diff --git a/db/exploration.go b/db/exploration.go
index 4b6aef3..f41ef99 100644
--- a/db/exploration.go
+++ b/db/exploration.go
@@ -1272,7 +1272,7 @@ func (d *DB) TokenTotalsAll() (map[int64]TokenUsage, error) {
 // LastActivityAll returns the unix time of the most recent activity per
 // exploration (exploration_id → max created_at epoch), one query for all tasks.
 // Persisted (unlike Engine.LastActivity's in-memory map), so it survives restarts
-// and gives终态任务 a stable "ran until" time for computing run duration.
+// and gives终态任务 a stable last-activity time for history views.
 func (d *DB) LastActivityAll() (map[int64]int64, error) {
 	rows, err := d.Query(`SELECT exploration_id, EXTRACT(EPOCH FROM MAX(created_at))::bigint FROM activity GROUP BY exploration_id`)
 	if err != nil {
diff --git a/db/schema.sql b/db/schema.sql
index e855921..7599e7c 100644
--- a/db/schema.sql
+++ b/db/schema.sql
@@ -528,6 +528,8 @@ CREATE TABLE IF NOT EXISTS tasks (
     pinned_at      TIMESTAMPTZ,
     first_run_at   TIMESTAMPTZ,
     deadline_at    TIMESTAMPTZ,
+    active_run_seconds BIGINT NOT NULL DEFAULT 0,
+    run_segment_started_at TIMESTAMPTZ,
     archived_at    TIMESTAMPTZ,
     deleted_at     TIMESTAMPTZ,
     completed_at   TIMESTAMPTZ,
@@ -562,6 +564,8 @@ ALTER TABLE tasks ADD COLUMN IF NOT EXISTS pinned_at TIMESTAMPTZ;
 ALTER TABLE tasks ADD COLUMN IF NOT EXISTS active_llm_profile_id BIGINT REFERENCES llm_profiles(id) ON DELETE SET NULL;
 ALTER TABLE tasks ADD COLUMN IF NOT EXISTS llm_chain_revision BIGINT NOT NULL DEFAULT 0;
 ALTER TABLE tasks ADD COLUMN IF NOT EXISTS archived_at TIMESTAMPTZ;
+ALTER TABLE tasks ADD COLUMN IF NOT EXISTS active_run_seconds BIGINT NOT NULL DEFAULT 0;
+ALTER TABLE tasks ADD COLUMN IF NOT EXISTS run_segment_started_at TIMESTAMPTZ;
 CREATE INDEX IF NOT EXISTS idx_tasks_category ON tasks(category_id, created_at DESC)
     WHERE deleted_at IS NULL AND category_id IS NOT NULL;
 CREATE INDEX IF NOT EXISTS idx_tasks_pinned ON tasks(pinned_at DESC)
diff --git a/db/task_runtime_test.go b/db/task_runtime_test.go
new file mode 100644
index 0000000..492343f
--- /dev/null
+++ b/db/task_runtime_test.go
@@ -0,0 +1,172 @@
+package db
+
+import (
+	"database/sql"
+	"testing"
+)
+
+func TestTaskRunSegmentLifecycle(t *testing.T) {
+	d, err := Open(testDSN(t))
+	if err != nil {
+		t.Skipf("postgres unavailable (%v) — skipping", err)
+	}
+	defer d.Close()
+
+	task, err := d.CreateTask("runtime lifecycle", "runtime lifecycle test", nil, 0, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() { _ = d.DeleteTask(task.ID) })
+
+	active, started, err := d.StartTaskRunSegment(task.ID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if started == nil {
+		t.Fatal("StartTaskRunSegment did not open a segment")
+	}
+	if active != 0 {
+		t.Fatalf("new task active seconds=%d, want 0", active)
+	}
+	if _, err := d.Exec(`UPDATE tasks SET run_segment_started_at=now()-interval '3 seconds' WHERE id=$1`, task.ID); err != nil {
+		t.Fatal(err)
+	}
+
+	active, started, err = d.FinalizeTaskRunSegment(task.ID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if active <= 0 || started != nil {
+		t.Fatalf("first finalize active=%d started=%v, want positive and NULL", active, started)
+	}
+	firstActive := active
+
+	// Pause folds the open segment exactly once and closes it. Repeated
+	// finalization after wall-clock advancement remains a no-op.
+	if _, _, err := d.StartTaskRunSegment(task.ID); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := d.Exec(`UPDATE tasks SET run_segment_started_at=now()-interval '3 seconds' WHERE id=$1`, task.ID); err != nil {
+		t.Fatal(err)
+	}
+	active, started, err = d.SetPausedRuntime(task.ID, true)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if active <= firstActive || started != nil {
+		t.Fatalf("pause active=%d started=%v, want increase and NULL", active, started)
+	}
+	pausedActive := active
+	if active, started, err = d.FinalizeTaskRunSegment(task.ID); err != nil {
+		t.Fatal(err)
+	} else if active != pausedActive || started != nil {
+		t.Fatalf("repeated finalize after pause active=%d started=%v, want %d and NULL", active, started, pausedActive)
+	}
+
+	// Resuming opens a fresh segment, whose elapsed time is added on top of the
+	// paused total rather than replacing it.
+	if _, _, err := d.SetPausedRuntime(task.ID, false); err != nil {
+		t.Fatal(err)
+	}
+	if _, started, err = d.StartTaskRunSegment(task.ID); err != nil {
+		t.Fatal(err)
+	} else if started == nil {
+		t.Fatal("resume did not open a segment")
+	}
+	if _, err := d.Exec(`UPDATE tasks SET run_segment_started_at=now()-interval '3 seconds' WHERE id=$1`, task.ID); err != nil {
+		t.Fatal(err)
+	}
+	active, started, err = d.FinalizeTaskRunSegment(task.ID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if active <= pausedActive || started != nil {
+		t.Fatalf("resume finalize active=%d started=%v, want increase and NULL", active, started)
+	}
+
+	// Both terminal status paths fold an open segment and leave no live clock.
+	if _, started, err = d.StartTaskRunSegment(task.ID); err != nil {
+		t.Fatal(err)
+	} else if started == nil {
+		t.Fatal("terminal status setup did not open a segment")
+	}
+	if _, err := d.Exec(`UPDATE tasks SET run_segment_started_at=now()-interval '3 seconds' WHERE id=$1`, task.ID); err != nil {
+		t.Fatal(err)
+	}
+	beforeTerminal := active
+	active, started, err = d.SetStatusRuntime(task.ID, "done")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if active <= beforeTerminal || started != nil {
+		t.Fatalf("SetStatusRuntime terminal active=%d started=%v, want increase and NULL", active, started)
+	}
+
+	if _, _, err = d.SetStatusRuntime(task.ID, "running"); err != nil {
+		t.Fatal(err)
+	}
+	if _, started, err = d.StartTaskRunSegment(task.ID); err != nil {
+		t.Fatal(err)
+	} else if started == nil {
+		t.Fatal("guarded terminal setup did not open a segment")
+	}
+	if _, err := d.Exec(`UPDATE tasks SET run_segment_started_at=now()-interval '3 seconds' WHERE id=$1`, task.ID); err != nil {
+		t.Fatal(err)
+	}
+	beforeGuarded := active
+	active, started, won, err := d.SetTerminalStatusGuardedRuntime(task.ID, "failed")
+	if err != nil || !won {
+		t.Fatalf("SetTerminalStatusGuardedRuntime: active=%d started=%v won=%v err=%v", active, started, won, err)
+	}
+	if active <= beforeGuarded || started != nil {
+		t.Fatalf("guarded terminal active=%d started=%v, want increase and NULL", active, started)
+	}
+	finalActive := active
+	active, started, won, err = d.SetTerminalStatusGuardedRuntime(task.ID, "timeout")
+	if err != nil || won {
+		t.Fatalf("second guarded terminal: active=%d started=%v won=%v err=%v", active, started, won, err)
+	}
+	if active != finalActive || started != nil {
+		t.Fatalf("second guarded terminal returned active=%d started=%v, want unchanged active=%d and NULL segment", active, started, finalActive)
+	}
+	got, err := d.GetTask(task.ID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got == nil || got.ActiveRunSeconds != finalActive || got.RunSegmentStartedAt != nil {
+		t.Fatalf("persisted terminal runtime=%+v, want active=%d and NULL segment", got, finalActive)
+	}
+}
+
+func TestClearOpenTaskRunSegmentsPreservesAccumulatedRuntime(t *testing.T) {
+	d, err := Open(testDSN(t))
+	if err != nil {
+		t.Skipf("postgres unavailable (%v) — skipping", err)
+	}
+	defer d.Close()
+
+	task, err := d.CreateTask("runtime restart clear", "runtime restart clear test", nil, 0, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() { _ = d.DeleteTask(task.ID) })
+	if _, err := d.Exec(`UPDATE tasks SET active_run_seconds=17, run_segment_started_at=now()-interval '1 hour' WHERE id=$1`, task.ID); err != nil {
+		t.Fatal(err)
+	}
+
+	cleared, err := d.ClearOpenTaskRunSegments()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if cleared < 1 {
+		t.Fatalf("ClearOpenTaskRunSegments cleared %d rows, want at least 1", cleared)
+	}
+	var active int64
+	var started sql.NullTime
+	if err := d.QueryRow(`SELECT active_run_seconds, run_segment_started_at FROM tasks WHERE id=$1`, task.ID).Scan(&active, &started); err != nil {
+		t.Fatal(err)
+	}
+	if active != 17 || started.Valid {
+		t.Fatalf("restart clear changed runtime: active=%d started=%v, want 17 and NULL", active, started)
+	}
+}
diff --git a/db/tasks.go b/db/tasks.go
index c17f1b6..ac5c19e 100644
--- a/db/tasks.go
+++ b/db/tasks.go
@@ -42,9 +42,11 @@ type Task struct {
 	CreatedAt          time.Time  `json:"created_at"`
 	CompletedAt        *time.Time `json:"completed_at,omitempty"` // 进入终态(done/failed/timeout)的时刻;非终态为 nil
 	// 任务级超时(见 docs/任务级超时与收尾设计.md)。
-	TimeoutSeconds int        `json:"timeout_seconds"`        // 0=不限时
-	FirstRunAt     *time.Time `json:"first_run_at,omitempty"` // 首次真正开始运行的时刻(非 created_at);nil=尚未运行
-	DeadlineAt     *time.Time `json:"deadline_at,omitempty"`  // = first_run_at + timeout_seconds;nil=不限或未运行
+	TimeoutSeconds      int        `json:"timeout_seconds"`        // 0=不限时
+	FirstRunAt          *time.Time `json:"first_run_at,omitempty"` // 首次真正开始运行的时刻(非 created_at);nil=尚未运行
+	DeadlineAt          *time.Time `json:"deadline_at,omitempty"`  // = first_run_at + timeout_seconds;nil=不限或未运行
+	ActiveRunSeconds    int64      `json:"active_run_seconds"`
+	RunSegmentStartedAt *time.Time `json:"run_segment_started_at,omitempty"`
 	// planner 心跳触发间隔(秒)：距上轮 plan 结束/任务开始满该值且期间无触发 → 触发一轮。
 	// 下限=默认=300(5min)，低于一律抬到 300(在 CreateTask 归一)。见 docs/planner-trigger-impl-plan.md
 	PlanHeartbeatSeconds int `json:"plan_heartbeat_seconds"`
@@ -403,11 +405,11 @@ func insertTaskLLMProfiles(tx *sql.Tx, taskID int64, profileIDs []int64) error {
 
 const taskCols = `id, COALESCE(name,''), remark, category_id,
 COALESCE((SELECT category.name FROM task_categories category WHERE category.id=tasks.category_id),''),
-description, goal, exploration_id, status, paused, queued, queued_at, COALESCE(queue_mode,''), llm_profile_id, active_llm_profile_id, COALESCE(parent_ref,''), pinned_at, created_at, completed_at, COALESCE(timeout_seconds,0), COALESCE(plan_heartbeat_seconds,300), COALESCE(coverage_enabled,true), COALESCE(worker_count,0), first_run_at, deadline_at`
+description, goal, exploration_id, status, paused, queued, queued_at, COALESCE(queue_mode,''), llm_profile_id, active_llm_profile_id, COALESCE(parent_ref,''), pinned_at, created_at, completed_at, COALESCE(timeout_seconds,0), COALESCE(plan_heartbeat_seconds,300), COALESCE(coverage_enabled,true), COALESCE(worker_count,0), first_run_at, deadline_at, COALESCE(active_run_seconds,0), run_segment_started_at`
 
 func scanTask(sc interface{ Scan(...any) error }) (*Task, error) {
 	var t Task
-	if err := sc.Scan(&t.ID, &t.Name, &t.Remark, &t.CategoryID, &t.CategoryName, &t.Description, &t.Goal, &t.ExplorationID, &t.Status, &t.Paused, &t.Queued, &t.QueuedAt, &t.QueueMode, &t.LLMProfileID, &t.ActiveLLMProfileID, &t.ParentRef, &t.PinnedAt, &t.CreatedAt, &t.CompletedAt, &t.TimeoutSeconds, &t.PlanHeartbeatSeconds, &t.CoverageEnabled, &t.WorkerCount, &t.FirstRunAt, &t.DeadlineAt); err != nil {
+	if err := sc.Scan(&t.ID, &t.Name, &t.Remark, &t.CategoryID, &t.CategoryName, &t.Description, &t.Goal, &t.ExplorationID, &t.Status, &t.Paused, &t.Queued, &t.QueuedAt, &t.QueueMode, &t.LLMProfileID, &t.ActiveLLMProfileID, &t.ParentRef, &t.PinnedAt, &t.CreatedAt, &t.CompletedAt, &t.TimeoutSeconds, &t.PlanHeartbeatSeconds, &t.CoverageEnabled, &t.WorkerCount, &t.FirstRunAt, &t.DeadlineAt, &t.ActiveRunSeconds, &t.RunSegmentStartedAt); err != nil {
 		return nil, err
 	}
 	t.Pinned = t.PinnedAt != nil
@@ -493,10 +495,67 @@ func (d *DB) GetTask(id int64) (*Task, error) {
 
 // SetPaused persists a task's paused flag.
 func (d *DB) SetPaused(id int64, paused bool) error {
-	_, err := d.Exec(`UPDATE tasks SET paused=$1 WHERE id=$2`, paused, id)
+	_, _, err := d.SetPausedRuntime(id, paused)
 	return err
 }
 
+// SetPausedRuntime persists a task's paused flag and, when pausing, folds any
+// open execution segment into active_run_seconds. Keeping this in the DB helper
+// makes direct callers safe even when they do not go through Manager pause
+// orchestration.
+func (d *DB) SetPausedRuntime(id int64, paused bool) (int64, *time.Time, error) {
+	var active int64
+	var started *time.Time
+	err := d.QueryRow(`UPDATE tasks
+SET paused=$1,
+    active_run_seconds=active_run_seconds + CASE WHEN $1 AND run_segment_started_at IS NOT NULL THEN GREATEST(0, FLOOR(EXTRACT(EPOCH FROM (now() - run_segment_started_at)))::bigint) ELSE 0 END,
+    run_segment_started_at=CASE WHEN $1 THEN NULL ELSE run_segment_started_at END
+WHERE id=$2
+RETURNING active_run_seconds, run_segment_started_at`, paused, id).Scan(&active, &started)
+	if err == sql.ErrNoRows {
+		return 0, nil, nil
+	}
+	return active, started, err
+}
+
+// StartTaskRunSegment begins the currently active execution segment. It is
+// idempotent and refuses to start while a task is paused or waiting in the
+// concurrency queue.
+func (d *DB) StartTaskRunSegment(id int64) (int64, *time.Time, error) {
+	var active int64
+	var started *time.Time
+	err := d.QueryRow(`UPDATE tasks
+SET run_segment_started_at=COALESCE(run_segment_started_at, now())
+WHERE id=$1 AND deleted_at IS NULL AND status IN ('created','running') AND NOT paused AND NOT queued
+RETURNING active_run_seconds, run_segment_started_at`, id).Scan(&active, &started)
+	if err == sql.ErrNoRows {
+		err = d.QueryRow(`SELECT active_run_seconds, run_segment_started_at FROM tasks WHERE id=$1`, id).Scan(&active, &started)
+		if err == sql.ErrNoRows {
+			return 0, nil, nil
+		}
+	}
+	return active, started, err
+}
+
+// FinalizeTaskRunSegment folds the current segment into active_run_seconds.
+// A NULL segment makes this a safe no-op for repeated pause/terminal calls.
+func (d *DB) FinalizeTaskRunSegment(id int64) (int64, *time.Time, error) {
+	var active int64
+	var started *time.Time
+	err := d.QueryRow(`UPDATE tasks
+SET active_run_seconds=active_run_seconds + GREATEST(0, FLOOR(EXTRACT(EPOCH FROM (now() - run_segment_started_at)))::bigint),
+    run_segment_started_at=NULL
+WHERE id=$1 AND run_segment_started_at IS NOT NULL
+RETURNING active_run_seconds, run_segment_started_at`, id).Scan(&active, &started)
+	if err == sql.ErrNoRows {
+		err = d.QueryRow(`SELECT active_run_seconds, run_segment_started_at FROM tasks WHERE id=$1`, id).Scan(&active, &started)
+		if err == sql.ErrNoRows {
+			return 0, nil, nil
+		}
+	}
+	return active, started, err
+}
+
 // Enqueue places a task at the tail of the persistent admission queue. Repeating
 // the operation while it is already queued keeps its original FIFO position.
 func (d *DB) Enqueue(id int64, mode string) error {
@@ -506,6 +565,8 @@ func (d *DB) Enqueue(id int64, mode string) error {
 	_, err := d.Exec(`UPDATE tasks
 SET queued=true,
     queued_at=CASE WHEN queued THEN COALESCE(queued_at, now()) ELSE now() END,
+    active_run_seconds=active_run_seconds + CASE WHEN run_segment_started_at IS NOT NULL THEN GREATEST(0, FLOOR(EXTRACT(EPOCH FROM (now() - run_segment_started_at)))::bigint) ELSE 0 END,
+    run_segment_started_at=NULL,
     queue_mode=CASE
         WHEN queue_mode='bootstrap' OR $2='bootstrap' THEN 'bootstrap'
         ELSE 'resume'
@@ -539,12 +600,27 @@ func (d *DB) SetQueued(id int64, queued bool) error {
 // stable); moving back to a non-terminal state clears it, so a re-run has no stale
 // finish time.
 func (d *DB) SetStatus(id int64, status string) error {
-	_, err := d.Exec(`
+	_, _, err := d.SetStatusRuntime(id, status)
+	return err
+}
+
+// SetStatusRuntime updates a task status and returns the committed runtime
+// fields from the same UPDATE. Terminal transitions finalize any open segment.
+func (d *DB) SetStatusRuntime(id int64, status string) (int64, *time.Time, error) {
+	var active int64
+	var started *time.Time
+	err := d.QueryRow(`
 UPDATE tasks
    SET status = $1,
-       completed_at = CASE WHEN $1 IN ('done','failed','timeout') THEN COALESCE(completed_at, now()) ELSE NULL END
- WHERE id = $2`, status, id)
-	return err
+       completed_at = CASE WHEN $1 IN ('done','failed','timeout') THEN COALESCE(completed_at, now()) ELSE NULL END,
+       active_run_seconds = active_run_seconds + CASE WHEN $1 IN ('done','failed','timeout') AND run_segment_started_at IS NOT NULL THEN GREATEST(0, FLOOR(EXTRACT(EPOCH FROM (now() - run_segment_started_at)))::bigint) ELSE 0 END,
+       run_segment_started_at = CASE WHEN $1 IN ('done','failed','timeout') THEN NULL ELSE run_segment_started_at END
+ WHERE id = $2
+ RETURNING active_run_seconds, run_segment_started_at`, status, id).Scan(&active, &started)
+	if err == sql.ErrNoRows {
+		return 0, nil, nil
+	}
+	return active, started, err
 }
 
 // SetTerminalStatusGuarded sets a terminal status only when the task is NOT already
@@ -552,16 +628,43 @@ UPDATE tasks
 // Returns won=false (no error) when another terminal status already stuck — the
 // caller then leaves it alone. Non-terminal transitions / re-run still use SetStatus.
 func (d *DB) SetTerminalStatusGuarded(id int64, status string) (won bool, err error) {
-	res, err := d.Exec(`
+	_, _, won, err = d.SetTerminalStatusGuardedRuntime(id, status)
+	return won, err
+}
+
+// SetTerminalStatusGuardedRuntime is the runtime-returning form used by the
+// Manager so it can mirror the terminal clock before any follow-up hydration.
+func (d *DB) SetTerminalStatusGuardedRuntime(id int64, status string) (active int64, started *time.Time, won bool, err error) {
+	err = d.QueryRow(`
 UPDATE tasks
    SET status = $1,
-       completed_at = COALESCE(completed_at, now())
- WHERE id = $2 AND status NOT IN ('done','failed','timeout')`, status, id)
-	if err != nil {
-		return false, err
+       completed_at = COALESCE(completed_at, now()),
+       active_run_seconds = active_run_seconds + CASE WHEN run_segment_started_at IS NOT NULL THEN GREATEST(0, FLOOR(EXTRACT(EPOCH FROM (now() - run_segment_started_at)))::bigint) ELSE 0 END,
+       run_segment_started_at = NULL
+ WHERE id = $2 AND status NOT IN ('done','failed','timeout')
+ RETURNING active_run_seconds, run_segment_started_at`, status, id).Scan(&active, &started)
+	if err == sql.ErrNoRows {
+		// Preserve the authoritative runtime fields for the losing terminal
+		// writer. The guarded transition itself is still a no-op.
+		err = d.QueryRow(`SELECT active_run_seconds, run_segment_started_at FROM tasks WHERE id=$1`, id).Scan(&active, &started)
+		if err == sql.ErrNoRows {
+			return 0, nil, false, nil
+		}
+		return active, started, false, err
 	}
-	n, _ := res.RowsAffected()
-	return n > 0, nil
+	return active, started, err == nil, err
+}
+
+// ClearOpenTaskRunSegments drops execution segments that were live when the
+// process stopped. Their wall time is unknowable after a crash or deploy, so
+// startup deliberately begins with no live segment; the engine starts a fresh
+// segment only when it actually resumes work.
+func (d *DB) ClearOpenTaskRunSegments() (int64, error) {
+	res, err := d.Exec(`UPDATE tasks SET run_segment_started_at=NULL WHERE run_segment_started_at IS NOT NULL`)
+	if err != nil {
+		return 0, err
+	}
+	return res.RowsAffected()
 }
 
 // StampFirstRun records a task's first-real-run moment and computes its absolute
diff --git a/server/dto.go b/server/dto.go
index 339c1f2..fabfd65 100644
--- a/server/dto.go
+++ b/server/dto.go
@@ -44,10 +44,13 @@ type TaskDTO struct {
 	Goal               string             `json:"goal"`
 	Status             string             `json:"status"` // created | running | paused | done | failed
 	CreatedAt          string             `json:"created_at"`
-	CreatedUnix        int64              `json:"created_unix"`       // created_at as unix seconds (for run-duration calc)
+	CreatedUnix        int64              `json:"created_unix"`
 	CompletedAt        string             `json:"completed_at"`       // RFC3339 finish time (done/failed); "" if unfinished
 	CompletedUnix      int64              `json:"completed_unix"`     // completed_at as unix seconds (0 if unfinished)
 	LastActivity       int64              `json:"last_activity_unix"` // unix seconds of the last activity (0 if none)
+	RunSeconds         int64              `json:"run_seconds"`
+	ActiveRunSeconds   int64              `json:"active_run_seconds"`
+	RunSegmentStarted  int64              `json:"run_segment_started_unix"`
 	Paused             bool               `json:"paused"`
 	Queued             bool               `json:"queued"`
 	Tokens             TokenTotalDTO      `json:"tokens"` // whole-task token consumption
@@ -107,6 +110,7 @@ func tokenTotalDTO(u db.TokenUsage) TokenTotalDTO {
 
 func taskDTO(t *Task, status string) TaskDTO {
 	lifecycle := t.lifecycleSnapshot()
+	runSeconds := taskRunSeconds(lifecycle.ActiveRunSeconds, lifecycle.RunSegmentStartedAt, time.Now().Unix(), status, lifecycle.Paused, lifecycle.Queued)
 	llmState := t.llmStateSnapshot()
 	sourceIDs := make([]string, 0, len(lifecycle.SourceTaskIDs))
 	for _, id := range lifecycle.SourceTaskIDs {
@@ -127,6 +131,9 @@ func taskDTO(t *Task, status string) TaskDTO {
 		Status:             status,
 		CreatedAt:          rfc3339(time.Unix(t.CreatedAt, 0)),
 		CreatedUnix:        t.CreatedAt,
+		RunSeconds:         runSeconds,
+		ActiveRunSeconds:   lifecycle.ActiveRunSeconds,
+		RunSegmentStarted:  lifecycle.RunSegmentStartedAt,
 		CompletedAt:        completedRFC(lifecycle.CompletedAt),
 		CompletedUnix:      lifecycle.CompletedAt,
 		Paused:             lifecycle.Paused,
diff --git a/server/engine.go b/server/engine.go
index 7c61b74..04f610c 100644
--- a/server/engine.go
+++ b/server/engine.go
@@ -937,6 +937,9 @@ func (e *Engine) plannerLoop(ctx context.Context, t *Task) {
 			return
 		}
 		defer e.decInflight(t.ID)
+		if err := e.m.StartTaskRunSegment(t.ID); err != nil {
+			log.Printf("[runtime] task %s start segment failed: %v", t.ID, err)
+		}
 		e.stampFirstRun(t) // 首次真正规划 → 盖 first_run_at + 算 deadline(仅带 timeout 的任务)
 		e.touch(t.ID)
 		emit := func(r db.Activity) { e.emitActivity(t, r) }
@@ -1086,6 +1089,9 @@ func (e *Engine) runIntent(ctx context.Context, t *Task, name string, worker *ag
 		}
 		return true
 	}
+	if err := e.m.StartTaskRunSegment(t.ID); err != nil {
+		log.Printf("[runtime] task %s start segment failed: %v", t.ID, err)
+	}
 	// per-work child context so the planner's kill_work can stop just this work.
 	workCtx, workCancel := context.WithCancelCause(ectx)
 	e.registerWork(intent.ID, workCancel)
diff --git a/server/goals.go b/server/goals.go
index 4603149..45b67f6 100644
--- a/server/goals.go
+++ b/server/goals.go
@@ -252,6 +252,11 @@ func (s *Server) hasReadyQueuedTask(excludeID string) bool {
 }
 
 func (s *Server) startAdmittedTask(t *Task, mode string) {
+	if s.engine.ReadyFor(t) {
+		if err := s.m.StartTaskRunSegment(t.ID); err != nil {
+			log.Printf("[runtime] task %s start segment failed: %v", t.ID, err)
+		}
+	}
 	if mode == "bootstrap" {
 		if !s.engine.beginTaskOperation(t.ID) {
 			return
diff --git a/server/manager.go b/server/manager.go
index 5718eb3..bd7b1f3 100644
--- a/server/manager.go
+++ b/server/manager.go
@@ -63,6 +63,8 @@ type Task struct {
 	WorkerCount          int                    `json:"worker_count"`           // 本任务 Worker 数;0=用全局默认
 	FirstRunAt           int64                  `json:"first_run_at,omitempty"`
 	DeadlineAt           int64                  `json:"deadline_at,omitempty"`
+	ActiveRunSeconds     int64                  `json:"active_run_seconds"`
+	RunSegmentStartedAt  int64                  `json:"run_segment_started_at,omitempty"`
 	Store                *pgdb.ExplorationStore `json:"-"`
 	Guard                *guard.Guard           `json:"-"`
 	notify               chan struct{}
@@ -81,21 +83,23 @@ type Task struct {
 // updateLifecycle instead of reading or writing the corresponding Task fields
 // directly after the task has been published by Manager.
 type taskLifecycleState struct {
-	Name          string
-	Remark        string
-	PinnedAt      int64
-	Status        string
-	Paused        bool
-	Queued        bool
-	QueuedAt      int64
-	QueueMode     string
-	CompletedAt   int64
-	FirstRunAt    int64
-	DeadlineAt    int64
-	SourceTaskIDs []int64
-	CompanyIDs    []int64
-	CategoryID    *int64
-	CategoryName  string
+	Name                string
+	Remark              string
+	PinnedAt            int64
+	Status              string
+	Paused              bool
+	Queued              bool
+	QueuedAt            int64
+	QueueMode           string
+	CompletedAt         int64
+	FirstRunAt          int64
+	DeadlineAt          int64
+	ActiveRunSeconds    int64
+	RunSegmentStartedAt int64
+	SourceTaskIDs       []int64
+	CompanyIDs          []int64
+	CategoryID          *int64
+	CategoryName        string
 }
 
 func (t *Task) lifecycleSnapshot() taskLifecycleState {
@@ -109,21 +113,23 @@ func (t *Task) lifecycleSnapshot() taskLifecycleState {
 
 func (t *Task) lifecycleSnapshotLocked() taskLifecycleState {
 	return taskLifecycleState{
-		Name:          t.Name,
-		Remark:        t.Remark,
-		PinnedAt:      t.PinnedAt,
-		Status:        t.Status,
-		Paused:        t.Paused,
-		Queued:        t.Queued,
-		QueuedAt:      t.QueuedAt,
-		QueueMode:     t.QueueMode,
-		CompletedAt:   t.CompletedAt,
-		FirstRunAt:    t.FirstRunAt,
-		DeadlineAt:    t.DeadlineAt,
-		SourceTaskIDs: append([]int64(nil), t.SourceTaskIDs...),
-		CompanyIDs:    append([]int64(nil), t.CompanyIDs...),
-		CategoryID:    cloneInt64Ptr(t.CategoryID),
-		CategoryName:  t.CategoryName,
+		Name:                t.Name,
+		Remark:              t.Remark,
+		PinnedAt:            t.PinnedAt,
+		Status:              t.Status,
+		Paused:              t.Paused,
+		Queued:              t.Queued,
+		QueuedAt:            t.QueuedAt,
+		QueueMode:           t.QueueMode,
+		CompletedAt:         t.CompletedAt,
+		FirstRunAt:          t.FirstRunAt,
+		DeadlineAt:          t.DeadlineAt,
+		ActiveRunSeconds:    t.ActiveRunSeconds,
+		RunSegmentStartedAt: t.RunSegmentStartedAt,
+		SourceTaskIDs:       append([]int64(nil), t.SourceTaskIDs...),
+		CompanyIDs:          append([]int64(nil), t.CompanyIDs...),
+		CategoryID:          cloneInt64Ptr(t.CategoryID),
+		CategoryName:        t.CategoryName,
 	}
 }
 
@@ -145,6 +151,8 @@ func (t *Task) updateLifecycle(update func(*taskLifecycleState)) {
 	t.CompletedAt = state.CompletedAt
 	t.FirstRunAt = state.FirstRunAt
 	t.DeadlineAt = state.DeadlineAt
+	t.ActiveRunSeconds = state.ActiveRunSeconds
+	t.RunSegmentStartedAt = state.RunSegmentStartedAt
 	t.SourceTaskIDs = append(t.SourceTaskIDs[:0], state.SourceTaskIDs...)
 	t.CompanyIDs = append(t.CompanyIDs[:0], state.CompanyIDs...)
 	t.CategoryID = cloneInt64Ptr(state.CategoryID)
@@ -525,6 +533,13 @@ func NewManager(dir, proxyAddr string) (*Manager, error) {
 	if err != nil {
 		return nil, err
 	}
+	// A live segment cannot be trusted across a process restart: its end time
+	// could be deployment/crash downtime. Clear it before tasks are restored so
+	// the next engine admission starts a fresh segment at actual execution time.
+	if _, err := pg.ClearOpenTaskRunSegments(); err != nil {
+		_ = pg.Close()
+		return nil, fmt.Errorf("clear stale task run segments: %w", err)
+	}
 	if err := pg.RecoverFindingRetests(); err != nil {
 		pg.Close()
 		return nil, fmt.Errorf("recover finding retests: %w", err)
@@ -1009,6 +1024,7 @@ func taskFromPG(pt *pgdb.Task, store *pgdb.ExplorationStore, ic *intercept.Inter
 		TimeoutSeconds: pt.TimeoutSeconds, PlanHeartbeatSeconds: pt.PlanHeartbeatSeconds,
 		CoverageEnabled: pt.CoverageEnabled, WorkerCount: pt.WorkerCount,
 		FirstRunAt: unixOrZero(pt.FirstRunAt), DeadlineAt: unixOrZero(pt.DeadlineAt),
+		ActiveRunSeconds: pt.ActiveRunSeconds, RunSegmentStartedAt: unixOrZero(pt.RunSegmentStartedAt),
 		Store: store, Guard: guard.NewWithInterceptor(ic), notify: make(chan struct{}, 1),
 	}
 }
@@ -1289,13 +1305,16 @@ func (m *Manager) SetTaskPaused(id string, paused bool) error {
 	if err != nil {
 		return err
 	}
-	if err := m.pg.SetPaused(n, paused); err != nil {
+	active, started, err := m.pg.SetPausedRuntime(n, paused)
+	if err != nil {
 		return err
 	}
 	m.mu.Lock()
 	if t := m.tasks[id]; t != nil {
 		t.updateLifecycle(func(state *taskLifecycleState) {
 			state.Paused = paused
+			state.ActiveRunSeconds = active
+			state.RunSegmentStartedAt = unixOrZero(started)
 		})
 	}
 	m.mu.Unlock()
@@ -1331,7 +1350,8 @@ func (m *Manager) applyTaskAdmission(id, expectedStatus, status string, queued b
 		mode = ""
 	}
 
-	var queuedAt, completedAt, firstRunAt, deadlineAt sql.NullTime
+	var queuedAt, completedAt, firstRunAt, deadlineAt, segmentStartedAt sql.NullTime
+	var activeRunSeconds int64
 	var committedMode string
 	err = m.pg.QueryRow(`UPDATE tasks
 	SET status=$2,
@@ -1360,9 +1380,11 @@ func (m *Manager) applyTaskAdmission(id, expectedStatus, status string, queued b
 	        WHEN $6='timeout' AND $2 NOT IN ('done','failed','timeout') THEN NULL
 	        ELSE deadline_at
 	    END
+	    ,active_run_seconds=active_run_seconds + CASE WHEN ($3 OR $2 IN ('done','failed','timeout')) AND run_segment_started_at IS NOT NULL THEN GREATEST(0, FLOOR(EXTRACT(EPOCH FROM (now() - run_segment_started_at)))::bigint) ELSE 0 END
+	    ,run_segment_started_at=CASE WHEN $3 OR $2 IN ('done','failed','timeout') THEN NULL ELSE run_segment_started_at END
 	WHERE id=$1 AND deleted_at IS NULL AND status=$6
-	RETURNING queued_at, queue_mode, completed_at, first_run_at, deadline_at`, n, status, queued, mode, preservePosition, expectedStatus, manualUntil).
-		Scan(&queuedAt, &committedMode, &completedAt, &firstRunAt, &deadlineAt)
+	RETURNING queued_at, queue_mode, completed_at, first_run_at, deadline_at, active_run_seconds, run_segment_started_at`, n, status, queued, mode, preservePosition, expectedStatus, manualUntil).
+		Scan(&queuedAt, &committedMode, &completedAt, &firstRunAt, &deadlineAt, &activeRunSeconds, &segmentStartedAt)
 	if errors.Is(err, sql.ErrNoRows) {
 		return fmt.Errorf("task %s lifecycle changed before admission (expected status %q)", id, expectedStatus)
 	}
@@ -1393,6 +1415,11 @@ func (m *Manager) applyTaskAdmission(id, expectedStatus, status string, queued b
 			if deadlineAt.Valid {
 				state.DeadlineAt = deadlineAt.Time.Unix()
 			}
+			state.ActiveRunSeconds = activeRunSeconds
+			state.RunSegmentStartedAt = 0
+			if segmentStartedAt.Valid {
+				state.RunSegmentStartedAt = segmentStartedAt.Time.Unix()
+			}
 		})
 	}
 	m.mu.Unlock()
@@ -1413,11 +1440,15 @@ func (m *Manager) ApplyTaskPauseOrigin(id string, scheduled bool) error {
 		return err
 	}
 	var mode string
+	var activeRunSeconds int64
+	var segmentStartedAt sql.NullTime
 	err = m.pg.QueryRow(`UPDATE tasks
-		SET paused=true, queued=false, queued_at=NULL, schedule_paused=$2, schedule_manual_until=NULL
+		SET paused=true, queued=false, queued_at=NULL, schedule_paused=$2, schedule_manual_until=NULL,
+		    active_run_seconds=active_run_seconds + CASE WHEN run_segment_started_at IS NOT NULL THEN GREATEST(0, FLOOR(EXTRACT(EPOCH FROM (now() - run_segment_started_at)))::bigint) ELSE 0 END,
+		    run_segment_started_at=NULL
 		WHERE id=$1 AND deleted_at IS NULL AND paused=false
 		  AND status NOT IN ('done','failed','timeout')
-		RETURNING COALESCE(queue_mode,'')`, n, scheduled).Scan(&mode)
+		RETURNING COALESCE(queue_mode,''), active_run_seconds, run_segment_started_at`, n, scheduled).Scan(&mode, &activeRunSeconds, &segmentStartedAt)
 	if errors.Is(err, sql.ErrNoRows) {
 		return fmt.Errorf("task %s is unavailable for pause", id)
 	}
@@ -1431,6 +1462,11 @@ func (m *Manager) ApplyTaskPauseOrigin(id string, scheduled bool) error {
 			state.Queued = false
 			state.QueuedAt = 0
 			state.QueueMode = mode
+			state.ActiveRunSeconds = activeRunSeconds
+			state.RunSegmentStartedAt = 0
+			if segmentStartedAt.Valid {
+				state.RunSegmentStartedAt = segmentStartedAt.Time.Unix()
+			}
 		})
 	}
 	m.mu.Unlock()
@@ -1449,16 +1485,20 @@ func (m *Manager) EnqueueTask(id, mode string) error {
 		return fmt.Errorf("invalid queue mode %q", mode)
 	}
 	var queuedAt time.Time
+	var activeRunSeconds int64
+	var segmentStartedAt sql.NullTime
 	var committedMode string
 	err = m.pg.QueryRow(`UPDATE tasks
 		SET queued=true,
 		    queued_at=CASE WHEN queued THEN COALESCE(queued_at, now()) ELSE now() END,
+		    active_run_seconds=active_run_seconds + CASE WHEN run_segment_started_at IS NOT NULL THEN GREATEST(0, FLOOR(EXTRACT(EPOCH FROM (now() - run_segment_started_at)))::bigint) ELSE 0 END,
+		    run_segment_started_at=NULL,
 		    queue_mode=CASE
 		        WHEN queue_mode='bootstrap' OR $2='bootstrap' THEN 'bootstrap'
 		        ELSE 'resume'
 		    END
 		WHERE id=$1 AND deleted_at IS NULL
-		RETURNING queued_at, queue_mode`, n, mode).Scan(&queuedAt, &committedMode)
+		RETURNING queued_at, queue_mode, active_run_seconds, run_segment_started_at`, n, mode).Scan(&queuedAt, &committedMode, &activeRunSeconds, &segmentStartedAt)
 	if errors.Is(err, sql.ErrNoRows) {
 		return fmt.Errorf("task %s is unavailable for enqueue", id)
 	}
@@ -1471,6 +1511,80 @@ func (m *Manager) EnqueueTask(id, mode string) error {
 			state.QueuedAt = queuedAt.UnixNano()
 			state.Queued = true
 			state.QueueMode = committedMode
+			state.ActiveRunSeconds = activeRunSeconds
+			state.RunSegmentStartedAt = 0
+			if segmentStartedAt.Valid {
+				state.RunSegmentStartedAt = segmentStartedAt.Time.Unix()
+			}
+		})
+	}
+	m.mu.Unlock()
+	return nil
+}
+
+// StartTaskRunSegment records the start of actual execution, once the engine
+// has admitted a task and is about to run planner/worker work.
+func (m *Manager) StartTaskRunSegment(id string) error {
+	m.taskStateMu.Lock()
+	defer m.taskStateMu.Unlock()
+	n, err := strconv.ParseInt(id, 10, 64)
+	if err != nil {
+		return err
+	}
+	m.mu.RLock()
+	if t := m.tasks[id]; t != nil && t.lifecycleSnapshot().RunSegmentStartedAt > 0 {
+		m.mu.RUnlock()
+		return nil
+	}
+	m.mu.RUnlock()
+	active, started, err := m.pg.StartTaskRunSegment(n)
+	if err != nil {
+		return err
+	}
+	if started != nil {
+		m.mirrorTaskRuntime(id, active, started)
+	}
+	return nil
+}
+
+// FinalizeTaskRunSegment is idempotent and is used by pause/terminal paths that
+// may race with a late engine cancellation.
+func (m *Manager) FinalizeTaskRunSegment(id string) error {
+	m.taskStateMu.Lock()
+	defer m.taskStateMu.Unlock()
+	n, err := strconv.ParseInt(id, 10, 64)
+	if err != nil {
+		return err
+	}
+	active, started, err := m.pg.FinalizeTaskRunSegment(n)
+	if err != nil {
+		return err
+	}
+	m.mirrorTaskRuntime(id, active, started)
+	return nil
+}
+
+func (m *Manager) mirrorTaskRuntime(id string, active int64, started *time.Time) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	if t := m.tasks[id]; t != nil {
+		t.updateLifecycle(func(state *taskLifecycleState) {
+			state.ActiveRunSeconds = active
+			state.RunSegmentStartedAt = unixOrZero(started)
+		})
+	}
+}
+
+func (m *Manager) syncTaskRuntime(id string, n int64) error {
+	pt, err := m.pg.GetTask(n)
+	if err != nil || pt == nil {
+		return err
+	}
+	m.mu.Lock()
+	if t := m.tasks[id]; t != nil {
+		t.updateLifecycle(func(state *taskLifecycleState) {
+			state.ActiveRunSeconds = pt.ActiveRunSeconds
+			state.RunSegmentStartedAt = unixOrZero(pt.RunSegmentStartedAt)
 		})
 	}
 	m.mu.Unlock()
@@ -1559,20 +1673,30 @@ func (m *Manager) SetTaskStatusGuarded(id, status string) (won bool, err error)
 	if err != nil {
 		return false, err
 	}
-	won, err = m.pg.SetTerminalStatusGuarded(n, status)
+	active, started, won, err := m.pg.SetTerminalStatusGuardedRuntime(n, status)
 	if err != nil || !won {
 		return won, err
 	}
+	// Mirror the committed terminal transition before any optional hydration.
+	// This keeps the in-memory clock stopped even if GetTask later fails.
 	m.mu.Lock()
 	if t := m.tasks[id]; t != nil {
 		t.updateLifecycle(func(state *taskLifecycleState) {
 			state.Status = status
-			if state.CompletedAt == 0 {
-				state.CompletedAt = time.Now().Unix()
+			state.ActiveRunSeconds = active
+			state.RunSegmentStartedAt = unixOrZero(started)
+			if pgdb.IsTerminal(status) {
+				state.RunSegmentStartedAt = 0
+				if state.CompletedAt == 0 {
+					state.CompletedAt = time.Now().Unix()
+				}
 			}
 		})
 	}
 	m.mu.Unlock()
+	if err := m.syncTaskRuntime(id, n); err != nil {
+		return true, err
+	}
 	return true, nil
 }
 
@@ -1585,16 +1709,20 @@ func (m *Manager) SetTaskStatus(id, status string) error {
 	if err != nil {
 		return err
 	}
-	if err := m.pg.SetStatus(n, status); err != nil {
+	active, started, err := m.pg.SetStatusRuntime(n, status)
+	if err != nil {
 		return err
 	}
+	// Mirror the successful UPDATE immediately. A later GetTask hydration is
+	// best-effort and must not reopen a terminal clock in memory.
 	m.mu.Lock()
 	if t := m.tasks[id]; t != nil {
 		t.updateLifecycle(func(state *taskLifecycleState) {
 			state.Status = status
-			// Mirror the DB's completed_at stamp on the live handle so the DTO shows
-			// the finish time without a reload (terminal -> stamp once; else clear).
+			state.ActiveRunSeconds = active
+			state.RunSegmentStartedAt = unixOrZero(started)
 			if pgdb.IsTerminal(status) {
+				state.RunSegmentStartedAt = 0
 				if state.CompletedAt == 0 {
 					state.CompletedAt = time.Now().Unix()
 				}
@@ -1604,6 +1732,9 @@ func (m *Manager) SetTaskStatus(id, status string) error {
 		})
 	}
 	m.mu.Unlock()
+	if err := m.syncTaskRuntime(id, n); err != nil {
+		return err
+	}
 	return nil
 }
 
diff --git a/server/orchestration.go b/server/orchestration.go
index bca694b..33052c6 100644
--- a/server/orchestration.go
+++ b/server/orchestration.go
@@ -175,10 +175,9 @@ func (s *Server) delegateToTask(ctx context.Context, in json.RawMessage, pick fu
 
 func (s *Server) toolListTasks() actool.CoreTool {
 	return roTool("list_tasks",
-		"列出所有任务(id/描述/目标/状态/运行时长/父任务/LLM 配置)，编排 agent 用它掌握全局、看哪些任务卡太久、各自用哪个 LLM。运行时长：运行中=创建→现在，终态=创建→最后活动(秒)。llm_profile：任务 planner/worker 用的配置名，(激活配置)=跟随全局激活。",
+		"列出所有任务(id/描述/目标/状态/运行时长/父任务/LLM 配置)，编排 agent 用它掌握全局、看哪些任务卡太久、各自用哪个 LLM。运行时长只累计实际执行时间，暂停、排队和终态后的时间不计入。llm_profile：任务 planner/worker 用的配置名，(激活配置)=跟随全局激活。",
 		objSchema(map[string]any{}),
 		func(context.Context, json.RawMessage) (actool.Result, error) {
-			lastAct, _ := s.m.PG().LastActivityAll()
 			// id -> name to resolve each task's pinned LLM profile.
 			profName := map[int64]string{}
 			if profs, err := s.m.pg.ListProfiles(); err == nil {
@@ -189,16 +188,8 @@ func (s *Server) toolListTasks() actool.CoreTool {
 			out := make([]map[string]any, 0)
 			for _, t := range s.m.List() {
 				status := s.deriveTaskStatus(t)
-				end := lastAct[t.ExpID]
-				if live := s.engine.LastActivity(t.ID); live > end {
-					end = live
-				}
-				dur := int64(0)
-				if status == "running" {
-					dur = time.Now().Unix() - t.CreatedAt
-				} else if end > t.CreatedAt {
-					dur = end - t.CreatedAt
-				}
+				lifecycle := t.lifecycleSnapshot()
+				dur := taskRunSeconds(lifecycle.ActiveRunSeconds, lifecycle.RunSegmentStartedAt, time.Now().Unix(), status, lifecycle.Paused, lifecycle.Queued)
 				row := map[string]any{"id": t.ID, "description": t.Description, "goal": t.Goal, "status": status, "run_seconds": dur}
 				if t.ParentRef != "" {
 					row["parent_ref"] = t.ParentRef
diff --git a/server/server.go b/server/server.go
index c0c7dad..6ee0cf5 100644
--- a/server/server.go
+++ b/server/server.go
@@ -1138,7 +1138,7 @@ func (s *Server) listTasks(w http.ResponseWriter, r *http.Request) {
 		metric := metrics[t.ExpID]
 		dto.Tokens = tokenTotalDTO(metric.Tokens)
 		// prefer the live in-memory heartbeat (fresher) and fall back to the
-		// persisted max activity time (survives restarts) for run-duration display.
+		// persisted max activity time (survives restarts) for activity display.
 		dto.LastActivity = metric.LastActivity
 		if live := s.engine.LastActivity(t.ID); live > dto.LastActivity {
 			dto.LastActivity = live
diff --git a/server/task_runtime.go b/server/task_runtime.go
new file mode 100644
index 0000000..4137d84
--- /dev/null
+++ b/server/task_runtime.go
@@ -0,0 +1,25 @@
+package server
+
+// taskRunSeconds computes displayed active runtime from persisted segment data.
+// Segment timestamps are unix seconds; a zero start means no active segment.
+func taskRunSeconds(active, segmentStarted, now int64, status string, paused, queued bool) int64 {
+	if active < 0 {
+		active = 0
+	}
+	if status == "running" && !paused && !queued && segmentStarted > 0 && now > segmentStarted {
+		return active + now - segmentStarted
+	}
+	return active
+}
+
+// finalizeTaskRunSeconds mirrors the database transition for deterministic unit
+// tests and callers that need to reason about a segment without a live database.
+func finalizeTaskRunSeconds(active, segmentStarted, now int64) (int64, int64) {
+	if active < 0 {
+		active = 0
+	}
+	if segmentStarted > 0 && now > segmentStarted {
+		active += now - segmentStarted
+	}
+	return active, 0
+}
diff --git a/server/task_runtime_test.go b/server/task_runtime_test.go
new file mode 100644
index 0000000..9f5c9c0
--- /dev/null
+++ b/server/task_runtime_test.go
@@ -0,0 +1,35 @@
+package server
+
+import "testing"
+
+func TestTaskRunSecondsRunningSegmentAccumulates(t *testing.T) {
+	if got := taskRunSeconds(12, 100, 145, "running", false, false); got != 57 {
+		t.Fatalf("running duration = %d, want 57", got)
+	}
+}
+
+func TestTaskRunSecondsPausedDoesNotGrow(t *testing.T) {
+	if got := taskRunSeconds(57, 100, 1000, "paused", true, false); got != 57 {
+		t.Fatalf("paused duration = %d, want 57", got)
+	}
+	if got := taskRunSeconds(57, 100, 1000, "running", false, true); got != 57 {
+		t.Fatalf("queued duration = %d, want 57", got)
+	}
+}
+
+func TestTaskRunSecondsResumeContinuesFromPriorTotal(t *testing.T) {
+	active, segment := finalizeTaskRunSeconds(12, 100, 145)
+	if active != 57 || segment != 0 {
+		t.Fatalf("finalized segment = (%d,%d), want (57,0)", active, segment)
+	}
+	if got := taskRunSeconds(active, 200, 230, "running", false, false); got != 87 {
+		t.Fatalf("resumed duration = %d, want 87", got)
+	}
+}
+
+func TestTaskRunSecondsTerminalFinalizesSegment(t *testing.T) {
+	active, segment := finalizeTaskRunSeconds(20, 500, 560)
+	if active != 80 || segment != 0 {
+		t.Fatalf("terminal finalization = (%d,%d), want (80,0)", active, segment)
+	}
+}
diff --git a/web/src/app/(main)/function/tasks/page.tsx b/web/src/app/(main)/function/tasks/page.tsx
index 3737d6d..df88c10 100644
--- a/web/src/app/(main)/function/tasks/page.tsx
+++ b/web/src/app/(main)/function/tasks/page.tsx
@@ -188,19 +188,15 @@ function fmtDuration(sec: number): string {
   return `${s}s`;
 }
 
-// taskDuration is the task's run duration in seconds: created → now while running,
-// created → completion for a finished task, else created → last activity. 0 when it
-// never ran (no activity yet).
+// taskDuration counts only active execution segments. A live segment ticks locally;
+// paused, queued, and terminal tasks stay fixed at their persisted active total.
 function taskDuration(task: Task, nowSec: number): number {
-  const start = task.created_unix ?? 0;
-  if (!start) return 0;
-  const end =
-    task.status === "running"
-      ? nowSec
-      : task.completed_unix && task.completed_unix > 0
-        ? task.completed_unix
-        : (task.last_activity_unix ?? 0);
-  return end > start ? end - start : 0;
+  const active = Math.max(0, Math.floor(task.active_run_seconds ?? 0));
+  const segmentStart = task.run_segment_started_unix ?? 0;
+  if (task.status === "running" && !task.paused && !task.queued && segmentStart > 0) {
+    return active + Math.max(0, Math.floor(nowSec - segmentStart));
+  }
+  return active;
 }
 
 // deleteDetails takes only the countable part of the result so callers can pass an
diff --git a/web/src/lib/mock/data.ts b/web/src/lib/mock/data.ts
index 96dea32..8c31178 100644
--- a/web/src/lib/mock/data.ts
+++ b/web/src/lib/mock/data.ts
@@ -60,6 +60,9 @@ export const tasks: Task[] = [
     status: "running",
     created_at: T("2026-07-24T09:12:00Z"),
     created_unix: 1785489120,
+    active_run_seconds: 28800,
+    run_segment_started_unix: 1785643102,
+    run_seconds: 28800,
     last_activity: T("2026-07-26T03:58:22Z"),
     last_activity_unix: 1785643102,
     paused: false,
@@ -86,6 +89,9 @@ export const tasks: Task[] = [
     status: "running",
     created_at: T("2026-07-25T14:05:00Z"),
     created_unix: 1785592500,
+    active_run_seconds: 14400,
+    run_segment_started_unix: 1785642010,
+    run_seconds: 14400,
     last_activity: T("2026-07-26T03:40:10Z"),
     last_activity_unix: 1785642010,
     paused: false,
@@ -112,6 +118,9 @@ export const tasks: Task[] = [
     status: "paused",
     created_at: T("2026-07-22T08:30:00Z"),
     created_unix: 1785313800,
+    active_run_seconds: 21600,
+    run_segment_started_unix: 0,
+    run_seconds: 21600,
     last_activity: T("2026-07-23T18:40:10Z"),
     last_activity_unix: 1785436810,
     paused: true,
@@ -137,6 +146,9 @@ export const tasks: Task[] = [
     status: "done",
     created_at: T("2026-07-18T08:00:00Z"),
     created_unix: 1784966400,
+    active_run_seconds: 86400,
+    run_segment_started_unix: 0,
+    run_seconds: 86400,
     completed_at: T("2026-07-20T22:11:00Z"),
     completed_unix: 1785190260,
     last_activity: T("2026-07-20T22:11:00Z"),
diff --git a/web/src/lib/mock/handler.ts b/web/src/lib/mock/handler.ts
index c979006..85b1882 100644
--- a/web/src/lib/mock/handler.ts
+++ b/web/src/lib/mock/handler.ts
@@ -951,6 +951,11 @@ function controlMockTask(id: string, action: "pause" | "resume"): BatchControlIt
     task.queued = false;
     task.status = "paused";
     task.engine_mode = "paused";
+    if (task.run_segment_started_unix && task.run_segment_started_unix > 0) {
+      task.active_run_seconds = (task.active_run_seconds ?? 0) + Math.max(0, Math.floor(Date.now() / 1000) - task.run_segment_started_unix);
+      task.run_seconds = task.active_run_seconds;
+    }
+    task.run_segment_started_unix = 0;
   } else {
     if (!task.paused && task.status !== "paused") {
       return { id, ok: false, status: task.status, error: "任务未暂停" };
@@ -959,6 +964,7 @@ function controlMockTask(id: string, action: "pause" | "resume"): BatchControlIt
     task.queued = false;
     task.status = "running";
     task.engine_mode = "exploring";
+    task.run_segment_started_unix = Math.floor(Date.now() / 1000);
   }
   return { id, ok: true, status: task.status, queued: false };
 }
@@ -1248,6 +1254,9 @@ function route(m: string, path: string, seg: string[], q: URLSearchParams, b: Re
       status: "created",
       created_at: now.toISOString(),
       created_unix: Math.floor(now.getTime() / 1000),
+      active_run_seconds: 0,
+      run_segment_started_unix: 0,
+      run_seconds: 0,
       paused: false,
       active: true,
       in_flight: 0,
diff --git a/web/src/lib/types.ts b/web/src/lib/types.ts
index 0e44355..2ff5cd1 100644
--- a/web/src/lib/types.ts
+++ b/web/src/lib/types.ts
@@ -34,10 +34,13 @@ export interface Task {
   goal: string;
   status: TaskStatus;
   created_at: string;
-  created_unix?: number; // created_at as unix seconds (run-duration calc)
+  created_unix?: number;
   completed_at?: string; // RFC3339 finish time (done/failed); "" if unfinished
   completed_unix?: number; // completed_at as unix seconds (0/undef if unfinished)
   last_activity_unix?: number; // unix seconds of the last activity (0/undef if none)
+  run_seconds?: number; // backend-computed active runtime seconds
+  active_run_seconds?: number; // completed running segments in seconds
+  run_segment_started_unix?: number; // current running segment start; 0 when inactive
   paused?: boolean;
   queued?: boolean;
   active?: boolean;