fix(deps): exclude relates-to from cycle detection (fixes #661)

relates-to dependencies are intentionally bidirectional ("see also" links)
and should not be reported as cycles by bd dep cycles. This matches the
existing behavior in AddDependency which already skips cycle prevention
for relates-to.

Changes:
- Filter relates-to edges in DetectCycles SQL query
- Add tests for relates-to exclusion from cycle detection
- Update existing test to reflect correct behavior

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/storage/sqlite/cycle_detection_test.go

@@ -505,3 +505,141 @@ func TestDetectCyclesMixedTypes(t *testing.T) {
 		t.Errorf("Expected cycle of length 3, got %d", len(cycle))
 	}
 }
+
+// TestDetectCyclesRelatesToNotACycle tests that bidirectional relates-to links are NOT reported as cycles
+// This is the fix for GitHub issue #661: relates-to relationships should be excluded from cycle detection
+// because they are inherently bidirectional ("see also" links) and don't affect work ordering.
+func TestDetectCyclesRelatesToNotACycle(t *testing.T) {
+	store, cleanup := setupTestDB(t)
+	defer cleanup()
+
+	ctx := context.Background()
+
+	// Create two issues
+	issue1 := &types.Issue{Title: "Todo 1", Status: types.StatusOpen, Priority: 2, IssueType: types.TypeTask}
+	issue2 := &types.Issue{Title: "Todo 2", Status: types.StatusOpen, Priority: 2, IssueType: types.TypeTask}
+
+	if err := store.CreateIssue(ctx, issue1, "test-user"); err != nil {
+		t.Fatalf("CreateIssue failed: %v", err)
+	}
+	if err := store.CreateIssue(ctx, issue2, "test-user"); err != nil {
+		t.Fatalf("CreateIssue failed: %v", err)
+	}
+
+	// Create bidirectional relates_to links (simulating what bd relate does)
+	// issue1 relates_to issue2
+	_, err := store.db.ExecContext(ctx, `
+		INSERT INTO dependencies (issue_id, depends_on_id, type, created_by, created_at)
+		VALUES (?, ?, ?, 'test-user', CURRENT_TIMESTAMP)
+	`, issue1.ID, issue2.ID, types.DepRelatesTo)
+	if err != nil {
+		t.Fatalf("Insert relates_to dependency failed: %v", err)
+	}
+
+	// issue2 relates_to issue1 (the reverse link)
+	_, err = store.db.ExecContext(ctx, `
+		INSERT INTO dependencies (issue_id, depends_on_id, type, created_by, created_at)
+		VALUES (?, ?, ?, 'test-user', CURRENT_TIMESTAMP)
+	`, issue2.ID, issue1.ID, types.DepRelatesTo)
+	if err != nil {
+		t.Fatalf("Insert relates_to dependency failed: %v", err)
+	}
+
+	// Detect cycles - should find NONE because relates_to is excluded
+	cycles, err := store.DetectCycles(ctx)
+	if err != nil {
+		t.Fatalf("DetectCycles failed: %v", err)
+	}
+
+	if len(cycles) != 0 {
+		t.Errorf("Expected no cycles for relates_to bidirectional links, but found %d cycles", len(cycles))
+		for i, cycle := range cycles {
+			t.Logf("Cycle %d:", i+1)
+			for _, issue := range cycle {
+				t.Logf("  - %s: %s", issue.ID, issue.Title)
+			}
+		}
+	}
+}
+
+// TestDetectCyclesRelatesToWithOtherCycle tests that relates-to is excluded but other cycles are still detected
+func TestDetectCyclesRelatesToWithOtherCycle(t *testing.T) {
+	store, cleanup := setupTestDB(t)
+	defer cleanup()
+
+	ctx := context.Background()
+
+	// Create three issues
+	issue1 := &types.Issue{Title: "Issue A", Status: types.StatusOpen, Priority: 2, IssueType: types.TypeTask}
+	issue2 := &types.Issue{Title: "Issue B", Status: types.StatusOpen, Priority: 2, IssueType: types.TypeTask}
+	issue3 := &types.Issue{Title: "Issue C", Status: types.StatusOpen, Priority: 2, IssueType: types.TypeTask}
+
+	if err := store.CreateIssue(ctx, issue1, "test-user"); err != nil {
+		t.Fatalf("CreateIssue failed: %v", err)
+	}
+	if err := store.CreateIssue(ctx, issue2, "test-user"); err != nil {
+		t.Fatalf("CreateIssue failed: %v", err)
+	}
+	if err := store.CreateIssue(ctx, issue3, "test-user"); err != nil {
+		t.Fatalf("CreateIssue failed: %v", err)
+	}
+
+	// Create bidirectional relates_to between issue1 and issue2 (should NOT trigger cycle)
+	_, err := store.db.ExecContext(ctx, `
+		INSERT INTO dependencies (issue_id, depends_on_id, type, created_by, created_at)
+		VALUES (?, ?, ?, 'test-user', CURRENT_TIMESTAMP)
+	`, issue1.ID, issue2.ID, types.DepRelatesTo)
+	if err != nil {
+		t.Fatalf("Insert relates_to dependency failed: %v", err)
+	}
+	_, err = store.db.ExecContext(ctx, `
+		INSERT INTO dependencies (issue_id, depends_on_id, type, created_by, created_at)
+		VALUES (?, ?, ?, 'test-user', CURRENT_TIMESTAMP)
+	`, issue2.ID, issue1.ID, types.DepRelatesTo)
+	if err != nil {
+		t.Fatalf("Insert relates_to dependency failed: %v", err)
+	}
+
+	// Create a real cycle with blocks: issue2 -> issue3 -> issue2
+	_, err = store.db.ExecContext(ctx, `
+		INSERT INTO dependencies (issue_id, depends_on_id, type, created_by, created_at)
+		VALUES (?, ?, ?, 'test-user', CURRENT_TIMESTAMP)
+	`, issue2.ID, issue3.ID, types.DepBlocks)
+	if err != nil {
+		t.Fatalf("Insert blocks dependency failed: %v", err)
+	}
+	_, err = store.db.ExecContext(ctx, `
+		INSERT INTO dependencies (issue_id, depends_on_id, type, created_by, created_at)
+		VALUES (?, ?, ?, 'test-user', CURRENT_TIMESTAMP)
+	`, issue3.ID, issue2.ID, types.DepBlocks)
+	if err != nil {
+		t.Fatalf("Insert blocks dependency failed: %v", err)
+	}
+
+	// Detect cycles - should find the blocks cycle but NOT the relates_to "cycle"
+	cycles, err := store.DetectCycles(ctx)
+	if err != nil {
+		t.Fatalf("DetectCycles failed: %v", err)
+	}
+
+	if len(cycles) == 0 {
+		t.Fatal("Expected to find the blocks cycle, but found none")
+	}
+
+	// Verify the cycle contains issue2 and issue3, but NOT issue1
+	foundIDs := make(map[string]bool)
+	for _, cycle := range cycles {
+		for _, issue := range cycle {
+			foundIDs[issue.ID] = true
+		}
+	}
+
+	if !foundIDs[issue2.ID] || !foundIDs[issue3.ID] {
+		t.Errorf("Expected cycle to contain issue2 and issue3. Found: %v", foundIDs)
+	}
+
+	// Verify issue1 is NOT in the cycle (it's only connected via relates-to)
+	if foundIDs[issue1.ID] {
+		t.Errorf("issue1 should NOT be in cycle (only connected via relates-to), but was found")
+	}
+}