P2-02 (server side): schedule reconciliation push + ack handling

Server is now the source of truth for the agent's cron set.

* Helpers in schedule_push.go:
  - loadScheduleSetPayload reads the host's schedules + canonical
    version into the wire shape.
  - pushScheduleSetOnConn writes directly to a just-handshaken conn
    (avoids racing against Hub.Register on a brand-new connection).
  - pushScheduleSetAsync is the post-CRUD flavour — no-op when the
    host is offline (the next reconnect's on-hello path catches it
    up, so a missed push is non-fatal).
  - applyScheduleAck records what version the agent has confirmed.

* onAgentHello restructured: was returning early when the host had
  no repo credentials, which made the schedule push unreachable for
  fresh hosts. Split into pushRepoCredsOnHello (silent no-op on
  ErrNotFound) + pushScheduleSetOnConn (always runs). Empty schedule
  list is a valid push: tells the agent to drop stale cron entries.

* WS dispatcher gains an OnScheduleAck hook on HandlerDeps; the
  http server wires it to applyScheduleAck. MsgScheduleAck moves
  out of the "TODO(P2)" group into a real case that decodes the
  payload and forwards to the callback.

* Schedule CRUD handlers each fire pushScheduleSetAsync after the
  audit-log write so the agent picks up changes within seconds.

Tests cover:
  - On-hello push of an already-created schedule, agent acks,
    applied_schedule_version flips on the host row.
  - Connect-then-CRUD: empty initial push (version 0), then a
    follow-on push at version 1 after the operator creates a
    schedule via REST.

Agent-side `schedule.set` handler (parse, replace local cron,
emit `schedule.ack`) is the remainder of P2-02 and lands with
P2-03's local scheduler.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/server/http/schedule_push.go

@@ -0,0 +1,152 @@
+package http
+
+import (
+	"context"
+	"encoding/json"
+	"log/slog"
+	"time"
+
+	"gitea.dcglab.co.uk/steve/restic-manager/internal/api"
+	"gitea.dcglab.co.uk/steve/restic-manager/internal/server/ws"
+	"gitea.dcglab.co.uk/steve/restic-manager/internal/store"
+)
+
+// loadScheduleSetPayload reads the host's current schedule set + the
+// canonical version into a wire-shape payload. Returns an empty
+// (but well-formed) payload with version 0 if the host has nothing
+// scheduled yet — that's still a valid state to push so the agent
+// drops any stale cron entries from a previous deployment.
+func (s *Server) loadScheduleSetPayload(ctx context.Context, hostID string) (api.ScheduleSetPayload, error) {
+	rows, err := s.deps.Store.ListSchedulesByHost(ctx, hostID)
+	if err != nil {
+		return api.ScheduleSetPayload{}, err
+	}
+	version, err := s.deps.Store.GetHostScheduleVersion(ctx, hostID)
+	if err != nil {
+		return api.ScheduleSetPayload{}, err
+	}
+	out := api.ScheduleSetPayload{
+		Version:   version,
+		Schedules: make([]api.Schedule, 0, len(rows)),
+	}
+	for _, r := range rows {
+		retJSON, _ := json.Marshal(r.RetentionPolicy)
+		optJSON, _ := json.Marshal(r.Options)
+		out.Schedules = append(out.Schedules, api.Schedule{
+			ID:              r.ID,
+			Kind:            api.JobKind(r.Kind),
+			CronExpr:        r.CronExpr,
+			Paths:           r.Paths,
+			Excludes:        r.Excludes,
+			Tags:            r.Tags,
+			RetentionPolicy: retJSON,
+			Options:         optJSON,
+			PreHook:         r.PreHook,
+			PostHook:        r.PostHook,
+			Enabled:         r.Enabled,
+		})
+	}
+	return out, nil
+}
+
+// pushScheduleSet ships the current schedule list to the agent over
+// the hub. Caller has already determined the agent is connected.
+// Errors are logged and returned; the next push (or the next hello)
+// will retry. Idempotent — sending the same version twice is a
+// harmless no-op on the agent side.
+func (s *Server) pushScheduleSet(ctx context.Context, hostID string) error {
+	pl, err := s.loadScheduleSetPayload(ctx, hostID)
+	if err != nil {
+		slog.Warn("push schedule.set: load failed", "host_id", hostID, "err", err)
+		return err
+	}
+	env, err := api.Marshal(api.MsgScheduleSet, "", pl)
+	if err != nil {
+		return err
+	}
+	sendCtx, cancel := context.WithTimeout(ctx, 5*time.Second)
+	defer cancel()
+	if err := s.deps.Hub.Send(sendCtx, hostID, env); err != nil {
+		slog.Warn("push schedule.set: hub send failed",
+			"host_id", hostID, "version", pl.Version, "err", err)
+		return err
+	}
+	return nil
+}
+
+// pushScheduleSetOnConn is the on-hello flavour: writes directly to
+// the just-handshaken conn rather than racing through the hub. Used
+// by onAgentHello so a brand-new connection can't miss an early
+// push because Register hasn't completed yet.
+func (s *Server) pushScheduleSetOnConn(ctx context.Context, hostID string, conn *ws.Conn) {
+	pl, err := s.loadScheduleSetPayload(ctx, hostID)
+	if err != nil {
+		slog.Warn("on-hello: load schedules", "host_id", hostID, "err", err)
+		return
+	}
+	env, err := api.Marshal(api.MsgScheduleSet, "", pl)
+	if err != nil {
+		slog.Error("on-hello: marshal schedule.set", "host_id", hostID, "err", err)
+		return
+	}
+	sendCtx, cancel := context.WithTimeout(ctx, 5*time.Second)
+	defer cancel()
+	if err := conn.Send(sendCtx, env); err != nil {
+		slog.Warn("on-hello: send schedule.set",
+			"host_id", hostID, "version", pl.Version, "err", err)
+	}
+}
+
+// pushIfConnected dispatches a schedule.set push asynchronously when
+// the agent is online. Used by CRUD handlers: a missed push is
+// non-fatal because the next reconnect's on-hello path will catch
+// the agent up. Decoupled from the request so the operator's HTTP
+// response doesn't wait on the WS round-trip.
+func (s *Server) pushScheduleSetAsync(hostID string) {
+	if s.deps.Hub == nil || !s.deps.Hub.Connected(hostID) {
+		return
+	}
+	go func() {
+		ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+		defer cancel()
+		_ = s.pushScheduleSet(ctx, hostID)
+	}()
+}
+
+// applyScheduleAck records the version the agent has confirmed via
+// schedule.ack. Called from the WS dispatcher (wired below). A bad
+// version (zero, or higher than what we've issued) is logged but
+// not fatal — the next push will set the agent straight.
+func (s *Server) applyScheduleAck(ctx context.Context, hostID string, version int64, appliedAt time.Time) {
+	if version <= 0 {
+		return
+	}
+	canonical, err := s.deps.Store.GetHostScheduleVersion(ctx, hostID)
+	if err != nil {
+		slog.Warn("schedule.ack: load canonical version",
+			"host_id", hostID, "err", err)
+		return
+	}
+	if version > canonical {
+		slog.Warn("schedule.ack: agent reported version ahead of server",
+			"host_id", hostID, "agent", version, "server", canonical)
+		return
+	}
+	if err := s.deps.Store.SetHostAppliedScheduleVersion(ctx, hostID, version); err != nil {
+		slog.Warn("schedule.ack: persist applied version",
+			"host_id", hostID, "version", version, "err", err)
+		return
+	}
+	slog.Info("schedule.ack: applied",
+		"host_id", hostID, "version", version, "applied_at", appliedAt)
+}
+
+// Compile-time guard that the store actually implements the methods
+// schedule_push.go calls. Useful when mocking the store in tests.
+var _ scheduleStore = (*store.Store)(nil)
+
+type scheduleStore interface {
+	ListSchedulesByHost(ctx context.Context, hostID string) ([]store.Schedule, error)
+	GetHostScheduleVersion(ctx context.Context, hostID string) (int64, error)
+	SetHostAppliedScheduleVersion(ctx context.Context, hostID string, version int64) error
+}