fix: respect hierarchy.max-depth config setting (GH#995) (#997)

* fix: respect hierarchy.max-depth config setting (GH#995)

The hierarchy.max-depth config setting was being ignored because storage
implementations had the depth limit hardcoded to 3. This fix:

- Registers hierarchy.max-depth default (3) in config initialization
- Adds hierarchy.max-depth to yaml-only keys for config.yaml storage
- Updates SQLite and Memory storage to read max depth from config
- Adds validation to reject hierarchy.max-depth values < 1
- Adds tests for configurable hierarchy depth

Users can now set deeper hierarchies:
  bd config set hierarchy.max-depth 10

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

* refactor: extract shared CheckHierarchyDepth function (GH#995)

- Extract duplicated depth-checking logic to types.CheckHierarchyDepth()
- Update sqlite and memory storage backends to use shared function
- Add t.Cleanup() for proper test isolation in sqlite test
- Add equivalent test coverage for memory storage backend
- Add comprehensive unit tests for CheckHierarchyDepth function

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

---------

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

internal/types/id_generator.go

@@ -90,3 +90,25 @@ func ParseHierarchicalID(id string) (rootID, parentID string, depth int) {
 // MaxHierarchyDepth is the maximum nesting level for hierarchical IDs.
 // Prevents over-decomposition and keeps IDs manageable.
 const MaxHierarchyDepth = 3
+
+// CheckHierarchyDepth validates that adding a child to parentID won't exceed maxDepth.
+// Returns an error if the depth would be exceeded.
+// If maxDepth < 1, it defaults to MaxHierarchyDepth.
+func CheckHierarchyDepth(parentID string, maxDepth int) error {
+	if maxDepth < 1 {
+		maxDepth = MaxHierarchyDepth
+	}
+
+	// Count dots to determine current depth
+	depth := 0
+	for _, ch := range parentID {
+		if ch == '.' {
+			depth++
+		}
+	}
+
+	if depth >= maxDepth {
+		return fmt.Errorf("maximum hierarchy depth (%d) exceeded for parent %s", maxDepth, parentID)
+	}
+	return nil
+}

internal/types/id_generator_test.go

@@ -209,3 +209,46 @@ func BenchmarkGenerateChildID(b *testing.B) {
 		GenerateChildID("bd-af78e9a2", 42)
 	}
 }
+
+func TestCheckHierarchyDepth(t *testing.T) {
+	tests := []struct {
+		name     string
+		parentID string
+		maxDepth int
+		wantErr  bool
+		errMsg   string
+	}{
+		// Default maxDepth (uses MaxHierarchyDepth = 3)
+		{"root parent with default depth", "bd-abc123", 0, false, ""},
+		{"depth 1 parent with default depth", "bd-abc123.1", 0, false, ""},
+		{"depth 2 parent with default depth", "bd-abc123.1.2", 0, false, ""},
+		{"depth 3 parent with default depth - exceeds", "bd-abc123.1.2.3", 0, true, "maximum hierarchy depth (3) exceeded for parent bd-abc123.1.2.3"},
+
+		// Custom maxDepth
+		{"root parent with max=1", "bd-abc123", 1, false, ""},
+		{"depth 1 parent with max=1 - exceeds", "bd-abc123.1", 1, true, "maximum hierarchy depth (1) exceeded for parent bd-abc123.1"},
+		{"depth 3 parent with max=5", "bd-abc123.1.2.3", 5, false, ""},
+		{"depth 4 parent with max=5", "bd-abc123.1.2.3.4", 5, false, ""},
+		{"depth 5 parent with max=5 - exceeds", "bd-abc123.1.2.3.4.5", 5, true, "maximum hierarchy depth (5) exceeded for parent bd-abc123.1.2.3.4.5"},
+
+		// Negative maxDepth falls back to default
+		{"negative maxDepth uses default", "bd-abc123.1.2.3", -1, true, "maximum hierarchy depth (3) exceeded for parent bd-abc123.1.2.3"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			err := CheckHierarchyDepth(tt.parentID, tt.maxDepth)
+			if tt.wantErr {
+				if err == nil {
+					t.Errorf("expected error, got nil")
+				} else if err.Error() != tt.errMsg {
+					t.Errorf("expected error %q, got %q", tt.errMsg, err.Error())
+				}
+			} else {
+				if err != nil {
+					t.Errorf("unexpected error: %v", err)
+				}
+			}
+		})
+	}
+}