refactor(log): replace stdlib log with the application JSON logger

Every log.Printf/Fatalf becomes a structured slog call through
internal/log: request handlers use the request-scoped logger
(applog.FromContext, carrying request_id), startup failures exit via a
fatal() helper that still emits JSON, and the seedsample/dumpschema CLIs
bootstrap the same JSON logger. Stale client_test expectations aligned
with the refactored wrapper-call logging (message casing, result attr,
ERROR level).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

backend/cmd/dumpschema/main.go

@@ -10,11 +10,12 @@ package main
 
 import (
 	"fmt"
-	"log"
+	"log/slog"
 	"os"
 	"path/filepath"
 	"strings"
 
+	applog "geniusrun/backend/internal/log"
 	"geniusrun/backend/internal/store"
 )
 
@@ -26,6 +27,7 @@ type schemaEntry struct {
 }
 
 func main() {
+	slog.SetDefault(applog.NewLogger("info", os.Stdout))
 	tmpDir, err := os.MkdirTemp("", "geniusrun-dumpschema")
 	must(err)
 	defer os.RemoveAll(tmpDir)
@@ -91,11 +93,12 @@ func main() {
 
 	outPath := "../docs/DATABASE.md"
 	must(os.WriteFile(outPath, []byte(b.String()), 0644))
-	log.Printf("wrote %s", outPath)
+	slog.Info("wrote schema doc", "path", outPath)
 }
 
 func must(err error) {
 	if err != nil {
-		log.Fatal(err)
+		slog.Error("dumpschema", "error", err)
+		os.Exit(1)
 	}
 }

backend/cmd/geniusrund/main.go

@@ -5,7 +5,6 @@ package main
 
 import (
 	"context"
-	"log"
 	"log/slog"
 	"net/http"
 	"os"
@@ -17,30 +16,42 @@ import (
 	"geniusrun/backend/internal/auth"
 	"geniusrun/backend/internal/config"
 	"geniusrun/backend/internal/garmin"
-	"geniusrun/backend/internal/log"
+	applog "geniusrun/backend/internal/log"
 	"geniusrun/backend/internal/store"
 )
 
+// fatal logs through the application JSON logger and exits -- the
+// structured replacement for log.Fatalf, so even startup failures come
+// out as JSON lines.
+func fatal(msg string, err error) {
+	slog.Error(msg, "error", err)
+	os.Exit(1)
+}
+
 func main() {
+	// Bootstrap logger at info so failures loading the env config itself
+	// (which carries the real log level) are still emitted as JSON.
+	slog.SetDefault(applog.NewLogger("info", os.Stdout))
+
 	envCfg, err := config.LoadEnv()
 	if err != nil {
-		log.Fatalf("config: %v", err)
+		fatal("load env config", err)
 	}
 	slog.SetDefault(applog.NewLogger(envCfg.LogLevel, os.Stdout))
 
 	db, err := store.Open(envCfg.DBPath)
 	if err != nil {
-		log.Fatalf("open database: %v", err)
+		fatal("open database", err)
 	}
 	defer db.Close()
 
 	overrides, err := db.ConfigValues(context.Background())
 	if err != nil {
-		log.Fatalf("app config: %v", err)
+		fatal("read app config overrides", err)
 	}
 	appCfg, err := config.LoadApp(overrides)
 	if err != nil {
-		log.Fatalf("app config: %v", err)
+		fatal("load app config", err)
 	}
 
 	authVerifier, err := auth.NewOIDCVerifier(context.Background(), auth.OIDCConfig{
@@ -51,7 +62,7 @@ func main() {
 		RequiredRole: envCfg.OIDCRequiredRole,
 	})
 	if err != nil {
-		log.Fatalf("oidc: %v", err)
+		fatal("oidc verifier setup", err)
 	}
 
 	server := api.NewServer(
@@ -80,17 +91,17 @@ func main() {
 
 	httpServer := &http.Server{Addr: envCfg.BackendAddr, Handler: server.Router()}
 	go func() {
-		log.Printf("geniusrund listening on %s", envCfg.BackendAddr)
+		slog.Info("geniusrund listening", "addr", envCfg.BackendAddr)
 		if err := httpServer.ListenAndServe(); err != nil && err != http.ErrServerClosed {
-			log.Fatalf("http server: %v", err)
+			fatal("http server", err)
 		}
 	}()
 
 	<-ctx.Done()
-	log.Println("shutting down...")
+	slog.Info("shutting down")
 	shutdownCtx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
 	defer cancel()
 	if err := httpServer.Shutdown(shutdownCtx); err != nil {
-		log.Printf("http server shutdown: %v", err)
+		slog.Error("http server shutdown", "error", err)
 	}
 }

backend/cmd/seedsample/main.go

@@ -9,22 +9,25 @@ import (
 	"context"
 	"flag"
 	"fmt"
-	"log"
+	"log/slog"
+	"os"
 	"time"
 
 	"geniusrun/backend/internal/classify"
 	"geniusrun/backend/internal/garmin"
+	applog "geniusrun/backend/internal/log"
 	"geniusrun/backend/internal/store"
 )
 
 func main() {
+	slog.SetDefault(applog.NewLogger("info", os.Stdout))
 	dbPath := flag.String("db", "geniusrun_sample.db", "path to the SQLite database to seed")
 	flag.Parse()
 
 	ctx := context.Background()
 	db, err := store.Open(*dbPath)
 	if err != nil {
-		log.Fatalf("open db: %v", err)
+		fatal("open db", err)
 	}
 	defer db.Close()
 
@@ -233,10 +236,17 @@ func seedIntervalLapsAndSamples(ctx context.Context, db *store.DB, userID, activ
 
 func must(err error) {
 	if err != nil {
-		log.Fatal(err)
+		fatal("seedsample", err)
 	}
 }
 
+// fatal logs through the application JSON logger and exits -- the
+// structured replacement for log.Fatal.
+func fatal(msg string, err error) {
+	slog.Error(msg, "error", err)
+	os.Exit(1)
+}
+
 func mustFindKindID(ctx context.Context, db *store.DB, userID int64, name string) int64 {
 	kinds, err := db.ListWorkoutKinds(ctx, userID, false)
 	must(err)
@@ -245,6 +255,7 @@ func mustFindKindID(ctx context.Context, db *store.DB, userID int64, name string
 			return k.ID
 		}
 	}
-	log.Fatalf("seedsample: no workout kind named %q found for the seeded user (did ProvisionUser seed the taxonomy?)", name)
+	slog.Error("no workout kind with that name for the seeded user (did ProvisionUser seed the taxonomy?)", "kind", name)
+	os.Exit(1)
 	return 0
 }