Install lint-phase libraries with apt-get, not apk (closes #83)

The note under the canonical Go Dockerfile example said to install
system libraries for linting with `apk add`, but the lint phase is
based on the Debian golangci-lint image, which has no apk. It now
gives the apt-get command with the Debian package name (libvips-dev)
and removes the package lists in the same RUN. No other canonical
sentence describes installing a library in the lint phase; the
remaining apk mentions concern the alpine build stage or the host.
Nothing is pinned or unpinned.

Model: opus-5-5

TODO.md

@@ -27,6 +27,15 @@ fmt-check, and commit.
   image is Debian-based and has no `apk`, so the old `apk add` instruction
   failed as written. Nothing is pinned or unpinned; that is still open on
   issue 72.
+- 2026-10-04: Fixed the server lifecycle example in
+  `prompts/GO_HTTP_SERVER_CONVENTIONS.md` (issue 86). Only fx handles SIGINT and
+  SIGTERM, and `Run()` in `main` exits with the shutdown's exit code. A listen
+  error asks fx to shut down with exit code 1 through `fx.Shutdowner`; a Sentry
+  start failure is returned from the server's start hook instead of calling
+  `os.Exit` from a goroutine, so the stop hooks of what had started still run.
+  The server's stop hook shuts the HTTP server down within 5 seconds and fails
+  when requests are still running. A new paragraph says who owns signals and the
+  exit code.
 - 2026-10-04: `REPO_POLICIES.md` now says how a Go tool a repo needs on the host
   is pinned (issue 37): installed with `go install` pinned to a commit hash,
   never tracked as a `go.mod` tool dependency or through a `tools.go` file.

prompts/GO_HTTP_SERVER_CONVENTIONS.md

@@ -106,6 +106,9 @@ project-root/
 package main
 
 import (
+    "os/signal"
+    "syscall"
+
     "yourproject/internal/config"
     "yourproject/internal/database"
     "yourproject/internal/globals"
@@ -126,6 +129,9 @@ func main() {
     globals.Appname = Appname
     globals.Version = Version
 
+    // A write to a closed stdout or stderr must not end the process.
+    signal.Ignore(syscall.SIGPIPE)
+
     fx.New(
         fx.Provide(
             config.New,
@@ -198,7 +204,8 @@ Providers are resolved automatically by fx, but conceptually follow this order:
    Database)
 6. `middleware.New` - Middleware (depends on Logger, Globals, Config)
 7. `handlers.New` - Handlers (depends on Logger, Globals, Database, Healthcheck)
-8. `server.New` - Server (depends on all above)
+8. `server.New` - Server (depends on all above, and on `fx.Shutdowner`, which fx
+   provides itself)
 
 ---
 
@@ -217,16 +224,14 @@ type ServerParams struct {
     Config     *config.Config
     Middleware *middleware.Middleware
     Handlers   *handlers.Handlers
+    Shutdowner fx.Shutdowner
 }
 
 type Server struct {
     startupTime   time.Time
     port          int
-    exitCode      int
     sentryEnabled bool
     log           *slog.Logger
-    ctx           context.Context
-    cancelFunc    context.CancelFunc
     httpServer    *http.Server
     router        *chi.Mux
     params        ServerParams
@@ -248,13 +253,15 @@ func New(lc fx.Lifecycle, params ServerParams) (*Server, error) {
     lc.Append(fx.Hook{
         OnStart: func(ctx context.Context) error {
             s.startupTime = time.Now()
-            go s.Run()
-            return nil
-        },
-        OnStop: func(ctx context.Context) error {
-            // Server shutdown logic
+            if err := s.enableSentry(); err != nil {
+                return err
+            }
+            s.SetupRoutes()
+            s.httpServer = s.newHTTPServer()
+            go s.serveUntilShutdown()
             return nil
         },
+        OnStop: s.cleanShutdown,
     })
     return s, nil
 }
@@ -264,23 +271,25 @@ func New(lc fx.Lifecycle, params ServerParams) (*Server, error) {
 
 ```go
 // internal/server/http.go
-func (s *Server) serveUntilShutdown() {
-    listenAddr := fmt.Sprintf(":%d", s.params.Config.Port)
-    s.httpServer = &http.Server{
-        Addr:           listenAddr,
+func (s *Server) newHTTPServer() *http.Server {
+    return &http.Server{
+        Addr:           fmt.Sprintf(":%d", s.params.Config.Port),
         ReadTimeout:    10 * time.Second,
         WriteTimeout:   10 * time.Second,
         MaxHeaderBytes: 1 << 20,
         Handler:        s,
     }
+}
 
-    s.SetupRoutes()
-
-    s.log.Info("http begin listen", "listenaddr", listenAddr)
+// serveUntilShutdown returns when the stop hook shuts the HTTP server down.
+// If it stops for any other reason, such as its port being taken, it asks fx
+// to shut down with exit code 1.
+func (s *Server) serveUntilShutdown() {
+    s.log.Info("http begin listen", "listenaddr", s.httpServer.Addr)
     if err := s.httpServer.ListenAndServe(); err != nil && err != http.ErrServerClosed {
         s.log.Error("listen error", "error", err)
-        if s.cancelFunc != nil {
-            s.cancelFunc()
+        if err := s.params.Shutdowner.Shutdown(fx.ExitCode(1)); err != nil {
+            s.log.Error("shutdown request failed", "error", err)
         }
     }
 }
@@ -292,43 +301,30 @@ func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 
 ## Signal Handling and Graceful Shutdown
 
+fx owns SIGINT, SIGTERM and the exit code. `Run()` in `main` waits for one of
+those signals or for a call to `Shutdown()` on `fx.Shutdowner`, runs the stop
+hooks, and exits 0 after a signal, or with the code the call gave in
+`fx.ExitCode`. It exits 1 instead when a start hook or a stop hook returns an
+error; when a start hook fails, fx first runs the stop hooks of everything
+already started. No other code calls `signal.Notify` or `os.Exit`: the listen
+error above asks fx to shut down with `fx.ExitCode(1)`, and a Sentry start
+failure is returned from the start hook. Each component releases its own
+resources in its own stop hook, which fx runs in the reverse order of start.
+
 ```go
-func (s *Server) serve() int {
-    s.ctx, s.cancelFunc = context.WithCancel(context.Background())
-
-    // Signal watcher
-    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 s.serveUntilShutdown()
-
-    for range s.ctx.Done() {
-    }
-    s.cleanShutdown()
-    return s.exitCode
-}
-
-func (s *Server) cleanShutdown() {
-    s.exitCode = 0
-    ctxShutdown, shutdownCancel := context.WithTimeout(context.Background(), 5*time.Second)
-    if err := s.httpServer.Shutdown(ctxShutdown); err != nil {
-        s.log.Error("server clean shutdown failed", "error", err)
-    }
-    if shutdownCancel != nil {
-        shutdownCancel()
-    }
-    s.cleanupForExit()
+// cleanShutdown is the server's stop hook. It fails when requests are still
+// running after 5 seconds.
+func (s *Server) cleanShutdown(ctx context.Context) error {
+    ctxShutdown, shutdownCancel := context.WithTimeout(ctx, 5*time.Second)
+    defer shutdownCancel()
+    err := s.httpServer.Shutdown(ctxShutdown)
     if s.sentryEnabled {
         sentry.Flush(2 * time.Second)
     }
+    if err != nil {
+        return fmt.Errorf("http server shutdown: %w", err)
+    }
+    return nil
 }
 ```
 
@@ -1160,11 +1156,11 @@ s.router.Get("/.well-known/healthcheck", s.h.HandleHealthCheck())
 Sentry is conditionally enabled based on `SENTRY_DSN` environment variable:
 
 ```go
-func (s *Server) enableSentry() {
+func (s *Server) enableSentry() error {
     s.sentryEnabled = false
 
     if s.params.Config.SentryDSN == "" {
-        return
+        return nil
     }
 
     err := sentry.Init(sentry.ClientOptions{
@@ -1172,15 +1168,17 @@ func (s *Server) enableSentry() {
         Release: fmt.Sprintf("%s-%s", s.params.Globals.Appname, s.params.Globals.Version),
     })
     if err != nil {
-        s.log.Error("sentry init failure", "error", err)
-        os.Exit(1)
-        return
+        return fmt.Errorf("sentry init failure: %w", err)
     }
     s.log.Info("sentry error reporting activated")
     s.sentryEnabled = true
+    return nil
 }
 ```
 
+The server's start hook calls `enableSentry()` and returns its error, so a DSN
+Sentry rejects stops startup and fx exits 1.
+
 Sentry middleware with repanic (bubbles panics to chi's Recoverer):
 
 ```go
@@ -1192,7 +1190,7 @@ if s.sentryEnabled {
 }
 ```
 
-Flush Sentry on shutdown:
+Flush Sentry in the server's stop hook, `cleanShutdown()`:
 
 ```go
 if s.sentryEnabled {