Logging: structured slog messages throughout, and WithLogger options so callers choose the logger

Log messages are lower-case event names with their details as key/value
attributes ("error" for errors), in place of formatted strings.

Loggable package take a WithLogger option as part of their "New*" call,
defaulting to slog.Default(). Each tags its lines with its `component`.

Some debug loggers print directly rather than using slog when in
terminal logging mode.

cmd/jobsearch/main.go

@@ -52,17 +52,16 @@ opportunities.
 		PersistentPreRunE: func(cmd *cobra.Command, args []string) error {
 			cli.SetupInitialLogging(cmd)
 
-			slog.Debug("root.PersistentPreRun")
+			slog.Debug("command persistent pre-run", "command", "root")
 			slog.Debug(
-				"command: \"" +
-					strings.Join(strings.Split(cmd.CommandPath(), " ")[1:], " ") +
-					"\"",
+				"command",
+				"path", strings.Join(strings.Split(cmd.CommandPath(), " ")[1:], " "),
 			)
 
 			return nil
 		},
 		PersistentPostRunE: func(cmd *cobra.Command, args []string) error {
-			slog.Debug("root.PersistentPostRun")
+			slog.Debug("command persistent post-run", "command", "root")
 
 			return opts.Finish()
 		},

cmd/mock-fts/main.go

@@ -24,6 +24,7 @@ import (
 	"errors"
 	"fmt"
 	"log"
+	"log/slog"
 	"net/http"
 	"os"
 	"os/signal"
@@ -206,15 +207,13 @@ func run(ctx context.Context, o *options) (err error) {
 	if err != nil {
 		return err
 	}
-	log.Printf(
-		"catalog: %d buyers, %d suppliers, %d subjects, %d methods, %d classifications",
-		len(
-			cat.Buyers,
-		),
-		len(cat.Suppliers),
-		len(cat.Subjects),
-		len(cat.Methods),
-		len(cat.Classifications),
+	slog.Info(
+		"catalog loaded",
+		"buyers", len(cat.Buyers),
+		"suppliers", len(cat.Suppliers),
+		"subjects", len(cat.Subjects),
+		"methods", len(cat.Methods),
+		"classifications", len(cat.Classifications),
 	)
 
 	// ----- store -----
@@ -223,7 +222,7 @@ func run(ctx context.Context, o *options) (err error) {
 		if err := os.Remove(storePath); err != nil && !errors.Is(err, os.ErrNotExist) {
 			return err
 		}
-		log.Print("store: reset")
+		slog.Info("store reset", "path", storePath)
 	}
 	store, err := mock.OpenStore(storePath)
 	if err != nil {
@@ -238,7 +237,7 @@ func run(ctx context.Context, o *options) (err error) {
 		return err
 	}
 
-	log.Printf("store: %d releases (%d generated to catch up)", store.Len(), n)
+	slog.Info("store ready", "releases", store.Len(), "generated", n)
 
 	// The generator and server share a context that also ends if the server
 	// fails, so the generator is never left running after run returns.
@@ -286,11 +285,11 @@ func run(ctx context.Context, o *options) (err error) {
 		)
 		defer cancelShutdown()
 		if err := httpSrv.Shutdown(shutdownCtx); err != nil {
-			log.Printf("shutdown: %v", err)
+			slog.Error("shutdown failed", "error", err)
 		}
 	}()
 
-	log.Printf("FTS mock listening on %s%s (query times in %s)", o.addr, mock.BasePath, loc)
+	slog.Info("mock listening", "addr", o.addr, "path", mock.BasePath, "time_zone", loc.String())
 	serveErr := httpSrv.ListenAndServe()
 
 	cancel() // stop the worker (and the shutdown goroutine) if the server failed