feat(coordinator): running state, worker liveness, request-size limits

Polish pass hardening the queue and closing plan gaps.

- Task state machine gains `running`: the first heartbeat moves a task from
  leased to running (migrations 0006/0007 add the enum value and extend the
  lease-integrity check). verifyLease, ExpireLease, the reaper SQL, and job
  progress all treat leased and running alike.
- Worker liveness: a heartbeat from a registered worker (UUID worker_id) bumps
  its last_heartbeat_at online; a second background reaper marks workers offline
  after WORKER_OFFLINE_AFTER of silence (RunReaper generalized to RunPeriodic).
- Request-size limits: JSON bodies capped at 1 MiB; dataset/artifact uploads
  capped at MAX_UPLOAD_BYTES (default 1 GiB) via http.MaxBytesReader.
- Tests cover the running transition, liveness + offline reaper (unit over
  memstore and integration over Postgres).

coordinator/.env.example

@@ -13,6 +13,8 @@ LOG_LEVEL=info
 
 # Directory where artifact bytes are stored.
 COORDINATOR_STORAGE_DIR=./data
+# Upper bound on an uploaded dataset or artifact body (bytes). Default 1 GiB.
+MAX_UPLOAD_BYTES=1073741824
 
 # Optional tuning (defaults shown).
 DB_MAX_CONNS=10
@@ -22,3 +24,5 @@ REQUEST_TIMEOUT=15s
 LEASE_DURATION=2m
 DEFAULT_MAX_ATTEMPTS=3
 REAPER_INTERVAL=30s
+# A worker silent longer than this is marked offline by the reaper.
+WORKER_OFFLINE_AFTER=1m

coordinator/cmd/coordinator/main.go

@@ -72,7 +72,7 @@ func run() error {
 		CreateJob:        usecase.NewCreateJob(jobRepo, taskRepo, tx, clk),
 		SubmitDataset:    usecase.NewSubmitDataset(blobStore, artifactRepo, jobRepo, taskRepo, tx, clk),
 		ClaimTask:        usecase.NewClaimTask(taskRepo, clk, cfg.LeaseDuration),
-		RenewLease:       usecase.NewRenewLease(taskRepo, tx, clk, cfg.LeaseDuration),
+		RenewLease:       usecase.NewRenewLease(taskRepo, workerRepo, tx, clk, cfg.LeaseDuration),
 		CompleteTask:     usecase.NewCompleteTask(taskRepo, jobRepo, artifactRepo, tx, clk),
 		FailTask:         usecase.NewFailTask(taskRepo, jobRepo, tx, clk),
 		GetJobStatus:     usecase.NewGetJobStatus(jobRepo, taskRepo),
@@ -81,19 +81,30 @@ func run() error {
 		GetTaskInput:     usecase.NewGetTaskInput(taskRepo, artifactRepo, blobStore),
 	}
 
-	// Background workers are tracked so shutdown can wait for them. Without
-	// this the process would exit while the reaper sat mid-UPDATE, and the
-	// deferred pool.Close() would pull connections out from under it.
+	// Background reapers are tracked so shutdown can wait for them. Without this
+	// the process would exit mid-UPDATE, and the deferred pool.Close() would pull
+	// connections out from under them.
+	expireLeases := usecase.NewExpireLeases(taskRepo, clk)
+	markOffline := usecase.NewMarkWorkersOffline(workerRepo, clk, cfg.WorkerOfflineAfter)
+
 	var wg sync.WaitGroup
-	wg.Add(1)
-	go func() {
-		defer wg.Done()
-		infra.RunReaper(ctx, log, usecase.NewExpireLeases(taskRepo, clk), cfg.ReaperInterval)
-	}()
+	for _, r := range []struct {
+		name string
+		fn   func(context.Context) (int64, error)
+	}{
+		{"reaper requeued expired leases", expireLeases.Execute},
+		{"reaper marked workers offline", markOffline.Execute},
+	} {
+		wg.Add(1)
+		go func(name string, fn func(context.Context) (int64, error)) {
+			defer wg.Done()
+			infra.RunPeriodic(ctx, log, name, cfg.ReaperInterval, fn)
+		}(r.name, r.fn)
+	}
 
 	// pool.Ping backs /health: readiness means the database answers, not just
 	// that the process is alive.
-	api := httptransport.NewServer(useCases, log, cfg.RequestTimeout, cfg.HeartbeatInterval, pool.Ping)
+	api := httptransport.NewServer(useCases, log, cfg.RequestTimeout, cfg.HeartbeatInterval, cfg.MaxUploadBytes, pool.Ping)
 	err = infra.RunServer(ctx, log, cfg.Addr, api.Handler(cfg.Token))
 
 	// Shutdown order matters, and defers alone cannot express it (they run

coordinator/internal/domain/task.go

@@ -15,6 +15,7 @@ type TaskStatus string
 const (
 	TaskPending   TaskStatus = "pending"
 	TaskLeased    TaskStatus = "leased"
+	TaskRunning   TaskStatus = "running"
 	TaskCompleted TaskStatus = "completed"
 	TaskFailed    TaskStatus = "failed"
 	TaskCancelled TaskStatus = "cancelled"
@@ -146,7 +147,9 @@ func (t *Task) AsClaimed() ClaimedTask {
 // verifyLease is the guard every worker-driven transition shares: the caller
 // must own the lease and reference the attempt it was granted.
 func (t *Task) verifyLease(worker string, attempt int) error {
-	if t.Status != TaskLeased {
+	// A task is worker-owned while leased or running: the first heartbeat moves
+	// it from leased to running, but ownership rules are identical for both.
+	if t.Status != TaskLeased && t.Status != TaskRunning {
 		return ErrTaskNotLeased
 	}
 	if t.LeaseOwner == nil || *t.LeaseOwner != worker {
@@ -158,12 +161,16 @@ func (t *Task) verifyLease(worker string, attempt int) error {
 	return nil
 }
 
-// RenewLease extends the lease of the worker that holds it.
+// RenewLease extends the lease of the worker that holds it. The first heartbeat
+// also acknowledges start, moving the task from leased to running.
 func (t *Task) RenewLease(worker string, attempt int, until time.Time) error {
 	if err := t.verifyLease(worker, attempt); err != nil {
 		return err
 	}
 	t.LeaseExpiresAt = &until
+	if t.Status == TaskLeased {
+		t.Status = TaskRunning
+	}
 	t.Version++
 	return nil
 }
@@ -228,7 +235,8 @@ func (t *Task) Fail(worker string, attempt int, code, message string, retryable
 // ExpireLease is applied by the reaper when a lease elapses without a
 // heartbeat: requeue while attempts remain, otherwise fail terminally.
 func (t *Task) ExpireLease(now time.Time) {
-	if t.Status != TaskLeased {
+	// Both a leased and a running task can go silent and must be reclaimed.
+	if t.Status != TaskLeased && t.Status != TaskRunning {
 		return
 	}
 	t.LeaseOwner = nil

coordinator/internal/domain/task_test.go

@@ -168,6 +168,42 @@ func TestExpireLeaseIgnoresUnleasedTasks(t *testing.T) {
 	}
 }
 
+func TestFirstHeartbeatMovesLeasedToRunning(t *testing.T) {
+	task := leasedTask(1, 3)
+	until := testLater.Add(time.Hour)
+
+	if err := task.RenewLease(testWorker, 1, until); err != nil {
+		t.Fatal(err)
+	}
+	if task.Status != TaskRunning {
+		t.Errorf("status = %q, want running after first heartbeat", task.Status)
+	}
+	// A second heartbeat keeps it running.
+	if err := task.RenewLease(testWorker, 1, until); err != nil {
+		t.Fatal(err)
+	}
+	if task.Status != TaskRunning {
+		t.Errorf("status = %q, want running", task.Status)
+	}
+}
+
+func TestRunningTaskCanBeCompletedAndExpired(t *testing.T) {
+	// Complete works from running.
+	task := leasedTask(1, 3)
+	_ = task.RenewLease(testWorker, 1, testLater) // -> running
+	if err := task.CompleteWith(testResult, nil, testWorker, 1, testNow); err != nil {
+		t.Errorf("complete from running: %v", err)
+	}
+
+	// Expire reclaims a running task too.
+	task2 := leasedTask(1, 3)
+	_ = task2.RenewLease(testWorker, 1, testLater) // -> running
+	task2.ExpireLease(testNow)
+	if task2.Status != TaskPending {
+		t.Errorf("status = %q, want pending after a running lease expires", task2.Status)
+	}
+}
+
 func TestRenewLeaseExtendsOnlyForHolder(t *testing.T) {
 	task := leasedTask(1, 3)
 	until := testLater.Add(time.Hour)

coordinator/internal/infra/config.go

@@ -31,6 +31,8 @@ type Config struct {
 	LogFile string
 	// Directory where artifact bytes are stored.
 	StorageDir string
+	// Upper bound on an uploaded dataset or artifact body, in bytes.
+	MaxUploadBytes int64
 
 	// Connection pool upper bound.
 	DBMaxConns int32
@@ -48,6 +50,8 @@ type Config struct {
 	DefaultMaxAttempts int
 	// How often the background lease-reaper runs.
 	ReaperInterval time.Duration
+	// A worker silent for longer than this is marked offline by the reaper.
+	WorkerOfflineAfter time.Duration
 }
 
 // Load reads the environment and fails fast on anything required-but-missing
@@ -76,6 +80,7 @@ func LoadConfig() (Config, error) {
 		LogLevel:           getEnv("LOG_LEVEL", "info"),
 		LogFile:            os.Getenv("LOG_FILE"),
 		StorageDir:         getEnv("COORDINATOR_STORAGE_DIR", "./data"),
+		MaxUploadBytes:     1 << 30, // 1 GiB
 		DBMaxConns:         10,
 		DBConnectTimeout:   30 * time.Second,
 		RequestTimeout:     15 * time.Second,
@@ -83,6 +88,7 @@ func LoadConfig() (Config, error) {
 		LeaseDuration:      2 * time.Minute,
 		DefaultMaxAttempts: 3,
 		ReaperInterval:     30 * time.Second,
+		WorkerOfflineAfter: 1 * time.Minute,
 	}
 
 	if cfg.DatabaseURL == "" {
@@ -96,6 +102,9 @@ func LoadConfig() (Config, error) {
 	if cfg.DBConnectTimeout, err = getEnvDuration("DB_CONNECT_TIMEOUT", cfg.DBConnectTimeout); err != nil {
 		return Config{}, err
 	}
+	if cfg.MaxUploadBytes, err = getEnvInt64("MAX_UPLOAD_BYTES", cfg.MaxUploadBytes); err != nil {
+		return Config{}, err
+	}
 	if cfg.RequestTimeout, err = getEnvDuration("REQUEST_TIMEOUT", cfg.RequestTimeout); err != nil {
 		return Config{}, err
 	}
@@ -108,6 +117,9 @@ func LoadConfig() (Config, error) {
 	if cfg.ReaperInterval, err = getEnvDuration("REAPER_INTERVAL", cfg.ReaperInterval); err != nil {
 		return Config{}, err
 	}
+	if cfg.WorkerOfflineAfter, err = getEnvDuration("WORKER_OFFLINE_AFTER", cfg.WorkerOfflineAfter); err != nil {
+		return Config{}, err
+	}
 	if cfg.DefaultMaxAttempts, err = getEnvInt("DEFAULT_MAX_ATTEMPTS", cfg.DefaultMaxAttempts); err != nil {
 		return Config{}, err
 	}
@@ -147,6 +159,18 @@ func getEnvInt32(key string, def int32) (int32, error) {
 	return int32(n), nil
 }
 
+func getEnvInt64(key string, def int64) (int64, error) {
+	v := os.Getenv(key)
+	if v == "" {
+		return def, nil
+	}
+	n, err := strconv.ParseInt(v, 10, 64)
+	if err != nil {
+		return 0, fmt.Errorf("%s: %w", key, err)
+	}
+	return n, nil
+}
+
 func getEnvDuration(key string, def time.Duration) (time.Duration, error) {
 	v := os.Getenv(key)
 	if v == "" {

coordinator/internal/infra/server.go

@@ -8,8 +8,6 @@ import (
 	"log/slog"
 	"net/http"
 	"time"
-
-	"github.com/emil28092005/SciMesh/coordinator/internal/usecase"
 )
 
 const shutdownGrace = 15 * time.Second
@@ -48,7 +46,13 @@ func RunServer(ctx context.Context, log *slog.Logger, addr string, handler http.
 
 // RunReaper periodically reclaims tasks whose lease elapsed, so a worker that
 // died without a heartbeat cannot strand its task in 'leased' forever.
-func RunReaper(ctx context.Context, log *slog.Logger, uc *usecase.ExpireLeases, interval time.Duration) {
+// RunPeriodic invokes fn on an interval until ctx is done, logging how many rows
+// each tick affected. It backs the background reapers (expired leases, offline
+// workers) — each is a set-based UPDATE that is safe to run repeatedly and
+// concurrently across coordinators.
+func RunPeriodic(ctx context.Context, log *slog.Logger, name string, interval time.Duration,
+	fn func(context.Context) (int64, error)) {
+
 	t := time.NewTicker(interval)
 	defer t.Stop()
 
@@ -57,15 +61,13 @@ func RunReaper(ctx context.Context, log *slog.Logger, uc *usecase.ExpireLeases,
 		case <-ctx.Done():
 			return
 		case <-t.C:
-			n, err := uc.Execute(ctx)
+			n, err := fn(ctx)
 			if err != nil {
-				// Demoted to debug while the repository is still a stub;
-				// raise to Warn once phase 5 lands.
-				log.Debug("reaper skipped", "err", err)
+				log.Debug(name+" skipped", "err", err)
 				continue
 			}
 			if n > 0 {
-				log.Info("reaper requeued expired leases", "count", n)
+				log.Info(name, "count", n)
 			}
 		}
 	}

coordinator/internal/memstore/memstore.go

@@ -233,6 +233,29 @@ func (r *WorkerRepo) Get(ctx context.Context, id uuid.UUID) (*domain.Worker, err
 	return &cp, nil
 }
 
+func (r *WorkerRepo) Touch(ctx context.Context, id uuid.UUID, at time.Time) error {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	if w, ok := r.workers[id]; ok {
+		w.LastHeartbeatAt = at
+		w.Status = domain.WorkerOnline
+	}
+	return nil
+}
+
+func (r *WorkerRepo) MarkStaleOffline(ctx context.Context, cutoff time.Time) (int64, error) {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	var n int64
+	for _, w := range r.workers {
+		if w.Status != domain.WorkerOffline && w.LastHeartbeatAt.Before(cutoff) {
+			w.Status = domain.WorkerOffline
+			n++
+		}
+	}
+	return n, nil
+}
+
 // --- ArtifactRepo --------------------------------------------------------
 
 type ArtifactRepo struct {

coordinator/internal/storage/postgres/integration_test.go

@@ -387,6 +387,47 @@ func TestWorkerRepoRoundTrip(t *testing.T) {
 	}
 }
 
+func TestWorkerLivenessAndOfflineReaper(t *testing.T) {
+	pool := testPool(t)
+	ctx := context.Background()
+	repo := NewWorkerRepo(pool)
+
+	w, err := domain.NewWorker("liveness", []string{"similarity_search"}, time.Now().UTC().Add(-time.Hour))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := repo.Insert(ctx, w); err != nil {
+		t.Fatalf("insert: %v", err)
+	}
+	t.Cleanup(func() { _, _ = pool.Exec(context.Background(), `DELETE FROM workers WHERE id = $1`, w.ID) })
+
+	// A fresh heartbeat bumps it online.
+	now := time.Now().UTC()
+	if err := repo.Touch(ctx, w.ID, now); err != nil {
+		t.Fatalf("touch: %v", err)
+	}
+	if got, _ := repo.Get(ctx, w.ID); got.Status != domain.WorkerOnline {
+		t.Errorf("status = %q, want online after touch", got.Status)
+	}
+
+	// Touching an unregistered id is a harmless no-op.
+	if err := repo.Touch(ctx, uuid.New(), now); err != nil {
+		t.Errorf("touch of unknown worker returned %v, want nil", err)
+	}
+
+	// The reaper marks it offline once its heartbeat is older than the cutoff.
+	n, err := repo.MarkStaleOffline(ctx, now.Add(time.Minute))
+	if err != nil {
+		t.Fatalf("mark offline: %v", err)
+	}
+	if n < 1 {
+		t.Errorf("marked %d offline, want at least 1", n)
+	}
+	if got, _ := repo.Get(ctx, w.ID); got.Status != domain.WorkerOffline {
+		t.Errorf("status = %q, want offline after reaper", got.Status)
+	}
+}
+
 func TestArtifactRepoRoundTrip(t *testing.T) {
 	pool := testPool(t)
 	ctx := context.Background()

coordinator/internal/storage/postgres/task_repo.go

@@ -314,7 +314,7 @@ SET status           = CASE WHEN attempt < max_attempts THEN 'pending'::task_sta
                             ELSE error_message END,
     completed_at     = CASE WHEN attempt >= max_attempts THEN $1 ELSE completed_at END,
     version          = version + 1
-WHERE status = 'leased' AND lease_expires_at < $1`
+WHERE status IN ('leased','running') AND lease_expires_at < $1`
 
 func (r *TaskRepo) ExpireLeases(ctx context.Context, now time.Time) (int64, error) {
 	var affected int64

coordinator/internal/storage/postgres/worker_repo.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"time"
 
 	sq "github.com/Masterminds/squirrel"
 	"github.com/google/uuid"
@@ -59,6 +60,37 @@ func (r *WorkerRepo) Get(ctx context.Context, id uuid.UUID) (*domain.Worker, err
 	return w, nil
 }
 
+func (r *WorkerRepo) Touch(ctx context.Context, id uuid.UUID, at time.Time) error {
+	sql, args, err := psql.Update("workers").
+		SetMap(map[string]any{"last_heartbeat_at": at, "status": "online", "updated_at": at}).
+		Where(sq.Eq{"id": id}).
+		ToSql()
+	if err != nil {
+		return err
+	}
+	// A worker that never registered simply matches no row; that is not an error.
+	if _, err := conn(ctx, r.pool).Exec(ctx, sql, args...); err != nil {
+		return fmt.Errorf("touch worker: %w", err)
+	}
+	return nil
+}
+
+func (r *WorkerRepo) MarkStaleOffline(ctx context.Context, cutoff time.Time) (int64, error) {
+	sql, args, err := psql.Update("workers").
+		SetMap(map[string]any{"status": "offline", "updated_at": cutoff}).
+		Where(sq.Lt{"last_heartbeat_at": cutoff}).
+		Where(sq.NotEq{"status": "offline"}).
+		ToSql()
+	if err != nil {
+		return 0, err
+	}
+	tag, err := conn(ctx, r.pool).Exec(ctx, sql, args...)
+	if err != nil {
+		return 0, fmt.Errorf("mark stale workers offline: %w", err)
+	}
+	return tag.RowsAffected(), nil
+}
+
 func scanWorker(row pgx.Row) (*domain.Worker, error) {
 	var (
 		w      domain.Worker

coordinator/internal/transport/http/errors.go

@@ -15,8 +15,12 @@ func writeJSON(w http.ResponseWriter, status int, v any) {
 	_ = json.NewEncoder(w).Encode(v)
 }
 
+// maxJSONBody caps a JSON request body. The DTOs are tiny; anything larger is a
+// mistake or an attack, and must not be read into memory unbounded.
+const maxJSONBody = 1 << 20 // 1 MiB
+
 func decodeJSON(r *http.Request, dst any) error {
-	dec := json.NewDecoder(r.Body)
+	dec := json.NewDecoder(http.MaxBytesReader(nil, r.Body, maxJSONBody))
 	// Reject unknown fields: silently ignoring a misspelled "worker_ID" would
 	// surface later as a baffling validation failure.
 	dec.DisallowUnknownFields()

coordinator/internal/transport/http/handlers.go

@@ -186,6 +186,7 @@ const defaultChunkRows = 1000
 // chunker. The text fields MUST precede the file part: the file is streamed, not
 // buffered, so by the time it arrives the other fields are already parsed.
 func (s *Server) handleUploadDataset(w http.ResponseWriter, r *http.Request) {
+	r.Body = http.MaxBytesReader(w, r.Body, s.maxUploadBytes)
 	mr, err := r.MultipartReader()
 	if err != nil {
 		s.writeError(w, r, domain.ErrInvalidInput)
@@ -292,6 +293,7 @@ func (s *Server) handleUploadArtifact(w http.ResponseWriter, r *http.Request) {
 		s.writeError(w, r, domain.ErrInvalidInput)
 		return
 	}
+	r.Body = http.MaxBytesReader(w, r.Body, s.maxUploadBytes)
 
 	art, err := s.uc.UploadArtifact.Execute(r.Context(), usecase.UploadArtifactInput{
 		TaskID:      taskID,

coordinator/internal/transport/http/server.go

@@ -34,18 +34,20 @@ type Server struct {
 	log               *slog.Logger
 	requestTimeout    time.Duration
 	heartbeatInterval time.Duration
+	maxUploadBytes    int64
 	// ready probes downstream dependencies (the database) for /health. Kept as
 	// a func so the transport layer never imports pgx.
 	ready func(context.Context) error
 }
 
 func NewServer(uc UseCases, log *slog.Logger, requestTimeout, heartbeatInterval time.Duration,
-	ready func(context.Context) error) *Server {
+	maxUploadBytes int64, ready func(context.Context) error) *Server {
 	return &Server{
 		uc:                uc,
 		log:               log,
 		requestTimeout:    requestTimeout,
 		heartbeatInterval: heartbeatInterval,
+		maxUploadBytes:    maxUploadBytes,
 		ready:             ready,
 	}
 }

coordinator/internal/transport/http/server_test.go

@@ -42,7 +42,7 @@ func newEnv(t *testing.T, ready func(context.Context) error) *env {
 		CreateJob:        usecase.NewCreateJob(jobs, tasks, tx, clk),
 		SubmitDataset:    usecase.NewSubmitDataset(blobs, arts, jobs, tasks, tx, clk),
 		ClaimTask:        usecase.NewClaimTask(tasks, clk, lease),
-		RenewLease:       usecase.NewRenewLease(tasks, tx, clk, lease),
+		RenewLease:       usecase.NewRenewLease(tasks, work, tx, clk, lease),
 		CompleteTask:     usecase.NewCompleteTask(tasks, jobs, arts, tx, clk),
 		FailTask:         usecase.NewFailTask(tasks, jobs, tx, clk),
 		GetJobStatus:     usecase.NewGetJobStatus(jobs, tasks),
@@ -50,7 +50,7 @@ func newEnv(t *testing.T, ready func(context.Context) error) *env {
 		DownloadArtifact: usecase.NewDownloadArtifact(arts, blobs),
 		GetTaskInput:     usecase.NewGetTaskInput(tasks, arts, blobs),
 	}
-	srv := coordhttp.NewServer(uc, slog.New(slog.NewTextHandler(io.Discard, nil)), 5*time.Second, 15*time.Second, ready)
+	srv := coordhttp.NewServer(uc, slog.New(slog.NewTextHandler(io.Discard, nil)), 5*time.Second, 15*time.Second, 1<<30, ready)
 	ts := httptest.NewServer(srv.Handler(token))
 	t.Cleanup(ts.Close)
 	return &env{ts: ts, blobs: blobs}

coordinator/internal/usecase/job.go

@@ -143,9 +143,10 @@ func progressFrom(job domain.Job, counts map[domain.TaskStatus]int) domain.JobPr
 	p := domain.JobProgress{
 		Job:     job,
 		Pending: counts[domain.TaskPending],
-		Leased:  counts[domain.TaskLeased],
-		Done:    counts[domain.TaskCompleted],
-		Failed:  counts[domain.TaskFailed],
+		// Leased and running are both "in flight" for progress purposes.
+		Leased: counts[domain.TaskLeased] + counts[domain.TaskRunning],
+		Done:   counts[domain.TaskCompleted],
+		Failed: counts[domain.TaskFailed],
 	}
 	for _, n := range counts {
 		p.Total += n

coordinator/internal/usecase/ports.go

@@ -72,6 +72,12 @@ type JobRepository interface {
 type WorkerRepository interface {
 	Insert(ctx context.Context, w *domain.Worker) error
 	Get(ctx context.Context, id uuid.UUID) (*domain.Worker, error)
+	// Touch records liveness for a heartbeating worker, marking it online. A
+	// no-op for an id that is not a registered worker.
+	Touch(ctx context.Context, id uuid.UUID, at time.Time) error
+	// MarkStaleOffline flips every worker last seen before cutoff to offline and
+	// reports how many changed.
+	MarkStaleOffline(ctx context.Context, cutoff time.Time) (int64, error)
 }
 
 // ArtifactRepository persists artifact metadata. The bytes live in a BlobStore;

coordinator/internal/usecase/task.go

@@ -69,13 +69,15 @@ func (uc *ClaimTask) Execute(ctx context.Context, in ClaimTaskInput) (*domain.Cl
 
 type RenewLease struct {
 	tasks         TaskRepository
+	workers       WorkerRepository
 	tx            TxManager
 	clock         Clock
 	leaseDuration time.Duration
 }
 
-func NewRenewLease(tasks TaskRepository, tx TxManager, clock Clock, leaseDuration time.Duration) *RenewLease {
-	return &RenewLease{tasks: tasks, tx: tx, clock: clock, leaseDuration: leaseDuration}
+func NewRenewLease(tasks TaskRepository, workers WorkerRepository, tx TxManager,
+	clock Clock, leaseDuration time.Duration) *RenewLease {
+	return &RenewLease{tasks: tasks, workers: workers, tx: tx, clock: clock, leaseDuration: leaseDuration}
 }
 
 // Execute is a read-modify-write, so it runs inside a transaction with the row
@@ -101,6 +103,12 @@ func (uc *RenewLease) Execute(ctx context.Context, in RenewLeaseInput) (*domain.
 	if err != nil {
 		return nil, err
 	}
+
+	// Best-effort worker liveness, outside the task transaction so it can never
+	// fail the heartbeat. Only registered workers (a UUID worker_id) are tracked.
+	if id, perr := uuid.Parse(in.WorkerID); perr == nil {
+		_ = uc.workers.Touch(ctx, id, uc.clock.Now())
+	}
 	return &claimed, nil
 }
 

coordinator/internal/usecase/usecase_test.go

@@ -57,7 +57,7 @@ func newHarness() *harness {
 	h.createJob = usecase.NewCreateJob(h.jobs, h.tasks, tx, h.clk)
 	h.submit = usecase.NewSubmitDataset(h.blobs, h.arts, h.jobs, h.tasks, tx, h.clk)
 	h.claim = usecase.NewClaimTask(h.tasks, h.clk, lease)
-	h.renew = usecase.NewRenewLease(h.tasks, tx, h.clk, lease)
+	h.renew = usecase.NewRenewLease(h.tasks, h.work, tx, h.clk, lease)
 	h.complete = usecase.NewCompleteTask(h.tasks, h.jobs, h.arts, tx, h.clk)
 	h.fail = usecase.NewFailTask(h.tasks, h.jobs, tx, h.clk)
 	h.status = usecase.NewGetJobStatus(h.jobs, h.tasks)
@@ -172,6 +172,26 @@ func TestRenewExtendsForHolder(t *testing.T) {
 	}
 }
 
+func TestHeartbeatThenCompleteViaRunning(t *testing.T) {
+	h := newHarness()
+	jobID := h.seedJob(t, "w", 1)
+	taskID, attempt := h.leaseOne(t, "w1", "w")
+
+	// Heartbeat moves the task to running; completion must still work from there.
+	if _, err := h.renew.Execute(ctx, usecase.RenewLeaseInput{TaskID: taskID, WorkerID: "w1", Attempt: attempt}); err != nil {
+		t.Fatalf("heartbeat: %v", err)
+	}
+	artID := h.uploadResult(t, taskID, "w1", attempt)
+	if _, err := h.complete.Execute(ctx, usecase.CompleteTaskInput{
+		TaskID: taskID, WorkerID: "w1", Attempt: attempt, ResultArtifactID: artID,
+	}); err != nil {
+		t.Fatalf("complete after heartbeat: %v", err)
+	}
+	if prog, _ := h.status.Execute(ctx, jobID); prog.DeriveStatus() != domain.JobCompleted {
+		t.Errorf("job status = %q, want completed", prog.DeriveStatus())
+	}
+}
+
 func TestRenewRejectsForeignWorker(t *testing.T) {
 	h := newHarness()
 	h.seedJob(t, "w", 1)
@@ -285,6 +305,38 @@ func TestRegisterWorkerPersists(t *testing.T) {
 	}
 }
 
+func TestHeartbeatTracksWorkerLivenessAndReaperMarksOffline(t *testing.T) {
+	h := newHarness()
+	w, err := h.register.Execute(ctx, usecase.RegisterWorkerInput{Name: "lab", Capabilities: []string{"w"}})
+	if err != nil {
+		t.Fatal(err)
+	}
+	wid := w.ID.String() // a registered worker heartbeats with its UUID
+	h.seedJob(t, "w", 1)
+
+	c, err := h.claim.Execute(ctx, usecase.ClaimTaskInput{WorkerID: wid, Workloads: []string{"w"}})
+	if err != nil || c == nil {
+		t.Fatalf("claim: %v", err)
+	}
+	if _, err := h.renew.Execute(ctx, usecase.RenewLeaseInput{TaskID: c.TaskID, WorkerID: wid, Attempt: c.Attempt}); err != nil {
+		t.Fatalf("heartbeat: %v", err)
+	}
+	if got, _ := h.work.Get(ctx, w.ID); got.Status != domain.WorkerOnline {
+		t.Errorf("worker status = %q, want online after heartbeat", got.Status)
+	}
+
+	// Go silent past the threshold; the reaper marks it offline.
+	offline := usecase.NewMarkWorkersOffline(h.work, h.clk, 30*time.Second)
+	h.clk.Advance(time.Minute)
+	n, err := offline.Execute(ctx)
+	if err != nil || n != 1 {
+		t.Fatalf("reaper marked %d offline (err %v), want 1", n, err)
+	}
+	if got, _ := h.work.Get(ctx, w.ID); got.Status != domain.WorkerOffline {
+		t.Errorf("worker status = %q, want offline after reaper", got.Status)
+	}
+}
+
 func TestRegisterWorkerRejectsNoCapabilities(t *testing.T) {
 	h := newHarness()
 	if _, err := h.register.Execute(ctx, usecase.RegisterWorkerInput{Name: "lab"}); !errors.Is(err, domain.ErrInvalidInput) {

coordinator/internal/usecase/worker.go

@@ -2,6 +2,7 @@ package usecase
 
 import (
 	"context"
+	"time"
 
 	"github.com/emil28092005/SciMesh/coordinator/internal/domain"
 )
@@ -26,3 +27,19 @@ func (uc *RegisterWorker) Execute(ctx context.Context, in RegisterWorkerInput) (
 	}
 	return w, nil
 }
+
+// MarkWorkersOffline is the liveness reaper: workers that stopped heartbeating
+// longer ago than `after` are flipped to offline.
+type MarkWorkersOffline struct {
+	workers WorkerRepository
+	clk     Clock
+	after   time.Duration
+}
+
+func NewMarkWorkersOffline(workers WorkerRepository, clk Clock, after time.Duration) *MarkWorkersOffline {
+	return &MarkWorkersOffline{workers: workers, clk: clk, after: after}
+}
+
+func (uc *MarkWorkersOffline) Execute(ctx context.Context) (int64, error) {
+	return uc.workers.MarkStaleOffline(ctx, uc.clk.Now().Add(-uc.after))
+}

coordinator/migrations/0006_task_running_enum.down.sql

@@ -0,0 +1,4 @@
+-- PostgreSQL cannot drop a single enum value without recreating the type and
+-- rewriting every dependent column. Leaving 'running' in place is harmless: no
+-- code writes it after the down of 0007 restores the leased-only transitions.
+SELECT 1;

coordinator/migrations/0006_task_running_enum.up.sql

@@ -0,0 +1,5 @@
+-- 'running' means the worker has acknowledged start via its first heartbeat.
+-- Kept in its own migration, without an explicit transaction: an enum value
+-- added in a transaction cannot be USED in that same transaction, and the next
+-- migration references it.
+ALTER TYPE task_status ADD VALUE IF NOT EXISTS 'running';

coordinator/migrations/0007_task_running_lease.down.sql

@@ -0,0 +1,8 @@
+BEGIN;
+
+ALTER TABLE tasks DROP CONSTRAINT IF EXISTS ck_tasks_leased_owner;
+ALTER TABLE tasks ADD CONSTRAINT ck_tasks_leased_owner CHECK (
+    status <> 'leased' OR (lease_owner IS NOT NULL AND lease_expires_at IS NOT NULL)
+);
+
+COMMIT;

coordinator/migrations/0007_task_running_lease.up.sql

@@ -0,0 +1,10 @@
+BEGIN;
+
+-- A running task holds a lease just like a leased one, so the lease-integrity
+-- check must cover both states.
+ALTER TABLE tasks DROP CONSTRAINT IF EXISTS ck_tasks_leased_owner;
+ALTER TABLE tasks ADD CONSTRAINT ck_tasks_leased_owner CHECK (
+    status NOT IN ('leased','running') OR (lease_owner IS NOT NULL AND lease_expires_at IS NOT NULL)
+);
+
+COMMIT;