Bound every slog line against client-chosen text (closes #176)

internal/handlers/webhook.go

@@ -9,6 +9,7 @@ import (
 	"gorm.io/gorm"
 	"sneak.berlin/go/webhooker/internal/database"
 	"sneak.berlin/go/webhooker/internal/delivery"
+	"sneak.berlin/go/webhooker/internal/logfield"
 )
 
 const (
@@ -125,9 +126,16 @@ func (h *Handlers) lookupEntrypoint(
 		"path = ?", entrypointUUID,
 	).First(&entrypoint)
 	if result.Error != nil {
+		// The receiver is unauthenticated and /webhook/{uuid}
+		// matches any single segment, so this value is entirely
+		// client-chosen on exactly the branch where the lookup
+		// failed. DEBUG is off by default; the cap is what keeps
+		// turning it on from restoring an unbounded write.
 		h.log.Debug(
 			"entrypoint not found",
-			"path", entrypointUUID,
+			"path", logfield.Truncate(
+				entrypointUUID, logfield.MaxBytes,
+			),
 		)
 		http.NotFound(w, r)