feat(01-03): pgxpool wrapper, RequestID/slog middleware, slog handler switch

- Remove //go:build red_gate tag from internal/web/handlers_test.go and
  internal/db/pool_test.go now that consumer symbols are about to exist
- go mod tidy after real importers land (deferred from Plan 01-01 per
  Codex concern #1) — chi/v5, templ, pgx/v5, google/uuid now in require list
- internal/db/pool.go: NewPool(ctx, dsn) builds a pgxpool.Pool with
  MaxConns=10, MinConns=1; no eager Ping (RESEARCH Pitfall 2)
- internal/web/slog.go: NewSlogHandler returns JSON when env='production',
  text otherwise; pure helper, no slog.SetDefault side effect
- internal/web/middleware.go: RequestIDMiddleware (UUIDv4 → ctx +
  X-Request-ID header), LoggerFromContext helper, SlogLoggerMiddleware
  factory using chi WrapResponseWriter; field allowlist per V7/T-01-09

backend/go.mod

@@ -2,4 +2,17 @@ module backend
 
 go 1.26.1
 
-require github.com/a-h/templ v0.3.1020
+require (
+	github.com/a-h/templ v0.3.1020
+	github.com/go-chi/chi/v5 v5.2.5
+	github.com/google/uuid v1.6.0
+	github.com/jackc/pgx/v5 v5.9.2
+)
+
+require (
+	github.com/jackc/pgpassfile v1.0.0 // indirect
+	github.com/jackc/pgservicefile v0.0.0-20240606120523-5a60cdf6a761 // indirect
+	github.com/jackc/puddle/v2 v2.2.2 // indirect
+	golang.org/x/sync v0.17.0 // indirect
+	golang.org/x/text v0.29.0 // indirect
+)

backend/go.sum

@@ -1,8 +1,12 @@
 github.com/a-h/templ v0.3.1020 h1:ypAT/L5ySWEnZ6Zft/5yfoWXYYkhFNvEFOeeqecg4tw=
 github.com/a-h/templ v0.3.1020/go.mod h1:A2DlK61v+K+NRoGnhmYbNYVmtYHcFO5/AisMvBdDxTM=
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/go-chi/chi/v5 v5.2.5 h1:Eg4myHZBjyvJmAFjFvWgrqDTXFyOzjj7YIm3L3mu6Ug=
 github.com/go-chi/chi/v5 v5.2.5/go.mod h1:X7Gx4mteadT3eDOMTsXzmI4/rwUpOwBHLpAfupzFJP0=
+github.com/google/go-cmp v0.6.0 h1:ofyhxvXcZhMsU5ulbFiLKl/XBFqE1GSq7atu8tAmTRI=
+github.com/google/go-cmp v0.6.0/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
 github.com/google/uuid v1.6.0 h1:NIvaJDMOsjHA8n1jAhLSgzrAzy1Hgr+hNrb57e+94F0=
 github.com/google/uuid v1.6.0/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=
 github.com/jackc/pgpassfile v1.0.0 h1:/6Hmqy13Ss2zCq62VdNG8tM1wchn8zjSGOBJ6icpsIM=
@@ -11,23 +15,20 @@ github.com/jackc/pgservicefile v0.0.0-20240606120523-5a60cdf6a761 h1:iCEnooe7Ulw
 github.com/jackc/pgservicefile v0.0.0-20240606120523-5a60cdf6a761/go.mod h1:5TJZWKEWniPve33vlWYSoGYefn3gLQRzjfDlhSJ9ZKM=
 github.com/jackc/pgx/v5 v5.9.2 h1:3ZhOzMWnR4yJ+RW1XImIPsD1aNSz4T4fyP7zlQb56hw=
 github.com/jackc/pgx/v5 v5.9.2/go.mod h1:mal1tBGAFfLHvZzaYh77YS/eC6IX9OWbRV1QIIM0Jn4=
-github.com/mfridman/interpolate v0.0.2 h1:pnuTK7MQIxxFz1Gr+rjSIx9u7qVjf5VOoM/u6BbAxPY=
+github.com/jackc/puddle/v2 v2.2.2 h1:PR8nw+E/1w0GLuRFSmiioY6UooMp6KJv0/61nB7icHo=
-github.com/mfridman/interpolate v0.0.2/go.mod h1:p+7uk6oE07mpE/Ik1b8EckO0O4ZXiGAfshKBWLUM9Xg=
+github.com/jackc/puddle/v2 v2.2.2/go.mod h1:vriiEXHvEE654aYKXXjOvZM39qJ0q+azkZFrfEOc3H4=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
-github.com/pressly/goose/v3 v3.27.1 h1:6uEvcprBybDmW4hcz3gYujhARhye+GoWKhEWyzD5sh4=
-github.com/pressly/goose/v3 v3.27.1/go.mod h1:maruOxsPnIG2yHHyo8UqKWXYKFcH7Q76csUV7+7KYoM=
-github.com/sethvargo/go-retry v0.3.0 h1:EEt31A35QhrcRZtrYFDTBg91cqZVnFL2navjDrah2SE=
-github.com/sethvargo/go-retry v0.3.0/go.mod h1:mNX17F0C/HguQMyMyJxcnU471gOZGxCLyYaFyAZraas=
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
 github.com/stretchr/testify v1.3.0/go.mod h1:M5WIy9Dh21IEIfnGCwXGc5bZfKNJtfHm1UVUgZn+9EI=
 github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
-go.uber.org/multierr v1.11.0 h1:blXXJkSxSSfBVBlC76pxqeO+LN3aDfLQo+309xJstO0=
+github.com/stretchr/testify v1.11.1 h1:7s2iGBzp5EwR7/aIZr8ao5+dra3wiQyKjjFuvgVKu7U=
-go.uber.org/multierr v1.11.0/go.mod h1:20+QtiLqy0Nd6FdQB9TLXag12DsQkrbs3htMFfDN80Y=
+github.com/stretchr/testify v1.11.1/go.mod h1:wZwfW3scLgRK+23gO65QZefKpKQRnfz6sD981Nm4B6U=
-golang.org/x/sync v0.20.0 h1:e0PTpb7pjO8GAtTs2dQ6jYa5BWYlMuX047Dco/pItO4=
+golang.org/x/sync v0.17.0 h1:l60nONMj9l5drqw6jlhIELNv9I0A4OFgRsG9k2oT9Ug=
-golang.org/x/sync v0.20.0/go.mod h1:9xrNwdLfx4jkKbNva9FpL6vEN7evnE43NNNJQ2LF3+0=
+golang.org/x/sync v0.17.0/go.mod h1:9KTHXmSnoGruLpwFjVSX0lNNA75CykiMECbovNTZqGI=
 golang.org/x/text v0.29.0 h1:1neNs90w9YzJ9BocxfsQNHKuAT4pkghyXc4nhZ6sJvk=
 golang.org/x/text v0.29.0/go.mod h1:7MhJOA9CD2qZyOKYazxdYMF85OwPdEr9jTtBpO7ydH4=
-golang.org/x/text v0.36.0 h1:JfKh3XmcRPqZPKevfXVpI1wXPTqbkE5f7JA92a55Yxg=
-golang.org/x/text v0.36.0/go.mod h1:NIdBknypM8iqVmPiuco0Dh6P5Jcdk8lJL0CUebqK164=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

backend/internal/db/pool.go

@@ -0,0 +1,23 @@
+// Package db owns the Postgres connection pool wiring and (in later phases)
+// sqlc-generated query methods.
+package db
+
+import (
+	"context"
+
+	"github.com/jackc/pgx/v5/pgxpool"
+)
+
+// NewPool constructs a *pgxpool.Pool from the supplied DSN. Connections are
+// lazy — NewPool does NOT call Ping (RESEARCH Pitfall 2: lazy is the
+// canonical pgxpool behavior; callers exercise the pool via /healthz instead
+// of an eager startup ping). Returns an error if the DSN cannot be parsed.
+func NewPool(ctx context.Context, dsn string) (*pgxpool.Pool, error) {
+	cfg, err := pgxpool.ParseConfig(dsn)
+	if err != nil {
+		return nil, err
+	}
+	cfg.MaxConns = 10
+	cfg.MinConns = 1
+	return pgxpool.NewWithConfig(ctx, cfg)
+}

backend/internal/db/pool_test.go

@@ -1,5 +1,3 @@
-//go:build red_gate
-
 package db
 
 import (

backend/internal/web/handlers_test.go

@@ -1,5 +1,3 @@
-//go:build red_gate
-
 package web
 
 import (

backend/internal/web/middleware.go

@@ -0,0 +1,70 @@
+package web
+
+import (
+	"context"
+	"log/slog"
+	"net/http"
+	"time"
+
+	chimw "github.com/go-chi/chi/v5/middleware"
+	"github.com/google/uuid"
+)
+
+// ctxKey is the unexported type used for context.Context keys owned by the
+// web package. Per Go convention, using an unexported named type prevents
+// accidental collisions with other packages' context keys.
+type ctxKey string
+
+const requestIDKey ctxKey = "request_id"
+
+// RequestIDMiddleware emits a UUIDv4 for each request, attaches it to the
+// request context under requestIDKey, and sets the X-Request-ID response
+// header. The downstream handler (and any nested middleware) can recover
+// the ID via LoggerFromContext for structured logging.
+func RequestIDMiddleware(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		id := uuid.NewString()
+		ctx := context.WithValue(r.Context(), requestIDKey, id)
+		w.Header().Set("X-Request-ID", id)
+		next.ServeHTTP(w, r.WithContext(ctx))
+	})
+}
+
+// LoggerFromContext returns slog.Default() decorated with the request_id
+// attribute if one is present in ctx, otherwise plain slog.Default().
+// Handlers should prefer this helper over slog.Default() so per-request
+// log lines carry the request_id correlator.
+func LoggerFromContext(ctx context.Context) *slog.Logger {
+	if id, ok := ctx.Value(requestIDKey).(string); ok && id != "" {
+		return slog.Default().With("request_id", id)
+	}
+	return slog.Default()
+}
+
+// SlogLoggerMiddleware returns chi-compatible middleware that emits one
+// structured log line per request. The line carries method, path, status,
+// duration_ms, and request_id (when present). Per RESEARCH Pitfall 6 this
+// REPLACES chi's built-in middleware.Logger — never register both.
+//
+// The middleware deliberately allowlists fields (V7 / T-01-09): it never
+// logs request bodies, Authorization headers, Cookie headers, or the DSN.
+func SlogLoggerMiddleware(logger *slog.Logger) func(http.Handler) http.Handler {
+	return func(next http.Handler) http.Handler {
+		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			start := time.Now()
+			ww := chimw.NewWrapResponseWriter(w, r.ProtoMajor)
+			next.ServeHTTP(ww, r)
+
+			l := logger
+			if id, ok := r.Context().Value(requestIDKey).(string); ok && id != "" {
+				l = l.With("request_id", id)
+			}
+			l.Info("request",
+				"method", r.Method,
+				"path", r.URL.Path,
+				"status", ww.Status(),
+				"duration_ms", time.Since(start).Milliseconds(),
+			)
+		})
+	}
+}

backend/internal/web/slog.go

@@ -0,0 +1,23 @@
+package web
+
+import (
+	"io"
+	"log/slog"
+)
+
+// NewSlogHandler returns a slog.Handler appropriate for the supplied
+// environment. When env == "production" the returned handler emits
+// machine-parseable JSON; for any other value (including the empty string
+// and "development") the handler emits human-readable text. Both handlers
+// are configured at slog.LevelInfo.
+//
+// The caller is responsible for wiring the returned handler into a
+// slog.Logger (typically via slog.SetDefault) — this function is a pure
+// helper and intentionally has no side effects.
+func NewSlogHandler(env string, w io.Writer) slog.Handler {
+	opts := &slog.HandlerOptions{Level: slog.LevelInfo}
+	if env == "production" {
+		return slog.NewJSONHandler(w, opts)
+	}
+	return slog.NewTextHandler(w, opts)
+}