Show a progress bar and live log while Hammerhead, edges and sites update

The updater reports each step (checking, downloading with percent, verifying, installing, restarting).
Edges and sites send that progress and their log with their reports; Hammerhead serves it to a dialog
that opens when an update starts, and keeps its own last update log on disk across the restart.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

update.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"errors"
 	"net/http"
+	"os"
 	"strings"
 	"sync"
 	"time"
@@ -45,13 +46,32 @@ func (s *Server) applyUpdate(w http.ResponseWriter, r *http.Request, p *principa
 		fail(w, 400, errors.New("auto-update is off: set HAMMERHEAD_AUTO_UPDATE=1 and restart Hammerhead, or update it by hand"))
 		return
 	}
+	u := &s.selfUpd
+	u.mu.Lock()
+	if u.running {
+		u.mu.Unlock()
+		fail(w, 409, errors.New("an update is already running"))
+		return
+	}
+	u.running, u.stage, u.pct, u.lines = true, "starting", 0, nil
+	u.mu.Unlock()
+	os.WriteFile(s.updateLogPath(), nil, 0o600) // a new run starts a new log
 	cfg := s.updateConfig("hammerhead", s.opts.Version)
-	cfg.Restart = func(exe string) error { s.Close(); return selfupdate.Restart(exe) }
+	cfg.Progress = func(e selfupdate.Event) { s.selfNote(e.Stage, e.Pct, e.Line) }
+	cfg.Restart = func(exe string) error {
+		s.selfNote("restarting", 100, "Closing the database and restarting")
+		s.Close()
+		return selfupdate.Restart(exe)
+	}
+	s.selfNote("starting", 0, "Update requested by "+p.User.Email)
 	s.audit("", p.User.Email, "server.update", "")
 	go func() {
 		ctx, cancel := context.WithTimeout(context.Background(), 10*time.Minute)
 		defer cancel()
 		selfupdate.CheckOnce(ctx, cfg) // on success the process is replaced and this never returns
+		u.mu.Lock()
+		u.running = false
+		u.mu.Unlock()
 	}()
 	writeJSON(w, 200, map[string]any{"started": true})
 }
@@ -121,6 +141,7 @@ func (s *Server) updateEdge(w http.ResponseWriter, r *http.Request, p *principal
 		fail(w, 400, err)
 		return
 	}
+	delete(s.updRuns, e.ID) // a new request starts a new log
 	s.bump()
 	s.audit("", p.User.Email, "edge.update", e.Name)
 	ok(w)
@@ -142,6 +163,7 @@ func (s *Server) updateSite(w http.ResponseWriter, r *http.Request, c *orgCtx) {
 		fail(w, 400, err)
 		return
 	}
+	delete(s.updRuns, st.ID)
 	s.bump()
 	s.audit(c.Org.ID, c.Actor, "site.update", st.Name)
 	ok(w)