diff --git a/.prettierignore b/.prettierignore
new file mode 100644
index 0000000..d87c685
--- /dev/null
+++ b/.prettierignore
@@ -0,0 +1,2 @@
+# Vendored, minified third-party bundles must never be reformatted.
+*.min.js
diff --git a/Dockerfile b/Dockerfile
index f31025e..1a996e8 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -8,8 +8,12 @@ RUN go mod download
 
 COPY . .
 
+# golangci-lint is invoked directly here, not via `make lint`: script/lint
+# now runs the linter by building Dockerfile.lint, and shelling out to
+# `docker build` from inside this image build would be docker-in-docker.
+# This image is golangci/golangci-lint, so the pinned linter is on PATH.
 RUN make fmt-check
-RUN make lint
+RUN golangci-lint run --config .golangci.yml ./...
 
 # Build stage — tests and compilation
 # golang:1.25-alpine
diff --git a/Dockerfile.lint b/Dockerfile.lint
new file mode 100644
index 0000000..9836aef
--- /dev/null
+++ b/Dockerfile.lint
@@ -0,0 +1,23 @@
+# Lint image — runs golangci-lint inside a container so every lint uses
+# the pinned linter, never a host binary. Linting is a build step, so a
+# successful build is a clean lint. Built by script/lint.
+# golangci/golangci-lint:v2.12.2 (Debian-based), 2026-08-07
+FROM golangci/golangci-lint:v2.12.2@sha256:5cceeef04e53efe1470638d4b4b4f5ceefd574955ab3941b2d9a68a8c9ad5240
+
+WORKDIR /src
+
+COPY go.mod go.sum ./
+RUN go mod download
+
+COPY . .
+
+# Caching is waived for linting: on an unchanged tree a cached build runs
+# no linter and still exits 0 in under a second. script/lint passes a
+# fresh GATE_RUN every time, and referencing it here forces this step to
+# re-run, so the linter always executes.
+#
+# `golangci-lint config verify` is deliberately NOT run: it fetches its
+# JSON schema over an unpinned live HTTPS call, which REPO_POLICIES.md
+# forbids (all external references must be pinned by hash).
+ARG GATE_RUN
+RUN echo "lint run: ${GATE_RUN}"; golangci-lint run --config .golangci.yml ./...
diff --git a/TODO.md b/TODO.md
index 2f051a0..ae65dff 100644
--- a/TODO.md
+++ b/TODO.md
@@ -20,6 +20,24 @@ main cannot regress.
 
 # Completed Steps
 
+- 2026-09-22: Fixed the flaky `t.TempDir` cleanup race in
+  `internal/service/webhook` by tracking the async deployment goroutine
+  in a `sync.WaitGroup` and exposing `WaitForDeployments`; tests now
+  synchronize on completion instead of sleeping (#198).
+- 2026-09-22: Linting now runs only in Docker. Added `Dockerfile.lint`
+  (pinned golangci-lint v2.12.2, cache-busted via a `GATE_RUN` build arg
+  so the linter always executes), reduced `script/lint` to building it,
+  dropped the golangci-lint install from `script/bootstrap`, and switched
+  the `Dockerfile` lint stage to invoke `golangci-lint` directly instead
+  of `make lint` to avoid docker-in-docker (#188).
+- 2026-09-22: Added `.prettierignore` so `make fmt` no longer rewrites
+  the vendored `static/js/alpine.min.js` bundle (#185).
+- 2026-09-22: Fixed the gosec G703 path-traversal finding in the deploy
+  log download handler by verifying the resolved path stays within the
+  deploy log directory before serving, returning 404 on escape (#177).
+- 2026-09-22: `script/bootstrap` now installs a pinned `goimports`
+  (`golang.org/x/tools` v0.49.0) into `/usr/local/bin`, so `make fmt`
+  succeeds on a fresh machine after `make bootstrap` (#184).
 - 2026-09-09: Fixed four deployability blockers found by QA: CSRF origin
   check over plain HTTP (`UPAAS_PLAINTEXT_HTTP`, #189), pulling the git
   image when absent (#190), the env-var editor CSRF token lookup (#191),
diff --git a/internal/handlers/app.go b/internal/handlers/app.go
index aa83aed..a985c11 100644
--- a/internal/handlers/app.go
+++ b/internal/handlers/app.go
@@ -611,7 +611,13 @@ func (h *Handlers) HandleDeploymentLogDownload() http.HandlerFunc {
 			return
 		}
 
-		// Get the log file path from deploy service
+		// The log path is derived from request data (the app is looked
+		// up by a URL parameter), so open it through an os.Root confined
+		// to the deploy log directory. Root.Open rejects any path that
+		// escapes the root, so a traversal attempt fails rather than
+		// serving an arbitrary file.
+		logDir := h.deploy.GetLogDir()
+
 		logPath := h.deploy.GetLogFilePath(application, deployment)
 		if logPath == "" {
 			http.NotFound(writer, request)
@@ -619,28 +625,43 @@ func (h *Handlers) HandleDeploymentLogDownload() http.HandlerFunc {
 			return
 		}
 
-		// Check if file exists — logPath is constructed internally, not from user input
-		_, err := os.Stat(logPath) // #nosec G703 -- internal path, not user input
-		if os.IsNotExist(err) {
+		relPath, relErr := filepath.Rel(logDir, logPath)
+		if relErr != nil {
 			http.NotFound(writer, request)
 
 			return
 		}
 
-		if err != nil {
-			h.log.Error("failed to stat log file", "error", err, "path", logPath)
+		root, rootErr := os.OpenRoot(logDir)
+		if rootErr != nil {
+			http.NotFound(writer, request)
+
+			return
+		}
+		defer func() { _ = root.Close() }()
+
+		file, openErr := root.Open(relPath)
+		if openErr != nil {
+			http.NotFound(writer, request)
+
+			return
+		}
+		defer func() { _ = file.Close() }()
+
+		info, statErr := file.Stat()
+		if statErr != nil {
+			h.log.Error("failed to stat log file", "error", statErr, "path", logPath)
 			http.Error(writer, "Internal Server Error", http.StatusInternalServerError)
 
 			return
 		}
 
-		// Extract filename for Content-Disposition header
 		filename := filepath.Base(logPath)
 
 		writer.Header().Set("Content-Type", "text/plain; charset=utf-8")
 		writer.Header().Set("Content-Disposition", "attachment; filename=\""+filename+"\"")
 
-		http.ServeFile(writer, request, logPath) // #nosec G703 -- internal path
+		http.ServeContent(writer, request, filename, info.ModTime(), file)
 	}
 }
 
diff --git a/internal/handlers/handlers_test.go b/internal/handlers/handlers_test.go
index 6e0624a..68e116e 100644
--- a/internal/handlers/handlers_test.go
+++ b/internal/handlers/handlers_test.go
@@ -42,6 +42,7 @@ type testContext struct {
 	database   *database.Database
 	authSvc    *auth.Service
 	appSvc     *app.Service
+	deploySvc  *deploy.Service
 	middleware *middleware.Middleware
 }
 
@@ -186,6 +187,7 @@ func setupTestHandlers(t *testing.T) *testContext {
 		database:   dbInstance,
 		authSvc:    authSvc,
 		appSvc:     appSvc,
+		deploySvc:  deploySvc,
 		middleware: mw,
 	}
 }
diff --git a/internal/handlers/log_download_test.go b/internal/handlers/log_download_test.go
new file mode 100644
index 0000000..cbbfd08
--- /dev/null
+++ b/internal/handlers/log_download_test.go
@@ -0,0 +1,121 @@
+package handlers_test
+
+import (
+	"context"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"path/filepath"
+	"strconv"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"sneak.berlin/go/upaas/internal/models"
+)
+
+// doLogDownload issues a log-download request for the given app and
+// deployment and returns the recorder.
+func doLogDownload(
+	t *testing.T,
+	testCtx *testContext,
+	appID string,
+	deploymentID int64,
+) *httptest.ResponseRecorder {
+	t.Helper()
+
+	idStr := strconv.FormatInt(deploymentID, 10)
+
+	request := httptest.NewRequestWithContext(
+		t.Context(),
+		http.MethodGet,
+		"/apps/"+appID+"/deployments/"+idStr+"/log",
+		nil,
+	)
+	request = addChiURLParams(request, map[string]string{
+		"id":           appID,
+		"deploymentID": idStr,
+	})
+
+	recorder := httptest.NewRecorder()
+	testCtx.handlers.HandleDeploymentLogDownload().ServeHTTP(recorder, request)
+
+	return recorder
+}
+
+// TestHandleDeploymentLogDownloadServesLegitimateFile verifies a normal
+// log file is served for download.
+func TestHandleDeploymentLogDownloadServesLegitimateFile(t *testing.T) {
+	t.Parallel()
+
+	testCtx := setupTestHandlers(t)
+	createdApp := createTestApp(t, testCtx, "log-download-app")
+
+	deployment := models.NewDeployment(testCtx.database)
+	deployment.AppID = createdApp.ID
+	deployment.Status = models.DeploymentStatusSuccess
+	require.NoError(t, deployment.Save(context.Background()))
+
+	// Write the log file where the handler will look for it.
+	logPath := testCtx.deploySvc.GetLogFilePath(createdApp, deployment)
+	require.NoError(t, os.MkdirAll(filepath.Dir(logPath), 0o750))
+	require.NoError(t, os.WriteFile(logPath, []byte("deploy log contents"), 0o600))
+
+	recorder := doLogDownload(t, testCtx, createdApp.ID, deployment.ID)
+
+	assert.Equal(t, http.StatusOK, recorder.Code)
+	assert.Contains(t, recorder.Body.String(), "deploy log contents")
+}
+
+// TestHandleDeploymentLogDownloadRejectsPathTraversal verifies the
+// os.Root containment guard. A traversal-shaped app name drives the
+// resolved log path out of the deploy log directory onto a sentinel
+// file that really exists. The handler must refuse to serve it (404)
+// rather than leak its contents. Removing the guard makes this test
+// fail, which the earlier version — pointed at a non-existent path that
+// 404s either way — did not.
+func TestHandleDeploymentLogDownloadRejectsPathTraversal(t *testing.T) {
+	t.Parallel()
+
+	testCtx := setupTestHandlers(t)
+	createdApp := createTestApp(t, testCtx, "log-traversal-app")
+
+	createdApp.Name = "../.."
+	require.NoError(t, createdApp.Save(context.Background()))
+
+	// The log root must exist so os.OpenRoot succeeds and the rejection
+	// comes from the containment check, not a missing directory.
+	logDir := testCtx.deploySvc.GetLogDir()
+	require.NoError(t, os.MkdirAll(logDir, 0o750))
+
+	deployment := models.NewDeployment(testCtx.database)
+	deployment.AppID = createdApp.ID
+	deployment.Status = models.DeploymentStatusSuccess
+	require.NoError(t, deployment.Save(context.Background()))
+
+	// Where the handler resolves the log path to. The traversal name
+	// makes this land outside logDir; require that it truly escapes so
+	// the test cannot silently stop covering the guard.
+	escapedPath := testCtx.deploySvc.GetLogFilePath(createdApp, deployment)
+	relPath, relErr := filepath.Rel(logDir, escapedPath)
+	require.NoError(t, relErr)
+	require.True(t, strings.HasPrefix(relPath, ".."),
+		"resolved path must escape the log dir, got %q", relPath)
+
+	// Plant a sentinel where the traversal points; a missing guard would
+	// open and serve it.
+	require.NoError(t, os.MkdirAll(filepath.Dir(escapedPath), 0o750))
+
+	const sentinel = "SENTINEL-outside-log-dir-must-not-be-served"
+
+	require.NoError(t, os.WriteFile(escapedPath, []byte(sentinel), 0o600))
+	t.Cleanup(func() { _ = os.Remove(escapedPath) })
+
+	recorder := doLogDownload(t, testCtx, createdApp.ID, deployment.ID)
+
+	assert.Equal(t, http.StatusNotFound, recorder.Code)
+	assert.NotContains(t, recorder.Body.String(), sentinel,
+		"containment guard must not serve a file outside the log dir")
+}
diff --git a/internal/service/deploy/deploy.go b/internal/service/deploy/deploy.go
index 887a094..ab1f2c8 100644
--- a/internal/service/deploy/deploy.go
+++ b/internal/service/deploy/deploy.go
@@ -294,6 +294,12 @@ func (svc *Service) GetLogFilePath(
 	return filepath.Join(svc.config.DataDir, "logs", hostname, app.Name, filename)
 }
 
+// GetLogDir returns the root directory under which all deployment log
+// files live. Paths returned by GetLogFilePath are always inside it.
+func (svc *Service) GetLogDir() string {
+	return filepath.Join(svc.config.DataDir, "logs")
+}
+
 // HasActiveDeploy returns true if there is an active deployment for the given app.
 func (svc *Service) HasActiveDeploy(appID string) bool {
 	_, ok := svc.activeDeploys.Load(appID)
diff --git a/internal/service/webhook/webhook.go b/internal/service/webhook/webhook.go
index 69c1f6c..02a51ee 100644
--- a/internal/service/webhook/webhook.go
+++ b/internal/service/webhook/webhook.go
@@ -6,6 +6,7 @@ import (
 	"database/sql"
 	"fmt"
 	"log/slog"
+	"sync"
 
 	"go.uber.org/fx"
 
@@ -31,6 +32,10 @@ type Service struct {
 	db     *database.Database
 	deploy *deploy.Service
 	params *ServiceParams
+
+	// deployments tracks the deployment goroutines started by
+	// triggerDeployment so callers can wait for them to finish.
+	deployments sync.WaitGroup
 }
 
 // New creates a new webhook Service.
@@ -108,6 +113,14 @@ func (svc *Service) HandleWebhook(
 	return nil
 }
 
+// WaitForDeployments blocks until every deployment goroutine started by
+// HandleWebhook has finished, including all writes under the data
+// directory. It exists so callers and tests can synchronize on async
+// deployment completion instead of polling or sleeping.
+func (svc *Service) WaitForDeployments() {
+	svc.deployments.Wait()
+}
+
 func (svc *Service) triggerDeployment(
 	ctx context.Context,
 	app *models.App,
@@ -117,7 +130,7 @@ func (svc *Service) triggerDeployment(
 	eventID := event.ID
 	appName := app.Name
 
-	go func() {
+	svc.deployments.Go(func() {
 		// Use context.WithoutCancel to ensure deployment completes
 		// even if the HTTP request context is cancelled.
 		deployCtx := context.WithoutCancel(ctx)
@@ -130,5 +143,5 @@ func (svc *Service) triggerDeployment(
 		// Mark event as processed
 		event.Processed = true
 		_ = event.Save(deployCtx)
-	}()
+	})
 }
diff --git a/internal/service/webhook/webhook_test.go b/internal/service/webhook/webhook_test.go
index bda7a98..619b271 100644
--- a/internal/service/webhook/webhook_test.go
+++ b/internal/service/webhook/webhook_test.go
@@ -7,7 +7,6 @@ import (
 	"os"
 	"path/filepath"
 	"testing"
-	"time"
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
@@ -828,8 +827,9 @@ func TestExtractBranch(testingT *testing.T) {
 			)
 			require.NoError(t, err)
 
-			// Allow async deployment goroutine to complete before test cleanup
-			time.Sleep(100 * time.Millisecond)
+			// Wait for the async deployment goroutine to finish so its
+			// writes under the temp dir complete before test cleanup.
+			svc.WaitForDeployments()
 
 			events, err := app.GetWebhookEvents(context.Background(), 10)
 			require.NoError(t, err)
@@ -867,8 +867,9 @@ func TestHandleWebhookMatchingBranch(t *testing.T) {
 	)
 	require.NoError(t, err)
 
-	// Allow async deployment goroutine to complete before test cleanup
-	time.Sleep(100 * time.Millisecond)
+	// Wait for the async deployment goroutine to finish so its writes
+	// under the temp dir complete before test cleanup.
+	svc.WaitForDeployments()
 
 	events, err := app.GetWebhookEvents(context.Background(), 10)
 	require.NoError(t, err)
@@ -962,8 +963,9 @@ func assertHandleWebhookDeploys(
 	err := svc.HandleWebhook(context.Background(), app, source, pushEventType, payload)
 	require.NoError(t, err)
 
-	// Allow async deployment goroutine to complete before test cleanup
-	time.Sleep(100 * time.Millisecond)
+	// Wait for the async deployment goroutine to finish so its writes
+	// under the temp dir complete before test cleanup.
+	svc.WaitForDeployments()
 
 	events, err := app.GetWebhookEvents(context.Background(), 10)
 	require.NoError(t, err)
diff --git a/script/bootstrap b/script/bootstrap
index f1b3e30..095afa8 100755
--- a/script/bootstrap
+++ b/script/bootstrap
@@ -3,18 +3,18 @@
 # this repo. Idempotent: every install is guarded by a check so already
 # installed tools are skipped. Base tooling comes from nix, apt, brew,
 # or apk (detected in that order); assumes NOTHING is present (not git,
-# make, or go). golangci-lint is packaged in nix, brew, and apk; on apt
-# it is installed from a hash-verified GitHub release archive (never
-# curl | sh).
+# make, or go). goimports is installed with `go install` at a pinned
+# version (integrity via the Go module checksum database) into
+# /usr/local/bin so it is on PATH. The linter is not installed here: it
+# runs only in Docker via script/lint, so docker is its sole prerequisite.
 set -eu
 
 ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 
-# Pinned versions, 2026-08-07. Never "latest"; exact versions only.
-GOLANGCI_LINT_VERSION="2.12.2"
-# sha256 of golangci-lint-2.12.2-linux-<arch>.tar.gz release archives
-GOLANGCI_LINT_SHA256_AMD64="8df580d2670fed8fa984aac0507099af8df275e665215f5c7a2ae3943893a553"
-GOLANGCI_LINT_SHA256_ARM64="44cd40a8c76c86755375adfeea52cfd3533cb43d7bd647771e0ae065e166df3a"
+# Pinned versions. Never "latest"; exact versions only.
+# golang.org/x/tools goimports, 2026-08-13. v0.49.0 requires Go 1.25 (matches
+# go.mod); v0.50.0 needs Go 1.26. Integrity via the Go module checksum database.
+GOIMPORTS_VERSION="v0.49.0"
 
 PKGMGR=""
 SUDO=""
@@ -56,50 +56,17 @@ missing() {
     ! command -v "$1" >/dev/null 2>&1
 }
 
-# verify_sha256 <file> <expected-hash>
-verify_sha256() {
-    if command -v sha256sum >/dev/null 2>&1; then
-        actual="$(sha256sum "$1" | cut -d' ' -f1)"
-    else
-        actual="$(shasum -a 256 "$1" | cut -d' ' -f1)"
-    fi
-    if [ "$actual" != "$2" ]; then
-        echo "bootstrap: sha256 mismatch for $1" >&2
-        echo "  expected: $2" >&2
-        echo "  actual:   $actual" >&2
-        exit 1
-    fi
-}
-
-# apt has no golangci-lint package: install a pinned release archive
-# from GitHub, verified by hardcoded sha256 (never curl | sh).
-install_golangci_lint_release() {
-    case "$(uname -m)" in
-        x86_64) goarch="amd64"; sha="$GOLANGCI_LINT_SHA256_AMD64" ;;
-        aarch64|arm64) goarch="arm64"; sha="$GOLANGCI_LINT_SHA256_ARM64" ;;
-        *)
-            echo "bootstrap: unsupported architecture $(uname -m)" >&2
-            exit 1
-            ;;
-    esac
-    if missing curl; then pkg_install curl curl curl curl; fi
-    name="golangci-lint-${GOLANGCI_LINT_VERSION}-linux-${goarch}"
-    tmp="$(mktemp -d)"
-    curl -fsSL -o "$tmp/$name.tar.gz" \
-        "https://github.com/golangci/golangci-lint/releases/download/v${GOLANGCI_LINT_VERSION}/${name}.tar.gz"
-    verify_sha256 "$tmp/$name.tar.gz" "$sha"
-    tar -xzf "$tmp/$name.tar.gz" -C "$tmp"
-    $SUDO install -m 0755 "$tmp/$name/golangci-lint" /usr/local/bin/golangci-lint
-    rm -rf "$tmp"
-}
-
-ensure_golangci_lint() {
-    if ! missing golangci-lint; then return 0; fi
+# goimports is not packaged uniformly across nix/apt/brew/apk, so install it
+# with `go install` at a pinned version and place the binary in /usr/local/bin
+# so it is on PATH regardless of shell config. Requires go, which main
+# installs first.
+ensure_goimports() {
+    if ! missing goimports; then return 0; fi
     detect_pkgmgr
-    case "$PKGMGR" in
-        apt) install_golangci_lint_release ;;
-        *) pkg_install golangci-lint golangci-lint golangci-lint golangci-lint ;;
-    esac
+    tmp="$(mktemp -d)"
+    GOBIN="$tmp" go install "golang.org/x/tools/cmd/goimports@${GOIMPORTS_VERSION}"
+    $SUDO install -m 0755 "$tmp/goimports" /usr/local/bin/goimports
+    rm -rf "$tmp"
 }
 
 main() {
@@ -109,9 +76,17 @@ main() {
     if missing git; then pkg_install git git git git; fi
     if missing make; then pkg_install gnumake make make make; fi
 
-    # Go toolchain and linter
+    # Go toolchain
     if missing go; then pkg_install go golang go go; fi
-    ensure_golangci_lint
+    ensure_goimports
+
+    # The linter runs only in Docker (script/lint). Warn, don't fail: the
+    # rest of the repo works without it.
+    if missing docker; then
+        echo "bootstrap: WARNING: docker not found; make lint and" >&2
+        echo "bootstrap: make check require it. Install docker to run" >&2
+        echo "bootstrap: the linter." >&2
+    fi
 
     go mod download
 
diff --git a/script/lint b/script/lint
index 8017180..1d56b58 100755
--- a/script/lint
+++ b/script/lint
@@ -1,12 +1,24 @@
 #!/bin/sh
-# script/lint: run the linter.
+# script/lint: run golangci-lint. The linter is never installed on the
+# host; it runs only inside Docker, from the pinned image in
+# Dockerfile.lint, so every run uses the same linter version everywhere.
+# Linting is a build step there, so a successful build is a clean lint.
+#
+# GATE_RUN differs every run so the lint layer always executes; a cached
+# build would otherwise exit 0 in under a second having linted nothing.
+# --output=type=cacheonly discards the image and keeps only build cache,
+# so no tagged image is left behind.
 set -eu
 
 ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 
 main() {
     cd "$ROOT"
-    golangci-lint run --config .golangci.yml ./...
+    docker build \
+        --build-arg GATE_RUN="$(date +%s)-$$" \
+        --output=type=cacheonly \
+        -f Dockerfile.lint \
+        .
 }
 
 main "$@"