;
+    justify-content: center;
+    min-height: 2.75rem;
+}
+
 .sparkline-container {
     background: linear-gradient(
         to bottom,
@@ -38,9 +70,10 @@ body {
         gap: 0.75rem;
     }
 
-    /* Pause button: smaller on mobile */
+    /* Pause button: smaller on mobile, but not below the tap-target floor */
     #pause-btn {
         padding: 0.5rem 1rem;
+        min-height: 2.75rem;
     }
 
     #pause-btn svg {

test/viewport/README.md

@@ -0,0 +1,112 @@
+# Responsive-layout harness
+
+Automated verification of the responsive layout that landed in #5. Run it with:
+
+```bash
+make frontend-viewport-test
+```
+
+It builds `dist/`, serves it from the same digest-pinned `nginx` image and the
+same `nginx.conf` the shipping container uses, drives a digest-pinned headless
+Chrome against it over CDP, and asserts on computed layout at every viewport
+width derived from the app's own CSS. Screenshots land in `tmp/viewport/`
+alongside a `results.json`; they are artifacts for a human to look at when
+something fails, not the evidence. The assertions are the evidence.
+
+The target is deliberately outside `make check`: it needs Docker and takes
+minutes, and `make test` has to stay under 20 seconds.
+
+## How the widths are chosen
+
+Not from a list of phone models. `viewports.js` parses the `@media` conditions
+out of `src/styles.css` and scans `src/main.js` and `index.html` for Tailwind
+responsive prefixes, then tests every breakpoint it finds at one pixel below it,
+exactly on it, and one pixel above it. A generic 375px "phone" test sails
+straight past an off-by-one at a media query boundary; `max-width: 768px`
+matches _at_ 768, and the sweep pins down which side of that line each layout is
+on.
+
+Nothing hardcodes 768. Add a second media block or start using `md:` classes and
+the new breakpoint is covered without this directory being touched. The app is
+desktop-first today (all narrow rules live in `max-width` blocks); a
+`min-width`-only, mobile-first set is handled as its inverse, and a set that
+mixes the two makes the run fail loudly rather than test the right widths with
+the wrong expectation. Four further viewports are fixed anchors, each with a
+stated reason: a 320px floor, a 1280px desktop baseline, and two phone-landscape
+sizes straddling the breakpoint for the rotation case.
+
+## What it asserts
+
+- **app-rendered** — enough host rows exist and enough of them show a numeric
+  latency. This one exists so the rest cannot pass vacuously against a blank
+  page.
+- **no-horizontal-overflow** — `documentElement.scrollWidth` fits the layout
+  viewport, with the widest offending element named.
+- **nothing-past-viewport-edge** — no visible element's box extends past the
+  viewport edge.
+- **no-clipped-text** — nothing hides text behind `overflow: hidden`. Deliberate
+  ellipsis truncation (Tailwind's `truncate`, used on host names and URLs) is
+  excluded: it is a design choice, not breakage.
+- **tap-targets-44px** — every interactive control is at least 44x44 CSS px on
+  touch viewports, _and_ each selector in the control list matched at least the
+  number of visible elements it declares. The second half is what stops the
+  check passing vacuously: with size alone, a renamed class would take its
+  controls out of the measured set and the check would report "all 0 controls
+  are at least 44x44" and pass. See below.
+- **host-rows-stacked / host-rows-side-by-side** — the rows genuinely reflow.
+  Computed `flex-direction` _and_ the actual geometry are checked, and in the
+  narrow layout the info block and the sparkline must each occupy essentially
+  the full row width. A row that merely shrank its 420px column would fail.
+- **probing-still-runs / gateway-detection-still-runs** — narrow viewports keep
+  probing and keep detecting the gateway. The mobile early-return path proposed
+  in #8 was rejected; this is what would catch it coming back.
+
+### The tap-target threshold
+
+44x44 CSS px. That is the figure in Apple's Human Interface Guidelines and in
+WCAG 2.2 SC 2.5.5 "Target Size (Enhanced)". WCAG 2.2 SC 2.5.8 (level AA) sets a
+lower 24x24 floor, but that floor comes with a spacing exception these controls
+do not qualify for — the pin buttons sit directly against the host name they
+belong to.
+
+## Determinism
+
+The browser container runs on an `--internal` docker network and has no route to
+the internet, so the app's latency probes cannot reach anything real. The
+harness answers them itself from a fixed delay table, with a deterministic
+fraction failed outright, so the rows render a realistic spread of one-, two-
+and three-digit latencies plus some unreachable rows. That spread is what the
+layout has to survive; 24 identical `---` placeholders would not exercise it.
+
+## What this cannot verify
+
+Real limits, so nobody re-parks this issue as needing hardware:
+
+- **Non-Chromium engines.** This is Chrome. iOS Safari is WebKit and cannot be
+  emulated by it; Safari-specific bugs (viewport units under a collapsing URL
+  bar, `-webkit-fill-available`, form control metrics) will not show up here.
+- **Real touch input.** `hasTouch` emulation changes what the page is told, not
+  how a finger behaves. Gesture handling, scroll momentum, double-tap zoom and
+  hover-state fallbacks on touch are out of scope.
+- **Physical pixel density and rendering.** `deviceScaleFactor` is set, but
+  subpixel antialiasing, OLED colour rendering and actual legibility at a given
+  physical size are not measurable here.
+- **Fonts.** The container has DejaVu, not the platform's own UI monospace. Text
+  metrics are therefore close to, but not identical to, a real device — a layout
+  that fits here by a few pixels might not there.
+- **On-device performance.** Canvas sparkline redraw cost, battery, and
+  behaviour on a slow radio are not measured.
+- **Browser chrome.** The address bar, safe-area insets and notch cutouts are
+  not simulated.
+
+Everything else this issue was actually about — does the layout reflow, does
+anything overflow, is content clipped, are the controls big enough — is a
+function of viewport width and CSS, and is covered above.
+
+## Relation to the unit test framework (#21)
+
+Complementary layers, not two stacks. `vitest` (#21) will exercise module-level
+logic in-process with no browser. This harness exercises rendered layout in a
+real engine and is the only thing here that can see a media query. Neither
+replaces the other; assertions about computed styles and element geometry belong
+here, assertions about functions belong in `vitest`.

test/viewport/checks.js

@@ -0,0 +1,245 @@
+// Pass/fail decisions for the responsive-layout harness.
+//
+// Kept in node rather than in the page so that a failure can be reported
+// with the measurements that produced it. Every check runs at every
+// viewport; none of them short-circuits, so one failure does not hide the
+// rest.
+
+// Minimum tap target, in CSS pixels. 44x44 is the figure in Apple's Human
+// Interface Guidelines and in WCAG 2.2 SC 2.5.5 "Target Size (Enhanced)".
+// WCAG 2.2 SC 2.5.8 (level AA) sets a lower 24x24 floor, but that floor
+// comes with a spacing exception these controls do not qualify for: the
+// pin buttons sit directly against the host name they belong to. Held at
+// 44 deliberately.
+export const MIN_TAP_TARGET_PX = 44;
+
+// The controls named in the definition of done, plus the pause button.
+// Each carries the smallest number of *visible* instances the page has to
+// contain for the tap-target oracle to be measuring anything at all.
+//
+// Without those floors the check is inert: `undersized` is empty both when
+// every control is large enough and when the selectors have gone stale and
+// matched nothing, and the pass condition cannot tell those apart. A single
+// combined floor would not be enough either — 26 pin buttons would cover
+// for all three singleton controls vanishing at once — so the floor is per
+// selector, and one stale selector out of four fails the check.
+export const INTERACTIVE_CONTROLS = [
+    { selector: "#pause-btn", minCount: 1 },
+    { selector: "#interval-select", minCount: 1 },
+    // One per pinnable host row. `app-rendered` already requires at least
+    // 10 host rows, so a count below that means the pin buttons stopped
+    // being rendered per row rather than that there were fewer hosts.
+    { selector: ".pin-btn", minCount: 10 },
+    { selector: "#debug-toggle", minCount: 1 },
+];
+
+export const INTERACTIVE_SELECTORS = INTERACTIVE_CONTROLS.map(
+    (control) => control.selector,
+);
+
+// A host row is only "reflowed" if it stacked *and* went full width.
+// A row that merely shrank its 420px info column would keep
+// flex-direction: row, and a row that stacked but left the info column at
+// its fixed width would fail the width test.
+const FULL_WIDTH_FRACTION = 0.9;
+
+function summarise(items, format, limit = 3) {
+    const shown = items.slice(0, limit).map(format).join("; ");
+    const rest = items.length > limit ? ` (+${items.length - limit} more)` : "";
+    return shown + rest;
+}
+
+// Collapse an overflow report to the elements actually responsible.
+// Identical elements (24 host rows all doing the same thing) are counted
+// rather than listed, and the deepest ones come first, since every
+// ancestor of an overflowing element also reports as overflowing.
+function deepestOffenders(entries) {
+    const byElement = new Map();
+    for (const entry of entries) {
+        const reach = entry.reach ?? entry.right;
+        const existing = byElement.get(entry.el);
+        if (existing) {
+            existing.count += 1;
+            existing.reach = Math.max(existing.reach, reach);
+        } else {
+            byElement.set(entry.el, { ...entry, reach, count: 1 });
+        }
+    }
+    return [...byElement.values()].sort(
+        (a, b) => b.depth - a.depth || b.reach - a.reach,
+    );
+}
+
+function checkRowLayout(row, expectStacked) {
+    if (expectStacked) {
+        if (row.flexDirection !== "column") {
+            return `row ${row.index}: flex-direction is ${row.flexDirection}, expected column`;
+        }
+        if (row.sparkline.top < row.info.bottom - 1) {
+            return `row ${row.index}: sparkline top ${row.sparkline.top} is above info bottom ${row.info.bottom} — still side by side`;
+        }
+        const minWidth = row.containerWidth * FULL_WIDTH_FRACTION;
+        if (row.info.width < minWidth) {
+            return `row ${row.index}: info block is ${row.info.width}px of ${row.containerWidth}px — shrunk, not reflowed`;
+        }
+        if (row.sparkline.width < minWidth) {
+            return `row ${row.index}: sparkline is ${row.sparkline.width}px of ${row.containerWidth}px — shrunk, not reflowed`;
+        }
+        return null;
+    }
+
+    if (row.flexDirection !== "row") {
+        return `row ${row.index}: flex-direction is ${row.flexDirection}, expected row`;
+    }
+    if (row.sparkline.left < row.info.right - 1) {
+        return `row ${row.index}: sparkline left ${row.sparkline.left} overlaps info right ${row.info.right} — not side by side`;
+    }
+    return null;
+}
+
+export function evaluateChecks(facts, viewport, probes) {
+    const checks = [];
+    const check = (name, ok, detail) => checks.push({ name, ok, detail });
+
+    // Guard against the whole harness passing vacuously because the page
+    // never rendered. Everything below is only meaningful if this holds.
+    check(
+        "app-rendered",
+        facts.rowCount >= 10 && facts.numericLatencies >= 5,
+        `${facts.rowCount} host rows, ${facts.numericLatencies} showing a numeric latency`,
+    );
+
+    const viewportWidth = Math.min(facts.innerWidth, facts.documentClientWidth);
+    const culprits = deepestOffenders([
+        ...facts.overflowing,
+        ...facts.contentOverflowing,
+    ]);
+    check(
+        "no-horizontal-overflow",
+        facts.documentScrollWidth <= viewportWidth,
+        `documentElement.scrollWidth ${facts.documentScrollWidth} vs viewport ${viewportWidth}` +
+            (culprits.length === 0
+                ? ""
+                : "; widest content: " +
+                  summarise(
+                      culprits,
+                      (c) =>
+                          `${c.el} reaches ${Math.round(c.reach)}px${c.count > 1 ? ` (x${c.count})` : ""}`,
+                  )),
+    );
+
+    check(
+        "nothing-past-viewport-edge",
+        facts.overflowing.length === 0,
+        facts.overflowing.length === 0
+            ? "no element extends past the viewport"
+            : `${facts.overflowing.length} element(s) past the edge: ` +
+                  summarise(
+                      facts.overflowing,
+                      (o) => `${o.el} spans ${o.left}..${o.right}`,
+                  ),
+    );
+
+    check(
+        "no-clipped-text",
+        facts.clipped.length === 0,
+        facts.clipped.length === 0
+            ? "no element hides text behind overflow (deliberate ellipsis excluded)"
+            : `${facts.clipped.length} element(s) clipping text: ` +
+                  summarise(
+                      facts.clipped,
+                      (c) =>
+                          `${c.el} scrollWidth ${c.scrollWidth} > clientWidth ${c.clientWidth}`,
+                  ),
+    );
+
+    if (viewport.touch) {
+        // Presence first: a selector that matches nothing contributes no
+        // undersized targets, so without this the check would report
+        // "all 0 controls are at least 44x44" and pass.
+        const seen = new Map();
+        for (const target of facts.tapTargets) {
+            seen.set(target.selector, (seen.get(target.selector) ?? 0) + 1);
+        }
+        const missing = INTERACTIVE_CONTROLS.filter(
+            (control) => (seen.get(control.selector) ?? 0) < control.minCount,
+        );
+
+        const undersized = facts.tapTargets.filter(
+            (t) => t.width < MIN_TAP_TARGET_PX || t.height < MIN_TAP_TARGET_PX,
+        );
+        const bySelector = new Map();
+        for (const target of undersized) {
+            const existing = bySelector.get(target.selector);
+            if (!existing || target.width * target.height < existing.area) {
+                bySelector.set(target.selector, {
+                    ...target,
+                    area: target.width * target.height,
+                    count: (existing?.count ?? 0) + 1,
+                });
+            } else {
+                existing.count += 1;
+            }
+        }
+        const detail = [];
+        if (missing.length > 0) {
+            detail.push(
+                "oracle is not measuring the page: " +
+                    summarise(
+                        missing,
+                        (c) =>
+                            `${c.selector} matched ${seen.get(c.selector) ?? 0} visible element(s), expected at least ${c.minCount}`,
+                        4,
+                    ),
+            );
+        }
+        detail.push(
+            undersized.length === 0
+                ? `${facts.tapTargets.length} controls measured, all at least ${MIN_TAP_TARGET_PX}x${MIN_TAP_TARGET_PX}`
+                : `${undersized.length} of ${facts.tapTargets.length} controls below ${MIN_TAP_TARGET_PX}x${MIN_TAP_TARGET_PX}: ` +
+                      summarise(
+                          [...bySelector.values()],
+                          (t) =>
+                              `${t.selector} ${t.width}x${t.height}${t.count > 1 ? ` (x${t.count})` : ""}`,
+                          4,
+                      ),
+        );
+        check(
+            `tap-targets-${MIN_TAP_TARGET_PX}px`,
+            missing.length === 0 && undersized.length === 0,
+            detail.join("; "),
+        );
+    }
+
+    const badRows = facts.rows
+        .map((row) => checkRowLayout(row, viewport.expectStacked))
+        .filter(Boolean);
+    check(
+        viewport.expectStacked ? "host-rows-stacked" : "host-rows-side-by-side",
+        facts.rows.length > 0 && badRows.length === 0,
+        facts.rows.length === 0
+            ? "no host rows were measured"
+            : badRows.length === 0
+              ? `all ${facts.rows.length} rows laid out as expected`
+              : `${badRows.length} of ${facts.rows.length} rows wrong: ` +
+                summarise(badRows, (r) => r),
+    );
+
+    // The mobile early-return path proposed in #8 was rejected: narrow
+    // viewports must keep probing and keep detecting the gateway, not
+    // quietly skip work.
+    check(
+        "probing-still-runs",
+        probes.attempted > 0,
+        `${probes.attempted} outbound probe requests issued`,
+    );
+    check(
+        "gateway-detection-still-runs",
+        facts.gatewayDetected,
+        facts.gatewayDetected
+            ? "Local Gateway row present"
+            : "no Local Gateway row — gateway detection did not run or did not complete",
+    );
+
+    return checks;
+}

test/viewport/facts.js

@@ -0,0 +1,184 @@
+// Layout facts collected from inside the page.
+//
+// This function is serialised and evaluated in the browser, so it must be
+// entirely self-contained: no imports, no closures over module scope. It
+// only *measures*; every pass/fail decision is made back in node by
+// checks.js, so failures can be reported with real numbers attached.
+
+export function collectLayoutFacts(options) {
+    const describe = (el) => {
+        const id = el.id ? "#" + el.id : "";
+        const classes =
+            typeof el.className === "string" && el.className.trim()
+                ? "." + el.className.trim().split(/\s+/).slice(0, 3).join(".")
+                : "";
+        return el.tagName.toLowerCase() + id + classes;
+    };
+
+    const round = (n) => Math.round(n * 10) / 10;
+
+    // Overflow propagates up every ancestor, so a single wide element
+    // reports as body, #app, the row, and so on. Depth lets the report
+    // name the deepest — that is, the actual — offender.
+    const depthOf = (el) => {
+        let depth = 0;
+        for (let node = el.parentElement; node; node = node.parentElement) {
+            depth++;
+        }
+        return depth;
+    };
+
+    const isVisible = (el) => {
+        const style = getComputedStyle(el);
+        if (style.display === "none") return false;
+        if (style.visibility === "hidden") return false;
+        const rect = el.getBoundingClientRect();
+        return rect.width > 0 && rect.height > 0;
+    };
+
+    const innerWidth = window.innerWidth;
+    const clientWidth = document.documentElement.clientWidth;
+    // Under mobile emulation Chrome lets window.innerWidth *grow* to the
+    // width of overflowing content, exactly as a phone zooms out to fit a
+    // too-wide page. Measuring against it would therefore hide the
+    // overflow it is supposed to expose: at a 320px device width a page
+    // that spills to 350 reports innerWidth 350 and looks clean. Every
+    // comparison below is against the layout viewport instead.
+    const viewportWidth = Math.min(innerWidth, clientWidth);
+    const elements = Array.from(document.querySelectorAll("body *"));
+
+    // Elements sticking out past the right (or left) edge of the viewport.
+    // The document-level scrollWidth check says *that* the page overflows;
+    // this says *what* is doing it.
+    const overflowing = [];
+    // Elements clipping their own text. Deliberate ellipsis truncation
+    // (Tailwind's `truncate`) is opt-in and excluded: it is a design
+    // choice, not breakage.
+    const clipped = [];
+    // Elements whose content spills out of their own box without being
+    // clipped, past the right edge of the viewport. A block element is
+    // only ever as wide as its container, so text overflowing it has no
+    // element rect of its own to catch — but it is exactly what drags
+    // documentElement.scrollWidth past the viewport width, so without
+    // this the page-level overflow failure has nothing to point at.
+    const contentOverflowing = [];
+
+    for (const el of elements) {
+        if (!isVisible(el)) continue;
+        const rect = el.getBoundingClientRect();
+        if (rect.right > viewportWidth + 1 || rect.left < -1) {
+            overflowing.push({
+                el: describe(el),
+                depth: depthOf(el),
+                left: round(rect.left),
+                right: round(rect.right),
+            });
+        }
+        const style = getComputedStyle(el);
+        const clips =
+            style.overflowX === "hidden" || style.overflowX === "clip";
+        const ellipsis = style.textOverflow === "ellipsis";
+        const hasText = el.textContent.trim().length > 0;
+        const spills =
+            el.clientWidth > 0 && el.scrollWidth > el.clientWidth + 1;
+        if (clips && !ellipsis && hasText && spills) {
+            clipped.push({
+                el: describe(el),
+                scrollWidth: el.scrollWidth,
+                clientWidth: el.clientWidth,
+            });
+        }
+        if (
+            !clips &&
+            spills &&
+            rect.left + el.scrollWidth > viewportWidth + 1
+        ) {
+            contentOverflowing.push({
+                el: describe(el),
+                depth: depthOf(el),
+                scrollWidth: el.scrollWidth,
+                clientWidth: el.clientWidth,
+                reach: round(rect.left + el.scrollWidth),
+            });
+        }
+    }
+
+    // Interactive controls. The measured target is the nearest thing that
+    // is genuinely tappable — for a checkbox that is the <label> wrapping
+    // it, which is larger than the box itself and is what a finger hits.
+    const tapTargets = [];
+    for (const selector of options.interactiveSelectors) {
+        for (const el of document.querySelectorAll(selector)) {
+            if (!isVisible(el)) continue;
+            const target = el.closest("button, a, label, select") || el;
+            const rect = target.getBoundingClientRect();
+            tapTargets.push({
+                selector,
+                el: describe(target),
+                width: round(rect.width),
+                height: round(rect.height),
+            });
+        }
+    }
+
+    // Host rows. The question is not "did it get narrower" but "did it
+    // reflow": the info block and the sparkline must end up stacked
+    // vertically and full width in the narrow layout, and side by side in
+    // the wide one. Both the computed flex-direction and the actual
+    // geometry are recorded so a row that claims to be a column but is
+    // still laid out side by side cannot slip through.
+    const rows = [];
+    for (const row of document.querySelectorAll(".host-row")) {
+        const inner = row.firstElementChild;
+        if (!inner) continue;
+        const sparkline = inner.querySelector(".sparkline-container");
+        const info = sparkline ? sparkline.previousElementSibling : null;
+        if (!sparkline || !info) continue;
+        const innerStyle = getComputedStyle(inner);
+        const innerRect = inner.getBoundingClientRect();
+        const infoRect = info.getBoundingClientRect();
+        const sparkRect = sparkline.getBoundingClientRect();
+        rows.push({
+            index: row.dataset.index,
+            flexDirection: innerStyle.flexDirection,
+            containerWidth: round(innerRect.width),
+            info: {
+                left: round(infoRect.left),
+                right: round(infoRect.right),
+                bottom: round(infoRect.bottom),
+                width: round(infoRect.width),
+            },
+            sparkline: {
+                left: round(sparkRect.left),
+                top: round(sparkRect.top),
+                width: round(sparkRect.width),
+            },
+        });
+    }
+
+    const localRows = Array.from(
+        document.querySelectorAll("#local-hosts .host-row"),
+    );
+
+    return {
+        innerWidth,
+        // innerWidth includes any classic scrollbar, clientWidth does not.
+        // Reported separately so the overflow check can hold itself to the
+        // narrower of the two rather than to whichever one is more
+        // forgiving.
+        documentClientWidth: document.documentElement.clientWidth,
+        documentScrollWidth: document.documentElement.scrollWidth,
+        overflowing,
+        contentOverflowing,
+        clipped,
+        tapTargets,
+        rows,
+        rowCount: document.querySelectorAll(".host-row").length,
+        numericLatencies: Array.from(
+            document.querySelectorAll(".latency-value"),
+        ).filter((el) => /\d/.test(el.textContent)).length,
+        gatewayDetected: localRows.some((row) =>
+            row.textContent.includes("Local Gateway"),
+        ),
+    };
+}

test/viewport/harness.js

@@ -0,0 +1,258 @@
+// Responsive-layout harness.
+//
+// Drives the built frontend in a real, containerised, digest-pinned Chrome
+// over CDP and asserts on computed layout at every viewport width derived
+// from the app's own CSS. Screenshots are written alongside as artifacts;
+// they are not the evidence, the assertions are.
+//
+// This is not meant to be run by hand. `make frontend-viewport-test` brings
+// up the browser and the web server and then runs this; every input it
+// needs arrives in the environment.
+
+import { mkdirSync, writeFileSync } from "node:fs";
+import { join } from "node:path";
+import puppeteer from "puppeteer-core";
+import { collectLayoutFacts } from "./facts.js";
+import { evaluateChecks, INTERACTIVE_SELECTORS } from "./checks.js";
+import { deriveViewports } from "./viewports.js";
+
+function required(name) {
+    const value = process.env[name];
+    if (!value) {
+        throw new Error(
+            `${name} is not set; run this via script/frontend-viewport-test`,
+        );
+    }
+    return value;
+}
+
+const ROOT = required("NETWATCH_ROOT");
+const BASE_URL = required("NETWATCH_BASE_URL");
+const CDP_URL = required("NETWATCH_CDP_URL");
+const ARTIFACT_DIR = required("NETWATCH_ARTIFACT_DIR");
+
+const BROWSER_TIMEOUT_MS = 60000;
+const PAGE_TIMEOUT_MS = 30000;
+
+// Canned responses for the app's outbound latency probes. The browser
+// container sits on an --internal docker network and physically cannot
+// reach the internet, so nothing here is about blocking traffic; it is
+// about determinism. Real probes would render 24 rows of whatever the
+// network happened to be doing. These delays make the rows show a
+// realistic spread of value widths — one, two and three digit latencies,
+// plus some unreachable rows — because that spread is what the layout has
+// to survive.
+const PROBE_DELAYS_MS = [2, 45, 123, 456, 780];
+// One in every UNREACHABLE_MODULUS probes is failed outright so that the
+// offline row rendering is exercised too.
+const UNREACHABLE_MODULUS = 7;
+// The gateway candidate that "answers", so gateway detection succeeds and
+// the Local Gateway row renders. Matches GATEWAY_CANDIDATES in src/main.js.
+const RESPONSIVE_GATEWAY = "http://192.168.1.1";
+
+const sleep = (ms) => new Promise((resolve) => setTimeout(resolve, ms));
+
+function stableHash(text) {
+    let hash = 0;
+    for (let i = 0; i < text.length; i++) {
+        hash = (hash * 31 + text.charCodeAt(i)) | 0;
+    }
+    return Math.abs(hash);
+}
+
+async function connectBrowser() {
+    const deadline = Date.now() + BROWSER_TIMEOUT_MS;
+    let lastError;
+    for (;;) {
+        try {
+            const response = await fetch(`${CDP_URL}/json/version`);
+            const info = await response.json();
+            // The endpoint advertises whatever Host it was reached on;
+            // pin it back to the address we actually dialled.
+            const endpoint = new URL(info.webSocketDebuggerUrl);
+            endpoint.host = new URL(CDP_URL).host;
+            const browser = await puppeteer.connect({
+                browserWSEndpoint: endpoint.toString(),
+                protocolTimeout: BROWSER_TIMEOUT_MS,
+            });
+            return { browser, version: info.Browser };
+        } catch (error) {
+            lastError = error;
+            if (Date.now() > deadline) {
+                throw new Error(`browser never came up: ${lastError}`);
+            }
+            await sleep(250);
+        }
+    }
+}
+
+function installProbeResponder(page, probes) {
+    const respond = (request, delayMs) =>
+        sleep(delayMs).then(() =>
+            request.respond({
+                status: 200,
+                contentType: "text/plain",
+                body: "",
+            }),
+        );
+
+    page.on("request", (request) => {
+        const url = request.url();
+        const settle = async () => {
+            if (url.startsWith(BASE_URL) || url.startsWith("data:")) {
+                return request.continue();
+            }
+            probes.attempted++;
+            if (url.startsWith(RESPONSIVE_GATEWAY)) {
+                probes.fulfilled++;
+                return respond(request, 5);
+            }
+            const hash = stableHash(url);
+            if (hash % UNREACHABLE_MODULUS === 0) {
+                probes.failed++;
+                return request.abort("connectionfailed");
+            }
+            probes.fulfilled++;
+            return respond(
+                request,
+                PROBE_DELAYS_MS[hash % PROBE_DELAYS_MS.length],
+            );
+        };
+        // The page may be torn down while a delayed response is pending;
+        // that is not a harness failure.
+        settle().catch(() => {});
+    });
+}
+
+async function runViewport(browser, viewport) {
+    const page = await browser.newPage();
+    const probes = { attempted: 0, fulfilled: 0, failed: 0 };
+    try {
+        page.setDefaultTimeout(PAGE_TIMEOUT_MS);
+        await page.setRequestInterception(true);
+        installProbeResponder(page, probes);
+        await page.setViewport({
+            width: viewport.width,
+            height: viewport.height,
+            deviceScaleFactor: viewport.deviceScaleFactor,
+            isMobile: viewport.touch,
+            hasTouch: viewport.touch,
+            isLandscape: viewport.width > viewport.height,
+        });
+
+        await page.goto(BASE_URL, { waitUntil: "load" });
+        await page.waitForSelector(".host-row");
+
+        // The app discards its first tick as a cold start, so rows only
+        // carry real values from the second one. Changing the interval
+        // restarts the loop at 1s, which reaches a populated UI without
+        // waiting out two default 3s intervals — and exercises the
+        // interval dropdown while we are at it.
+        await page.select("#interval-select", "1000");
+        await page.waitForFunction(
+            () =>
+                Array.from(document.querySelectorAll(".latency-value")).filter(
+                    (el) => /\d/.test(el.textContent),
+                ).length >= 5,
+        );
+        // Let the resize/redraw handlers settle before measuring.
+        await page.evaluate(
+            () =>
+                new Promise((resolve) =>
+                    requestAnimationFrame(() => requestAnimationFrame(resolve)),
+                ),
+        );
+
+        const facts = await page.evaluate(collectLayoutFacts, {
+            interactiveSelectors: INTERACTIVE_SELECTORS,
+        });
+
+        const screenshot = join(
+            ARTIFACT_DIR,
+            `${viewport.width}x${viewport.height}-${viewport.name}.png`,
+        );
+        await page.screenshot({ path: screenshot, fullPage: true });
+
+        return {
+            viewport,
+            probes,
+            facts,
+            screenshot,
+            checks: evaluateChecks(facts, viewport, probes),
+        };
+    } finally {
+        await page.close().catch(() => {});
+    }
+}
+
+function report(results, conditions, browserVersion) {
+    const label = (viewport) =>
+        `${viewport.width}x${viewport.height}`.padEnd(9) +
+        " " +
+        viewport.name.padEnd(24);
+
+    console.log(`browser:     ${browserVersion}`);
+    console.log(`served from: ${BASE_URL} (built dist/)`);
+    console.log(
+        "breakpoints: " +
+            conditions
+                .map((c) => `${c.type}-width ${c.px}px (${c.source})`)
+                .join(", "),
+    );
+    console.log("");
+
+    let passed = 0;
+    let failed = 0;
+    for (const result of results) {
+        const bad = result.checks.filter((c) => !c.ok);
+        passed += result.checks.length - bad.length;
+        failed += bad.length;
+        // Passing viewports get one line. Detail is for failures.
+        console.log(
+            `${bad.length === 0 ? "PASS" : "FAIL"} ${label(result.viewport)} ` +
+                `${result.checks.length - bad.length}/${result.checks.length} checks` +
+                `${result.viewport.expectStacked ? "  [narrow layout expected]" : ""}`,
+        );
+        for (const check of bad) {
+            console.log(`       ${check.name}: ${check.detail}`);
+        }
+        if (bad.length > 0) {
+            console.log(`       why this width: ${result.viewport.why}`);
+            console.log(`       screenshot: ${result.screenshot}`);
+        }
+    }
+
+    console.log("");
+    console.log(
+        `${results.length} viewports, ${passed + failed} checks: ` +
+            `${passed} passed, ${failed} failed`,
+    );
+    console.log(`artifacts: ${ARTIFACT_DIR}`);
+    return failed;
+}
+
+async function main() {
+    const { conditions, viewports } = deriveViewports(ROOT);
+    mkdirSync(ARTIFACT_DIR, { recursive: true });
+
+    const { browser, version } = await connectBrowser();
+    const results = [];
+    try {
+        for (const viewport of viewports) {
+            results.push(await runViewport(browser, viewport));
+        }
+    } finally {
+        await browser.disconnect().catch(() => {});
+    }
+
+    writeFileSync(
+        join(ARTIFACT_DIR, "results.json"),
+        JSON.stringify({ browser: version, conditions, results }, null, 2) +
+            "\n",
+    );
+
+    const failed = report(results, conditions, version);
+    process.exitCode = failed === 0 ? 0 : 1;
+}
+
+await main();

test/viewport/viewports.js

@@ -0,0 +1,224 @@
+// Viewport derivation for the responsive-layout harness.
+//
+// The widths tested are read out of the CSS the application actually
+// ships, not taken from a list of popular phone models. A generic 375px
+// "phone" test sails straight past an off-by-one error at a media query
+// boundary, which is the classic way a responsive layout breaks, so
+// every breakpoint found in the sources is probed three times: one pixel
+// below it, exactly on it, and one pixel above it.
+//
+// Nothing here hardcodes 768. If someone adds a second media block or
+// starts using Tailwind responsive prefixes, that breakpoint starts
+// being covered without this file being edited.
+
+import { readFileSync } from "node:fs";
+import { join } from "node:path";
+
+// Tailwind CSS v4 default breakpoints, in rem. The app currently uses
+// none of these prefixes, so the whole table is inert until someone
+// writes an `md:`-prefixed utility class.
+const TAILWIND_BREAKPOINT_REM = {
+    sm: 40,
+    md: 48,
+    lg: 64,
+    xl: 80,
+    "2xl": 96,
+};
+
+// The app does not override the root font size, so rem and em in media
+// queries resolve against the browser default.
+const ROOT_FONT_SIZE_PX = 16;
+
+// Extract every min-width / max-width condition from the @media blocks in
+// a stylesheet. Returns e.g. [{ type: "max", px: 768, source: "..." }].
+export function mediaConditionsFromCss(css, source) {
+    const conditions = [];
+    for (const block of css.matchAll(/@media([^{]+)\{/g)) {
+        const features = block[1].matchAll(
+            /\(\s*(min|max)-width\s*:\s*([\d.]+)(px|rem|em)\s*\)/g,
+        );
+        for (const feature of features) {
+            const scale = feature[3] === "px" ? 1 : ROOT_FONT_SIZE_PX;
+            conditions.push({
+                type: feature[1],
+                px: Math.round(Number(feature[2]) * scale),
+                source,
+            });
+        }
+    }
+    return conditions;
+}
+
+// Extract the breakpoints implied by Tailwind responsive prefixes used in
+// markup. A prefix only counts when it opens a utility class, so `text-sm`
+// does not masquerade as the `sm:` breakpoint.
+export function mediaConditionsFromMarkup(sources) {
+    const conditions = [];
+    for (const { path, text } of sources) {
+        for (const [name, rem] of Object.entries(TAILWIND_BREAKPOINT_REM)) {
+            const used = new RegExp(
+                `(^|["'\\s])${name}:[a-z0-9[\\](),_./%-]+`,
+                "m",
+            ).test(text);
+            if (used) {
+                conditions.push({
+                    type: "min",
+                    px: rem * ROOT_FONT_SIZE_PX,
+                    source: path,
+                });
+            }
+        }
+    }
+    return conditions;
+}
+
+// Whether a given width should be rendering the app's narrow (stacked)
+// layout.
+//
+// Two breakpoint styles can be answered from the condition list alone:
+//
+//   - Desktop-first, which is what the app ships today: the wide layout is
+//     unconditional and every narrow rule lives in a `max-width` block, so
+//     a width is narrow exactly when one of those blocks matches. Note that
+//     `max-width: 768px` matches *at* 768 — getting this inclusive boundary
+//     wrong in either direction is what the three-widths-per-breakpoint
+//     sweep exists to catch.
+//   - Mobile-first, which is what Tailwind's `sm:`/`md:` prefixes are: the
+//     stacked layout is the unconditional base and a `min-width` block is
+//     what widens it, so a width is narrow exactly when it sits below every
+//     `min-width` breakpoint.
+//
+// A mix of the two cannot be resolved from the breakpoints alone — which
+// block owns the host-row reflow is a property of the rules inside it, not
+// of the condition — so this throws rather than guessing. Guessing is how
+// the wrong expectation gets applied at the right widths and the whole
+// sweep quietly verifies nothing.
+export function expectsStackedLayout(width, conditions) {
+    const kinds = new Set(conditions.map((c) => c.type));
+    for (const kind of kinds) {
+        if (kind !== "max" && kind !== "min") {
+            throw new Error(
+                `unsupported media condition type "${kind}" in ` +
+                    "expectsStackedLayout (test/viewport/viewports.js)",
+            );
+        }
+    }
+    if (kinds.has("max") && kinds.has("min")) {
+        throw new Error(
+            "the app now mixes max-width and min-width breakpoints (" +
+                conditions
+                    .map((c) => `${c.type}-width ${c.px}px in ${c.source}`)
+                    .join(", ") +
+                "), so which layout a width should be showing can no longer " +
+                "be inferred from the breakpoint list; teach " +
+                "expectsStackedLayout in test/viewport/viewports.js which " +
+                "block owns the host-row reflow",
+        );
+    }
+    if (kinds.has("min")) {
+        return !conditions.some((c) => width >= c.px);
+    }
+    return conditions.some((c) => width <= c.px);
+}
+
+// Viewports that are not derived from a breakpoint. Each one is here for
+// a stated reason; none of them is a stand-in for "a phone".
+const ANCHOR_VIEWPORTS = [
+    {
+        name: "floor-portrait",
+        width: 320,
+        height: 568,
+        deviceScaleFactor: 2,
+        touch: true,
+        why: "320px is the narrowest viewport still in mainstream use; nothing has to work below it",
+    },
+    {
+        name: "phone-landscape-narrow",
+        width: 667,
+        height: 375,
+        deviceScaleFactor: 2,
+        touch: true,
+        why: "phone rotated to landscape, still inside the narrow layout",
+    },
+    {
+        name: "phone-landscape-wide",
+        width: 844,
+        height: 390,
+        deviceScaleFactor: 3,
+        touch: true,
+        why: "large phone rotated to landscape: crosses into the wide layout while still being a touch device",
+    },
+    {
+        name: "desktop",
+        width: 1280,
+        height: 800,
+        deviceScaleFactor: 1,
+        touch: false,
+        why: "desktop baseline",
+    },
+];
+
+export function deriveViewports(root) {
+    const conditions = [
+        ...mediaConditionsFromCss(
+            readFileSync(join(root, "src/styles.css"), "utf8"),
+            "src/styles.css",
+        ),
+        ...mediaConditionsFromMarkup([
+            {
+                path: "src/main.js",
+                text: readFileSync(join(root, "src/main.js"), "utf8"),
+            },
+            {
+                path: "index.html",
+                text: readFileSync(join(root, "index.html"), "utf8"),
+            },
+        ]),
+    ];
+
+    if (conditions.length === 0) {
+        throw new Error(
+            "no responsive breakpoints found in src/styles.css, src/main.js or " +
+                "index.html — either the responsive layout was deleted or this " +
+                "derivation has stopped matching the sources",
+        );
+    }
+
+    const viewports = new Map();
+    const add = (viewport) => {
+        const key = `${viewport.width}x${viewport.height}`;
+        if (!viewports.has(key)) viewports.set(key, viewport);
+    };
+
+    for (const condition of conditions) {
+        for (const [offset, label] of [
+            [-1, "below"],
+            [0, "at"],
+            [+1, "above"],
+        ]) {
+            const width = condition.px + offset;
+            add({
+                name: `${condition.type}-width-${condition.px}-${label}`,
+                width,
+                // Tall enough that the whole app is laid out in one column
+                // without the viewport height influencing wrapping.
+                height: 1024,
+                deviceScaleFactor: 2,
+                touch: true,
+                why: `${offset === 0 ? "exactly on" : `1px ${label}`} the ${condition.type}-width: ${condition.px}px breakpoint declared in ${condition.source}`,
+            });
+        }
+    }
+
+    for (const anchor of ANCHOR_VIEWPORTS) add(anchor);
+
+    return {
+        conditions,
+        viewports: [...viewports.values()]
+            .map((viewport) => ({
+                ...viewport,
+                expectStacked: expectsStackedLayout(viewport.width, conditions),
+            }))
+            .sort((a, b) => a.width - b.width || a.height - b.height),
+    };
+}

vite.config.js

@@ -7,6 +7,13 @@ const commitFull = execSync("git rev-parse HEAD").toString().trim();
 
 export default defineConfig({
     plugins: [tailwindcss()],
+    server: {
+        // Proxy /api to a locally running netwatch-server so `yarn dev`
+        // exercises the real report-posting path.
+        proxy: {
+            "/api": "http://127.0.0.1:8080",
+        },
+    },
     define: {
         __COMMIT_HASH__: JSON.stringify(commitHash),
         __COMMIT_FULL__: JSON.stringify(commitFull),

yarn.lock

@@ -197,6 +197,14 @@
     "@emnapi/runtime" "^1.7.1"
     "@tybys/wasm-util" "^0.10.1"
 
+"@puppeteer/browsers@3.1.0":
+  version "3.1.0"
+  resolved "https://registry.yarnpkg.com/@puppeteer/browsers/-/browsers-3.1.0.tgz#5728ae0bc649263133ac1f8bd5d360eb75d11748"
+  integrity sha512-RDLpio3fH/qrj5k4DVY6eyiN8tCS0Zovd/6jW//n605oeqkWcUjn+3k+9ZtZBnbwMpsu0F7xDIiKXvVmG5c5Bw==
+  dependencies:
+    modern-tar "^0.7.6"
+    yargs "^18.0.0"
+
 "@rollup/rollup-android-arm-eabi@4.57.0":
   version "4.57.0"
   resolved "https://registry.yarnpkg.com/@rollup/rollup-android-arm-eabi/-/rollup-android-arm-eabi-4.57.0.tgz#f762035679a6b168138c94c960fda0b0cdb00d98"
@@ -441,6 +449,16 @@
   resolved "https://registry.yarnpkg.com/@types/estree/-/estree-1.0.8.tgz#958b91c991b1867ced318bedea0e215ee050726e"
   integrity sha512-dWHzHa2WqEXI/O1E9OjrocMTKJl2mSrEolh1Iomrv6U+JuNwaHXsXx9bLu5gG7BUWFIN0skIQJQ/L1rIex4X6w==
 
+ansi-regex@^6.2.2:
+  version "6.2.2"
+  resolved "https://registry.yarnpkg.com/ansi-regex/-/ansi-regex-6.2.2.tgz#60216eea464d864597ce2832000738a0589650c1"
+  integrity sha512-Bq3SmSpyFHaWjPk8If9yc6svM8c56dB5BAtW4Qbw5jHTwwXXcTLoRMkpDJp6VL0XzlWaCHTXrkFURMYmD0sLqg==
+
+ansi-styles@^6.2.1:
+  version "6.2.3"
+  resolved "https://registry.yarnpkg.com/ansi-styles/-/ansi-styles-6.2.3.tgz#c044d5dcc521a076413472597a1acb1f103c4041"
+  integrity sha512-4Dj6M28JB+oAH8kFkTLUo+a2jwOFkuqb3yucU0CANcRRUbxS0cP0nZYCGjcc3BNXwRIsUVmDGgzawme7zvJHvg==
+
 autoprefixer@^10.4.23:
   version "10.4.23"
   resolved "https://registry.yarnpkg.com/autoprefixer/-/autoprefixer-10.4.23.tgz#c6aa6db8e7376fcd900f9fd79d143ceebad8c4e6"
@@ -473,16 +491,43 @@ caniuse-lite@^1.0.30001759, caniuse-lite@^1.0.30001760:
   resolved "https://registry.yarnpkg.com/caniuse-lite/-/caniuse-lite-1.0.30001766.tgz#b6f6b55cb25a2d888d9393104d14751c6a7d6f7a"
   integrity sha512-4C0lfJ0/YPjJQHagaE9x2Elb69CIqEPZeG0anQt9SIvIoOH4a4uaRl73IavyO+0qZh6MDLH//DrXThEYKHkmYA==
 
+chromium-bidi@17.0.2:
+  version "17.0.2"
+  resolved "https://registry.yarnpkg.com/chromium-bidi/-/chromium-bidi-17.0.2.tgz#921a586deecd0c2d8b9242c4c1b73c3aa39ff77c"
+  integrity sha512-5v9GQFhTktFvotn/OFNJBmKLKRAb6n9r0bVCwf7sHgWc3/JryK0bj1nn93L3pHFrfgcsu6Be6EWsDi+1XHTGDg==
+  dependencies:
+    mitt "^3.0.1"
+    zod "^3.24.1"
+
+cliui@^9.0.1:
+  version "9.0.1"
+  resolved "https://registry.yarnpkg.com/cliui/-/cliui-9.0.1.tgz#6f7890f386f6f1f79953adc1f78dec46fcc2d291"
+  integrity sha512-k7ndgKhwoQveBL+/1tqGJYNz097I7WOvwbmmU2AR5+magtbjPWQTS1C5vzGkBC8Ym8UWRzfKUzUUqFLypY4Q+w==
+  dependencies:
+    string-width "^7.2.0"
+    strip-ansi "^7.1.0"
+    wrap-ansi "^9.0.0"
+
 detect-libc@^2.0.3:
   version "2.1.2"
   resolved "https://registry.yarnpkg.com/detect-libc/-/detect-libc-2.1.2.tgz#689c5dcdc1900ef5583a4cb9f6d7b473742074ad"
   integrity sha512-Btj2BOOO83o3WyH59e8MgXsxEQVcarkUOpEYrubB0urwnN10yQ364rsiByU11nZlqWYZm05i/of7io4mzihBtQ==
 
+devtools-protocol@0.0.1653615:
+  version "0.0.1653615"
+  resolved "https://registry.yarnpkg.com/devtools-protocol/-/devtools-protocol-0.0.1653615.tgz#c600e0c619612156b2422a66d958ba188d87dbe8"
+  integrity sha512-pGVkY3T/qXxAp2nFPodwYqOevk6ncNMSmvL8QfRCx5ZWGd6Vor7AFNmyaA8Zs6uJyP1QAfjuLandCgvSix1BNA==
+
 electron-to-chromium@^1.5.263:
   version "1.5.282"
   resolved "https://registry.yarnpkg.com/electron-to-chromium/-/electron-to-chromium-1.5.282.tgz#6695816e5b170210d6aa07561546ed7d97347630"
   integrity sha512-FCPkJtpst28UmFzd903iU7PdeVTfY0KAeJy+Lk0GLZRwgwYHn/irRcaCbQQOmr5Vytc/7rcavsYLvTM8RiHYhQ==
 
+emoji-regex@^10.3.0:
+  version "10.6.0"
+  resolved "https://registry.yarnpkg.com/emoji-regex/-/emoji-regex-10.6.0.tgz#bf3d6e8f7f8fd22a65d9703475bc0147357a6b0d"
+  integrity sha512-toUI84YS5YmxW219erniWD0CIVOo46xGKColeNQRgOzDorgBi1v4D71/OFzgD9GO2UGKIv1C3Sp8DAn0+j5w7A==
+
 enhanced-resolve@^5.18.3:
   version "5.18.4"
   resolved "https://registry.yarnpkg.com/enhanced-resolve/-/enhanced-resolve-5.18.4.tgz#c22d33055f3952035ce6a144ce092447c525f828"
@@ -523,7 +568,7 @@ esbuild@^0.27.0:
     "@esbuild/win32-ia32" "0.27.2"
     "@esbuild/win32-x64" "0.27.2"
 
-escalade@^3.2.0:
+escalade@^3.1.1, escalade@^3.2.0:
   version "3.2.0"
   resolved "https://registry.yarnpkg.com/escalade/-/escalade-3.2.0.tgz#011a3f69856ba189dffa7dc8fcce99d2a87903e5"
   integrity sha512-WUj2qlxaQtO4g6Pq5c29GTcWGDyd8itL8zTlipgECz3JesAiiOKotd8JU6otB3PACgG6xkJUyVhboMS+bje/jA==
@@ -543,6 +588,16 @@ fsevents@~2.3.2, fsevents@~2.3.3:
   resolved "https://registry.yarnpkg.com/fsevents/-/fsevents-2.3.3.tgz#cac6407785d03675a2a5e1a5305c697b347d90d6"
   integrity sha512-5xoDfX+fL7faATnagmWPpbFtwh/R77WmMMqqHGS65C3vvB0YHrgF+B1YmZ3441tMj5n63k0212XNoJwzlhffQw==
 
+get-caller-file@^2.0.5:
+  version "2.0.5"
+  resolved "https://registry.yarnpkg.com/get-caller-file/-/get-caller-file-2.0.5.tgz#4f94412a82db32f36e3b0b9741f8a97feb031f7e"
+  integrity sha512-DyFP3BM/3YHTQOCUL/w0OZHR0lpKeGrxotcHWcqNEdnltqFwXVfhEBQ94eIo34AfQpo0rGki4cyIiftY06h2Fg==
+
+get-east-asian-width@^1.0.0, get-east-asian-width@^1.5.0:
+  version "1.6.0"
+  resolved "https://registry.yarnpkg.com/get-east-asian-width/-/get-east-asian-width-1.6.0.tgz#216900f91df11a8b2c198c3e1d93d6c035a776b9"
+  integrity sha512-QRbvDIbx6YklUe6RxeTeleMR0yv3cYH6PsPZHcnVn7xv7zO1BHN8r0XETu8n6Ye3Q+ahtSarc3WgtNWmehIBfA==
+
 graceful-fs@^4.2.4:
   version "4.2.11"
   resolved "https://registry.yarnpkg.com/graceful-fs/-/graceful-fs-4.2.11.tgz#4183e4e8bf08bb6e05bbb2f7d2e0c8f712ca40e3"
@@ -634,6 +689,16 @@ magic-string@^0.30.21:
   dependencies:
     "@jridgewell/sourcemap-codec" "^1.5.5"
 
+mitt@^3.0.1:
+  version "3.0.1"
+  resolved "https://registry.yarnpkg.com/mitt/-/mitt-3.0.1.tgz#ea36cf0cc30403601ae074c8f77b7092cdab36d1"
+  integrity sha512-vKivATfr97l2/QBCYAkXYDbrIWPM2IIKEl7YPhjCvKlG3kE2gm+uBo6nEXK3M5/Ffh/FLpKExzOQ3JJoJGFKBw==
+
+modern-tar@^0.7.6:
+  version "0.7.7"
+  resolved "https://registry.yarnpkg.com/modern-tar/-/modern-tar-0.7.7.tgz#ca71d79603630076b10733b0751ccab284bbc1ef"
+  integrity sha512-t9VmxaqrmANnEOBhpSDI6HD192Ge48k8vmWqQQL7hSFEqHEYwZbbsu49+aKLWZeRvFs3j1pMhXOqqF4kPlvjkQ==
+
 nanoid@^3.3.11:
   version "3.3.11"
   resolved "https://registry.yarnpkg.com/nanoid/-/nanoid-3.3.11.tgz#4f4f112cefbe303202f2199838128936266d185b"
@@ -673,6 +738,18 @@ prettier@^3.8.1:
   resolved "https://registry.yarnpkg.com/prettier/-/prettier-3.8.1.tgz#edf48977cf991558f4fcbd8a3ba6015ba2a3a173"
   integrity sha512-UOnG6LftzbdaHZcKoPFtOcCKztrQ57WkHDeRD9t/PTQtmT0NHSeWWepj6pS0z/N7+08BHFDQVUrfmfMRcZwbMg==
 
+puppeteer-core@25.5.0:
+  version "25.5.0"
+  resolved "https://registry.yarnpkg.com/puppeteer-core/-/puppeteer-core-25.5.0.tgz#a41b14d582056b998e0bc3561ac47c7615d38a53"
+  integrity sha512-XPNT0dQJtphqQ4I29zxlG4IIPbg1iEHAQKWuQgtMJGXjACV77pZSmJvDi51IIIfd+DTKICcopJwUx4upVQ4XbA==
+  dependencies:
+    "@puppeteer/browsers" "3.1.0"
+    chromium-bidi "17.0.2"
+    devtools-protocol "0.0.1653615"
+    typed-query-selector "^2.12.2"
+    webdriver-bidi-protocol "0.4.2"
+    ws "^8.21.1"
+
 rollup@^4.43.0:
   version "4.57.0"
   resolved "https://registry.yarnpkg.com/rollup/-/rollup-4.57.0.tgz#9fa13c1fb779d480038f45708b5e01b9449b6853"
@@ -712,6 +789,30 @@ source-map-js@^1.2.1:
   resolved "https://registry.yarnpkg.com/source-map-js/-/source-map-js-1.2.1.tgz#1ce5650fddd87abc099eda37dcff024c2667ae46"
   integrity sha512-UXWMKhLOwVKb728IUtQPXxfYU+usdybtUrK/8uGE8CQMvrhOpwvzDBwj0QhSL7MQc7vIsISBG8VQ8+IDQxpfQA==
 
+string-width@^7.0.0, string-width@^7.2.0:
+  version "7.2.0"
+  resolved "https://registry.yarnpkg.com/string-width/-/string-width-7.2.0.tgz#b5bb8e2165ce275d4d43476dd2700ad9091db6dc"
+  integrity sha512-tsaTIkKW9b4N+AEj+SVA+WhJzV7/zMhcSu78mLKWSk7cXMOSHsBKFWUs0fWwq8QyK3MgJBQRX6Gbi4kYbdvGkQ==
+  dependencies:
+    emoji-regex "^10.3.0"
+    get-east-asian-width "^1.0.0"
+    strip-ansi "^7.1.0"
+
+string-width@^8.2.1:
+  version "8.2.2"
+  resolved "https://registry.yarnpkg.com/string-width/-/string-width-8.2.2.tgz#7310516493df575742fe98af6fae87d85d5ed0ac"
+  integrity sha512-GaPUh5gfdrYzqeVNZvUfT23vYYxXzKYidUcnMtJg/3rxRV63EFZy3k6xfKlmfeJD0176lnUV/Usr3XcwSvFzpg==
+  dependencies:
+    get-east-asian-width "^1.5.0"
+    strip-ansi "^7.1.2"
+
+strip-ansi@^7.1.0, strip-ansi@^7.1.2:
+  version "7.2.0"
+  resolved "https://registry.yarnpkg.com/strip-ansi/-/strip-ansi-7.2.0.tgz#d22a269522836a627af8d04b5c3fd2c7fa3e32e3"
+  integrity sha512-yDPMNjp4WyfYBkHnjIRLfca1i6KMyGCtsVgoKe/z1+6vukgaENdgGBZt+ZmKPc4gavvEZ5OgHfHdrazhgNyG7w==
+  dependencies:
+    ansi-regex "^6.2.2"
+
 tailwindcss@4.1.18, tailwindcss@^4.1.18:
   version "4.1.18"
   resolved "https://registry.yarnpkg.com/tailwindcss/-/tailwindcss-4.1.18.tgz#f488ba47853abdb5354daf9679d3e7791fc4f4e3"
@@ -735,6 +836,11 @@ tslib@^2.4.0:
   resolved "https://registry.yarnpkg.com/tslib/-/tslib-2.8.1.tgz#612efe4ed235d567e8aba5f2a5fab70280ade83f"
   integrity sha512-oJFu94HQb+KVduSUQL7wnpmqnfmLsOA/nAh6b6EH0wCEoK0/mPeXU6c3wKDV83MkOuHPRHtSXKKU99IBazS/2w==
 
+typed-query-selector@^2.12.2:
+  version "2.12.2"
+  resolved "https://registry.yarnpkg.com/typed-query-selector/-/typed-query-selector-2.12.2.tgz#65e2462ac6b0aecfae1bfac1a4f3027070dbabaa"
+  integrity sha512-EOPFbyIub4ngnEdqi2yOcNeDLaX/0jcE1JoAXQDDMIthap7FoN795lc/SHfIq2d416VufXpM8z/lD+WRm2gfOQ==
+
 update-browserslist-db@^1.2.0:
   version "1.2.3"
   resolved "https://registry.yarnpkg.com/update-browserslist-db/-/update-browserslist-db-1.2.3.tgz#64d76db58713136acbeb4c49114366cc6cc2e80d"
@@ -756,3 +862,49 @@ vite@^7.3.1:
     tinyglobby "^0.2.15"
   optionalDependencies:
     fsevents "~2.3.3"
+
+webdriver-bidi-protocol@0.4.2:
+  version "0.4.2"
+  resolved "https://registry.yarnpkg.com/webdriver-bidi-protocol/-/webdriver-bidi-protocol-0.4.2.tgz#f51bb71c2606e90e3d5727607c728b25d617b58b"
+  integrity sha512-VSV+fzfChirL3e7jay2yUC7B4HQCGtEWEg/MSSQbK+qWbqeGlRLlXTzPpYr3XGUvbpDHumWZBJxgesg4N7dbtA==
+
+wrap-ansi@^9.0.0:
+  version "9.0.2"
+  resolved "https://registry.yarnpkg.com/wrap-ansi/-/wrap-ansi-9.0.2.tgz#956832dea9494306e6d209eb871643bb873d7c98"
+  integrity sha512-42AtmgqjV+X1VpdOfyTGOYRi0/zsoLqtXQckTmqTeybT+BDIbM/Guxo7x3pE2vtpr1ok6xRqM9OpBe+Jyoqyww==
+  dependencies:
+    ansi-styles "^6.2.1"
+    string-width "^7.0.0"
+    strip-ansi "^7.1.0"
+
+ws@^8.21.1:
+  version "8.21.3"
+  resolved "https://registry.yarnpkg.com/ws/-/ws-8.21.3.tgz#660b4faddb6a3e575c86e078126919961f4de4fc"
+  integrity sha512-201TZ/kPWxoPr/OKWjquZR1SWKXcvxdH+e1xrx89b3YbmzLMFCLfnaG1HFIgWzJOEWZ7MvpK++odZufgYR50Rw==
+
+y18n@^5.0.5:
+  version "5.0.8"
+  resolved "https://registry.yarnpkg.com/y18n/-/y18n-5.0.8.tgz#7f4934d0f7ca8c56f95314939ddcd2dd91ce1d55"
+  integrity sha512-0pfFzegeDWJHJIAmTLRP2DwHjdF5s7jo9tuztdQxAhINCdvS+3nGINqPd00AphqJR/0LhANUS6/+7SCb98YOfA==
+
+yargs-parser@^22.0.0:
+  version "22.0.0"
+  resolved "https://registry.yarnpkg.com/yargs-parser/-/yargs-parser-22.0.0.tgz#87b82094051b0567717346ecd00fd14804b357c8"
+  integrity sha512-rwu/ClNdSMpkSrUb+d6BRsSkLUq1fmfsY6TOpYzTwvwkg1/NRG85KBy3kq++A8LKQwX6lsu+aWad+2khvuXrqw==
+
+yargs@^18.0.0:
+  version "18.1.0"
+  resolved "https://registry.yarnpkg.com/yargs/-/yargs-18.1.0.tgz#cd7e98c703ef51695bbbf062ed58f28e94291b56"
+  integrity sha512-2rAgRKu54VsHkqI0/tYkmluGXHD4KW7yZoycuqDQ15QOTnc2VVfy0nN/1eMhnQLO00A+dwtK20xuCnc1YGeUyg==
+  dependencies:
+    cliui "^9.0.1"
+    escalade "^3.1.1"
+    get-caller-file "^2.0.5"
+    string-width "^8.2.1"
+    y18n "^5.0.5"
+    yargs-parser "^22.0.0"
+
+zod@^3.24.1:
+  version "3.25.76"
+  resolved "https://registry.yarnpkg.com/zod/-/zod-3.25.76.tgz#26841c3f6fd22a6a2760e7ccb719179768471e34"
+  integrity sha512-gzUt/qt81nXsFGKIFcC3YnfEAx5NkunCfnDlvuBSSFS02bcXu4Lmea0AFIUwbLWxWPx3d9p8S5QoaujKcNQxcQ==