3 files changed, 195 insertions, 0 deletions
diff --git a/internal/store/chains_test.go b/internal/store/chains_test.go
index 6359d11..bcfc09e 100644
--- a/internal/store/chains_test.go
+++ b/internal/store/chains_test.go
@@ -263,3 +263,117 @@ func TestGetChain_UnknownID_ReturnsErrNotFound(t *testing.T) {
 		t.Errorf("err = %v, want ErrNativeTaskNotFound", err)
 	}
 }
+
+// TestDeleteNativeTask_LockedChainTask_ClosesPositionGap proves deleting a
+// not-yet-reached chain step doesn't strand the chain: positions after the
+// deleted one shift down by one and stay a contiguous 0..N-1 sequence, since
+// advanceChain's chain_position+1 lookup depends on that contiguity.
+func TestDeleteNativeTask_LockedChainTask_ClosesPositionGap(t *testing.T) {
+	s := newNativeTasksTestStore(t)
+
+	chain, err := s.CreateChain("Track", chainTasks("Step 1", "Step 2", "Step 3"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	tasks, err := s.GetChainTasks(chain.ID)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if err := s.DeleteNativeTask(tasks[1].ID); err != nil {
+		t.Fatalf("DeleteNativeTask: %v", err)
+	}
+
+	after, err := s.GetChainTasks(chain.ID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(after) != 2 {
+		t.Fatalf("len(after) = %d, want 2", len(after))
+	}
+	if after[0].Content != "Step 1" || after[1].Content != "Step 3" {
+		t.Errorf("unexpected content order: %q, %q", after[0].Content, after[1].Content)
+	}
+	if after[1].ChainPosition != 1 {
+		t.Errorf("Step 3 chain_position = %d, want 1 (gap closed)", after[1].ChainPosition)
+	}
+	if !after[0].ChainUnlocked {
+		t.Errorf("position 0 should still be unlocked")
+	}
+	if after[1].ChainUnlocked {
+		t.Errorf("position 1 (formerly locked position 2) should still be locked")
+	}
+
+	// Completing position 0 should now correctly advance to the
+	// renumbered position 1 (Step 3), proving advanceChain's
+	// chain_position+1 lookup still works post-deletion.
+	if err := s.CompleteNativeTask(after[0].ID); err != nil {
+		t.Fatalf("CompleteNativeTask: %v", err)
+	}
+	final, err := s.GetChainTasks(chain.ID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !final[1].ChainUnlocked {
+		t.Errorf("Step 3 should be unlocked after completing Step 1")
+	}
+}
+
+// TestDeleteNativeTask_UnlockedChainTask_PromotesSuccessor proves deleting
+// the currently-actionable (unlocked) step unlocks whatever now sits at its
+// position, rather than leaving the chain with nothing unlocked.
+func TestDeleteNativeTask_UnlockedChainTask_PromotesSuccessor(t *testing.T) {
+	s := newNativeTasksTestStore(t)
+
+	chain, err := s.CreateChain("Track", chainTasks("Step 1", "Step 2"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	tasks, err := s.GetChainTasks(chain.ID)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if err := s.DeleteNativeTask(tasks[0].ID); err != nil {
+		t.Fatalf("DeleteNativeTask: %v", err)
+	}
+
+	after, err := s.GetChainTasks(chain.ID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(after) != 1 {
+		t.Fatalf("len(after) = %d, want 1", len(after))
+	}
+	if !after[0].ChainUnlocked || after[0].DueDate == nil {
+		t.Errorf("Step 2 should be promoted to unlocked with a due date, got ChainUnlocked=%v DueDate=%v", after[0].ChainUnlocked, after[0].DueDate)
+	}
+}
+
+// TestDeleteNativeTask_LastRemainingChainTask_MarksChainCompleted proves
+// deleting the sole unlocked task with nothing left to promote finishes the
+// chain instead of leaving it active with zero unlocked tasks forever.
+func TestDeleteNativeTask_LastRemainingChainTask_MarksChainCompleted(t *testing.T) {
+	s := newNativeTasksTestStore(t)
+
+	chain, err := s.CreateChain("Track", chainTasks("Only step"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	tasks, err := s.GetChainTasks(chain.ID)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if err := s.DeleteNativeTask(tasks[0].ID); err != nil {
+		t.Fatalf("DeleteNativeTask: %v", err)
+	}
+
+	updatedChain, err := s.GetChain(chain.ID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if updatedChain.Status != "completed" {
+		t.Errorf("chain.Status = %q, want completed", updatedChain.Status)
+	}
+}
diff --git a/internal/store/native_tasks.go b/internal/store/native_tasks.go
index 11a9197..9d9af2c 100644
--- a/internal/store/native_tasks.go
+++ b/internal/store/native_tasks.go
@@ -161,6 +161,67 @@ func (s *Store) UpdateNativeTaskDescription(id, description string) error {
 	return err
 }
 
+// DeleteNativeTask permanently removes a task. Returns ErrNativeTaskNotFound
+// if id doesn't match any row. If the task belongs to a chain, this also
+// closes the resulting gap in chain_position (advanceChain looks up
+// chain_position+1, so a gap would either strand the chain mid-sequence or,
+// if the deleted task was the unlocked one, silently stop it from ever
+// advancing) and, if the deleted task was itself the unlocked position,
+// unlocks whatever now occupies that position -- or marks the chain
+// completed if nothing does (the deleted task was the last one left).
+func (s *Store) DeleteNativeTask(id string) error {
+	task, err := s.GetNativeTaskByID(id)
+	if err != nil {
+		return err
+	}
+
+	if task.ChainID == "" {
+		result, err := s.db.Exec(`DELETE FROM native_tasks WHERE id = ?`, id)
+		if err != nil {
+			return err
+		}
+		return checkRowsAffected(result)
+	}
+
+	tx, err := s.db.Begin()
+	if err != nil {
+		return err
+	}
+	defer func() { _ = tx.Rollback() }()
+
+	if _, err := tx.Exec(`DELETE FROM native_tasks WHERE id = ?`, id); err != nil {
+		return err
+	}
+	if _, err := tx.Exec(`
+		UPDATE native_tasks SET chain_position = chain_position - 1
+		WHERE chain_id = ? AND chain_position > ?
+	`, task.ChainID, task.ChainPosition); err != nil {
+		return err
+	}
+
+	if task.ChainUnlocked {
+		now := config.Now()
+		result, err := tx.Exec(`
+			UPDATE native_tasks SET chain_unlocked = 1, due_date = ?, updated_at = ?
+			WHERE chain_id = ? AND chain_position = ?
+		`, now, now, task.ChainID, task.ChainPosition)
+		if err != nil {
+			return err
+		}
+		successorPromoted, err := result.RowsAffected()
+		if err != nil {
+			return err
+		}
+		if successorPromoted == 0 {
+			if _, err := tx.Exec(`UPDATE task_chains SET status = 'completed' WHERE id = ?`, task.ChainID); err != nil {
+				return err
+			}
+		}
+	}
+
+	return tx.Commit()
+}
+
 // ErrChainTaskLocked is returned by CompleteNativeTask when the task
 // belongs to a chain but isn't the currently-unlocked position -- without
 // this guard, completing a locked task directly by id (bypassing the UI,
diff --git a/internal/store/native_tasks_test.go b/internal/store/native_tasks_test.go
index d82576e..9a7e55f 100644
--- a/internal/store/native_tasks_test.go
+++ b/internal/store/native_tasks_test.go
@@ -698,3 +698,23 @@ func TestCreateNextIteration_CarriesEstimatedMinutesForward(t *testing.T) {
 		t.Errorf("EstimatedMinutes = %d, want 60 (carried forward)", next.EstimatedMinutes)
 	}
 }
+
+func TestDeleteNativeTask_PlainTask_Removed(t *testing.T) {
+	s := newNativeTasksTestStore(t)
+
+	if err := s.DeleteNativeTask("real-1"); err != nil {
+		t.Fatalf("DeleteNativeTask: %v", err)
+	}
+
+	if _, err := s.GetNativeTaskByID("real-1"); !errors.Is(err, ErrNativeTaskNotFound) {
+		t.Errorf("err = %v, want ErrNativeTaskNotFound", err)
+	}
+}
+
+func TestDeleteNativeTask_UnknownID_ReturnsErrNotFound(t *testing.T) {
+	s := newNativeTasksTestStore(t)
+
+	if err := s.DeleteNativeTask("does-not-exist"); !errors.Is(err, ErrNativeTaskNotFound) {
+		t.Errorf("err = %v, want ErrNativeTaskNotFound", err)
+	}
+}